Slide Deck 3: Chemotherapeutic Agents 1 Cytotoxic Chemo

Classes of Anticancer Agents

Categorize the following as either an alkylating agent or an antimetabolite.

1. Pyrimidines

2. Methylators

3. Antifolates

4. Nitrogen Mustards

5. Platinums

6. Purines

1. Alkylating Agent

   1. Nitrogen mustard

   2. Methylators

   3. Platinums

2. Antimetabolite

   1. Purines

   2. Pyrimidines

   3. Antifolates

Reminder: alkylating agents damage a cell’s DNA to stop cancer cells from growing and dividing

Antimetabolites trick cells into using a fake building block instead of real ones, which stop them from making new DNA and dividing

Alkylating Agents

Are alkylating agents cell-cycle non-specific or specific?

non-specific: they act at multiple phases of the cell cycle

Alkylating Agents

All alkylating agents are _____ (electrophilic or nucleophilic) molecules that ___ (ionically or covalently) modify nucleic acid bases on DNA.

electrophilic

covalently

Alkylating Agents

All alkylating agents are either monofunctional or bifunctional. What do these respective terms mean?

Monofunctional: cause single strand DNA breaks

Bifunctional: Inhibit DNA replication and transcription by cross-linking DNA

Alkylating Agents

Categorize the following drugs as either Nitrogen Mustards, Methylators, or Platinums.

1. Temozolomide

2. Cyclophosphamide

3. Cisplatin

4. Dacarbazine

1. Nitrogen Mustards

   1. Cyclophosphamide (Cytoxan)

2. Methylators

   1. Temozolomide

   2. Dacarbazine

3. Platinums

   1. Cisplatin

Alkylating Agents

How do nitrogen mustards, like cyclophosphamide, produce cytotoxicity?

By forming covalent inter-strand cross-links in DNA.

• the nitrogen mustard cross-link has been demonstrated to occur in the G-C rich region of DNA

• (cyclophosphamide) contains two reactive arms [is bifunctional]: as seen in the picture

Alkylating Agents

Cyclophosphamide is an ORAL PRODRUG that forms active metabolites through first-pass hepatic metabolism. A byproduct of cyclophosphamide metabolism is a______, which is toxic to the bladder epithelium and can lead to hemorrhagic cystitis. What is given co-administratively or as prophylaxis for cyclo…?

Acrolein

MESNA [MESNEX] (a thiol drug): it scavenges acrolein

Alkylating Agents

1. List 5 common AEs of cyclophosphamide.

2. What condition is a risk but it mitigated with MESNA therapy?

3. What syndrome is is generally observed with high doses of cyclophosphamide?

1. Myelosuppression, Fever, Alopecia, CINV, Diarrhea

2. Hemorrhagic cystitis

3. Cardiotoxicity (potentially fatal): presents as severe cardiac failure ~10 days after drug admin.

Alkylating Agents: Temozolomide (Temodar)

1. Prodrug? Yes or No

2. What is its anti-tumor activity?

3. Indication?

1. Yes

2. Methylation of purines (adenine and guanine) on DNA

3. Glioblastoma multiforme (brain cancer)

Alkylating Agents

What leads to the development of acquired resistance to temozolomide, and what inhibition stops resistance mechanisms and increases cytotoxicity of TMZ?

Resistance Mechanisms:

1. MGMT enzyme repairing the O6-methylguanine

2. BER pathway alkylation repair of N7/N3 positions

Inhibits resistance + increases cytotoxicity:

• PARP inhibitors (synthetic lethality): they block BER pathways

Alkylating Agents: Methylators

Dacarbazine:

1. Indications:

2. Part of the polychemotherapy regimen: _ _ _ _

3. Prodrug? Yes or No

1. melanoma and Hodgkin’s kymphoma

2. ABVD (Adriamycin, Bleomycin, Vinblastine, Dacarbazine) [first-line treatment of Hodgkin’s lymphoma

3. yes

Alkylating Agents

What drug is a platinum?

Cisplatin

• have drastically improved outcomes of patients with testicular and bladder cancer

Alkylating Agents

What is the MOA of cisplatin (platinum)?

The platinum atom of cisplatin binds covalently to DNA bases to form crosslinks.

• Cisplatin-DNA bonds cause various cellular responses (ex. replication arrest, transcription inhibition, cell-cycle arrest, DNA repair and apoptosis)

Cisplatin AEs

List 7 of cisplatin’s most common adverse effects.

1. Ototoxicity

2. Cardiotoxicity

3. Nephrotoxicity

4. Hematological toxicity

5. GI toxicity

6. Hepatotoxicity

7. Neurotoxicity

Summary: Ear, Heart, Kidney, Blood, GI, Liver, Neurons

Cisplatin Major Adverse Events (BOXED WARNINGS)

List the 4 boxed warnings associated with cisplatin.

1. Nephrotoxicity

   1. Acute kidney injury (PTS NEED TO HYDRATE)

   2. hypomagnesemia (MG SUPPLEMENTATION)

2. Peripheral Neuropathy

3. Nausea and Vomiting

   1. Antiemetics

4. Myelosuppression

Antimetabolites

Drugs are used to ____ structures of normal precursor molecules used in DNA synthesis.

Act in the ___ phase and are non-cell specific or cell specific?

counterfeit

S phase; cell specific

Antimetabolites

Put the following drugs in their categories (dihydrofolate reductase [DHFR] inhibitors, pyrimidine analogs, purine analogs).

1. Capacetabine

2. Methotrexate (MTX)

3. 6-mercaptopurine

4. 5-fluorouracil (5-FU)

DHFR inhibitors

1. MTX

Pyrimidine analogs

1. 5-FU

2. Capecitabine

Purine analogs

1. 6-mercaptopurine

Antimetabolites: DHFR Inhibitors

Folate (folic acid) is essential for the synthesis of _____. It is converted to dihydrofolate (FH2) then tetrahydrofolate (FH4) which provides the single carbon groups for the synthesis of dTMP. Methotrexate is administered high dose and is approved for cancers like acute ____ ____.

Purines; acute lymphoblastic leukemia (ALL)

Methotrexate

The minimal effective and minimal toxic concentration of MTX is ___ and the therapeutic index is ___. There are 5 notable toxicities, which include:______. _____ can be managed.

small; narrow; mucositis, renal failure, liver injury, neurotoxicity, myelosuppression; nephrotoxicity

Rescue for the HD-MTX

What treatment is there to prevent toxicity from administering MTX at high doses? Why does it work?

Leucovorin (folinic acid); it works because it allows for some purine synthesis to happen in the presence of DHFR inhibition by MTX, so that DNA replication/RNA transcription processes can proceed in normal cells - this mitigates toxicity.

ADMINISTER LEUCOVORIN 24-42 HOURS AFTER ADMINISTERING MTX

HD-MTX - Supportive Care

What is a crucial aspect of MTX clearance and prevention of renal toxicity?

1. Urine alkalization (increases solubility and decreases precipitation within the renal tubuli)

   1. With sodium bicarbonate

2. Hydration

Tx for Patients with MTX Toxicity due to Renal Impairment

This is indicated for the treatment of toxic plasma MTX concentrations (>1 uM) in patients with delayed MTX clearance due to impaired renal function.

Route: IV

MOA: recombinant carboxypeptidase G2 (CPDG2) enzyme which rapid lowers blood levels of MTX

Voraxaze (Glucarpidase)

Pyrimidines: Fluoropyrimidines

What is the prodrug of 5-FU?

Capecitabine (Xeloda)

5-FU

How does 5-FU exert its anti-tumor effects?

Through inhibiting thymidylate synthase

• other sites of action comprise incorporation into RNA AND DNA

Capecitabine (Xeloda)

Which step is very critical in capecitabine becoming active 5-FU, and for what reason?

Thymidine Phosphorylase - some tumors express thymidine phosphorylase in higher concentrations than normal tissue; this is has 2 advantages over 5-FU, enhanced drug concentrations at the tumor and reduced drug levels in normal tissues, therefore decreasing systemic toxicity

5-FU Metabolism and Anticancer Mechanism

The anticancer pathway of 5-FU is the formation of cytotoxic triphosphates. The metabolism is clearance pathways. What enzyme is the focus?

DPD Enzyme

5-FU PGX Issues and DPD

1. What fraction of 5-FU is converted into cytotoxic phosphorylated species required to kill cancer cells?

2. In what patients is administered 5-FU converted into the inactive metabolite (80%)?

3. What patients have a decreased metabolism of 5-FU, which leads to increasing levels of cytotoxic metabolites?

80%

patients with two copies of functional DPD

DPD deficient patients

Fluoropyrimidines and the DPYD Gene

1. What gene encodes for the enzyme dihydropyrimidine dehydrogenase (DPD)?

2. Which patients are at risk of 5-FU toxicity?

3. What does the FDA-approved drug label for 5-FU state?

1. DPYD

2. Poor metabolizer phenotypes

3. No dose has been proven safe in individuals with absent DPD activity

DPD Enzyme Activity Scores and Phenotype

What is the activity score for the DPD enzyme?

1. Each Normal function allele:

2. Each Reduced function allele:

3. Each CPIC LOF allele:

1

0.5

0

CPIC Guidelines for Fluoropyrimidines

Which activity score results in dose reductions of fluoropyrimidines? What about avoiding 5-FU or capecitabine altogether?

Dose reductions: 1 (50%) -1.5 (25-50%)

Avoiding: 0-0.5

Capecitabine

Capecitabine’s NEW Boxed Warning as of 2025:

DPYD (deficiency)

Gemcitabine (Gemzar)

1. What is the MOA?

2. What are the 3 most common adverse reactions?

1. Inhibits DNA synthesis; fraudulent nucleoside; converted to nucleotides by sequential phosphorylation to triphosphate.

2. Nausea/vomiting, myelosuppression

   1. Generally well tolerated (can cause GI disturbances, renal impairment, pulmonary toxicity, and flu-like symptoms)

Purine Analog: Thiopurines

Examples: 6-mercapto, 6-thioguanine, azathioprine (ALL PRODRUGS)

1. Mainly used in ALL (acute lymphoblastic leukemia) treatment

2. Describe the therapeutic index, and a major toxicity associated with thiopurines.

3. What enzyme do thiopurines have an issue with regarding PGx (remember: these are prodrugs that require sequential ribosylation (sugar addition) and phosphorylation by kinases as part of the MOA against cancer cells)?

1. TI = very narrow; life-threatening myelosuppression

2. TPMT (thiopurinemethyltransferase)

Not a question: Just about thiopurine dosing in those with TPMT deficiencies.