American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Which drug is known to inhibit mTOR signaling?

1. FK506

2. Sirolimus

3. Cyclosporine

4. Mycophenolate mofetil

The correct answer is: Sirolimus

Sirolimus, also known as rapamycin, is recognized for its ability to inhibit the mammalian target of rapamycin (mTOR) signaling pathway. This pathway is crucial for regulating cell growth, proliferation, and survival, and is implicated in various physiological processes, including immune responses and metabolism. By inhibiting mTOR, sirolimus can effectively suppress the immune system, making it useful in preventing organ transplant rejection and in treating certain cancers. The mTOR pathway consists of two complexes, mTORC1 and mTORC2, both of which play significant roles in cellular functions. Sirolimus primarily inhibits the mTORC1 complex, leading to effects such as decreased protein synthesis and cell growth. This inhibition has therapeutic implications in conditions where excessive cell proliferation is problematic, such as in transplants or certain tumors. In contrast, other options like FK506, cyclosporine, and mycophenolate mofetil do not exert their primary effects by inhibiting mTOR signaling. FK506 and cyclosporine are both calcineurin inhibitors that prevent T-cell activation, while mycophenolate mofetil primarily inhibits purine synthesis, affecting lymphocyte proliferation. Therefore, their mechanisms do not directly target the m