Pharmacological Aspects of the Enzastaurin-Pemetrexed Combination in Non-Small Cell Lung Cancer (NSCLC)

Conventional regimens have limited impact against NSCLC. Current research is focusing on multiple pathways as potential targets, and this review describes pharmacological aspects underlying the combination of the PKCβ-inhibitor enzastaurin with the multitargeted antifolate pemetrexed. Pemetrexed is commonly used, alone or combined with platinum compounds, in NSCLC treatment, and ongoing studies are evaluating its target, thymidylate synthase (TS), as predictor of drug activity. Enzastaurin is a biological targeted agent actively being investigated against different tumors as single agent or in combination. All the downstream events following PKCβ inhibition by enzastaurin are not completely known, and assays to evaluate possible biomarkers, such as expression of PKC, VEGF and GSK3β, in tissues and/or in blood samples, are being developed. Enzastaurin-pemetrexed combination was synergistic in preclinical models, including NSCLC cells, where enzastaurin reduced phosphoCdc25C, resulting in G2/M-checkpoint abrogation, and Akt and GSK3β phosphorylation, favoring apoptosis induction in pemetrexed-damaged cells. Enzastaurin also significantly reduced VEGF secretion and pemetrexed-induced upregulation of TS expression, possibly via E2F-1 reduction, while the combination decreased TS activity. Similarly, the accumulation of deoxyuridine (a marker of TS inhibition) and the reduction of GSK3β phosphorylation were detectable in clinical samples from a phase-Ib trial of pemetrexed-enzastaurin combination. In conclusion, the favorable toxicity profile and the multiple effects of enzastaurin on signaling pathways involved in cell cycle control, apoptosis and angiogenesis, as well as on proteins involved in pemetrexed activity, provide experimental basis for future studies on enzastaurin-pemetrexed combination and their possible pharmacodynamic markers in NSCLC patients.