Aspirin is chemopreventive against colon and probably other
cancers, but this effect is relatively weak and its chronic administration to humans is associated with significant side effects. Because of these limitations, extensive effort has been exerted to improve the pharmacological properties of
aspirin. We have determined the anticancer activity and mechanisms of action of the novel para positional isomer of
phosphoaspirin [P-ASA;
MDC-43; 4-((diethoxyphosphoryloxy)methyl)phenyl 2-acetoxybenzoate]. P-ASA inhibited the growth of 10 human
cancer cell lines originating from colon, lung, liver, pancreas and breast, at least 18- to 144-fold more potently than conventional
aspirin. P-ASA achieved this effect by modulating cell kinetics; compared with controls, P-ASA reduced cell proliferation by up to 68%, increased apoptosis 5.5-fold and blocked cell cycle progression in the G(2)/M phase. P-ASA increased intracellular levels of
reactive oxygen species (ROS), depleted
glutathione levels and modulated cell signaling predominantly through the
mitogen-activated protein kinase (p38 and
c-jun N-terminal kinase),
cyclooxygenase (COX) and
nuclear factor-kappa B pathways. P-ASA targeted the mitochondria, increasing mitochondrial
superoxide anion levels; this effect on ROS led to collapsed mitochondrial membrane potential and triggered the intrinsic apoptotic pathway. The
antioxidant N-acetyl
cysteine abrogated the cell growth inhibitory and signaling effects of P-ASA, underscoring the centrality of ROS in its mechanism of action. Our results, establishing P-ASA as a potent inhibitor of the growth of several human
cancer cell lines, suggest that it may possess broad anticancer properties. We conclude that the novel P-ASA is a promising
anticancer agent, which merits further evaluation.