1,2,4‐Triazolo[4,3‐c]quinazolines: A bioisosterism-guided approach towards the development of novel PCAF inhibitors with potential anticancer activity

Targeting PCAF with small inhibitor molecules has emerged as a potential therapeutic strategy for the treatment of cancer. Recently, L-45 was identified as a potent triazolophthalazine inhibitor of the PCAF bromodomain. Here, we report the bioisosteric modification of the triazolophthalazine ring system of L-45 to its bioisosteric triazoloquinazoline while maintaining other essential structural fragments for effective binding with the binding site of PCAF. Consequently, a set of sixteen triazoloquinazoline derivatives were designed, synthesized, and investigated for their anticancer activity against four human cancer cell lines. Five derivatives demonstrated comparable cytotoxic activity with that of doxorubicin as a reference anticancer drug. Among them, compound 23 showed the most potent activity with IC50 values of 6.12, 4.08, 7.17, and 6.42 μM against HePG2, MCF-7, PC3, and HCT-116, respectively. Also, compound 21 exhibited comparable cytotoxic effects with that of doxorubicin against the selected cancer cell lines with IC50 values in the range of 7.41–9.58 μM. Molecular docking and pharmacokinetic studies were additionally performed to rationalize the binding affinities of the newly designed triazoloquinazolines toward the active site of histone acetyltransferase PCAF and to evaluate the druggability of new compounds. The results of these studies suggested that PCAF binding could be the mechanism of action of these derivatives.