Phosphodiesterase Inhibition to Sensitize Non-Small-Cell Lung Cancer to Pemetrexed: A Double-Edged Strategy.

Simple Summary: We evaluated the repurposing of a class of non-cancer drugs, phosphodiesterase inhibitors, to increase the potency of an anti-folate chemotherapy drug against non-small-cell lung cancer. We showed that this approach represents a double-edged strategy. While the use of phosphodiesterase inhibitors potentiated the killing of lung cancer cells by combination low-dose anti-folate chemotherapy, in half of the tumors evaluated, the benefit was lost when using higher doses of chemotherapy. Phosphosidesterases (PDEs) are key regulators of cyclic nucleotide signaling, controlling many hallmarks of cancer and playing a role in resistance to chemotherapy in non-small-cell lung cancer (NSCLC). We evaluated the anti-tumor activity of the anti-folate agent pemetrexed (PMX), alone or combined with biochemical inhibitors of PDE5, 8, 9, or 10, against squamous and non-squamous NCSLC cells. Genomic alterations to PDE genes (PDE^mut) or PDE biochemical inhibition (PDEi) can sensitize NSCLC to PMX in vitro (observed in 50% NSCLC evaluated). The synergistic activity of PDEi with PMX required microdosing of the anti-folate drug. As single agents, none of the PDEis evaluated have anti-tumor activity. PDE biochemical inhibitors, targeting either cAMP or cGMP signaling (or both), resulted in significant cross-modulation of downstream pathways. The use of PDEi may present a new strategy to overcome PMX resistance of PDE^wt NSCLC tumors but comes with important caveats, including the use of subtherapeutic PMX doses. [ABSTRACT FROM AUTHOR]