Abstract 1220: A novel PTK7-targeted antibody-drug conjugate eliminates tumor-initiating cells and induces sustained tumor regressions

Disease relapse after treatment is common in triple-negative breast cancer (TNBC), ovarian cancer and non-small cell lung cancer (NSCLC). Therapies that target tumor-initiating cells (TICs) should improve patient survival by eliminating the cells that can drive tumor regrowth and metastasis. Here we identify Protein Tyrosine Kinase 7 (PTK7), a highly conserved but catalytically inactive receptor tyrosine kinase, as an antigen that is enriched on TICs in low-passage patient-derived xenografts (PDX) of TNBC, NSCLC and other tumor types. An anti-PTK7 antibody-drug conjugate (ADC) was generated from a humanized anti-PTK7 monoclonal antibody, a cleavable valine-citrulline-based linker and the Aur0101 auristatin microtubule inhibitor. The anti-PTK7 ADC induced sustained regressions of TNBC, NSCLC and ovarian cancer PDX, with improved activity over standard-of-care chemotherapy, and reduced the frequency of TICs as determined by serial transplantation experiments. Moreover, the ADC may have additional mechanisms of action, including an anti-angiogenic effect, that promote anti-tumor immune responses. Together these preclinical results indicate the potential of the anti-PTK7 ADC to improve the long-term survival of cancer patients. The ADC is currently being tested in a Phase 1 clinical trial, from which interim results will be presented.

Citation Format: Marc Isaac Damelin, Alex Bankovich, Jeff Bernstein, Justin Lucas, Liang Chen, Sam Williams, Albert Park, Jorge Aguilar, Elana Ernstoff, Manoj Charati, Russell Dushin, Amy Jackson-Fisher, Monette Aujay, Christina Lee, Hanna Ramoth, Milly Milton, Johannes Hampl, Sasha Lazetic, Virginia Pulito, Douglas Armellino, Edward Rosfjord, Magali Guffroy, Hadi Falahatpisheh, Lindsay King, Frank Barletta, Robert Stull, Marybeth Pysz, Paul Escarpe, David Liu, Orit Foord, Brenda Gibson, Eric Powell, Christopher O’Donnell, Xiaohua Xin, Hans Peter Gerber, Puja Sapra, Scott Dylla. A novel PTK7-targeted antibody-drug conjugate eliminates tumor-initiating cells and induces sustained tumor regressions. [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 1220.

Abstract 5425: An anti-Ephrin-A4 calicheamicin conjugate effectively targets triple-negative breast and ovarian tumor-initiating cells to result in sustained tumor regression

Triple-negative breast cancer (TNBC) and ovarian cancer comprise heterogeneous tumors, and neither targeted therapies nor traditional chemotherapies have provided consistent clinical benefit. Novel therapies that target and actively eradicate the subpopulation of tumor cells that mediate drug resistance and tumor relapse could significantly improve patient survival. Tumor-initiating cells (TIC) are functionally defined as the subpopulation of cells that drive long-term tumor growth, resistance to therapy and disease relapse. We herein identified CD324 as a surface antigen able to reproducibly enrich for TIC in well annotated, low passage TNBC and ovarian cancer patient-derived xenografts (PDXs). Gene expression analysis of TIC led to the identification of Ephrin-A4 as a prospective therapeutic TIC target. Humanized Ephrin-A4-specific monoclonal antibodies (mAbs) were generated and demonstrated to internalize to mediate the delivery of potent cytotoxins. An antibody-drug conjugate (ADC) comprising a humanized anti-Ephrin-A4 mAb conjugated to the DNA damaging agent calicheamicin achieved sustained tumor regressions in vivo in both TNBC and ovarian cancer PDX. Anti-Ephrin-A4-ADC (PF-06647263) actively reduced TIC frequency as evidenced by limiting dilution analysis in serial transplantation assays. Unexpectedly, TNBC tumors of the non-Claudin low molecular subtype exhibited higher Ephrin-A4 expression and more robust responses to the ADC than other breast cancer subtypes, which suggests a specific translational application for breast tumor subtype classification. Together these findings demonstrate the potential of the Ephrin-A4-targeted calicheamicin conjugate as a first-in-class compound designed to eradicate TIC and improve long-term survival of cancer patients. PF-06647263 is currently being evaluated in a Phase I clinical trial.

Citation Format: Marc Damelin, Alex Bankovich, Albert Park, Jorge Aguilar, Wade Anderson, Marianne Santaguida, Sarah Fong, Monette Aujay, Kiran Khandke, Virginia Pulito, Elana Ernstoff, Paul Escarpe, Jeff Bernstein, Marybeth A. Pysz, Wenyan Zhong, Erik Upeslacis, Judy Lucas, Justin Lucas, Timothy Nichols, Kathryn Loving, Orit Foord, Johannes Hampl, Robert Stull, Frank Barletta, Hadi Falahatpisheh, Puja Sapra, Hans Peter Gerber, Scott J. Dylla. An anti-Ephrin-A4 calicheamicin conjugate effectively targets triple-negative breast and ovarian tumor-initiating cells to result in sustained tumor regression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5425. doi:10.1158/1538-7445.AM2015-5425

Anti-EFNA4 Calicheamicin Conjugates Effectively Target Triple-Negative Breast and Ovarian Tumor-Initiating Cells to Result in Sustained Tumor Regressions

PURPOSE

Triple-negative breast cancer (TNBC) and ovarian cancer each comprise heterogeneous tumors, for which current therapies have little clinical benefit. Novel therapies that target and eradicate tumor-initiating cells (TIC) are needed to significantly improve survival.

EXPERIMENTAL DESIGN

A panel of well-annotated patient-derived xenografts (PDX) was established, and surface markers that enriched for TIC in specific tumor subtypes were empirically determined. The TICs were queried for overexpressed antigens, one of which was selected to be the target of an antibody-drug conjugate (ADC). The efficacy of the ADC was evaluated in 15 PDX models to generate hypotheses for patient stratification.

RESULTS

We herein identified E-cadherin (CD324) as a surface antigen able to reproducibly enrich for TIC in well-annotated, low-passage TNBC and ovarian cancer PDXs. Gene expression analysis of TIC led to the identification of Ephrin-A4 (EFNA4) as a prospective therapeutic target. An ADC comprising a humanized anti-EFNA4 monoclonal antibody conjugated to the DNA-damaging agent calicheamicin achieved sustained tumor regressions in both TNBC and ovarian cancer PDX in vivo. Non-claudin low TNBC tumors exhibited higher expression and more robust responses than other breast cancer subtypes, suggesting a specific translational application for tumor subclassification.

CONCLUSIONS

These findings demonstrate the potential of PF-06647263 (anti-EFNA4-ADC) as a first-in-class compound designed to eradicate TIC. The use of well-annotated PDX for drug discovery enabled the identification of a novel TIC target, pharmacologic evaluation of the compound, and translational studies to inform clinical development.

Development of a sensitive assay for detection of replication-competent recombinant lentivirus in large-scale HIV-based vector preparations

Lentiviral vectors have demonstrated great potential as gene therapy vectors mediating efficient ex vivo and in vivo gene delivery and long-term transgene expression in both dividing and nondividing cells. However, for clinical studies it must be demonstrated that lentiviral vector preparations are safe and not contaminated by replication-competent recombinants related to the parental pathogenic virus. Here we describe a sensitive assay for the detection of replication-competent lentiviruses (RCL) in large-scale preparations of HIV-based lentiviral vectors. This RCL assay for lentiviral vectors is based on the principles used for retroviral vectors, using a highly permissive cell line, C8166-45, for RCL amplification and an appropriate positive control virus to establish the assay sensitivity. The assay is capable of detecting 1 RCL infectious unit in a background of 2.5 x 10(8) transducing units of vector in a single test culture. Statistically representative samples from large-scale lentiviral vector productions were assayed using multiple test cultures for each lot. Overall, a total of 1.4 x 10(10) transducing units of vector from 10 independent 14-liter production lots were screened and no RCL was detected. We propose to implement this assay as a release testing for clinical-grade lentiviral vector preparations intended for gene therapy clinical trials.