Although recent decades have seen a significant improvement in the treatment outcome of leukemia in the pediatric population, those who are treated for relapsed disease still face significant morbidity and mortality. However, current salvage regimens are often assembled with agents that have similar mode of activity as the chemotherapeutics used in the initial treatment. Hence, novel therapeutic agents that are capable of distinct and diverse mechanisms of activity in, now resistant, leukemia cells are of great interest. We have investigated the opioid agonist methadone for its anti-leukemic activity, initially reported in studies with cell lines derived from adult patients. Our findings show that, compared to normal cells, methadone has enhanced cytotoxicity against specimens and cell lines established from refractory childhood leukemia. In addition, methadone's activity synergized with that of the anti-Bcl-2 agent ABT-737 and was characterized by the induction of distinct changes in tumor cell mitochondria. Data presented also identify biological correlates and a potential mechanism for methadone activity by its effects on Mcl-1 and other members of the apoptosis cascade. We provide mechanistic data for the therapeutic potential of a family of agents that is largely unexplored for anti-leukemic activity.
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