Www.radbiol.ucla.edu WMcB2008 Tumor Responses to RT Bill McBride Dept. Radiation Oncology David Geffen School Medicine UCLA, Los Angeles, Ca. [email protected]

www.rwww.radbioladbiol.ucla.ed.ucla.eduu

WMcB2008

Tumor Responses to RTTumor Responses to RT

Bill McBrideBill McBrideDept. Radiation OncologyDept. Radiation Oncology

David Geffen School MedicineDavid Geffen School MedicineUCLA, Los Angeles, Ca.UCLA, Los Angeles, [email protected]@mednet.ucla.edu


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Determinants of Tumor CureDeterminants of Tumor Cure

• Size of the clonogenic pool (stem cells)Size of the clonogenic pool (stem cells)• Intrinsic radiosensitivityIntrinsic radiosensitivity

– S.F. 2Gy (pro-apoptotic tendency?)S.F. 2Gy (pro-apoptotic tendency?)• RepairRepair

– T1/2 (HR, NHEJ, SLDR, PLDR, fast and slow T1/2 (HR, NHEJ, SLDR, PLDR, fast and slow repair?) repair?)

• Rate of repopulation/regeneration during therapyRate of repopulation/regeneration during therapy– Tpot (L/I., Ki67?)Tpot (L/I., Ki67?)

• Reoxygenation (extent of hypoxia)Reoxygenation (extent of hypoxia)– POPO22 (dependence on tissue type, vascularity?) (dependence on tissue type, vascularity?)

• RedistributionRedistribution– Growth fraction (dependence on cell type, growth Growth fraction (dependence on cell type, growth factors?)factors?)


WMcB2008

Determinants of Tumor Cure Determinants of Tumor Cure (continued)(continued)

Heterogeneity:Heterogeneity:• BiologicalBiological

– Number of clonogenic Number of clonogenic ““stem cellsstem cells””• Intrinsic radiosensitivityIntrinsic radiosensitivity• Proliferative potentialProliferative potential

– Tumor microenvironmentTumor microenvironment• HypoxiaHypoxia• MetabolismMetabolism• Host cell infiltratesHost cell infiltrates• Interstitial pressureInterstitial pressure

– GeneticGenetic• OncogenesOncogenes• Tumor suppressor genesTumor suppressor genes• Single Nucleotide Polymorphisms (SNPs)?Single Nucleotide Polymorphisms (SNPs)?

• PhysicalPhysical– Dose heterogeneityDose heterogeneity– Geographic missGeographic miss


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TD50 AssayTD50 Assay1. Inject varying numbers of tumor cells into mice1. Inject varying numbers of tumor cells into mice

2. Determine the number of cells that are needed to form tumors in 50% 2. Determine the number of cells that are needed to form tumors in 50% of mice.of mice.

100100

5050

00

Percent ofPercent ofmice with mice with tumorstumors

10 1010 1022 10 1033 10 1044 10 1055 10 1066 10 1077

Size of tumor inoculumSize of tumor inoculum

To grow, tumors must To grow, tumors must have arisen in that have arisen in that specific strain of specific strain of mice, or the mice must mice, or the mice must be immune deficient. be immune deficient. Even then, not all Even then, not all tumors will grow, and tumors will grow, and most need an inoculum most need an inoculum size of at least 10size of at least 1044 cellscells

Concept: Only Concept: Only cancer cancer ““stemstem”” cells will growcells will grow


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Renewing stem cell

Non-stem cell

Tumor regenerationfrom stem cell pool

The cancer stem cell hypothesis suggests that there are a small number of clonogenic stem cells in a tumor and that, if they are therapy-resistant, they are responsible for recurrences, and accelerated tumor repopulation during therapy.

stem cell

Tumor cure


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MCF-7 Breast Cancer Stem Cells are MCF-7 Breast Cancer Stem Cells are Radioresistant and are enriched Following Radioresistant and are enriched Following

IrradiationIrradiation

“Stem” cells

At least some human tumors have a clonogenic subpopulation with stem-like characteristics that can be grown in cytokines as spheres and that are radioresistant and are selected for by fractionated irradiation. Phillips et al J Natl Cancer Inst 98:1777, 2006


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TCD50 AssayTCD50 Assay1. Inject mice with enough cells to form a tumor1. Inject mice with enough cells to form a tumor

3. Determine the dose of radiation that is needed to cure 50% 3. Determine the dose of radiation that is needed to cure 50% of mice.of mice.

100100

5050

00

Percent ofPercent ofmice with mice with tumorstumors

2. Irradiate when 6mm diam2. Irradiate when 6mm diam

0 10 20 30 40 50 60 70 800 10 20 30 40 50 60 70 80

GyGy

Threshold-sigmoid Threshold-sigmoid curve that goes curve that goes from 10% to 90% from 10% to 90% cure over about cure over about 10Gy in a clinical 10Gy in a clinical fractionation fractionation scheme (which is scheme (which is hard to do in hard to do in mice).mice).


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Tumor Control ProbabilityTumor Control Probability

• In order to cure a tumor, the last surviving In order to cure a tumor, the last surviving clonogen must be killed, and even then it is a clonogen must be killed, and even then it is a probability function of dose.probability function of dose.

• TCP = eTCP = e-x-x = e = e-(m. SF) -(m. SF)

or eor e-m.e-(-m.e-(d+d+D2)D2) or e or e -(m. e -(D/D0))-(m. e -(D/D0))

– Where x is the number of surviving clonogenic Where x is the number of surviving clonogenic stem cells, stem cells,

– m is the initial number of clonogensm is the initial number of clonogens

• If there is an average of 1 cell surviving TCP=37%If there is an average of 1 cell surviving TCP=37%


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DOSE (Gy)DOSE (Gy)

00

2020

4040

6060

8080

100100

00 1010 2020 3030 4040 5050 6060 7070 8080 9090 100100 110110 120120 130130

N=10N=109 9

SFSF22=0.3=0.3

SFSF22=0.4=0.4

SFSF22=0.5=0.5

SFSF22=0.6=0.6

SFSF22=0.7=0.7TCP (%)TCP (%)

Heterogeneity in RadiosensitivityHeterogeneity in Radiosensitivity

Rafi Suwinski


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DOSE (Gy)DOSE (Gy)

00

2020

4040

6060

8080

100100

00 1010 2020 3030 4040 5050 6060 7070 8080 9090

N=10N=1099

2Gy2Gy = 0.5= 0.5

N=10N=101010

N=10N=101111

SFSF

TCP (%)TCP (%)

Heterogeneity in Clonogen NumberHeterogeneity in Clonogen Number

AverageAverage

Rafi Suwinski


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DOSE (Gy)DOSE (Gy)

PERCENT REDUCTION IN

PERCENT REDUCTION IN

METASTASES RISK

METASTASES RISK

00

2020

4040

6060

8080

100100

00 1010 2020 3030 4040 5050 6060 7070

n=10n=1055

N =10-10

N =10-10

8 8

SFSF2Gy2Gy=0.5=0.5

N=10N=10 88N=10N=103 3 N=10N=10

Heterogeneity in tumor volumeHeterogeneity in tumor volume

Micrometastatic DiseaseMicrometastatic Disease


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Tumor Growth and RegressionTumor Growth and RegressionThe The kinetics kinetics of tumor growth and regression depend of tumor growth and regression depend

uponupon • Cell cycleCell cycle• Growth fraction (G.F.)Growth fraction (G.F.)

• G.F. is the proportion of proliferating cellsG.F. is the proportion of proliferating cells• G.F. = P / (P + Q) where P = proliferating cells and Q = G.F. = P / (P + Q) where P = proliferating cells and Q =

non-proliferating cells non-proliferating cells (quiescent/senescent/differentiated cells)(quiescent/senescent/differentiated cells)

• Cell loss factorCell loss factor• Cell Loss Factor Cell Loss Factor measures loss of cells from a tissuemeasures loss of cells from a tissue• If If = 0, Td = Tpot= 0, Td = Tpot where Td is the actual volume doubling where Td is the actual volume doubling

time and Tpot is potential volume doubling time time and Tpot is potential volume doubling time • = 1 - Tpot / Td= 1 - Tpot / Td• if G.F. = 1 then Tpot = Tc if G.F. = 1 then Tpot = Tc • Under steady state conditions, constant cell number is Under steady state conditions, constant cell number is

maintained by the balance between cell proliferation and maintained by the balance between cell proliferation and cell loss i.e. cell loss i.e. = 1.0. In tumors (and embryos) = 1.0. In tumors (and embryos) < 1.0 < 1.0


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Tumor KineticsTumor Kinetics

Tc Cell cycle timeTc Cell cycle time

G.F. Growth fraction G.F. Growth fraction

Tpot Pot. doubling timeTpot Pot. doubling time

TdTd Actual doubling time Actual doubling time

Cell loss factorCell loss factor

Human SCCHuman SCC

36 hrs36 hrs

0.250.25

6 days6 days

60 days60 days

0.90.9

Rate of tumor growth and rate of tumor regression after therapy Rate of tumor growth and rate of tumor regression after therapy are determined largely by the cell loss factor, that varies are determined largely by the cell loss factor, that varies

greatly from tumor to tumorgreatly from tumor to tumor

(36hr x 4)(36hr x 4)

(1-6/60)(1-6/60)


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Tumor Growth and RegressionTumor Growth and Regression

• Slow growing tumors may regress rapidlySlow growing tumors may regress rapidly• Slow regression is Slow regression is notnot an indication of treatment an indication of treatment

failurefailure• Rapidly growing tumors would be expected to Rapidly growing tumors would be expected to

regress and regrow rapidlyregress and regrow rapidly

• In general, the rate of tumor regression after Tx In general, the rate of tumor regression after Tx is not prognosticis not prognostic


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Tumor RegenerationTumor Regeneration

Rat rhabdomyosarcomaRat rhabdomyosarcomaHermans and Barendsen, 1969Hermans and Barendsen, 1969

Tumors can Tumors can regenerate regenerate at the same at the same time as they time as they regress!regress!

ControlControlIrradiatedIrradiated

Surviving clonogensSurviving clonogensmeasured in vitromeasured in vitro

Growth delay Growth delay

TimeTime

Relative tumor Relative tumor volumevolume

20Gy X-rays20Gy X-rays


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The regrowth rate The regrowth rate of surviving of surviving clonogens varies clonogens varies with the surviving with the surviving fraction - Lewis fraction - Lewis Lung CarcinomaLung Carcinoma(Stephens and (Stephens and Steel)Steel)

ControlControl15 Gy15 Gy25 Gy25 Gy35 Gy35 Gy


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EVIDENCE FOR ACCELERATED EVIDENCE FOR ACCELERATED REPOPULATION IN TUMORSREPOPULATION IN TUMORS

• After RT, tumors recur faster than After RT, tumors recur faster than than would be expected from the than would be expected from the original growth rate original growth rate

• Split-course RT often gives poor Split-course RT often gives poor resultsresults

• Protraction of treatment time often Protraction of treatment time often gives poor resultsgives poor results

• Accelerated treatment is sometimes of Accelerated treatment is sometimes of benefit.benefit.


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Accelerated Tumor RepopulationAccelerated Tumor Repopulation

• T2 and T3 SCC head and neckT2 and T3 SCC head and neck (excluding nasopharynx and vocal (excluding nasopharynx and vocal cord). TCDcord). TCD5050 values are consistent with values are consistent with onset of repopulation at 4 onset of repopulation at 4 weeksweeks followed by accelerated repopulation with a 3-4 day followed by accelerated repopulation with a 3-4 day doubling time, implying a loss in dose of about 0.6 Gy/dydoubling time, implying a loss in dose of about 0.6 Gy/dy

• If the red line is correct, onset may be about day 21 and If the red line is correct, onset may be about day 21 and repopulation may not be constant. It may increase from 0.6 Gy/dy repopulation may not be constant. It may increase from 0.6 Gy/dy around week 3-4 to even 1.6 – 1.8 Gy/day around week 6-7.around week 3-4 to even 1.6 – 1.8 Gy/day around week 6-7.

T2 T3T2 T3local controllocal control

no local controlno local control

Withers et al, 1988Withers et al, 1988Maciejewski et al., 1989Maciejewski et al., 1989

Total DoseTotal Dose(2 Gy equiv.)(2 Gy equiv.)

Treatment DurationTreatment Duration

local controllocal control

no local controlno local control

7070

5555

4040

T2 T3T2 T3


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476 patients

Tpot in a Large Multicenter Tpot in a Large Multicenter HNSC TrialHNSC Trial

(Begg (Begg et alet al 1999) 1999)

• It was thought that shortening treatment time by It was thought that shortening treatment time by accelerated hyperfractionation and that this might accelerated hyperfractionation and that this might be predicted by Tbe predicted by Tpot pot , but a large multicenter trial , but a large multicenter trial was unable to confirm thiswas unable to confirm this

• But note that TBut note that Tpotpot in HNSCC was 3-5dys for most in HNSCC was 3-5dys for most patients, confirming the potential for very rapid patients, confirming the potential for very rapid growthgrowth


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Sources of HeterogeneitySources of Heterogeneity

• Biological DoseBiological Dose– Number of clonogenic Number of clonogenic ““stem cellsstem cells””

• Intrinsic radiosensitivityIntrinsic radiosensitivity• Proliferative potentialProliferative potential

– Tumor microenvironmentTumor microenvironment• HypoxiaHypoxia• MetabolismMetabolism

• Physical DosePhysical Dose– Need to know the importance of Need to know the importance of dose-volume constraintsdose-volume constraints


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• HistoryHistory– 19091909

• Schwarz - radium dose on human skinSchwarz - radium dose on human skin– 1930-19501930-1950

• Gray, Mottram, Flanders - oxygen effects in Gray, Mottram, Flanders - oxygen effects in biologybiology

– 19551955• Thomlinson & Gray - tumor cordsThomlinson & Gray - tumor cords

– 1960-19651960-1965• Powers & Tolmach - survival curves Powers & Tolmach - survival curves in vivoin vivo• Churchill Davidson - HBO in patientsChurchill Davidson - HBO in patients


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•Chronic hypoxia is a result largely of Chronic hypoxia is a result largely of – Limited OLimited O22 diffusion due to diffusion due to

•oxygen consumption (oxygen consumption (””diffusion limited hypoxiadiffusion limited hypoxia””))•irregular vascular geometryirregular vascular geometry

•Acute/transient/intermittent hypoxia is a Acute/transient/intermittent hypoxia is a result largely of result largely of – Chaotic vasculature and interstitial Chaotic vasculature and interstitial pressurepressure•vascular stasisvascular stasis•flow instabilitiesflow instabilities

Hypoxia in TumorsHypoxia in Tumors


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• Within areas of need, oxygen is released from red Within areas of need, oxygen is released from red blood cells and enters tumor tissue by diffusion. It blood cells and enters tumor tissue by diffusion. It is metabolized by respiring cells. As a result, at is metabolized by respiring cells. As a result, at distances greater than about 100 µm from the nearest distances greater than about 100 µm from the nearest blood vessel insufficient oxygen remains to maintain blood vessel insufficient oxygen remains to maintain cell viability. cell viability.

Chronic HypoxiaChronic Hypoxia

VVVVVV

VVVV

VVVV

VVVV

VV VVVVVV

VVVVVVVV

VV

VV

BLOODBLOODVESSELVESSEL

NecrosisNecrosis

HypoxiaHypoxia

ProliferationProliferation

100100HIGH.................LOWHIGH.................LOW

Proliferation, O2, Proliferation, O2, pH, cell viabilitypH, cell viability

• Adjacent to areas of necrosis, Adjacent to areas of necrosis, one may find a region 1-2 cell one may find a region 1-2 cell layers thick where oxygen layers thick where oxygen tensions are hypoxic. Within a tensions are hypoxic. Within a solid tumor mass, mitotic solid tumor mass, mitotic index and viability decrease index and viability decrease with distance from the nearest with distance from the nearest blood vessel (Tomlinson and blood vessel (Tomlinson and Gray; Tannock, Cancer Res 30: Gray; Tannock, Cancer Res 30: 2470, 1970)2470, 1970)

• Hypoxia does NOT correlate Hypoxia does NOT correlate with tumor volumewith tumor volume


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Brown & Giaccia, 1994

Normal Tissue

Neoplastic tissue

Konerding et al., 1998

•The vascular The vascular network that network that develops in develops in tumors is tumors is structurally structurally abnormalabnormal•Vessels are Vessels are dilated, dilated, tortuous, tortuous, elongated, with elongated, with A-V shunts and A-V shunts and blind endsblind ends•Pericytes are Pericytes are frequently absentfrequently absent•The basement The basement membrane is thinmembrane is thin•Vessels are more Vessels are more permeable giving permeable giving increased increased interstitial interstitial pressure pressure •The abnormal The abnormal vasculature vasculature results in results in spatial and spatial and temporal temporal heterogeneity in heterogeneity in blood flow that blood flow that in turn produce in turn produce regions of regions of temporary or temporary or acuteacute hypoxia, hypoxia, acidity and acidity and nutrient nutrient depletiondepletion

Acute HypoxiaAcute Hypoxia


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THE OXYGEN EFFECTTHE OXYGEN EFFECT• Oxygen is a powerful oxidizing agent and therefore acts as a Oxygen is a powerful oxidizing agent and therefore acts as a

radiosensitizer if it is present at the time of irradiation (within radiosensitizer if it is present at the time of irradiation (within secs)secs)

• The magnitude of the OER is critically dependent upon oxygen tension. The magnitude of the OER is critically dependent upon oxygen tension. The greatest increase occurs between 0-20 mm Hg with further modest The greatest increase occurs between 0-20 mm Hg with further modest increases to air (155 mm Hg) and above (760 mm Hg=100% oxygen). increases to air (155 mm Hg) and above (760 mm Hg=100% oxygen).

• Its effects are measured as the oxygen enhancement ratio (O.E.R.)Its effects are measured as the oxygen enhancement ratio (O.E.R.)– O.E.R. = the ratio of doses needed to obtain a given level of biological effect under O.E.R. = the ratio of doses needed to obtain a given level of biological effect under

anoxic and oxic conditions = D(anox)/D(ox)anoxic and oxic conditions = D(anox)/D(ox)– For low LET radiation the O.E.R. is 2.5-3.0 and in the higher range at higher dosesFor low LET radiation the O.E.R. is 2.5-3.0 and in the higher range at higher doses– For neutrons, O.E.R is about 1.6For neutrons, O.E.R is about 1.6

Dose (Gy)Dose (Gy)

S.F.S.F.

O.E.R.= 2.67O.E.R.= 2.67

0 2 4 6 8 10 0 2 4 6 8 10

1.01.0

0.10.1

0.010.01

oxicoxic

hypoxichypoxic

1.0

1.5

2.0

2.5

3.0

O.E.R.

76020050403020100Partial Pressure of Oxygen (mm Hg) at 37o C

air 100% oxygen


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RBE and OER as a function of LETRBE and OER as a function of LET

Linear Energy Transfer (LET in keV/Linear Energy Transfer (LET in keV/m)m)

RBERBE(for cell kill)(for cell kill)

1000100010010010101100

22

44

66

88

RBERBEDiagnosticDiagnosticX-raysX-rays

Fast Fast NeutronsNeutrons

Alpha Alpha ParticlesParticles

0.10.1

Co-60Co-60gamma raysgamma rays

00

11

22

33

44

OEROER

OEROER

OER is the inverse of RBE because it depends on the indirect action of ionizing radiation


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• Differential radiation sensitivityDifferential radiation sensitivity• Eppendorf polarographic electrodeEppendorf polarographic electrode • ImmunohistochemistryImmunohistochemistry

– MisonidazoleMisonidazole– Hypoxyprobe™ immunohistochemistry with Hypoxyprobe™ immunohistochemistry with

pimonidazolepimonidazole– HIF-1 and productsHIF-1 and products

• PET imaging PET imaging – 18F-fluoromisonidazole (FMISO-PET)18F-fluoromisonidazole (FMISO-PET)– EF5 - EF5 - etanidazoleetanidazole – Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone

(Cu-ATSM)(Cu-ATSM)

Demonstrating hypoxic Demonstrating hypoxic regions/cells within tumorsregions/cells within tumors


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14 Days

Plate cells

Colony assay

IRRADIATEtumor

After 24hrs make cell suspension

Tumor Cell Survival : In vivo-in vitro assayTumor Cell Survival : In vivo-in vitro assay

0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22

11

1010

1010

1010

1010

1010

-1-1

-2-2

-3-3

-4-4

-5-5

1010-6-6

DOSE (Gy)DOSE (Gy)

HYPOXICHYPOXIC

AIRAIR

S.F.S.F.

OXICOXIC

Hypoxic Hypoxic FractionFraction

• If solid tumors in mice are irradiated with single doses of radiation under hypoxic conditions or in air and an in vitro clonogenic assay performed, normally a dog-leg curve is obtained in air indicating a radioresistant population whose magnitude can be estimated by extrapolation onto the Y axis. After Rockwell and Kalman, 1973


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Tumor HypoxiaTumor Hypoxia

• If murine tumors are If murine tumors are irradiated with irradiated with varying sized single varying sized single doses of radiation doses of radiation under clamped under clamped (hypoxic) and normal (hypoxic) and normal conditions and the % conditions and the % of tumors controlled of tumors controlled plotted, the TCP plotted, the TCP curve is shifted to curve is shifted to the right by hypoxia the right by hypoxia and the O.E.R. can be and the O.E.R. can be calculated.calculated.

Moulder and Rockwell, Moulder and Rockwell, 19841984


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Probe Probe CasingCasing300 300 mm

Gold WireGold Wire12 12 m m

Insulating Insulating glassglass

MembraneMembrane

Eppendorf Polarographic Fine Eppendorf Polarographic Fine Needle pONeedle pO22 Probe Probe

• A 700 mV polarizing voltage is applied against the Ag/AgCl A 700 mV polarizing voltage is applied against the Ag/AgCl anode. The measured current is proportional to the local anode. The measured current is proportional to the local oxygen tensionoxygen tension

• No longer sold, but other versions are possibleNo longer sold, but other versions are possible


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0%

10%

20%

30%

40%

50%

<6 <12 <18 <24 <30 <36 <42 <48

NFSANFSA IL7

0%

10%

20%

30%

40%

<6 <12 <18 <24 <30 <36 <42 <48

NFSANFSA TNF

Eppendorf Polarographic ProbeEppendorf Polarographic Probe

mmHg


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Pimonidazole staining of human CRC tumorPimonidazole staining of human CRC tumor

• Misonidazole forms adducts in hypoxic cells in vitro and in vivo with thiol groups in proteins, peptides and amino acids. Hypoxia (pO2 < 10 mmHg) is required for binding.

• FMISO-PET is one of 2 commonly used PET tracers (the other being Cu-ATSM), but it accumulates slowly. Other imidazoles are under study.

• EF5 is a fluorinated derivative of etanidazole

• Pimonidazole is generally injected in vivo and the adducts stained using antibodies.

• Intracellular Cu-ATSM is a non-nitroimidazole that has been shown to be bioreduced and trapped in hypoxic cells and is used for PET.

Bioreductive DrugsBioreductive Drugs


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Hypoxia and proliferation in a solid tumorHypoxia and proliferation in a solid tumor

blood vessels

proliferating cells(IdUrd +)

Hypoxia(pimonidazole +)

Biopsy of head/neck squamous cell carcinoma

necrosis

From: Albert Van der Kogel


WMcB2008From Bussink et al., 2001

Chronic Acute

Pimonidazole (green) and vascular staining (red)in human head and neck tumor


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Hypoxia-induced gene expressionHypoxia-induced gene expression• Transcription factorsTranscription factors– AP-1, NF-kB, SP-1 activation AP-1, NF-kB, SP-1 activation

•which can mediate radioresistancywhich can mediate radioresistancy

– p53 inductionp53 induction•which can cause apoptosis with hypoxia-driven p53 which can cause apoptosis with hypoxia-driven p53 mutant selection and increasing genetic instabilitymutant selection and increasing genetic instability

– HIF-1HIF-1 and products and products eg VEGF, CA IX, OPN etceg VEGF, CA IX, OPN etc •HIF-1alpha is a target for prolyl hydroxylation by HIF HIF-1alpha is a target for prolyl hydroxylation by HIF prolyl-hydroxylase, targeting it for rapid degradation prolyl-hydroxylase, targeting it for rapid degradation in normoxic conditions. Under hypoxia, HIF prolyl-in normoxic conditions. Under hypoxia, HIF prolyl-hydroxylase is inhibited, since it utilizes oxygen as a hydroxylase is inhibited, since it utilizes oxygen as a cosubstrate, stabilizing HIF-1α. This upregulates cosubstrate, stabilizing HIF-1α. This upregulates several genes to promote survival in low-oxygen several genes to promote survival in low-oxygen conditions, including glycolytic enzymes and VEGF, conditions, including glycolytic enzymes and VEGF, which promotes angiogenesis. which promotes angiogenesis.

•In general these surrogate markers do not correlate In general these surrogate markers do not correlate well with hypoxia, probably because more than hypoxia well with hypoxia, probably because more than hypoxia stabilizes HIF-1stabilizes HIF-1


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• Enhances resistance to radiation and chemotherapy Enhances resistance to radiation and chemotherapy because of classic oxygen effectbecause of classic oxygen effect

• Induces expression of genes that Induces expression of genes that – confer resistance to radiation and other pro-confer resistance to radiation and other pro-

apoptotic insultsapoptotic insults– triggers genetic instabilitytriggers genetic instability– cause angiogenesis and potentiate metastasiscause angiogenesis and potentiate metastasis

Contribution of hypoxia to tumor progressionContribution of hypoxia to tumor progression

From Giaccia, 1999


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Regulation of hypoxia-induced gene Regulation of hypoxia-induced gene expressionexpression

HIF-1HIF-1 synthesissynthesisPI3KPI3K

HER2HER2

FRAPFRAP

PTENPTEN

RapamycinRapamycin

LY294002LY294002

AKTAKT

IGFRIGFR EGFREGFR

SrcSrc

HIF-1HIF-1 mRNAmRNAHIF-1HIF-1proteinprotein

Target geneTarget geneexpressionexpression

VEGFVEGF

IGF-2IGF-2

GlucoseGlucoseProlyl Prolyl hydroxylationhydroxylation

UbiquitinationUbiquitinationVHLVHL

p53p53

HYPOXIAHYPOXIA

HIF-1HIF-1FIH-1FIH-1

AngiogenesisAngiogenesis

MetabolismMetabolism

HIF-1HIF-1 degradationdegradation

transporterstransporters



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angiogenesis

energymetabolism

HIF-1

apoptosis/necrosis

proliferation

Glucose transporters Glut1,3Glycolytic enzymes

ALDA, PGK1, PKM, PFKL, LDHAALDA, PGK1, PKM, PFKL, LDHA

BNip3(BCl2 family)

VEGFVEGFREPO EGF

EGFRPDGF-BPDGF-BIGF-1IGF-2

carbonic Anhydrases

CA9

pH regulatio

n

Redoxregulatio

n

Inflammatory

Cytokines

IL-1IL-1, IL-8, IL-8Heme oxygenase 1,Heme oxygenase 1,metallothionein, metallothionein, diaphorase, diaphorase, GSH,GSH,


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Clinical Relevance of Tumor Clinical Relevance of Tumor HypoxiaHypoxia

• Evidence for hypoxia in human tumorsEvidence for hypoxia in human tumors– Hyperbaric chambers anecdotally show benefitHyperbaric chambers anecdotally show benefit

• normobaric oxygen/carbogen has alsonormobaric oxygen/carbogen has also been applied and, at been applied and, at times, combined with nicotinamide, a Btimes, combined with nicotinamide, a B66

vitamin analog vitamin analog thought to counteract the acute hypoxia (ARCON)thought to counteract the acute hypoxia (ARCON)

– Anemia correction has benefit especially in cervix caAnemia correction has benefit especially in cervix ca• Note that erythropoietin has a deleterious effect in Note that erythropoietin has a deleterious effect in HNSCC due to stimulating tumor growthHNSCC due to stimulating tumor growth

– Nitroimidazoles - immunohistochemistry and PET Nitroimidazoles - immunohistochemistry and PET – Microelectrode measurements - several studies have Microelectrode measurements - several studies have

correlated hypoxia with poor local response and survivalcorrelated hypoxia with poor local response and survival• Nordsmark et al. Radiother Oncol 41, 31, 1996 showed local tumor Nordsmark et al. Radiother Oncol 41, 31, 1996 showed local tumor

control correlates with pre-treatment oxygen levels in head and control correlates with pre-treatment oxygen levels in head and neck ca. neck ca.

• Brizel et al IJROBP 38:285, 1997 showed DFS correlates with Brizel et al IJROBP 38:285, 1997 showed DFS correlates with hypoxia in T3 and T4 and large node mets from head and neckhypoxia in T3 and T4 and large node mets from head and neck

• Hockel et al Cancer Res 56:4509, 1996 showed hypoxia correlated Hockel et al Cancer Res 56:4509, 1996 showed hypoxia correlated with local invasion and survival in cases treated with RT or with local invasion and survival in cases treated with RT or only only with surgerywith surgery


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Hypoxia and Local Tumor Hypoxia and Local Tumor ControlControl

Small Hypoxic FractionSmall Hypoxic Fraction

Large Hypoxic FractionLarge Hypoxic Fraction

• Local tumor control Local tumor control correlates with pre-correlates with pre-treatment oxygen levels treatment oxygen levels in head and neck ca., as in head and neck ca., as measured with an measured with an Eppendorf electrode. Eppendorf electrode. Tumors were stratified Tumors were stratified by whether the fraction by whether the fraction of pO2 values less than of pO2 values less than 2.5 mm Hg was above or 2.5 mm Hg was above or below the median (15%).below the median (15%).66-68 Gy was given in 66-68 Gy was given in 33-34 Fx.33-34 Fx.

• Nordsmark et al Nordsmark et al Radiother Oncol 41, 31, Radiother Oncol 41, 31, 19961996


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Tumor Hypoxia and DFSTumor Hypoxia and DFS

• DFS in cervix ca DFS in cervix ca depends on pOdepends on pO22, , irrespective of type irrespective of type of treatment, of treatment, surgery/RT. Hockel et surgery/RT. Hockel et al, Sem. Radiat. al, Sem. Radiat. Oncol. 6:30, 1996.Oncol. 6:30, 1996.

• This suggests that This suggests that hypoxia is linked to hypoxia is linked to tumor aggression tumor aggression


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RadiosensitizersRadiosensitizers

From Zeman, 2000


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RadiosensitizersRadiosensitizers

• Radiosensitizers such as Radiosensitizers such as nitroimidazoles can nitroimidazoles can ““mimicmimic”” oxygen oxygen and fix damageand fix damage– Associated with some toxicity and there were Associated with some toxicity and there were

only rarely efforts to determine if the tumors only rarely efforts to determine if the tumors were hypoxic in advance of treatmentwere hypoxic in advance of treatment

– However there have been positive trialsHowever there have been positive trials • DAHANCA 5 trial using nimorazole in treatment of advanced squamous cell carcinoma of the head and neck


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And a meta-analysis by Jens Overgaard has shown significantly improved survival and

loco-regional control

Journal of Clinical Oncology, 25: pp. 4066-4074, 2007


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Hypoxic CytotoxinsHypoxic Cytotoxins• QuinonesQuinones

– Mitomycin CMitomycin C• NitroaromaticsNitroaromatics• Benzotriazine di-N-Benzotriazine di-N-oxidesoxides– TirapazamineTirapazamine

• Phase III clinical Phase III clinical trials with cisplatintrials with cisplatin

• Phase II with RTPhase II with RT• Currently off the Currently off the market!market!


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Tumor ReoxygenationTumor Reoxygenation

• Since well oxygenated cells are more sensitive Since well oxygenated cells are more sensitive than hypoxic cells to ionizing radiation, one than hypoxic cells to ionizing radiation, one might reasonably expect that the hypoxic might reasonably expect that the hypoxic fraction (fraction (i.e.i.e. the proportion of hypoxic the proportion of hypoxic cells) to increase during the course of cells) to increase during the course of radiation therapy radiation therapy

• In fact, Putten & Kallman and others In fact, Putten & Kallman and others demonstrated that the proportion of hypoxic demonstrated that the proportion of hypoxic cells present within a tumor varies a lot, but cells present within a tumor varies a lot, but does not does not increaseincrease during a course of during a course of fractionated radiation therapy showing fractionated radiation therapy showing REOXYGENATIONREOXYGENATION exists. Multiple mechanisms exists. Multiple mechanisms exist and the variation seems considerable exist and the variation seems considerable from tumor to tumor.from tumor to tumor.


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Days post RT

Hypoxic Fraction

N.B. All single dose!


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• Development of new blood vessels from pre-Development of new blood vessels from pre-existing capillaries.existing capillaries.

• Although tumors smaller than approximately 1 mm Although tumors smaller than approximately 1 mm can receive sufficient oxygen and nutrients by can receive sufficient oxygen and nutrients by diffusion, continued growth depends upon the diffusion, continued growth depends upon the development of an adequate blood supply. In the development of an adequate blood supply. In the absence of angiogenesis, tumors do not increase absence of angiogenesis, tumors do not increase in size and remain localizedin size and remain localized

• Angiogenesis also occurs Angiogenesis also occurs duringduring – wound repairwound repair– pregnancypregnancy– certain times in the menstrual cycle certain times in the menstrual cycle

AngiogenesisAngiogenesis


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• In response to various tissue-derived pro-In response to various tissue-derived pro-angiogenic signals, endothelial cells in nearby angiogenic signals, endothelial cells in nearby blood vesselsblood vessels

Major Steps in the Angiogenic ProcessMajor Steps in the Angiogenic Process

Degradation of basement membraneDegradation of basement membrane

MigrationMigration


DifferentiationDifferentiation

Lumen formationLumen formation

Angiogenic factors:Angiogenic factors:

VEGF, FGF, PDGF,VEGF, FGF, PDGF,EGF, HGF, TGF EGF, HGF, TGF

HypoxiaHypoxia

COCO22COX-2COX-2NONO Tumor suppressor genesTumor suppressor genes

OncogenesOncogenes

Ischemia and reperfusionIschemia and reperfusion

– Degrade their basement Degrade their basement membrane and invade the membrane and invade the adjacent extravascular adjacent extravascular spacespace

– Endothelial cells behind Endothelial cells behind the leading edge the leading edge proliferate to replace proliferate to replace the migrating cellsthe migrating cells

– Newly generated Newly generated endothelial cells migrate endothelial cells migrate through connective tissue through connective tissue toward the source of pro-toward the source of pro-angiogenic signalsangiogenic signals

– Endothelial cells Endothelial cells assemble into a new assemble into a new vessel, form a lumen, lay vessel, form a lumen, lay down a basement membrane down a basement membrane and join other vessels to and join other vessels to allow flow.allow flow.


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• There is a relationship between There is a relationship between microvascular density and the microvascular density and the probability of metastasis, probability of metastasis, relapse free survival and/or relapse free survival and/or prognosis. prognosis.

• Weidner Weidner et alet al (N Engl J Med 324: (N Engl J Med 324: 1, 1991) demonstrated that the 1, 1991) demonstrated that the likelihood of developing likelihood of developing metastasis increased directly as metastasis increased directly as the density of tumor associated the density of tumor associated blood vessels increasedblood vessels increased

Tumor Vasculature and MetastasisTumor Vasculature and Metastasis

# microvessels/unit area% with metastasis

1/7

9/20

5/7

15/15


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Inhibition of tumor growthInhibition of tumor growth• chronic exposurechronic exposure

Induction of tumor necrosisInduction of tumor necrosis• acute exposureacute exposure

Blood vesselBlood vesselBlood vesselBlood vessel

Vascular TargetingVascular Targeting Induction of selective Induction of selective and irreversible damage and irreversible damage to to establishedestablished tumor- tumor-

associated blood vesselsassociated blood vessels

Anti-AngiogenesisAnti-AngiogenesisPreventing the growth Preventing the growth

of of newnew tumor- tumor-associated blood associated blood

vesselsvessels


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• Since many thousands of tumor cells depend upon Since many thousands of tumor cells depend upon each blood vessel for the delivery of oxygen each blood vessel for the delivery of oxygen and nutrients, theoretically even limited and nutrients, theoretically even limited damage to tumor vasculature may occlude a damage to tumor vasculature may occlude a vessel and cause vessel and cause ““an avalanche of tumour cell an avalanche of tumour cell deathdeath””..

• Since cells being targeted are in contact with Since cells being targeted are in contact with the blood stream, delivery problems that limit the blood stream, delivery problems that limit the efficacy of therapies directed toward tumor the efficacy of therapies directed toward tumor cells are not an issuecells are not an issue

• Since endothelial cells are genetically stable Since endothelial cells are genetically stable and non-transformed, treatment-related and non-transformed, treatment-related resistance is less likely to emergeresistance is less likely to emerge

Advantages of vascular targetingAdvantages of vascular targeting


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Questions:Questions: Tumor Responses to RadiotherapyTumor Responses to Radiotherapy


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78. The probability of tumor cure 78. The probability of tumor cure (TCP) in a series of tumors that (TCP) in a series of tumors that have on average 1 cell surviving have on average 1 cell surviving isis– 00– 0.370.37– 0.50.5– 1.01.0#2 – it follows a Poisson distribution –

events in space


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79. If a tumor contains 1079. If a tumor contains 1099 clonogenic cells and RT reduces clonogenic cells and RT reduces survival by 10survival by 10-9-9, what is the , what is the probability of tumor cureprobability of tumor cure– minimalminimal– 37%37%– 50%50%– 90%90%

#2 – P of cure = e-x , where x is the average number of surviving clonogens, with 1 cell on average surviving the TCP will be 37% - e-1


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80. If a tumor contains 1080. If a tumor contains 1099 clonogenic cells and RT reduces clonogenic cells and RT reduces survival by 10survival by 10-10-10, what is the , what is the probability of tumor cureprobability of tumor cure– 10%10%– 37%37%– 50%50%– 90%90%

#4 – P of cure = e-x , where x is the average number of surviving clonogens, in this case 0.1 - or 90.5%


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81. Tumorgenicity is a stem cell 81. Tumorgenicity is a stem cell property of tumors that is best property of tumors that is best assessed byassessed by– TD50 assayTD50 assay– TCD50 assayTCD50 assay– In vivo - in vitro assayIn vivo - in vitro assay– Tumor regrowth assayTumor regrowth assay

#1 – varying numbers of cells are injected and the number required to cause 50% to grow is the tumor dose 50.


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82. Which of the following is not a 82. Which of the following is not a property of stem cells in tumorsproperty of stem cells in tumors– TumorgenicityTumorgenicity– PluripotentialityPluripotentiality– Expression of developmental Expression of developmental markersmarkers

– Radiation resistanceRadiation resistance– Cause of tumor regressionCause of tumor regression#5 –cancer stem cells are a subpopulation

of cancer cells that are responsible for tumor recurrence. Regression is probably more a property of the non-stem cell population.


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83. The rate of tumor regression 83. The rate of tumor regression after RT is determined primarily after RT is determined primarily byby– Tumor cell cycle timeTumor cell cycle time– Tumor growth fractionTumor growth fraction– TpotTpot– Labeling indexLabeling index– Cell loss factor Cell loss factor

#5 – the cell loss factor is the major influence on the rate of tumor growth and regression


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84. If the cell cycle time of a 84. If the cell cycle time of a tumor is 48hrs and the growth tumor is 48hrs and the growth fraction 10%, what is the fraction 10%, what is the potential volume doubling time?potential volume doubling time?– 2 days2 days– 10 days10 days– 20 days20 days– 3 months 3 months

#3 – the the GF was 100% the Tpot would be 2 days. If 10% it will be 20 days.


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85. If the Tpot for a tumor is 3 days 85. If the Tpot for a tumor is 3 days and the actual volume doubling time and the actual volume doubling time is estimated as 30 days, what is the is estimated as 30 days, what is the cell loss factorcell loss factor– 0.10.1– 0.30.3– 0.50.5– 0.90.9– 1.01.0

#4 – 1- 3/30 = 0.9


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86. The increase in tumor control 86. The increase in tumor control probability with dose for clinically probability with dose for clinically detectable tumors is theoretically detectable tumors is theoretically best described by which of the best described by which of the followingfollowing– A log-linear curveA log-linear curve– A sigmoid curve with a dose A sigmoid curve with a dose thresholdthreshold

– A sigmoid curve with no thresholdA sigmoid curve with no threshold– A curve that is close to linear with A curve that is close to linear with no threshold no threshold

#2 – a certain dose will be needed until you begin to see cures. After that it will be determined by the killing of the last surviving clonogens, which will be a sigmoid curve.


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87. The probability of eliminating 87. The probability of eliminating metastatic disease theoretically metastatic disease theoretically increases with dose and is best increases with dose and is best described by which of the followingdescribed by which of the following– A log-linear curveA log-linear curve– A sigmoid curve with a dose A sigmoid curve with a dose thresholdthreshold

– A sigmoid curve with no thresholdA sigmoid curve with no threshold– A flat curve that is close to A flat curve that is close to linear with no thresholdlinear with no threshold

#4 – palpable tumors have a restricted range of clonogens around 109-1010. Micrometastatic disease can be anywhere between 1 cell and palpable tumor – a wide range. Any dose could be effective up to what would be needed for palpable tumor i.e. the curve will be flat.


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88. Which of the following is NOT 88. Which of the following is NOT correct about accelerated correct about accelerated repopulationrepopulation– It involves a decrease in the cell It involves a decrease in the cell loss factorloss factor

– It can be promoted by treatment It can be promoted by treatment breaksbreaks

– It explains why tumor recur faster It explains why tumor recur faster than expected after RTthan expected after RT

– It occurs only in tumors It occurs only in tumors #4 – accelerated repopulation/regeneration spares normal tissues from the effects of radiation eg mucositis


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89. In T2-T3 HNSCC, what percent of 89. In T2-T3 HNSCC, what percent of a 2Gy dose is estimated may be a 2Gy dose is estimated may be lost to accelerated repopulation lost to accelerated repopulation later in the courselater in the course– 5%5%– 20%20%– 33%33%– 70%70%

#3 – This has been estimated by Maciejewski et al., 1989 Maciejewski et al., 1989 from the relationship between treatment time and total dose for control to be 0.6 Gy/day, but may be higher


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90. In T2-T3 HNSCC, when is 90. In T2-T3 HNSCC, when is accelerated repopulation thought accelerated repopulation thought to be initiatedto be initiated– 1 week1 week– 4 weeks4 weeks– 8 weeks8 weeks– 12 weeks12 weeks

#2 – there is a lag period before dose is ‘lost’ to accelerated repopulation that in HNSCC is about 4 weeks.


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91. In T2-T3 HNSCC, tumor doubling 91. In T2-T3 HNSCC, tumor doubling time may become close to Tpot, time may become close to Tpot, which on average is which on average is – 2-7 days2-7 days– 1-4 weeks1-4 weeks– 1-2 months1-2 months– 2-6 months2-6 months

#1 – Tpot has been measured in HNSCC patients and is in the order of 2-7days


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92. What occurs in tumors with 92. What occurs in tumors with distance from a blood vesseldistance from a blood vessel– Increased cell proliferationIncreased cell proliferation– Poor oxygen diffusionPoor oxygen diffusion– Decreased oxygen levels due to Decreased oxygen levels due to high consumption near the vesselhigh consumption near the vessel

– Increased pHIncreased pH

#3 – the reason for areas of chronic hypoxia is that oxygen is consumed by cells nearer the vessels.


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93. At what distance from a blood 93. At what distance from a blood vessel does radiobiologically vessel does radiobiologically relevant hypoxia occurrelevant hypoxia occur– 50 micrometers50 micrometers– 100 micrometers100 micrometers– 200 micrometers200 micrometers– 500 micrometers500 micrometers

#2 – As shown by Tomlinson and Gray


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94. Hypoxic areas in tumors are 94. Hypoxic areas in tumors are best assessed bybest assessed by– Pimonidazole uptakePimonidazole uptake– Carbonic anhydrases, like CAIXCarbonic anhydrases, like CAIX– Expression of hypoxia inducible Expression of hypoxia inducible factor (HIF-1)factor (HIF-1)

– VEGF expressionVEGF expression

#1 Pimonidazole is an oxygen mimetic that binds in hypoxic areas. The others are downstream events that are less reliable measures of hypoxia as they are induced by other stimuli also.


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95. Which of the following is true of 95. Which of the following is true of tumor vasculaturetumor vasculature– Its abnormal vasculature results in Its abnormal vasculature results in acute transient areas of hypoxiaacute transient areas of hypoxia

– It has a thin basement membrane but It has a thin basement membrane but no increase in permeabilityno increase in permeability

– It is responsible for low It is responsible for low interstitial tumor pressureinterstitial tumor pressure

– Poor angiogenesis limits it, causing Poor angiogenesis limits it, causing hypoxiahypoxia#1 – it is unable to sustain an open

configuration for long and constantly collapses causing transient hypoxia.


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96. The concentration of oxygen that 96. The concentration of oxygen that gives half-maximal gives half-maximal radiosensitization isradiosensitization is– 1mm Hg1mm Hg– 3mm Hg3mm Hg– 10mm Hg10mm Hg– 100 mm Hg100 mm Hg

#3 – this is half-maximal value. Relevant hypoxia is often taken as <5mm Hg, but there is no standard.


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97. For low LET radiation, the OER 97. For low LET radiation, the OER for an isoeffect isfor an isoeffect is– 1.0-1.61.0-1.6– 1.7-2.31.7-2.3– 2.3-3.02.3-3.0– 3.0-3.7 3.0-3.7

#3 – a huge effect in keeping with oxygen being a great radiosensitizer


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98. For 15MeV fast neutrons, the 98. For 15MeV fast neutrons, the OER is approximatelyOER is approximately– 1.61.6– 2.32.3– 3.03.0– 3.7 3.7

#1 – this may be attributed to a low LET component


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99. For alpha particle radiation, 99. For alpha particle radiation, the OER is closest tothe OER is closest to– 1.01.0– 1.71.7– 2.32.3– 3.0 3.0

#1 – OER falls inversely with RBE as LET increases


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100. The OER is lowest at an LET 100. The OER is lowest at an LET closest toclosest to– 1 keV/1 keV/mm– 10 keV/10 keV/mm– 50 50 keV/keV/mm– 100 100 keV/keV/mm

#4 – Due to direct action of ionizing radiation predominating


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101. Which tracer is NOT used to 101. Which tracer is NOT used to detect hypoxic areas in tumors by detect hypoxic areas in tumors by PETPET– FMISOFMISO– HypoxyprobeHypoxyprobe– EF5 - etanidazoleEF5 - etanidazole– Cu-ATSMCu-ATSM

#2 – hydroxyprobe is a kit that include a nitroimidazole and an antibody for staining fixed tissues.


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102. Which of the following is NOT 102. Which of the following is NOT induced by hypoxiainduced by hypoxia– Carbonic anhydrasesCarbonic anhydrases– VEGFVEGF– ErythropoietinErythropoietin– NF-NF-BB– EGFR downregulationEGFR downregulation

#5 – in fact hypoxia tends to up-regulate EGFR expression. The first 3 are downstream of HIF-1


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103. The generally accepted gold 103. The generally accepted gold standard in measuring hypoxia in standard in measuring hypoxia in a human tumor isa human tumor is– Polarographic needle probesPolarographic needle probes– HydroxyprobeHydroxyprobe– Carbonic anhydrase levelsCarbonic anhydrase levels– Osteopontin levelsOsteopontin levels– HIF-1 expressionHIF-1 expression

#1 – this may be replaced by 18F-miso as the needles are invasive and difficult to use reliable.


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104. How does HIF-1 act?104. How does HIF-1 act?– It is a transcription factor that is It is a transcription factor that is activated by phosphorylationactivated by phosphorylation

– It is a transcription factor that is It is a transcription factor that is activated by VHL (Von-Hippel Lindau) activated by VHL (Von-Hippel Lindau) proteinprotein

– Oxygen inhibits prolyl hydroxylase Oxygen inhibits prolyl hydroxylase that targets it for VHL (Von-Hippel that targets it for VHL (Von-Hippel Lindau) protein-mediated degradationLindau) protein-mediated degradation

– Hypoxia inhibits prolyl hydroxylase Hypoxia inhibits prolyl hydroxylase leading to HIF-1leading to HIF-1 stabilization stabilization

#4 – hypoxia stabilizes HIF-1 expression through inhibiting prolyl hydrolases and hence its degradation


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105. Clinically, pretreatment hypoxia 105. Clinically, pretreatment hypoxia has NOT been correlated withhas NOT been correlated with– Distant failure following surgeryDistant failure following surgery– Loco-regional failure in HNSCC Loco-regional failure in HNSCC following RTfollowing RT

– Decreased tumor recurrence in Decreased tumor recurrence in clinical trials of erythropoietin clinical trials of erythropoietin with RT in HNSCCwith RT in HNSCC

– Microvessel densityMicrovessel density

#3 – hypoxia drives tumor aggression and metastasis. Attempts to use EPO to improve RT gave a 10% decrease in local control because it stimulates tumor growth


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106. Which of the following is true for 106. Which of the following is true for nitroimidazolesnitroimidazoles– They mimic oxygen and radiosensitize They mimic oxygen and radiosensitize tumorstumors

– They radioprotect normal tissue by They radioprotect normal tissue by scavenging reactive oxygen speciesscavenging reactive oxygen species

– They are unable to sensitize acute They are unable to sensitize acute hypoxic areashypoxic areas

– A metanalysis by Overgaard has shown A metanalysis by Overgaard has shown that they improve locoregional control that they improve locoregional control to RT, but not survivalto RT, but not survival

– They can not kill hypoxic cellsThey can not kill hypoxic cells#1 – they are oxygen mimetic radiosensitizers that can be hypoxic cell cytotoxins. In the metanalysis survival was improved.


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107. Which of the following is 107. Which of the following is correct for Tirapazaminecorrect for Tirapazamine– It is a radioprotectorIt is a radioprotector– It has been shown to effectively It has been shown to effectively radiosensitize tumors in phase radiosensitize tumors in phase III clinical trails in HNSCCIII clinical trails in HNSCC

– it is a hypoxic cell cytotoxinit is a hypoxic cell cytotoxin– It radioprotects normal tissuesIt radioprotects normal tissues

#3 – It is driven to be toxic by low oxygen concentrations but has yet to be put into a Phase III trial with RT.


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108. Vascular targeting refers to108. Vascular targeting refers to– The effects of agents like The effects of agents like Avastin on tumor angiogenesisAvastin on tumor angiogenesis

– The interaction of anti-The interaction of anti-angiogenesis factors with RTangiogenesis factors with RT

– The selective effects of agents The selective effects of agents on established vasculatureon established vasculature

– The effects of agents like The effects of agents like erythropoietin on oxygen erythropoietin on oxygen delivery into tumors delivery into tumors #3 Vascular targeting sometimes is used

loosely to refer to any anti-vascular effects but really should be used for established vasculature where the aim is to be cytotoxic, as opposed to anti-angiogenesis factors which are more cytostatic

Documents

Www.radbiol.ucla.edu WMcB2008 Tumor Responses to RT Bill McBride Dept. Radiation Oncology David Geffen School Medicine UCLA, Los Angeles, Ca. [email protected]