Anti-Cancer Effects of Rapamycin on U937 Cell Line.

Purpose: Cytotoxicity of rapamycin alone or in combination with arsenic trioxide in lymphoma cell line U937 was assessed, for the study of Anti-cancer effects of rapamycin.

Methods: cell vability and proliferation was analyzed by MTT and cell counting, clone formulating ability was analyzed by semisolid medium, cell cycle was analyzed by Propidium Iodide/RN-ase stain, the phosphorylation level of mammalian target of rapamycin (mTOR) was detected after marked by Phospho-mTOR antibody (Ser2448) and FITC. Expression of P27 was assessed by western- blot.

Result: 1.MTT measurement showed with increasing concentrations of RAPA (10 nM 100 nM, 1000 nM) cell proliferation inhibition rate was follwed 16.2%, 25.5%, 47.8%. Clonogenic assay showed the U937 proliferation inhibition rate was 80.5% in a 7-day leukemia colony-forming assay with concentration of 10 nM RAPA.2 RAPA 10nM, As2O3 0.6uM, As2O3 0.9uM alone, RAPA 10nM in combination with As2O3 0.6uM and 0.9uM, cell proliferation inhibition rate was followed 13%, 26%, 35%, 43%, 54%. 3. Propidium Iodide/RN-ase measurement showed RAPA resulted in U937 cell arrested in G1-phase, and was blocked in S-phase. 4. FCM showed the phosphorylation level of mTOR down-regulated significantly after treated by rapamycin (10 nM),5.The expression of P27 enhanced after treatd by rapamycin (10 nM)

Conclutions: From the experiment we can see rapamycin alone can inhibit the proliferation and clone formulating ability of U937 cell line. mTOR kinase is involved in the regulation of cell growth and proliferation. Rapamycin can down-regulate the phosphorylation level of mTOR, which can induce increasing expression of P27, As a result U937 arrest in G1-phase and block in S-phase. Interestingly rapamycin exert additive effect in proliferation experiment when combind with As2O3, higher than rapamycin or As2O3 alone.