Design and Preclinical Evaluation of a Novel B7-H4-Directed Antibody-Drug Conjugate, AZD8205, Alone and in Combination with the PARP1-Selective Inhibitor AZD5305

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 PARP1-selective inhibitor AZD5305, in preclinical models.

EXPERIMENTAL DESIGN

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 (HRR) deficiency (HRD) and elevated levels of B7-H4 in HRR-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.

CONCLUSIONS

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). See related commentary by Pommier and Thomas, p. 991.

Abstract 1765: Discovery and first disclosure of AZD8205, a B7-H4-targeted antibody-drug conjugate utilizing a novel topoisomerase I linker-warhead

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.

Interplay of primary sequence, position and secondary RNA structure determines alternative splicing of LMNA in a pre-mature aging syndrome

Aberrant splicing in exon 11 of the LMNA gene causes the premature aging disorder Hutchinson-Gilford Progeria Syndrome. A de novo C1824T mutation activates an internal alternative 5' splice site, resulting in formation of the disease-causing progerin protein. The underlying mechanism for this 5' splice site selection is unknown. Here, we have applied a combination of targeted mutational analysis in a cell-based system and structural mapping by SHAPE-MaP to comprehensively probe the contributions of primary sequence, secondary RNA structure and linear splice site position in determining in vivo mechanisms of splice site choice in LMNA. While splice site choice is in part defined by sequence complementarity to U1 snRNA, we identify RNA secondary structural elements near the alternative 5' splice sites and show that splice site choice is significantly influenced by the structural context of the available splice sites. Furthermore, relative positioning of the competing sites within the primary sequence of the pre-mRNA is a predictor of 5' splice site usage, with the distal position favored over the proximal, regardless of sequence composition. Together, these results demonstrate that 5' splice site selection in LMNA is determined by an intricate interplay among RNA sequence, secondary structure and splice site position.