Antineoplastic agents

Cancer Cancer is a group of neoplastic diseases that occur in humans in all ages and in all races as well as in animals It is basically a disease of cells characterized by uncontrolled cell division. Factors inducing cancer (carcinogenic factors): Physical factors : e.g. exposure to radiation (X-Ray, UV) Viruses have been implicated in human cancer (e.g.HCV) Chemical substances; ( e.g. cigarette smoke, Aflatoxin B1) Metabolic and hormonal factors Genetic factors Food and environment

According to the type of tissue from which they arise Classification of types of cancer According to the type of tissue from which they arise Sarcoma Carcinoma Mesodermal tissue Epithelial tissue Liver Kidney Brain Lung Connective tissue Muscle bone Leukemia Lymphoma Blood Lymphoid The cells divide excessively forming local tumor that invades adjacent organs. They also can migrate through blood or lymph to other organs causing metastasis

Chemotherapeutic agents Treatment of cancer In order to obtain good result in cancer treatment, the concept of total cell eradication must be applied. Three main lines are adopted either individually or in combination Surgical line : Total excision of the tumor if localized Radiation therapy: Using different types of ionizing radiations. Chemotherapy: Used alone or along with surgery or radiation Chemotherapeutic agents They are also called antineoplastic, cytotoxic, cytostatic, antitumor or anticancer. They act in different way on cell division. They show activity only on cells in the process of division (high growth rate). Accordingly malignancies showing high percentage of cells in the process of division are more susceptible to chemotherapeutic agent. Normal cells that divide rapidly are affected e.g. Hair follicle, mucous membrane of the stomach.

Classification of chemotherapeutics Alkylating agents Nitrogen mustards Alkyl sulfonates Nitrosoureas Aziridines Triazines Antimetabolites Folic acid antagonist Purine antagonist Pyrimidine antagonist III. Natural products Vinca Alkaloids Antibiotics IV. Hormones V. Miscellaneous

Mechanism of action of alkylating agents (nitrogen mustard) They are highly electrophilic agents that react by alkylation of important nucleophilic groups including: Proteins ( NH2, SH, COOH) N7 in guanine base of DNA causing cell death Alkylation of DNA leads to cell death because they cause: Miscoding and formation of abnormal base pair of guanine with thymine instead of cytosine Interstrand cross-linking : the 2 chloroethyl chain with 2 guanidine bases Depurination by excision of purine moiety from the strand residue Cleavage of imidazole ring.

Cross linking

nucleotide A T C G T A G C

Alkylating agents (1) Nitrogen mustards SAR ethylene moiety between N and Cl is essential for activity to form the aziridinium ion CH2 or CH2CH2CH2 abolish activity Halogen other than Cl ↓ activity

A) Nitrogen mustard Mechlorethamine HCL Mustine HCL Synthesis In 1st world war sulphur mustard gas was used as a war gas however, it was found that it cause atrophy of the lymphoid tissue. Mechlorethamine HCL Mustine HCL Synthesis

Mechanism of action Formation of reactive aziridinium cation which can alkylate DNA (SN2) Assay Hydrolysis with KOH yields KCl which can be determined using Volhard’s method

Chlorambucil COOH gp improve water solubility (water soluble Na form absorbed orally) Aromatic ring electron density of N therefore no formation of aziridinium cation The reaction goes through ( SN1 ) reaction

Cyclophosphamide Oxazaphosphorines The most commonly used It has a broad application It is a prodrug and is not toxic itself Activation takes place by cytochrome P 450 monooxygenase in the liver

Activation of cyclophosphamide in the liver by cytochromeP450 The active phosphoramide mustard reacts with nucleophile

Unfortunately How to overcome this toxicity The acrolein released cause kidney toxicity? Because it reacts with cysteine residues in cell protein How to overcome this toxicity Toxicity can be reduced by co-administration of 2-mercaptoethane sufonate sodium (Mesna) that interacts with acrolein and convert it to water soluble product eliminated in urine acrolein Mesna Safe addition product

Synthesis SAR Bis(2-chlorothyl) is essential for activity Replacement of Cl with F, Br or I →↓ activity

Melphalan Has COOH group, so has good water solubility It mimic amino acids , as a result the drug can be recognized as amino acid and taken into cells by carrier protein It has also good stability (can be take orally)

B) Nitrosourea CARMUSTINE 1,3-Bis-(2-chloroethyl)-1-nitrosourea It is a chloroethylnitrosourea derivative It is lipid soluble (can cross BBB) Used for treatment of brain tumor

Mechanism of activation Decompose spontaneously in the body to release Alkylating agent (alkylation of DNA Carbamoylating agent that reacts with proteins

Busulfan C) 3-Methane sulfonate Sulfonate gp is a good leaving gp act as chlorine in nitrogen mustard Mechanism: SN1 and does not involve intermediate like aziridinium ion It alkylate the N7 position in guanidine

Synthesis Assay Busulfan is hydrolyzed in water and liberate methane sulfonic acid that can be titrated with NaOH using phenolphthalein as indicator

D) Aziridines They are strained ring system (aziridine ring). The reactivity of the aziridine group is increased by protonation.

Thiotepa N,N`,N``Triethylenethiophosphoramide, tris(1-aziridinyl) phosphine sulfide.

Uses of Thiotepa Thiotepa is most active at low pH. It has been used in carcinomas of the breast and ovary and malignant lymphomas.

E) Triazenes Dacarbazine: Deticene, DTIC, 5-(3,3-dimethyl-1-triazenyl)-1H-imidazol-4-carboxamide.

Uses of Dacarbazine It is taken parenterally for the treatment of metastatic malignant melanoma and in combination therapy for Hodgkin`s disease.

Mechanism of action of Dacarbazine Activation of DTIC by a microsomal enzyme in the liver can produce a methyldiazonium ion, a precursor to methyl carbonium ion.

II. Antimetabolites Folic acid Purines Pyrimidines Nucleoside Nucleotide DNA PROTEINS RNA ENZYMES

A) Folic acid antagonist Methotrexate DHFR Folic acid Dihydrofolic acid FH2 tetrahydrofolic acid (FH4) FH4 transfer 1 carbon (CHO formyl group) Methotrexate binds to DHF reductase 10000 stronger than DHF and therefore inhibits1 carbon transfer essential for purine de novo synthesis FR DHFR

6-Mercaptopurine B) Purine antagonist: It is prodrug that is converted in the body to thio-dGTP which Inhibits the synthesis of guanine nucleotides 6-MP is incorporated into DNA instead of guanine base leading to cell death Metabolism

Fluorouracil C) Pyrimidine antagonist: Inhibits thymidylate synthase (suicidal inhibition) Thymidylate synthase convert dUMP → dTMP This reaction require loss of proton as H+ in case of 5-fluorouracil , fluorine atom can not leave as positive ion So the enzyme is irreversibly inhibited → no dTMP → no DNA synthesis

D) DNA polymerases inhibitor They are enzymes that catalyse the synthesis of DNA using the nucleotide bases dATP, dGTP, dCTP & dTTP Cytarabine It is prodrug It is an analogue of deoxycytidine It is competitive inhibitor of DNA polymerase S.E.: metabolized by hepatic deamination to give inactive uracil derivatives

e.g.1,2. Doxarubicin and Daunorubicin III. NATURAL PRODUCTS A) Antibiotics Anthracyclines e.g.1,2. Doxarubicin and Daunorubicin

They are coloured crystalline compounds and are administered intravenously as hydrochloride. Daunorubicin is used in the treatment of acute lymphocytic and granulocytic leukemias. Doxorubicin, on other hand, has a significant role in the treatment of solid tumors, such as, carcinoma of breast, lung, thyroid, and ovary, as well as, soft tissue sarcoma Mechanism of action: They act by different postulated mechanisms: 1) Intercalation. Initially they were found to bind DNA by intercalation between base pairs perpendicular to the long axis of the double helix. This intercalation causes partial unwinding of the helix and thus disrupts DNA polymerases and transcription. 2) Free-radical generation. Free-radical formation (highly reactive compounds with an unpaired electron) occurs during the metabolism of anthracyclines. 3) Membrane interaction. When anthracyclines bind to cell membrane, changes in membrane glycoproteins, transmembrane flux of ions, and membrane morphology have been demonstrated in a variety of cells. 4) Metal ion chelation. The anthracyclines are capable to chelate divalent cations such as calcium and ferrous ions by virtue of the quinone and phenolic functions.

e.g.3. Mitomycin C Mechanism Alkylating agent (Interstrand cross linking) In the body it is activated by reduction and loss of methoxy group Work better in anaerobic condition (as in solid tumor) Has several side effects (one of the most toxic)

b) Natural alkaloids Vinca alkaloids: (vincrestine & vinblastine ) & its semisynthetic derivative vindesine, They appear to exert their major anti-tumor effect by binding to critical microtubular proteins within cells Which are essential contractile proteins for the mitotic spindle of dividing cells, this binding leads to mitotic arrest. Acridone alkaloids e.g. acronycine

IV- Hormone-based therapies A) Therapy for treatment prostate cancer 1)Estrogens & 2)Antiandrogens B) Therapy for treatment breast cancer and or endometrial carcinoma 1)Antiestrogens & 2) Aromatase inhibitors & 3)Progestins

A) Therapy for treatment prostate cancer 1) Estrogens Diethylstilbestrol is used in treatment of prostatic cancer, but a feminizing effect is observed, this has been overcome by its phosphate derivative fosfesterol, which is more specific due to the presence of phosphatase enzyme in cancer cells, and it is used also in the treatment of prostatic cancer.

Estramustine sodium phosphate It was designed to carry the nitrogen mustard selectively into cells with estrogen receptors. It is used also in the treatment of prostatic cancer. Has 2 mechanisms of action :alkylating agent and estrogenic activity

2) Antiandrogens Flutamide It is used to treat the prostate cancer by blocking the action of androgens on their receptors

B) Therapy for treatment breast cancer and or endometrial carcinoma 1) Antiestrogens Tamoxifen has been used successfully in the treatment of advanced breast cancer in postmenopausal women.

2) Aromatase inhibitors Anastrazole They tend to be used as second line drugs for the treatment of oestrogen-dependent breast cancers that prove resistant to tamoxifen.

3) Progestins They are active against certain neoplasms that are stimulated by estrogens. They appear to exert anti-estrogenic effects of uncertain mechanism. Megestrol acetate is used against endometrial carcinoma.

IV. Miscellaneous 1- Cisplatin In the body the 2Cl groups are replaced by nucleophiles in DNA especially N7 guanine It is bifunctional alkylates 2 guanine base causing cross linking

2- Hydroxyurea, hydrea. It can be given orally. It is active against melanoma, chronic myelocytic leukemia, and metastatic ovarian carcinoma.

Mechanism of action It interferes with DNA synthesis by inhibiting ribonucleotide reductase, and this action results in decreased levels of deoxyribonucleotides. Hydroxyurea may interfere with the function of the enzyme by chelating with its ferrous iron cofactor.

3- Protein kinase inhibitors They are enzymes which phosphorylate specific amino acids in protein substrate. Tyrosine kinases Serine kinases Histidine kinases

A) non-receptor enzyme inhibitors Imatinib mesylate (Gleevec) Tyrosine kinase inhibitors: A) non-receptor enzyme inhibitors B) receptor enzyme inhibitors A) non-receptor enzyme inhibitors Imatinib mesylate (Gleevec) Gleevec is It is administered orally and indicated for the treatment of patients with chronic myeloid leukemia (CML).

4-[(4-methyl-1-piprazinyl)methyl]-N-[4-methyl-3-[[4-(3-pyridinyl)-2-pyrimidinyl]amino]-phenyl]-benzamide methanesulfonate.

Mechanism of action Protein tyrosine kinases are important in the transduction of signals initiating cellular replication and transformation. Gleevec is a protein tyrosine kinase inhibitor that inhibits the constitutive active abnormal tyrosine kinase (protein termed bcr-abl) created by the philadelphia chromosome abnormality in CML. It inhibits proliferation and induces apoptosis in leukemia cells.

B) receptor enzyme inhibitors Gefitinib (Iressa®) Gefitinib is designated chemically as N-(3-chloro-4-fluorophenyl)-7-methoxy-6-(3-morpholinopropoxy)-quinazolin-4-amine.

Gefitinib is currently only indicated for the treatment of locally advanced or metastatic non-small cell lung cancer (NSCLC) in patients who have previously received chemotherapy. It is used in the treatment of other cancers where EGFR overexpression is involved. Gefitinib is the first selective inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase.

4- Intercalating agents Amsacrine It contain a planar heteroaromatic ring system which can slip into the double helix of the DNA and distort its structure. As a result it can inhibit replication and transcription