【 Background and purpose 】Introduction of novel drugs such as immunomodulatory drugs (IMIDs), and proteasome inhibitors has significantly prolonged survival of multiple myeloma (MM). However, MM harboring high-risk cytogenic changes such as del 17 and t(4;14) is still significantly associated with short survival. Immunotherapy including monoclonal antibodies against MM cells or chimeric antigen receptor expressing T cell (CAR-T) therapy has also showed excellent response to high-risk MM, although the cost of these treatments is expensive. Some of conventional anti-cancer drugs, such as anthracyclines, have been reported to cause induction of immunomodulatory effects by cell surface expression of calreticulin (CRT) followed by release of high mobility group box 1 (HMGB 1) and ATP from cancer cells. Dendritic cells (DCs) recognize CRT, HMGB1 and ATP through CD91, TLR4, P2X7 receptors respectively, and take up cancer cells. This series of events is called immunogenic cell death (ICD). However, there is substantially no information on ICD in MM. The purpose of this study is to investigate whether anti-MM drugs can induce ICD. 【 Methods 】Myeloma cell line harboring high-risk cytogenetic changes, MUM24, KMS34, and KMS21 were treated with anti-myeloma drugs at the IC50, including dexamethasone(320µM), melphalan(2µM), lenalidomide(3.5µM), bortezomib(3nM), carfilzomib(4nM), and panobinostat(6nM). Expression of cell surface CRT and HMGB1 release, which are indicators of ICD, were detected using flow cytometry 48hr after drug treatment and western blotting 24hr after treatment, respectively. We also checked CRT expression on CD138+ cells derived from bone marrow samples of myeloma patients (n=3). Furthermore, the phagocytosis of drug-treated MM cells by DCs generated from healthy human peripheral blood mononuclear cells was evaluated by flow cytometry. 【 Results / Discussion 】Bortezomib and carfilzomib significantly induced expression of CRT and release of HMGB1 in MM cell lines and bone marrow CD138+ cells obtained from MM patients compared with other anti-MM drugs. Especially carfilzomib induced CRT expression at lower concentration. It was also observed that MUM24 cells treated with bortezomib or carfilzomib were effectively taken up by DCs compared to cells treated with other drugs. 【 Conclusion 】Our results suggest that proteasome inhibitors could not only directly kill MM cells but also induce anti-myeloma immune response via ICD. In particular, these immune effects are expected to improve the prognosis of patients in continuous therapy setting after induction therapies by evoking immune memories against residual MM cells, which might contribute to decrease recurrence or formation of extramedullary disease. Moreover, synergistic effects with other cancer immunotherapy such as immune checkpoint inhibitors and CAR-T therapy can be expected. Figure. Figure. Disclosures Hattori: IDAC inc.: Research Funding; Takeda: Research Funding. Matsushita:Amgen: Research Funding.

Background: Development of novel drugs, such as immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs), or monoclonal antibodies, has prolonged survival of multiple myeloma (MM) patients. However, high-risk patients harboring del 17, t(14;17), or t(11;14) still have poor prognosis. Therefore, clarification of the drugs that could potentiate the effect of these treatments is necessary. Several drugs have been reported to cause cell surface expression of calreticulin (CRT), release of high mobility group box 1 (HMGB 1) and ATP, activating an immune response, which is called immunogenic cell death (ICD). However, there is almost no information on ICD in MM. The purpose of this study is to investigate whether anti-MM drugs can induce not only direct cell-killing effect but also immunomodulatory effects in high-risk MM cells. Methods: High-risk myeloma cell line, MUM24 was treated with dexamethasone, melphalan, lenalidomide, bortezomib, carfilzomib, and panobinostat. Expression of cell surface CRT and HMGB1 release were detected using flow cytometry and Western blotting, respectively. We then co-cultured DiD-labeled monocyte-derived dendritic cells with GFP-induced MUM24 treated with each drug and evaluated phagocytosis of DCs using fluorescence microscope. Results: After treatment with drugs, bortezomib and carfilzomib induced higher expression of CRT and release of HMGB1 in MUM24 compared with other drugs. We also observed that DCs could engulf MUM24 cells treated with carfilzomib. Conclusion: Our results suggest that PIs, such as bortezomib or carfilzomib, could not only kill MM cells but also induce ICD. These effects are expected to improve the prognosis of MM patients by evoking strong immune response against MM cells. Citation Format: Maiko Matsushita, Sho Kashiwazaki, Satoshi Kamiko, Ryo Uozaki, Daiju Ichikawa, Yutaka Hattori. Analysis of immunogenic cell death (ICD) induced in multiple myeloma cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B177.

[Introduction] Recent development of novel drugs significantly improved prognosis of Multiple Myeloma (MM). Immunomodulatory drugs (IMiDs) and proteasome inhibitors play central roles in MM therapy. However expanded usage of lenalidomide (Len) has increased the number of Len-resistant patients. And limited information is obtainable with regand to Len-resistant mechanism, such as overexpression and genetic mutation of IMiDs-binding protein, celeblon (CRBN); thus, elucidating the Len-resistant mechanism and development of drugs overcoming the Len-resistance are very important for improving the outcome of MM. The purposes of this study are [1] to clarify the molecular mechanism of Len-resistance using Len-resistant MM cell lines [2] to confirm the mechanism of CRBN independent myeloma cell death by novel phthalimide-derivatives, TC11 and PEG(E)-TC11. [Method] [1] In our laboratory, Len-resistant cell lines, KMS21R, KMS27R and MUM24R have been established by long-term co-culture with low-dose Len. Using these cell lines, we examined expression of CRBN and the downstream molecules, IKZF1/3, IRF4 and c-MYC by western blotting. We also examined the mutation of CRBN in KMS27R. [2] We have originally developed a novel phthalimide-derivative, TC11 and PEG(E)-TC11 synthesized for improving water solubility. We examined whether TC11 and PEG(E)-TC11 induced cell death to Len-resistance MM or not. [Result] [1] First, we validated expression of CRBN and the down-stream molecules, which mediate pharmacological action of Len. Decreased expression of CRBN and subsequent up-regulation of down-stream IKZF1 were confirmed in KMS21R cell. In KMS27R cell, IKZF 1/3 expressions are increased without alteration of CRBN expression level. Thus, genetic mutation in CRBN or IKZF1 is suspected in KMS27R cells. In MUM24R cell, no significant change in the expression levels of the CRBN pathway molecules was confirmed, suggesting other molecular alternation than CRBN pathway. [2] TC11 significantly induced apoptosis of Len-resistant cells. We have previously reported that TC11 didn't bind to CRBN and TC11 directly bound to nucleophosmin1 (NPM1) and α-tubulin. It was found that TC11 induced G2/M arrest and subsequent apoptosis by inhibition of tubulin polymerization and NPM1 oligomerization. Fluorescence microscopy observation showed that TC11 treatment induced hyper duplication of centrosomes in MM cells. Water solubility and blood absorption of PEG(E)-TC11 were significantly improved compared with those of TC11. As a consequence, PEG-(E)TC11 significantly delayed tumor growth in xenograft model mice. [Discussion & Conclusion] [1] Our present data suggested diversity of Len-resistant mechanism in MM patients. For example, in KMS21R, decreased expression of CRBN was likely the cause of Len-resistance. In KMS27R, genetic mutation in CRBN-IKZF1 pathway caused inhibition of IKZF1 degradation. In MUM24R, the Len-resistant mechanism didn't relate to the CRBN pathway but to unknown molecular mechanism. Len-resistant cell lines are useful tools for studying Len-resistant mechanisms and developing drugs overcoming Len-resistance. [2]TC11 abrogated tubulin polymerization and NPM1 oligomerization, induced centrosome disruption and G2/M arrest. Since G2/M check point doesn't closely rely on p53. TC11 was able to induce apoptosis of MM cells with high-risk cytogenetic mutations such as deletion of TP53 gene. TC11 and PEG-(E)TC11 are expected as a candidate compound overcoming Len-resistance and high-risk MM. Disclosures Matsushita: Amgen: Research Funding. Hattori:Takeda: Research Funding; IDAC inc.: Research Funding.