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Purpose:The prognosis of patients with multiple myeloma who are resistant to proteasome inhibitors, immunomodulatory drugs (IMiD), and daratumumab is extremely poor. Even B-cell maturation antigen–specific chimeric antigen receptor T-cell therapies provide only a temporary benefit before patients succumb to their disease. In this article, we interrogate the unique sensitivity of multiple myeloma cells to the alternative strategy of blocking protein translation with omacetaxine.Experimental Design:We determined protein translation levels (n = 17) and sensitivity to omacetaxine (n = 51) of primary multiple myeloma patient samples. Synergy was evaluated between omacetaxine and IMiDs in vitro, ex vivo, and in vivo. Underlying mechanism was investigated via proteomic analysis.Results:Almost universally, primary patient multiple myeloma cells exhibit >2.5-fold increased rates of protein translation compared with normal marrow cells. Ex vivo treatment with omacetaxine resulted in >50% reduction in viable multiple myeloma cells. In this cohort, high levels of translation serve as a biomarker for patient multiple myeloma cell sensitivity to omacetaxine. Unexpectedly, omacetaxine demonstrated synergy with IMiDs in multiple myeloma cell lines in vitro. In addition, in an IMiD-resistant relapsed patient sample, omacetaxine/IMiD combination treatment resensitized the multiple myeloma cells to the IMiD. Proteomic analysis found that the omacetaxine/IMiD combination treatment produced a double-hit on the IRF4/c-MYC pathway, which is critical to multiple myeloma survival.Conclusions:Overall, protein translation inhibitors represent a potential new drug class for myeloma treatment and provide a rationale for conducting clinical trials with omacetaxine alone and in combination with IMiDs for patients with relapsed/refractory multiple myeloma.

Purpose:New therapies have changed the outlook for patients with multiple myeloma, but novel agents are needed for patients who are refractory or relapsed on currently approved drug classes. Novel targets other than CD38 and BCMA are needed for new immunotherapy development, as resistance to daratumumab and emerging anti-BCMA approaches appears inevitable. One potential target of interest in myeloma is ICAM1. Naked anti-ICAM1 antibodies were active in preclinical models of myeloma and safe in patients, but showed limited clinical efficacy. Here, we sought to achieve improved targeting of multiple myeloma with an anti-ICAM1 antibody–drug conjugate (ADC).Experimental Design:Our anti-ICAM1 human mAb was conjugated to an auristatin derivative, and tested against multiple myeloma cell lines in vitro, orthotopic xenografts in vivo, and patient samples ex vivo. The expression of ICAM1 was also measured by quantitative flow cytometry in patients spanning from diagnosis to the daratumumab-refractory state.Results:The anti-ICAM1 ADC displayed potent anti-myeloma cytotoxicity in vitro and in vivo. In addition, we have verified that ICAM1 is highly expressed on myeloma cells and shown that its expression is further accentuated by the presence of bone marrow microenvironmental factors. In primary samples, ICAM1 is differentially overexpressed on multiple myeloma cells compared with normal cells, including daratumumab-refractory patients with decreased CD38. In addition, ICAM1-ADC showed selective cytotoxicity in multiple myeloma primary samples.Conclusions:We propose that anti-ICAM1 ADC should be further studied for toxicity, and if safe, tested for clinical efficacy in patients with relapsed or refractory multiple myeloma.

Supplementary Tables and Figures

Defects in the pancreatic β-cell’s secretion system are well-described in type 2 diabetes (T2D) and include impaired proinsulin processing and a deficit in mature insulin-containing secretory granules; however, the cellular mechanisms underlying these defects remain poorly understood. To address this, we used an in situ fluorescent pulse-chase strategy to study proinsulin trafficking. We show that insulin granule formation and the appearance of nascent granules at the plasma membrane are decreased in rodent and cell culture models of prediabetes and hyperglycemia. Moreover, we link the defect in insulin granule formation to an early trafficking delay in endoplasmic reticulum (ER) export of proinsulin, which is independent of overt ER stress. Using a ratiometric redox sensor, we show that the ER becomes hyperoxidized in β-cells from a dietary model of rodent prediabetes and that addition of reducing equivalents restores ER export of proinsulin and insulin granule formation and partially restores β-cell function. Together, these data identify a critical role for the regulation of ER redox homeostasis in proinsulin trafficking and suggest that alterations in ER redox poise directly contribute to the decline in insulin granule production in T2D. This model highlights a critical link between alterations in ER redox and ER function with defects in proinsulin trafficking in T2D. Hyperoxidation of the ER lumen, shown as hydrogen peroxide, impairs proinsulin folding and disulfide bond formation that prevents efficient exit of proinsulin from the ER to the Golgi. This trafficking defect limits available proinsulin for the formation of insulin secretory granules during the development of T2D.

Insulin is synthesized by pancreatic β-cells and stored into secretory granules (SGs). SGs fuse with the plasma membrane in response to a stimulus and deliver insulin to the bloodstream. The mechanism of how proinsulin and its processing enzymes are sorted and targeted from the trans-Golgi network (TGN) to SGs remains mysterious. No cargo receptor for proinsulin has been identified. Here, we show that chromogranin (CG) proteins undergo liquid–liquid phase separation (LLPS) at a mildly acidic pH in the lumen of the TGN, and recruit clients like proinsulin to the condensates. Client selectivity is sequence-independent but based on the concentration of the client molecules in the TGN. We propose that the TGN provides the milieu for converting CGs into a “cargo sponge” leading to partitioning of client molecules, thus facilitating receptor-independent client sorting. These findings provide a new receptor-independent sorting model in β-cells and many other cell types and therefore represent an innovation in the field of membrane trafficking.

Purpose: New therapies have changed the outlook for patients with multiple myeloma, but novel agents are needed for patients who are refractory or relapsed on currently approved drug classes. Novel targets other than CD38 and BCMA are needed for new immunotherapy development, as resistance to daratumumab and emerging anti-BCMA approaches appears inevitable. One potential target of interest in myeloma is ICAM1. Naked anti-ICAM1 antibodies were active in preclinical models of myeloma and safe in patients, but showed limited clinical efficacy. Here, we sought to achieve improved targeting of multiple myeloma with an anti-ICAM1 antibody–drug conjugate (ADC). Experimental Design: Our anti-ICAM1 human mAb was conjugated to an auristatin derivative, and tested against multiple myeloma cell lines in vitro, orthotopic xenografts in vivo, and patient samples ex vivo. The expression of ICAM1 was also measured by quantitative flow cytometry in patients spanning from diagnosis to the daratumumab-refractory state. Results: The anti-ICAM1 ADC displayed potent anti-myeloma cytotoxicity in vitro and in vivo. In addition, we have verified that ICAM1 is highly expressed on myeloma cells and shown that its expression is further accentuated by the presence of bone marrow microenvironmental factors. In primary samples, ICAM1 is differentially overexpressed on multiple myeloma cells compared with normal cells, including daratumumab-refractory patients with decreased CD38. In addition, ICAM1-ADC showed selective cytotoxicity in multiple myeloma primary samples. Conclusions: We propose that anti-ICAM1 ADC should be further studied for toxicity, and if safe, tested for clinical efficacy in patients with relapsed or refractory multiple myeloma.

Insulin is a key regulator of human metabolism, and its dysfunction leads to diseases such as type 2 diabetes. It remains unknown how proinsulin is targeted from the trans-Golgi network (TGN) to secretory storage granules as no cargo receptor has been identified. Chromogranin proteins (CGs) are central regulators of granule biosynthesis, and it was proposed that their aggregation is critical for this process. However, the molecular mechanism by which these molecules facilitate sorting at the TGN is poorly understood. Here, we show that CGs undergo liquid–liquid phase separation (LLPS) at low pH independently of divalent cations, such as calcium. Liquid CG condensates, but not aggregates, recruit and sort proinsulin and other granule-destined cargo molecules towards secretory granules. Cargo selectivity is independent of sequence or structural elements but is based on the size and concentration of the client molecules at the TGN. Finally, electrostatic interactions and the N-terminal intrinsically disordered domain of chromogranin B facilitate LLPS and are critical for granule formation. We propose that phase-separated CGs act as a “cargo sponge” within the TGN lumen, gathering soluble client proteins into the condensate independently of specific sequence or structural elements, facilitating receptor-independent sorting. These findings challenge the canonical TGN sorting models and provide insights into granule biosynthesis in insulin-secreting β-cells.One sentence summaryLiquid Chromogranin condensates recruit cargo molecules at the TGN for their delivery to secretory storage granules.

Defects in the {beta}-cells secretion system are well-described in Type 2 diabetes (T2D), including reduced insulin storage and impaired proinsulin processing; however, the cellular mechanisms underlying these secretory defects and the contribution of chronic hyperglycemia to this process remain poorly understood. In this study, we provide evidence that oxidative protein folding in the endoplasmic reticulum (ER) is perturbed in models of {beta}-cell dysfunction, leading to delays in proinsulin trafficking and insulin granule formation. Using an in situ fluorescent pulse-chase labeling strategy and APEX2-based proximity labeling, we demonstrate that enriched interactions of proinsulin with ER oxidoreductases coincides with a delay in proinsulin ER export. Furthermore, our data show that proinsulin ER export can be regulated by metabolically derived NADPH and reducing equivalent (glutathione) availability. Together, these data highlight an emerging role for nutrient metabolism and mitochondrial dysfunction in the maladaptive remodeling of the {beta}-cells secretory pathway during the decline of {beta}-cell function in T2D.

There is urgent need for new drug regimens that more rapidly cure tuberculosis (TB). Existing TB drugs and regimens vary in treatment-shortening activity, but the molecular basis of these differences is unclear, and no existing assay directly quantifies the ability of a drug or regimen to shorten treatment. Here, we show that drugs historically classified as sterilizing and non-sterilizing have distinct impacts on a fundamental aspect of Mycobacterium tuberculosis physiology: ribosomal RNA (rRNA) synthesis. In culture, in mice, and in human studies, measurement of precursor rRNA reveals that sterilizing drugs and highly effective drug regimens profoundly suppress M. tuberculosis rRNA synthesis, whereas non-sterilizing drugs and weaker regimens do not. The rRNA synthesis ratio provides a readout of drug effect that is orthogonal to traditional measures of bacterial burden. We propose that this metric of drug activity may accelerate the development of shorter TB regimens., It is unclear why different antibiotics vary in their ability to shorten treatment of tuberculosis. Here, the authors show that a measure based on ribosomal RNA synthesis in Mycobacterium tuberculosis correlates with treatment shortening in culture, in mice and in human studies.

Purpose:The prognosis of patients with multiple myeloma who are resistant to proteasome inhibitors, immunomodulatory drugs (IMiD), and daratumumab is extremely poor. Even B-cell maturation antigen–specific chimeric antigen receptor T-cell therapies provide only a temporary benefit before patients succumb to their disease. In this article, we interrogate the unique sensitivity of multiple myeloma cells to the alternative strategy of blocking protein translation with omacetaxine.Experimental Design:We determined protein translation levels (n = 17) and sensitivity to omacetaxine (n = 51) of primary multiple myeloma patient samples. Synergy was evaluated between omacetaxine and IMiDs in vitro, ex vivo, and in vivo. Underlying mechanism was investigated via proteomic analysis.Results:Almost universally, primary patient multiple myeloma cells exhibit >2.5-fold increased rates of protein translation compared with normal marrow cells. Ex vivo treatment with omacetaxine resulted in >50% reduction in viable multiple myeloma cells. In this cohort, high levels of translation serve as a biomarker for patient multiple myeloma cell sensitivity to omacetaxine. Unexpectedly, omacetaxine demonstrated synergy with IMiDs in multiple myeloma cell lines in vitro. In addition, in an IMiD-resistant relapsed patient sample, omacetaxine/IMiD combination treatment resensitized the multiple myeloma cells to the IMiD. Proteomic analysis found that the omacetaxine/IMiD combination treatment produced a double-hit on the IRF4/c-MYC pathway, which is critical to multiple myeloma survival.Conclusions:Overall, protein translation inhibitors represent a potential new drug class for myeloma treatment and provide a rationale for conducting clinical trials with omacetaxine alone and in combination with IMiDs for patients with relapsed/refractory multiple myeloma.

Chromogranin B (CgB, also known as CHGB) is abundantly expressed in dense core secretory granules of multiple endocrine tissues and has been suggested to regulate granule biogenesis in some cell types, including the pancreatic islet β-cell, though the mechanisms are poorly understood. Here, we demonstrate a critical role for CgB in regulating secretory granule trafficking in the β-cell. Loss of CgB impairs glucose-stimulated insulin secretion, impedes proinsulin processing to yield increased proinsulin content, and alters the density of insulin-containing granules. Using an in situ fluorescent pulse-chase strategy to track nascent proinsulin, we show that loss of CgB impairs Golgi budding of proinsulin-containing secretory granules, resulting in a substantial delay in trafficking of nascent granules to the plasma membrane with an overall decrease in total plasma membrane-associated granules. These studies demonstrate that CgB is necessary for efficient trafficking of secretory proteins into the budding granule, which impacts the availability of insulin-containing secretory granules for exocytic release. This article has an associated First Person interview with the first author of the paper.

Introduction: The prognosis of patients with multiple myeloma (MM) who are resistant to proteasome inhibitors (PIs) and immunomodulatory drugs (IMiDs) is extremely poor. Even daratumumab and BCMA CAR-T cell therapies appear to provide only temporary benefit before patients eventually succumb to their disease. We show that protein translation is upregulated in MM cells. We also demonstrate that translational inhibition with omacetaxine (Oma) is specifically cytotoxic in a manner that is preserved in MM cells from PI/IMiD resistant patients. Furthermore, protein translation inhibition is synergistic with IMiDs, even in IMiD refractory patients. We hypothesize these findings stem from the origin of MM cells as professional antibody secretory cells, with highly active protein translation fundamental to their biology. Here, we show these findings and provide support to test the translation inhibitor omacetaxine with a clinical trial in multiple myeloma patients. Methods: Primary MM cells in mononuclear cell (MNC) cultures were assayed ex vivo for Oma effect at 48-hrs by high-throughput flow cytometry using our myeloma drug sensitivity testing (My-DST) platform. Protein synthesis rates were measured via flow cytometry using the Cayman OP-puromycin assay. Initial drug combination matrices were performed in MM cell lines via MTS assay after 96-hr incubation. Cell line xenograft study of the Oma and IMiD combination in vivo were performed using an orthometastatic MM model with MM1.S luciferase-expressing cells injected IV in NSG mice. Vehicle control, Oma, pomalidomide (Pom) and the combination were dosed 5 days/week by IP injection beginning on day 30. Disease burden was monitored with imaging of luciferase bioluminescence. Results: Oma had specific cytotoxicity across 5 MM cell lines (EC50 = 15-35 nM, data not shown). Oma also showed MM cell specific cytotoxicity in patient samples with EC50 ranging from 25-100 nM (Fig 1A). Ex vivo treatment with 50 nM Oma for 48 hrs caused >50% reduction in viable MM cells in 39/50 (78%) patient samples. Importantly, 50 nM Oma retained activity in PI/IMiD-refractory patients compared to sensitive patients (64.2% vs 71.6% mean decrease in MM cell viability, respectively, P = 0.44, Fig 1B). Primary MM cells exhibited significantly higher levels of baseline protein translation than other bone marrow MNCs with mean 3.9-fold increase (n = 14, P = Conclusion: Protein translation inhibitors represent a potential new drug class for clinical myeloma treatment. We have shown that the protein synthesis inhibitor omacetaxine possesses a potent and specific killing effect against MM cells. Importantly, this anti-myeloma cytotoxicity was equally active in biopsy samples obtained from patients at diagnosis and patients with disease advanced to the late stage of PI/IMiD resistance. The pretreatment level of MM cell protein translation may serve as a biomarker for clinical response. In further exploration of the optimized treatment approach for clinical trials, we found synergy between omacetaxine and pomalidomide in vitro, in vivo and using patient samples ex vivo. A phase I clinical trial of omacetaxine single agent and in combination with pomalidomide is currently in development at the University of Colorado. Disclosures Mark: Janssen: Honoraria; Takeda: Honoraria; Amgen: Honoraria; Celgene: Honoraria.