8/26- Common Cancer Drugs 1: Classes & Mechanisms Flashcards
What are the 5 major classes of traditional antineoplastic drugs?
- Alkylating Agents
- Antimetabolites
- Anticancer antibiotics
- Platinum Coordination Complexes
- Plant Derived Products
What are alkylating agents (basics)?
Strong electrophiles that form positively charged intermediates or transition complexes with target molecules and cause DNA damage
What is the mechanism of action for alkylating agents?
- Inhibit DNA synthesis and cell division by covalent attachment at 2 points on DNA
- Crosslink DNA and achieve a 50-100x enhancement in cytotoxicity
What are categories of alkylating agents?
- Nitrogen mustards
- Nitrosoureas
- Alkyl sulfonates
- Ethylenimines and methylmelamines
- Triazenes
What are some nitrogen mustard agents?
- Mechlorethamine (nitrogen mustard)
- Cyclophosphamide
- Ifosfamide
- Melphalan
- Chlorambucil
“cyclophosphamide is the most useful and versatile of the nitrogen mustards”
What is the mechanism of cyclophosphamide?
- Activated by the cytochrome P450 mixed function oxidase system
- 2-chloroethyl groups form a cyclic ethylenimonium ion
- This positively charged ion interacts with electrophilic groups
What are the kinetics of Cyclophosphamide?
- Absorption
- Half life
- Elimination
- Well absorbed orally
- Plasma t1/2 of 6.5 hr
- Eliminated by kidney
What is Cyclophosphamide used for?
Lymphoma in regimens:
- CVP
- COP
- MOPP
Breast cancer in the CMF regimen
Ovarian cancer
Oat cell lung cancer
What are the combo chemo regimens:
- CVP/COP
- MOPP/C-MOPP
- CMF
- CVP/COP
- cyclophosphamide, vincristine (Oncovin), prednisone
- MOPP/C-MOPP
- mechlorethamine or cyclophosphamide, vincritine (Oncovin), procarbazine, prednisone
- CMF
- cyclophosphamide, methotrexate, 5-fluorouracil
What are the adverse effects of Cyclophosphamide?
- Myelosuppression is dose-limiting
- Alopecia
- Humoral and cellular immuno-suppression
- Cystitis
Acrolein accumulates from poly-phosphamide breakdown in bladder; can be managed with mesna and adequate hydration
What are antimetabolites (broadly)?
Drugs that are structurally related to naturally occurring compounds and compete for the utilization of normal metabolites
- May inhibit key enzyme or get incorporated into nucleic acids
Classes:
- Folate antagonists
- Purine analogues
- Pyrimidine analogues
What is the mechanism of folate antagonists?
Block the biosynthesis of fully reduced tetrahydrofolic acid (PGA?) and prevent one-carbon transfer reactions needed to synthesize:
- Thymidylate
- Purines
- Methionine
- Glycine
What are some folate antagonists?
May be large or small folate analogs
- Methotrexate (MTX)- an analog of folic acid
What is the mechanism of Methotrexate (MTX)?
Competitively inhibits folic acid binding to the enzyme DHFR (binds DHFR stronger than folic acid does)
- Cell death occurs as a result of the thymidylate and purine blockage
- S-phase specific agent
Kinetics of Methotrexate (MTX)?
- Absorption
- Distribution
- Elimination
- Well absorbed orally
- Triphasic decay from plasma following IV injection
- Excreted by the kidney
Use of methotrexate (MTX)?
Part of a curative regimen for:
- Acute lymphoblastic leukemia (ALL)
- Trophoblastic choriocarcinoma
- Burkitt’s lymphoma
What are the adverse effects of methotrexate (MTX)?
- Dose-limiting myelosuppression (Leucovorin rescue)
- Hepatotoxicity
Contraindications for methotrexate (MTX)?
Patients with renal impairment
Drug interactions with methotrexate (MTX)?
- Salicylates
- Probenecid
- Sulfonamides
What is myelosuppression?
In what conditions is it observed/what is the effect on cells/outcomes?
Chemo-induced bone marrow suppression
Summary: Alkylating agents
- Subclass
- Drug
- Mechanism
- Use
- Adverse Effect
Alkylating agents
- Subclass: N-mustard
- Drug: cyclophosphamide
- Mechanism: bivalent alk of DNA
- Use: lymphoma
- Adverse Effect: myelosuppressive
Summary: Anti-folate
- Subclass
- Drug
- Mechanism
- Use
- Adverse Effect
Anti-folate
- Subclass: large folate
- Drug: MTX
- Mechanism: inhibits DHF and thymidine synthesis
- Use: ALL
- Adverse Effect: myelosuppressive
What is the mechanism for Purine Analogues?
- Prevent the biosynthesis of purine precursors needed for RNA and DNA synthesis
- Get incorporated into RNA and DNA; fraudulent nucleic acids are made
- Require activation: antitumor purine analogs undergo “lethal synthesis” to convert them into 5’-phosphate ribonucleotides
Type 1- “Lethal Synthesis” for BOTH purines and pyrimidines
What are some categories of purine analogs? Agents?
- Thiolated purine analogs
- Inhibitors of glutamine dependent synthesis
- Inhibitors of xanthine oxidase
Agents:
- Thioguanine (6-thioguaniine)
- Mercaptopurine (6-MP) Analogs of guanine
What is the mechanism for thioguanine?
Following “lethal synthesis” it inhibits purine biosynthesis; gets incorporated into DNA >> RNA
What are the kinetics of thioguanine?
- Absolute
- Distribution volume
- Elmination
- Oral absorption is slow, incomplete, and erratic
- Excreted by the kidney
What is the mechanism of Pseudo-feedback Inhibition?
What are some uses for thioguanine?
- AGL
- ALL
- CGL
Adverse effects of thioguanine?
- Myelosuppression
- Concommitant use of allopurinal with thioguanine is okay
- Use of allopurinal with 6-MP increases its toxicity
What is the mechanism of Pyrimidine Analogues?
- Prevent the synthesis of pyrimidine precursors needed for RNA and DNA synthesis
- Get incorporated into RNA >> DNA; fraudulent nucleic acids are made
- Require activation: pyrimidine analogs undergo “lethal synthesis” to convert them to 5’-phosphate ribonucleotides
Type- 2“Lethal Synthesis” for pyrimidines ONLY
What are some categories of pyrimidine analogues? Agents?
- Halogenated pyrimidines
- Modified sugar
- Azapyrimidines
Agents:
- 5-fluorouracil (5-FU)- an analog of thymine
What is the mechanism of 5-fluorouracil?
Following ‘lethal synthesis’ 5-FU inhibits DNA synthesis by inhibiting thymidylate synthase, causing TTP levels to drop; gets incorporated into RNA >> DNA