Abstract 890: TGFâ upregulation mediates growth retardation in EGFR T790M mutant non-small cell lung cancer

Abstract

Abstract Introduction: A subset of non-small cell lung cancer is driven by activating mutations in the epidermal growth factor receptor (EGFR). The majority of EGFR-driven lung cancers respond to EGFR kinase inhibitors gefitinib and erlotinib, although the clinical efficacy these inhibitors is limited by the development of drug resistance. A secondary missense mutation encoding EGFR T790M is the most prevalent resistance mechanism observed in patients, accounting for nearly 60% of relapse following gefitinib or erlotinib treatment. Although the T790M mutation enhances EGFR kinase activity, T790M harboring tumors exhibit indolent growth and are associated with favorable prognosis compared to tumors that acquire alternative mechanisms of drug resistance. The mechanism(s) underlying the indolent growth mediated by EGFR T790M are not well characterized. Methods: To identify the factor(s) mediating T790M associated growth retardation, we characterized T790M amplified drug resistant cells. EGFR mutant parental lung cancer cell lines PC9 and H3255 were selected through sequential treatment with gefitinib and the irreversible EGFR inhibitor dacomitinib. The resulting drug resistant cells, PC9DR and H3255DR, harbored amplified EGFR T790M and exhibited marked growth retardation. These T790M amplified models were characterized to identify factors conferring indolent growth. T790M expressing patient tumor samples were also analyzed to validate T790M associated changes. Results: Ectopic overexpression of EGFR T790M induced growth retardation in EGFR inhibitor-naïve cells. Incubation of parental PC9 cells in media conditioned on PC9DR cells was sufficient to slow PC9 growth rates, suggesting that a secreted factor was responsible for the growth retardation observed in the T790M amplified cells. A Luminex assay of PC9DR cells revealed upregulation of transforming growth factor beta 2 (TGFâ2), which was confirmed at the transcript level by qPCR. Treatment of parental PC9 cells with recombinant TGFâ was sufficient to induce slowed growth, while inhibition of TGFâ signaling using a TGFâ receptor inhibitor rescued growth rates in T790M amplified cell lines. Finally, T790M harboring patient tumor samples showed a trend of TGFâ2 transcript upregulation. Conclusions: We have demonstrated that TGFâ2 is upregulated in EGFR T790M amplified lung cancer cells, and is sufficient to elicit T790M associated growth retardation. The correlation between TGFâ expression and indolent growth of T790M expressing tumors identifies TGFâ as a potential biomarker to predict patient prognosis and outcome. Citation Format: Claire E. Repellin, Pinar O. Eser, Marzia Capelletti, Takeshi Shimamura, Dalia Ercan, Chunxiao Xu, Nathanael S. Gray, Kwok-Kin Wong, Pasi A. Jänne. TGFâ upregulation mediates growth retardation in EGFR T790M mutant non-small cell lung cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 890.