Targeting GPRC5D in multiple myeloma

INTRODUCTION

The prognosis of multiple myeloma (MM) continues to improve. Recent progress in therapies, using immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs), and anti-CD38 monoclonal antibodies, has greatly improved patients' outcomes. Despite these advancements, relapses still happen often, and patients can become resistant to the usual treatments. Newer treatments, such as chimeric antigen receptor (CAR) T-cell therapy and bispecific antibodies (BsAbs) targeting B-cell maturation antigen (BCMA), have resulted in excellent outcomes in patients with limited treatment options. G protein - coupled receptor, class C group 5 member D (GPRC5D) is considered a very promising target with early results from clinical trials showing high response rates in patients with relapsed or refractory multiple myeloma.

AREAS COVERED

This review covers the efficacy and safety of CAR-T and BsAbs targeting GPRC5D in MM, focusing on talquetamab - the inaugural FDA-approved BsAb targeting GPRC5D. Talquetamab has exhibited promising response rates alongside a distinctive side effect profile. Additionally, ongoing trials examining talquetamab in combination with agents like daratumumab and teclistamab are discussed.

EXPERT OPINION

We offer insights into the potential utilization of various GPRC5D-based therapies in the treatment paradigm for MM, either independently or in combination with established therapies.

Quad-class exposed/refractory myeloma is associated with short survival

Very scarce data exist about outcomes of relapsed multiple myeloma patients who have failed proteasome inhibitor, immunomodulatory drug, anti-CD38 monoclonal antibody and therapies targeting B-cell maturation antigen (BCMA) (Quad-class exposed [QCE]). In this retrospective single-centre study, we determined progression-free survival (PFS) and overall survival (OS) from anti-BCMA failure in 45 QCE patients. Seven (16%) patients received antibody-drug conjugate, 20 (44%) bispecific antibodies and 18 (40%) CAR-T cell. Thirty patients (67%) received ≥1 subsequent line of treatment. PFS was 4.4 months (95% CI = 2.4-12.5) and OS 6.3 months (95% CI = 3.9-14.4). Having an adverse prognosis, QCE myeloma patients remain an unmet medical need.

BR109, a Novel Fully Humanized T-Cell-Engaging Bispecific Antibody with GPRC5D Binding, Has Potent Antitumor Activities in Multiple Myeloma

At present, multiple myeloma (MM) is still an essentially incurable hematologic malignancy. Although BCMA-targeted therapies have achieved remarkable results, BCMA levels were found to be downregulated in patients with MM who relapsed after these treatments. Therefore, the search for other antigens specific to MM has become a priority. Independently of BCMA expression, G-protein-coupled receptor family C group 5 member D (GPRC5D) is mainly expressed in the plasma cells of MM patients, while it is expressed in a limited number of normal tissues. Combining MM-specific antigen GPRC5D and T-cell-mediated therapies would be a promising therapeutic strategy for MM. Recently, we constructed a new anti-GPRC5D × anti-CD3 T-cell-engaging bispecific antibody (TCB), BR109, which was capable of binding to human GPRC5D and human CD3ε. Moreover, BR109 was proven to have relatively good stability and antitumor activity. BR109 could specifically trigger T-cell-mediated cytotoxicity against many GPRC5D-positive MM cells in vitro. Meanwhile, antitumor activity was demonstrated in MM cell line xenograft mouse models with human immune cell reconstitution. These preclinical studies have formed a solid foundation for the evaluation of MM treatment efficacy in clinical trials.

Chimeric Antigen Receptor T Cells in Multiple Myeloma

Multiple myeloma is the second most common hematological malignancy with an approximate incidence of up to 8.5 cases per 100,000 persons per year. Over the last decade, therapy for multiple myeloma has undergone a revolutionary change. Chimeric antigen receptor (CAR) T-cell therapy has played a major role in this evolution. In this review, we discuss the existing state of CAR T-cell therapy in myeloma while evaluating several newer therapies and targets expected in the near future.

Beyond BCMA, why GPRC5D could be the right way: treatment strategies with immunotherapy at relapse after anti-BCMA agents

Multiple Myeloma remains incurable, and there is a need for therapies with novel mechanisms of action. Recently, B cell maturation antigen targeted therapy has demonstrated deep and durable responses in a largely treated population. However, the relapse rate of myeloma patients after anti-BCMA treatment strategies is increasing worldwide, and one of the most challenging issues for them is to choose the best therapy sequencing. After anti-BCMA treatment, retreatment with anti-BCMA drugs remains an option, but new targets are emerging strongly. One of them is G protein-coupled receptor, class C group 5 member D (GPRC5D), that due to the very promising data from the use of chimeric antigen receptor T-cells (CAR-T) and bispecific antibodies (BsAb) seems to be the ideal candidate in the relay of myeloma treatment at relapse. In this literature review, we discuss data from treatment with the new drugs at relapse after anti-BCMA therapies, observing an undeniable benefit from the use of drugs directed against GPRC5D.

Plain language summary of the MonumenTAL-1 study of talquetamab in people with relapsed or refractory multiple myeloma

WHAT IS THIS SUMMARY ABOUT?

This plain language summary describes the results of a phase 1 research study (or clinical trial) called MonumenTAL-1 published in the New England Journal of Medicine in December 2022. A phase 1 study is an early clinical trial where researchers evaluate how safe a medicine is at different doses in a small number of people. In the MonumenTAL-1 study, researchers looked at a new medicine under development called talquetamab, for people living with multiple myeloma (a type of blood cancer) who did not respond (refractory), stopped responding (relapsed), or who had difficulty dealing with their previous treatments.

HOW WAS THE STUDY CONDUCTED?

The phase 1 MonumenTAL-1 study was performed in 2 parts. Safety was the main focus of Part 1 in which side effects, and how serious they were, were assessed. The results of Part 1 were used to identify doses of talquetamab that were well tolerated, without a need to stop treatment or reduce the doses, for further study in Part 2. Part 2 of the study examined how well talquetamab worked to decrease signs of the cancer and what side effects, and their severity, people experienced at the doses identified in Part 1.

WHAT WERE THE RESULTS?

In Part 1 of the study, researchers identified 2 doses of talquetamab for further study: 405 micrograms for every kilogram of body weight (μg/kg) given weekly and 800 μg/kg every other week. All participants experienced at least one side effect of treatment at these 2 doses. Less than half of participants (43% at 405 μg/kg weekly dose and 34% at the 800 μg/kg every other week dose) experienced serious side effects which are those side effects that led to hospitalization, death, or permanent or life-threatening damage). The most common side effects at both doses were a condition known as cytokine release syndrome (CRS); changes in blood cell levels (where different types of cells in the blood were measured); changes in skin such as itching, dry skin, eczema, ulcers or shedding; changes in nails such as discoloration or ridging (lines or dents); and changes in sense of taste such as food tasting sour or metallic. CRS is caused by the overactivation of the immune system (the body's natural defense system) and can result in fever, feeling sick (nausea), being tired (fatigue), low blood pressure, low blood oxygen levels and body aches. Most cases of CRS, as well as most other side effects, were mild or moderate. Most common serious events were CRS, fever and bone pain. Most people had fewer signs of the cancer after taking talquetamab, and the response was similar between the 2 doses. The median duration of response at the 2 identified doses was 8-10 months.

WHAT DO THE RESULTS MEAN?

Most of the side effects people experienced when taking talquetamab were mild or moderate. Most people who took talquetamab responded to the treatment even though they hadn't responded or stopped responding to previous multiple myeloma treatments or stopped taking those treatments because they were unable to tolerate them. These results demonstrate the potential of talquetamab as a treatment option in people who have used up other available therapy options. The 2 doses of talquetamab identified here are being examined in a larger group of participants to further test for safety and to test how well people respond.

Bispecific antibodies targeting BCMA, GPRC5D, and FcRH5 for multiple myeloma therapy: latest updates from ASCO 2023 Annual Meeting

Several bispecific antibodies (bsAbs) targeting BCMA, GPRC5D, and FcRH5 are in clinical trials for heavily pretreated multiple myeloma (MM) patients. Teclistamab was approved for relapsed/refractory MM therapy in 2022, while elranatamab, linvoseltamab, F182112, talquetamab, and cevostamab are currently undergoing clinical trials. This study summarizes several latest reports on bsAbs for the treatment of MM from the ASCO 2023 Annual Meeting.

T-cell redirecting bispecific antibodies in multiple myeloma: Current landscape and future directions

T-cell engaging bispecific antibodies (BsAbs) have substantial activity in heavily pretreated patients with multiple myeloma (MM). The overall response rate obtained with B-cell maturation antigen (BCMA)-targeting BsAbs is approximately 60%-70%, including a high proportion of patients achieving very good partial response or complete response. Comparable efficacy is seen with BsAbs targeting GPRC5D or FcRH5. Cytokine release syndrome is frequently observed with BsAb treatment, but mostly during the step-up doses and the first full dose. Early intervention with IL-6 receptor blocking antibodies (e.g., tocilizumab) prevents escalation to severe manifestations. Infections are also common during treatment and related to the extent of exposure to immune suppressive anti-MM agents, as well as development of hypogammaglobulinemia due to elimination of normal plasma cells, and probably because of T-cell exhaustion resulting from continuous BsAb-mediated T-cell activation. Adequate monitoring for infections and institution of infectious prophylaxis are essential. Patients treated with GPRC5D-targteing BsAbs often develop skin and nail disorders and loss of taste, which is likely related to GPRC5D expression in cells that produce hard keratin. Currently ongoing studies are aiming at further improving these results by evaluating BsAbs in combination with other drugs, such as immunomodulatory agents and anti-CD38 antibodies, as well as the application of BsAbs in earlier lines of therapy, including patients with newly diagnosed disease. We expect that the outcomes of patients with MM will further improve by the introduction of this novel type of T-cell immunotherapy.

Immunotherapies targeting GPRC5D in relapsed or refractory multiple myeloma: latest updates from 2022 ASH Annual Meeting

B cell maturation antigen (BCMA)-targeted immunotherapy has shown unprecedented results in the treatment of relapsed or refractory (R/R) multiple myeloma (MM). However, disease progression remains an issue attributed to variable BCMA expression, BCMA downregulation, and heterogeneity of tumor antigens in MM. Therefore, additional treatment options with novel therapeutic targets are warranted. G protein-coupled receptor, class C group 5 member D (GPRC5D), an orphan receptor expressed on malignant plasma cells with limited expression in normal tissue, has emerged as a promising therapeutic target for R/R MM. GPRC5D-targeted chimeric antigen receptor (CAR)-T and CAR-NK cell therapy, as well as bispecific T cell engagers, offer remarkable anti-tumor activities. We summarized some latest reports on GPRC5D-targeted treatments for R/R MM from the 2022 ASH Annual Meeting (ASH 2022).

SOHO State-of-the-Art Updates and Next Questions | BCMA-Directed CAR T-Cells: Early Results and Future Directions

Despite continued advances that have led to improved survival of patients with multiple myeloma (MM) over the years, MM remains largely incurable with overall survival in patients who have progressed after proteasome inhibitor, immunomodulatory drug, and anti-CD38 monoclonal antibody therapy measured in months. Better understanding of the immunopathology of MM has led to the discovery of newer treatment targets like B-cell maturation antigen (BCMA). BCMA is a tumor necrosis factor receptor superfamily expressed on normal B-lymphocytes and malignant plasma cells with a vital role in proliferation, maturation, and differentiation of normal and malignant plasma cells. Antibody drug conjugates, chimeric antigen receptor (CAR) T-cells and bispecific T-cell engagers targeting the BCMA antigen are now available within and outside of clinical trials for treatment of triple class refractory MM. This review article focuses on the evolution, safety, efficacy, and limitations of BCMA-directed CAR T-cell therapies. It also discusses the challenges unveiled by the incorporation of these CAR T-cells in the treatment paradigm of MM and deliberates on the future of CAR T-cell therapy within MM.

Newly approved and forthcoming T-cell-redirecting bispecific antibodies for the treatment of relapsed/refractory multiple myeloma

OBJECTIVE

Summarize the background, clinical trials, and place in therapy for the newly Food and Drug Administration (FDA) approved and forthcoming bispecific antibodies for relapsed/refractory (R/R) multiple myeloma.

DATA SOURCES

A search of the PubMed database was conducted using the following search terms: B-cell maturation antigen (BCMA), teclistamab, myeloma, BsAbs, GPRC5D, and bispecific. Ongoing clinical trials as well as abstracts from ASH and ASCO evaluating the efficacy and safety of novel agents were evaluated. Prescribing information was also reviewed.

SUMMARY

For patients with R/R multiple myeloma who have failed available therapies, treatment options are limited and survival is short. The FDA recently approved teclistamab, a T-cell-redirecting bispecific antibody, in patients with R/R multiple myeloma who have failed four prior lines of therapy. Teclistamab targets both CD3 expressed on T-cells and BCMA expressed on the surface of myeloma cells, mediating T-cell activation and lysis of plasma cells that express BCMA. Accelerated approval was granted based upon the results of the MajesTEC-1 study, which showed a durable response in a high proportion of heavily pretreated patients. Teclistamab is the first bispecific antibody approved for use in patients with multiple myeloma and the fourth approved agent targeting BCMA. Additional T-cell redirecting bispecific antibodies for use in multiple myeloma are also currently being studied.

CONCLUSION

Teclistamab is the newest agent granted FDA approval for use in R/R multiple myeloma and represents a promising new option for patients. Ongoing trials are investigating teclistamab and other novel bispecific antibodies in the upfront and R/R setting.

RAMIHM generates fully human monoclonal antibodies by rapid mRNA immunization of humanized mice and BCR-seq

As a clinical vaccine, lipid nanoparticle (LNP) mRNA has demonstrated potent and broad antibody responses, leading to speculation about its potential for antibody discovery. Here, we developed RAMIHM, a highly efficient strategy for developing fully human monoclonal antibodies that employs rapid mRNA immunization of humanized mice followed by single B cell sequencing (scBCR-seq). We immunized humanized transgenic mice with RAMIHM and generated 15 top-ranked clones from peripheral blood, plasma B, and memory B cell populations, demonstrating a high rate of antigen-specificity (93.3%). Two Omicron-specific neutralizing antibodies with high potency and one broad-spectrum neutralizing antibody were discovered. Furthermore, we extended the application of RAMIHM to cancer immunotherapy targets, including a single transmembrane protein CD22 and a multi-transmembrane G protein-coupled receptor target, GPRC5D, which is difficult for traditional protein immunization methods. RAMIHM-scBCR-seq is a broadly applicable platform for the rapid and efficient development of fully human monoclonal antibodies against an assortment of targets.

Bispecific antibodies in multiple myeloma treatment: A journey in progress

The incorporation of novel agents and monoclonal antibody-based therapies into the treatment of multiple myeloma (MM) has significantly improved long-term patient survival. However, the disease is still largely incurable, with high-risk patients suffering shorter survival times, partly due to weakened immune systems. Bispecific molecules, including bispecific antibodies (BisAbs) and bispecific T-cell engagers (BiTEs), encourage immune cells to lyse MM cells by simultaneously binding antigens on MM cells and immune effector cells, bringing those cells into close proximity. BisAbs that target B-cell maturation antigen (BCMA) and GPRC5D have shown impressive clinical activity, and the results of early-phase clinical trials targeting FcRH5 in patients with relapsed/refractory MM (RRMM) are also promising. Furthermore, the safety profile of these agents is favorable, including mainly low-grade cytokine release syndrome (CRS). These off-the-shelf bispecific molecules will likely become an essential part of the MM treatment paradigm. Here, we summarize and highlight various bispecific immunotherapies under development in MM treatment, as well as the utility of combining them with current standard-of-care treatments and new strategies. With the advancement of novel combination treatment approaches, these bispecific molecules may lead the way to a cure for MM.

Promising Antigens for the New Frontier of Targeted Immunotherapy in Multiple Myeloma

Simple Summary

Defining the specificity and biological sequalae induced by receptors differentiated expressed in multiple myeloma cells are critical for the development of effective immunotherapies based on monoclonal antibodies. Ongoing studies continue to discover new antigens with superior tumor selectivity and defined function in regulating the pathophysiology of myeloma cells directly or indirectly in the immunosuppressive bone marrow microenvironment. Meanwhile, it is urgent to identify mechanisms of immune resistance and design more potent immunotherapies, alone and/or with best combination partners to further prolong anti-MM immunity.

Abstract

The incorporation of novel agents in recent treatments in multiple myeloma (MM) has improved the clinical outcome of patients. Specifically, the approval of monoclonal antibody (MoAb) against CD38 (daratumumab) and SLAMF7 (elotuzumab) in relapsed and refractory MM (RRMM) represents an important milestone in the development of targeted immunotherapy in MM. These MoAb-based agents significantly induce cytotoxicity of MM cells via multiple effector-dependent mechanisms and can further induce immunomodulation to repair a dysfunctional tumor immune microenvironment. Recently, targeting B cell maturation antigen (BCMA), an even MM-specific antigen, has shown high therapeutic activities by chimeric antigen receptor T cells (CAR T), antibody-drug conjugate (ADC), bispecific T-cell engager (BiTE), as well as bispecific antibody (BiAb), with some already approved for heavily pretreated RRMM patients. New antigens, such as orphan G protein-coupled receptor class C group 5 member D (GPRC5D) and FcRH5, were identified and rapidly moved to ongoing clinical studies. We here summarized the pathobiological function of key MM antigens and the status of the corresponding immunotherapies. The potential challenges and emerging treatment strategies are also discussed.

Current State of the Art and Prospects of T Cell-Redirecting Bispecific Antibodies in Multiple Myeloma

Multiple myeloma (MM) patients eventually develop multi-drug-resistant disease with poor survival. Hence, the development of novel treatment strategies is of great importance. Recently, different classes of immunotherapeutic agents have shown great promise in heavily pre-treated MM, including T cell-redirecting bispecific antibodies (BsAbs). These BsAbs simultaneously interact with CD3 on effector T cells and a tumor-associated antigen on MM cells, resulting in redirection of T cells to MM cells. This leads to the formation of an immunologic synapse, the release of granzymes/perforins, and subsequent tumor cell lysis. Several ongoing phase 1 studies show substantial activity and a favorable toxicity profile with BCMA-, GPRC5D-, or FcRH5-targeting BsAbs in heavily pre-treated MM patients. Resistance mechanisms against BsAbs include tumor-related features, T cell characteristics, and impact of components of the immunosuppressive tumor microenvironment. Various clinical trials are currently evaluating combination therapy with a BsAb and another agent, such as a CD38-targeting antibody or an immunomodulatory drug (e.g., pomalidomide), to further improve response depth and duration. Additionally, the combination of two BsAbs, simultaneously targeting two different antigens to prevent antigen escape, is being explored in clinical studies. The evaluation of BsAbs in earlier lines of therapy, including newly diagnosed MM, is warranted, based on the efficacy of BsAbs in advanced MM.