Evaluating rational non-cross-resistant combination therapy in advanced clear cell renal cell carcinoma: combined mTOR and AKT inhibitor therapy

Abstract

Purpose Inhibition of the mammalian target of rapamycin (mTOR), a regulator of hypoxia inducible factor (HIF), is an established therapy for advanced renal cell cancer (RCC). Inhibition of mTOR results in compensatory AKT activation, a likely resistance mechanism. We evaluated whether addition of the Akt inhibitor perifosine to the mTOR inhibitor rapamycin would synergistically inhibit RCC. Methods Select RCC cell lines were studied [786-O, A498 (VHL mutant), CAKI-1 (VHL wild type), and 769-P (VHL methylated)] with single agent and combination therapy. Growth inhibition was assessed by MTT and cell cycling by flow cytometry. Phospho-AKT (S473) and HIF-2α were assessed by Western blot. Total RNA was isolated from 786-O cells subjected to single agent and combination treatments. In these cells, genome-wide expression profiles were assessed, and real-time PCR was used to confirm a limited set of expression results. Results Three out of four cell lines (CAKI-1, 769-P, and 786-O) were sensitive to single-agent perifosine with 50% inhibitory concentrations ranging from 5 to 10 µM. Pe-rifosine blocked phosphorylation of AKT induced by rapamycin and inhibited HIF-2α expression in 786-O and CAKI-1. Combined treatment resulted in sub-additive growth inhibition. GeneChip analysis and pathway modeling revealed inhibition of the IL-8 pathway by these agents, concomitant with up-regulation of the KLF2 gene, a known suppressor of HIF1a. Conclusions Perifosine is active in select RCC lines, abrogating the induction of AKT phosphorylation mediated by mTOR inhibition. Combined mTOR and AKT inhibition resulted in the modulation of pro-angiogenesis pathways, providing a basis for future investigations.

Two phase 2 trials of the novel Akt inhibitor perifosine in patients with advanced renal cell carcinoma after progression on vascular endothelial growth factor‐targeted therapy

“…Furthermore, many investigators have demonstrated additive benefits from combining perifosine with a rapalogue in preclinical studies of multiple tumor types, including RCC. [20][21][22] These findings, combined with the observation that perifosine is very well tolerated with toxicities that generally do not overlap with those of VEGF antagonists and rapalogues, suggest that perifosine may be an attractive agent to assess clinically in combination with currently available agents in RCC. Indeed, a clinical trial is already underway combining perifosine with temsirolimus in patients with malignant glioma (National Clinical Trial identifier NCT01051557).…”

Induction of Epithelial-Mesenchymal Transition via Activation of Epidermal Growth Factor Receptor Contributes to Sunitinib Resistance in Human Renal Cell Carcinoma Cell Lines

“…1). ACHN and Caki-1 cells are wild type, whereas the 786-O cell line is mutated for VHL (Stickle et al, 2005;Ishimaru et al, 2010;Holland et al, 2012). Moreover, 786-O cells are deficient in PDGFR-b, which is the target molecule of sunitinib.…”

Perifosine in renal cell carcinoma

“…Therefore, the assumption that an Akt inhibitor may simply be a better mTOR inhibitor in RCC may not be valid. Indeed, many investigators have shown additive benefits from combining perifosine with a rapalogue in preclinical studies in multiple tumor types including RCC and similar clinical studies are underway [46][47][48]. Given the aforementioned observation that perifosine is very well tolerated with toxicities which are in general non-overlapping with those of VEGF-antagonists and rapalogues, it likely remains that the future of perifosine in RCC is not as a single-agent, but in combination with other molecularly targeted agents, particularly the rapalogues.…”