Abstract 1598: Individualized longitudinal assessment reveals therapy-induced tumor and microenvironment dynamics in preclinical pancreatic cancer models
Authors: Siveke Jens T. , Fang Rui , Cheung Phyllis Fung-Yi , Yang Jiajin , Peng Juanfei , Althoff Kristina , Savvatakis Konstantinos 
Published: March 2024

Abstract
Background & Aim: Progression and therapeutic resistance in pancreatic cancer depends on the ability of cancer cells to adopt specific cell states. These phenotypes largely depend on environmental tissue niches. Here, we investigated therapy-induced tumor dynamics in vivo at single-cell spatial and temporal resolution in different subtypes of PDAC using several genetically engineered mouse models, which reflect distinct human PDAC ecosystems.
Methods & Results: We established orthotopic tumor models of pancreatic cancer with distinct tumor microenvironment (TME) formation (reactive vs deserted stroma), which were monitored for tumor growth to define tumor response patterns under MAPK inhibition. Serial ultrasound-guided biopsy sampling was performed to collect tissues from the same tumors at pre-treatment, responsive and recurrence periods.Transcriptomic analysis of biopsies using the Mfuzz algorithm delineated highly dynamic gene and pathway activities during treatment. Reactive, but not deserted, TME showed an upregulation of immune-related pathways (antigen presentation, T cell receptor, NK cytotoxicity) immediately after MAPK inhibition in regressed tumors that dropped dramatically during recurrence of tumors, in which upregulation of TGF-b signaling was observed. In the deserted stroma model, on the other hand, an enrichment in drug metabolic pathways during recurrence was observed.CAF cluster deconvolution analysis revealed an increase in a LRRC15+ CAF cluster, which was TGF-b-driven and immunosuppressive, during recurrence period only in the reactive model. The dynamic changes of immune cells and CAFs were validated at protein level by multiplex immunofluorescent imaging. Cmputational spatial analysis revealed a tumor-encapsulating and CD8+ cytotoxic T cell-repelling pattern exhibited by LRRC15+FAP+ CAFs, implying a potential role of this CAF subset in T cell suppression during recurrence in reactive subtype. Using spectral cell sorting with CellView image technology, specific CAF subsets, tumor cells as well as immune cell subsets based on 30+ markers and cell morphology were isolated, characterized and assessed by ex vivo functional assays to confirm the immunosuppressive and tumor protective mechanism mediated by CAFs.
Conclusion: Longitudinal in vivo assessment of distinct PDAC subtypes provides deep mechanistic insights to accurately unlock specific response patterns of tumors with heterogeneous TME dynamics upon therapeutic perturbation, leveraging identification of key nodes for intervention.
Citation Format: Jens T. Siveke, Rui Fang, Phyllis Fung-Yi Cheung, Jiajin Yang, Juanfei Peng, Kristina Althoff, Konstantinos Savvatakis. Individualized longitudinal assessment reveals therapy-induced tumor and microenvironment dynamics in preclinical pancreatic cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1598.