The Resistance Mechanisms Against Proteasome And Topoisomerase Inhibitors In Small Cell Lung Cancer

Part one:Combinations of Proteasome Inhibitors with Obatoclax are Effective for Small Cell Lung CancerProteasome inhibitors,bortezomib and carfilzomib have been clinically approved to treat hematological malignancies.However,their clinical efficiencies are limited in solid tumors.Small cell lung cancer is a clinically aggressive subtype of neuroendocrine carcinoma with very high mortality.In this paper,we identified the therapeutic efficacy and possible resistance mechanisms of bortezomib and carfilzomib in small cell lung cancer,and explored MCL-1 inhibitors as chemo-sensitizers on small cell lung cancer.In this study,using a mass spectrometry(MS)-based deep-coverage proteomic analysis,we found that bortezomib and carfilzomib induced totally differential changes of proteomic profiling,thereby affecting different signaling pathways in small cell lung cancer cells.Bortezomib treatment enriched the proteins involved in cell division and regulation of cell cycle,while carfilzomib treatment affected protein phosphorylation-related proteins.Cell viability assays showed that IC50 values of bortezomib were much higher than carfilzomib,suggesting that SCLC cells are more sensitive to carfilzomib than bortezomib.Proteomic profiling analysis revealed that bortezomib treatment tended to induce the accumulation of MCL-1,an anti-apoptotic protein,which might,at least partially,contribute the tolerance of SCLC cells to bortezomib treatment.Integrative Proteomic profiling analysis of transcription factors and molecular biology techniques showed that the accumulation of MCL-1 was due to the inhibition of the degradation of transcription factor FOXM1 rather than the suppression of degradation mediated by bortezomib or carfilzomib.The increased accumulation of FOXM1 by bortezomib or carfilzomib transcriptionally activated MCL-1.Targeting MCL-1 by its inhibitor obatoclax,both in vitro and in vivo,significantly enhanced the anti-tumor activities of bortezomib and carfilzomib in small cell lung cancer.Therefore,our data suggested that co-targeting MCL-1 and Proteasome could be an effective way to treat small cell lung cancer or probably other solid cancers.Part two:FK288 renders small cell lung cancer cells to topotecan via induction of by SLFN11 expressionTopotecan is a small molecule specific inhibit Top I.Topotecan could associate with Top I and form stable DNA enzyme complex,leading to double strand breaks(DSBs)and cell death.As the only second-line chemo drug for small cell lung cancer,the treatment efficacy of topotecan is limited,with a low response rate at 20%.In our study,we demonstrated that the sensitivity of topotecan to small cell lung cancer was associated with the expression of SLFN11.Cell viability assay indicated that the SCLC cell lines with high expression of SLFN11 were more sensitive to topotecan than those with low expression of SLFN11.Mechanically,SCLC cell lines with low expression of SLFN11 could activate DNA damage response more efficiently than SCLC cell lines with high expression of SLFN11 in response to topotecan.Knockdown or overexpression of SLFN11 confirmed that expression of SLFN11 contributed to the sensitivity of SCLC cells to topotecan.Furthermore,we unraveled that SLFN11 expression was negatively correlated to the methylation level at SLFN11 promoter.HDAC inhibitor FK228 and SAHA could induce SLFN11 expression through suppression of DNA methylation at SLFN11 promoter,thereby sensitizing SCLC cells to topotecan.Finally,we evaluated the methylation status of SLFN11 promoter in SCLC clinical specimens and found that majority of the clinical samples showed DNA methylation at the promoter of SLFN11,indicating that combination of topotecan with FK228 significantly improves the response rate of topotecan in SCLC.In summary,DNA methylation might be used as a biomarker to predict the potential of the combination strategy of topotecan and FK228 in SCLC treatment.