anti-MM Activity Research Articles

Preclinical and Translational Biomarker Analyses to Inform Clinical Development of Mezigdomide (CC-92480) in Combination with Dexamethasone and Daratumumab in Multiple Myeloma

Introduction: Mezigdomide (MEZI) is a novel, oral cereblon (CRBN) E3 ligase modulator (CELMoD) that induces rapid and potent degradation of lkaros and Aiolos. Reduction of these transcription factors results in direct tumoricidal and immunomodulatory effects in multiple myeloma (MM). MEZI showed promising efficacy and safety in combination with dexamethasone in the phase 1/2 CC-92480-MM-001 trial (NCT03374085) in Relapsed/Refractory MM. MEZI is currently being investigated in combination with daratumumab and dexamethasone (MEZI + DARA + DEX or MEZI-Dd) in the phase 1/2 CC-92480-MM-002 trial (NCT03989414). In MEZI-Dd cohort, MEZI is administered at three different schedules (B1 for 21/28 days; B2 for 14/21 days; B3 for 7/14 days), and at two different doses (0.3mg; 0.6mg). Here we report preclinical data and pharmacodynamic (PD) biomarker analyses from blood and bone marrow samples collected in CC-92480-MM-002 to support dose and schedule optimization of MEZI-Dd. Methods:Preclinical studies on the pro-apoptotic effects of MEZI on daratumumab-mediated complement-dependent cytotoxicity (CDC) and peripheral blood mononuclear cell-based antibody-dependent cell-mediated cytotoxicity (ADCC) were performed in MM cell lines treated with MEZI-D in comparison to single-agent MEZI or DARA. Clinical PD biomarker analyses included peripheral blood samples collected on treatment Cycle (C)1 Day (D)1 and mid C1-C3 for the expression of Aiolos in T-cells and immunomodulation by flow cytometry. Bone marrow samples were collected for immunohistochemistry at screening and mid C2. Serum free light chain (sFLC) and soluble B-cell maturation antigen (BCMA) were analyzed as biomarkers for tumor burden from C1-C6. Results: Preclinically, combinations of MEZI-D induced synergistic anti-tumor activity in MOLP-8 cells. The MEZI-D combination showed greater anti-MM activities across the dosing gradient than either single-agent DARA (~2-4.5 fold) or MEZI (~1.7-2.4 fold) in a CDC assay. MEZI-D also induced significantly more cell apoptosis than POM-D (p<0.05) in an ADCC assay. In the clinic, MEZI-Dd was sufficient to induce rapid Aiolos degradation in the peripheral blood T-cells for doses as low as 0.3mg MEZI, but 0.6mg MEZI was necessary to result in >50% substrate degradation, suggesting 0.6mg MEZI induced deeper substrate degradation. While 0.3mg MEZI-Dd decreased total CD56+/CD16+ NK-cell counts (Median -83.8%) by mid C1 via immunophenotyping analyses, the combination increased %Ki67+ proliferative NK-cell (Median 251.9%). 0.3mg MEZI-Dd also showed consistent trends of schedule-dependent PD immune effects by mid C3, including increased %Ki67+ proliferative CD3+ T-cell (Median B1: 113.1%, B2: 365.1%, B3: 37.4%), decreased CD45RA+CCR7+ naïve CD4+ T-cell (Median B1: -82.0%, B2: -62.3%, B3: -43.9%), increased CD45RO+CCR7- effector memory CD4+ T-cell (Median B1: 142.3%, B2: 82.9%, B3: 13.9%), and increased HLA-DR expressing CD4+ T-cell activation (Median B1: 149.3%, B2: 107.9%, B3: 17.1%). Thus, greater PD immune effects were observed with schedules of 21/28 and 14/21 days, compared to the 7/14 schedule. At 0.6mg MEZI-Dd, greater median changes of PD immune effects were induced with the 7/14 schedule, compared to 0.3mg MEZI-Dd. Conversely, at continuous dosing schedules longer than 7 days, MEZI-Dd PD immune effects of 0.6mg MEZI were similar to 0.3mg MEZI. In addition, greater reduction of tumor burden was observed at 0.6mg MEZI-Dd, compared to 0.3mg MEZI-Dd across different schedules, as assessed by sFLC and soluble BCMA analyses. Conclusions: Our data show dose- and schedule-dependent PD effects of MEZI-Dd. PD analyses at 0.3mg MEZI suggest at least two weeks of continuous dosing may be needed for greater PD activities in combination with daratumumab, compared to one week of dosing. For continuous dosing of one week, a higher dose at 0.6mg MEZI may be needed to achieve greater PD activities. Further investigation of doses at 0.6mg and 1mg MEZI is underway to determine the optimal dose. Moreover, MEZI induction of NK-cell proliferation and/or activation may provide mechanistic rationale for possible MEZI-D synergy in the clinic.

High levels of CRBN isoform lacking IMiDs binding domain predicts for a worse response to IMiDs-based upfront therapy in newly diagnosed myeloma patients

In recent years, the immunoderivative (IMiD) agents have been extensively used for the treatment of multiple myeloma (MM). IMiDs and their newer derivatives CRBN E3 ligase modulator bind the E3 ligase substrate recognition adapter protein cereblon (CRBN), which has been recognized as one of the IMiDs’ direct target proteins, and it is essential for the therapeutic effect of these agents.High expression of CRBN was associated with improved clinical response in patients with MM treated with IMiDs, further confirming that the expression of IMiDs’ direct target protein CRBN is required for the anti-MM activity. CRBN’s central role as a target of IMiDs suggests potential utility as a predictive biomarker of response or resistance to IMiDs therapy. Additionally, the presence of alternatively spliced variants of CRBN in MM cells, especially those lacking the drug-binding domain for IMiDs, raise questions concerning their potential biological function, making difficult the transcript measurement, which leads to inaccurate overestimation of full-length CRBN transcripts. In sight of this, in the present study, we evaluated the CRBN expression, both full-length and spliced isoforms, by using real-time assay data from 87 patients and RNA sequencing data from 50 patients (n = 137 newly diagnosed MM patients), aiming at defining CRBN’s role as a predictive biomarker for response to IMiDs-based induction therapy. We found that the expression level of the spliced isoform tends to be higher in not-responding patients, confirming that the presence of a more CRBN spliced transcript predicts for lack of IMiDs response.

Antibody-Mediated Nanodrug of Proteasome Inhibitor Carfilzomib Boosts the Treatment of Multiple Myeloma.

Multiple myeloma (MM) is the second most common hematological malignancy. For relapsed and refractory MM, a proteasome inhibitor, carfilzomib (CFZ), has become one of the few clinical options. CFZ suffers, nevertheless, metabolic instability and poor bioavailability and may induce severe cardiovascular and renal adverse events. Here, we report that daratumumab (Dar)-decorated polypeptide micelles (Dar-PMs) mediate the targeted delivery of CFZ to CD38-positive MM, effectively boosting its anti-MM efficacy. CFZ-loaded Dar-PMs (Dar-PMs-CFZ) exhibited an average diameter of ca. 80 nm and Dar density-dependent cell endocytosis and anti-MM activity, in which over 6-fold greater inhibitory effect to LP-1 and MM.1S MM cells than nontargeted PMs-CFZ control was achieved at a Dar density of 3.2 (Dar3.2-PMs-CFZ). Interestingly, Dar3.2-PMs-CFZ markedly enhanced the growth inhibition of orthotopic LP-1 MM in mice and significantly extended the median survival time compared with PMs-CFZ and free CFZ (95 days vs 60 and 54 days, respectively). In line with its high MM targetability and anti-MM efficacy, Dar3.2-PMs-CFZ revealed little toxic effects and effectively prevented osteolytic lesions. The antibody-targeted nanodelivery of a proteasome inhibitor appears to be an appealing strategy to treat multiple myeloma.

Molecular mechanism by which RRM2-inhibitor (cholagogue osalmid) plus bafilomycin A1 cause autophagic cell death in multiple myeloma

Despite significant improvement in the prognosis of multiple myeloma (MM), the disease remains incurable; thus, more effective therapies are required. Ribonucleoside-diphosphate reductase subunit M2 (RRM2) is significantly associated with drug resistance, rapid relapse, and poor prognosis. Previously, we found that 4-hydroxysalicylanilide (osalmid), a specific inhibitor of RRM2, exhibits anti-MM activity in vitro, in vivo, and in human patients; however, the mechanism remains unclear. Osalmid inhibits the translocation of RRM2 to the nucleus and stimulates autophagosome synthesis but inhibits subsequent autophagosome–lysosome fusion. We confirm that RRM2 binds to receptor-interacting protein kinase 3 (RIPK3) and reduces RIPK3, inhibiting autophagosome–lysosome fusion. Interestingly, the combination of osalmid and bafilomycin A1 (an autophagy inhibitor) depletes RIPK3 and aggravates p62 and autophagosome accumulation, leading to autophagic cell death. Combination therapy demonstrates synergistic cytotoxicity both in vitro and in vivo. Therefore, we propose that combining osalmid and bafilomycin A1(BafA1) may have clinical benefits against MM.

GPER1 Activation Exerts Anti-Tumor Activity in Multiple Myeloma.

G protein-coupled estrogen receptor 1 (GPER1) activation is emerging as a promising therapeutic strategy against several cancer types. While GPER targeting has been widely studied in the context of solid tumors, its effect on hematological malignancies remains to be fully understood. Here, we show that GPER1 mRNA is down-regulated in plasma cells from overt multiple myeloma (MM) and plasma cell leukemia patients as compared to normal donors or pre-malignant conditions (monoclonal gammopathy of undetermined significance and smoldering MM); moreover, lower GPER1 expression associates with worse overall survival of MM patients. Using the clinically applicable GPER1-selective agonist G-1, we demonstrate that the pharmacological activation of GPER1 triggered in vitro anti-MM activity through apoptosis induction, also overcoming the protective effects exerted by bone marrow stromal cells. Noteworthy, G-1 treatment reduced in vivo MM growth in two distinct xenograft models, even bearing bortezomib-resistant MM cells. Mechanistically, G-1 upregulated the miR-29b oncosuppressive network, blunting an established miR-29b-Sp1 feedback loop operative in MM cells. Overall, this study highlights the druggability of GPER1 in MM, providing the first preclinical framework for further development of GPER1 agonists to treat this malignancy.

Novel c-Myc G4 stabilizer EP12 promotes myeloma cytotoxicity by disturbing NF-κB signaling

Multiple myeloma (MM) is a B-cell malignancy characterized by the excessive proliferation of bone marrow plasma cells and the production of abnormal immunoglobulins. Despite advances in therapeutic strategies, it remains an incurable disease. Recently, innovative anticancer drugs have been developed and approved, leading to improvements in MM therapy; however, drug resistance continues to be a major obstacle that results in treatment failure. Therefore, the development of novel agents is imperative to achieve superior therapeutic outcomes for relapsed/refractory multiple myeloma (MM) patients. Previously, we identified EP12 as a c-Myc G4 stabilizer that could induce cytotoxicity in MM cells in vitro. However, further investigation is required to elucidate the underlying molecular mechanisms and anti-MM activity of EP12 in vivo. In this study, we have discovered that the compound EP12 effectively inhibits primary myeloma growth in vivo by destabilizing c-Myc and disrupting the canonical nuclear factor-κB (NF-κB) signaling pathway. Overall, our findings suggest that EP12, as a potent c-Myc inhibitor, holds great promise as a therapeutic agent for MM.

C-FOS is an integral component of the IKZF1 transactivator complex and mediates lenalidomide resistance in multiple myeloma.

The immunomodulatory drug lenalidomide, which is now widely used for the treatment of multiple myeloma (MM), exerts pharmacological action through the ubiquitin-dependent degradation of IKZF1 and subsequent down-regulation of interferon regulatory factor 4 (IRF4), a critical factor for the survival of MM cells. IKZF1 acts principally as a tumour suppressor via transcriptional repression of oncogenes in normal lymphoid lineages. In contrast, IKZF1 activates IRF4 and other oncogenes in MM cells, suggesting the involvement of unknown co-factors in switching the IKZF1 complex from a transcriptional repressor to an activator. The transactivating components of the IKZF1 complex might promote lenalidomide resistance by residing on regulatory regions of the IRF4 gene to maintain its transcription after IKZF1 degradation. To identify unknown components of the IKZF1 complex, we analyzed the genome-wide binding of IKZF1 in MM cells using chromatin immunoprecipitation-sequencing (ChIP-seq) and screened for the co-occupancy of IKZF1 with other DNA-binding factors on the myeloma genome using the ChIP-Atlas platform. We found that c-FOS, a member of the activator protein-1 (AP-1) family, is an integral component of the IKZF1 complex and is primarily responsible for the activator function of the complex in MM cells. The genome-wide screening revealed the co-occupancy of c-FOS with IKZF1 on the regulatory regions of IKZF1-target genes, including IRF4 and SLAMF7, in MM cells but not normal bone marrow progenitors, pre-B cells or mature T-lymphocytes. c-FOS and IKZF1 bound to the same consensus sequence as the IKZF1 complex through direct protein-protein interactions. The complex also includes c-JUN and IKZF3 but not IRF4. Treatment of MM cells with short-hairpin RNA against FOS or a selective AP-1 inhibitor significantly enhanced the anti-MM activity of lenalidomide in vitro and in two murine MM models. Furthermore, an AP-1 inhibitor mitigated the lenalidomide resistance of MM cells. C-FOS determines lenalidomide sensitivity and mediates drug resistance in MM cells as a co-factor of IKZF1 and thus, could be a novel therapeutic target for further improvement of the prognosis of MM patients.

Dendritic Cell-Derived Exosomes Driven Drug Co-Delivery Biomimetic Nanosystem for Effective Combination of Malignant Melanoma Immunotherapy and Gene Therapy.

Malignant melanoma (MM), the most lethal skin cancer, is highly invasive and metastatic. These qualities are related to not only genetic mutations in MM itself but also the interaction of MM cells with the immune system and microenvironment. This study aimed to construct a combined immunotherapy and gene therapy drug delivery system for the effective treatment of MM. Mature dendritic cell (mDC) exosomes (mDexos) with immune induction functions were used as carriers. BRAF siRNA (siBRAF) with the ability to silence mutated BRAF in MM was encapsulated in mDexos by electroporation to construct a biomimetic nanosystem for the codelivery of immunotherapy and gene therapy drugs (siBRAF-mDexos) to the MM microenvironment. Then, we investigated the nanosystem's serum stability and biocompatibility, uptake efficiency in mouse melanoma cells (B16-F10 cells), cytotoxicity against B16-F10 cells and inhibitory effect on BRAF expression. Furthermore, we evaluated its antimelanoma activity and safety in vivo. SiBRAF-mDexos were nanosized. Compared to siBRAF, siBRAF-mDexos displayed significantly increased serum stability, biocompatibility, uptake efficiency in B16-F10 cells, and cytotoxicity to B16-F10 melanoma cells; they also had a significantly greater inhibitory effect on BRAF expression and induced T-lymphocyte proliferation. Moreover, compared with siBRAF, siBRAF-mDexos showed significantly enhanced anti-MM activity and a high level of safety in vivo. The study suggests that the siBRAF-mDexo biomimetic drug codelivery system can be used to effectively treat MM, which provides a new strategy for combined gene therapy and immunotherapy for MM.

Combinations of ivermectin with proteasome inhibitors induce synergistic lethality in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of plasma cells. Ivermectin is a US Food and Drug Administration-approved drug for antiparasitic use. Here, we showed that ivermectin exerted anti-MM effects and significantly synergized with proteasome inhibitors in vitro and in vivo. Ivermectin alone exhibited mild anti-MM activity in vitro. Further investigation suggested that ivermectin inhibited proteasome activity in the nucleus by repressing the nuclear import of proteasome subunits, such as PSMB5-7 and PSMA3-4. Therefore, ivermectin treatment caused the accumulation of ubiquitylated proteins and the activation of the UPR pathway in MM cells. Furthermore, ivermectin treatment caused DNA damage and DNA damage response (DDR) signaling pathway activation in MM cells. Ivermectin and bortezomib exhibited synergized anti-MM activity in vitro. The dual-drug treatment resulted in synergistic inhibition of proteasome activity and increased DNA damage. An in vivo study using a human MM cell line xenograft mouse model showed that ivermectin and bortezomib efficiently repressed MM tumor growth in vivo, while the dual-drug treatment was well tolerated by experimental animals. Overall, our results demonstrated that ivermectin alone or cotreated with bortezomib might be promising in MM treatment.

Simultaneously Targeting Two Coupled Signalling Molecules in the Mesenchymal Stem Cell Support Efficiently Sensitises the Multiple Myeloma Cell Line H929 to Bortezomib.

Several studies have shown that diverse components of the bone marrow (BM) microenvironment play a central role in the progression, pathophysiology, and drug resistance in multiple myeloma (MM). In particular, the dynamic interaction between BM mesenchymal stem cells (BM-MSC) and MM cells has shown great relevance. Here we showed that inhibiting both PKC and NF-κB signalling pathways in BM-MSC reduced cell survival in the MM cell line H929 and increased its susceptibility to the proteasome inhibitor bortezomib. PKC-mediated cell survival inhibition and bortezomib susceptibility induction were better performed by the chimeric peptide HKPS than by the classical enzastaurin inhibitor, probably due to its greatest ability to inhibit cell adhesion and its increased capability to counteract the NF-κB-related signalling molecules increased by the co-cultivation of BM-MSC with H929 cells. Thus, inhibiting two coupled signalling molecules in BM-MSC was more effective in blocking the supportive cues emerging from the mesenchymal stroma. Considering that H929 cells were also directly susceptible to PKC and NF-κB inhibition, we showed that treatment of co-cultures with the HKPS peptide and BAY11-7082, followed by bortezomib, increased H929 cell death. Therefore, targeting simultaneously connected signalling elements of BM-MSC responsible for MM cells support with compounds that also have anti-MM activity can be an improved treatment strategy.

Preclinical discovery and initial clinical data of WVT078, a BCMA × CD3 bispecific antibody.

B-cell maturation antigen (BCMA) is an ideal target in multiple myeloma (MM) due to highly specific expression in malignant plasma cells. BCMA-directed therapies including antibody drug conjugates, chimeric antigen receptor-T cells and bispecific antibodies (BsAbs) have shown high response rates in MM. WVT078 is an anti-BCMA× anti-CD3 BsAb that binds to BCMA with subnanomolar-affinity. It was selected based on potent T cell activation and anti-MM activity in preclinical models with favorable tolerability in cynomolgus monkey. In the ongoing first-in-human phase I dose-escalation study (NCT04123418), 33 patients received intravenous WVT078 once weekly at escalated dosing. At the active doses of 48-250 µg/kg tested to date (n = 26), the overall response rate (ORR) was 38.5% (90% CI: 22.6-56.4%) and the complete response rate (CRR, stringent complete response + complete response) was 11.5%, (90% CI: 3.2-27.2%). At the highest dose level tested, the ORR was 75% (3 of 4 patients). 26 (78.8%) patients reported at least one Grade ≥3 AE and 16 of these AEs were suspected to be drug related. 20 patients (60.6%) experienced cytokine release syndrome. WVT078 has an acceptable safety profile and shows preliminary evidence of clinical activity at doses tested to date.

Abstract 2851: ALK-inhibitors as a novel potential therapy for proteasome inhibitor-resistant multiple myeloma

Abstract Background: Proteasome inhibitors (PI) disrupt the equilibrium between production and disposal of excess and/or misfolded proteins in multiple myeloma (MM) cells, leading to apoptosis. Resistance to PI bortezomib (BTZ) and carfilzomib (CFZ) is a major obstacle to the successful treatment of MM. The drug repurposing approach offers a promising strategy to classical drug development in particular in MM. Previously, ALK-inhibitors were shown to have anti-MM activity ex vivo. Therefore, we aimed to identify the mechanism of action of ALK-inhibitors against MM cells and to identify promising drug therapy combinations of ALK-inhibitors for refractory MM. Methods: A set of PI-naïve and PI-resistant cells was used in the study. Viability of the cells was determined by CCK8 viability assay. Genome-wide CRISPR/Cas9-based loss-of-function screening with Brunello library was used in MM AMO-1 cell line to identify mechanism of action of ceritinib. Western blot was used to assess levels of total and phosphorylated proteins. RNA-seq was used to determine the amount of transcripts in PI-sensitive and PI-resistant cells. Results: Initially, 7 different ALK-inhibitors were tested across PI-naïve and PI-adapted MM cell lines. Based on the IC50 values, the most effective ALK-inhibitors to induce cytotoxicity in MM were ceritinib > brigatinib > crizotinib > entrectinib. The combination of ceritinib, brigatinib and entrectinib showed synergistic cytotoxicity with the PI BTZ and CFZ and overcame PI-resistance in 4 different sets of PI-adapted cells. The strongest synergistic cytotoxicity was observed between ceritinib and CFZ in CFZ-adapted cells. CRISPR/Cas9-screening identified genes involved in negative regulation of mTORC signalling (NPRL2, NPRL3, TSC1, TSC2) and transcription factor FOXO1 as the major resistance candidates to ceritinib. Subsequently, ceritinib treatment significantly inhibited mTORC signaling, suggesting a shut-down of cellular proliferation due to targeting of the upstream receptor-tyrosine kinases (RTK), essential for cell viability and thus not identified by the screening. Further search identified InsR and IGF1R as the overlapping RTK inhibited by ceritinib and brigatinib. Co-treatment of PI-resistant cells with the combination of InsR/IGF1R inhibitors and CFZ induced strong synergistic cytotoxicity, resembling the synergistic cytotoxicity observed for ceritinib and CFZ, whereas InsR/IGF1R inhibitors did not show any synergistic cytotoxicity with ceritinib, suggesting targeting the same pathway. Our data further show that PI-naïve and resistant cells are negative for ALK, but positive for InsR and IGF1R expression. Conclusion: Crizotinib inhibits InsR/IGF1R signaling in MM, which is essential for MM survival and together with CFZ it overcomes PI-resistance. Therefore, it represents a promising and already available therapy for PI-resistant MM patients. Citation Format: Lenka Besse, Andrej Besse, Marianne Kraus, Matej Jasik, Ondrej Slaby, Christoph Driessen. ALK-inhibitors as a novel potential therapy for proteasome inhibitor-resistant multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2851.

TERRA G-quadruplex stabilization as a new therapeutic strategy for multiple myeloma

BackgroundMultiple myeloma (MM) is a hematologic malignancy characterized by high genomic instability, and telomere dysfunction is an important cause of acquired genomic alterations. Telomeric repeat-containing RNA (TERRA) transcripts are long non-coding RNAs involved in telomere stability through the interaction with shelterin complex. Dysregulation of TERRAs has been reported across several cancer types. We recently identified a small molecule, hit 17, which stabilizes the secondary structure of TERRA. In this study, we investigated in vitro and in vivo anti-MM activities of hit 17.MethodsAnti-proliferative activity of hit 17 was evaluated in different MM cell lines by cell proliferation assay, and the apoptotic process was analyzed by flow cytometry. Gene and protein expressions were detected by RT-qPCR and western blotting, respectively. Microarray analysis was used to analyze the transcriptome profile. The effect of hit 17 on telomeric structure was evaluated by chromatin immunoprecipitation. Further evaluation in vivo was proceeded upon NCI-H929 and AMO-1 xenograft models.ResultsTERRA G4 stabilization induced in vitro dissociation of telomeric repeat‐binding factor 2 (TRF2) from telomeres leading to the activation of ATM-dependent DNA damage response, cell cycle arrest, proliferation block, and apoptotic death in MM cell lines. In addition, up-regulation of TERRA transcription was observed upon DNA damage and TRF2 loss. Transcriptome analysis followed by gene set enrichment analysis (GSEA) confirmed the involvement of the above-mentioned processes and other pathways such as E2F, MYC, oxidative phosphorylation, and DNA repair genes as early events following hit 17-induced TERRA stabilization. Moreover, hit 17 exerted anti-tumor activity against MM xenograft models.ConclusionOur findings provide evidence that targeting TERRA by hit 17 could represent a promising strategy for a novel therapeutic approach to MM.

Molecular Basis and Potential Molecular Mechanisms of Action in Natural Products as Therapeutic Agents Towards Multiple Myeloma

Multiple myeloma (MM) is a bone marrow-based neoplasm of clonal plasma cells resulting in substantial mortality and morbidity. It is classified as a mature B-cell neoplasm in which clonal plasma cell proliferation results in anaemia, hypercalcaemia and organ/tissue damage such as kidneys and skeletal system. The response rates of myeloma improved significantly following the introduction of novel therapies such as immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs), monoclonal antibodies (MoAbs), hematopoietic stem cell transplant and cellular therapies such as chimeric antigen receptor (CAR) T-cells. However, MM remains incurable. In addition, adverse effects, exorbitant costs, and problems with accessibility to drugs and therapeutic modalities prevent many patients from reaping the potential benefits of these novel therapies. Therefore, it is essential to investigate new therapeutic targets and agents. Many cell signalling pathways are described in MM. Some facilitate the evasion of apoptosis and long periods of cell survival. Natural products contain a variety of secondary metabolites targeting these signalling pathways responsible for anti-MM activities such as apoptosis, cell cycle arrest, anti-angiogenesis, and miRNA modulation. The role of natural compounds as therapeutic agents in the treatment of multiple myeloma has drawn a considerable interest in research in recent past. This review attempts to collate available information on natural products from terrestrial plants, animals, and macrofungi, and their potential molecular mechanisms in MM.

Lenalidomide in Multiple Myeloma: Review of Resistance Mechanisms, Current Treatment Strategies and Future Perspectives.

Multiple myeloma (MM) is the second most common hematologic malignancy, accounting for approximately 1% of all cancers. Despite the initial poor prognosis for MM patients, their life expectancy has improved significantly with the development of novel agents. Immunomodulatory drugs (IMiDs) are widely used in MM therapy. Their implementation has been a milestone in improving the clinical outcomes of patients. The first molecule belonging to the IMiDs was thalidomide. Subsequently, its novel derivatives, lenalidomide (LEN) and pomalidomide (POM), were implemented. Almost all MM patients are exposed to LEN, which is the most commonly used IMiD. Despite the potent anti-MM activity of LEN, some patients eventually relapse and become LEN-resistant. Drug resistance is one of the greatest challenges of modern oncology and has become the main cause of cancer treatment failures. The number of patients receiving LEN is increasing, hence the problem of LEN resistance has become a great obstacle for hematologists worldwide. In this review, we intended to shed more light on the pathophysiology of LEN resistance in MM, with particular emphasis on the molecular background. Moreover, we have briefly summarized strategies to overcome LEN resistance and we have outlined future directions.

Natural Agents as Novel Potential Source of Proteasome Inhibitors with Anti-Tumor Activity: Focus on Multiple Myeloma.

Multiple myeloma (MM) is an aggressive and incurable disease for most patients, characterized by periods of treatment, remission and relapse. The introduction of new classes of drugs, such as proteasome inhibitors (PIs), has improved survival outcomes in these patient populations. The proteasome is the core of the ubiquitin-proteasome system (UPS), a complex and conserved pathway involved in the control of multiple cellular processes, including cell cycle control, transcription, DNA damage repair, protein quality control and antigen presentation. To date, PIs represent the gold standard for the treatment of MM. Bortezomib was the first PI approved by the FDA, followed by next generation of PIs, namely carfilzomib and ixazomib. Natural agents play an important role in anti-tumor drug discovery, and many of them have recently been reported to inhibit the proteasome, thus representing a new potential source of anti-MM drugs. Based on the pivotal biological role of the proteasome and on PIs' significance in the management of MM, in this review we aim to briefly summarize recent evidence on natural compounds capable of inhibiting the proteasome, thus triggering anti-MM activity.

Liposome-Encapsulated Melphalan Exhibits Potent Antimyeloma Activity and Reduced Toxicity.

Multiple myeloma (MM), a plasma cell cancer in bone marrow, remains an incurable disease. Melphalan, an alkylating agent, is a conventional anticancer drug that is still widely used for MM treatment in clinics. However, melphalan-induced organ toxicity and side effects are common. In this study, we loaded melphalan into a liposomal capsule and constituted liposomal melphalan (liposomal MEL). Liposomal MEL particles were approximately 120 nm in size and stable in vitro. The liposomal particles could be effectively taken up by MM cells. In vitro cytotoxicity assays using MM cell lines and primary MM cells showed that liposomal MEL exhibited similar anti-MM activity compared to an equivalent amount of free melphalan (free MEL) compound. In animal models, liposomal particles had bone marrow enrichment and prolonged half-life in vivo. Liposomal MEL exposure resulted in less liver and colon organ toxicity than exposure to an equivalent amount of free MEL-treated mice. Importantly, liposomal MEL had potent anti-MM activity in vivo in a human MM xenograft mouse model. Overall, our findings suggested that liposome-encapsulated melphalan was an effective drug modification of the melphalan compound and showed promise in MM treatment.

Beyond the cell: novel noncellular immunotherapy approaches to multiple myeloma

The development of novel cellular therapies and bispecific T-cell-engaging antibodies is occurring at breakneck speed in multiple myeloma (MM). While groundbreaking, these agents have their unique logistical and toxicity issues and currently do not represent a curative approach. In this context, there continues to be an urgent need to develop novel, off-the-shelf immunotherapy approaches to add to the armamentarium. This article explores novel agents being investigated in combination with standard immunomodulatory drugs as well as next-generation cereblon E3 ligase modulators. These novel agents include drugs being repurposed from their use in other diseases as well as novel monoclonal antibodies. In addition, agents under development such as immunocytokines, immunotoxins, and natural killer-cell activators/engagers are reviewed. These novel therapeutic strategies hold the promise of countermanding the immunosuppressive tumor microenvironment, leading to enhanced anti-MM activity.

Design, synthesis, and biological evaluation of novel benzimidazolyl isoxazole derivatives as potential c-Myc G4 stabilizers to suppress c-Myc transcription and myeloma growth

The c-Myc oncogene is one of the most frequently deregulated driver genes in human cancer, and its rearrangement is closely associated with the development of multiple myeloma (MM). However, c-Myc is a disordered protein that lacks adequate binding pockets on its surface and has a half-life of only 20 to 30 minutes, so it is challenging to design small-molecule inhibitors. The guanine-rich nuclease hypersensitive element III1 (NHEIII1) upstream of the P1 promoter of the c-Myc gene can form intramolecular parallel G-quadruplexes (G4) structures. It has been established that c-Myc G4 controls 85-90% of the transcriptional activation of the c-Myc, which represents one of the most sought-after drug targets in cancer. Therefore, targeting c-Myc G4 to inhibit c-Myc protein would be a potential strategy for the treatment of MM. Herein, a series of benzimidazolyl isoxazole derivatives (EP1-EP19) were designed and synthesized. Among them, compound EP12 exhibited better RPMI-8226 cell inhibition activity (IC50 = 6.16 µM). Moreover, compound EP12 induced apoptosis and inhibited the expression of c-Myc mRNA and c-Myc protein at 5 µM. Circular dichroism (CD) and molecular dynamics (MD) simulation studies indicated that compound EP12 could firmly stabilize c-Myc G4. Accordingly, compound EP12 displayed potent anti-MM activities in vitro and might be a potential c-Myc G4 small molecular stabilizer to warrant further investigation.

Preclinical Activity of Allogeneic CS1-Specific CAR T-Cells (UCARTCS1) in Multiple Myeloma

Introduction: The substantial activity of chimeric antigen receptor (CAR) T-cells in multiple myeloma (MM) has recently been shown by the success of BCMA-CAR T-cell therapy. Nevertheless the difficulties in (timely) generation of CART cells for each patient, the limited availability of manufacturing slots, and the frequent BCMAlow MM relapses after therapy urge the investigators to search for i) alternative, "off the shelf", available sources of CAR T-cells and ii) alternative target antigens than BCMA. UCARTCS1 cells are "off the shelf" allogeneic CAR T-cells derived from healthy donors targeting CS1 (SLAMF7), which is a highly attractive target, due to its overexpression on MM cells. Furthermore, the genes coding for the TCRα chain of the TCRab receptor and for CS1 are disrupted in UCARTCS1 cells using Cellectis' TALEN® gene-editing technology. These modifications aim to minimize the potential risk for allo-TCR-mediated graft-versus-host disease (GvHD) upon infusion in patients and diminish CS1-mediated fratricide. In this study, we evaluated the preclinical activity of UCARTCS1 in MM cell lines, in bone marrow (BM) samples obtained from MM patients and in a MM mouse model. We also investigated the potential impact of previous therapy and tumor characteristics on the in vitro efficacy of UCARTCS1. Methods: Luciferase-transduced MM cell lines with different expression levels of CS1 were incubated with UCARTCS1 cells or control (non-transduced CS1/TCRαβ double knock-out) T-cells at different E:T ratios for 24 hours. MM cell lysis was assessed by bioluminescence. Anti-MM activity of UCARTCS1 was also evaluated in 25 BM samples obtained from newly diagnosed (n=10; NDMM), daratumumab-naïve relapsed/refractory patients (n=10; RRMM; median of 3 prior therapies) and from daratumumab-refractory patients (n=5; DRMM; median of 3 prior therapies) in 24-hour flow cytometry-based cytotoxicity assays. The results were correlated to CS1 expression levels of MM cells, Treg frequency, and several other patient characteristics such as treatment history. Results: UCARTCS1 induced strong CS1 CAR-mediated and dose-dependent lysis of different MM cell lines expressing variable levels of CS1 (MM1s, L363, UM9, U266). UCARTCS1 cells also effectively lysed primary MM cells in a dose-dependent and CAR-mediated manner, with a mean maximal lysis of 96.9% (Figure 1). In these BM samples, UCARTCS1 cells also targeted CS1+ non-malignant hematopoietic cells, such as CD4+ T-cells, CD8+ T-cells, B cells, and NK cells, while sparing the CS1low fraction in each cell subset. However, the lysis of normal cells was less efficient than MM cell lysis, which could be explained by substantially lower CS1 expression on normal cells compared to MM cells (Figure 2). CS1 expression on MM cells and UCARTCS1 cytotoxic activity were both comparable in the different patient subgroups. In addition, baseline tumor and immune characteristics, such as the expression level of CS1 on MM cells, the tumor load (MM cell percentage in BM), or frequency of Treg cells in the BM did not affect CAR T-cell mediated cytotoxicity. Finally, UCARTCS1 exhibited durable dose-dependent anti-MM activity in mouse xenograft models after i.v. injection of CAR T-cells compared to mice treated with CAR- control T-cells. Conclusion: UCARTCS1 has potent anti-MM activity against MM cell lines and primary MM cells, as well as in a MM xenograft model. There was no difference in activity between heavily pretreated and newly diagnosed patients, indicating that mechanisms of resistance to prior therapies do not result in reduced susceptibility to UCARTCS1-mediated lysis in vitro. UCARTCS1 was also effective in samples from patients with relatively low CS1 expression, with high tumor burden, or with high Treg numbers. These data support the ongoing phase 1 clinical trial with UCARTCS1 in heavily pretreated MM patients (NCT04142619). Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal