Temsirolimus

Temsirolimus is an mTOR inhibitor and a water-soluble prodrug of sirolimus. After entering the body, temsirolimus is metabolized into its active form, sirolimus (rapamycin). After entering T cells or B cells, sirolimus first binds to the intracellular protein FKBP12 (FK506-binding protein 12), forming a sirolimus-FKBP12 complex. This complex selectively inhibits mTORC1 (mTOR complex 1). Under normal conditions, when the IL-2 receptor on T cells and B cells binds IL-2, the mTORC1 pathway drives these cells into S phase. When mTORC1 is inhibited by sirolimus, T cells and B cells are unable to proliferate.