CUDC-907 Suppresses HDAC6 To Downregulate C-Myc And Enhances Therapeutic Activity Against Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma is one of the most malignant and lethal common digestive system neoplasms,and its diagnosis and treatment are so challenging that the mortality rate has increased significantly in recent years,with an overall 5-year survival rate under 5% and a median survival of 6 months.Therefore,it is important to look for effective and specific drugs to improve the treatment of pancreatic cancer patients.Lately,emerging evidence has suggested that c-Myc,the amplification and/or overexpression of which is extremely common in pancreatic cancer,is often correlated with mutant KRAS.Thus,inhibition of c-Myc protein expression may be a potential strategy for the treatment of pancreatic cancer.c-Myc is considered as an important gene participating in the development of the pancreatic cancer,resulting in poor progression.It plays a pivotal role in the regulation of many physiological processes,including cell cycle control,apoptosis,protein synthesis,and others.In addition,c-Myc has been shown to regulate the expression of approximately 15% of all human genes.Although strategies have emerged to reduce c-Myc expression,no drug currently targets the c-Myc protein specifically and directly.In our study,we systematically evaluated the anti-tumor efficacy of CUDC-907,a novel dual-acting inhibitor of phosphoinositide 3-kinase(PI3K)and histone deacetylase(HDAC),against pancreatic cancer in vitro and in vivo,and tentatively explored the intrinsic mechanisms.Previous research on CUDC-907 have revealed that CUDC-907 can target PI3 K and HDAC directly,as well as induce the significant downregulation of the c-Myc protein.However,some issues remains to be explored that the function of c-Myc protein on tumor growth and how CUDC-907 to regulate the expression of c-Myc protein.To explore the mechanisms underlying,we characterized the ability of CUDC-907 to inhibit histone deacetylase and the kinase activity of PI3 K.The results revealed that CUDC-907 dose-dependently reduced AKT phosphorylation and caused H3K27 ac and H3K9 ac accumulation in Aspc-1,PANC-1,and Capan-1 cells.Next,CUDC-907 was treated to test c-Myc protein and mRNA level down-regulation through Western Blot and RT-PCR,indicating that c-Myc is one of the most crucial proteins that can be regulated by CUDC-907 treatment in cells.We next tried to explore the role of c-Myc on pancreatic cancer cell proliferation.To this end,we used siRNAs to knockdown c-Myc or c-Myc overexpression cells to identify that the expression of c-Myc protein is directly related to cell proliferation activity.Furthermore,for CUDC-907 is a dual inhibitor of PI3 K and HDACs,we aimed to confirm the effect of individually inhibiting the PI3 K pathway and/or HDACs on c-Myc protein regulation in pancreatic cancer cells.The PI3 K inhibitor GDC-0941 and the HDACs inhibitor Vorinostat(SAHA)were individually administrated.The results revealed that CUDC-907 or GDC-0941 treatment resulted in a reduction in AKT phosphorylation,which was thought to lead to the accumulation of c-Myc Thr58 phosphorylation and the caspase-independent reduction of c-Myc protein.At the other aspect,CUDC-907 could inhibit HDAC pathways to curb c-Myc protein synthesis.This effect is mainly dependent on HDAC6-FOXO1-c-Myc axis to inhibit c-Myc transcription for CUDC-907 could inhibit the enzyme activity of HDAC6,which is a family member of HDAC.Given the encouraging results of CUDC-907,we examined the pharmacodynamic evaluation of CUDC-907.Flow cytometry results showed that CUDC-907 arrested pancreatic cancer cells in the G2/M phase and induced apoptosis,eventually led to cell death.This result is corresponding with the results of Western Blot,which detected the key factors that involved in cell apoptosis and cell cycle arrest after treatment of CUDC-907.Also,a human pancreatic xenograft model was established by subcutaneously injecting human pancreatic cancer Aspc-1 cells into nude mice,and CUDC-907 inhibits the growth of pancreatic xenografts in vivo.Additionally,the expression of c-Myc is profoundly downregulated in the CUDC-907-treated groups.These results illustrated that CUDC-907 suppress pancreatic tumor growth mainly by inhibiting the activity of c-Myc protein.In summary,these data suggest that CUDC-907 is an effective drug in pancreatic cancer treatment in vitro and in vivo that warrants further clinical development.In addition,we found that CUDC-907 mainly by inhibiting the activity of c-Myc protein to inhibit pancreatic tumor growth,and both the PI3 K pathway and HDAC pathway contribute to suppress c-Myc function,this mechanism is promising to provide a new way for finding new anti-pancreatic caner drugs and benefitting pancreatic cancer treatment.