Abstract 4035: Protein tyrosine kinase 7 (PTK7) biomarker analysis in patients (pts) treated with PF-06647020, a PTK7 antibody-drug conjugate (ADC), in a phase I dose expansion study

Background: PF-06647020, an ADC comprising a humanized monoclonal antibody against PTK7, a cleavable valine-citrulline linker, and an auristatin payload, is being investigated in an ongoing Phase I clinical trial in pts with advanced solid tumors. We hypothesized that response to a PTK7-directed ADC would correlate with PTK7 expression in the pts tumor. We report preliminary baseline PTK7 expression in pts tumors and clinical response using a novel CLIA validated laboratory developed test (LDT). Methods: We developed and validated an LDT comprising an anti-PTK7 immunohistochemistry assay with digital tissue analysis using Flagship Biosciences Inc’s cTA® platform to detect membrane-associated PTK7 in formalin-fixed paraffin embedded (FFPE) epithelial malignancies of ovary, breast and lung. Tumor samples were immunolabeled with the LDT and image analysis was applied to derive a digital H-score. Specifically the digital image annotation included desired regions of analysis (ROA) and excluded regions not of interest. The cTA® platform identified each cell in a given ROA and quantified an overall H-score for malignant epithelial cell membranes immunolabeled for PTK7. Non-small cell lung cancer (NSCLC) pts with H-scores ≥ 56.8 were eligible for enrollment whereas ovarian cancer (OVCA) pts were enrolled unselected. Triple negative breast cancer (TNBC) pts were initially enrolled unselected, but after review a requirement for H-scores ≥ 92.8 was implemented for enrollment. Results: PTK7 IHC was performed on baseline FFPE samples from 69 pts and digital H-scores were generated (Table 1). An additional 7 pt samples were not amenable to analysis with the cTA® platform. Conclusions: A novel CLIA validated LDT was developed and implemented to assess PTK7 baseline levels in FFPE tumors from pts treated with PF-06647020. Clinical responses tended to correlate with H-scores that were higher than the mean for each tumor type. Citation Format: Amy Jackson-Fisher, Navi Mehra, Roberto Gianani, Pamela Whalen, Pamela Vizcarra, Shibing Deng, Stephen McComish, Xiaohua Xin, Eric L. Powell. Protein tyrosine kinase 7 (PTK7) biomarker analysis in patients (pts) treated with PF-06647020, a PTK7 antibody-drug conjugate (ADC), in a phase I dose expansion study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4035.