Abstract
Epidermal growth factor receptor (EGFR) inhibitors such as gefitinib show antitumor activity in a subset of non-small cell lung cancer (NSCLC) patients having mutated EGFR. Recent work shows that phosphatidylinositol-3-kinase (PI3-K) is coupled to the EGFR only in NSCLC cell lines expressing ErbB-3 and that EGFR inhibitors do not inhibit PI3-K signaling in these cells. The central role PI3-K plays in cell survival suggests that a PI3-K inhibitor offers a strategy to increase the antitumor activity of EGFR inhibitors in resistant NSCL tumors that do not express ErbB-3. We show that PX-866, a PI3-K inhibitor with selectivity for p110alpha, potentiates the antitumor activity of gefitinib against even large A-549 NSCL xenografts giving complete tumor growth control in the early stages of treatment. A-549 xenograft phospho-Akt was inhibited by PX-866 but not by gefitinib. A major toxicity of PX-866 administration was hyperglycemia with decreased glucose tolerance, which was reversed upon cessation of treatment. The decreased glucose tolerance caused by PX-866 was insensitive to the AMP-activated protein kinase inhibitor metformin but reversed by insulin and by the peroxisome proliferator-activated receptor-gamma activator pioglitazone. Prolonged PX-866 administration also caused increased neutrophil counts. Thus, PX-866, by inhibiting PI3-K signaling, may have clinical use in increasing the response to EGFR inhibitors such as gefitinib in patients with NSCLC and possibly in other cancers who do not respond to EGFR inhibition.