Antibody-drug conjugate (ADC) which delivers cytotoxic drugs specifically into targeted cells through internalization and lysosomal trafficking has emerged as an effective cancer therapy. We show that a bivalent biparatopic antibody targeting two non-overlapping epitopes on HER2 can induce HER2 receptor clustering, which in turn promotes robust internalization, lysosomal trafficking, and degradation. When conjugated with a tubulysin-based microtubule inhibitor, the biparatopic ADC demonstrates superior anti-tumor activity over ado-trastuzumab emtansine (T-DM1) in tumor models representing various patient subpopulations, including T-DM1 eligible, T-DM1 ineligible, and T-DM1 relapsed/refractory. Our findings indicate that this biparatopic ADC has promising potential as an effective therapy for metastatic breast cancer and a broader patient population may benefit from this unique HER2-targeting ADC.

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In the originally published version of this article, in Figure 2E the representative immunoblots of lysates from antibody-treated cells did not indicate spliced lines between lane 7 and lane 8. When preparing the figure for publication, these lanes had been spliced together from the same immunoblot, as indicated in the corrected Figure 2E shown here, to remove an irrelevant lane. The authors apologize for any confusion this may have caused.948 Cancer Cell 35, 948-949, June 10, 2019 ª 2019 Elsevier Inc.

Abstract. Antibody drug conjugates (ADCs) are biopharmaceutical molecules consisting of a cytotoxic small molecule covalently linked to a targeted protein carrier via a stable cleavable or noncleavable linker. The process of conjugation yields a highly complex molecule with biochemical properties that are distinct from those of the unconjugated components. The impact of these biochemical differences on the safety and pharmacokinetic (PK) profile of the conjugate must be considered when determining the types of nonclinical safety studies required to support clinical development of ADCs. The hybrid nature of ADCs highlights the need for a science-based approach to safety assessment that incorporates relevant aspects of small and large molecule testing paradigms. This thinking is reflected in current regulatory guidelines, where sections pertaining to conjugates allow for a flexible approach to nonclinical safety testing. The aim of this article is to review regulatory expectations regarding early assessment of nonclinical safety considerations and discuss how recent advances in our understanding of ADCmediated toxicity can be used to guide the types of nonclinical safety studies needed to support ADC clinical development. The review will also explore nonclinical testing strategies that can be used to streamline ADC development by assessing the safety and efficacy of next generation ADC constructs using a rodent screen approach.

Antibody-drug conjugates (ADC) are used to selectively deliver cytotoxic agents to tumors and have the potential for increased clinical benefit to cancer patients. 5T4 is an oncofetal antigen overexpressed on the cell surface in many carcinomas on both bulk tumor cells as well as cancer stem cells (CSC), has very limited normal tissue expression, and can internalize when bound by an antibody. An anti-5T4 antibody was identified and optimized for efficient binding and internalization in a target-specific manner, and engineered cysteines were incorporated into the molecule for site-specific conjugation. ADCs targeting 5T4 were constructed by site-specifically conjugating the antibody with payloads that possess different mechanisms of action, either a DNA cross-linking pyrrolobenzodiazepine (PBD) dimer or a microtubule-destabilizing tubulysin, so that each ADC had a drug:antibody ratio of 2. The resulting ADCs demonstrated significant target-dependent activity in vitro and in vivo; however, the ADC conjugated with a PBD payload (5T4-PBD) elicited more durable antitumor responses in vivo than the tubulysin conjugate in xenograft models. Likewise, the 5T4-PBD more potently inhibited the growth of 5T4-positive CSCs in vivo, which likely contributed to its superior antitumor activity. Given that the 5T4-PBD possessed both potent antitumor activity as well as anti-CSC activity, and thus could potentially target bulk tumor cells and CSCs in target-positive indications, it was further evaluated in non-GLP rat toxicology studies that demonstrated excellent in vivo stability with an acceptable safety profile. Taken together, these preclinical data support further development of 5T4-PBD, also known as MEDI0641, against 5T4 þ cancer indications. Mol Cancer Ther;16(8); 1576-87. Ó2017 AACR.