Identification of Novel Regulatory Pathway for Immunoglobulin Production Provides Rational Treatment for Bortezomib-Resistant Multiple Myeloma Patients

Introduction Monoclonal immunoglobulin (Ig) is a valuable diagnostic marker in patients with multiple myeloma (MM). An inevitable consequence of extensive Ig synthesis is overload of misfolded proteins that saturate proteasome capacity making the myeloma cells highly sensitive to proteasome inhibitors (PI). Even though PI are regularly used in the clinic, resistance often emerges leaving clinicians with limited treatment options. Therefore, there is a need for a robust marker selecting MM patients for precise PI-based combination therapy. Methods We performed a multiple database search for genes associated with Ig production and MM patients' survival. Additionally, we compared gene expression profiles (RNAseq) of primary MM cells with low and high Ig levels. Next, we validated the identified hits by shRNA knockdown and overexpression studies using myeloma cell lines, primary MM samples, and mouse models. We also applied mass spectrometry-based proteomic analysis, advanced biochemical approaches, and genetic models to reveal the Ig production pathway components and function. Finally, we performed a limited rational drug screening to select suitable compounds for combination treatment. Results RNAseq and database mining revealed a strong association between the expression of plasma cell-specific deubiquitinase OTUD1, Ig production, and MM patient survival. Suppression of OTUD1 with shRNAs in RPMI8226 and MM1.S cell lines reduced Ig levels, increased proliferation, and induced bortezomib resistance. Conversely, inducible OTUD1 overexpression enhanced Ig production, slowed down proliferation, and increased bortezomib sensitivity. In the xenografts mouse models cells with high OTUD1 levels synthesized more Ig and developed smaller tumors. Intriguingly, the transcription of Ig genes was not influenced by OTUD1 expression suggesting that OTUD1 functions as a posttranslational regulator of Ig assembly. To gain mechanistic insight into the Ig pathway regulation by OTUD1, we utilized the biotin proximity labeling method (Turbo-ID) combined with mass spectrometry analysis. We found several novel OTUD1 interaction partners including the E3 ubiquitin ligase KEAP1 and endoplasmic reticulum (ER) redox protein PRDX4. We demonstrated that KEAP1 acts upstream of OTUD1 by regulating OTUD1 ubiquitination and stability. Consistently, survival analysis revealed that MM patients with high KEAP1 expression (low OTUD1) had a worse prognosis than patients with low levels of KEAP1 (high OTUD1). PRDX4 regulates disulfite bonds formation during protein folding and is uniquely expressed in fully differentiated plasma cells. Here, we revealed that OTUD1 specifically deubiquitinates and thus stabilizes PRDX4 inside the ER. Additionally, we performed rescue genetic experiments and found a direct link between the OTUD1-PRDX4 axis and Ig production. The increase in OTUD1 expression (high Ig) led to a dramatic increase in the total pool of ubiquitinated proteins formed mainly by misfolded Ig, while OTUD1 knockdown (low Ig) had an opposite effect. We showed that changes in the level of ubiquitinated proteins correlated with PI sensitivity. Of note, OTUD1 did not affect the expression of proteasome subunits, either their enzymatic activity. Our mechanistic findings prompted us to propose a novel therapeutic opportunity in PI resistant MM patients. We hypothesize that the resensitization of Ig low MM cells to PI could be achieved by enhancing ER stress leading to an increase in misfolded proteins that would ultimately saturate proteasomes. Indeed, from clinically relevant drugs tested so far, the HSP-90 inhibitor (17-AAG) reverted the PI resistance in OTUD1 low (Ig low) myeloma cells. An in vivo validation of the combination treatment and testing of Ig involvement in PI sensitivity and proliferation of MM cells is ongoing. Conclusion Here we present the discovery of a novel regulatory mechanism for Ig production in plasma cells. Based on our results and previously published studies, we conclude that Ig synthesis is a clinically significant factor related to PI response and MM patient survival. Our findings suggest that the intracellular Ig level is an important biomarker to identify patients benefiting the most from PI-based therapies. Finally, we provide a rational solution for selective, combination therapy to overcome PI resistance in MM patients with a decreased capacity to synthesize Ig. Figure Disclosures Hajek: Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Consultancy, Honoraria; PharmaMar: Consultancy, Honoraria; Oncopeptides: Consultancy.

The association of intrathecal immunoglobulin synthesis and cortical lesions predicts disease activity in clinically isolated syndrome and early relapsing–remitting multiple sclerosis

Background: The intrathecal production of immunoglobulin (Ig) is a major biological feature of multiple sclerosis (MS), and immunopathological studies have suggested a primary role of the humoral immune response in causing irreversible brain damage. Objective: To evaluate whether, in the early phases of MS, intrathecal Ig synthesis correlates with the presence of cortical lesions (CLs), and if their association could predict the clinical course of the disease. Methods: Eighty-six patients presenting with symptoms and signs suggestive of MS underwent a diagnostic work-up that included magnetic resonance imaging and cerebrospinal fluid examination. The risk ratios (RR) for conversion to MS and for a new disease activity were calculated. Results: Patients with clinically isolated syndromes (CIS) having CLs and intrathecal synthesis of Ig had the highest risk of conversion to MS (RR = 3.4; Wald 95% CI = 1.7–7.0, p < 0.001) whereas CIS patients without CLs and intrathecal synthesis of Ig had the lowest risk of conversion to MS (RR = 0.1, Wald 95% CI = 0.02–0.7, p < 0.001). The highest risk of having disease-related activity during the follow-up was observed in CIS and relapsing–remitting MS patients showing CLs and intrathecal Ig synthesis (RR = 2.1; Wald 95% CI = 1.5–3.1, p < 0.001) while the lowest in CIS and relapsing–remitting MS patients without CLs and intrathecal Ig synthesis (RR = 0.3; Wald 95% CI = 0.1–0.7, p < 0.001). Conclusion: We observed that the association of intrathecal immunoglobulin synthesis and CLs was highly predictive of an earlier CIS conversion to MS as well as of a higher disease activity.

Clinical, diagnostic and immunological characteristics of patients with possible neuroborreliosis without intrathecal Ig-synthesis against Borrelia antigen in the cerebrospinal fluid

The diagnosis of neuroborreliosis is not always straightforward. Intrathecal immunoglobulin (Ig) synthesis against Borrelia antigen may not be detected, at least early in the disease course. Also other neurological and infectious diagnoses have to be considered. We have studied patients with clinical possible neuroborreliosis without intrathecal Ig synthesis against Borrelia antigen in the cerebrospinal fluid (CSF) (n=17). Diagnosis was based on typical clinical history and at least one of the following findings; mononuclear leucocytosis in the CSF (n=4); typical erythema migrans >5 cm in diameter in relation to debut of symptoms (n=8); prompt clinical response to antibiotic teratment (n=14). Also other possible diagnoses had to be excluded. Seventeen patients first investigated because of suspected neuroborreliosis but later confirmed with other diagnoses were used as controls. All patients had a lumbar puncture. Borrelia specific IFN-&gamma; and IL-4 secretion was investigated in peripheral blood (PBL) and CSF with an ELISPOT assay. Polymerase chain reaction (PCR) was used to reveal any Borrelia antigen in the CSF. Six of 17 patients with possible neuroborreliosis showed high IFN-g secretion in peripheral blood, otherwise we found no statistically significant differences between the groups. PCR did not reveal any Borrelia antigen in CSF. The diagnosis and treatment of possible but not confirmed neuroborreliosis is a clinical challenge. The clinical response to treatment may be the best option in these cases.

Proteasome Stress Causes Apoptotic Sensitivity of Multiple Myeloma Cells to Proteasome Inhibition

Proteasome inhibitors (PI) proved to be extremely effective against different types of cancer, particularly against Multiple Myeloma (MM), a frequent and still incurable plasma cell malignancy. Phase II clinical trials showed that more than 50% of MM patients fail to respond to bortezomib, the only PI currently approved for clinical use. However, the mechanisms of action and bases of individual susceptibility to PI remain largely unclear, with no reliable predictor of response identified so far. Recent evidences linking proteasome activity and Ig synthesis to susceptibility to PI suggest that the exquisite sensitivity of MM cells (MMC) to PI might be explained by an imbalance between the efficiency of the ubiquitin (Ub)-proteasome pathway and the demand for proteasome-mediated degradation. We set out to explore this hypothesis both in vitro and ex vivo. To achieve this aim, we employed human MM cell lines characterized by differential apoptotic sensitivity to PI (U266 and RPMI8226, fairly resistant cell lines, versus MM.1S, an extremely sensitive one) and primary, patient derived MMC. In MM cell lines, we found that high apoptotic sensitivity to PI is associated with lower expression of active proteasomes (as assessed by decreased expression of cleaved catalytic subunits and enzymatic assays with fluorogenic substrates in cell extracts), together with higher proteasomal workload (demonstrated by higher proteasome-dependent loss of TCA-insoluble radioactivity in pulse-chase assays). Indeed, MM.1S cells displayed 2–3 times lower proteasomal activity as compared to the more resistant U266 and RPMI8226 cells, both on a per cell basis and upon normalization by protein content. Together with the reduced proteasome capacity, MM.1S cells showed a consistently higher production of client proteins for the Ub-proteasome pathway. Such an increased load appears to be the consequence of a higher production of Rapidly Degraded Polypeptides (RDP). These are newly synthesized proteins which are quickly redirected to proteasome-mediated degradation. The imbalance between proteasomal load and capacity results in remarkable accumulation of poly-Ub proteins at the expense of free Ub (as established by both western blotting and immunofluorescence), unveiling basal proteasome stress in PI-sensitive MMC. In order to establish a causal link between proteasome stress and sensitivity to PI, we pharmacologically modulated either proteasome expression or workload and successfully altered PI-induced apoptosis. As predicted, increasing proteasome workload by means of ER stressors (e.g. tunicamycin, thapsigargin, brefeldin A) dramatically enhances susceptibility to PI, while a raise in proteasomal activity (achieved by exploiting the proteasome stress response, an adaptive mechanism by which mammalian cells induce proteasome biogenesis in response to either decreased proteasome function or increased proteasomal demand), confers marked resistance to PI-induced apoptosis. Having established cause-effect relationships between determinants of proteasome stress and vulnerability to PI in vitro, we then asked if our model could be used to predict responsiveness to PI in MM patients. In keeping with this hypothesis, intracellular immunostaining in primary, patient-derived MMC reveals that accumulation of poly-Ub proteins specifically hallmarks neoplastic plasma cells, indicating that the cancer compartment in MM patients suffers from proteasome stress. Moreover, poly-Ub levels positively correlate with Ig content, both intra- and inter-patient, suggesting a direct effect of Ig synthesis and/or retention on proteasome functional load. Finally, overall proteasome activity of primary MMC inversely correlates with the intrinsic apoptotic sensitivity to PI as assessed ex vivo, providing a rationale for the assessment of this parameter as a potential predictor of the in vivo response to bortezomib or other PI. Altogether, our data indicate that the balance between proteasome workload and degradative capacity represents a critical determinant of apoptotic sensitivity of MMC to PI, providing both a novel predictive tool of potential prognostic value and the framework for novel combination therapies aimed at exacerbating proteasome stress in MM.

Differential Effects of Hsp70 Inhibition within the Tumor and Microenvironment in Multiple Myeloma.

Multiple myeloma (MM) remains fatal despite prolonged survival by recent advances in treatment, including the use of proteasome inhibitors. It has been proposed that proteasome inhibitors target MM by modulating the NF-κB pathway. Alternatively, proteasome inhibitors may target MM cells because the proteasome helps alleviate the unfolded protein response (UPR) that results from the accumulation of aberrant proteins in the endoplasmic reticulum (ER), which in turn may trigger apoptosis. Indeed, the UPR is induced in neoplastic plasma cells, possibly because of increased immunoglobulin (IG) synthesis that exceeds the protein folding capacity of the ER. Consequently, the degree to which inhibition of the proteasome induces apoptosis may be related to the concentration of unfolded light chains within the ER in MM. We therefore examined whether inhibition of a protein-folding mediator, the Hsp70 molecular chaperone, results in synergistic induction of MM cell apoptosis when combined with a proteasome inhibitor. To this end, the effects of MAL3-101, a novel inhibitor of Hsp70 function, both alone and in combination with a proteasome inhibitor (MG132) on three MM cell lines as well as primary patient MM cells were examined. Dose-response and time course studies in MM cell lines U266, RPMI-8226, and NCI-H929 showed increasing apoptosis and inhibition of proliferation after 16 hours of exposure to MAL3-101 (IC50: 0.9 μM) or to MG132 (IC50: 7 μM). Strikingly, when sub-effective concentrations of MG132 and MAL3-101 were combined, a strong, synergistic apoptotic response was observed in the NCI cell line after 16 hours, and synergistic effects were observed in all cell lines after 36 hours of exposure to the two drugs. Next, we studied MM cells and endothelial progenitor cells (EPCs) derived from the bone marrow of five untreated patients. These two cell populations, which were shown to bear clonotypic similarities, also showed sensitivity to dual targeting. However, these effects occurred at drug concentrations different than those found to be most potent in the cell lines. Moreover, semi-quantitative RT-PCR studies indicated that RPMI cells but not U266 cells exhibited a strong UPR induction after 16 hours of exposure to 7 μM MG132. These data correlated with the greater degree of IG secretion observed in RPMI cells compared to U266 cells as assessed by pulse-chase analysis. Taken together, these results suggest that the apoptotic response of MM cells via targeting the UPR and ER stress pathways may be dependent on basal protein production, including IG synthesis. Studies relating the secretion “index” to UPR induction and sensitivity to Hsp70 and proteasome inhibition in primary tumor cells as well as in microvascular cells from MM patients are ongoing.

Recovery of Polyclonal Immunoglobulin Synthesis after Autologous Stem Cell Transplantation in Multiple Myeloma Patients as a Prognostic Factor for Event-Free Survival.

Suppression of polyclonal immunoglobulin (Ig) synthesis is one feature of multiple myeloma (MM). To evaluate if recovery of polyclonal Ig synthesis after autologous stem cell transplantation (ABSCT) influences prognosis, we have retrospectively analyzed the prognostic value of clinical and laboratory variables of 348 multiple myeloma patients who underwent their first autologous stem cell transplantation between 06.1992 and 10.2002 at the University Hospital of Heidelberg. The median follow-up was 34 months (range, 3 to 136 months). The median number of chemotherapy courses prior to first ABSCT was 5 (range, 3 to 30). Twenty-two of 348 patients underwent altogether three ABSCTs (including 18 patients with tandem transplantations), 141 had two ABSCTs (including 87 tandem transplantations) and 29 patients were treated with allogeneic transplantation as second line treatment. Recovery of polyclonal Ig synthesis was studied by serumelectrophoresis on day 100 after first ABSCT (±30 days). Full polyclonal Ig recovery was observed in 93 of 348 patients (28%), partial recovery (reduced polyclonal Ig, no monoclonal Ig) in 58 (17%), no recovery (almost no polyclonal Ig and no monoclonal Ig) in 16 (5%), polyclonal Ig recovery associated with monoclonal Ig in 95 (27%) and monoclonal Ig without polyclonal Ig in 72 patients (21%) (data missing in 14 patients (4%)). On multivariate analysis (333 patients), using Cox proportional hazards regression model stratified with respect to tandem transplantation, superior event-free survival was observed with recovery of polyclonal Ig synthesis, low beta2-microglobulin at diagnosis (<2.5mg/L) and a high haemoglobin at diagnosis, whereas MM type IgA and a high number of chemotherapy courses prior to first ABSCT were identified as adverse prognostic factors. Regarding polyclonal recovery, patients with polyclonal Ig recovery associated with monoclonal Ig had a superior event-free survival compared to patients with only monoclonal Ig without any polyclonal Ig recovery. Overall survival was superior in patients with a low β2-microglobulin at diagnosis (<2.5mg/L) and a high haemoglobin at diagnosis, and worse in patients with a high number of chemotherapy courses prior to first ABSCT. We conclude that any recovery of polyclonal Ig synthesis even when associated with monoclonal Ig, improves event-free survival, and therefore can be used as a predictor of prognosis in the follow-up of multiple myeloma patients who underwent ABSCT.