Anti Neoplastic Agents

Antineoplastic agents

Cancer/Neoplasm• Cancer refers to a heterogeneous group of diseases caused by an

impairment of the normal functioning of genes• Cancer cells are also referred to as tumors or neoplasms • Tumors result from a single abnormal cell, which continues to divide

indefinitely• Cancer is characterized by uncontrolled growth, ability to invade

local tissues, and ability to spread or metastasize• The mechanism of carcinogenesis is multistage and multi factorial

process that involves both genetic and environmental factors– Initiation. The first step involves the exposure of normal cells to a

carcinogen producing genetic damage to a cell– Promotion. The environment becomes altered to allow preferential

growth of mutated cells over normal cells. • The mutated cells becomes cancerous

– Progression. Increased proliferation of cancer cells allows for invasion into local tissue and metastasis

Types of cancer

• Depending on the location cancer can be classified into two

(a). Solid tumors• Carcinomas are tumors of epithelial cells

– Carcinomas include specific tissue cancers e.g lung, colon, breast

• Sarcomas include tumors of connective tissue such as bone (osteosarcoma) or muscle (liomyosarcoma)

(b). Hematological malignancies• Lymphomas are tumors of the lymphatic system and

include Hodgkin and non-Hodgkin lymphomas• Leukemias are tumors of blood-forming elements and

are classified into acute or chronic

Causes of cancer

• Viruses including Epstein-Barr virus, hepatitis B virus and human papilloma virus

• Environmental and occupational exposures such as ionizing and ultraviolet radiation and exposure to chemicals including vinyl chloride, benzene, and asbestos

• Lifestyle factors such as high fat, low fiber diets as well as tobacco and ethanol use

• Medications including alkylating agents and immunosuppressants

• Genetic factors including inherited mutations, cancer causing genes (oncogenes), and defective suppressor genes

Molecular mechanisms of cancer

• All the causes of cancer finally leads to abnormality in the expression of proto-oncogenes

• Proto-oncogenes are normal genes that can become oncogene due to mutations or increased expression

• Proto-oncogenes code for proteins that help to regulate cell growth and differentiation

• The mutation of these genes to oncogenes in a sequential, multistep process leads to cancer

Cell life cycle

• The knowledge of cell life cycle is essential to the understanding of the activity of chemotherapeutic agents

• Cells reproduce through a very specific scheme called the cell cycle• The M (mitosis) phase is the phase in which the cell divides into two

daughter cells• After division, the cells go into either a resting phase (G0) or a presynthetic

(postmitotic) gap phase (G1)• Cells in the G0 phase are not sensitive to chemotherapy

Cont’• In G1, RNA and proteins required for the specialized

function of the cell are synthesized in preparation for DNA synthesis

• Synthesis of DNA occurs in the S phase• In G2 phase (premitotic or postsynthetic gap), RNA,

critical proteins, and the mitotic spindle apparatus are produced in preparation for the duplication of the cell

• Some anticancer drugs are cell cycle phase-specific• Antimetabolite anti-cancer agents damage the cell in the

S phase • Mitosis inhibitors have their maximum effect in the M

phase• Other antineoplastic agents such as DNA alkylating

agents and most antineoplastic antibiotics are toxic to cells regardless of the phase of the cycle

TerminologyNomenclature-Nomenclature of types of cancer is sometimes

ambiguous. -Cancer may be named after the discoverer as

Wilm’s tumor, Hodgkin’s disease, Kaposi sarcoma.

Sometimes named after the tissue from which the neoplasm is derived.

-The Suffix -oma indicates a benign tumor: adenoma; osteoma, chondroma. However, notable exceptions are lymphomas, myelomas; both are examples of malignant tumors.

-The Suffix –blastoma means tumor with primitive, embryonic appearance (neuroblastoma: nerve tissue; myoblastoma: muscle tissue).

-During embryonic developments tissues derive from three layers:

ectodermal, (form skin and nerve)

mesodermal (form bone, muscle, and cartilage) endodermal (form intestinal system).

-Sarcoma: derived from mesodermal tissues.

-Carcinoma: derived from ecto- or endodermal tissues

- Carcinosarcoma: derived from two tissue types ecto- or intradermal and mesodermal.

- Teratoma: derived from all three tissue types.

- Leukemia: derived from blood leukocytes

Antineoplastic agents

• Antineoplastic means against new growth• Generally, all antineoplastic agent act by interfering with

cellular synthesis or the function of RNA, DNA, and the proteins that sustain life

• All antineoplastic agents are designed to kill cells, therefore not specific to cancer cells

• An ideal therapeutic agent would only destroy cancer cells only

• Antineoplastic agents nonspecifically destroy the rapidly dividing cells of:

- GIT leading to severe nausea and vomiting - hair follicles resulting in alopecia - bone marrow leading to fatigue

Treatment of Cancer-The specific approach used to treat cancer

depends upon the specific type of cancer, location, and its stage.

-However, in most therapeutic approaches there will be a contribution of a chemical anticancer compound.

1) Surgery-Surgery may be applied when cancer is still in

the primary stages and when be sure that the entire tumor can be excised without causing significant damage of the vital organs.

-Surgery can also be used for diagnostic purposes.

2) Photo radiation therapy

-Tumors are localized selectively by injection of HPD (Haematoporphyrin derivatives).

-After a 24 - 72 hours interval, fluorescence can be observed in tumor tissues by the use of probes of fiber optics.

-To destroy tumors, light from a tunable dye laser of (620 - 640 nm) is directed onto the tumors. -Normal tissues which have minimal absorbency (620 - 640 nm) are minimally damaged.

3) Radiation therapy-Gamma rays from radio isotopes as Co 60 or X-ray are

used.-Radiation therapy may be superior to surgeries in case

of cancer of larynx. It can destroy microscopic cancer cells after surgery.

-Before surgery it reduces tumor and decreases metastasis.

-Because ionizing radiation is carcinogenic, radiation therapy is subjected to limitations.

-Radiation sensitizers are of help to increase damaging effect of radiation without increase in radiation dose. e.g. 5-fluorouracil, dactinomycin, misonidazole and razoxane, which is + 1,2-bis(3,5- dioxopiperazin- 1-yl) propane.

RAZOXANE

CH CH2 N N

4) Immunotherapy-In follow up treatment, the body’s own defenses may be

stimulated by immunotherapy to destroy the last few cancer cells remaining after surgery, radiotherapy or chemotherapy.

-The methodology attempts to boost the levels of lymphocytes, specifically T-cells and B-cells lymphocytes.

-The major role of T- cells is to destroy foreign cells, including malignant and premalignant cells.

-B-cells produced in the bone marrow and lymph nodes make antibodies in response to a foreign protein which may be expressed by cancer cells.

-Therapy of this type consists of the administration of interferon.

5) Chemotherapy -The intent of administering these agents may to

cure a specific cancer, reduce the size of a tumor prior to surgery, and sensitize tumors to radiation therapy or to destroy microscopic metastases after tumors are surgically removed.

-Chemotherapeutic agents are complementary to either surgery or radiation therapy.

-Their usefulness in treatment of cancer relies on the assumption that malignant cells, which are rapidly proliferating cells, take-up extra cellular materials at a great rate than the normal cells.

-However there are few normal cell types that are rapidly proliferating including hair cells, bone marrow cells and cells lining the gastrointestinal tract.

-Consequently, patients undergoing chemotherapy, suffer hair loss, depression

of their immune system, nausea or diarrhea.

However, chemotherapeutic agents have some drawbacks:

1-They are less useful for large tumors since such tumors are not well perfused with blood.

2-They are basically cytotoxic and can kill normal cells too.

6) Combined Chemotherapy It is highly effective in treating a

wide range of cancer conditions. Each drug in the combination should have a unique mechanism of action providing that the drugs did not have overlapping toxicity.

7 (Adjuvant ChemotherapyIt means Chemotherapy with surgery and radiation. Chemotherapy kills the microscopic rests of cells adjacent to primary tumor outside the surgical margin and the distant metastasis. Both of these cells are in infancy stage and are highly susceptible to drugs.

8) Gene Therapy

-Gene therapy is defined as the treatment of any condition through the transfer of genetic material.

-Gene delivery systems are based on viral and non viral approaches.

-Non viral approaches involve small liposomes, which can bypass the reticular endothelial system in the liver and therefore remain in the circulation for a long period of time.

-They can enter tumor tissue due to the increased permeability of tumor vessel walls and may be used as tumor target transport vehicles for DNA or drugs.

-Viral delivery approaches that employ certain modified viruses.

-This approach requires mechanisms to control the viral replication, in order to avoid dissemination of the therapeutic gene to non-target tissues.

-The strategy used to achieve this goal involves the replacement of viral genes related to replication in the host cell with the desired therapeutic gene.

The gene therapy can be divided into three groups:

a) Introduction of suicide genes: A strategy employs the delivery to tumor cells of genes encoding product-converting enzymes and then treatment with systemic administration of the respective nontoxic prodrug. This approach is termed suicide gene therapy.

b) Replacement of defective tumor suppressor genes: This strategy tends to replace either a missing or muted

defective gene. However, this strategy is less effective if cancer is oligo- or multygenic in origin.

c) Genetic immunopotentiation: Malignant cells show antigenic differences to normal cells. However their immunogenicity is not recognized by the host’s immune system.

The goal of immunological strategies is either to boost the immune system in a way that enables it to identify and efficiently eliminate tumor cells or to modify the immunogenicities of tumor cells so they can no remain undiscovered.

1. ALKYLATING AGENTS

• Alkylating agents can be strictly defined as electrophiles that can replace a hydrogen atom by an alkyl group under physiological conditions, but the term is usually more broadly interpreted to include any compound that can replace hydrogen under these conditions, including metal complexes forming coordinate bonds

• Alkylating agents contain chemical groups which have the ability of forming covalent bonds with nucleophilic substances in the cell (DNA, RNA and certain enzymes).

• Most of the anticancer alkylating agents are bifunctional; possessing two alkylating groups.

• They are thus able to react with two groups and can cause intra- or inter-chain cross-linking, that can interfere with transcription and replication of DNA.

Classification of alkylating agents

A. Nitrogen mustards

B. Nitrosoureas

C. Aziridines

D. Sulfonic acid esters

E. Triazines

F. Platinum complexes

A. Nitrogen Mustards

-Their original use stems from the observation during world war I, that individuals heavily exposed to mustard gas suffered damage to bone marrow and lymphoid tissues.

-Mustard gas: highly toxic, insoluble in water.

-Nitrogen mustard derivatives: less toxic, salts are solids and water soluble.

Mechanism of Action of Nitrogen Mustards

1. Aliphatic Substituted Nitrogen Mustards

-The molecules undergo neighboring group reactions in which the nitrogen atoms displaces a chlorine atom to give strained three-memberd aziridinium intermediates.

-The highly strained three-membered ring rearranges by scission to the carbonium ion, which in turns reacts with the nucleophilic groups.

-The attack leads to irreversible covalent bond formation with the substrate.

CH2 CH2Cl

Aziridinium ion

Nu H3C

CH2 CH2

Nu = nucleophilic center rich in electrons (OH, NH2, SH, COOH, SO3H ) present in

enzymes, proteins RNA and DNA

1. Aromatic Substituted Nitrogen Mustards

• Aryl substituted nitrogen mustards are relatively stable toward aziridinium ion formation, because the aromatic ring decreases the nucleophilicity of the N atom.

• The highly reactive carbonium ion species react with nucleophilic (electron-rich) sites on nucleic acids and proteins (alkylation occurs via SN1 mechanism)

+ -ClCH2

Stability in Water An inactive product is formed. So, drugs are marketed as dried powders to be put in solution before use as I.V. infusion fluid.

Alkylation of DNA by Nitrogen Mustards-In DNA, the N7 of guanine, being strongly

nucleophilic, is probably the main molecular target for alkylation in DNA.

-However N1 and N3 of adenine and N3 of cytosine may also be affected.

-The alkylated structure has a positive charge in its imidazole ring which renders the guanine-ribose linkage susceptible to cleavage.

-Guanine is also implicated in the cross-linking of double helical DNA, which interferes with separation of the strands and prevents mitosis.

2 Steps

+ +Cl- Cl-

Structure-Activity Relationship

1. Aliphatic nitrogen mustards are more soluble in lipid therefore more bioactive.

2. The more localized the unshared pair of electrons on N the higher is the reactivity.

3. Aromatic nitrogen mustards are of low basicity with a slow rate of C+ formation therefore the molecules can reach distant sites.

4. The presence of an Amino acid moiety with nitrogen mustard may direct the drug to a metabolic site affecting cancer.

5. Monofunctional alkylating agents are less bioactive.

6. Iodine or fluorine atoms instead of

chlorine decrease the activity (slow

formation of C+ ion); bromine atoms lead

to very reactive molecules but with high

toxicity.

Cl- 2,2’- Dichloro-N-methyldiethylamine hydrochloride

i. Mechlorethamine HCl (Mustine HCl)

is used in the treatment of Hodgkin’s diseases and other malignant neoplasm including lung carcinoma, chronic myelocytic leukemia and brain tumors. Adverse effects

include bone-marrow depression, nausea and vomiting, neurological disorders, and liver disorders. It is

administered intravenously and intracavitary.

synthesis

RNH2 O+ N

H3CSOCl2

ii. Mustrone (Mechlorethamine-N-oxide) 2,2’-Dichloro-N-methyldiethylamine-N-oxide.

-The toxicity of the parent compound is greatly reduced with only slight reduction inactivity.

- It is active after metabolic reduction to mechlorethamine.

iii. Chlorambucil (Leukeran)

4-[4’-Bis-(2-chloroethyl)aminophenyl]butyric acid

-Chlorambucil is an alkylating agent used for its antineoplastic properties in the treatment of leukemias, lymphomas and various other malignant neoplasms.

-It is the slowest acting and least toxic nitrogen mustard.

-Adverse effects include bone-marrow depression, GIT disturbances, neurotoxicity, lung disorders and sterility.

- It is administered orally.

434-[ Di-(2-Chloroethyl)amino]-L-phenylalanine

iv. Melphalan (Alkeran)

Phenylalanine-N-mustard

4-[ Di-(2-Chloroethyl)amino]-L-phenylalanine

-Melphalan is used for its antineoplastic action in the treatment of multiple myeloma and in other malignant neoplasm including tumors of the breast and ovary.

-Adverse effects include bone marrow depression, rashes, and GIT disturbances. It is active orally.

ClNH2HO

v. Cyclophosphamide (Endoxan)• Cyclophosphamide is an alkylating antineoplastic agent,

which can be given by mouth or by intravenous injection: • Although it is chemically related to the nitrogen

mustards, the nucleophilicity of the mustard nitrogen is less likely to form an aziridinium ion than are the alkyl-substituted nitrogen mustards.

• It requires activation in the body to take effect.

2-[Di-(2-Chloroethylamino]-1-oxa-3-aza-2-phosphacyclohexane-2-oxide.

Bioactivation of Cyclophosphamide

-It is biologically active in vivo, it is converted to the active compound mainly in the liver.

-It must be enzymatically oxidized to give an active metabolite, which is converted to 4-hydroxycyclophosphamide and aldophosphamide.

-The latter is chemically unstable, undergoing conversion to acrolein and phosphamide mustard.

-Acrolein causes urotoxicity, therefore Mesna which is acrolein antidote should be given HSCH2CH2SO3Na (Sodium mercaptoethanesulfonic acid).

-Mesna is water soluble and forms a non-toxic product with acrolein.

HCOCH2CH-S-CH2CH2SO3 Na

CYP450

Unstable carbinolamine

(Active)

Phosphoramide mustard

CH2 CH CHO+

Aldophosphamide (unstable)

Acrolein

-Cyclophosphamide is used in the treatment of various malignant diseases including lymphoma, myeloma and a variety of solid tumors.

-Adverse effects include myelosuppresion and hemorrhagic cystitis (which may be prevented with mesna) as well as GIT, pulmonary, and cardiac toxicity, alopecia and sterility.

-It is administered as tablets.

Structure-Activity Relationship1. The Bis(2-chloroethyl) is essential for activity. 2. Other halogen atoms decrease the activity. 3. The trimethylene chain between N & Cl shows no

activity because of the aziridinium cation formation is not going to be possible.

4. Cyclophosphamide has an asymmetric P atom, the S (-) isomer is more active than the R (+) isomer.

vi. MafosamideIt is a combination between cyclophosphamide and mesna.

vi. Uracil

5-[Bis(2-Chloroethyl) amino] uracil.

-It is a combination of the structural features of

N-mustard and a nucleotide which acts as a carrier for the active species.

-It is administered orally.

B. Nitrosoureas

i.Carmustine (BCNU)

1,3-Bis(Chloroethyl)-1-nitrosourea

-Carmustine is a neutral molecule that is highly lipophilic and poorly soluble in water.-These properties allow for efficient crossing of blood-

brain barrier.-Although carmustine administration is thought to

alkylate DNA and RNA as a mechanism of action, it is not cross resistant with nitrogen mustards and alternate mechanisms of action involving enzyme inhibition by carbamoylation of proteins have been suggested.

-It is rapidly metabolized after intravenous administration to form metabolites that have antineoplastic activity.

-These are vinyl cation, the ultimate alkylating agent and 2-chloroethylisocyanate which gives 2-chloroethylamine, an additional alkylating agent

Carmustine

Cyclic oxazolidine

Vinyl diazotic acid 2-Chloroethylisocyanate

H2C=CH +

2-Chloroethylamine

H2N Cl

Vinyl cation

-Carmustine is used in the treatment of leukemia, lymphomas, malignant melanoma and brain tumors.

-Adverse effects include bone-marrow depression, pulmonary fibrosis, and effects on liver, kidneys, and eyes.

ii. Lomustine (CCNU)1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea-It is a nitrosourea antineoplastic agent

similar to carmustine.

- It is formulated as capsules.

C. Aziridines (Ethyleneimines)-Aziridine is a 3 membered nitrogen heterocycle that reacts with

nucleophiles in order to relief ring strain.- At acidic pH, the aziridine group is protonated to provide a reactive

aziridinium ion that is known to alkylate DNA.

Triethylenemelamine (TEM, Tetramine) 2,4,6-Tris(1-aziridinyl)-s-triazine

Thiotepa Tris(1-aziridinyl )phosphine sulfide

•used in carcinoma of breast, bladder, Hodgkin’s and non-Hodgkin’s lymphoma. •Metabolic desulfuration leads to a toxic metabolite.

Toxic metabolite

D. Sulphonic Acid EstersBusulphan (Myleran)1,4-Butanediol dimethylsulfonateBusulphan is an alkylating agent with a methanesulfonic

acid acting as a leaving group. -It is used to treat chronic myelocytic leukemia. - It is formulated as tablets.-Adverse effects include prolonged and sometimes

irreversible bone-marrow depression, and pulmonary fibrosis.

- It is formulated as a tablet.

CH3H3C

E. Platinum compounds

i. Cisplatin (Platinol)

ii. Carboplatin (Paraplatin)

H3NCis-Dichlorodiaminoplatinum (II)

It is less toxic than cisplatin and used in ovarian cancer .

Chemical structures of cisplatin, carboplatin, oxaliplatin, satraplatin, andpicoplatin

Schematic image illustrating the G-GDNA intrastrand cross-linksproduced by cisplatin or carboplatin, oxaliplatin, satraplatin, and picoplatin

-It is a platin complex containing two ammonia molecules and two chlorine atoms in a cis configuration.

- It reacts with nitrogen atoms of DNA preferentially with N7 of deoxyguanylic acid forming intrastrand and interstrand cross-links.

- -It is active against testicular cancer, lymphoma, carcinoma of the head and neck, ovarian cancer and bladder cancer, However it induces renal and neurotoxicities.

- -It is administered intravenously.

Transplatin is inactive as it lacks the stereochemistry required for cross linking.

Mechanism of Action

H3N Cl

ClH3NH2O

H3N Cl

H3NNH3

H2NSugar

H3NNH3

DNA adductCross link

2. ANTIMETABOLITES

-Antimetabolites are compounds that prevent the biosynthesis or utilization of normal cellular metabolites.

-They are closely related in structure to the metabolite being antagonized.

-Many antimetabolites are enzyme inhibitors.

-They may combine with the active site as if they are the substrate or cofactor.

A. Folic acid Antagonists

-Folic acid is essential for the synthesis of nucleic acids.

-It is reduced to dihydrofolic acid (DHFA) then to tetrahydrofolic acid (THFA) by folate reductase.

-Tetrahydrofolic acid picks up a methyl group from serine or methionine and is converted into N5,N10-methylene tetrahydrofolic acid.

-This compound is oxidized to N5,N10-methenyl tetrahydrofolic acid.

-Breaking of the covalent bond between the formyl carbon atom and either N5 or N10 results in N10-formyl or N5-formyl tetrahydrofolic acid (folinic acid, leucovorin), respectively.

-In this loosely bound N5,N10-bridged position the one-carbon formyl group is transferred to other compounds that are then utilized in various essential pathways.

-It finds its way into C2 and C8 of purine bases, the C5 of deoxyuridilic acid and the methyl group of thymine.

-Tetrahydrofolic acid is also involved in biologically important reactions not directly involved in cell proliferation.

N5 -Formyl THFA Folinic acid, Leucovorin, N10 -Formyl THFA

glutamic acid

Oxidation

glutamic acid

Methenyl THFA-N5N10,

glutamic acid

Folate reductaseFolate reductase Tetrahydrofolic acidFolic acid Dihydrofolic acid

Folic acid

CH2 COOH

Folic acid OH H MetaboliteAminopterin NH2 H AntimetaboliteMethotrexate NH2 CH3 Antimetabolite

CH2 COOH

-Methotrexate is 4-amino-N10-methyl petroylglutamic acid.

-Methotrexate acts as an antifolate by binding almost irreversibly to the enzyme dihydroflate reductase and preventing the formation of the co-enzyme tetrahydrofolic acid, essential for DNA Synthesis and for replication of animal cell.

-Methotrexate inhibits not only the enzyme DHFR, but also thymidylate synthetase, these processes are vital for the metabolism of nucleic acid in the cells.

-Methotrexate inhibits folate reductase at two steps. -The drug binds much more strongly to the enzyme than does folic acid.

-Folic acid therefore cannot reverse the toxic effects of the drug which accounts for the relatively long lasting effects of methotrexate.

- Folinic acid, unlike folic acid can compete with methotrxate since it can still carry out one-carbon in spite of the fact that folate reductase is inhibited.

- This is the rationale for using folinic acid (leucovorin) as an antidote for methotrexate.

- Methotrexate is administered in tablet form and used to treat acute leukemia, meningeal leukemia, carcinoma of breast, head, neck, lung, ovarian and bladder carcinoma.

Leucovorin Rescue

NN COOH

O COOHCHO

-24 Hours infusion of methotrexate is more toxic than one push injection of the same amount. So giving the patient about 200 times the therapeutic dose will allow cancer cells to be exposed rapidly to very high doses in short time.

-Injection of leucovorin after few hours will supply normal cells with THFA despite inhibition of folate reductase by methtroxate.

-The result is a short exposure time of cancer cells to high doses of methotrexate and much more favorable therapeutic index.

B. Purine Antagonists

-6-Mercaptopurine (6MP) and 6-thioguanine (6TG) are examples of purine antimetabolites.

-Both are not active until they are converted to their respective nucleotides by a pyrophosphorylase enzyme in the cell.

-Since this is an intrinsically destructive process to the cell, it is referred to as a lethal synthesis.

-Tumor cells or normal cells that have very low levels of this enzyme are resistant to these two agents.

-Absence of this enzyme function is not lethal to the cell since the synthesis of purines in the cell occurs by different pathways.

-They interfere with the de novo synthesis of purines.

Adenine GuanineH

Natural bases

Co-Administration of Allopurinol with 6-Mercapotopurine

-6MP is metabolized by xanthine oxidase (XO) to 6-thioxanthine then to 6-thiouric acid, while 6TG is not affected by this enzyme.

-On the other hand, XO is responsible for the oxidation of hypoxanthine to uric acid which deposits in joints leading to gout.

-Allopurinol is a structural isomer to hypoxanthine and is a xanthine oxidase inhibitor but is not uricosuric acid.

-When allopurinol is given with 6MP, it will prevent the metabolic effect of the enzyme on 6MP, consequently the normal dose of 6MP will be toxic.

-Therefore, in case of administering 6MP with allopurinol the dose must be reduced; decreasing the risks of nephrotoxicity and acute gout formation.

X.O.X.O.

Inactivation

6-Thiouric acid6-Thioxanthine6-Mercaptopurine

Uric acidXanthineHypoxanthine

The main importance of allopurinol as an adjuvant to chemotherapy is that it prevents uric acid toxicity caused by the release of purines from destroyed cancer cells.

Allopurinol

Alloxanthine

C. Pyrimidine Antagonists

Uracil Cytosine Thymine

H HH H

In RNA In DNA

Natural pyrimidines

i. 5-Fluorouracil (5FU)

-Uridylic acid, the uracil nucleotide, goes through several steps to form deoxyuridylic acid which

-when methylated at position 5 becomes deoxy- thymidylic acid, the pyrimidine nucleotide found only in DNA.

-The enzyme that carries out this transfer and reduction of a CH3 group from the reduced folates is thymidylate synthetase.

-Thus a very close analog of uracil or its nucleotide would be able to bind to the reactive site of the enzyme and prevent the methylating step.

-The molecular modification that affected this was the substitution of the hydrogen in position 5 of uracil with a fluorine atom.

1-Since fluorine is only slightly larger than the hydrogen atom, very little molecular perturbation occurred resulting in the enzyme not recognizing the difference and accepting it instead of the natural substrate, in fact, the affinity for the drug was greater. H= 1.2 Å, F= 1.33 Å Cl= 1.73 Å, Br= 1.95 Å and CH3= 2 Å. Cl and Br are close to CH3 leading to bypass, so no enzyme blockade.

2-Since position 5 is occupied, it cannot be methylated.

Thus inhibition of thymidylate synthetase by 5-fluorouracil is the major reason for its cytotoxicity.

This substitution accomplishes two things:

Ribose-P

Deoxyribose-P

CH3(From folinic acid)

Deoxyribose-P

ReductionThymidylate synthetase enzyme surface

Deoxyribose-P

Thymidylate synthetase enzyme surface

Several steps

Uridylic acid Deoxyuridylic acid

-Actually 5-fluorouracil is not intrinsically toxic.

-It only becomes effective after the metabolic steps outlined in the above scheme.

-It is administered intravenously for the treatment of carcinoma of breast, colon, rectal, stomach, ovarian, cervical, prostate, bladder, head and neck carcinoma.

-It is administered topically for the treatment of skin and actinic keratoses.

Cont’ii. Floxuridine (5-

Fluorodeoxyuridine)5- Fluorouracil-2’-deoxyribose,

-It is easier to be activated than 5FU since it needs only the phosphate group to be added.

-Cancerous cells may undergo mutation and develop resistance upon prolonged treatment with purine and pyrimidine antimetabolites.

- The formation of alkaline phosphatase enzyme would break 6-mercaptopurine.

HO-H2C

3. HORMONES and ANTIHORMONES

-Tumors derived from hormone-sensitive tissues may be hormone dependent.

-Their growth can be inhibited by hormones of opposing actions, by hormone antagonists or by agents that inhibit the synthesis of the relevant hormone.

- Hormones essential for reproduction are also responsible for development and growth of breast, prostate and uterine cancer.

A. Hormone-Dependent Breast Cancer

-Estrogens bind to an estrogen receptor in estrogen target site (uterus, vagina, pituitary gland) to give E-R complex with subsequent response.

-The more is the cells in the tumor that contain estrogen; the higher is the estrogen receptor content.

-The tumor is said to be estrogen receptor rich (estrogen receptor positive).

-This tumor type responds well to endocrine therapy (antiestrogen).

-On the other hand, tumor with low estrogen receptors is said to be estrogen poor (estrogen receptor negative) responds poorly to endocrine treatment.

-The presence of progesterone receptors indicates active estrogen system.

-Ethinylestradiol is given orally in the treatment of breast cancer in post menopausal women. Androgens are active against metastatic breast cancer about 20% of postmenopausal women.

-Progesterone and its analogs are active against certain neoplasms that are stimulated by estrogens.

-High doses of progestines or androgens antagonize the proliferative action of estrogen. Endometrial carcinoma is treated with estrogens

i. Tamoxifen

2-[4-(1,2-Diphenyl-1-butenyl)phenoxy]-N,N-dimethylethanamine

-It is a Nonsteroidal antiestrogen used in the treatment of the advanced breast cancer.

-In breast tissues, tamoxifen competes with endogenous estrogen for the estrogen receptor and inhibits the transcription of estrogen-responsive genes.

-It is bioactivated first to produce the active hydroxylated derivative.

Bioactivation

B. Hormone-Dependent Prostatic Cancer

-Most of prostatic tumors are androgen-dependent.

-The action of androgens in prostate involves metabolic activation of circulatory androgens to a derivative with high binding affinity for androgen receptors.

Testosterone

Bioactivation

5-Reductasefound in neoplasm

-Androgen antagonists are used for the treatment of metastatic prostate cancer.

-They block the action of testosterone and dihydrotestosterone.

Antiandrogens may be classified into :

a. Steroidal compounds as cyprotone , chlormadinone and megesterol.

b. Nonsteroidal compounds as flutamide (eulexin) which is bioactivated first

i. Flutamide (Eulexin)2-Methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide

Bioactivation

It is administered as capsules

4. ANTIBIOTICS

-Several compounds that were originally evaluated for their antibiotic activity have been clinically useful anticancer agents.

-However, they were rejected as antibiotics because of their toxicity.

-This property was subsequently turned into asset with their application as anticancer agents.

-The source of most antitumor antibiotics is from microbial fermentation.

Anthracyclines-These antibiotics represent a major class of

antineoplastic agents. - It is characterized by having a tetracyclic

quinone containing ring nucleus to which is attached a unique daunosamine sugar.

-It was isolated from the fermentation broths of Streptomyces peucetius.

-Several semisynthetic derivatives have been prepared in an attempt to reduce the cardiotoxicity common to this class of compounds.

-These include daunorubicin, doxorubicin, idaurubicin and epirubicin.

OHR4=,OHR1 R2= CH3O, == OH, R3

Epirubicin:

, R4 = OHH=R3=R2=R1Idarubicin:

OH=R4,H=R3,H=R2= CH3O, R1Daunorubicin:

OH=R4,HR3,OH= == CH3O, R2

R1 Doxorubicin:

Mechanism of action

-The flat structure of anthraquinone nucleus results in the ability of anthracyclines to interact with DNA perpendicularly to its long axis.

-The amino sugar confers added stability to this binding through its interaction with the sugar phosphate backbone of DNA.

-The results of interaction can lead to single- and double-stranded DNA breaks.

-Because of the anthraquinone ring system, the anthracyclines are capable of generating reactive oxygen species such as .OH radical and super oxide radical anions( .O-O- ).

-These free radicals produce destructive effects upon the cell.

-The generation of free radicals may also account for the cardiotoxicity of the anthracyclines.

- Due to lack of oral activity, they are administered intravenously.

ii. Bleomycins

-Bleomycins are a group of metal-chelating glycopeptide antibiotics that degrade DNA; its molecule features two pivotal domains.

-One is the DNA domain, which allows interaction with DNA and RNA.

-The second binding site is a metal binding domain which is involved in chelation of ferrous iron and interaction with the oxygen, resulting in the oxidation of the iron and generation of superoxide.

-It is used for the treatment of squamous cell carcinomas of the head and neck.

iv. Dactinomycin (Actinomycin D)-Dactinomycin is the main antibiotic of Streptomyces

parvullus. -It consists of tricyclic phenoxazone ring and two

identical pentapeptide lactones.-The pentapeptides are made up of L-proline and L-

threonine plus the essential amino acids D-valine, sarcosine and N-methylvaline.

-The ring system is planar and can intercalate or insert into DNA between base pairs.

-The distortion caused by the presence of the intercalating agent affects the action of topoisomerase II, which normally regulates unwinding of coiled double-stranded DNA.

-This in turn, interferes with DNA replication and transcription.

CH3CH3

L-Pro L-Meval

D-ValL-Thr

L-ThrD-Val

L-Pro L-Meval

5-PLANT PRODUCTS (ANTIMITOTIC AGENTS)

-These agents prevent cellular mitosis, and in particular, interfere with the formation of the mitotic spindle.

- During mitosis; the protein tubulin undergoes polymerization to form mitotic spindle.

- -Antimitotic agents interfere with this either by depolymerization of the microtubules or by causing structures other than the normal mitotic spindle to be formed.

- -In the absence of a properly formed mitotic spindle, the chromosomes cannot correctly segregate and this ultimately leads to cellular death.

i. Vinca Alkaloids:Vincristine, Vinblastin and Vinorelbine

-These alkaloids are composed of two multi ringed units. -The vinca alkaloids contain tertiary amino groups that form salts which are freely soluble in water.

CH2-CH3

COOCH3

OCOCH3

CH2-CH3

CO2CH3OHHN

Vincristine: R = CHOVinblastin: R = CH3

H2SO4.

COOCH3

OCOCH3

CH2-CH3

CO2CH3OHHN

Venorelbine

ii. Taxans-Paclitaxel and docetaxel are taxan derivatives of yew

tree black. -Docetaxel is active in patients with breast cancer

resistant to anthracyclines. -Both derivatives are excellent choices for the first and

second line treatment of patients with metastatic breast cancer.

-Paclitaxel is administered intravenously in non aqueous solution.

-Docetaxal is a taxoid differing in structure from paclitaxel in having one less acetate group and a tertiary butyl carbamate group in place of the benzamido group.

-The injectable solution must be diluted prior to use.

R2-O OCH3

OCOCH3

Paclitaxel: R1 = C6H5; R2 = Acetyl

Docetaxal: R1 = (CH3)3C-O; R2 = H

6. MISCELLANEOUS ANTICANCER AGENTS

i. Podophyllotoxins

- They are obtained as extracts of the May apple plant, used to treat small cell carcinomas of the lung and Hodgkin’s diseases.

-They cause DNA linkages or DNA strand breaks by inhibiting topoisomerase II.

-It may be applied topically as paint.

ii. Hydroxyurea H2N-CO-NH-OH

-It inhibits ribonucleotide diphosphate reductase, thus interferes with the conversion of ribonucleotides to deoxyribonucleotides required for DNA synthesis.

-The action may be due to chelation of Fe2+ cofactor.

It is a cell-cyclespecific for S-phase and causes cells to arrest at the G1-S interface.

-This is useful for radiation therapy as cells in the G1 phase are particularly resistant to radiation.

-It is used in head and neck carcinoma, ovarian carcinoma, leukemia and malignant melanoma administered as capsules.

iii. Mitotane

1,1-Dichloro-2-(o-chlorophenyl-2-(p-chlorophenyl)ethane.

*It is related in structure to the insecticide DDT.

*It is used in adrenal cortex carcinoma and administered as tablets.

ClCHCl2

iv. Procarbazine (Matulane)

N-(1-Methyl)-4-[(2-methylhydrazino)methyl]benzamide

It is an alkylating agent.

Mechanism of Action

-At physiologic pH and in the presence of oxygen, procarbazine decomposes by auto oxidation pathway to release H2O2 and the formation of azocarbazin.

-The azocarbazine undergoes hydrolysis to yield a benzaldehyde derivative and methylhydrazine.

-Methylhydrazine oxidation produces methyldiazene and then methyl radical.

-Methylhydrazine can methylate RNA and DNA. The drug is used to treat hodgkin’s diseases.

-It is administered as capsules.

N2++ H+CH3+

Methylhydrazine

+ CH3-NH-NH2

ProcarbazineAzoprocarbazine

H2O2O2

N NH3C HMethyldiazene

v. Pipobromane

1,4-bis(3-Bromopropionyl)piperazine

It is used for the treatment of polycithemia.

vi. Mitobronitol (Dibromomannitol

1,6-Dibromo-1,6-dihydroxy-D-mannitol

-It is a sugar derivative that can penetrate the blood-brain barrier.

- It acts as busulphan (alkylating age

Anti Neoplastic Agents

Documents

Chapter 3. Anti-Neoplastic Drugs

ISSN 2278 EISSN 5396 DRUG DISCOVERYdiscoveryjournals.org/drugdiscovery/current_issue/2019/A5.pdf · Most of the anti-neoplastic agents act by interfering with cellular synthesis or

ANTI-INFLAMMATORY AGENTS

Anti hyperlipidemic agents

Anti Tuberculosis Agents

Anti-plaque & Anti-calculus Agents

Anti-epilepsy Agents

Anti-fungal agents

Anti Neoplastic Agents Utd

Hazardous Chemical Agents (anti-neoplastic, carcinogens

Anti – VEGF Agents

Anti fungal agents

BILLING & CODING MEDICAL ONCOLOGY€¦ · Chemotherapy administration includes: • Certain monoclonal antibodies & other biologic response modifiers • Anti-neoplastic agents provided

ANTI VIRAL Agents

Uncaria tomentosaExerts Extensive Anti-Neoplastic Effects

2019 Clinically Preferred Drug ListLeprostatic Agents 10 ANTIEMETICS 10 NEUROLOGIC AGENTS 11 Anti-Parkinsons Agents 11 Anti Migraine Agents 11 Alzheimers Agents 12 Anti-Convulsants

Postulating a Dermal Pathway for Exposure to Anti- Neoplastic

Anti hypertensives agents

Anti Tubercular Agents

Anti-infective Agents