Abstract 4204: Subcutaneous vs. orthotopic tumor models: A comparative assessment
Authors: Bright Kerry-Ann , Barnes Sheri , Germain Derrik , Kucharczyk Lauren 
Published: March 2024

Abstract
The failure of murine tumor models to adequately simulate the native biological milieu and tissue architecture of human malignancies, has fomented much discourse surrounding the discord that exists between experimental outcomes and clinical settings. Orthotopic (OT) models, which are generated by the engraftment of tumor cells or fragments into recipient organs of the same histotype from which they were derived, has the advantage of recapitulating the appropriate vasculature, as well as cellular and stromal components as the site of origin. In the context of immunotherapy, there is increasing evidence that subcutaneous (SC) tumors bear a vastly different immunological profile compared to OT implants, a phenomenon dictated by tissue-specific recruitment of various immune subsets, and subsequently, impacts overall response. Therefore, establishing cancer models that better represent the natural tumor environment is imperative for addressing some of the foibles inherent to preclinical mouse models. To demonstrate the significance of the anatomical site of the tumor, we present a comparative assessment of the MC38 murine colon carcinoma model, in the context of SC and OT settings. In the SC model of MC38, administration of either 5mg/kg anti-mPD1, anti-mPDL1, or anti-mCTLA-4, failed to elicit any notable anti-tumor activity, as evidenced by 0% incidences of complete regressions (CR) and tumor free survivors (TFS) for all three therapeutic agents, and incidences of 11%, 5% and -22% increase in time to progression (ITP), respectively. However, mice bearing OT tumors, exhibited meaningful response to 5mg/kg anti-mPD1 and anti-mPDL1, both evoking incidences of 25% CR, 25% TFS and 108% ITP. Though the anti-mCTLA-4 treated cohort did not produce any CRs or TFS, there was, nonetheless, a 50% incidence of ITP. Taken together, the data clearly illustrates the distinct disparities in response between SC and OT tumors, with respect to immunomodulatory agents. Characterization of immune phenotype within both settings, and interrogation of additional mouse models are ongoing. The exigencies and profound limitations associated with bench to bedside translation have long encumbered the drug development process. Despite staggering financial investment in oncology research, effective treatments for a myriad of cancers remain elusive, and only 3.4% of cancer drug candidates are conferred with clinical approval. Employing modalities that adequately reproduce the molecular and structural frameworks of human tumors, is crucial to better elucidating the natural trajectory of cancer progression, thus facilitating more accurate evaluation of drug activity and therapeutic response in preclinical settings. OT models therefore represent a more disease-relevant preclinical approach compared to their subcutaneous counterparts, as they more reliably preserve the intrinsic infrastructure and complexities of patient tumors in situ.
Citation Format: Kerry-Ann Bright, Sheri Barnes, Derrik Germain, Lauren Kucharczyk. Subcutaneous vs. orthotopic tumor models: A comparative assessment [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 4204.