P1246: DIFFERENTIAL ROLE OF MICROENVIRONMENT AND STROMAL-CELL INDUCED VENETOCLAX RESISTANCE IN MANTLE CELL LYMPHOMA

Abstract

Background: Venetoclax is an inhibitor of the anti-apoptotic protein BCL-2 and a promising drug for MCL treatment. However, resistance towards venetoclax has already been reported in several MCL studies. There is growing evidence suggesting that interactions between lymphoma cells and their surrounding microenvironment might play a key role in not only promoting tumor cell survival but also facilitating resistance to certain chemotherapeutic agents, but little is known about the role of microenvironment in drug resistance in MCL. Aims: To understand the cellular and molecular resistance mechanisms mediated by the lymphoma microenvironment to prevent MCL patients from developing resistance to venetoclax treatment. To investigate the interactions of MCL cell lines with Mesenchymal Stromal Cells (MSCs), a key component of the microenvironment, in an in vitro co-culture system. Methods: MCL cell lines (MAVER-1, MINO) were cultured alone or in co-culture with HS-5, a human MSC cell line, or MS-5, a murine MSC cell line and exposed to different drugs, including venetoclax. Flow cytometry was used to assess cell viability. RNA sequencing of suspension and adherent MCL cells was used to identify differentially expressed genes. ELISA multiplex analysis was used to identify human or murine pro-inflammatory cytokines in co-culture supernatant. Results: Co-culture of MCL cell lines with both HS-5 and MS-5 induced resistance in MCL cells to doxorubicin and vincristine. However, only co-culture with MS-5 induced venetoclax resistance in MCL cells. Interestingly, conditioned media alone from MS-5 cultures was sufficient to induce venetoclax resistance, suggesting that soluble factors (such as cytokines and microvesicles) might mediate the venetoclax resistance mechanisms in MCL cells. Induction of apoptosis through MCL-1 inhibition with drug S6338 was also abrogated by co-culture with both HS-5 and MS-5, while BCL-xL inhibition using drug WEHI-549 was only ineffective in MINO cells in MS-5 co-culture. MCL cells in HS-5 co-cultures exhibited upregulation of genes involved in inflammatory response, cytokine signaling, and apoptosis, compared to MS-5 co-cultures. Accordingly, we identified unique sets of genes that were significantly upregulated in adherent MCL cells in HS-5 co-cultures, mainly involved in cell adhesion and cytokine signaling. Moreover, HS-5 co-cultures contained high levels of IL-6 and IL-8, corresponding with the increased gene expression levels of genes involved in the IL-6 signaling pathway in MCL cells. On the contrary, MS-5 co-cultures contained only high levels of murine KC/GRO, corresponding to human chemokine CXCL1. Image:Summary/Conclusion: We show that HS-5 provides MCL cells resistance to drugs, such as vincristine and doxorubicin, but not venetoclax, reflecting the different mechanisms of action of these therapies as well as their differential effects in the MCL microenvironment. MCL cells were resistant to venetoclax only in murine MSCs co-cultures, and further transcriptome and cytokine analysis supported this difference. Among others, our data questions how reliable murine MSCs are for obtaining translatable results, as MS-5 is the most used MSC cell line for co-cultures studies. These findings together provide a rationale to further investigate the role of MSCs in MCL drug resistance, as understanding the role of microenvironment in venetoclax sensitivity in MCL will potentially allow for more effective and targeted therapy.