Pdox Models Empower Preclinical Drug Evaluation and Mechanistic Studies Via Faithful Recapitulation of the Pathology, Complex Heterogeneity, Genetic-Transcriptomic Landscape, and Therapeutic Response of Mantle Cell Lymphoma

Introduction: Mantle cell lymphoma is an aggressive subtype of non-Hodgkin lymphoma with poor prognosis. MCL cells display complex inter- and intra-patient heterogeneity and various dissemination patterns involving nodal and extranodal sites across patients. Due to its microenvironment distinct from patients' microenvironments, heterotopic or subcutaneous patient-derived xenograft (PDX) models are not ideal for studying clinical disease pathology, tumor heterogeneity, and clinical therapeutic responses. In contrast, patient-derived orthotopic xenografts (PDOXs) have been shown in many cancer types to faithfully recapitulate the primary patient cancers. Although a few MCL PDOX models have reportedly been established, these models have not been clearly defined or applied in mechanistic studies or preclinical drug studies.

Methods: We established multiple MCL PDOX models from primary patient samples via intravenous or intraosseous routes and characterized these models for the first time in multiple dimensions. We performed longitudinal pathological and histological characterization of PDOX cells involved in the spleen, liver, stomach, lymph nodes, bone marrow, and/or peripheral blood across generations and disease stages, whole exon sequencing across dissemination sites and generations, and single-cell RNA sequencing across dissemination sites. We evaluated in vivo response to ibrutinib and venetoclax in one PDOX model derived from an ibrutinib-venetoclax dual-resistant MCL patient. An in vivo drug efficacy screen was performed to search for potential therapies to overcome ibrutinib-venetoclax dual resistance.

Results: Longitudinal pathological and histological characterization of the PDOX models revealed faithful recapitulation of the clinical disease of MCL patients, and the PDOX models can be stably passed on to a series of generations. In vivo drug treatments including ibrutinib and venetoclax recapitulated the clinical response to these therapies. Whole exon sequencing and single-cell RNA sequencing of one ibrutinib-venetoclax dual-resistant PDOX model and its parental primary patient cells reflected reliable recapitulation of primary patient disease in genetic, cellular, and transcriptomic profiles, providing insights into potential targets to overcome therapeutic resistance. Single-cell transcriptomic profiling also revealed increased cancer hallmark signaling in the PDOX model compared to the primary patient samples used to established the PDOX model. Based on this, we performed an in vivo drug screen for the PDOX model and identified promising drugs that dramatically inhibited tumor burden in the spleen, liver, bone marrow, and peripheral blood. Intriguingly, a subcutaneous model (scPDOX) was derived from this PDOX model via subcutaneous implantation of its G1 PDOX cells and was found to be ibrutinib-resistant but venetoclax-sensitive in vivo. To understand the differential response to venetoclax and differential microenvironment of the PDOX model and its derived scPDOX model, whole exon sequencing and single-cell RNA sequencing of the cells from these models is currently being pursued.

Conclusions: Our MCL PDOX models faithfully resembled the original MCL disease in histopathology, disease progression, tumor heterogeneity, genetic-transcriptomic profiling, and therapeutic responses. Therefore, these models provide invaluable platforms for mechanistic studies and preclinical drug studies.