sHA 14-1, a stable and ROS-free antagonist against anti-apoptotic Bcl-2 proteins, bypasses drug resistances and synergizes cancer therapies in human leukemia cell

HA 14-1, a small-molecule antagonist against anti-apoptotic Bcl-2 proteins, was demonstrated to induce selective cytotoxicity toward malignant cells and to overcome drug resistance. Due to its poor stability and the reactive oxygen species (ROS) generated by its decomposition, chemical modification of HA 14-1 is needed for its future development. We have synthesized a stabilized analog of HA 14-1 - sHA 14-1, which did not induce the formation of ROS. As expected from a putative antagonist against anti-apoptotic Bcl-2 proteins like HA 14-1, sHA 14-1 disrupted the binding interaction of a Bak BH3 peptide with Bcl-2 or Bcl-X_L protein, inhibited the growth of tumor cells through the induction of apoptosis, and circumvented the drug resistance induced by the over-expression of anti-apoptotic Bcl-2 and Bcl-X_L proteins. Interestingly, the impairment of extrinsic apoptotic pathway induced moderate resistance to sHA 14-1. The moderate resistance suggested that sHA 14-1 generated part of its apoptotic stress through the intrinsic pathway, possibly through its antagonism against anti-apoptotic Bcl-2 proteins. The resistance indicated that sHA 14-1 generated apoptotic stress through the extrinsic apoptotic pathway as well. The ability of sHA 14-1 to induce apoptotic stress through both pathways was further supported by the synergism of sHA 14-1 towards the cytotoxicities of Fas ligand and dexamethasone in Jurkat cells. Taken together, these findings suggest that sHA 14-1 may represent a promising candidate for the treatment of drug-resistant cancers either as a monotherapy or in combination with current cancer therapies.