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Purpose: We evaluated the activity of AZD8205, a B7-H4–directed antibody-drug conjugate (ADC) bearing a novel topoisomerase I inhibitor (TOP1i) payload, alone and in combination with the poly-ADP ribose polymerase 1 (PARP1)–selective inhibitor AZD5305, in preclinical models. Experimental Design: Immunohistochemistry (IHC) and deep-learning–based image analysis algorithms were used to assess prevalence and intratumoral heterogeneity of B7-H4 expression in human tumors. Several TOP1i-ADCs, prepared with Val-Ala or Gly-Gly-Phe-Gly peptide linkers, with or without a PEG8 spacer were compared in biophysical, in vivo efficacy, and rat toxicology studies. AZD8205 mechanism of action and efficacy studies were conducted in human cancer cell line and patient-derived xenograft (PDX) models. Results: Evaluation of IHC staining density on a per-cell basis revealed a range of heterogeneous B7-H4 expression across patient tumors. This informed selection of bystander-capable Val-Ala–PEG8–TOP1i payload AZ14170133 and development of AZD8205, which demonstrated improved stability, efficacy, and safety compared with other linker-payload ADCs. In a study of 26 PDX tumors, single administration of 3.5 mg/kg AZD8205 provided a 69% overall response rate, according to modified RECIST criteria, which correlated with homologous recombination repair deficiency (HRD) and elevated levels of B7-H4 in homologous recombination repair-proficient models. Addition of AZD5305 sensitized very low B7-H4–expressing tumors to AZD8205 treatment, independent of HRD status and in models representing clinically relevant mechanisms of PARPi resistance. Conclusion: These data provide evidence for the potential utility of AZD8205 for treatment of B7-H4–expressing tumors and support the rationale for an ongoing phase 1 clinical study (NCT05123482).

Antibody–drug conjugate (ADC) research has typically focused on the release of highly potent cytotoxic agents to achieve antitumor efficacy. However, recently approved ADCs trastuzumab deruxtecan and sacituzumab govitecan release lower-potency topoisomerase inhibitors. This has prompted interest in ADCs that release lower-potency cytotoxic drugs to potentially enhance therapeutic index and reduce unwanted toxicity. Pyrrolobenzodiazepine (PBD) dimer ADCs have been widely investigated in human clinical trials, which have focused on high-potency PBDs. In this study, we evaluated five ADCs that release the low-potency PBD dimer SG3650. The relatively low clogD for this agent facilitated higher drug-to-antibody ratio (DAR) conjugation without the need for antibody engineering or functionalization of the drug. The rank order of potency for DAR 2 site-specific ADCs (conjugated at the C239i position) matched the order for the corresponding free drugs in vitro. Despite free drug SG3650 being inactive in vivo, the DAR 2 ADCs derived from the corresponding drug-linker SG3584 showed antitumor efficacy in solid (anti-HER2) and hematologic (anti-CD22) xenograft models. Antitumor activity could be enhanced by conjugating SG3584 to trastuzumab at higher DARs of 4 and 8 and by adjusting dosing and schedule. Higher-DAR conjugates were stable and displayed good rat pharmacokinetic profiles as measured by ELISA and LC/MS-MS. A single intravenous dose of isotype control SG3584 DAR 2 ADC resulted in no mortality in rats or monkeys at doses of up to 25 and 30 mg/kg, respectively. These findings suggest that further investigations of low-potency PBD dimers in ADCs that target hematologic and solid tumors are warranted.

The cell-surface glycoprotein B7-H4 is overexpressed in a range of solid tumors including breast cancer, ovarian serous carcinoma, endometrial carcinoma, and cholangiocarcinoma, yet has limited expression in normal tissue, making it an attractive target for an antibody-drug conjugate (ADC). This presentation describes for the first time the development of AZD8205, a B7-H4 targeted ADC incorporating a novel topoisomerase 1 inhibitor (TOP1i) linker-warhead, AZ’0133 which was designed to exploit the full potential of B7-H4 as an ADC target. Initially, we investigated a series of more than 35 TOP1i compounds as warheads and achieved activity in a clinically relevant nM range. We further optimized the conjugation site and chemistry to reduce the potential for aggregation while maintaining potency, overcoming major synthetic challenges to deliver a robust synthetic route amenable to scale-up. Finally, with a series of optimized linker-warheads, we explored the impact of linker-warhead design on ADC hydrophobicity, stability, efficacy, pharmacokinetics and tolerability culminating in the development of AZD8205. The primary mechanism of action of AZD8205 is intracellular delivery of the TOP1i warhead to B7-H4 positive cells, leading to DNA damage and apoptotic cell death. AZD8205 drove bystander killing of target negative cells in mixed cultures in vitro, which is further supported by robust antitumor activity observed in in vivo studies with patient-derived xenograft (PDX) tumors with heterogeneous target expression, representing multiple tumor indications. In a study of 26 human TNBC PDX tumors, a single IV administration of 3.5 mg/kg AZD8205 provided an overall response rate of 69% (tumor regression of 30% or greater from baseline) and complete responses observed in 9/26 (36%) of models. To understand the biology underlying antitumor response, we conducted a multiparametric analysis including genomics, proteomics and computational pathology and found that deeper antitumor activity was observed in models with elevated B7-H4 expression as well as in models with defects in DNA damage repair (DDR). To further exploit the DNA damage elicited by the TOP1i warhead, we examined combinations of AZD8205 with small molecules, including a novel PARP1 selective inhibitor, in a BRCA wild type MDA-MB-468 model. These data suggest that AZD8205 is a promising therapeutic candidate for the treatment of B7-H4 positive solid tumors. A first in human phase 1 study in patients with advanced solid tumors is currently ongoing (NCT05123482). Citation Format: Krista Kinneer, Niall J. Dickinson, Luke Masterson, Thais Cailleau, Ian Hutchinson, Balakumar Vijayakrishnan, Nazzareno Dimasi, R. James Christie, Mary McFarlane, Kathryn Ball, Arthur Lewis, Sofia Koch, Lee Brown, Yue Huang, Anton I. Rosenbaum, Jiaqi Yuan, Si Mou, Noel R. Monks, Jon Chesebrough, Ravinder Tammali, Judith Anderton, Darrin Sabol, Frances Anne Tosto, Philipp Wortmann, Zachary A. Cooper, Pauline Ryan, John Hood, Carlos Fernandez Teruel, Carlos Serra Traynor, Andy Pike, Michael Davies, Elisabetta Leo, Kimberly Cook, Nadia Luheshi, Philip W. Howard, Puja Sapra. Discovery and first disclosure of AZD8205, a B7-H4-targeted antibody-drug conjugate utilizing a novel topoisomerase I linker-warhead [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1765.

Utilizing decision making biomarkers in drug development requires thorough assay validation. Special considerations need to be taken into account when monitoring biomarkers using immunoassays in the presence of therapeutic antibodies. We have developed robust and sensitive assays to assess target engagement and proof of mechanism to support the clinical progression of a human monoclonal antibody against the neurotoxic amyloid-β (Aβ)42 peptide. Here we present the introduction of novel pre-treatment steps to ensure drug-tolerant immunoassays and describe the validation of the complete experimental procedures to measure total Aβ42 concentration (bound and unbound) in cerebrospinal fluid (CSF) and plasma, free Aβ42 concentration (unbound) in CSF, and Aβ40 concentration in CSF. The difference in composition of the matrices (CSF and plasma) and antigen levels therein, in combination with the hydrophobic properties of Aβ protein, adds to the complexity of validation. Monitoring pharmacodynamics of an Aβ42 specific monoclonal antibody in a non-human primate toxicology study using these assays, we demonstrated a 1500-fold and a 3000-fold increase in total Aβ42 in plasma, a 4-fold and 8-fold increase in total Aβ42 in CSF together with a 95% and 96% reduction of free Aβ42 in CSF following weekly intravenous injections of 10 mg/kg and 100 mg/kg, respectively. Levels of Aβ40 were unchanged. The accuracy of these data is supported by previous pre-clinical studies as well as predictive pharmacokinetic/pharmacodynamics modeling. In contrast, when analyzing the same non-human primate samples excluding the pre-treatment steps, we were not able to distinguish between free and total Aβ42. Our data clearly demonstrate the importance of thorough evaluation of antibody interference and appropriate validation to monitor different types of biomarkers in the presence of a therapeutic antibody.

Supplementary Data from Efficacy, Tolerability, and Pharmacokinetic Studies of Antibody–Drug Conjugates Containing a Low-Potency Pyrrolobenzodiazepine Dimer