Development and Preclinical Applications of Pancreatic Adenocarcinoma Models

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

The main research emphasis in pancreatic models experimentations currently conducted by CAPR PDAC modelling program has been placed on interrogating the role of highly desmoplastic microenvironment in pancreatic adenocarcinomas and its implications for disease severity, metastatic potential and eventually therapeutic options to treat advanced PDAC. Pancreatic tumor microenvironment is known to be highly immunosuppressive and refractory for infiltration with cells capable of conducting immunosurveillance, such as cytotoxic T cells. This feature of PDAC is broadly believed to be connected to a high abundance of M2 polarized macrophages in transformed pancreatic tissue and is connected with low level of success in applying immune-oncology therapeutics for PDAC treatment. In order to reverse the suppressive PDAC landscape, targeting M2 macrophages pharmacologically appears to be an attractive option. CAPR pancreatic team has joined efforts with Dr. Rudloff's lab to examine in vivo therapeutic signatures of several formulations developed by NCATS medicinal chemists to recognize the CD206 receptor selectively present on macrophages polarized by M2 type. Such formulations - including a highly affine to CD206 synthetic peptide RP-182 and a small molecule NCGC00413972 - have been demonstrated in vitro to possess cytotoxic and reprogramming signatures against CD206-expressing macrophages. In collaboration with Dr. Rudloff's (NCI) and Dr. Marugan's (NCATS) teams, CAPR has conducted several informative PK and efficacy studies, and found both RP-182 and NCGC00413972 formulations effective in vivo in reversing the immunosuppressive PDAC milieu as was evidenced by decreased ratios of M2-to-M1 macrophages with concomitant influx into tumor tissues of cytotoxic CD8+ T-lymphocytes. Furthermore, CAPR researchers also discovered an increased incidence of phagocytosis of PDAC tumor cells by tumor-associated macrophages and supported additional experimentation to identify the involvement of specific inflammatory signaling pathways, such as NF-kappaB, as molecular basis for reversing the predominantly immunosuppressive PDAC microenvironment. This work resulted in several collaborative publications, including the one in Science Transl. Medicine (2020) and was recognized by the Annual NCATS Director's Award. In another collaborative project, we have explored synergies between CAPR preclinical capabilities and clinical expertise of Dr. Alewine's lab to embark on a study aimed at targeting mesothelin (MSLN) protein. Many pancreatic tumors synthesize high amounts of MSLN - a membrane-tethered differentiation antigen present mostly on the surface of normal mesothelial cells such as serous membranes of the heart and the lungs, but also produced by several cancers, such as pancreatic and ovarian cancers and mesothelioma. Although the exact molecular implications of MSLN pathogenic re-expression remain obscure, this molecule has been explored as an attractive targeting moiety to deliver therapeutic specifically to PDAC tissue. A family of such therapeutic biologicals known as MSLN-targeting immunotoxins (iTox) is currently undergoing assessment in multiple clinical trials, albeit co-clinical characterization of these reagents in PDAC murine models is impeded by their low affinity to the orthologous mouse MSLN protein. In collaboration with Dr. Alewine's lab, CAPR prepared an allelic series of models expressing human isoform of MSLN either in thyroid organ by conventional transgenesis, or in an endogenous mouse MSLN genomic locus by conventional knock-in and CRISPR/Cas9 technologies. The former model has been subsequently employed as pre-tolerized to human MSLN protein recipient animals engrafted orthotopically with PDAC cells engineered by viral transduction to express human mesothelin; whereas the latter allele has been successfully intercrossed onto the KPC background to derive KPC animals expressing human MSLN in place of its murine counterpart, in all cells normally producing MSLN, as well as in pancreatic tumors. Both types of animal models have been used in recently completed preclinical testing of iTox formulation, alone or in combination with checkpoint inhibitors CTLA-4 and PD-1, to discover the deleterious impact of PDAC desmoplastic stroma on accessibility of iTox protein in tumor tissues. Some of our findings have been recently published in Mol. Cancer. Ther (2021), another manuscript is in final stages of preparation to illuminate the biological role of re-expressed by transformed pancreatic tissue MSLN in disease progression, metastatic spread and evasion from immune system surveillance.