Neutrophil-mediated nonoxidative tumor lysis stimulated by high concentrations of phorbol myristate acetate

The mechanism of neutrophil-mediated lysis of tumor targets was investigated. Tumor lysis was directly related to the concentration of phorbol myristate acetate (PMA) used to stimulate PMNs. Lysis increased as the PMA concentration increased between 10(-7) and 10(-4) M. In contrast, the production of H2O2 plateaued between concentrations of 10(-5) and 10(-4) M. The K562 erythroleukemia cell, the target used in this study, was found to be relatively resistant to preformed H2O2, with an LD50 of 8.3 X 10(-3) M. Myeloperoxidase was not capable of enhancing K562 lysis. Although resistant to preformed H2O2, K562 lysis mediated by PMNs stimulated with 10(-7) M PMA was oxidative in nature. It was sensitive to inhibition by catalase and was not significant when PMNs from patients with chronic granulomatous disease were used. In contrast, PMN lysis stimulated by 10(-4) M PMA was nonoxidative in nature. The inhibitors catalase and superoxide dismutase had no effect on lysis, lysis was significant when the assay was performed in an anaerobic atmosphere, and PMNs from patients with chronic granulomatous disease were comparable to control PMNs in tumor lysis. A single-cell conjugate and cytotoxicity assay demonstrated that PMA was both able to increase the ability of PMNs to bind to tumor targets and to enhance their lysis of bound targets. These data indicate that PMNs are capable of achieving tumor lysis by nonoxidative pathways under certain conditions. The high-dose PMA model may be valuable as a tool for investigating these alternative mechanisms of tumor lysis.