SPHINX31, a SRPK1 inhibitor, regulates the ATR/DNA-PKcs/CHK1 replicative checkpoint to inhibit cell growth in NSCLC cells

Abstract

Introduction

Lung cancer, including the non-small cell lung carcinoma (NSCLC) histological subtype, is a leading cause of cancer-related death worldwide. Acquisition of resistance to therapies such as platinum salts, the gold standard chemotherapy in NSCLC, is one of the major trick supporting patients’ poor prognosis. Deregulation of splicing patterns as well as of some splicing factors and/or their regulators participate in the process of carcinogenesis and lung tumor progression. However, less is known regarding the contribution of RNA splicing defects to lung tumor escape from therapies. Recently, pharmacological inhibitors targeting different components/regulators of the spliceosome machinery have emerged as potential anti-cancer drugs, such as SPHINX31 that inhibits SRPK1, a kinase implicated in splicing regulation through the phosphorylation of various serine/arginine (SR)-rich proteins.

Methods

In order to investigate whether RNA splicing defects contribute to acquired resistance to platinum salts in NSCLC, we have worked in cellular models of resistance derived from NSCLC cell line sub-cultured with increasing concentrations of cisplatin during 4–6 months in order to obtain resistant cells. We treated both the parental and resistant cells with SPHINX31 in order to investigate the role of SRPK1 in cell cycle regulation and apoptosis. Western blot and co-immunoprecipitation assays were used to study the effect of SPHINX31 on the expression/interaction of some ATR signaling pathway components. Then, RNA-seq analysis was performed to predict the potential signaling pathway by which SRPK1 inhibition induces cell death.

Results

In this study, we demonstrated that SPHINX31 inhibits ATR signaling, the main pathway involved in the management of replicative stress, notably in NSCLC cells with acquired resistance to platinum salts. This leads to cell growth inhibition and enhanced genomic instability. At the molecular level, we demonstrated that SRPK1 is recruited at stalled replication forks upon replicative stress, co-immunoprecipitates with the ATR/ATRIP/TOPBP1 complex and is required for TOPBP1/ATRIP recruitment to chromatin and TOPBP1 nuclear foci formation which contribute to ATR full activation. We further provided evidence that SPHINX31 and SRPK1 regulate the splicing of WIZ, in favor of splice variants involved in ATR activation, thereby identifying both splicing-dependent and -independent functions of SRPK1 by which it controls ATR signaling pathway. Last, we showed that the inhibitory effects of SPHINX31 on ATR are counterbalanced by the activation of DNA-PKcs and we identified a strong synergistic cytotoxic effect of the combination SPHINX31 and DNA-PKcs inhibitor in vitro. We propose that SPHINX31, alone or combined with DNA-PKcs inhibitor, could be benefit for NSCLC patients who relapse after platinum based-chemotherapy (Fig. 1).

Conclusion

In summary, our results identify a role of SRPK1 in the management of DNA replicative stress and the control of genomic stability in NSCLC cellular models with acquired resistance to platinum salts and highly suggest that the use of SRPK1 inhibitors in combination with DNA-PKcs inhibitors could counteract platinum salts resistance in lung cancer.