Antimetabolites in Cancer Treatment

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Questions and Answers

How does pemetrexed differ from methotrexate in terms of mechanism of action?

Inhibits dihydrofolate reductase (DHFR) and replenishes the folate pool
Promotes the synthesis of tetrahydrofolic acid (FH4) and inhibits RNA synthesis
Inhibits DHFR and thymidylate synthase, as well as other enzymes involved in folate metabolism and DNA synthesis (correct)
Acts as an antagonist to folic acid and competes with purine nucleotide precursors

What is the primary mechanism of action of methotrexate?

Competing with purine nucleotide precursors in RNA synthesis
Inhibiting dihydrofolate reductase (DHFR) and interfering with DNA synthesis (correct)
Acting as an antagonist to folic acid and inhibiting thymidylate synthase
Promoting the synthesis of tetrahydrofolic acid (FH4)

Why is the maximal cytotoxic effect of antimetabolites observed in S phase of the cell cycle?

Because antimetabolites directly inhibit cell replication during this phase
Because cells are most actively synthesizing DNA during this phase (correct)
As S phase presents increased availability of purine and pyrimidine nucleotide precursors
Due to increased vulnerability of DNA to interference during this phase

How can the inhibition of dihydrofolate reductase (DHFR) by methotrexate be reversed?

<p>By administration of leucovorin, which bypasses the blocked enzyme and replenishes the folate pool. (C)</p> Signup and view all the answers

What role does folic acid play in cellular processes?

<p>Essential for metabolic reactions involving transfer of one-carbon units and for cell replication (C)</p> Signup and view all the answers

Flashcards

Methotrexate's mechanism of action

Inhibits dihydrofolate reductase (DHFR), a key enzyme in folate metabolism, leading to a decrease in tetrahydrofolic acid (THF) and disruption of DNA synthesis.

Pemetrexed's action vs. Methotrexate

Pemetrexed inhibits not only DHFR but also thymidylate synthase, an enzyme involved in thymine (a DNA base) synthesis. This double-whammy makes it more potent.

Why S phase is crucial

The S phase of the cell cycle is when DNA replication happens. Antimetabolites like methotrexate mess with this process, causing the most damage during this phase.