Experimental therapy for advanced renal cell carcinoma

Rapamycin, the mTOR kinase inhibitor, sensitizes acute myeloid leukemia cells, HL-60 cells, to the cytotoxic effect of arabinozide cytarabine

The mammalian target of rapamycin (mTOR) kinase is a key regulator of cell growth and proliferation. Overexpression of the mTOR signaling pathway has been described in several tumor cells, including the majority of acute myeloid leukemia (AML) cases. The anti-tumor efficacy of mTOR inhibitors was shown in several preclinical and clinical studies. In AML, however, the potential antineoplastic effect of mTOR inhibitors has received little attention thus far. In this in-vitro study of the human AML cell line, HL-60, we aimed to assess the antileukemic activity of rapamycin (RAPA), an mTOR inhibitor, alone and in combination with cytarabine (Ara-C). The study showed that RAPA in concentrations of 1-10 nmol/l arrested the cell cycle progression of Hl-60 cells in the G1 phase, without evident cytotoxic effect. This effect was associated with significant inhibition of cyclin E expression. At concentrations higher than 10 nmol/l, RAPA exerted a significant proapoptotic effect, with the collapse of mitochondrial potential and caspase-3 activation. The most prominent proapoptotic effect was observed for a combination of 1 nmol/l of RAPA and 50 nmol/l of Ara-C, especially when Ara-C was added at a 24-h interval after RAPA. In conclusion, these data indicate that RAPA might be effective in the treatment of acute leukemia patients, especially in combination with Ara-C, the drug routinely used in AML treatment. On the basis of these results, attempts to combine classical induction chemotherapy with an inhibitor of the mTOR kinase in AML treatment could be warranted.

Nelfinavir induces mitochondria protection by ERK1/2-mediated mcl-1 stabilization that can be overcome by sorafenib

The HIV protease inhibitor nelfinavir is an investigational drug for cancer treatment. We have previously demonstrated induction of apoptosis by nelfinavir even in chemo-resistant ovarian cancer cells. In contrast to the pro-apoptotic effect of nelfinavir on human cancer cells, we noticed a significant upregulation of the anti-apoptotic mitochondrial membrane protein mcl-1 by nelfinavir, resulting in a mitochondria-independent induction of apoptosis. Upregulation of mcl-1 was associated with enhanced phosphorylation of both mcl-1 and of ERK1/2 (extracellular signal-regulated kinases 1/2). ERK1/2 enhanced stability of mcl-1 protein expression by serine-163 phosphorylation. The combination of nelfinavir with sorafenib, a clinically applied inhibitor of the RAS/RAF/ERK1/2 pathway, inhibited nelfinavir-induced ERK1/2 activation and mcl-1 protein upregulation. Further, the combination of nelfinavir with sorafenib induced mitochondrial membrane potential disruption and resulted in an improved activity of nelfinavir on ovarian cancer cells. Thus, a combination of these two investigational anti-cancer drugs could be of interest especially because of their unique mechanism of apoptosis induction even in otherwise chemo-resistant human cancer cells.

Multiple roles and therapeutic implications of Akt signaling in cancer

The prominence of the PI3K-Akt signaling pathway in several tumors indicates a relationship with tumor grade and proliferation. Critical cellular processes are driven through this pathway. More detailed knowledge of the pathogenesis of tumors would enable us to design targeted drugs to block both membrane tyrosine kinase receptors and the intracellular kinases involved in the transmission of the signal. The newly approved molecular inhibitors sunitinib (an inhibitor of vascular endothelial growth factor receptor, platelet-derived growth factor receptor, and other tyrosine kinase receptors), sorafenib (a serine-threonine kinase inhibitor that acts against B-Raf) and temsirolimus (an mTOR inhibitor) shown clinical activity in advanced kidney cancer. Chronic myeloid leukemia has changed its natural history thanks to imatinib and dasatinib, both of which inhibit the intracellular bcr/abl protein derived from the alteration in the Philadelphia chromosome. Intracellular pathways are still important in cancer development and their blockade directly affects outcome. Cross-talk has been observed but is not well understood. Vertical and horizontal pathway blockade are promising anticancer strategies. Indeed, preclinical and early clinical data suggest that combining superficial and intracellular blocking agents can synergize and leverage single-agent activity. The implication of the Akt signaling pathway in cancer is well established and has led to the development of new anticancer agents that block its activation.