Abstract P3-05-22: Anti-uPAR antibody drug conjugates for targeted therapy of triple-negative breast cancer
Authors: Harel E , McFarland J , Bleck G , Brain S , Drake P , Rabuka D , Vantveer L , Craik C 
Published: February 2018

Abstract
Background: Triple negative Breast Cancer (TNBC) is a highly aggressive BC subtype, with an increased likelihood of distant recurrence and of death compared with other types of BC. Patients diagnosed with TNBC lack the estrogen and progesterone receptors, the human epidermal growth factor 2 receptor and do not respond well to current therapies. One hallmark of TNBC is increased uPAR expression. As uPAR was observed in BC and its metastasis but not in normal tissue, anti-uPAR Abs can serve as a targeted therapy for TNBC. The Craik lab used recombinant phage display technology to identify anti-human-uPAR Abs. Two of those human antibodies, 2G10 and 3C6, were tested in in vitro and in vivo TNBC models and demonstrated therapeutic potential. In the mouse model of TNBC the “naked” Abs targeting two distinct subdomains of the receptor slowed or blocked tumor growth. Moving forward in validating the antibodies as a therapeutic for aggressive breast cancer, we have chosen to develop them as a 'weaponized antibody' therapy in the form of antibody-drug conjugates (ADCs). Excellent proof of concept for the therapeutic potential of anti uPAR ADC was achieved with anti uPAR (2G10) conjugated to the therapeutic radioisotope 177Lu. With the current limitations of radiotherapy we conjugated 2G10 and 3C6 to make ADCs with a known cytotoxic agent that is available for the treatment of cancer.
Hypothesis:We hypothesize that human anti uPAR mAbs, when coupled to a cytotoxic drug will demonstrate cancer-selective cell killing in mouse xenograft models of TNBC, and are safe with a large therapeutic window, thereby validating uPAR as a therapeutic target for TNBC and anti-uPAR antibodies as a potential therapeutic.
Study design:We tested the ability of the ADCs to target the urokinase receptor that is over-expressed in breast cancer, for therapy. Six- SMART TAG (CATALENT) based anti uPAR (2G10 and 3C6) ADCs have been assembled and characterized. The 6 ADCs with cleavable and non-cleavable linkers, 3 different toxins (alkylation agent and antimitotic agents) and drug antibody ratio (DAR) of˜2 were produced in reagent quantities. The ADCs were tested in vitro in head-to-head comparisons between the ADC form and unconjugated mAb for their cell killing ability using cell culture assays. Further characterization was performed in in vivo TNBC models.
Results: The anti uPAR ADCs were able to recognize uPAR in TNBC cell lines. The ADC 3C6 AzaHIPS-4AP-MMAE exhibited the greatest therapeutic effect in vitro in TNBC cell lines and showed significant slowing or blocking tumor growth in a mouse model of TNBC
Conclusions: Our results indicate the therapeutic potential of anti-uPAR ADC for TNBC.
Acknowledgments: This work was supported by the Target Validation Initiative grant from the UCSF Helen Diller Family Comprehensive Cancer Center and a grant from Susan G. Komen (PDF15330246) made possible through fundings from American Airlines.
Citation Format: Harel E, McFarland J, Bleck G, Brain S, Drake P, Rabuka D, Vantveer L, Craik C. Anti-uPAR antibody drug conjugates for targeted therapy of triple-negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-22.