Bortezomib In Multiple Myeloma Research Articles

Metformin and chidamide synergistically suppress multiple myeloma progression and enhance lenalidomide/bortezomib sensitivity.

Multiple myeloma (MM) is a common hematological malignancy, and patients with MM are recommended to take immunomodulatory drugs such as lenalidomide along with proteasome inhibitors such as bortezomib to extend survival. However, drug resistance influences the efficacy of treatment for MM. In our study, we found that metformin and chidamide both suppressed MM cell growth in a concentration- and time-dependent way (p < .001). Moreover, combined therapy with metformin and chidamide exhibited enhanced inhibition of the growth of MM cells compared with monotherapy (p < .05). Additionally, the triple-drug combination of metformin and chidamide with lenalidomide or bortezomib was used to stimulate the MM cells, and the results revealed that metformin and chidamide treatment sensitized MM cells to lenalidomide and bortezomib. As a result, the apoptosis (p < .001) together with cell cycle arrest at G0/G1 phase (p < .05) was stimulated by lenalidomide and bortezomib, and showed significant elevation in the triple-drug combination group compared with the lenalidomide or bortezomib treatment alone group (p < .05). Furthermore, the impacts of different drugs on glycolysis in MM cells were examined. We found that metformin and chidamide combined treatment significantly promoted glucose uptake and reduced energy production in MM cells treated with lenalidomide and bortezomib (p < .001), suggesting that metformin and chidamide affected glycolysis in MM cells and enhanced the sensitivity of lenalidomide and bortezomib in MM by regulating glucose metabolism. In conclusion, metformin and chidamide synergistically hindered MM cell growth and sensitized cells to lenalidomide/bortezomib. The findings of this study might provide novel clues to improve MM therapy.

Targeting RBM39-MEK5 Axis Synergizes with Bortezomib to Inhibit Multiple Myeloma Malignancy

Multiple myeloma (MM) is a type of haematological malignancy characterised by the accumulation and expansion of malignant plasma cells in the bone marrow (BM). Despite recent advances in chemotherapy, MM remains an incurable disease for most patients and therefore requires novel therapies. Abnormal alternative splicing is a hallmark of cancer and is associated with poor survival and an ultra-high-risk population in MM (Bauer et. al. Haematologica 2021). Targeting splicing is a promising therapeutic strategy in MM. Our previous study showed that RBM39 is highly expressed in primary MM cells and cell lines and correlates with poor overall survival (Tong et. al. Haematologica 2020). To investigate the underlying role of RBM39 in MM, we knocked down RBM39 in MM cell lines. We found that knockdown of RBM39 inhibited MM cell proliferation, induced apoptosis and cell cycle arrest at the G2/M phase, and inhibited subcutaneous tumour growth. Indisulam has been reported to induce RBM39 degradation via the proteasomal pathway by acting as a molecular glue to link RBM39 to the E3 ubiquitin ligase DCAF15 (Han et. al. Science 2017). In our study, Indisulam treatment in MM cells was shown to degrade RBM39 via DCAF15. Indisulam could induce apoptosis and G2/M phase arrest in MM cell lines and inhibite tumour growth in vivo. It also significantly decreased MM cell viability in a co-culture system with MM BM-derived mesenchymal stromal cells. Indisulam was also able to inhibit primary CD138+ cells isolated from newly diagnosed MM patients. To explore the mechanistic role of RBM39 in promoting MM malignancy, we performed RNA immunoprecipitation (RIP)-Seq and RNA sequencing in RBM39 knockdown MM cells to investigate the alternative splicing targets of RBM39. KEGG pathway analysis of differentially expressed and alternatively spliced genes revealed the enrichment of the MAPK pathway. We then identified MEK5, a non-redundant member of the MAPK family, as a potential target of RBM39, which is highly expressed in MM. Full-length MEK5 contributes to increased proliferation and survival of MM cells. We further demonstrated that MEK5 is bound and alternatively spliced by RBM39 and that splicing of full-length MEK5 is dependent on RBM39. Given the importance of the RBM39-MEK5 axis in MM, we also found that inhibition of RBM39 with Indisulam or MEK5 with the inhibitor BIX02189 increased the cytotoxicity of bortezomib in vivo and in vitro. In conclusion, we have demonstrated that the RBM39-MEK5 axis, in which RBM39 maintains splicing of full-length MEK5, is essential for MM cell survival and proliferation. Mechanistically, shRNA-mediated knockdown or Indisulam-mediated degradation of RBM39 caused extensive altered splicing, including mis-splicing of MEK5. Targeting RBM39 or MEK5 could not only inhibit MM malignancy, but also enhance the cytotoxicity of bortezomib for MM.

Potential Significance of CTPS1 in Multiple Myeloma

Introduction With the increasing interest to the metabolism of multiple myeloma (MM), a number of metabolic genes and their associated regulatory networks are essential for MM progression. Our team's prior work indicated that high expression of metabolism-related gene CTPS1 (CTP synthase 1) correlated with poor prognosis of MM. However, the mechanism of CTPS1 in MM is unknown. Methods The difference in CTPS1 expression level in patients with plasma cell malignancies, various stages, and drug-resistant recurrence was examined using publicly available data. MM cell lines were engineered to overexpress or knockdown CTPS1. RNA-seq was used to unbiased interrogate the downstream effector genes modulated by CTPS1. Severe immunodeficient NRG-SGM mice expressing humanized myeloid cytokines were used to determine the effect of CTPS1 on MM proliferation in vivo. Results CTPS1 expression levels varied substantially in various plasma cell malignancies. High CTPS1 expression was associated with shorter overall survival and progression-free survival in newly diagnosed MM patients. Moreover, there was a strong correlation between CTPS1 and sex, albumin, β2 microglobulin, lactate dehydrogenase, and ISS/R-ISS stage. In vitro, CTPS1 overexpressing cells proliferated more quickly than CTPS1 knockdown cells. NRG-SGM3 mouse experiments demonstrated that tumor growth was significantly accelerated in vivo in the CTPS1 overexpression group. In the pharmacological experiment, CTPS1 overexpression group's sensitivity to 20 nM bortezomib reduced, but CTPS1 down-knocked group's sensitivity to 20 nM bortezomib rose. CTPS1 was also shown to be involved in metabolism and synthesis, notably mRNA metabolism, DNA metabolism, chromosomal combination, cell cycle, spliceosome, and cellular senescence. Furthermore, Myc was found to be tightly connected to CTPS1 in both MM cell lines and newly diagnosed MM. Conclusions This study found that increased CTPS1 expression is associated with a poor prognosis and reduced sensitivity to bortezomib in MM. Additionally, CTPS1 upregulated Myc-signaling genes, which promoted progression of MM.

Pharmacologic targeting of the p62 ZZ domain enhances both anti-tumor and bone-anabolic effects of bortezomib in multiple myeloma.

Multiple myeloma (MM) is a malignancy of plasma cells whose antibody secretion creates proteotoxic stress relieved by the N-end rule pathway, a proteolytic system that degrades N-arginylated proteins in the proteasome. When the proteasome is inhibited, protein cargo is alternatively targeted for autophagic degradation by binding to the ZZ-domain of p62/ sequestosome-1. Here, we demonstrate that XRK3F2, a selective ligand for the ZZ-domain, dramatically improved two major responses to the proteasome inhibitor bortezomib (Btz) by increasing: i) killing of human MM cells by stimulating both Btz-mediated apoptosis and necroptosis, a process regulated by p62; and ii) preservation of bone mass by stimulating osteoblast differentiation and inhibiting osteoclastic bone destruction. Co-administration of Btz and XRK3F2 inhibited both branches of the bimodal N-end rule pathway exhibited synergistic anti-MM effects on MM cell lines and CD138+ cells from MM patients, and prevented stromal-mediated MM cell survival. In mice with established human MM, co-administration of Btz and XRK3F2 decreased tumor burden and prevented the progression of MM-induced osteolytic disease by inducing new bone formation more effectively than either single agent alone. The results suggest that p62-ZZ ligands enhance the anti- MM efficacy of proteasome inhibitors and can reduce MM morbidity and mortality by improving bone health.

LncRNA MEG3 promotes the sensitivity of bortezomib by inhibiting autophagy in multiple myeloma

BackgroundBortezomib resistance hampers the long-term survival of multiple myeloma (MM) patients. Our previous study has proved that downregulated lncRNA MEG3 is associated with the poor clinical outcome in MM. However, the effect of MEG3 on the sensitivity of bortezomib in MM and its possible molecular mechanism remains muddled. MethodsIn this study, CCK8 and flow cytometry techniques were used to assess cell viability in MEG3 overexpressed MM cells after bortezomib treatment. The expression of autophagy-related protein LC3 and p62 were distinguished by Western blot, and the mCherry-GFP-LC3 puncta reflecting autophagy level was observed under fluorescence microscope. RNA immunoprecipitation (RIP) technology was used to detect the binding relationship of MEG3 and ATG2B to PTBP1. ResultsIncreased toxicity of bortezomib and diminished autophagy level were found in MEG3 overexpressed MM cells. Mechanistically, we discovered that RNA-binding protein PTBP1 could bind to MEG3 and ATG2B by RIP assay. Upregulation of MEG3 promoted PTBP1 expression and inhibited the expression level of ATG2B, suggesting that MEG3 recruited PTBP1 and then decayed ATG2B expression. ConclusionIn summary, our study illustrated that MEG3 increased bortezomib sensitivity by hindering autophagy through the PTBP1/ATG2B axis, providing a new therapeutic target for bortezomib-resistant MM patients.

Discovery of the oncogenic MDM2, a direct binding target of berberine and a potential therapeutic, in multiple myeloma.

Recent studies have suggested the potency of berberine (BBR) for multiple cancer treatments, including multiple myeloma (MM). However, the direct target and underlying mechanism of BBR remain largely understood in MM. Here, we demonstrated that BBR inhibited cell proliferation and acted synergistically with bortezomib in MM.1S cells. BBR treatment induced MM cell cycle arrest by downregulating several cell cycle-related proteins. Murine double minute 2 (MDM2) as a BBR-binding protein was identified by surface plasmon resonance image (SPRi) analysis and molecular docking. Overexpression of MDM2 is associated with MM progression and a poor prognosis. Knockdown MDM2 by siRNA transfection can repress MM malignant progression and attenuate the BBR sensitivity to MM.1S cells. BBR treatment induced the degradation of MDM2 through the ubiquitin-proteasome system and reactivated P53/P21 in MM cells. Overall, our data has illustrated that MDM2, as a binding protein of BBR for the first time, may serve as a potential therapeutic option for MM.

PLK4 inhibitor plus bortezomib exhibits a synergistic effect on treating multiple myeloma via inactivating PI3K/AKT signaling.

The anti-tumor effect of polo-like kinase 4 (PLK4) inhibitor has been explored in several neoplasms, while its synergy with bortezomib in multiple myeloma (MM) remains elusive. Hence, the present study aimed to investigate the effect of PLK4 inhibitor on the sensitivity of MM to bortezomib treatment and its underlying mechanism. MM cell lines (RPMI-8226 and U266) were cultured in different concentrations of CFI-400945 (PLK4 inhibitor), bortezomib, or their combination. Subsequently, 740 Y-P (PI3K activator) was added in the combination of CFI-400945 and bortezomib. Besides, cell viability and apoptosis were measured by CCK-8 reagent and TUNEL apoptosis kit, separately; meanwhile, western blot was carried out for detecting PLK4, p-PI3K, PI3K, p-AKT, and AKT. CFI-400945 and bortezomib decreased the cell viability in dose-dependent manners in MM cell lines, respectively. The combination of different concentrations of CFI-400945 and bortezomib reduced cell viability compared with monotherapy in MM cell lines (all P < 0.05). Interestingly, 200nM CFI-400945 and 4nM bortezomib showed the maximum synergy in MM cell lines. Furthermore, 200nM CFI-400945 plus 4nM bortezomib showed a better effect on decreasing cell viability and promoting cell apoptosis than CFI-400945 or bortezomib monotherapy in MM cells cell lines (all P < 0.05). Moreover, 740 Y-P alleviated the effect of bortezomib and CFI-400945 on PI3K/AKT signaling, cell viability, and apoptosis in MM cell lines. PLK4 inhibitor plus bortezomib shows synergy in decreasing cell viability and enhancing cell apoptosis via repressing PI3K/AKT signaling in MM.

Tetrahydrobiopterin induces proteasome inhibitor resistance and tumor progression in multiple myeloma

Multiple myeloma (MM) still remains an incurable disease due to widespread drug resistance and high frequency of relapse. In this study, we found that tetrahydrobiopterin (BH4) promotes MM cell proliferation and tumor growth in vivo. BH4 also increases MM bortezomib (Bor) resistance in vitro and in vivo. We show that BH4 increases the expressions of USP7 and USP46 in MM cells, which are responsible for MM Bor resistance primed by BH4. BH4 promotes the degradation of P53 and the activation of NF-κB signaling through the up-regulation of USP7 and USP46. Furthermore, the inhibition of USPs increases the therapeutic effects of Bor in MM tumor bearing mice. Our results demonstrate the important role of BH4 in MM Bor resistance and tumor progression in vivo. These findings could potentially have clinical implications.

CC-92480 Enhances Cell-Autonomous Cytotoxicity through Blockade of G 2/M Transition When Combined with Bortezomib/Dexamethasone in Pre-Clinical Multiple Myeloma

Background: Pomalidomide (POM) is an established agent in relapsed/refractory (R/R) multiple myeloma (MM). CC-92480, a novel cereblon E3 ligase modulator (CELMoD ®) agent, is being investigated in R/R MM patients in combination with the proteasome inhibitor (PI) bortezomib (BTZ) and steroid dexamethasone (DEX) (NCT03374085/NCT03989414). Previously, we showed mechanistic synergy of POM/BTZ/DEX in MM cell line models (Bjorklund et al). Here we analyzed the cell autonomous cytotoxic activities of CC-92480 or POM alone and in combination with BTZ/DEX to compare and differentiate their mechanisms of action (MOA).Results:Comparative analysis of the anti-proliferative activity against H929 and MM1.S cell lines revealed that CC-92480 demonstrated a more potent inhibition of proliferation by 100-fold lower dose compared to POM. Combination experiments utilizing a titration of POM or CC-92480 in combination with a 1 hr BTZ pulse, to mimic the clinical pharmacokinetics (+/- DEX co-treatment) showed an enhancement of antiproliferative capacity in both doublet and triplet combinations compared to single agents. Combination indices for POM/BTZ/DEX or CC-92480/BTZ/DEX resulted in values <1 for most combinations indicating a synergistic effect. Additionally, POM or CC-92480 in combination with BTZ or DEX, or in triplet combinations increased induction of apoptosis (>90% for each triplet compared to POM (20%) and CC-92480 (40%). Flow cytometric analysis of Aiolos and Ikaros protein level in MM cells treated with POM/BTZ/DEX or CC-92480/BTZ/DEX resulted in a slight kinetic delay in substrate depletion at early time points (1-4 hr), where the effect is less apparent with CC-92480, and indistinguishable at 24 hr compared to single agent POM or CC-92480 in the clinically relevant concentrations.We performed transcriptomic analyses of H929 cells treated with POM/BTZ/DEX or CC-92480/BTZ/DEX for 24 hrs to identify key pathways responsible for the observed synergistic combination effect. Common pathways dysregulated by POM or CC-92480 included previously identified interferon, protein homeostasis and proliferation gene sets. Gene set enrichment analysis (GSEA) showed many significant pathway differences when comparing the triplets, including general cell cycle progression, cell division and chromatin segregation. Interestingly, genes involved in negative regulation of G 2/M transition were identified as one of the most significant differences between POM/BTZ/DEX and CC-92480/BTZ/DEX.To understand how these pathways contributed to cell cycle effects and apoptosis, we assessed DNA fragmentation by TUNEL in conjunction with cell cycle flow cytometry to examine cell cycle specific apoptotic induction. Temporal assessment (6, 12, 18, 24, and 48 hr treatments) demonstrated accumulation of BrdU incorporation in all cell cycle phases when treated with POM/BTZ/DEX or CC-92480/BTZ/DEX indicating cell death was occurring within all phases. However, there was a marked enhancement of G 2/M BrdU incorporation (80% vs. 40% of G 2/M population) at 18-24 hr when treated with CC-92480/BTZ/DEX compared to POM/BTZ/DEX, or other single agent treatments. Additionally, G 2/M transition-dependent cyclins A and B were shown to be dysregulated by CC-92480. These data indicate that CC-92480 potentiates a G 2/M arrest in combination with BTZ in MM cells.Conclusions: These results demonstrate that CC-92480 alone or in combination with BTZ/DEX elicits a more potent cytotoxic effect on MM cells compared to POM. Importantly, the combination of either POM or CC-92480 with a PI, like BTZ, does not appreciatively affect single agent MOA. We have also identified a key differentiating mechanism of cell autonomous activity for CC-92480 in combination with BTZ/DEX where MM cells enhance apoptotic induction at the G 2/M stage compared to POM. Clinically, this added mechanistic difference suggests a more cytotoxic response in patients treated with CC-92480/BTZ/DEX compared to POM/BTZ/DEX. DisclosuresBjorklund: BMS: Current Employment, Current equity holder in publicly-traded company. Amatangelo: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Kang: BMS: Current equity holder in publicly-traded company. Chiu: Bristol Myers Squibb: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Pourdehnad: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties: No royalty. Hagner: BMS: Current Employment, Current equity holder in publicly-traded company. Thakurta: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company.

Pre-Clinical and Clinical Immunomodulatory Effects of Pomalidomide or CC-92480 in Combination with Bortezomib in Multiple Myeloma

▪Background: Pomalidomide (POM) is an established agent in relapsed/refractory (R/R) multiple myeloma (MM) with direct cytotoxicity against MM cells and immunostimulatory activities in multiple cell types including T cells and NK cells. CC-92480 is a novel Aiolos/Ikaros degrading cereblon E3 ligase modulator (CELMoD ®) agent is currently being investigated in combination with the proteasome inhibitor (PI) bortezomib (BTZ) and corticosteroid dexamethasone (DEX), or with DEX only in R/R MM (CC-92480-MM-002 and CC-92480-MM-001). Previous results indicate that triplet combination of POM/BTZ/DEX may enhance some T, B and NK cell subpopulations, overcoming immunosuppression when compared to BTZ/DEX-only treated patients (Rao et al, 2019). Mechanisms of action (MOA) of CC-92480- and POM-mediated substrate depletion occurs via ubiquitination and proteasome degradation, where BTZ has been speculated as potentially antagonistic as a PI. Here, we report pre-clinical and clinical observations of an immune MOA of CC-92480 or POM in combination with BTZ.Results: To mimic the clinical pharmacokinetics, BTZ was utilized as a high-dose pulse method alone and in combination with POM or CC-92480, followed by flow cytometric measurements of Aiolos and Ikaros protein abundance in healthy donor (HD) T cells. The addition of BTZ modestly delayed CRBN-dependent substrate depletion compared to single agent POM or CC-92480; however, this effect was only apparent at early time points (1-6 hr) where the effect was negligible by 24 hr.To understand the functional implications of BTZ combination, we conducted CD3-stimulated PBMC-mediated cytotoxicity assay against H929 MM target cells in a co-culture model. The efficiency of POM or CC-92480 induced PBMC-mediated killing in a dose dependent manner (~65% increase compared to DMSO) were similar at a 100-fold lower dose range of CC-92480 compared to POM, with the effect not being altered by co-treatment with BTZ. These data were replicated with a POM or CC-92480 treated supernatant stimulation of purified NK cells co-culture, which induced an 80% reduction in target cell viability with the BTZ combination having no negative effects on CELMoD-mediated activity. Cytokine analysis on PBMC supernatants treated with either POM or CC-92480 in the absence or presence of BTZ-pulse showed a dose-dependent increase in IL-2 (>2.4-fold) and Granzyme B (>3.1-fold), which were not impacted by BTZ co-treatment.As a secondary readout on activation status, we measured multiple signaling molecules and activation markers on the cell surface of T and NK cell subsets in CD3 stimulated HD PBMCs treated with dose-dependent POM or CC-92480 with or without co-treatment of BTZ. Compared to DMSO controls, elevated expression levels of CD25 (IL2RA), CD278 (ICOS), Granzyme B, CD134 (OX40R) and HLA-DR were observed with both POM and CC-92480 on CD4, CD8 and NK cells demonstrating a CELMoD-mediated increase in immune activation. These effects were not impacted by the co-treatment of BTZ.Examination of peripheral blood samples from MM patients enrolled in the CC-92480-MM-001/002 (NCT03374085/NCT03989414) clinical trials revealed that CC-92480 promoted potent immunomodulation when administered in combination with DEX and with BTZ/DEX. These data included increased numbers of activated and central memory T cells, as well as increased Ki67+ proliferating T and NK cell populations compared to samples collected during the screening period before any drugs had been administered, consistent with earlier observation of POM in combination with BTZ/DEX treated patients.Conclusions: Taken together, these data demonstrate that POM and CC-92480 are potent immunomodulatory agents with enhanced induction of PBMC and NK mediated cell killing of MM tumor cells and activation of T and NK cells, at 100-fold lower concentrations of CC-92480 compared to POM. Additionally, we showed that combination with BTZ in preclinical assays and in the clinical setting did not antagonistically affect the immunostimulatory ability of POM or CC-92480. DisclosuresBjorklund: BMS: Current Employment, Current equity holder in publicly-traded company. Amatangelo: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Chiu: Bristol Myers Squibb: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Kang: BMS: Current equity holder in publicly-traded company. Civardi: Bristol Myers Squibb: Current Employment. Katz: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Maciag: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Hagner: BMS: Current Employment, Current equity holder in publicly-traded company. Pourdehnad: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties: No royalty. Bahlis: Pfizer: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Genentech: Consultancy; BMS/Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria. Richardson: Oncopeptides: Consultancy, Research Funding; Celgene/BMS: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Karyopharm: Consultancy, Research Funding; Protocol Intelligence: Consultancy; Janssen: Consultancy; Sanofi: Consultancy; Secura Bio: Consultancy; GlaxoSmithKline: Consultancy; Regeneron: Consultancy; AstraZeneca: Consultancy; AbbVie: Consultancy; Jazz Pharmaceuticals: Consultancy, Research Funding. Thakurta: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Resistance to Bortezomib By Increasing TSP-1-Dependent TGF-β1 Activation in Bone Marrow

Multiple myeloma (MM) is a plasma cell malignancy that thrives in the bone marrow (BM). The proteasome inhibitor bortezomib (BTZ) is one of the most effective front-line chemotherapeutic drugs for MM; however, 15-20% of high-risk patients do not respond to or become resistant to this drug and the mechanisms of chemoresistance remain unclear. We previously demonstrated that MM cells inhibit Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OBs). In the current study, we investigated the impact of OB-Runx2 deficiency on the outcome of BTZ treatment using our syngeneic mouse model of MM in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2 -/- mice) and OB-Runx2 +/+ mice as control.Five-week-old OB-Runx2 +/+ mice and OB-Runx2 -/- mice were i.v. injected with 5TGM1-Luc murine MM cells (2×10 6). On day 8, after the tumor injection, mice were randomly assigned to treatment for 4 weeks, with either BTZ (i.p. injection, 0.5 mg/kg body weight, twice/week) or PBS. Bioluminescence imaging and serum IgG2bκ (a soluble marker of 5TGM1 MM cells) ELISA showed that BTZ significantly inhibited tumor growth in OB-Runx2 +/+ mice, but not in OB-Runx2 -/- mice. Cytokine array and ELISA showed that in PBS-treated, tumor-bearing OB-Runx2 -/- mice, BM levels of thrombospondin-1 (TSP-1), a matricellular protein that converts latent TGF-β1 to its active form, and active TGF-β1 were significantly higher than levels in tumor-bearing OB-Runx2 +/+ counterparts. Interestingly, BTZ treatment further increased the levels of both TSP-1 and active TGF-β1 in the BM of tumor-bearing OB-Runx2 -/- mice, but it did not affect the level of either TSP-1 or TGF-β1 in the BM of tumor-bearing OB-Runx2 +/+ mice. These results suggest that OB-Runx2 deficiency increases TGF-β1 activation via TSP-1 in BM and BTZ treatment further enhances this effect.SRI31277 is a tripeptide antagonist that blocks TSP-1-mediated activation of TGF-β1 and it has been shown to reduce tumor burden, TGF-β signaling, and osteolytic bone disease in multiple mouse models of MM. To confirm the involvement of TSP-1/TGF-β1 activation in MM BTZ resistance induced by OB-Runx2 deficiency and to test whether blocking TSP1-mediated TGF-β1 activation can alleviate BTZ resistance, 5TGM1-Luc MM tumor-bearing OB-Runx2 +/+ and OB-Runx2 -/- mice were treated with PBS, BTZ, SRI31277 (osmotic pump, 30 mg/kg body weight per day), or BTZ + SRI31277 for 4 weeks. While SRI31277 did not further increase BTZ-induced MM inhibition in OB-Runx2 +/+ mice, SRI31277 treatment significantly reduced the tumor burden in OB-Runx2 -/- mice. Furthermore, treatment with BTZ + SRI31277 augmented the reduction in tumor burden induced by SRI31277 treatment alone. Flow cytometry and Western blot analyses demonstrated that SRI31277 treatment enhanced apoptosis, reduced Ki-67 expression as well as the activity of both canonical (SMAD2/3) and non-canonical (ERK1/2) signaling pathways of TGF-β1 in MM cells in OB-Runx2 -/- mice; and BTZ+SRI31277 treatment augmented these effects. Furthermore, TGF-β has immunosuppressive effects in MM and our data show that SRI31277 overcomes this by reducing myeloid derived suppressor cells, checkpoint, and T cell exhaustion markers and by increasing cytotoxic T cells.In conclusion, OB-Runx2 deficiency, induced by MM cells, promotes MM resistance to BTZ through the upregulation of TGF-β1 activation in the BM and TGF-β1 signaling in MM cells. Importantly, blocking TSP-1-mediated TGF-β1 activation with SRI31277 can reverse this resistance and immune dysfunction. Our findings demonstrate a novel mechanism for BTZ resistance in MM and identify a new target and strategy for overcoming immune dysregulation and chemoresistance in MM. DisclosuresMurphy-Ullrich: Millipore Sigma: Patents & Royalties.

MM-368: Foot Drop in Patients Treated with Bortezomib- A Case Series and Review of the Literature

Context Bortezomib-induced peripheral neuropathy (BIPN) has a profound impact on quality of life, which is an important issue considering the growing number of survivors in multiple myeloma (MM) and light-chain amyloidosis. BIPN is typically symmetric, distal, “stocking and glove” distribution and predominantly consists of sensory rather than motor symptoms. Motor neuropathy induced by bortezomib is uncommon and has been addressed specifically only in case reports and case series. No data has been published on foot drop in the context of bortezomib treatment. Objective Define the characteristics of foot drop associated with bortezomib treatment. Methods We identified the hospital records of 6 patients treated with bortezomib for MM or amyloidosis that developed foot drop, temporally related to bortezomib treatment. Results Six patients, 5 of whom are males, with a median age of 65 years (range 46–74), experienced foot drop. Patients were treated between 2010 and 2020. Three patients had MM, and 3 had AL amyloidosis. In four patients, the involved light chain was lambda, and in two, it was kappa. Two patients received the bortezomib intravenously, and 4 received it subcutaneously. Two patients received bortezomib at a twice-weekly schedule. Two patients did not have “classical” bortezomib peripheral neuropathy prior to the development of the foot drop. Two patients developed the foot drop in the first cycle, and 1 developed it 1 month after treatment discontinuation. One patient developed a foot drop that resolved after bortezomib was discontinued and recured when bortezomib was resumed. One patient had bilateral foot drop. Four patients reported complete resolution 1 year after treatment discontinuation, whereas two patients had gradual improvement but not complete resolution of their foot drop. Conclusions Clinicians need to be aware of the risk for “non-classical” rare neuropathies associated with bortezomib and should monitor for these toxicities and promptly discontinue bortezomib to prevent irreversible nerve damage. Other possible reasons for foot drop, such as compressions due to tumor infiltration or weight loss, should be considered.

PSMB9 Mediates Resistance to Bortezomib in Multiple Myeloma

▪Introduction: Proteasomes are the chief degradation components of the ubiquitin proteasome system (UPS) and are comprised of several (α) structural and (ß) catalytic subunits. Targeting the ß5 subunit, with agents such bortezomib (Btz, 20S proteasome inhibitor, PI) has proven highly successful in MM pts. However, resistance to Btz (Btz-R) invariably ensues with disease evolution resulting in relapse and mortality. Our data highlight that in Btz-R cells, proteasome function is upregulated with increased reliance on other ß-catalytic subunits. We have uncovered a novel association between the ß5 subunit acting in concert with the ß1i proteasome subunit, to promote resistance to Btz. We hypothesized that targeting ß5 and ß1i together would be lethal to Btz-R MM cells.Methods: CD138+ cells from MM patients, Btz-sensitive (Btz-S) MM cell lines (OPM2, KMS11 and U266) and their isogenic Btz-R subclones were used in experiments. Fluorogenic peptide substrates were used to measure ß-subunit-specific enzymatic activity. Gene disruption was conducted using 2 different shRNA hairpins for PSMB5 (ß5) and PSMB9 (ß9). Affymetrix HT12v4 gene expression array and NanoString mRNA quantification were used for gene expression profiling (GEP), followed by qPCR for confirmation. Novel dual ß5-ß1i PI were synthesized and tested in vitro. Apoptosis was determined by annexin-V/PI staining and MTS/CellTiter Glo assay used to determine cell viability.Results: Btz IC50 was noted to be 284nM in Btz-R vs. 4nM in Btz-S cells. Sanger seq. revealed no mutations in PSMB5 indicating that Btz should effectively bind the ß5 subunit. ß-subunit chymotrypic activity in Btz-R vs. Btz-S cells was significantly increased (3.5 fold, p<0.001) but remained amenable to downregulation with Btz (as well as other PI). This suggested that ß5-subunit-independent mechanisms may account for increased proteasome function and resistance to Btz. GEP analysis revealed modulation of several genes; in particular, PSMB9 (ß1i) in Btz-R vs. Btz-S MM cells. Proteomic analysis confirmed protein/enzymatic upregulation of PSMB5/ß5 in conjunction with PSMB9/ß1i in primary cells from Btz-R MM patients and Btz-R MM cell lines. Clinical significance of PSMB9 upregulation was queried using the MMRF CoMMPass database (IA10), with analysis in pts. who received either Btz+dex or Len+Dex and did not respond to treatment. PSMB9 mRNA was significantly upregulated in Btz+Dex non-responders (n=42) vs. responders (n=92), whereas in Len+Dex pts. this difference was not significant. We hypothesized that downregulation of PSMB9 would resensitize Btz-R cells to Btz and noted a significant shift in IC50 (235nM to 108nM) in Btz-R-PSMB9 shRNA transfected cells. While ß1i knockdown alone was able to reduce Btz-R cell viability by ~25%, we posited that concurrent disruption of ß1i and ß5 would significantly reduce cell viability and proliferation. Targeted GEP in dual-ß5/ß1i knockdown Btz-R cells, showed >2-fold increase in CASP8, CASP9, CASP10, CDKN2A, CDKN1A , TNFRSF10B, FOXO4 and RNF43 (apoptosis genes) and decrease in CCB1, CCNA2, WNT5A, SKP2, CDC6 and FEN1 (cell cycle genes) vs. scramble-transfected controls. Indeed, both Btz-S and Btz-R MM cells demonstrated significantly compromised growth capacity and viability (Dual knockdown ß5/ß1i Btz-R cells: 0.32 million/mL vs. scramble Btz-R cells: 1.6 million/mL) (Fig 1). This prompted us to develop novel dual-ß5 and ß1i chemical inhibitors. Using a highly modified carbamate scaffold we developed 20 cmpds that display binding affinity for both ß5 and ß1i. In vitro screening of the top 5 cmpds showed >2 fold lower EC50 in Btz-R vs. Btz-S MM cell lines. 2 cmpds in particular showed ß1i and ß5 enzymatic inhibition of >50% at 1uM and 5uM, respectively and are being further optimized.Conclusions: We have found that upregulation of PSMB9/ß1i and PSMB5/ß5 is associated with resistance to Btz. These findings were confirmed in both MM cell lines as well as in primary MM cells from Btz-R pts. Moreover, increased PSMB9 mRNA expression in non-responding Btz+Dex pts. but not Len+dex MM pts. highlights this as a resistance mechanism unique to Btz. Direct genetic disruption or with novel dual-chemical inhibitors directed toward ß1i and ß5 induced lethality in Btz-R (as well as Btz-S) MM cells. Thus, our investigations point to development of agents, which inhibit ß1i and ß5-proteasome subunits to overcome resistance to Btz. [Display omitted] DisclosuresAilawadhi:Takeda: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pharmacyclics: Research Funding; Amgen: Consultancy, Honoraria.

IL-32γ Induces M2 Macrophage Polarization with Enhanced Ability of Macrophage-Mediated Drug Resistance in Myeloma Cells through STAT3 and NF-κB Activation

Background: Macrophages(MΦs) are an abundant and important component of multiple myeloma (MM) microenvironment, and support the survival of MM cells and promote their resistance to chemotherapy. It has been proposed that MΦs have great plasticity and can differentiate into 2 major polarized states, M1 (“classically activated”) and M2 (“alternatively activated”). M1 macrophages are considered to be anti-tumoural and pro-inflammatory, whereas M2 macrophages are characterized by efficient activity of tumour promotion and suppression of adaptive immunity.IL-32, a novel proinflammatory cytokine, has been found to play a crucial role in a variety of inflammatory diseases and cancers. In this study, we investigated the immunomodulatory effects and underlying mechanisms of IL-32γ on macrophage polarization and MΦ-mediated drug resistance in myeloma cells.Results: First, we found that both bone marrow supernatant and peripheral blood supernatant of MM patients showed significantly higher levels of IL-32 as compared with those of healthy controls. We also detected IL-32 in MM cell lines and M-CSF-induced MØs by qRT-PCR and Western blot, which showed that IL-32 expression was higher in MM cell lines than in MØs. We next investigated the polarization profiles and functional activities of IL-32γ-treated MØs. After stimulated with recombinant IL-32γ,MØs exhibited upregulated expression of cell-surface molecules and cytokines associated with M2 polarization(CD206,Dectin-1, and IL-10), while M1-polarizing marker(CD86) were down-regulated.Further, Western blot was applied to detect the inflammation molecular pathway in MØs, which showed that IL-32γ treatment activated the JAK-STAT3 pathway and NF-κB pathway. This pro-M2MØ polarization effect of IL-32γ was inhibited by the addition of specific inhibitors of STAT3 and NF-kB. Moreover, co-culture experiments revealed that IL-32γ-educated MØs provided a survival benefit to myeloma cells, as tested with several anti-myeloma agents including bortezomib and doxorubicin. The pro-survival effect was associated with less cleavage of caspase-3 and PARP in myeloma cells, and thus less apoptosis. The STAT3 and NF-κB inhibitors partially inhibited the observed IL-32γ-induced and MØs -mediated resistance to bortezomib in MM cells.Conclusions:IL-32γ could effectively induce the polarization of M2 MØs, leading to enhanced MØ-mediated drug resistance in myeloma cells as the result of activating the JAK-STAT3 and NF-κB pathways in MØs. DisclosuresNo relevant conflicts of interest to declare.

Gambogenic Acid Enhances Chemosensitivity of Multiple Myeloma to Bortezomib through p53/ROS/p38 MAPK Apoptotic Pathway

Background: Multiple myeloma (MM) is the second most prevalent hematological cancer (10%) with a five-year survival rate of only 49%. Approval of bortezomib, the first in-class proteasome inhibitor, has significantly improved outcomes of MM in the last few years; however, the almost inevitable refractory or resistance has made a cure of MM remains out of reach. Identification and validation of novel effective targeted agents are necessary. As one of the natural compounds isolated from Traditional Chinese Medicine gamboge, gambogenic acid (GNA) is a very promising antitumor agent and has been proved to have more potent anticancer effect and less systemic toxicity according to early investigations. In our previous studies, we have demonstrated that GNA could synergistically potentiate bortezomib-induced apoptosis of MM. In this study, our aim was to further explore and understand the concrete apoptotic action mechanism of GNA and bortezomib combination treatment against MM in pre-clinical models.Methods: We performed pre-clinical studies in myeloma cell lines and mouse models treated by GNA and bortezomib, alone and in combination. Cell counting kit-8 (CCK-8) assay, combination index (CI) isobologram, flow cytometry (FCM), western blot, xenograft tumor models, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), immunohistochemistry (IHC) and oxidation-sensitive fluorescent dye carboxy-DCFDA were applied in this study. The thiol antioxidant N-acetylcysteine (NAC) and p38 MAPK inhibitor SB203580 were used to detect the effect of GNA and bortezomib combination therapy on ROS, p53 and p38 MAPK.Results: Both p53 wild type cell line MM.1S and mutant type cell line RPMI 8226 myeloma cell lines were sensitive to GNA therapy. Interestingly, GNA only enhanced the chemosensitivity of bortezomib on p53 wild type cell line MM.1S. Both 0.51μM GNA combined with 2.3nM bortezomib and 0.90μM GNA combined with 4.0nM bortezomib to MM.1S cells showed a more markedly apoptotic rate of MM compared with that of the single agent group of each accordingly (p <0.01; p <0.01), and the apoptosis was presented in a dosage- and time-dependent manner. Increased apoptosis of MM.1S cells was found via the activation of PARP cleavage, p53, Caspase-3 cleavage and Bax and inhibition of Bcl-2 expression. An increased antitumor effect of combination therapy of GNA and bortezomib on MM.1S xenograft models were also observed. A significant generation of ROS was detected after exposure of GNA and bortezomib in MM.1S cells. The expression level of phospho-p38MAPK was upregulated by combination therapy compared with that of single agent (p<0.05; p<0.05). To characterize the mechanisms of action of GNA in combination with bortezomib, we pretreated MM.1S cells with NAC and SB203580. We found that the apoptosis of MM.1S cells could be inhibited by both NAC and SB203580 (p<0.01; p<0.01). However, the generation of ROS could only be inhibited by NAC (p<0.05), and the elevated expression of p53 could be inhibited neither by NAC nor SB203580. These results indicated that p53/ROS/p38 MAPK pathway is a pre-requisite for GNA to accomplish the enhancement of chemosensitivity of MM to bortezomib.Conclusions: We demonstrate that GNA could potentiate apoptosis of MM induced by bortezomib in vivo and in vitro, and p53/ROS/p38 MAPK pathway plays a central role of the apoptotic action. Thus, our data provide a persuasive rationale for the successful utilization of dual GNA and bortezomib for chemotherapy in MM patients in the future. DisclosuresNo relevant conflicts of interest to declare.

Machine Learning Applicability for Classification of PAD/VCD Chemotherapy Response Using 53 Multiple Myeloma RNA Sequencing Profiles.

Multiple myeloma (MM) affects ~500,000 people and results in ~100,000 deaths annually, being currently considered treatable but incurable. There are several MM chemotherapy treatment regimens, among which eleven include bortezomib, a proteasome-targeted drug. MM patients respond differently to bortezomib, and new prognostic biomarkers are needed to personalize treatments. However, there is a shortage of clinically annotated MM molecular data that could be used to establish novel molecular diagnostics. We report new RNA sequencing profiles for 53 MM patients annotated with responses on two similar chemotherapy regimens: bortezomib, doxorubicin, dexamethasone (PAD), and bortezomib, cyclophosphamide, dexamethasone (VCD), or with responses to their combinations. Fourteen patients received both PAD and VCD; six received only PAD, and 33 received only VCD. We compared profiles for the good and poor responders and found five genes commonly regulated here and in the previous datasets for other bortezomib regimens (all upregulated in the good responders): FGFR3, MAF, IGHA2, IGHV1-69, and GRB14. Four of these genes are linked with known immunoglobulin locus rearrangements. We then used five machine learning (ML) methods to build a classifier distinguishing good and poor responders for two cohorts: PAD + VCD (53 patients), and separately VCD (47 patients). We showed that the application of FloWPS dynamic data trimming was beneficial for all ML methods tested in both cohorts, and also in the previous MM bortezomib datasets. However, the ML models build for the different datasets did not allow cross-transferring, which can be due to different treatment regimens, experimental profiling methods, and MM heterogeneity.

The value of survival gains from therapeutic innovations for US patients with relapsed/refractory multiple myeloma.

Aims:This study quantifies the value of survival gains attributable to novel treatments approved since 2003 for United States (US) patients with relapsed/refractory multiple myeloma (RRMM).Methods:We estimated the increase in survival attributable to lenalidomide and bortezomib for multiple myeloma (MM) patients in the 1983–2013 Surveillance, Epidemiology, and End Results (SEER) registry. To estimate the survival benefit of treatments approved since 2015 (carfilzomib, elotuzomab, daratumumab, used in combination with lenalidomide and dexamethasone) we used clinical trial data to calibrate survival estimated using the SEER data. We then conducted an economic valuation of the estimated shift in survival curves for all therapies. Finally, we estimated the share of the value accruing to patients and manufacturers using treatment costs estimated from MarketScan data.Results:The introduction of bortezomib in combination with dexamethasone (Vd) and lenalidomide in combination with dexamethasone (Rd) resulted in substantial survival gains and societal value for multiple myeloma patients, generating 1.7 additional life-years per RRMM patient. More recently, approved novel treatments have improved survival over effective treatments (i.e. Rd/Vd) by an additional 2.5 life-years – the monetary value of this incremental survival benefit far exceeds the incremental cost of treatment. At the patient level, the incremental benefit of Rd/Vd is $335,500 and with novel treatments is $565,000. Applying this benefit to all future cohorts of US RRMM patients translates into a value of at least $75 billion and $130 billion with Rd/Vd and the novel treatments, respectively.Conclusions:SEER registry data were only available through 2013. Therefore, survival gains for recently approved treatments were estimated based on clinical trials, rather than observed survival. Our valuation analysis does not capture sources of value aside from survival gains, for example, better quality of life, increased productivity, or the value of surviving until subsequent novel therapies become available. Substantial extensions in life expectancy in RRMM since 2003 translate into real economic value gained by society.

Newly Diagnosed Childhood AML Patients Treated with Bortezomib Show Superior Survival If CD74 Is Expressed: A Report of 991 Patients from the Children's Oncology Group AAML1031 Protocol

Introduction: CD74 is a type II transmembrane protein expressed on antigen-presenting cells and an MHC class II chaperone. It has been associated with tumor progression and metastasis in solid tumors, and its expression has been suggested to serve as a prognostic factor in many cancers, with higher relative expression associated with oncogenesis. As the expression of CD74 has been associated with response to bortezomib in multiple myeloma, we inquired whether such correlation might be seen in pediatric AML. We prospectively evaluated CD74 expression by difference from normal (ΔN) flow cytometry and correlated expression with clinical characteristics and outcome as part of Children's Oncology Group protocol AAML1031 that randomized patients younger than 30 years of age with de novo AML to standard treatment with (Arm B) or without (Arm A) bortezomib. The addition of bortezomib to standard chemotherapy increased toxicity but did not improve survival. Given the association of CD74 with B-lymphoid neoplasms and bortezomib's known efficacy in B-cell neoplasms and multiple myeloma, we hypothesized that within Arm B, the patients with CD74 expression would have a more favorable outcome. Methods: In total, 1,139 newly diagnosed pediatric patients with de novo AML were randomized to standard chemotherapy (n=561, Arm A) or standard chemotherapy with bortezomib (n=578, Arm B). All patients received the identical chemotherapy backbone with either four intensive chemotherapy courses or three courses followed by allogeneic hematopoietic stem cell transplantation for high-risk patients. To qualify for this correlative study, 991 patients satisfied 2 criteria: (1) submitting a bone marrow aspirate for ΔN at diagnosis and (2) providing consent for correlative biology studies. All diagnostic specimens were centrally and prospectively evaluated for the expression of CD74 by ΔN. AML was considered to be CD74-positive if the MFI was more than two times above background autofluorescence and more than 40% of the leukemia was above background autofluorescence. Results: Among 991 patients, 263 were CD74-positive (26.5%) by ΔN, with similar prevalence in Arm A (27.9%) and Arm B (25.2%). Correlation of CD74 expression with clinical characteristics showed that those with CD74 expression had higher median age (p&amp;lt;0.001), lower median WBC (p&amp;lt;0.001), higher prevalence of low risk protocol status (p=0.039), lower frequency of CEBPA mutation (p=0.039), inv(16) (p=0.001), and KMT2A rearrangements (p=0.002), and were enriched for t(8;21) (p&amp;lt;0.001) and t(6;9) (p=0.014) fusions. All these features retained significance when patients were sub analyzed by respective treatment arms. CD74-positive patients had a higher morphologic CR rate (p=0.016), however, measurable residual disease by flow cytometry was not significant in the entire cohort or in the sub analysis of treatment arms (p=0.155). CD74-positive patients showed superior 5-year OS (70.6% vs 61.8%, p=0.003) and EFS survival (51.2% vs 43.1%, p=0.007) compared to those who were CD74-negative. For patients in Arm A (no bortezomib), the differences in OS (66.1% vs 61.0%, p=0.138) and EFS (48.9% vs 41.7% p=0.088) were not significant between those that were CD74-positive and those that were CD74-negative (Figure 1). However, patients in Arm B receiving bortezomib that were CD74-positive showed a significant improvement in OS (75.3% vs 62.5%, p=0.006) and EFS (53.6% vs 44.3%, p=0.028) compared to those who were CD74-negative (Figure 1). Comparison of the outcomes for CD74-positive patients with and without bortezomib exposure showed a difference in OS of 66.1% vs. 75.3% for those in Arm A vs. Arm B but did not reach significance (p=0.155). Multivariable analysis for OS yielded a hazard ratio of 0.67 (95% CI: 0.44 - 1.02) and p=0.061, approaching, but not reaching, statistical significance. Conclusions: These data demonstrate that CD74 expression is associated with more favorable disease characteristics and survival. Patients receiving bortezomib that were CD74-positive showed a superior response to therapy compared to patients who did not express CD74, by both OS and EFS, suggesting that CD74-positive childhood AML patients stand to benefit from bortezomib therapy. Bortezomib may induce a mechanistic response in CD74-positive AMLs similar to that in bortezomib-treated B-cell neoplasms and/or multiple myeloma, where bortezomib has proven to be beneficial. Disclosures Cooper: Celgene: Other: Spouse was an employee of Celgene (through August 2019). Pollard:Syndax Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees.

Non-Hematologic Toxicity of Bortezomib in Multiple Myeloma: The Neuromuscular and Cardiovascular Adverse Effects.

Simple SummaryMultiple myeloma (MM) is a still uncurable tumor of mainly elderly patients originating from the terminally differentiated B cells. Introduction to the treatment of MM patients of a new class of drugs called proteasome inhibitors (bortezomib followed by carfilzomib and ixazomib) significantly improved disease control. Proteasome inhibitors interfere with the major mechanism of protein degradation in a cell leading to the severe imbalance in the protein turnover that is deadly to MM cells. Currently, these drugs are the mainstream of MM therapy but are also associated with an increased rate of the injuries to multiple organs and tissues. In this review, we summarize the current knowledge on the molecular mechanisms of the first-in-class proteasome inhibitor bortezomib-induced disturbances in the function of peripheral nerves and cardiac and skeletal muscle.The overall approach to the treatment of multiple myeloma (MM) has undergone several changes during the past decade. and proteasome inhibitors (PIs) including bortezomib, carfilzomib, and ixazomib have considerably improved the outcomes in affected patients. The first-in-class selective PI bortezomib has been initially approved for the refractory forms of the disease but has now become, in combination with other drugs, the backbone of the frontline therapy for newly diagnosed MM patients, as well as in the maintenance therapy and relapsed/refractory setting. Despite being among the most widely used and highly effective agents for MM, bortezomib can induce adverse events that potentially lead to early discontinuation of the therapy with negative effects on the quality of life and outcome of the patients. Although peripheral neuropathy and myelosuppression have been recognized as the most relevant bortezomib-related adverse effects, cardiac and skeletal muscle toxicities are relatively common in MM treated patients, but they have received much less attention. Here we review the neuromuscular and cardiovascular side effects of bortezomib. focusing on the molecular mechanisms underlying its toxicity. We also discuss our preliminary data on the effects of bortezomib on skeletal muscle tissue in mice receiving the drug.

Upregulated expression and function of the α4β1 integrin in multiple myeloma cells resistant to bortezomib.

The interaction of multiple myeloma (MM) cells with the bone marrow (BM) microenvironment promotes MM cell retention, survival, and resistance to different anti-MM agents, including proteasome inhibitors (PIs) such as bortezomib (BTZ). The α4β1 integrin is a main adhesion receptor mediating MM cell-stroma interactions and MM cell survival, and its expression and function are downregulated by BTZ, leading to inhibition of cell adhesion-mediated drug resistance (CAM-DR) and MM cell apoptosis. Whether decreased α4β1 expression and activity are maintained or recovered upon development of resistance to BTZ represents an important question, as a potential rescue of α4β1 function could boost MM cell survival and disease progression. Using BTZ-resistant MM cells, we found that they not only rescue their α4β1 expression, but its levels were higher than in parental cells. Increased α4β1 expression in resistant cells correlated with enhanced α4β1-mediated cell lodging in the BM, and with disease progression. BTZ-resistant MM cells displayed enhanced NF-κB pathway activation relative to parental counterparts, which contributed to upregulated α4 expression and to α4β1-dependent MM cell adhesion. These data emphasize the upregulation of α4β1 expression and function as a key event during resistance to BTZ in MM, which might indirectly contribute to stabilize this resistance, as stronger MM cell attachment to BM stroma will regain CAM-DR and MM cell growth and survival. Finally, we found a strong correlation between high ITGB1 (integrin β1) expression in MM and poor progression-free survival (PFS) and overall survival (OS) during treatment of MM patients with BTZ and IMIDs, and combination of high ITGB1 levels and presence of the high-risk genetic factor amp1q causes low PFS and OS. These results unravel a novel prognostic value for ITGB1 in myeloma. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.