Individual dose and scheduling determine the efficacy of combining cytotoxic anticancer agents with a kinase inhibitor in non-small-cell lung cancer.

PURPOSE: To investigate the combination of conventional cytotoxic anticancer agents and a small molecule kinase inhibitor in preclinical models of non-small-cell lung cancer (NSCLC). METHODS: We compared the induction of apoptosis by DNA-damaging anticancer drugs and PKC412, a predominantly protein kinase C (PKC)-specific small molecule inhibitor, in six NSCLC cell lines of different histologic and genetic backgrounds. The outcome of various combinations and schedules of DNA-damaging agents and PKC412 was studied, and isobolograms were calculated. Conditional expression of pro-apoptotic BAK was applied to specifically target apoptotic signal transduction in combination with drug therapy. RESULTS: Resistance of NSCLC cells to DNA damage-induced apoptosis was mainly determined at the mitochondrial step of the intrinsic pathway of caspase activation. PKC412 effectively inhibited the growth factor signal transduction, but failed to induce apoptosis in NSCLC cells resistant to DNA-damaging agents. Combining conventional anticancer drugs with PKC412 at different doses and schedules resulted in unpredictable outcomes, including synergistic, additive, and antagonistic interactions. In contrast, conditional expression of BAK reliably sensitized drug-resistant NSCLC cells to apoptosis induced by cytotoxic agents or PKC412. CONCLUSIONS: Combining DNA-damaging anticancer drugs with a pharmacologic inhibitor of growth and survival factor signaling in NSCLC may result in unpredictable treatment outcomes. In contrast, targeting specific death effector mechanisms, such as apoptotic signal transduction, is a promising strategy to sensitize NSCLC to cytotoxic agents or kinase inhibitors.

Targeting BCL-2 family proteins to overcome drug resistance in non-small cell lung cancer.

Cytotoxic chemotherapies are standard of care for patients suffering from advanced non-small cell lung cancer (NSCLC). However, objective responses are only achieved in 20% of cases and long-term survival is rarely observed. Clinically applied anticancer drugs exert at least some of their activities by inducing apoptosis. A critical step in apoptotic signal transduction is the permeabilization of the mitochondrial outer membrane (MOM), which is regulated by the BCL-2 family of proteins. Hence, therapeutic targeting of BCL-2 proteins is a promising approach to increase the drug-sensitivity of cancers. To this end we have assessed the impact of conditional expression of the proapoptotic multidomain (BH1-2-3) protein BAK, which directly permeabilizes the MOM, and the BH3-mimetic ABT-737, which acts indirectly by derepressing BH1-2-3 proteins, on apoptosis and drug sensitivity of NSCLC cells. Conditionally expressed BAK sensitized resistant NSCLC cells to drug-induced apoptosis. In contrast, ABT-737 was ineffective in those NSCLC cells expressing high levels of the anti-apoptotic MCL-1 protein. Tissue microarray analysis of tumor samples from 84 chemotherapy-naïve NSCLC patients revealed MCL-1 expression in 56% of cases, thus supporting the relevance of this resistance factor in a clinical setting. Enforced expression of the BH3-only protein NOXA, which targets MCL-1, overcame resistance to ABT-737. Moreover, combining conditionally expressed BAK with ABT-737 enhanced apoptosis in NSCLC cells independently of their MCL-1 status. In conclusion, the heterogeneity of apoptosis defects observed in drug-resistant NSCLC demands individually tailored molecular therapies. Targeting the MOM permeabilizer BAK appears to have a broader apoptogenic activity than the BH3-only mimetic ABT-737.