Preclinical Evaluation of MEDI0641, a Pyrrolobenzodiazepine-Conjugated Antibody–Drug Conjugate Targeting 5T4

Abstract

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.

Improved Therapeutic Window in BRCA-mutant Tumors with Antibody-linked Pyrrolobenzodiazepine Dimers with and without PARP Inhibition

“…Enhanced killing of BRCA1or BRCA2-deficient xenograft tumors compared with BRCA wild-type tumors 5T4-PBD (MEDI0641) is an ADC in which anti-5T4 antibody was site-specifically conjugated to two PBD dimers (SG3249) per antibody. It has been shown to elicit a potent antitumor response in 5T4-positive xenograft models (36). In the process of characterizing 5T4-PBD, we noticed that it had superior antitumor activity in the models that carry BRCA mutations.…”

“…We performed retrospective analysis of 5T4 expression in untreated PDX tumors using methods described previously (36). IHC analysis demonstrated a wide range of 5T4 staining patterns across 23 BRCA-deficient and 3 BRCA wild-type PDX models.…”

Design and characterization of homogenous antibody-drug conjugates with a drug-to-antibody ratio of one prepared using an engineered antibody and a dual-maleimide pyrrolobenzodiazepine dimer

“…The SG3199 warhead was subsequently linked to a maleimidocaproyl-polyethylene glycol (PEG 8 ) linker via a self-immolative valine-alanine dipeptide at the N10 position to generate the SG3249 payload, which was used to prepare ADCs. [19][20][21][22][23][24] Drawing upon the success of SG3249 as an ADC payload, we hypothesized that functionalization of the symmetrical N10 nitrogen with an additional cathepsin-B cleavable valine-alanine dipeptide and PEG 8 -maleimide linker would result in a symmetrical dual-maleimide PBD dimer, SG3710 (Figure 1), which could be used to re-bridge two adjacent cysteines, such as the ones at the immunoglobulin G1 (IgG1) hinge. The symmetrical nature of the SG3710 payload offers several key structural features that not only expand the applicability of PBD dimers, but also offer enhancement of the biochemical properties of previous versions of PBD dimers, such as SG3249, which is composed of a single chemical linker (Figure 1).…”

A DNA-Interacting Payload Designed to Eliminate Cross-Linking Improves the Therapeutic Index of Antibody–Drug Conjugates (ADCs)

“…Despite (8). Since DNA-interacting agents are widely used in cancer therapy, and two of the four approved ADCs use a DNA interacting compound (calicheamicin), there has been a recent shift in emphasis towards using such compounds as payloads in ADCs (9)(10)(11)(12)(13)(14)(15). Indeed, the first ADC of a highly potent DNA interacting agent to be evaluated in the clinic was gemtuzumab ozogamicin, which incorporated calicheamicin, a compound that causes DNA double strand breaks.…”