Identification And Mechanism Study Of Sirt6allosteric Activators For Cancer Treatment

Cancers have emerged as the main threat to human life in diseases but with limited targets.It becomes a major challenge to identify novel targets and develop effective therapeutics with low toxicity for cancer treatment.SIRT6 is a member of a conserved nicotinamide adenine dinucleotide(NAD⁺)-dependent class III histone deacetylase Sirtuin family,which implicates in various pathological processes including tumorigenesis via histone H3 deacetylation,thus becoming an attractive drug target.Downregulation of SIRT6 is linked to the initiation,progression and poor prognosis of various cancers,and overexpression of SIRT6 suppresses tumorigenesis by histone H3deacetylation,suggesting that activation of SIRT6 deacetylation may exert an anti-cancer effect.However,the function and mechanism of SIRT6 activation in cancers have not been fully explored due to the lack of effective SIRT6pharmacological activators.Here,we demonstrated that our reported allosteric activator of SIRT6,MDL-800,inhibited non-small cell lung carcinoma(NSCLC)cell proliferation via activating SIRT6 deacetylase activity,and induced SIRT6-mediated cell cycle arrest,as well as showed favorable in vivo anti-tumor efficacy.Moreover,MDL-800 enhanced the anti-proliferation of Epidermal growth factor receptor tyrosine kinase inhibitors(EGFR-TKIs)in NSCLC Osimertinib-resistant cells and patient-derived primary tumor cells,and suppressed mitogen-activated protein kinase(MAPK)pathway in NSCLC.Based on structural optimizations,we identified a new series of more effective SIRT6 allosteric activators.The most potent activator,MDL-811,selectively activated SIRT6 deacetylation with an EC₅₀value of 5.7±0.8?M.MDL-811 remarkably enhanced SIRT6-specific histone H3 deacetylase activity and showed great anti-proliferative effects on multiple colorectal cancer(CRC)cell lines and patient-derived organoids.Moreover,in vivo anti-CRC efficacy of MDL-811was also well demonstrated across several cell-line-and patient-derived xenografts,as well as the APC^min/+spontaneous CRC model.By RNA profiling,we revealed that MDL-811 inhibited gene expression related to cell cycle including Cytochrome P450family 24 subfamily A member 1(CYP24A1),which is a potential downstream target gene of SIRT6,and activation of SIRT6 deacetylation by MDL-811 could suppress transcription of CYP24A1,thus inhibiting CRC proliferation.Based on the finding,we designed a combination strategy with MDL-811 to synergistically enhance the anti-CRC effect of vitamin D₃(VD₃)in vitro and in vivo.Collectively,our work identified potent SIRT6 activators,which substantially inhibited the proliferation of cancers in vitro and in vivo,systematically supporting the rationale for SIRT6activation as a promising translational strategy for cancer therapeutic intervention.