Abstract LB041: Exploiting a multi-center pre-clinical mouse PDX mini trial to identify new clinical opportunities for protein-drug conjugates (PDCs) targeting ROR1

Abstract The oncofetal cell surface receptor tyrosine kinase ROR1, is expressed on a broad range of solid tumors and hematological malignancies but is largely absent from normal adult tissue. Increased ROR1 expression correlates with poor clinical outcome in certain cancer indications, consistent with its functional role in tumorigenesis, increased metastatic potential and drug resistance. The oncofetal expression pattern of ROR1, coupled with its role in cancer pathology and therapy resistance, and its scaffolding function in caveolae, makes it a highly attractive target for a protein-drug conjugate (PDC) approach. A number of ROR1-targeting ADC and PDC agents are in clinical and pre-clinical development. Understanding the molecular determinants that drive the efficacy of these agents, may open-up patient selection strategies to improve clinical outcomes for ROR1-targeted ADC/PDC therapy. We utilized a small-domain protein-drug-conjugate platform to develop a PDC Candidate Drug (ADP-c389) which produced complete and sustained tumor regressions in patient-derived xenograft (PDX) models of triple negative breast cancer (TNBC) and had an excellent therapeutic index in mice and NHPs. To further inform our clinical planning and assess the broader clinical opportunity afforded by this agent, ADP-c389 was evaluated in a multi-center, multi-indication, 30-PDX mouse mini trial covering 5 different solid tumor indications (lung, ovarian, endometrial, esophageal, gastric). Covariates of target expression, site, model, mouse strain and treatment effect were analysed longitudinally and a multi-metric (TGI, AUC, Best Average Response (BAR), mRECIST) effects analysis undertaken to evaluate response. Efficacy was observed in each of the cancer indications tested, with 77% of models showing an anti-tumor response. Furthermore, the results in NSCLC lung and ovarian PDX models indicated that these are compelling additional cancer types in which to position ADP-c389 clinically. Whilst all responders are ROR1 positive, ROR1 expression itself is necessary but not sufficient to predict the degree of response. Linear Mixed Effect Model (LMM) and multi-omics (RNA-Seq and Proteomics) analysis of the resulting responder/non-responder cohorts has enabled us to determine markers of sensitivity to ADP-c389. In summary, ADP-c389 represents a highly differentiated product for the treatment of a variety of solid tumors. The learnings from this mouse mini trial are also being applied to bi-specific ROR1-based PDCs. Citation Format: Aaron N. Cranston, Mark Wappett, Estelle G. McLean, Chiara Saladino, Aidan McCann, Wei-Wei Kung, Jennifer Thom, Paul Trumper, Andy Porter, Caroline Barelle, Tim Harrison, Graham Cotton. Exploiting a multi-center pre-clinical mouse PDX mini trial to identify new clinical opportunities for protein-drug conjugates (PDCs) targeting ROR1 abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB041.