SAR650984 directly induces multiple myeloma cell death via lysosomal-associated and apoptotic pathways, which is further enhanced by pomalidomide

Monoclonal Antibodies to Treat Multiple Myeloma: A Dream Come True

Immunotherapy is increasingly used in the treatment of multiple myeloma (MM). Monoclonal antibodies (mAbs) are safe and effective ways to elicit immunotherapeutic responses. In 2015, daratumumab has become the first mAb approved by the Food and Drug Administration for clinical use in MM and, in the last 5 years, a lot of clinical and preclinical research has been done to optimize the use of this drug class. Currently, mAbs have already become part of standard-of-care combinations for the treatment of relapsed/refractory MM and very soon they will also be used in the frontline setting. The success of simple mAbs ('naked mAbs') prompted the development of new types of molecules. Antibody-drug conjugates (ADCs) are tumor-targeting mAbs that release a cytotoxic payload into the tumor cells upon antigen binding in order to destroy them. Bispecific antibodies (BiAbs) are mAbs simultaneously targeting a tumor-associated antigen and an immune cell-associated antigen in order to redirect the immune cell cytotoxicity against the tumor cell. These different constructs produced solid preclinical data and promising clinical data in phase I/II trials. The aim of this review article is to summarize all the recent developments in the field, including data on naked mAbs, ADCs and BiAbs.

The Role of Complement in the Mechanism of Action of Therapeutic Anti-Cancer mAbs

Unconjugated anti-cancer IgG1 monoclonal antibodies (mAbs) activate antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells and antibody-dependent cellular phagocytosis (ADCP) by macrophages, and these activities are thought to be important mechanisms of action for many of these mAbs in vivo. Several mAbs also activate the classical complement pathway and promote complement-dependent cytotoxicity (CDC), although with very different levels of efficacy, depending on the mAb, the target antigen, and the tumor type. Recent studies have unraveled the various structural factors that define why some IgG1 mAbs are strong mediators of CDC, whereas others are not. The role of complement activation and membrane inhibitors expressed by tumor cells, most notably CD55 and CD59, has also been quite extensively studied, but how much these affect the resistance of tumors in vivo to IgG1 therapeutic mAbs still remains incompletely understood. Recent studies have demonstrated that complement activation has multiple effects beyond target cell lysis, affecting both innate and adaptive immunity mediated by soluble complement fragments, such as C3a and C5a, and by stimulating complement receptors expressed by immune cells, including NK cells, neutrophils, macrophages, T cells, and dendritic cells. Complement activation can enhance ADCC and ADCP and may contribute to the vaccine effect of mAbs. These different aspects of complement are also briefly reviewed in the specific context of FDA-approved therapeutic anti-cancer IgG1 mAbs.

Isatuximab monotherapy in relapsed/refractory multiple myeloma: A Japanese, multicenter, phase 1/2, safety and efficacy study

Isatuximab, an anti‐CD38 monoclonal antibody, targets cells that strongly express CD38 including malignant plasma cells. This open‐label, single‐arm, multicenter, phase 1/2 trial investigated the tolerability/safety and efficacy of isatuximab monotherapy in Japanese patients with heavily pretreated, relapsed/refractory multiple myeloma (RRMM). In Phase 1, patients were sequentially assigned to receive isatuximab once weekly (QW) in cycle 1 (4 weeks) and every 2 weeks (Q2W) in subsequent cycles. Cohort 1 (n = 3) received 10 mg/kg QW/Q2W; cohort 2 (n = 5) received 20 mg/kg QW/Q2W. No dose‐limiting toxicities occurred; the recommended dose for the single‐arm phase 2 study (n = 28) was 20 mg/kg QW/Q2W. The overall safety profile was consistent with the current knowledge of isatuximab. The most common adverse events were infusion reactions (42.9%; 12/28); all were grade 1/2 and generally occurred during the first infusion. The overall response rate with 20 mg/kg QW/Q2W isatuximab was 36.4% (12/33); patients with high‐risk cytogenetic abnormalities had comparable results. In phase 2, the median progression‐free survival was 4.7 (95% confidence interval, 3.75 to not reached) months. Median overall survival was not reached. Isatuximab monotherapy was well tolerated and effective in patients with heavily pretreated RRMM including high‐risk cytogenetic patients. This trial is registered at ClinicalTrials.gov as NCT02812706.

Emerging immunotherapies in multiple myeloma

Despite considerable advances in treatment approaches in the past two decades, multiple myeloma remains an incurable disease. Treatments for myeloma continue to evolve with many emerging immunotherapies. The first immunotherapy used to treat hematologic cancers, including multiple myeloma, was an allogeneic stem cell transplant. In the mid-2000s, immunomodulatory drugs thalidomide, lenalidomide, and subsequently pomalidomide were proven to be effective in multiple myeloma and substantially improved survival. The next wave of immunotherapies for multiple myeloma included the monoclonal antibodies daratumumab and elotuzumab, which were approved by the Food and Drug Administration in 2015. Subsequently, a variety of immunotherapies have been developed for multiple myeloma, including chimeric antigen receptor T cells, bispecific antibodies, antibody drug conjugates, and checkpoint inhibitors. Many of these emerging treatments target the B cell maturation antigen, which is expressed on plasma cells, although several other novel receptors are also being studied. This review summarizes the evidence of these various immunotherapies, their mechanism of action, and data from clinical trials regarding the treatments' safety and efficacy.

CD38: targeted therapy in multiple myeloma and therapeutic potential for solid cancers

INTRODUCTION

CD38 is expressed by some cells of hematological malignancies and tumor-related immunosuppressive cells, including regulatory T cells, regulatory B cells, and myeloid-derived suppressor cells. CD38 is an effective target in some hematological malignancies such as multiple myeloma (MM). Daratumumab (Dara), a CD38-targeting antibody, can eliminate CD38^high immune suppressor cells and is regarded as a standard therapy for MM because of its outstanding clinical efficacy. Other CD38 monospecific antibodies, such as isatuximab, MOR202, and TAK079, showed promising effects in clinical trials.

AREA COVERED

This review examines the expression, function, and targeting of CD38 in MM and its potential to deplete immunosuppressive cells in solid cancers. We summarize the distribution and biological function of CD38 and discuss the application of anti-CD38 drugs in hematological malignancies. We also analyz the role of CD38⁺ immune cells in the tumor microenvironment to encourage additional investigations that target CD38 in solid cancers. PubMed and ClinicalTrials were searched to identify relevant literature from the database inception to 30 April 2020.

EXPERT OPINION

There is convincing evidence that CD38-targeted immunotherapeutics reduce CD38⁺ immune suppressor cells. This result suggests that CD38 can be exploited to treat solid tumors by regulating the immunosuppressive microenvironment.

Novel Approaches to Improve Myeloma Cell Killing by Monoclonal Antibodies

The monoclonal antibodies (mAbs) have significantly changed the treatment of multiple myeloma (MM) patients. However, despite their introduction, MM remains an incurable disease. The mAbs currently used for MM treatment were developed with different mechanisms of action able to target antigens, such as cluster of differentiation 38 (CD38) and SLAM family member 7 (SLAMF7) expressed by both, MM cells and the immune microenvironment cells. In this review, we focused on the mechanisms of action of the main mAbs approved for the therapy of MM, and on the possible novel approaches to improve MM cell killing by mAbs. Actually, the combination of anti-CD38 or anti-SLAMF7 mAbs with the immunomodulatory drugs significantly improved the clinical effect in MM patients. On the other hand, pre-clinical evidence indicates that different approaches may increase the efficacy of mAbs. The use of trans-retinoic acid, the cyclophosphamide or the combination of anti-CD47 and anti-CD137 mAbs have given the rationale to design these types of combinations therapies in MM patients in the future. In conclusion, a better understanding of the mechanism of action of the mAbs will allow us to develop novel therapeutic approaches to improve their response rate and to overcome their resistance in MM patients.

Oxidative damage of lysosomes in regulated cell death systems: Pathophysiology and pharmacologic interventions

Lysosomes are small specialized organelles containing a variety of different hydrolase enzymes that are responsible for degradation of all macromolecules, entering the cells through the endosomal system or originated from the internal sources. This allows for transport and recycling of nutrients and internalization of surface proteins for antigen presentation as well as maintaining cellular homeostasis. Lysosomes are also important storage compartments for metal ions and nutrients. The integrity of lysosomal membrane is central to maintaining their normal function, but like other cellular membranes, lysosomal membrane is subject to damage mediated by reactive oxygen species. This results in spillage of lysosomal enzymes into the cytoplasm, leading to proteolytic damage to cellular systems and organelles. Several forms of lysosomal dependent cell death have been identified in diseases. Examination of these events are important for finding treatment strategies relevant to cancer or neurodegenerative diseases as well as autoimmune deficiencies. In this review, we have examined the current literature on involvement of lysosomes in induction of programed cell death and have provided an extensive list of therapeutic approaches that can modulate cell death. Exploitation of these mechanisms can lead to novel therapies for cancer and neurodegenerative diseases.

Isatuximab Acts Through Fc-Dependent, Independent, and Direct Pathways to Kill Multiple Myeloma Cells

Isatuximab is a monoclonal antibody targeting the transmembrane receptor and ectoenzyme CD38, a protein highly expressed on hematological malignant cells, including those in multiple myeloma (MM). Upon binding to CD38-expressing MM cells, isatuximab is thought to induce tumor cell killing via fragment crystallizable (Fc)-dependent mechanisms, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), as well as via direct Fc-independent mechanisms. Here, these mechanisms of action were investigated in MM and diffuse large B-cell lymphoma (DLBCL) cell lines, as well as in peripheral blood mononuclear cells derived from healthy donors, and in MM patient-derived samples. Our findings show that isatuximab-mediated cytotoxicity occurred primarily via ADCC and ADCP in MM cell lines and via ADCC and apoptosis in DLBCL cell lines expressing high levels of CD38. We identified the programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) pathway and MM cell-secreted transforming growth factor-beta (TGF-β) as tumor cell-related features that could suppress CD38-mediated ADCC. Furthermore, we established that isatuximab can directly activate natural killer (NK) cells and promote NK cell-mediated cytotoxicity via crosslinking of CD38 and CD16. Finally, isatuximab-induced CDC was observed in cell lines with high CD38 receptor density (>250,000 molecules/cell) and limited expression of inhibitory complement regulatory proteins (CD46, CD55, and CD59; <50,000 molecules/cell). Taken together, our findings highlight mechanistic insights for isatuximab and provide support for a range of combination therapy approaches that could be tested for isatuximab in the future.

A novel BCMA PBD-ADC with ATM/ATR/WEE1 inhibitors or bortezomib induce synergistic lethality in multiple myeloma

To target mechanisms critical for multiple myeloma (MM) plasma cell adaptations to genomic instabilities and further sustain MM cell killing, we here specifically trigger DNA damage response (DDR) in MM cells by a novel BCMA antibody-drug conjugate (ADC) delivering the DNA cross-linking PBD dimer tesirine, MEDI2228. MEDI2228, more effectively than its anti-tubulin MMAF-ADC homolog, induces cytotoxicity against MM cells regardless of drug resistance, BCMA levels, p53 status, and the protection conferred by bone marrow stromal cells and IL-6. Distinctly, prior to apoptosis, MEDI2228 activates DDRs in MM cells via phosphorylation of ATM/ATR kinases, CHK1/2, CDK1/2, and H2AX, associated with expression of DDR-related genes. Significantly, MEDI2228 synergizes with DDR inhibitors (DDRi s) targeting ATM/ATR/WEE1 checkpoints to induce MM cell lethality. Moreover, suboptimal doses of MEDI2228 and bortezomib (btz) synergistically trigger apoptosis of even drug-resistant MM cells partly via modulation of RAD51 and accumulation of impaired DNA. Such combination further induces superior in vivo efficacy than monotherapy via increased nuclear γH2AX-expressing foci, irreversible DNA damages,  and tumor cell death, leading to significantly prolonged host survival. These results indicate leveraging MEDI2228 with DDRi s or btz as novel combination strategies, further supporting ongoing clinical development of MEDI2228 in patients with relapsed and refractory MM.

CD38 and Anti-CD38 Monoclonal Antibodies in AL Amyloidosis: Targeting Plasma Cells and beyond

Immunoglobulin light chain amyloidosis (AL amyloidosis) is a rare systemic disease characterized by monoclonal light chains (LCs) depositing in tissue as insoluble fibrils, causing irreversible tissue damage. The mechanisms involved in aggregation and deposition of LCs are not fully understood, but CD138/38 plasma cells (PCs) are undoubtedly involved in monoclonal LC production.CD38 is a pleiotropic molecule detectable on the surface of PCs and maintained during the neoplastic transformation in multiple myeloma (MM). CD38 is expressed on T, B and NK cell populations as well, though at a lower cell surface density. CD38 is an ideal target in the management of PC dyscrasia, including AL amyloidosis, and indeed anti-CD38 monoclonal antibodies (MoAbs) have promising therapeutic potential. Anti-CD38 MoAbs act both as PC-depleting agents and as modulators of the balance of the immune cells. These aspects, together with their interaction with Fc receptors (FcRs) and neonatal FcRs, are specifically addressed in this paper. Moreover, the initiallyavailable experiences with the anti-CD38 MoAb DARA in AL amyloidosis are reviewed.

Role of the Bone Marrow Milieu in Multiple Myeloma Progression and Therapeutic Resistance

Multiple myeloma (MM) is a cancer of the plasma cells within the bone marrow (BM). Studies have shown that the cellular and noncellular components of the BM milieu, such as cytokines and exosomes, play an integral role in MM pathogenesis and progression by mediating drug resistance and inducing MM proliferation. Moreover, the BM microenvironment of patients with MM facilitates cancer tolerance and immune evasion through the expansion of regulatory immune cells, inhibition of antitumor effector cells, and disruption of the antigen presentation machinery. These are of special relevance, especially in the current era of cancer immunotherapy. An improved understanding of the supportive role of the MM BM microenvironment will allow for the development of future therapies targeting MM in the context of the BM milieu to elicit deeper and more durable responses. In the present review, we have discussed our current understanding of the role of the BM microenvironment in MM progression and resistance to therapy and discuss novel potential approaches to alter its pro-MM function.

BCMA-Targeting Therapy: Driving a New Era of Immunotherapy in Multiple Myeloma

The treatment of multiple myeloma (MM) has entered into a new era of immunotherapy. Novel immunotherapies will significantly improve patient outcome via simultaneously targeting malignant plasma cell (PC) and reversing immunocompromised bone marrow (BM) microenvironment. B-cell maturation antigen (BCMA), selectively expressed in PCs and a key receptor for A proliferation-inducing ligand (APRIL), is highly expressed in MM cells from patients at all stages. The APRIL/BCMA signal cascades promote the survival and drug resistance of MM cells and further modulate immunosuppressive BM milieu. Impressively, anti-BCMA immunotherapeutic reagents, including chimeric antigen receptor (CAR), antibody-drug conjugate (ADC) and bispecific T cell engager (BiTE) have all shown high response rates in their first clinical trials in relapse and refractory patients with very limited treatment options. These results rapidly inspired numerous development of next-generation anti-BCMA biotherapeutics, i.e., bispecific molecule, bispecific or trispecific antibodies, a novel form of CAR T/NK cells and T Cell Antigen Coupler (TAC) receptors, antibody-coupled T cell receptor (ACTR) as well as a cancer vaccine. We here highlight seminal preclinical and clinical studies on novel BCMA-based immunotherapies as effective monotherapy and discuss their potential in combination with current anti-MM and novel checkpoint drugs in earlier disease stages to further achieve durable responses in patients.

Targeting of CD38 by the Tumor Suppressor miR-26a Serves as a Novel Potential Therapeutic Agent in Multiple Myeloma

Multiple myeloma is an incurable refractory hematologic malignancy arising from plasma cells in the bone marrow. Here we investigated miR-26a function in multiple myeloma and tested single-wall carbon nanotube delivery of miR-26a in vitro and in vivo. miR-26a was downregulated in patients with multiple myeloma cells compared with plasma cells from healthy donors. miR-26a overexpression inhibited proliferation and migration and induced apoptosis in multiple myeloma cell lines. To identify the targets of miR-26a, RPMI8226-V-miR-26-GFP and RPMI8226-V-GFP cells were cultured using stable isotope labeling by amino acids in cell culture (SILAC) medium, followed by mass spectrometry analysis. In multiple myeloma cells overexpressing miR-26a, CD38 protein was downregulated and subsequently confirmed to be a direct target of miR-26a. Depletion of CD38 in multiple myeloma cells duplicated the multiple myeloma inhibition observed with exogenous expression of miR-26a, whereas restoration of CD38 overcame the inhibition of miR-26a in multiple myeloma cells. In a human multiple myeloma xenograft mouse model, overexpression of miR-26a inhibited CD38 expression, provoked cell apoptosis, and inhibited cell proliferation. Daratumumab is the first CD38 antibody drug for monotherapy and combination therapy for patients with multiple myeloma, but eventually resistance develops. In multiple myeloma cells, CD38 remained at low level during daratumumab treatment, but a high-quality response is sustained. In daratumumab-resistant multiple myeloma cells, CD38 expression was completely restored but failed to correlate with daratumumab-induced cell death. Therefore, a therapeutic strategy to confer selection pressure to maintain low CD38 expression in multiple myeloma cells may have clinical benefit. SIGNIFICANCE: These results highlight the tumor suppressor function of miR-26a via its targeting of CD38 and suggest the therapeutic potential of miR-26a in patients with multiple myeloma.

A dose-finding Phase 2 study of single agent isatuximab (anti-CD38 mAb) in relapsed/refractory multiple myeloma

A Phase 2 dose-finding study evaluated isatuximab, an anti-CD38 monoclonal antibody, in relapsed/refractory multiple myeloma (RRMM; NCT01084252). Patients with ≥3 prior lines or refractory to both immunomodulatory drugs and proteasome inhibitors (dual refractory) were randomized to isatuximab 3 mg/kg every 2 weeks (Q2W), 10 mg/kg Q2W(2 cycles)/Q4W, or 10 mg/kg Q2W. A fourth arm evaluated 20 mg/kg QW(1 cycle)/Q2W. Patients (N = 97) had a median (range) age of 62 years (38–85), 5 (2–14) prior therapy lines, and 85% were double refractory. The overall response rate (ORR) was 4.3, 20.0, 29.2, and 24.0% with isatuximab 3 mg/kg Q2W, 10 mg/kg Q2W/Q4W, 10 mg/kg Q2W, and 20 mg/kg QW/Q2W, respectively. At doses ≥10 mg/kg, median progression-free survival and overall survival were 4.6 and 18.7 months, respectively, and the ORR was 40.9% (9/22) in patients with high-risk cytogenetics. CD38 receptor density was similar in responders and non-responders. The most common non-hematologic adverse events (typically grade ≤2) were nausea (34.0%), fatigue (32.0%), and upper respiratory tract infections (28.9%). Infusion reactions (typically with first infusion and grade ≤2) occurred in 51.5% of patients. In conclusion, isatuximab is active and generally well tolerated in heavily pretreated RRMM, with greatest efficacy at doses ≥10 mg/kg.

Therapeutic potential of isatuximab in the treatment of multiple myeloma: Evidence to date

Management of multiple myeloma represents an ever changing paradigm with monoclonal antibodies adding the ability to treat patients with 3 and 4 drug regimens with acceptable toxicity profiles. In recent years, we have seen the FDA approve a number of regimens with both elotuzumab and daratumumab in combination with the standard approaches of immunomodulatory drugs, proteasome inhibitors, and steroids. Isatuximab is a naked, humanized IgG1 monoclonal antibody directed against CD38. With the recent FDA approval in March 2020, we seek to summarize the presented data to date and where this drug will fit into the future gestalt of myeloma therapy.

Vulnerability of invasive glioblastoma cells to lysosomal membrane destabilization

The current clinical care of glioblastomas leaves behind invasive, radio‐ and chemo‐resistant cells. We recently identified mammary‐derived growth inhibitor (MDGI/FABP3) as a biomarker for invasive gliomas. Here, we demonstrate a novel function for MDGI in the maintenance of lysosomal membrane integrity, thus rendering invasive glioma cells unexpectedly vulnerable to lysosomal membrane destabilization. MDGI silencing impaired trafficking of polyunsaturated fatty acids into cells resulting in significant alterations in the lipid composition of lysosomal membranes, and subsequent death of the patient‐derived glioma cells via lysosomal membrane permeabilization (LMP). In a preclinical model, treatment of glioma‐bearing mice with an antihistaminergic LMP‐inducing drug efficiently eradicated invasive glioma cells and secondary tumours within the brain. This unexpected fragility of the aggressive infiltrating cells to LMP provides new opportunities for clinical interventions, such as re‐positioning of an established antihistamine drug, to eradicate the inoperable, invasive, and chemo‐resistant glioma cells from sustaining disease progression and recurrence.

Resistance Mechanisms Towards CD38-Directed Antibody Therapy in Multiple Myeloma

Antibodies targeting CD38 are rapidly changing the treatment landscape of multiple myeloma (MM). CD38-directed antibodies have several mechanisms of action. Fc-dependent immune effector mechanisms include complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and apoptosis. In addition, direct effects and immunomodulatory effects contribute to the efficacy of CD38-directed antibodies. Daratumumab, the first-in-class anti-CD38 monoclonal antibody, is now part of standard treatment regimens of both newly diagnosed as well as relapsed/refractory MM patients. The FDA has recently approved isatuximab in combination with pomalidomide and dexamethasone for relapsed/refractory MM patients after at least two prior therapies. Further, the other CD38-targeting antibodies (i.e., MOR202 and TAK-079) are increasingly used in clinical trials. The shift to front-line treatment of daratumumab will lead to an increase in patients refractory to CD38 antibody therapy already after first-line treatment. Therefore, it is important to gain insight into the mechanisms of resistance to CD38-targeting antibodies in MM, and to develop strategies to overcome this resistance. In the current review, we will briefly describe the most important clinical data and mechanisms of action and will focus in depth on the current knowledge on mechanisms of resistance to CD38-targeting antibodies and potential strategies to overcome this.

Novel Agents in Multiple Myeloma

The therapeutic landscape of multiple myeloma (MM) has dramatically changed in the last 15 years with the advent of immunomodulatory drugs and proteasome inhibitors. However, majority of MM patients relapse, and new therapies are needed. Various agents with diverse mechanisms of action and distinct targets, including cellular therapies, monoclonal antibodies, and small molecules, are currently under investigation. In this review, we report novel drugs recently approved or under advanced investigation that will likely be incorporated in the future as new standard for MM treatment, focusing on their mechanisms of action, cellular targets, and stage of development.

Multiple Myeloma: Available Therapies and Causes of Drug Resistance

Multiple myeloma (MM) is the second most common blood cancer. Treatments for MM include corticosteroids, alkylating agents, anthracyclines, proteasome inhibitors, immunomodulatory drugs, histone deacetylase inhibitors and monoclonal antibodies. Survival outcomes have improved substantially due to the introduction of many of these drugs allied with their rational use. Nonetheless, MM patients successively relapse after one or more treatment regimens or become refractory, mostly due to drug resistance. This review focuses on the main drugs used in MM treatment and on causes of drug resistance, including cytogenetic, genetic and epigenetic alterations, abnormal drug transport and metabolism, dysregulation of apoptosis, autophagy activation and other intracellular signaling pathways, the presence of cancer stem cells, and the tumor microenvironment. Furthermore, we highlight the areas that need to be further clarified in an attempt to identify novel therapeutic targets to counteract drug resistance in MM patients.

The Lysosomal Membrane Protein Lamp2 Alleviates Lysosomal Cell Death by Promoting Autophagic Flux in Ischemic Cardiomyocytes

Lysosomal membrane permeabilization (LMP) has recently been recognized as an important cell death pathway in various cell types. However, studies regarding the correlation between LMP and cardiomyocyte death are scarce. Lysosomal membrane-associated protein 2 (Lamp2) is an important component of lysosomal membranes and is involved in both autophagy and LMP. In the present study, we found that the protein content of Lamp2 gradually decreased in response to oxygen, glucose and serum deprivation (OGD) treatment in vitro. To further elucidate its role in ischemic cardiomyocytes, particularly with respect to autophagy and LMP, we infected cardiomyocytes with adenovirus carrying full-length Lamp2 to restore its protein level in cells. We found that OGD treatment resulted in the occurrence of LMP and a decline in the viability of cardiomyocytes, which were remarkably reversed by Lamp2 restoration. Exogenous expression of Lamp2 also significantly alleviated the autophagic flux blockade induced by OGD treatment by promoting the trafficking of cathepsin B (Cat B) and cathepsin D (Cat D). Through drug intervention and gene regulation to alleviate and exacerbate autophagic flux blockade respectively, we found that impaired autophagic flux in response to ischemic injury contributed to the occurrence of LMP in cardiomyocytes. In conclusion, our present data suggest that Lamp2 overexpression can improve autophagic flux blockade probably by promoting the trafficking of cathepsins and consequently conferring cardiomyocyte resistance against lysosomal cell death (LCD) that is induced by ischemic injury. These results may indicate a new therapeutic target for ischemic heart damage.

Nanobody-based CD38-specific heavy chain antibodies induce killing of multiple myeloma and other hematological malignancies

Rationale: CD38 is a target for the therapy of multiple myeloma (MM) with monoclonal antibodies such as daratumumab and isatuximab. Since MM patients exhibit a high rate of relapse, the development of new biologics targeting alternative CD38 epitopes is desirable. The discovery of single-domain antibodies (nanobodies) has opened the way for a new generation of antitumor therapeutics. We report the generation of nanobody-based humanized IgG1 heavy chain antibodies (hcAbs) with a high specificity and affinity that recognize three different and non-overlapping epitopes of CD38 and compare their cytotoxicity against CD38-expressing hematological cancer cells in vitro, ex vivo and in vivo. Methods: We generated three humanized hcAbs (WF211-hcAb, MU1067-hcAb, JK36-hcAb) that recognize three different non-overlapping epitopes (E1, E2, E3) of CD38 by fusion of llama-derived nanobodies to the hinge- and Fc-domains of human IgG1. WF211-hcAb shares the binding epitope E1 with daratumumab. We compared the capacity of these CD38-specific hcAbs and daratumumab to induce CDC and ADCC in CD38-expressing tumor cell lines in vitro and in patient MM cells ex vivo as well as effects on xenograft tumor growth and survival in vivo. Results: CD38-specific heavy chain antibodies (WF211-hcAb, MU1067-hcAb, JK36-hcAb) potently induced antibody-dependent cellular cytotoxicity (ADCC) in CD38-expressing tumor cell lines and in primary patient MM cells, but only little if any complement-dependent cytotoxicity (CDC). In vivo, CD38-specific heavy chain antibodies significantly reduced the growth of systemic lymphomas and prolonged survival of tumor bearing SCID mice. Conclusions: CD38-specific nanobody-based humanized IgG1 heavy chain antibodies mediate cytotoxicity against CD38-expressing hematological cancer cells in vitro, ex vivo and in vivo. These promising results of our study indicate that CD38-specific hcAbs warrant further clinical development as therapeutics for multiple myeloma and other hematological malignancies.

Mechanisms of Resistance to Anti-CD38 Daratumumab in Multiple Myeloma

Daratumumab (Dara) is the first-in-class human-specific anti-CD38 mAb approved for the treatment of multiple myeloma (MM). Although recent data have demonstrated very promising results in clinical practice and trials, some patients do not achieve a partial response, and ultimately all patients undergo progression. Dara exerts anti-MM activity via antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), complement-dependent cytotoxicity (CDC), and immunomodulatory effects. Deregulation of these pleiotropic mechanisms may cause development of Dara resistance. Knowledge of this resistance may improve the therapeutic management of MM patients.

[CD38 antibodies in multiple myeloma]

The high CD38 expression by plasma cells together with the biological functions of CD38 resulted in the development of CD38 antibodies for the treatment of multiple myeloma (MM) patients. The cytolytic activity of CD38 antibodies is mediated by complement-dependent cytoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), direct cell death effects and immunomodulatory effects. CD38 antibodies have demonstrated their clinical benefit as single agent or in combination for the treatment of multiple myeloma patients and will contribute to further improvement in the outcome of MM patients.

Therapeutic Monoclonal Antibodies and Antibody Products: Current Practices and Development in Multiple Myeloma

Immunotherapy is the latest innovation for the treatment of multiple myeloma (MM). Monoclonal antibodies (mAbs) entered the clinical practice and are under evaluation in clinical trials. MAbs can target highly selective and specific antigens on the cell surface of MM cells causing cell death (CD38 and CS1), convey specific cytotoxic drugs (antibody-drug conjugates), remove the breaks of the immune system (programmed death 1 (PD-1) and PD-ligand 1/2 (L1/L2) axis), or boost it against myeloma cells (bi-specific mAbs and T cell engagers). Two mAbs have been approved for the treatment of MM: the anti-CD38 daratumumab for newly-diagnosed and relapsed/refractory patients and the anti-CS1 elotuzumab in the relapse setting. These compounds are under investigation in clinical trials to explore their synergy with other anti-MM regimens, both in the front-line and relapse settings. Other antibodies targeting various antigens are under evaluation. B cell maturation antigens (BCMAs), selectively expressed on plasma cells, emerged as a promising target and several compounds targeting it have been developed. Encouraging results have been reported with antibody drug conjugates (e.g., GSK2857916) and bispecific T cell engagers (BiTEs^®), including AMG420, which re-directs T cell-mediated cytotoxicity against MM cells. Here, we present an overview on mAbs currently approved for the treatment of MM and promising compounds under investigation.

CD38 Expression by Myeloma Cells and Its Role in the Context of Bone Marrow Microenvironment: Modulation by Therapeutic Agents

In the last decades CD38 has emerged as an attractive target for multiple myeloma (MM). CD38 is a novel multifunctional glycoprotein that acts as a receptor, adhesion molecule interacting with CD31 and as an ectoenzyme. As an ectoenzyme, CD38 functions as a metabolic sensor catalyzing the extracellular conversion of NAD+ to the immunosuppressive factor adenosine (ADO). Other ectoenzymes, CD73 and CD203a, together with CD38, are also involved in the alternative axis of extracellular production of ADO, bypassing the canonical pathway mediated by CD39. CD38 is ubiquitously expressed in the bone marrow microenvironment; however, only MM cells display a very high surface density, which lead to the development of several anti-CD38 monoclonal antibodies (mAbs). The efficacy of anti-CD38 mAbs depends from the presence of CD38 on the surface of MM and immune-microenvironment cells. Interestingly, it has been reported that several drugs like lenalidomide, panobinostat, the all-trans retinoic acid and the DNA methyltransferase inhibitors may increase the expression of CD38. Hence, the possibility to modulate CD38 by increasing its expression on MM cells is the pre-requisite to potentiate the clinical efficacy of the anti-CD38 mAbs and to design clinical trials with the combination of anti-CD38 mAbs and these drugs.

Isatuximab plus pomalidomide and low-dose dexamethasone versus pomalidomide and low-dose dexamethasone in patients with relapsed and refractory multiple myeloma (ICARIA-MM): a randomised, multicentre, open-label, phase 3 study

BACKGROUND

Isatuximab is a monoclonal antibody that binds a specific epitope on the human CD38 receptor and has antitumour activity via multiple mechanisms of action. In a previous phase 1b study, around 65% of patients with relapsed and refractory multiple myeloma achieved an overall response with a combination of isatuximab with pomalidomide and low-dose dexamethasone. The aim of this study was to determine the progression-free survival benefit of isatuximab plus pomalidomide and dexamethasone compared with pomalidomide and dexamethasone in patients with relapsed and refractory multiple myeloma.

METHODS

We did a randomised, multicentre, open-label, phase 3 study at 102 hospitals in 24 countries in Europe, North America, and the Asia-Pacific regions. Eligible participants were adult patients with relapsed and refractory multiple myeloma who had received at least two previous lines of treatment, including lenalidomide and a proteasome inhibitor. Patients were excluded if they were refractory to previous treatment with an anti-CD38 monoclonal antibody. We randomly assigned patients (1:1) to either isatuximab 10 mg/kg plus pomalidomide 4 mg plus dexamethasone 40 mg (20 mg for patients aged ≥75 years), or pomalidomide 4 mg plus dexamethasone 40 mg. Randomisation was done using interactive response technology and stratified according to the number of previous lines of treatment (2-3 vs >3) and age (<75 years vs ≥75 years). Treatments were assigned based on a permuted blocked randomisation scheme with a block size of four. The isatuximab-pomalidomide-dexamethasone group received isatuximab intravenously on days 1, 8, 15, and 22 in the first 28-day cycle, then on days 1 and 15 in subsequent cycles. Both groups received oral pomalidomide on days 1 to 21 in each cycle, and oral or intravenous dexamethasone on days 1, 8, 15, and 22 of each cycle. Treatment continued until disease progression, unacceptable toxicity, or consent withdrawal. Dose reductions for adverse reactions were permitted for pomalidomide and dexamethasone, but not for isatuximab. The primary endpoint was progression-free survival, determined by an independent response committee and assessed in the intention-to-treat population. Safety was assessed in all participants who received at least one dose of study drug. This study is registered at ClinicalTrials.gov, number NCT02990338.

FINDINGS

Between Jan 10, 2017, and Feb 2, 2018, we randomly assigned 307 patients to treatment: 154 to isatuximab-pomalidomide-dexamethasone, and 153 to pomalidomide-dexamethasone. At a median follow-up of 11·6 months (IQR 10·1-13·9), median progression-free survival was 11·5 months (95% CI 8·9-13·9) in the isatuximab-pomalidomide-dexamethasone group versus 6·5 months (4·5-8·3) in the pomalidomide-dexamethasone group; hazard ratio 0·596, 95% CI 0·44-0·81; p=0·001 by stratified log-rank test. The most frequent treatment-emergent adverse events (any grade; isatuximab-pomalidomide-dexamethasone vs pomalidomide-dexamethasone) were infusion reactions (56 [38%] vs 0), upper respiratory tract infections (43 [28%] vs 26 [17%]), and diarrhoea (39 [26%] vs 29 [20%]). Adverse events with a fatal outcome were reported in 12 patients (8%) in the isatuximab-pomalidomide-dexamethasone group and 14 (9%) in the pomalidomide-dexamethasone group. Deaths due to treatment-related adverse events were reported for one patient (<1%) in the isatuximab-pomalidomide-dexamethasone group (sepsis) and two (1%) in the pomalidomide-dexamethasone group (pneumonia and urinary tract infection).

INTERPRETATION

The addition of isatuximab to pomalidomide-dexamethasone significantly improves progression-free survival in patients with relapsed and refractory multiple myeloma. Isatuximab is an important new treatment option for the management of relapsed and refractory myeloma, particularly for patients who become refractory to lenalidomide and a proteasome inhibitor.

FUNDING

Sanofi. VIDEO ABSTRACT.

CD38, a Receptor with Multifunctional Activities: From Modulatory Functions on Regulatory Cell Subsets and Extracellular Vesicles, to a Target for Therapeutic Strategies

CD38 is a multifunctional cell surface protein endowed with receptor/enzymatic functions. The protein is generally expressed at low/intermediate levels on hematological tissues and some solid tumors, scoring the highest levels on plasma cells (PC) and PC-derived neoplasia. CD38 was originally described as a receptor expressed by activated cells, mainly T lymphocytes, wherein it also regulates cell adhesion and cooperates in signal transduction mediated by major receptor complexes. Furthermore, CD38 metabolizes extracellular NAD+, generating ADPR and cyclic ADPR. This ecto-enzyme controls extra-cellular nucleotide homeostasis and intra-cellular calcium fluxes, stressing its relevance in multiple physiopathological conditions (infection, tumorigenesis and aging). In clinics, CD38 was adopted as a cell activation marker and in the diagnostic/staging of leukemias. Quantitative surface CD38 expression by multiple myeloma (MM) cells was the basic criterion used for therapeutic application of anti-CD38 monoclonal antibodies (mAbs). Anti-CD38 mAbs-mediated PC depletion in autoimmunity and organ transplants is currently under investigation. This review analyzes different aspects of CD38's role in regulatory cell populations and how these effects are obtained. Characterizing CD38 functional properties may widen the extension of therapeutic applications for anti-CD38 mAbs. The availability of therapeutic mAbs with different effects on CD38 enzymatic functions may be rapidly translated to immunotherapeutic strategies of cell immune defense.

Therapeutic Opportunities with Pharmacological Inhibition of CD38 with Isatuximab

CD38 is a transmembrane glycoprotein with ectoenzymatic activity involved in regulation of migration, signal transduction, and receptor-mediated adhesion. CD38 is highly expressed on various malignant cells, including multiple myeloma (MM), and at relatively low levels in other tissues, making it a suitable target for therapeutic antibodies. Several anti-CD38 therapies have been, or are being, developed for the treatment of MM, including daratumumab and isatuximab (SAR650984), respectively. Studies have shown that anti-CD38 therapies are effective in the treatment of relapsed/refractory MM and are well tolerated, with infusion reactions being the most common side effects. They can be used as monotherapy or in combination with immunomodulatory agents, such as pomalidomide, or proteasome inhibitors to potentiate their activity. Here we examine isatuximab and several anti-CD38 agents in development that were generated using new antibody engineering techniques and that may lead to more effective CD38 targeting. We also summarize trials assessing these antibodies in MM, other malignancies, and solid organ transplantation. Finally, we propose that further research on the mechanisms of resistance to anti-CD38 therapy and the development of biomarkers and new backbone regimens with CD38 antibodies will be important steps in building more personalized treatment for patients with MM.

Biological Background of Resistance to Current Standards of Care in Multiple Myeloma

A high priority problem in multiple myeloma (MM) management is the development of resistance to administered therapies, with most myeloma patients facing successively shorter periods of response and relapse. Herewith, we review the current knowledge on the mechanisms of resistance to the standard backbones in MM treatment: proteasome inhibitors (PIs), immunomodulatory agents (IMiDs), and monoclonal antibodies (mAbs). In some cases, strategies to overcome resistance have been discerned, and an effort should be made to evaluate whether resensitization to these agents is feasible in the clinical setting. Additionally, at a time in which we are moving towards precision medicine in MM, it is equally important to identify reliable and accurate biomarkers of sensitivity/refractoriness to these main therapeutic agents with the goal of having more efficacious treatments and, if possible, prevent the development of relapse.

B cell maturation antigen (BCMA)-based immunotherapy for multiple myeloma

Introduction: B cell maturation antigen (BCMA) contributes to MM pathophysiology and is a target antigen for novel MM immunotherapy. Complete responses have been observed in heavily pretreated MM patients after treatment with BCMA antibody-drug conjugates (ADC), chimeric antigen receptor T, and bi-specific T cell engagers (BiTE®). These and other innovative BCMA-targeted therapies transform the treatment landscape and patient outcome in MM. Areas covered: The immunobiological rationale for targeting BCMA in MM is followed by key preclinical studies and available clinical data on efficacy and safety of therapies targeting BCMA from recent phase I/II studies. Expert opinion: BCMA is the most selective MM target antigen, and BCMA-targeted approaches have achieved high responses even in relapse and refractory MM as a monotherapy. Long-term follow-up and correlative studies using immuno-phenotyping and -sequencing will delineate mechanisms of overcoming the immunosuppressive MM bone marrow microenvironment to mediate additive or synergistic anti-MM cytotoxicity. Moreover, they will delineate cellular and molecular events underlying the development of resistance underlying relapse of disease. Most importantly, targeted BCMA-based immunotherapies used earlier in the disease course and in combination (adoptive T cell therapy, mAbs/ADCs, checkpoint and cytokine blockade, and vaccines) have great promise to achieve long-term disease control and potential cure.

Novel targets for the treatment of relapsing multiple myeloma

Introduction: Multiple myeloma (MM) is characterized by the high tendency to relapse and develop drug resistance. Areas covered: This review focused on the main novel targets identified to design drugs for the treatment of relapsing MM patients. CD38 and SLAMF7 are the main surface molecules leading to the development of monoclonal antibodies (mAbs) recently approved for the treatment of relapsing MM patients. B cell maturation antigen (BCMA) is a suitable target for antibody-drug conjugates, bispecific T cell engager mAbs and Chimeric Antigen Receptor (CAR)-T cells. Moreover, the programmed cell death protein 1 (PD)-1/PD-Ligand (PD-L1) expression profile by MM cells and their microenvironment and the use of immune checkpoints inhibitors in MM patients are reported. Finally, the role of histone deacetylase (HDAC), B cell lymphoma (BCL)-2 family proteins and the nuclear transport protein exportin 1 (XPO1) as novel targets are also underlined. The clinical results of the new inhibitors in relapsing MM patients are discussed. Expert opinion: CD38, SLAMF7, and BCMA are the main targets for different immunotherapeutic approaches. Selective inhibitors of HDAC6, BCL-2, and XPO1 are new promising compounds under clinical investigation in relapsing MM patients.

Novel anti-CD38 humanized mAb SG003 possessed enhanced cytotoxicity in lymphoma than Daratumumab via antibody-dependent cell-mediated cytotoxicity

Background

In vivo use of monoclonal antibodies has become routine clinical practice in the treatment of human cancer. CD38 is an attractive target, because it has double roles, as a receptor and an ectoenzyme. Daratumumab, an anti-CD38 antibody, is currently in the clinical trials for multiple myeloma.

Results

Here we obtained a humanized anti-CD38 antibody, SG003, using SDR-grafting method. SG003 possessed stronger antigen binding activity than Daratumumab, and its epitope was far from that of Daratumumab, an anti-CD38 antibody currently in the clinical trials for multiple myeloma; besides, SG003 showed enhanced antibody-dependent cell-mediated cytotoxicity function and in vivo inhibitory efficacy of tumor growth in xenograft mice model.

Conclusion

SG003 seemed to be a good option to improve the curative effect of CD38-related cancers.

A phase 1b study of isatuximab plus pomalidomide/dexamethasone in relapsed/refractory multiple myeloma

This phase 1b dose-escalation study evaluated isatuximab plus pomalidomide/dexamethasone in patients with relapsed/refractory multiple myeloma (RRMM). Patients who had received ≥2 prior MM therapies, including lenalidomide and a proteasome inhibitor (PI), were enrolled and received isatuximab at 5, 10, or 20 mg/kg (weekly for 4 weeks, followed by every 2 weeks), pomalidomide 4 mg (days 1-21), and dexamethasone 40 mg (weekly) in 28-day cycles until progression/intolerable toxicity. The primary objective was to determine the safety and recommended dose of isatuximab with this combination. Secondary objectives included evaluation of pharmacokinetics, immunogenicity, and efficacy. Forty-five patients received isatuximab (5 [n = 8], 10 [n = 31], or 20 [n = 6] mg/kg). Patients received a median of 3 (range, 1-10) prior lines; most were refractory to their last regimen (91%), with 82% lenalidomide-refractory and 84% PI-refractory. Median treatment duration was 9.6 months; 19 patients (42%) remain on treatment. Most common adverse events included fatigue (62%), and upper respiratory tract infection (42%), infusion reactions (42%), and dyspnea (40%). The most common grade ≥3 treatment-emergent adverse event was pneumonia, which occurred in 8 patients (17.8%). Hematologic laboratory abnormalities were common (lymphopenia, leukopenia, anemia, 98% each; neutropenia, 93%; and thrombocytopenia, 84%). Overall response rate was 62%; median duration of response was 18.7 months; median progression-free survival was 17.6 months. These results demonstrate potential meaningful clinical activity and a manageable safety profile of isatuximab plus pomalidomide/dexamethasone in heavily pretreated patients with RRMM. The 10 mg/kg weekly/every 2 weeks isatuximab dose was selected for future studies. This trial was registered at www.clinicaltrials.gov as #NCT02283775.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

Reprint of "Immunomodulatory effects of CD38-targeting antibodies"

The fist in class CD38-targeting antibody, daratumumab, is currently approved as single agent and in combination with standards of care for the treatment of relapsed and refractory multiple myeloma. Based on the high activity and favorable toxicity profile of daratumumab, other CD38 antibodies, such as isatuximab, MOR202, and TAK-079, are being evaluated in MM and other malignancies. The CD38-targeting antibodies have classic Fc-dependent immune effector mechanisms, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). These mechanisms of action are dependent on CD38 expression on the tumor cells. There is increasing evidence that CD38 antibodies also improve host-anti-tumor immune response by eliminating CD38-positive immune suppressor cells, including regulatory T cells, regulatory B cells, and myeloid-derived suppressor cells. Indeed, daratumumab treatment results in a marked increase in T cell numbers and activity. CD38-targeting antibodies probably also reduce adenosine production in the bone marrow microenvironment, which may contribute to improved T cell activity. Preclinical and clinical studies have demonstrated that CD38-targeting antibodies have synergistic activity with several other anti-cancer drugs, including various agents with immune stimulating activity, such as lenalidomide and pomalidomide, as well as PD1/PD-L1 inhibitors.

Augmentation of Saporin-Based Immunotoxins for Human Leukaemia and Lymphoma Cells by Triterpenoid Saponins: The Modifying Effects of Small Molecule Pharmacological Agents

Triterpenoid saponins from Saponinum album (SA) significantly augment the cytotoxicity of saporin-based immunotoxins but the mechanism of augmentation is not fully understood. We investigated the effects of six small molecule pharmacological agents, which interfere with endocytic and other processes, on SA-mediated augmentation of saporin and saporin-based immunotoxins (ITs) directed against CD7, CD19, CD22 and CD38 on human lymphoma and leukaemia cell lines. Inhibition of clathrin-mediated endocytosis or endosomal acidification abolished the SA augmentation of saporin and of all four immunotoxins tested but the cytotoxicity of each IT or saporin alone was largely unaffected. The data support the hypothesis that endocytic processes are involved in the augmentative action of SA for saporin ITs targeted against a range of antigens expressed by leukaemia and lymphoma cells. In addition, the reactive oxygen species (ROS) scavenger tiron reduced the cytotoxicity of BU12-SAP and OKT10-SAP but had no effect on 4KB128-SAP or saporin cytotoxicity. Tiron also had no effect on SA-mediated augmentation of the saporin-based ITs or unconjugated saporin. These results suggest that ROS are not involved in the augmentation of saporin ITs and that ROS induction is target antigen-dependent and not directly due to the cytotoxic action of the toxin moiety.

The Mechanism of Action of the Anti-CD38 Monoclonal Antibody Isatuximab in Multiple Myeloma

PURPOSE

Knowledge about the mechanism of action (MoA) of monoclonal antibodies (mAb) is required to understand which patients with multiple myeloma (MM) benefit the most from a given mAb, alone or in combination therapy. Although there is considerable research about daratumumab, knowledge about other anti-CD38 mAbs remains scarce.

EXPERIMENTAL DESIGN

We performed a comprehensive analysis of the MoA of isatuximab.

RESULTS

Isatuximab induces internalization of CD38 but not its significant release from MM cell surface. In addition, we uncovered an association between levels of CD38 expression and different MoA: (i) Isatuximab was unable to induce direct apoptosis on MM cells with CD38 levels closer to those in patients with MM, (ii) isatuximab sensitized CD38^hi MM cells to bortezomib plus dexamethasone in the presence of stroma, (iii) antibody-dependent cellular cytotoxicity (ADCC) was triggered by CD38^lo and CD38^hi tumor plasma cells (PC), (iv) antibody-dependent cellular phagocytosis (ADCP) was triggered only by CD38^hi MM cells, whereas (v) complement-dependent cytotoxicity could be triggered in less than half of the patient samples (those with elevated levels of CD38). Furthermore, we showed that isatuximab depletes CD38^hi B-lymphocyte precursors and natural killer (NK) lymphocytes ex vivo-the latter through activation followed by exhaustion and eventually phagocytosis.

CONCLUSIONS

This study provides a framework to understand response determinants in patients treated with isatuximab based on the number of MoA triggered by CD38 levels of expression, and for the design of effective combinations aimed at capitalizing disrupted tumor-stroma cell protection, augmenting NK lymphocyte-mediated ADCC, or facilitating ADCP in CD38^lo MM patients.See related commentary by Malavasi and Faini, p. 2946.

Therapeutic antibodies for multiple myeloma

In recent years, many antibody therapies for multiple myeloma have been developed. Antibodies against SLAMF7, CD38, B-cell maturation antigen and PD-1 have been developed and clinical trials are currently under way. As of July 2017, antibodies clinically available in Japan for the treatment of multiple myeloma are elotuzumab against SLAMF7 and daratumumab against CD38. Elotuzumab is a humanized IgG1-kappa monoclonal antibody targeting human SLAMF7. SLAMF7 is a cell surface glycoprotein receptor highly expressed on multiple myeloma cells, and it is also expressed on natural killer cells and is critical for natural killer function. Binding of elotuzumab to natural killer cells leads to activation of natural killer cells, resulting in antibody-dependent cell-mediated cytotoxicity of elotuzumab-bound multiple myeloma cells, but not complement-dependent cytotoxicity. The result of a randomized phase III trial of elotuzumab+lenalidomide+dexamethasone (ELOQUENT-2) reduced the risk of disease progression/death by 30% vs lenalidomide+dexamethasone in relapse/refractory multiple myeloma. Daratumumab is a human anti-CD38 IgG1-kappa antibody. CD38 is expressed ubiquitously virtually in all tissues that are highly expressed on plasma cells and it represents an attractive target for immunotherapy using monoclonal antibodies. In the phase III CASTOR trial, patients treated with daratumumab+bortezomib+dexamethasone had a better CR rate and progression-free survival rate compared with bortezomib+dexamethasone-treated patients (29% vs 10%, median progression-free survival: 16.7 vs 7.1 months, respectively). Moreover, in the phase III POLLUX trial, patients treated with daratumumab+lenalidomide+dexamethasone had a better response and progression-free survival (CRR or better: 55% vs 23%, 30-month progression-free survival: 58% vs 35%), compared with lenalidomide+dexamethasone-treated patients.

Monoclonal Antibodies for the Treatment of Multiple Myeloma: An Update

The past two decades have seen a revolution in multiple myeloma (MM) therapy with the introduction of several small molecules, mostly orally effective, whose mechanisms are based on proteasome inhibition, histone deacetylase (HDAC) blockade, and immunomodulation. Immunotherapeutic approaches to MM treatment using monoclonal antibodies (mAbs), while long in development, began to reap success with the identification of CD38 and SLAMF7 as suitable targets for development, culminating in the 2015 Food and Drug Administration (FDA) approval of daratumumab and elotuzumab, respectively. This review highlights additional mAbs now in the developmental pipeline. Isatuximab, another anti-CD38 mAb, currently is under study in four phase III trials and may offer certain advantages over daratumumab. Several antibody-drug conjugates (ADCs) in the early stages of development are described, including JNJ-63723283, which has attained FDA breakthrough status for MM. Other mAbs described in this review include denosumab, recently approved for myeloma-associated bone loss, and checkpoint inhibitors, although the future status of the latter combined with immunomodulators has been clouded by unacceptably high death rates that caused the FDA to issue clinical holds on several of these trials. Also highlighted are the therapies based on the B Cell Maturation Antigen (BCMA), another very promising target for anti-myeloma development.

CD38: A Target for Immunotherapeutic Approaches in Multiple Myeloma

Multiple Myeloma (MM) is a hematological cancer characterized by proliferation of malignant plasma cells in the bone marrow (BM). MM represents the second most frequent hematological malignancy, accounting 1% of all cancer and 13% of hematological tumors, with ~9,000 new cases per year. Patients with monoclonal gammopathy of undetermined significance (MGUS) and asymptomatic smoldering MM (SMM) usually evolve to active MM in the presence of increased tumor burden, symptoms and organ damage. Despite the role of high dose chemotherapy in combination with autologous stem cell transplantation and the introduction of new treatments, the prognosis of MM patients is still poor, and novel therapeutic approaches have been tested in the last years, including new immunomodulatory drugs, proteasome inhibitors and monoclonal antibodies (mAbs). CD38 is a glycoprotein with ectoenzymatic functions, which is expressed on plasma cells and other lymphoid and myeloid cell populations. Since its expression is very high and uniform on myeloma cells, CD38 is a good target for novel therapeutic strategies. Among them, immunotherapy represents a promising approach. Here, we summarized recent findings regarding CD38-targeted immunotherapy of MM in pre-clinical models and clinical trials, including (i) mAbs (daratumumab and isatuximab), (ii) radioimmunotherapy, and (iii) adoptive cell therapy, using chimeric antigen receptor (CAR)-transfected T cells specific for CD38. Finally, we discussed the efficacy and possible limitations of these therapeutic approaches for MM patients.

Practical Considerations for Antibodies in Myeloma

The development of the monoclonal antibodies daratumumab and elotuzumab has expanded treatment options for multiple myeloma and led to great improvement in patient outcomes. These agents have favorable safety profiles and synergize effectively with established agents used in the management of myeloma, namely immunomodulatory drugs and proteasome inhibitors. This article reviews the rationale for use of monoclonal antibodies in myeloma, current approved indications for daratumumab and elotuzumab, the manner in which these agents are used in the overall management of myeloma, and specific challenges associated with their use in the clinic. It also highlights other, emerging drug combinations that incorporate daratumumab or elotuzumab and profiles new therapeutic antibodies currently under development.

CD38 Antibodies in Multiple Myeloma: Mechanisms of Action and Modes of Resistance

MM cells express high levels of CD38, while CD38 is expressed at relatively low levels on normal lymphoid and myeloid cells, and in some non-hematopoietic tissues. This expression profile, together with the role of CD38 in adhesion and as ectoenzyme, resulted in the development of CD38 antibodies for the treatment of multiple myeloma (MM). At this moment several CD38 antibodies are at different phases of clinical testing, with daratumumab already approved for various indications both as monotherapy and in combination with standards of care in MM. CD38 antibodies have Fc-dependent immune effector mechanisms, such as complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP). Inhibition of ectoenzymatic function and direct apoptosis induction may also contribute to the efficacy of the antibodies to kill MM cells. The CD38 antibodies also improve host-anti-tumor immunity by the elimination of regulatory T cells, regulatory B cells, and myeloid-derived suppressor cells. Mechanisms of primary and/or acquired resistance include tumor-related factors, such as reduced cell surface expression levels of the target antigen and high levels of complement inhibitors (CD55 and CD59). Differences in frequency or activity of effector cells may also contribute to differences in outcome. Furthermore, the microenvironment protects MM cells to CD38 antibody-induced ADCC by upregulation of anti-apoptotic molecules, such as survivin. Improved understanding of modes of action and mechanisms of resistance has resulted in rationally designed CD38-based combination therapies, which will contribute to further improvement in outcome of MM patients.

Osteoclast Immunosuppressive Effects in Multiple Myeloma: Role of Programmed Cell Death Ligand 1

Immunomodulatory drugs and monoclonal antibody-based immunotherapies have significantly improved the prognosis of the patients with multiple myeloma (MM) in the recent years. These new classes of reagents target malignant plasma cells (PCs) and further modulate the immune microenvironment, which prolongs anti-MM responses and may prevent tumor occurrence. Since MM remains an incurable cancer for most patients, there continues to be a need to identify new tumor target molecules and investigate alternative cellular approaches using gene therapeutic strategies and novel treatment mechanisms. Osteoclasts (OCs), as critical multi-nucleated large cells responsible for bone destruction in >80% MM patients, have become an attractive cellular target for the development of novel MM immunotherapies. In MM, OCs are induced and activated by malignant PCs in a reciprocal manner, leading to osteolytic bone disease commonly associated with this malignancy. Significantly, bidirectional interactions between OCs and MM cells create a positive feedback loop to promote MM cell progression, increase angiogenesis, and inhibit immune surveillance via both cell-cell contact and abnormal production of multiple cytokines/chemokines. Most recently, hyper-activated OCs have been associated with activation of programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway, which impairs T cell proliferation and cytotoxicity against MM cells. Importantly, therapeutic anti-CD38 monoclonal antibodies and checkpoint inhibitors can alleviate OC-induced immune suppression. Furthermore, a proliferation-inducing ligand, abundantly secreted by OCs and OC precursors, significantly upregulates PD-L1 expression on MM cells, in addition to directly promoting MM cell proliferation and survival. Coupled with increased PD-L1 expression in other immune-suppressive cells, i.e., myeloid-derived suppressor cells and tumor-associated macrophages, these results strongly suggest that OCs contribute to the immunosuppressive MM BM microenvironment. Based on these findings and ongoing osteoimmunology studies, therapeutic interventions targeting OC number and function are under development to diminish both MM bone disease and related immune suppression. In this review, we discuss the classical and novel roles of OCs in the patho-immunology of MM. We also describe novel therapeutic strategies simultaneously targeting OCs and MM interactions, including PD-1/PD-L1 axis, to overcome the immune-suppressive microenvironment and improve patient outcome.

Typical and Atypical Inducers of Lysosomal Cell Death: A Promising Anticancer Strategy

Lysosomes are conservative organelles with an indispensable role in cellular degradation and the recycling of macromolecules. However, in light of recent findings, it has emerged that the role of lysosomes in cancer cells extends far beyond cellular catabolism and includes a variety of cellular pathways, such as proliferation, metastatic potential, and drug resistance. It has been well described that malignant transformation leads to alterations in lysosomal structure and function, which, paradoxically, renders cancer cells more sensitive to lysosomal destabilization. Furthermore, lysosomes are implicated in the regulation and execution of cell death in response to diverse stimuli and it has been shown that lysosome-dependent cell death can be utilized to overcome apoptosis and drug resistance. Thus, the purpose of this review is to characterize the role of lysosome in cancer therapy and to describe how these organelles impact treatment resistance. We summarized the characteristics of typical inducers of lysosomal cell death, which exert its function primarily via alterations in the lysosomal compartment. The review also presents other anticancer agents with the predominant mechanism of action different from lysosomal destabilization, the activity of which is influenced by lysosomal signaling, including classical chemotherapeutics, kinase inhibitors, monoclonal antibodies, as well as photodynamic therapy.

Immunomodulatory effects of CD38-targeting antibodies

The fist in class CD38-targeting antibody, daratumumab, is currently approved as single agent and in combination with standards of care for the treatment of relapsed and refractory multiple myeloma. Based on the high activity and favorable toxicity profile of daratumumab, other CD38 antibodies, such as isatuximab, MOR202, and TAK-079, are being evaluated in MM and other malignancies. The CD38-targeting antibodies have classic Fc-dependent immune effector mechanisms, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). These mechanisms of action are dependent on CD38 expression on the tumor cells. There is increasing evidence that CD38 antibodies also improve host-anti-tumor immune response by eliminating CD38-positive immune suppressor cells, including regulatory T cells, regulatory B cells, and myeloid-derived suppressor cells. Indeed, daratumumab treatment results in a marked increase in T cell numbers and activity. CD38-targeting antibodies probably also reduce adenosine production in the bone marrow microenvironment, which may contribute to improved T cell activity. Preclinical and clinical studies have demonstrated that CD38-targeting antibodies have synergistic activity with several other anti-cancer drugs, including various agents with immune stimulating activity, such as lenalidomide and pomalidomide, as well as PD1/PD-L1 inhibitors.

CD38-targeting antibodies in multiple myeloma: mechanisms of action and clinical experience

INTRODUCTION

Multiple myeloma (MM) is generally an incurable hematological malignancy with heterogeneous overall survival rates ranging from a few months to more than 10 years. Survival is especially poor for patients who developed disease that is refractory to immunomodulatory drugs and proteasome inhibitors. Areas covered: This review will discuss the importance of CD38-targeting antibodies for the treatment of MM patients to improve their outcome. Expert commentary: Intense immuno-oncological laboratory research has resulted in the development of functionally active monoclonal antibodies against cell surface markers present on MM cells. In this respect, CD38-targeting antibodies such as daratumumab, MOR202, and isatuximab, have high single agent activity in heavily pretreated MM patients by virtue of their pleiotropic mechanisms of action including Fc-dependent effector mechanisms and immunomodulatory activities. Importantly, CD38-targeting antibodies are well tolerated, with infusion reactions as most frequent adverse event. Altogether, this makes them attractive combination partners with other anti-MM agents. Daratumumab is already approved as monotherapy and in combination with lenalidomide-dexamethasone as well as bortezomib-dexamethasone in pretreated MM patients. Furthermore, results from studies evaluating CD38-targeting antibodies in newly diagnosed MM patients are also promising, indicating that CD38-targeting antibodies will be broadly used in MM, resulting in further improvements in survival.