Preclinical evaluation of a GFRA1 targeted antibody-drug conjugate in breast cancer.

Emily E Bosco,Rosa Carrasco,Qun Du,Jiping Zha,Maryjane Hinrichs,Zhan Xiao,Sandrina Phipps,Binyam Bezabeh,Ronald Herbst,David A Tice,Karma Dacosta,Joanne Ayriss,R James Christie,Darrin Sabol,John Meekin,Haihong Zhong,Cui Chen,Rakesh Dixit,Molly Reed,Shannon Breen,Lee R Brown ,Partha S Chowdhury ,Margaret Kennedy

doi:10.18632/oncotarget.25160

Abstract

Despite recent advances in treatment, breast cancer remains the second-most common cause of cancer death among American women. A greater understanding of the molecular characteristics of breast tumors could ultimately lead to improved tumor-targeted treatment options, particularly for subsets of breast cancer patients with unmet needs. Using an unbiased genomics approach to uncover membrane-localized tumor-associated antigens (TAAs), we have identified glial cell line derived neurotrophic factor (GDNF) family receptor α 1 (GFRA1) as a breast cancer TAA. Immunohistochemistry (IHC) revealed that GFRA1 displays a limited normal tissue expression profile coupled with overexpression in specific breast cancer subsets. The cell surface localization as determined by fluorescence-activated cell sorting (FACS) and the rapid internalization kinetics of GFRA1 makes it an ideal target for therapeutic exploitation as an antibody-drug conjugate (ADC). Here, we describe the development of a pyrrolobenzodiazepine (PBD)-armed, GFRA1-targeted ADC that demonstrates cytotoxicity in GFRA1-positive cell lines and patient-derived xenograft (PDX) models. The safety profile of the rat cross-reactive GFRA1-PBD was assessed in a rat toxicology study to find transient cellularity reductions in the bone marrow and peripheral blood, consistent with known off-target effects of PBD ADC’s. These studies reveal no evidence of on-target toxicity and support further evaluation of GFRA1-PBD in GFRA1-positive tumors.

Highlights

70% of breast tumors are estrogen receptor α (ER) positive and amenable to endocrinedisrupting therapies
GFRA1 appeared on the cell surface in cells expressing the protein, and that expression was diminished in GFRA1-null or small interfering RNA (siRNA)-treated cells
GFRA1 IHC (4D12) was performed in order gain an understanding of the correlation between our IHC assay signal and GFRA1 receptor density values determined by fluorescence-activated cell sorting (FACS) (10H9) (Figure 2C)

Summary

Introduction

70% of breast tumors are estrogen receptor α (ER) positive and amenable to endocrinedisrupting therapies. Despite the many therapeutic successes in breast cancer, novel therapies are still needed for large subsets of patients. A greater understanding of the shared molecular characteristics of breast tumors could guide the development of optimal tumor-targeted therapeutic interventions. Over the past several years, the antibody-drug conjugate (ADC) has emerged as a therapeutic platform that can exploit tumor-specific molecular characteristics. One reason for limited success involves extremely potent payloads that can induce off-target toxicities before reaching therapeutic dose levels in Phase I clinical trials [5]. Another reason is the narrow therapeutic index of many ADC programs, which arises from the relative scarcity of tumor antigens that are overexpressed in tumor tissues but not in essential normal tissues. Identifying tumor-associated antigens (TAAs) with exceptionally limited expression in critical normal tissues can help in overcoming these problems

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Results

Conclusion