Conclusions
Our data provide proof of concept that targeting SIRT6 using a small-molecule activator is an attractive therapeutic strategy for CRC and that MDL-811 could be a promising lead compound for further preclinical and clinical studies of treatments for CRC.
Methods
We identified an allosteric SIRT6 activator, MDL-811. Its ability to enhance SIRT6 deacetylation at protein and cellular levels was evaluated by Fluor de Lys (FDL) and western blots. We assessed the proliferation of 26 CRC cell lines and patient-derived organoids (PDOs) treated with MDL-811. In vivo efficacy of MDL-811 was evaluated in HCT116 cell line- and patient-derived xenografts as well as a spontaneous CRC model. RNA sequencing and real-time quantitative PCR assays were performed to analyze gene expression changes in MDL-811-treated HCT116 cells. Along with controls in SIRT6-overexpressing HCT116 cells, the SIRT6-mediated histone H3 deacetylation at the Cytochrome P450 family 24 subfamily A member 1 (CYP24A1) gene locus was assessed by chromatin immunoprecipitation (ChIP) in MDL-811-treated HCT116 cells. A combination therapy against CRC based on the downstream gene of SIRT6 activation was evaluated in cells and mouse models.
Results
MDL-811 significantly activated SIRT6 histone H3 deacetylation (H3K9Ac, H3K18Ac, and H3K56Ac) in vitro and had broad antiproliferative effects on diverse CRC cell lines and PDOs. More importantly, the in vivo anti-tumor efficacy of MDL-811 was demonstrated across cell line- and patient-derived xenografts and in the APCmin/+ spontaneous CRC model. Mechanically, we identified a new downstream target gene of SIRT6 in CRC, CYP24A1. Based on these findings, a combination drug strategy with MDL-811 to synergistically enhance the anti-CRC effect of vitamin D3 was validated in vitro and in vivo. Conclusions: Our data provide proof of concept that targeting SIRT6 using a small-molecule activator is an attractive therapeutic strategy for CRC and that MDL-811 could be a promising lead compound for further preclinical and clinical studies of treatments for CRC.