Clinically, increased expression of Survivin is often associated with elevated resistance of cancer cells to apoptotic stimuli during chemotherapy

and is negatively correlated with response to proapoptotic drugs and/or radiotherapy in patients with bladder cancer, breast cancer, lymphoma and multiple myeloma[41–46]. Furthermore, overexpression of Survivin is a prognostic biomarker for decreased patient survival Romidepsin in multiple cancers, e.g., breast cancer, colorectal and gastric carcinomas, neuroblastoma and NSCLC. All these findings on Survivin indicate that it could be an attractive cancer target. In this study, we were intrigued to find that co-treatment with rapamycin and docetaxel significantly down-regulates the expression of Survivin, as shown in Figure 4. Although the underlying mechanism for this down-regulation is currently unclear, our finding is consistent with a previous report that found rapamycin reduced IGF-induced Survivin expression in prostate cancer cells[47]. Similarly, Vaira et al. also reported that treatment

of rapamycin with taxol at suboptimal Napabucasin molecular weight concentration resulted in a bigger reduction in Survivin expression than that by either treatment alone[47]. It is possible that when co-treatment of rapamycin and docetaxel synergistically reduced Survivin level beyond the threshold for its antiapoptotic activity in cancer cells, the cytotoxic effect of docetaxel becomes more effective in cancer treatment. In addition, our result suggests that Survivin is essentially involved in lung cancer maintenance and progression rather than initiation, which is in agreement with the prevailing hypothesis. Finally, because Survivin is selectively expressed at the G2/M phase of the cell cycle and is a known mitotic regulator of microtubule assembly, the target of action by docetaxel, it is tempting to speculate an antagonistic interplay between Survivin and docetaxel[48, 49]. Interestingly, recent Ribonucleotide reductase studies are converging

on the notion that inhibition of Survivin in conjunction with docetaxel treatment delivers better cancer-killing effect by reversing the resistance to docetaxel in cancer [50, 51]. Activation of the MEK/ERK axis is often associated with cell proliferation and survival[52, 53]. Similar to Survivin’s role in cancer, the phosphorylation level of ERK1/2 is often found upregulated in cancer cells and inhibitors against MEK are currently in Phase II clinical trials. In our study, we found that while monotherapies with either rapamycin or docetaxel did not significantly affect the phosphorylation level of ERK1/2, the combination of the two led to a considerable reduction in the amount of phosphorylated ERK1/2(Figure 5). This is significant, because ERK1/2 activation was known to counteract the cancer-killing activity of docetaxel in some malignancies such as leukemia and melanoma[54–56].