Sorafenib and Mek inhibition is synergistic in medullary thyroid carcinoma in vitro

Abstract

Clinical trials using kinase inhibitors have demonstrated transient partial responses and disease control in patients with progressive medullary thyroid cancer (MTC). The goal of this study was to identify potential combinatorial strategies to improve on these results using sorafenib, a multikinase inhibitor with activity in MTC, as a base compound to explore signaling that might predict synergystic interactions. Two human MTC cell lines, TT and MZ-CRC-1, which harbor endogenous C634W or M918T RET mutations, respectively, were exposed to sorafenib, everolimus, and AZD6244 alone and in combination. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide (MTT) and poly (ADP-ribose) polymerase (PARP) cleavage assays were performed to measure cell survival and apoptosis. Western blots were performed to confirm activity of the compounds and to determine possible mechanisms of resistance and predictors of synergy. As a solitary agent, sorafenib was the most active compound on MTT assay. Western blots confirmed that sorafenib, everolimus, and AZD6244 inhibited their anticipated targets. At concentrations below its IC50, sorafenib-treated TT and MZ-CRC-1 cells demonstrated transient inhibition and then re-activation of Erk over 6 h. In concordance, synergistic effects were only identified using sorafenib in combination with the Mek inhibitor AZD6244 (P<0.001 for each cell line). Cells treated with everolimus demonstrated activation of Akt and Ret via TORC2 complex-dependent and TORC2 complex-independent mechanisms respectively. Everolimus was neither additive nor syngergistic in combination with sorafenib or AZD6244. In conclusion, sorafenib combined with a Mek inhibitor demonstrated synergy in MTC cells in vitro. Mechanisms of resistance to everolimus in MTC cells likely involved TORC2-dependent and TORC2-independent pathways.

A biomaterial screening approach reveals microenvironmental mechanisms of drug resistance

“…ERK is downstream of both the lapatinib and sorafenib targets, which may explain why MEK/ERK signaling was so critical to drug response in our data. In agreement with our findings, myeloid leukemia cells have a stiffness-dependent response to drugs, including sorafenib and a MEK inhibitor, which target the RAF/MAPK pathway 48, 49 . We have previously shown that sorafenib resistance increased with increasing hydrogel stiffness 10 , and many others have also demonstrated that stiffness is a significant driving force for drug resistance 9, 10, 30, 31, 50–53 .…”

Dual Inhibition of MEK and PI3K/Akt Rescues Cancer Cachexia through both Tumor-Extrinsic and -Intrinsic Activities

“…Overall, single agent MEK inhibitors have been limited as a front-line targeted therapy due to compensatory activation of other oncogenic signaling pathways (42, 47-50). This has necessitated an approach whereby MEK inhibitors are being tested in combination with other agents (51-56). Amongst the most common partners for MEK therapy are inhibitors of the PI3K/Akt pathway (50, 57-59).…”

Novel targeted therapeutics for MEN2

“…This led the authors to test whether its effects could be enhanced by concomitant treatment with a MEK inhibitor. Indeed, combination with selumetinib (AZD6244, AstraZeneca) greatly increased growth inhibition compared to either single agent (Koh et al 2012). While this combination has not yet been further investigated in thyroid cancer, the addition of MEK/ERK inhibitors to upstream kinase inhibitors (e.g., BRAF) has proven very successful in other tumors (Robert et al 2015).…”