Targeting BCMA in Multiple Myeloma: Advances in Antibody-Drug Conjugate Therapy

Multiple myeloma (MM) is an incurable cancer of the plasma cells. In the last twenty years, treatment strategies have evolved toward targeting MM cells-from the shotgun chemotherapy approach to the slightly more targeted approach of disrupting important MM molecular pathways to the immunotherapy approach that specifically targets MM cells based on protein expression. Antibody-drug conjugates (ADCs) are introduced as immunotherapeutic drugs which utilize an antibody to deliver cytotoxic agents to cancer cells distinctively. Recent investigations of ADCs for MM treatment focus on targeting B cell maturation antigen (BCMA), which regulates B cell proliferation, survival, maturation, and differentiation into plasma cells (PCs). Given its selective expression in malignant PCs, BCMA is one of the most promising targets in MM immunotherapy. Compared to other BCMA-targeting immunotherapies, ADCs have several benefits, such as lower price, shorter production period, fewer infusions, less dependence on the patient's immune system, and they are less likely to over-activate the immune system. In clinical trials, anti-BCMA ADCs have shown safety and remarkable response rates in patients with relapsed and refractory MM. Here, we review the properties and clinical applications of anti-BCMA ADC therapies and discuss the potential mechanisms of resistance and ways to overcome them.

Antibody drug conjugates for the treatment of multiple myeloma

The treatment landscape of multiple myeloma (MM) has evolved substantially, but it remains largely incurable so new treatment options are required. Antibody drug conjugates (ADCs) are an emerging therapeutic class used in Cancer to deliver targeted therapy. ADCs are composed of three components, an antibody, a chemical linker and a payload which must be chosen carefully to be effective and safe. This alternative mechanism of action to standard treatments makes ADCs an attractive class for further development. However, several ADCs have been investigated but many have not moved further than phase 1 trials, highlighting the challenges in designing an effective and tolerable ADC. Belantamab Mafodotin is currently the only ADC licensed for MM although others are currently under evaluation. Belantamab Mafodotin demonstrated efficacy as monotherapy in triple class exposed patients and combinations are under development which maintain safety with encouraging efficacy particularly at earlier lines of therapy. Retaining an acceptable adverse event profile for ADCs remains vital for their success. Strategies to mitigate ocular events for Belantamab Mafodotin involve lower and less frequent dosing as well as the use of gamma secretase inhibitors. The optimal sequencing of ADCs within the treatment pathway including novel immunotherapies is now under evaluation.

Innovative Anti-CD38 and Anti-BCMA Targeted Therapies in Multiple Myeloma: Mechanisms of Action and Resistance

CD38 and B-cell maturation antigens (BCMAs) are prevalently expressed on neoplastic plasma cells in multiple myeloma (MM), making them ideal therapeutic targets. Anti-CD38 monoclonal antibodies, such as approved daratumumab and isatuximab, are currently the milestone in MM treatment because they induce plasma cell apoptosis and kill through several mechanisms, including antibody-dependent cellular cytotoxicity or phagocytosis. BCMA is considered an excellent target in MM, and three different therapeutic strategies are either already available in clinical practice or under investigation: antibody-drug conjugates, such as belantamab-mafodotin; bispecific T cell engagers; and chimeric antigen receptor-modified T cell therapies. Despite the impressive clinical efficacy of these new strategies in the treatment of newly diagnosed or multi-refractory MM patients, several mechanisms of resistance have already been described, including antigen downregulation, the impairment of antibody-dependent cell cytotoxicity and phagocytosis, T- and natural killer cell senescence, and exhaustion. In this review, we summarize the current knowledge on the mechanisms of action and resistance of anti-CD38 and anti-BCMA agents and their clinical efficacy and safety.

Current Status of Novel Agents for the Treatment of B Cell Malignancies: What's Coming Next?

Resistance to death is one of the hallmarks of human B cell malignancies and often contributes to the lack of a lasting response to today's commonly used treatments. Drug discovery approaches designed to activate the death machinery have generated a large number of inhibitors of anti-apoptotic proteins from the B-cell lymphoma/leukemia 2 family and the B-cell receptor (BCR) signaling pathway. Orally administered small-molecule inhibitors of Bcl-2 protein and BCR partners (e.g., Bruton's tyrosine kinase and phosphatidylinositol-3 kinase) have already been included (as monotherapies or combination therapies) in the standard of care for selected B cell malignancies. Agonistic monoclonal antibodies and their derivatives (antibody-drug conjugates, antibody-radioisotope conjugates, bispecific T cell engagers, and chimeric antigen receptor-modified T cells) targeting tumor-associated antigens (TAAs, such as CD19, CD20, CD22, and CD38) are indicated for treatment (as monotherapies or combination therapies) of patients with B cell tumors. However, given that some patients are either refractory to current therapies or relapse after treatment, novel therapeutic strategies are needed. Here, we review current strategies for managing B cell malignancies, with a focus on the ongoing clinical development of more effective, selective drugs targeting these molecules, as well as other TAAs and signaling proteins. The observed impact of metabolic reprogramming on B cell pathophysiology highlights the promise of targeting metabolic checkpoints in the treatment of these disorders.

Treatment Horizon in Multiple Myeloma

OBJECTIVES

This paper reviews current and emerging therapies for MM.

METHODS

Narrative review RESULTS: Multiple myeloma (MM) is a complex, heterogenous condition, and in recent years there has been an expansion in the number and range of treatments. Several new treatment approaches, including enhanced monoclonal antibodies, antibody-drug conjugates (ADC), bispecific T-cell engagers (BiTE) and chimeric antigen-T-cell therapy (CAR-T) are under development.

CONCLUSIONS

The emergence of new treatments that aim to tackle MM-associated immune dysfunction has led to improvements in overall survival.

Antibody-drug conjugate therapies in multiple myeloma—what’s next on the horizon?

Targeted immunotherapy has arisen over the past decade to the forefront of cancer care. Notably, targeted therapies such as antibody-drug conjugates (ADCs) are becoming more recognized for a novel approach in cancer treatment. The mechanism of action of ADCs incorporates a monoclonal antibody portion directed against the tumor cell antigen and attached to the tumoricidal portion via chemical linkage. The binding of the monoclonal antibody portion allows for tumor cell internalization of the ADC and precise release of the toxic payload within the cancer cell. Multiple myeloma (MM) is an incurable cancer for which belantamab mafodotin was the first-in-class ADC to achieve United States Food and Drug Administration (FDA) approval for treatment of this disease. Clinical trials are currently evaluating other ADCs in the treatment of MM. In this review, a look at the current ADCs being tested in MM clinical trials with a focus on those that are more promising and a potential next-in-line for FDA approval for treatment of MM is discussed.

Overcoming challenges associated with the bioanalysis of cysteine-conjugated metabolites in the presence of antibody-drug conjugates

Aim: Investigations have shown that for the antibody-drug conjugate (ADC) belantamab mafodotin, concentrations of the cysteine-conjugated metabolite, Cys-mcMMAF, were overestimated in the presence of the ADC during sample processing when utilizing a historical SPE method. Results: A new assay was developed utilizing an acidic protein precipitation to remove the ADC early in the extraction process, thus eliminating the risk of overestimating Cys-mcMMAF in the presence of belantamab mafodotin. In vitro experiments demonstrated a linear relationship between the concentration of belantamab mafodotin and the release of Cys-mcMMAF. Extensive stability assessments were performed to cover storage of study samples. Conclusion: This work emphasized the critical importance of understanding the performance of a bioanalytical method for free toxic payload in the presence of the ADC.

Immunotherapy of Multiple Myeloma: Promise and Challenges

Whereas the treatment of MM was dependent solely on alkylating agents and corticosteroids during the prior three decades, the landscape of therapeutic measures to treat the disease began to expand enormously early in the current century. The introduction of new classes of small-molecule drugs, such as proteasome blockers (bortezomib and carfilzomib), immunomodulators (lenalidomide and pomalidomide), nuclear export inhibitors (selinexor), and histone deacetylase blockers (panobinostat), as well as the application of autologous stem cell transplantation (ASCT), resulted in a seismic shift in how the disease is treated. The picture changed dramatically once again starting with the 2015 FDA approval of two monoclonal antibodies (mAbs) - the anti-CD38 daratumumab and the anti-SLAMF7 elotuzumab. Daratumumab, in particular, has had a great impact on MM therapy and today is often included in various regimens to treat the disease, both in newly diagnosed cases and in the relapse/refractory setting. Recently, other immunotherapies have been added to the arsenal of drugs available to fight this malignancy. These include isatuximab (also anti-CD38) and, in the past year, the antibody-drug conjugate (ADC) belantamab mafodotin and the chimeric antigen receptor (CAR) T-cell product idecabtagene vicleucel (ide-cel). While the accumulated benefits of these newer agents have resulted in a doubling of the disease's five-year survival rate to more than 5 years and improved quality of life, the disease remains incurable. Almost without exception patients experience relapse and/or become refractory to the drugs used, making the search for innovative therapies all the more essential. This review covers the current scope of anti-myeloma immunotherapeutic agents, both those in clinical use and on the horizon, including naked mAbs, ADCs, bi- and multi-targeted mAbs, and CAR T-cells. Emphasis is placed on the benefits of each along with the challenges that need to be overcome if MM is to be considered curable in the future.

BCMA-targeting approaches for treatment of multiple myeloma

Recent advances in treatment modalities have led to improved survival in patients with multiple myeloma (MM). However, despite these, MM remains an incurable disease. Many MM patients relapse through and become refractory to current treatment strategies or are intolerant due to toxicities arising from therapy. As such, novel strategies addressing new targets are crucial in improving care for MM patients. BCMA has emerged as a rationale therapeutic target for treatment of MM as it is preferentially expressed in mature B-lymphocytes and plasma cells with the overexpression and activation of BCMA via its ligands associated with the disease progression in multiple myeloma. Given the high expression of BCMA in malignant Plasma cells compared to those from normal healthy volunteers, targeting BCMA should reduce risks of on-target off-tumor toxicities. The main BCMA-targeting approaches currently used for treatment of MM include: 1) chimeric antigen receptor (CAR) T-cell therapy; 2) bi- and multi- specific antibodies; and 3) monoclonal antibodies and their drug conjugates. This review will outline these therapeutic agents and present their emerging clinical data.