3-Aminoisoquinolines inhibit selectively phosphodiesterase 4B in KRAS-mutated colorectal cancer cell lines in-vitro and in-vivo.

Phosphodiesterase 4B (PDE4B), an isoform of cyclic nucleotide phosphodiesterases, is integrated into cell membranes and hydrolyzes cyclic AMP in specific cellular compartments. Overexpression of PDE4B has been observed in hematological and gastrointestinal tumors harboring KRAS mutations, leading to the disruption of cell cycle regulation. Utilizing molecular docking, we identified 3-aminoisoquinolines as potential selective PDE4B inhibitors. Phenotypic screening on HKe3-KRAS cell lines confirmed that PDE4B is a selective target for these novel 3-aminoisoquinolines. We employed molecular docking and calculated ligand efficiency as predictive tools for methylthiazoltetrazolium assay activity to reduce the combinatorial library size. Six active compounds (047, 048, 086, 089, 091, and 099) were screened. Active compounds 047, 048, 086, 089, and 091 demonstrated selectivity toward HKe3-mtKRAS over wild-type cells. This 'synthetic lethality-like' approach was effective in predicting the anticancer properties of these compounds in KRAS-mutated cell lines. NCI-DTP 60 cell lines assays confirmed the activities of 047, 048, and 089. Compound 089 showed strong cytotoxicity against HCT-116 cells inhibitory concentration (IC50) = 1.6 μM, growth inhibition (GI50) = 0.53 μM, and an inhibitory concentration (IC50) against PDE4B = 2.5 μM. In addition, 089 exhibited good tolerability in a nude mouse HCT-116 xenograft model, but it was less effective at a dose of 40 mg/kg compared with Apremilast at a dose of 30 mg/kg in 8-s day's assay. While 089 had lower in-vivo efficacy than apremilast, its novel 3-aminoisoquinoline scaffold and high tolerability make it a superior candidate for further optimization.