NBME 24 Vincristine (NBME Answers)

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nbme24/Block 2/Question#46 (reveal difficulty score)
In a study of drug action on neoplastic cells ...
Vincristine 🔍 / 📺 / 🌳 / 📖
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+4 upvote downvote
submitted by ∗madojo(212)

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Cyclosporin is an immunosuppressant that blocks T cell activation by inhibiting IL-2, so we know thats not right. Cyclophosphamide is an alkylating agent. Doxorubicin is an antitumor antibiotic that generates free radicals and causes breaks in DNA. 5'fluorouracil is associate with pyrimidine synthesis. Leaving Vincristine which is a neoplastic drug that works on microtubules (other drugs that do this colchicine, paclitaxel.

As mentioned already, the cell is stuck in metaphase and cannot undergo the seperation anaphase. M cycle arrest is associated with vincristine and which the mitotic spindle which is what separates the chromosomes is not forming.

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suckitnbme The funny thing is that the image seems to show that the spindle did in fact form. +16

spaceboy98 EXACTLY They showed the mitotic spindle is formed, so paclitaxel would be ok, but for vincristine, the damn thing would not even form +8

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submitted by ∗m-ice(370)

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Vincristine is a chemotherapeutic drug that stabilizes microtubules and prevents them from disassembling. The cell in the picture is stuck in anaphase, with microtubules attached to its chromosomes, unable to pull them apart because it cannot disassemble its microtubules.

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vshummy So I get that by process of elimination cyclophosphamide, cyclosporine, doxorubicin, and 5-fluorouracil are not related to microtubules but vincristine in First Aid 2019 says it prevents microtubule formation, doesn’t stabilize it because the one that stabilizes microtubules is paclitaxel. +1

vshummy Okay, I realize now- the picture is stuck in metaphase, not anaphase. Both paclitaxel and vincristine stop the cell in metaphase but by two different mechanisms. Vincristine prevents mitotic *spindle* formation while paclitaxel prevents mitotic spindle *breakdown*. Mitotic spindle is needed to pull the chromosomes apart before anaphase begins. +16

azibird No, I think you were right to begin with. Without spindle formation the cell should be stuck in prophase (vincristine). Without breakdown it should be stuck in metaphase (paclitaxel). Metaphase is shown here with spindle fully formed, so it should be paclitaxel. +

sars I agree with the logic stated above. It could also be that the researchers added Drug X later on in M-phase, so therefore maybe the microtubules aren't even fully formed to fully reach metaphase. I think they're harping on "pick the best answer" +

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submitted by daddyyikes(2)

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it wasz the the shittiest question that i have ever read in my entire life ever!

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