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Abstract: Immunogenic cell death (ICD) is a form of cell death by which cancer treatments can induce a clinically relevant antitumor immune response in a broad range of cancers. In multiple myeloma (MM), the proteasome inhibitor bortezomib is an ICD inducer and creates durable therapeutic responses in patients. However, eventual relapse and resistance to bortezomib appear inevitable. Here, by integrating patient transcriptomic data with an analysis of calreticulin (CRT) protein interactors, we found that GABA type A receptor-associated protein (GABARAP) is a key player whose loss prevented tumor cell death from being perceived as immunogenic after bortezomib treatment. GABARAP is located on chromosome 17p, which is commonly deleted in patients with high risk MM. GABARAP deletion impaired the exposure of the eat-me signal CRT on the surface of dying MM cells in vitro and in vivo, thus reducing tumor cell phagocytosis by dendritic cells and the subsequent antitumor T-cell response. Low GABARAP was independently associated with shorter survival in patients with MM and reduced tumor immune infiltration. Mechanistically, we found that GABARAP deletion blocked ICD signaling by decreasing autophagy and altering Golgi apparatus morphology, with consequent defects in the downstream vesicular transport of CRT. Conversely, upregulating autophagy using rapamycin restored Golgi morphology, CRT exposure, and ICD signaling in GABARAPKO cells undergoing bortezomib treatment. Therefore, coupling an ICD inducer, such as bortezomib, with an autophagy inducer, such as rapamycin, may improve patient outcomes in MM, in which low GABARAP in the form of del(17p) is common and leads to worse outcomes., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

PSMD4/Rpn10 is a subunit of the 19S proteasome unit that is involved with feeding target proteins into the catalytic machinery of the 26S proteasome. Because proteasome inhibition is a common therapeutic strategy in multiple myeloma (MM), we investigated Rpn10 and found that it is highly expressed in MM cells compared with normal plasma cells. Rpn10 levels inversely correlated with overall survival in patients with MM. Inducible knockout or knockdown of Rpn10 decreased MM cell viability both in vitro and in vivo by triggering the accumulation of polyubiquitinated proteins, cell cycle arrest, and apoptosis associated with the activation of caspases and unfolded protein response-related pathways. Proteomic analysis revealed that inhibiting Rpn10 increased autophagy, antigen presentation, and the activation of CD4+ T and natural killer cells. We developed an in vitro AlphaScreen binding assay for high-throughput screening and identified a novel Rpn10 inhibitor, SB699551 (SB). Treating MM cell lines, leukemic cell lines, and primary cells from patients with MM with SB decreased cell viability without affecting the viability of normal peripheral blood mononuclear cells. SB inhibited the proliferation of MM cells even in the presence of the tumor-promoting bone marrow milieu and overcame proteasome inhibitor (PI) resistance without blocking the 20S proteasome catalytic function or the 19S deubiquitinating activity. Rpn10 blockade by SB triggered MM cell death via similar pathways as the genetic strategy. In MM xenograft models, SB was well tolerated, inhibited tumor growth, and prolonged survival. Our data suggest that inhibiting Rpn10 will enhance cytotoxicity and overcome PI resistance in MM, providing the basis for further optimization studies of Rpn10 inhibitors for clinical application.

Long noncoding RNAs (lncRNAs) can drive tumorigenesis and are susceptible to therapeutic intervention. Here, we used a large-scale CRISPR interference viability screen to interrogate cell-growth dependency to lncRNA genes in multiple myeloma (MM) and identified a prominent role for the miR-17-92 cluster host gene (MIR17HG). We show that an MIR17HG-derived lncRNA, named lnc-17-92, is the main mediator of cell-growth dependency acting in a microRNA- and DROSHA-independent manner. Lnc-17-92 provides a chromatin scaffold for the functional interaction between c-MYC and WDR82, thus promoting the expression of ACACA, which encodes the rate-limiting enzyme of de novo lipogenesis acetyl-coA carboxylase 1. Targeting MIR17HG pre-RNA with clinically applicable antisense molecules disrupts the transcriptional and functional activities of lnc-17-92, causing potent antitumor effects both in vitro and in vivo in 3 preclinical animal models, including a clinically relevant patient-derived xenograft NSG mouse model. This study establishes a novel oncogenic function of MIR17HG and provides potent inhibitors for translation to clinical trials., (© 2023 by The American Society of Hematology.)

Interaction of plasmacytoid dendritic cells (pDCs) with multiple myeloma (MM) cells, T- or NK-effector cells in the bone marrow (BM) microenvironment induces tumor cell growth, as well as inhibits innate and adaptive immune responses. Defining pDC-MM interaction-triggered immunosuppressive mechanism(s) will enable design of interventional therapies to augment anti-MM immunity. In the present study, we show that pDC-MM interactions induce metabolic enzyme Ecto-5' Nucleotidase/CD73 in both pDCs and MM cells. Gene expression database from MM patients showed that CD73 levels inversely correlate with overall survival. Using our pDC-MM coculture models, we found that blockade of CD73 with anti-CD73 Abs: decreases adenosine levels; activates MM patient pDCs; triggers cytotoxic T lymphocytes (CTL) activity against autologous patient MM cells. Combination of anti-CD73 Abs and an immune-stimulating agent TLR-7 agonist enhances autologous MM-specific CD8 + CTL activity. Taken together, our preclinical data suggest that the therapeutic targeting of CD73, alone or in combination with TLR-7 agonist, represents a promising novel strategy to restore host anti-MM immunity., (© 2022. The Author(s).)

Multiple myeloma (MM) is a malignancy of plasma cells accounting for ≈12% of hematological malignancies. In this study, the fabrication of a high-content in vitro MM model using a coaxial extrusion bioprinting method is reported, allowing formation of a human bone marrow-like microenvironment featuring an outer mineral-containing sheath and the inner soft hydrogel-based core. MM cells are mono-cultured or co-cultured with HS5 stromal cells that can release interleukin-6 (IL-6), where the cells show superior behaviors and responses to bortezomib in 3D models than in the planar cultures. Tocilizumab, a recombinant humanized anti-IL-6 receptor (IL-6R), is investigated for its efficacy to enhance the chemosensitivity of bortezomib on MM cells cultured in the 3D model by inhibiting IL-6R. More excitingly, in a proof-of-concept demonstration, it is revealed that patient-derived MM cells can be maintained in 3D-bioprinted microenvironment with decent viability for up to 7 days evaluated, whereas they completely die off in planar culture as soon as 5 days. In conclusion, a 3D-bioprinted MM model is fabricated to emulate some characteristics of the human bone marrow to promote growth and proliferation of the encapsulated MM cells, providing new insights for MM modeling, drug development, and personalized therapy in the future., (© 2021 Wiley-VCH GmbH.)