Stromal-Modulated Epithelial-to-Mesenchymal Transition in Cancer Cells

The ability of cancer cells to detach from the primary site and metastasize is the main cause of cancer- related death among all cancer types. Epithelial-to-mesenchymal transition (EMT) is the first event of the metastatic cascade, resulting in the loss of cell-cell adhesion and the acquisition of motile and stem-like phenotypes. A critical modulator of EMT in cancer cells is the stromal tumor microenvironment (TME), which can promote the acquisition of a mesenchymal phenotype through direct interaction with cancer cells or changes to the broader microenvironment. In this review, we will explore the role of stromal cells in modulating cancer cell EMT, with particular emphasis on the function of mesenchymal stromal/stem cells (MSCs) through the activation of EMT-inducing pathways, extra cellular matrix (ECM) remodeling, immune cell alteration, and metabolic rewiring.

Abstract PR016: Carcinoma-associated mesenchymal stem cells promote ovarian cancer metastasis by increasing tumor heterogeneity through direct mitochondrial transfer

Ovarian cancer is characterized by early, diffuse metastatic spread with most women presenting with widespread abdominal metastasis at the time of diagnosis. Prior work demonstrates carcinoma-associated mesenchymal stem cells (CA-MSCs) enhance ovarian cancer metastasis through a process of direct cellular interaction and formation of heterocellular CA-MSC and tumor cell complexes. Here we demonstrate CA-MSCs enhance metastasis via increasing tumor cell heterogeneity through mitochondrial donation. CA-MSCs directly interact with ovarian cancer cells forming tunneling nanotubules (TNTs). CA-MSCs transfer live mitochondria via these TNTs to ovarian cancer cells. This mitochondrial donation preferentially occurs in ovarian cancer cells with the least endogenous mitochondria (‘mito poor’ cancer cells). Mito poor cancer cells demonstrate decreased proliferation, increased sensitivity to chemotherapy and decreased oxidative phosphorylation compared to ‘mito rich’ cancer cells. CA-MSCs rescue the phenotype of these mito poor cancer cells restoring their proliferative capacity, increasing chemotherapy resistance and increasing oxidative phosphorylation. We validated these findings in a fully autologous system using CA-MSCs and cancer cells derived from the same patient to prevent confounding effects of cellular response to foreign organelle/DNA. Using a knockdown of the mitochondrial motor protein, MIRO1, we demonstrate mitochondrial transfer is necessary for the CA-MSC-mediated rescue of mito poor cancer cells. We developed a haplotype-specific quantification of mitochondrial DNA to differentiate CA-MSC derived mitochondria from endogenous tumor cell mitochondria. We used this system to both quantify the amount of CA-MSC mitochondrial donation and to demonstrate CA-MSC donated mitochondria persist in tumor cells over at least 14 days. Importantly, CA-MSC mitochondrial donation occurs in vivo and is associated with decreased survival in an orthotopic ovarian cancer mouse model. A DNA barcoding system was used to quantify tumor cell clonal heterogeneity. Using this system, we demonstrate CA-MSCs significantly enhance tumor cell heterogeneity, particularly during metastasis. This increase in tumor cell heterogeneity is dependent on CA-MSC mitochondrial transfer. Collectively, we report CA-MSC mitochondrial transfer as a critical mediator of ovarian cancer survival, heterogeneity and metastasis representing a potentially powerful therapeutic target.

Citation Format: Leonard G. Frisbie, Catherine A. Pressimone, Huda I. Atiya, Alexander T. Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem cells promote ovarian cancer metastasis by increasing tumor heterogeneity through direct mitochondrial transfer [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr PR016.

Phase I trial of ribociclib with platinum chemotherapy in recurrent ovarian cancer

BACKGROUND

New therapeutic combinations to improve the outcome of ovarian cancer patients are clearly needed. Preclinical studies with ribociclib (LEE-011), a CDK4/6 cell cycle checkpoint inhibitor, demonstrate a synergistic effect with platinum chemotherapy and efficacy as a maintenance therapy after chemotherapy. We tested the safety and initial efficacy of ribociclib in combination with platinum-based chemotherapy in recurrent ovarian cancer.

METHODS

This phase I trial combined weekly carboplatin and paclitaxel chemotherapy with ribociclib followed by ribociclib maintenance in patients with recurrent platinum-sensitive ovarian cancer. Primary objectives were safety and maximum tolerated dose (MTD) of ribociclib when given with platinum and taxane chemotherapy. Secondary endpoints were response rate (RR) and progression-free survival (PFS).

RESULTS

Thirty-five patients were enrolled. Patients had a mean 2.5 prior lines of chemotherapy, and 51% received prior maintenance therapy with Poly (ADP-ribose) polymerase inhibitors (PARPi) and/or Bevacizumab. The MTD was 400mg. The most common AEs included anemia (82.9%), neutropenia (82.9%), fatigue (82.9%), and nausea (77.1%). Overall RR was 79.3% with a stable disease (SD) rate of 18% resulting in a clinical benefit rate of 96.6%. The PFS was 11.4 months. RR and PFS did not differ based on number of lines of prior chemotherapy or prior maintenance therapy.

CONCLUSIONS

This work demonstrates the combination of ribociclib with chemotherapy in ovarian cancer is feasible and safe. With a clinical benefit rate of 97%, this work provides encouraging evidence of clinical efficacy in patients with recurrent platinum-sensitive disease.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT03056833.

FUNDING

This investigator-initiated trial was supported by Novartis who provided drug and funds for trial execution.

Abstract PO021: Carcinoma-associated mesenchymal stem/stromal cells enhance ovarian cancer metastasis and increase cancer cell clonal heterogeneity through direct mitochondrial transfer

Ovarian cancer is the most deadly gynecologic cancer largely due to early, diffuse metastatic spread. The ovarian cancer tumor microenvironment (TME) significantly impacts the metastatic capacity of ovarian cancer. We recently demonstrated that a critical stromal progenitor cell within the TME, termed carcinoma-associated mesenchymal stem/stromal cells (CA-MSCs), dramatically enhance the metastasis of ovarian cancer cells. CA-MSCs directly bind to cancer cells forming heterocellular units which co-metastasize. The goal of this work is to understand the mechanism driving CA-MSC-mediated ovarian cancer metastasis. We hypothesize that CA-MSCs increase the metastatic potential of ovarian cancer cells during the process of co-metastasis. Ovarian cancer uses both hematogenous and transcoelomic routes of metastasis therefore we used two ovarian cancer murine models to evaluate both modes of metastasis. We used a genomic barcode system to assess the clonal patterns of metastasis. Ovarian cancer cells with one unique barcode per cell were grown with or without CA-MSCs. Sites of metastasis were quantified and cancer cells were harvested from each site. Barcodes were sequenced to determined clonal representation at each metastatic site. We found CA-MSCs increased the number of metastatic sites in both the hematogenous and transcoelomic mouse models. Interestingly, CA-MSCs also increased the clonal heterogeneity at all metastatic sites (2.5 - 5 fold increase in blood, lung and liver). To investigate the mechanism enabling CA-MSC-mediated enhancement of clonal heterogeneity, we studied primary patient derived CA-MSCs and ovarian cancer cells. The process of metastasis poses unique metabolic stresses on cancer cells and normal mesenchymal stem cells are known to donate mitochondria to damaged epithelial cells. We therefore assessed if CA-MSCs use a similar mechanism to enhance survival of metastatic cancer cells. We stably labeled CA-MSC mitochondria with COX8-GFP via lentiviral transduction to enable the visualization and quantification of potential mitochondrial transfer. We demonstrate that CA-MSCs actively transfer mitochondria to cancer cells. This transfer is dependent on the physical interaction of CA-MSCs with cancer cells and is increased 2-4 fold when CA-MSCs and cancer cells form metastatic heterocellular units under non-adherent conditions. We tested the functional consequences of CA-MSC to cancer cell mitochondrial transfer and demonstrate cancer cells which receive mitochondria have increased chemotherapy resistance, increased sphere forming capacity and stem-like properties. Collectively, our results indicate CA-MSCs are a significant driver of ovarian cancer metastasis by forming heterocellular metastatic units which enable CA-MSC to cancer cell mitochondrial transfer. This leads to increased cancer cell survival and tumor initiation properties and represents a novel method of maintaining cancer cell heterogeneity during metastasis.

Citation Format: Catherine A. Pressimone, Leonard G. Frisbie, Alexander Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem/stromal cells enhance ovarian cancer metastasis and increase cancer cell clonal heterogeneity through direct mitochondrial transfer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO021.

Ovarian Carcinoma-Associated Mesenchymal Stem Cells Arise from Tissue-Specific Normal Stroma

Carcinoma-associated mesenchymal stem cells (CA-MSCs) are critical stromal progenitor cells within the tumor microenvironment (TME). We previously demonstrated that CA-MSCs differentially express bone morphogenetic protein family members, promote tumor cell growth, increase cancer "stemness," and chemotherapy resistance. Here, we use RNA sequencing of normal omental MSCs and ovarian CA-MSCs to demonstrate global changes in CA-MSC gene expression. Using these expression profiles, we create a unique predictive algorithm to classify CA-MSCs. Our classifier accurately distinguishes normal omental, ovary, and bone marrow MSCs from ovarian cancer CA-MSCs. Suggesting broad applicability, the model correctly classifies pancreatic and endometrial cancer CA-MSCs and distinguishes cancer associated fibroblasts from CA-MSCs. Using this classifier, we definitively demonstrate ovarian CA-MSCs arise from tumor mediated reprograming of local tissue MSCs. Although cancer cells alone cannot induce a CA-MSC phenotype, the in vivo ovarian TME can reprogram omental or ovary MSCs to protumorigenic CA-MSCs (classifier score of >0.96). In vitro studies suggest that both tumor secreted factors and hypoxia are critical to induce the CA-MSC phenotype. Interestingly, although the breast cancer TME can reprogram bone marrow MSCs into CA-MSCs, the ovarian TME cannot, demonstrating for the first time that tumor mediated CA-MSC conversion is tissue and cancer type dependent. Together these findings (a) provide a critical tool to define CA-MSCs and (b) highlight cancer cell influence on distinct normal tissues providing powerful insights into the mechanisms underlying cancer specific metastatic niche formation. Stem Cells 2019;37:257-269.