HSP90 Inhibitor Ganetespib(STA-9090) Inhibits Tumor Growth In C-Myc-dependent Esophageal Squamous Cell Carcinoma

Background and objective Esophageal squamous cell carcinoma(ESCC)is the most common type of esophageal cancer(EC)in China.Many patients with ESCC are diagnosed at an advanced stage,and the prognosis of ESCC is poor with a five-year survival rate of less than 20%.Currently,the paucity of classical effective pharmacological drugs to treat esophageal squamous cell carcinoma(ESCC)is a major problem.The c-Myc(MYC)is an oncogene which induces tumor cell growth and proliferation.Although the MYC protein which overexpressed in ESCC is a promising target,lacking of classical effective pharmacological inhibitors remains a significantly difficult problem.Therefore,it is necessary to develop novel MYC-targeting strategies.Furthermore,it is worth noting that MYC is a sensitive client protein of the heat shock protein 90(HSP90)and targeting the HSP90-MYC axis by inhibiting HSP90 is a potential therapeutic strategy for ESCC.Methods We evaluated the value of HSP90 inhibitor(ganetespib,STA-9090)as inhibiting of MYC-overexpressing ESCC tumor growth.In vitro:(1)The expression of MYC in 12 clinical tissue samples of ESCC and ESCC cells was analyzed by western blot.(2)We analyzed ESCC tissue microarrays and clinical tissue samples to determine MYC and HSP90 expression.(3)CCK-8 was used to analyze the growth and proliferation of ESCC cell lines with different concentrations of STA-9090 for 72 h.(4)PI staining was used to observe the cell cycle changes of ESCC cell lines and Annexin V-FITC/PI staining was used for apoptosis under STA-9090 treatment.(5)ESCC cell lines were transfected with MYC-si RNA,and the proliferation and apoptosis of the cells were detected by CCK8 and Annexin V-FITC / PI staining respectively.MYC protein expression was detected by western blot.(6)Relationship between MYC and HSP90 was analyzed by co-immunoprecipitation assays and immunofluorescence.In vivo:(1)The cell-derived xenograft(CDX)and patient-derived xenograft(PDX)were respectively established.(2)The antitumor activity of STA-9090 was assessed in two xenograft animal models.(3)The MYC expression under STA-9090 treatment was evaluated in ESCC xenograft models.Results(1)MYC was found to be overexpressed and positively associated with HSP90 expression in ESCC tissues.Compared to adjacent normal tissues,the positive rate of MYC expression in ESCC tissues was 58.33%(7/12) among 12 clinical tissue specimens.In TMA,the positive rate of MYC expression was 54%(58/107)and the HSP90 was 47%(50/107).50% of the samples with MYC positive expression were also positive for HSP90.(2)MYC-overexpressing ESCC cells were more sensitive to STA-9090 treatment,suppressing ESCC cell cycle progression and survival.(3)STA-9090 inhibited ESCC proliferation and promoted apoptosis by down-regulating MYC expression.The MYC gene was silenced in ESCC cells that the cell proliferation was weakened and apoptosis was increased.(4)MYC and HSP90 were co-localized in the nucleus and interacted with each other.STA-9090 reduced the half-life of the MYC protein.(5)In both xenograft models STA-9090 substantially inhibited the growth of MYC positive ESCC xenograft tumors and patient sample tumors in vivo.In contrast,STA-9090 treatment demonstrated no beneficial effects in mice with low-MYC expressing ESCC tumors.Conclusion Here,we evaluate the application value of the HSP90 inhibitor(ganetespib,STA-9090)as an anti-cancer agent for MYC positive ESCC.Our data supports that the HSP90 inhibitor,STA-9090,suppresses the expression of the MYC protein and interferes with HSP90-MYC protein-protein interaction.This,in turn,leads to inhibition of ESCC cell proliferation and promotion of apoptosis in ESCC cells in vitro and reduction of ESCC tumors in vivo.We propose,based on our findings,that STA-9090 could be a potential novel therapy for MYC positive ESCC.