Quinazolinone Based PI3Kδ/HDAC6 Bi-Functional Inhibitors : The Design,Synthesis And Biological Evaluation

Phosphatidylinositol-3-kinases（PI3Ks）,the key nodes of PI3K/AKT/m TOR pathway,are well-established targets for the development of therapeutic drugs against cancer.The PI3Kδisoform of class I PI3K has long been considered a therapeutic target for haematological cancers due to its preferential distribution in leukocytes and essential role in B-cell-mediated malignancies.In contrast,its application as a therapeutic target for solid tumors has been relatively poorly explored.Recently,the overexpression of PI3Kδin certain solid tumors has attracted increasing attention,and targeting PI3Kδcan suppress tumor progression by interfering with the aberrantly activated PI3Kδsignalling within tumor cells and reprogramming the tumor microenvironment and triggering anti-tumor immunity.Dual target inhibition of PI3Kδand histone deacetylase 6（HDAC6）has the potential to produce synergistic anti-tumor effects and is meaningful for delaying drug resistance.However,small molecule inhibitor targeting both PI3K and HDAC in clinical trials has a poor safety profile owing to its limited subtype selectivity.Accordingly,the design of dual-target PI3Kδ/HDAC6 inhibitors with anti-proliferative and immunomodulatory effects and subtype selectivity will provide new direction for the development of tumortherapeutic agents for battling solid tumors.In this study,structurally novel PI3Kδ/HDAC6 dual-target inhibitors were designed,synthesized and biologically evaluated via pharmacophore-merging strategy on the basis of the quinazolinone-derived PI3Kδinhibitor TGMXD-208 and the structural characteristics of HDAC6 inhibitors（HDAC6is）.Among the 27 target molecules,compounds 20,22,59,65,92 and 110-115 showed significant dual-target inhibitory activity with IC₅₀s at single or double digit nanomolar levels against PI3Kδand HDAC6.The representative compound 65 exhibited potent inhibitory activity and against PI3Kδ(IC₅₀=2.3 n M)and HDAC6(IC₅₀=13 n M),along with the favorable selectivity.In the in vitro anti-proliferative assay,65 showed remarkable activity against the B-NHL cell line SU-DHL-6,as well as the solid tumor cell lines KM-12,HCT116 and T47D,while exhibiting low cytotoxicity against normal cells.Further western blot assay showed that compound 65,at concentration as low as 30 n M,blocked the phosphorylation of AKT,the downstream kinase of PI3K,in T47D cell.Importantly,it simultaneously regulated tumor immune escape related STAT3signalling and the expression of the immune checkpoint PD-L1.In summary,a series of novel PI3Kδ/HDAC6 bi-functional inhibitors were designed and synthesized based on the scaffold of PI3Kδinhibitor TGMXD-208 in this thesis.The representative compound 65 exhibited prominent PI3Kδ/HDAC6 dual inhibitory activity and favorable isoform selectivity.Compared with the positive control Idelalisib and SAHA,compound 65 showed superior anti-proliferation activity in T47D cells.Notably,compound 65 also exhibited significant immunomodulatory effects at the cellular level.To date,no study has explored the dual function of PI3Kδ/HDAC6 dual inhibition in inhibiting solid tumor cell proliferation and modulating anti-tumor immunity.Compound 65,with the above merits,could be used as a lead for further structural optimization.