Discovery and optimization of novel 4-morpholinothieno[3,2-d]pyrimidine derivatives as potent BET inhibitors for cancer therapy.

The identification of structurally novel and potently active BET inhibitors represents a significant advancement in the field of anticancer therapeutics. In the present investigation, leveraging the outcomes of previous screening endeavors, we successfully optimized and synthesized a novel series of bromodomain and extra-terminal (BET) inhibitors with a 4-morpholinothieno[3,2-d]pyrimidine structure. Among the synthesized compounds, compound 6c emerged as a promising candidate, exhibiting exceptional inhibitory activities against various BET isoform proteins, with IC₅₀ values ranging from 3.3 to 42.0 nM. In cellular assays, compound 6c demonstrated robust antiproliferative effects in SU-DHL-4 cells, achieving an IC₅₀ value of 8.6 ± 3.3 nM. Further mechanistic studies revealed that compound 6c effectively decreased the expression of c-Myc, a critical oncogenic driver regulated by the BET protein, and induced cell cycle arrest at the G1 phase, as well as cell apoptosis, in a dose-dependent manner. Moreover, in-silico prediction of the physiochemical and pharmacokinetic properties clarified that compound 6c has acceptable drug-like profiles. Taken these findings together, compound 6c represents a novel and potent BET inhibitor, thus positioning it as a promising candidate for subsequent pre-clinical evaluations in the realm of cancer therapy.