IRX4204 in combination with erlotinib to target distinct pathways in lung cancer cells.
e14095 Background: IRX4204 is a Retinoid X Receptor (RXR) specific agonist (rexinoid). IRX4204 has high potency as a RXR agonist with low binding affinity to Retinoic Acid Receptors (RARs), PPAR, FXR or LXR. Our prior work with the less specific rexinoid bexarotene and erlotinib showed clinical activity in patients with lung cancer cases that harbored KRAS mutations. IRX4204 inhibits lung cancer cell proliferation and can chemoprevent carcinogen-induced lung cancers in mice. We sought to explore the underlying mechanisms engaged by the combination of IRX4204 and erlotinib. Materials and Methods: Human (H1703 and HOP62) and murine (ED1 and LKR13) lung cancer cell lines were treated with IRX4204, erlotinib, IRX4204 plus erlotinib, or vehicle. Reverse phase protein array (RPPA) and mRNA microarray analyses were performed to analyze comprehensively for differentially expressed growth regulatory proteins. Results: Combination of IRX4204 and erlotinib suppressed proliferation of both KRAS mutant (HOP62 and LKR13) and wild-type (H1703 and ED1) lung cancer cell lines. Additive effect was observed as compared to IRX4204 or erlotinib treatment alone. Combining IRX4204 with erlotinib markedly increased inhibition of specific therapeutic targets including Src, phosphorylated Akt and ribosomal S6 proteins. At the mRNA level, Ingenuity Pathway Analysis of species significantly increased or decreased by the combination treatment revealed multiple pathways related to oncogenic signaling. Specifically, we found in H1703 cell line regulation of Granzyme A and AMPK signaling and in HOP62 cell line inhibition of angiogenesis was implicated by altering TSP1 expression. Notably, in ED1 cell line PPARα/RXRα activation, PTEN signaling, PI3K/AKT signaling, TGF-β signaling, and AMPK signaling were each associated with effects of IRX4204 combined with erlotinib. Conclusions: Taken together, these data highlight specific mechanisms and candidate pharmacodynamic biomarkers of response to the combination of this rexinoid and EGFR-TKI in lung cancer. Based on these findings, a clinical trial (NCT02991651) with IRX4204 in combination with erlotinib is underway to treat patients with chemotherapy-refractory non-small cell lung cancer.