Targeting CDC7 sensitizes resistance melanoma cells to BRAFV600E-specific inhibitor by blocking the CDC7/MCM2-7 pathway

Shaimaa A Gad,Sanaa A Kenawy,Rania M Abdelsalam,Emad Kandil,Hamed I Ali,Hamdy E A Ali,Mourad Zerfaoui,Salwa H Salama,Zakaria Y Abd Elmageed,Rofaida Gaballa

doi:10.1038/s41598-019-50732-w

Abstract

Although the utilization of selective BRAFV600E inhibitors is associated with improved overall survival in patients with metastatic melanoma, a growing challenge of drug resistance has emerged. CDC7 has been shown to be overexpressed and associated with poor prognosis in various cancers including melanoma. Thus, we aimed to elucidate the biological role of CDC7 in promoting Vemurafenib resistance and the anticipated benefits of dual targeting of BRAFV600E and CDC7 in melanoma cells. We performed exosomes-associated microRNA profiling and functional assays to determine the role of CDC7 in drug resistance using Vemurafenib-sensitive and resistant melanoma cells. Our results demonstrated that Vemurafenib-resistant cells exhibited a persistent expression of CDC7 in addition to prolonged activity of MCM2 compared to drug-sensitive cells. Reconstitution of miR-3613-3p in resistant cells downregulated CDC7 expression and reduced the number of colonies. Treatment of cells with low concentrations of CDC7 inhibitor TAK-931 sensitized resistant cells to Vemurafenib and reduced the number of cell colonies. Taken together, CDC7 overexpression and downregulation of miR-3613-3p were associated with Vemurafenib resistance in BRAFV600E- bearing melanoma cells. Dual targeting of CDC7 and BRAFV600E reduced the development of resistance against Vemurafenib. Further studies are warranted to investigate the clinical effect of targeting CDC7 in metastatic melanoma.

Highlights

BRAF is a driver oncogene in various human cancers including melanoma, and was the first described oncoprotein with serine/threonine kinase activity[1,2]
Despite the remarkable clinical benefits associated with the selective BRAFV600E inhibition by Vemurafenib, emergence of drug resistance hampered the treatment of metastatic melanoma
A375- NRASQ61K (A375-R) and WM983B-R cells were insensitive to the increase of Vemurafenib concentrations up to 2.5 and 5 μM, respectively

Summary

Introduction

BRAF is a driver oncogene in various human cancers including melanoma, and was the first described oncoprotein with serine/threonine kinase activity[1,2]. Overexpression of specific microRNAs (miRs) restore the sensitivity of resistant melanoma cells by downregulating their target genes, which are closely related to acquired resistance to BRAFV600E inhibition[14]. This makes miRs as attractive therapeutic targets in resistant melanomas. CDC7 is a highly conserved serine-threonine protein kinase, which is required for initiating the replication machinery. It regulates G1/S phase transition, which is fundamental in cells proliferation, and its deregulation leads to oncogenesis[16]. The safety, tolerability, and activity of CDC7-specific inhibitor TAK-931 was evaluated in patients with solid tumors and showed a clinical promise[19]

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