Author Manuscript Published OnlineFirst on August 26, 2020; DOI: 10.1158/1535-7163.MCT-20-0149 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Targeting Multiple EGFR Expressing Tumors with a Highly Potent Tumor-Selective Antibody Drug Conjugate Mark G. Anderson1, Hugh D. Falls1, Michael J. Mitten1, Anatol Oleksijew1, Kedar S. Vaidya2, Erwin R. Boghaert1, Wenqing Gao1, Joann P. Palma1, Diana Cao3, Puey-Ling Chia3, Thomas John3, Hui K. Gan3, Andrew M. Scott3 and Edward B. Reilly1 Authors Affiliation 1 AbbVie Inc., 1 North Waukegan Rd., North Chicago, IL 60064 2 Former AbbVie employee 3Olivia Newton-John Cancer Research Institute, and School of Cancer Medicine, La Trobe University Austin Hospital, Heidelberg, Victoria, Australia Running Title Anti-EGFR PBD dimer ADC Correspondence Edward B. Reilly, Ph.D. AbbVie Oncology Discovery, R460 1 North Waukegan Road North Chicago, IL 60064-6099 Phone: (847) 937-0815 Email: [email protected] Authors Disclosure The design, study conduct, and financial support for the study were provided by AbbVie. AbbVie participated in the interpretation of the data, review, and approval of the publication. MGA, HDF, MJM, 1 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2020 American Association for Cancer Research. Author Manuscript Published OnlineFirst on August 26, 2020; DOI: 10.1158/1535-7163.MCT-20-0149 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. AO, ERB, WG, JPP and EBR are employees of AbbVie. KSV is a former employee of AbbVie. PLC, DC, TJ, have nothing to disclose, and HKG has been a consultant for AbbVie 2 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2020 American Association for Cancer Research. Author Manuscript Published OnlineFirst on August 26, 2020; DOI: 10.1158/1535-7163.MCT-20-0149 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract ABBV-321 (serclutamab talirine), a next-generation epidermal growth factor receptor (EGFR)- targeted antibody-drug conjugate (ADC) incorporates a potent pyrrolobenzodiazepine (PBD) dimer toxin conjugated to the EGFR-targeting ABT-806 affinity matured AM1 antibody. ABBV- 321 follows the development of related EGFR targeted ADCs including depatuxizumab mafodotin (depatux-m, ABT-414), ABT-806 conjugated to monomethyl auristatin F (MMAF), and ABBV-221 (losatuxizumab vedotin), AM1 antibody conjugated to monomethyl auristatin E (MMAE). The distinct tumor selectivity of ABBV-321 differentiates it from many previous highly active antibody PBD conjugates that lack a therapeutic window. Potency of the PBD dimer, combined with increased binding of AM1 to EGFR-positive tumor cells, opens the possibility to target a wide array of tumors beyond those with high levels of EGFR overexpression or amplification, including those insensitive to auristatin-based ADCs. ABBV-321 exhibits potent anti-tumor activity in cellular and in vivo studies including xenograft cell line and patient- derived xenograft (PDX) glioblastoma (GBM), colorectal, lung, head & neck and malignant mesothelioma tumor models which are less sensitive to depatux-m or ABBV-221. Combination studies with ABBV-321 and depatux-m suggest a promising treatment option permitting suboptimal, and potentially better tolerated, doses of both ADCs while providing improved potency. Collectively, these data suggest that ABBV-321 may offer an extended breadth of efficacy relative to other EGFR ADCs while extending utility to multiple EGFR-expressing tumor indications. Despite its highly potent PBD dimer payload, the tumor selectivity of ABBV-321 - coupled with its pharmacology, toxicology and pharmacokinetic profiles - support continuation of ongoing Phase 1 clinical trials in patients with advanced EGFR-expressing malignancies. 3 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2020 American Association for Cancer Research. Author Manuscript Published OnlineFirst on August 26, 2020; DOI: 10.1158/1535-7163.MCT-20-0149 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Introduction Targeted therapies are commonly prescribed anti-neoplastic agents in the United States and worldwide. EGFR plays a causal role in the development and maintenance of many human carcinomas. EGFR is a well-validated oncology target, as EGFR-directed therapies [monoclonal antibodies (mAbs) and small molecules] have gained widespread use for a variety of cancer types, including lung, head & neck, colon, and pancreatic cancer. These EGFR-directed therapies have shown improvements in both progression-free survival and overall survival while preserving quality of life (1-8). Despite the enhancements, these approaches are limited by toxic side effects and development of resistance. The most common toxicity of these agents is a well characterized skin rash, similar in appearance to acne, usually limited to the face, upper chest and back. Other reported toxicities include diarrhea, constipation, stomatitis, fatigue, and electrolyte disturbances (9,10). These mechanism based therapies are further limited by narrow efficacy profiles because the mutational status of tumorigenic genes including EGFR, K- Ras, B-Raf, phosphoinositide 3-kinase and the phosphatase and tensin homolog gene each play a role in EGFR resistance mechanisms (11-13). Oncology ADCs are a class of therapeutics that combine mAb specificity with cytotoxicity of potent anti-cancer small molecules. Significant advancements in linker stability and toxin potency are primarily responsible for the resurgence in ADC development. Recent examples of clinically relevant, approved ADCs include brentuximab vedotin/Adcetris®, an anti-CD30 ADC for Hodgkin's lymphoma and anaplastic large cell lymphoma, polatuzumab vedotin/Polivy®, an anti- CD79b ADC targeting the B-cell receptor for diffuse large B-cell lymphoma; trastuzumab emtansine/Kadcyla® , an anti-Her2 ADC for metastatic breast cancer; inotuzumab ozogamicin/Besponsa®, an anti-CD22 ADC for relapsed or refractory B-cell precursor acute lymphoblastic leukemia; gemtuzumab ozogamicin/Mylotarg® an anti-CD33 for acute myeloid leukemia; Trodelvy, an anti-Trop-2 ADC for metastatic TNB, and Enhertu, an anti-Her2 ADC for relapsed/recurrent metastatic Her2+ breast cancer (14-18). A distinct clinical advantage of ADCs is their ability to selectively deliver toxic loads to a tumor, bypassing downstream resistance mechanisms related to intracellular signaling (15,16). 4 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2020 American Association for Cancer Research. Author Manuscript Published OnlineFirst on August 26, 2020; DOI: 10.1158/1535-7163.MCT-20-0149 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. The ABT-806 antibody is a humanized derivative of the murine anti-EGFR mAb (mAb806) that binds preferentially to tumors expressing EGFR or EGFR with a deletion of exons 2-7 (EGFRvIII); the latter predominantly exposes a unique epitope that is also exposed when EGFR is expressed above physiological levels (19). Depatux-m, an ADC comprised of ABT-806 and MMAF cytotoxin, has been in multiple clinical studies in glioblastoma patients with amplified EGFR although dosing has been limited by corneal side effects common to MMAF conjugates (20-23). The ABT-806 component of depatux-m was affinity matured using recombinant extracellular domain EGFRC271A,C283A (a derivative exposing the ABT-806 epitope) and wild-type EGFR extracellular domain proteins as selection antigens (24). The resulting affinity matured antibody AM1 contains only three amino acid differences in the complementarity-determining region relative to parental ABT-806 but displays increased binding to wild-type EGFR. Despite increased affinity for EGFR, AM1 competes with ABT-806 to bind the same epitope, suggesting that the unique tumor-selective properties of ABT-806 are retained in AM1. ABBV-221, a second-generation ADC, is comprised of AM1 conjugated to a AM1 different toxin, MMAE (25). ABBV-221 demonstrated clinical activity in select patients with advanced solid tumor types (25,26). Results from this study, however, have shown dose-related infusion reactions to be a frequently occurring adverse event, potentially limiting the maximum tolerated dose. PBD dimers, DNA-crosslinking agents, represent an emerging class of warheads with enhanced potent anti-cancer activity compared to the clinically validated auristatins or maytansinoids (27). PBD dimers exhibit significant cell permeability, potentially enabling bystander killing of neighboring tumor cells (28). Multiple ADCs with PBD-dimer payloads and a drug antibody ratio (DAR) of 2 have advanced to the clinic although, at least partially owing to increased toxicities, there have been no approvals for clinical use (29). The highly tumor-selective nature of ABT-806 AM1 suggested that an AM1 PBD dimer conjugate may impart an expanded breadth of efficacy relative to depatux-m or ABBV-221, extending utility beyond tumors with amplified or highly expressed EGFR, while providing for an acceptable therapeutic window. To test this premise, an AM1 PBD dimer conjugate (ABBV-321; serclutamab talirine) was characterized and evaluated against EGFR positive tumor types in cellular and in vivo studies including PDX 5 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2020 American Association for Cancer Research. Author Manuscript