New <i>S</i>‐substituted‐3‐phenyltetrahydrobenzo[4,5]thieno[2,3‐<i>d</i>]pyrimidin‐4(3<i>H</i>)‐one scaffold with promising anticancer activity profile through the regulation and inhibition of mutated B‐RAF signaling pathway

Novel 3-phenyltetrahydrobenzo[4,5]thieno[2,3-d]pyrimidine derivatives were synthesized and screened for their antiproliferative activity against a panel of 60 cancer cell lines. Derivatives 5b, 5f, and 9c showed significant antitumor activity at a single dose with mean growth inhibition of 55.62%, 55.79%, and 71.40%, respectively. These compounds were further investigated against HCT-116, colon cancer cell line, and FHC, normal colon cell line. Compound 9c showed the highest activity with IC₅₀ = 0.904 ± 0.03 µM and SI = 20.42 excelling doxorubicin which scored IC₅₀ = 2.556 ± 0.09 µM and SI = 6.19. Compound 9c was also the most potent against B-RAF^WT and mutated B-RAF^V600E with IC₅₀ = 0.145 ± 0.005 and 0.042 ± 0.002 µM, respectively in comparison with vemurafenib with IC₅₀ = 0.229 ± 0.008 and 0.038 ± 0.001 µM, respectively. The cell cycle analysis showed that 9c increased the cell population and induced an arrest in the cell cycle of HCT-116 cancer cells at the G0-G1 stage with 1.23-fold. Apoptosis evaluation showed that compound 9c displayed an 18.18-fold elevation in total apoptosis of HCT-116 cancer cells in comparison to the control. Compound 9c increased the content of caspase-3 by 3.52-fold versus the control. A molecular modeling study determined the binding profile and interaction of 9c with the B-RAF active site.