The BH3 peptidomimetic obatoclax restores absent mitochondrial death signals in cisplatin resistant non-small cell lung cancer


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Nyree Crawford, Alex Chacko, Keenan Savage, Patrick Johnston, Dean Fennell

Queen's University Belfast, Northern Ireland, UK

Abstract

The BH3 peptidomimetic obatoclax restores absent mitochondrial death signals in cisplatin resistant non-small cell lung cancer

Background

Resistance to apoptosis is a hallmark of cancer and contributes significantly to the failure of cytotoxic therapy, particularly in relapsed non-small cell lung cancer (NSCLC) where response to therapy is < 10%. Mitochondria are master regulators of the apoptosis pathway, integrating multiple death signals that arise following cell damage, through activation of BAX/BAK. Understanding how this integrating function is modified in drug resistant NSCLC will be critical for improving the effectiveness of therapy.

Method and results

NSCLC cells were selected with log-fold resistance to cisplatin (cisRH460) compared to parental cells (parRH460). Cisplatin induced equal gamma-H2AX phosphorylation and cell cycle arrest, but failed to activate APAF-1 apoptosome dependent caspase 9 in CisRH460 despite equivalent mitochondrial prosurvival BCL-2 family expression. In contrast exogenous BH3 domains of BID or BIM were equally potent in inducing BAX/BAK dependent cell death and caspase 9 activation in cisRH460 versus parH460. In isolated mitochondria, BID-BH3 induced BAX/BAK dependent depolarization, SMAC release independent of cristae remodelling, with generation of hydrogen peroxide, cardiolipin peroxidation, and damaged ultrastructure. CisRH460/parH460 were equally sensitive to the MCL-1/A1 antagonist NOXA-BH3, which displaced BAK from its high molecular weight complex outer mitochondrial membrane complex, and activated BAX/BAK/caspase 9. Accordingly, the novel NOXA-BH3 mimetic obatoclax was equipotent in inhibiting ATP synthesis in both CisRH460 and parH460 and induced apoptosis at therapeutically relevant concentrations.

Conclusion

In summary, absent mitochondrial death signals underlie cisplatin resistance but can be restored by a BH3- mimetic, opening the way to rational therapy of drug resistant NSCLC.