Platelets enhance Multiple Myeloma progression via IL-1β upregulation.

Purpose: Tumor cell-platelet interactions contribute to tumor progression and metastasis in solid tumors. However, the role of platelets in hematological malignancies is not clear. We investigated the association of platelet activation status with clinical stages in multiple myeloma (MM) patients and explored the role of platelets in MM progression. Experimental Design: Platelets were obtained from healthy donors and MM patients. We examined platelet activation status in MM patients by flow cytometry and transmission electron microscopy. We also observed the enriched pathways that are involved with platelet activation in RNA sequencing of platelets. MM cell lines were used to assess the effect of platelets on MM cell proliferation in vitro and their engraftment in vivo. RNA sequencing of MM cell lines was performed to explore molecular mechanisms underlying MM cell-platelet interaction and a CRISPR/Cas9 knockout approach was used for validation. Results: Platelets from MM patients were highly activated with disease progression. RNA sequencing of platelets revealed that genes involved in platelets were enriched in patients with smoldering MM (SMM) or MM. Platelets promoted MM cell proliferation in vitro and contributed to tumor engraftment in bone marrow in vivo. RNA sequencing revealed that IL-1 beta was upregulated in MM cell tines co-cultured with platelets, whereas IL-1 beta knockout in MM cell lines abrogated the effects of platelets on MM cell proliferation and engraftment in vitro. Conclusions: Platelets from MM patients were highly activated with disease progression. It IL-1 beta is critical to platelet-mediated MM progression and might be a potential target for MM treatment. (C) 2018 AACR.