The CDK4/6 Inhibitor LY2835219 Overcomes Vemurafenib Resistance Resulting from MAPK Reactivation and Cyclin D1 Upregulation

Abstract

B-RAF selective inhibitors, including vemurafenib, were recently developed as effective therapies for melanoma patients with B-RAF V600E mutation. However, most patients treated with vemurafenib eventually develop resistance largely due to reactivation of MAPK signaling. Inhibitors of MAPK signaling, including MEK1/2 inhibitor trametinib, failed to show significant clinical benefit in patients with acquired resistance to vemurafenib. Here, we describe that cell lines with acquired resistance to vemurafenib show reactivation of MAPK signaling and upregulation of cyclin D1 and are sensitive to inhibition of LY2835219, a selective inhibitor of cyclin-dependent kinase (CDK) 4/6. LY2835219 was demonstrated to inhibit growth of melanoma A375 tumor xenografts and delay tumor recurrence in combination with vemurafenib. Furthermore, we developed an in vivo vemurafenib-resistant model by continuous administration of vemurafenib in A375 xenografts. Consistently, we found that MAPK is reactivated and cyclin D1 is elevated in vemurafenib-resistant tumors, as well as in the resistant cell lines derived from these tumors. Importantly, LY2835219 exhibited tumor growth regression in a vemurafenib-resistant model. Mechanistic analysis revealed that LY2835219 induced apoptotic cell death in a concentration-dependent manner in vemurafenib-resistant cells whereas it primarily mediated cell-cycle G 1 arrest in the parental cells. Similarly, RNAi-mediated knockdown of cyclin D1 induced significantly higher rate of apoptosis in the resistant cells than in parental cells, suggesting that elevated cyclin D1 activity is important for the survival of vemurafenib-resistant cells. Altogether, we propose that targeting cyclin D1-CDK4/6 signaling by LY2835219 is an effective strategy to overcome MAPK-mediated resistance to B-RAF inhibitors in B-RAF V600E melanoma.

A novel multi-CDK inhibitor P1446A-05 restricts melanoma growth and produces synergistic effects in combination with MAPK pathway inhibitors

“…Based on other studies of CDK4/6 inhibitors in melanoma that revealed a predominant G 1 phase arrest with little or no apoptosis, we expected that P1446A-05 would cause some G 1 phase arrest. 5,24 Our results, however, are more in line with those achieved by dinaciclib, a specific inhibitor of CDK1/2/5/9, which also causes G 2 /M phase cell cycle arrest and apoptosis. 12,23 We validated that P1446A-05 inhibits the kinase function of CDK4 and CDK9, so while we are confident that the anti-proliferative effects produced by this drug resulted in some part from appropriate CDK inhibition, it is impossible to rule out contributory off-target effects.…”

RB1: a prototype tumor suppressor and an enigma

“…However, Cdk4/6 inhibitors have shown great efficacy when combined with other inhibitors targeting key mitogenic and/or survival pathways. Cdk4/6 inhibitors synergize strongly with inhibition of HER2, PI3K/mTOR, MEK, IGF1R/IR, and B-RAF (Finn et al 2009;Franco et al 2014;Heilmann et al 2014;Vora et al 2014;Yadav et al 2014). In 2015, the Food and Drug Administration granted accelerated approval to a combination of the Cdk4/6 inhibitor palbociclib and letrozole for the treatment of hormone receptor-positive advanced breast cancer (Finn et al 2015), and the efficacy of palbociclib in this setting has been confirmed in subsequent large-scale trials (Turner et al 2015).…”

Progress with palbociclib in breast cancer: latest evidence and clinical considerations

“…Preclinical evidence of effectiveness of the combination of CDK4/6 inhibitors with inhibitors of the MAPK pathway also exists, particularly in melanoma [Yadav et al 2014] and in colorectal cancer [Ziemke et al 2016]. Additionally, the PDK1 inhibitor GSK2334470 was synergistic with CDK4/6 inhibitors in breast cancer cell lines and in xenograft models and was able to restore sensitivity to CDK4/6 inhibitors [Jansen et al 2016].…”