Abstract 3120: Evaluation of PYX-201, an EDB+FN-targeting ADC, in a comprehensive PDX mini-trial study enables identification of gene signatures associated with anti-tumor activity

PYX-201, a first-in-concept non-cellular targeting antibody-drug conjugate (ADC), is currently being tested in a Phase 1 clinical trial in a variety of solid tumors (NCT05720117). PYX-201 is designed to bind specifically to the extra-domain B splice variant of fibronectin (EDB+FN), a component of the extracellular matrix found in various solid tumors with absent or low expression in normal adult tissue (Hooper, 2022). Extracellular proteases can cleave the valine-citrulline peptide linker to release the optimized toxic payload Auristatin0101 into the tumor microenvironment which diffuses into tumor cells and induces cell killing. A comprehensive mini-trial study has been conducted to measure PYX-201 anti-tumor efficacy in multiple patient-derived xenograft (PDX) mouse models selected from ten solid tumor indications. Building on our previous analysis (Severe, 2024), full mini-trial results demonstrate that PYX-201 (3mg/kg, Q4Dx4) was well tolerated and resulted in broad anti-tumor activity as calculated by the Tumor Growth Inhibition percentage (%TGI) at study end for each individual PDX model. Our results show that 25% were non-responders (TGI<25%), 30% moderate (25%<TGI<70%), 20% strong (70%<TGI<90%) and 25% very strong responders (TGI>90%). Remarkably, PDX models with very strong PYX-201 responses (TGI>90%) were found across 9/10 solid tumor indications. Additionally, mice with complete responses to PYX-201 (tumor volume reached 0mm3 for at least two consecutive measurements) were found across several tumor indications. To investigate gene expression changes relevant to PYX-201 mechanism of action, a satellite mouse was included on study for tumor collection for each PDX model prior to treatment. To determine which gene signatures may be associated with PYX-201 response, analysis was performed on RNA extracted from satellite tumor samples. The Nanostring ADC Development panel was selected for expression analysis across 750 human genes. A comparison between PDX models with very strong PYX-201 responses (TGI>90%) to PYX-201 non-responders (TGI<25%) with all tumor indications combined identified several genes which were differentially expressed. In addition, gene set analysis was performed to identify gene categories which were associated with PYX-201 response. The gene sets with the greatest number of differentially expressed genes in our analysis were tumor stroma and enzymes, indicating these categories are important for PYX-201 response in pre-clinical PDX models. Overall, PYX-201 showed broad anti-tumor activity in PDX pre-clinical models, suggesting it is a promising ADC for further testing across solid tumor indications. Furthermore, tumor stroma and protease genes were associated with PYX-201 activity in PDX models, providing further insight into PYX-201 mechanism of action. Citation Format: Amanda Facklam, Justin Trickett, Sara Lewandowski, Chuan Shen, Frank Wang, Marsha Crochiere, Nicolas Severe, Jan Pinkas. Evaluation of PYX-201, an EDB+FN-targeting ADC, in a comprehensive PDX mini-trial study enables identification of gene signatures associated with anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3120.