Dual small-molecule targeting of procaspase-3 dramatically enhances zymogen activation and anticancer activity.

Combination anticancer therapy typically consists of drugs that target different biochemical pathways or those that act on different targets in the same pathway. Here we demonstrate a new concept in combination therapy, that of enzyme activation with two compounds that hit the same biological target, but through different mechanisms. Combinations of procaspase-3 activators PAC-1 and 1541B show considerable synergy in activating procaspase-3 in vitro, stimulate rapid and dramatic maturation of procaspase-3 in multiple cancer cell lines, and powerfully induce caspase-dependent apoptotic death to a degree well exceeding the additive effect. In addition, the combination of PAC-1 and 1541B effectively reduces tumor burden in a murine lymphoma model at dosages for which the compounds alone have minimal or no effect. These data suggest the potential of PAC-1/1541B combinations for the treatment of cancer and, more broadly, demonstrate that differentially acting enzyme activators can potently synergize to give a significantly heightened biological effect.