BACKGROUND: Non-small cell lung cancer (NSCLC) is a leading cause of death worldwide. There is a critical need to develop new therapeutic options for patients with advanced NSCLC. Androgen Receptor (AR) expression has been observed in lung cancer, along with castration associated inhibition of tumor growth in mouse models. The AR is a high value therapeutic target in prostate cancer and many targeted therapies are clinically available. However, significant genomic and functional alterations occur in NSCLC over the course of targeted therapies that may predict response and resistance to AR targeted therapies. The development of predictive and pharmacodynamic biomarkers of the AR signaling pathway in NSCLC may be critical to developing appropriate therapeutic strategies in this context. To evaluate AR expression and the AR signaling pathway, we developed a circulating tumor cell (CTC) assay to evaluate orthogonal endpoints across protein and gene expression analytics in patients with advanced NSCLC.
METHODS: CTCs were isolated from patients with metastatic NSCLC using an integrated CTC capture and analysis technology known as the VERSA (Versatile Exclusion-based Rare Sample Analysis) platform. This microscale platform integrates tumor cell capture, for any target of interest, with enumeration and nucleic acid extraction for analysis of orthogonal endpoints from a blood sample. CTCs were captured with multiple antibodies, including EpCAM, MUC1, and Vimentin. mRNA was extracted from CTCs for gene expression analysis of the AR, AR splice variants, downstream targets in the AR signaling pathway and activation markers in NSCLC.
RESULTS: Enumeration of CTCs from patients with metastatic NSCLC shows significant tumor burden, ranging from 10-150 CTCs per 7.5mL of blood. Gene expression analysis of CTCs identified expression of proliferative markers KRAS, BRAF, and RET. In our initial cohort of patients, full length AR expression was identified in 13/13 patients with NSCLC. The AR V7 splice variant was detected at low levels in 2/13 patients. PSMA, but not TMPRSS2, was identified in a subset of these patients suggesting activity of the canonical AR signaling pathway
CONCLUSIONS: The VERSA effectively captures CTCs with high sensitivity to detect the AR and AR variants in NSCLC CTCs. The AR is detectable in patients with NSCLC CTCs at high frequency. A subset of patient samples show activity in the AR signaling pathway that could potentially drive disease progression. The identification of the AR V7 splice variant suggests shared mechanisms of resistance in NSCLC and prostate cancer. These assays may serve as predictive and pharmacodynamic biomarkers for AR targeted therapies in NSCLC.
Citation Format: Jennifer L. Schehr, Zachery Schultz, Anwaar Saeed, Jamie M. Sperger, Ticiana Leal, Kara Mattox, Anne Traynor, Joshua M. Lang. Androgen receptor expression in non-small cell lung cancer circulating tumor cells. [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 2246.