Cellular Therapies Fill Unmet Needs in R/R Multiple Myeloma

Current approaches for multiple myeloma are stratified by patient fitness and age. For patients who can tolerate them, 3- or 4-drug combinations, with or without an autologous stem cell transplant (ASCT), can result in a complete remission, ideally with no residual disease. For patients who are elderly or fragile, 2-drug or 3-drug regimens are the standard.

For the standard-risk patient, a regimen of bortezomib (Velcade), lenalidomide (Revlimid), and dexamethasone (VRd) plus a CD38 monoclonal antibody such as daratumumab (Darzalex) or isatuximab (Sarclisa) is the norm. As a whole, these combinatorial approaches are needed because multiple myeloma is a heterogenous disease whose optimal treatment takes advantage of multiple mechanisms of action. These regimens can result in first remissions that range from 4 to 5 years.

Although these outcomes are promising, there is still an unmet need for patients with relapsed or refractory disease. Innovative approaches in multiple myeloma that focus on cellular therapies offer hope to these patients.

In a presentation during the 39th Annual CFS® Innovative Cancer Therapy for Tomorrow®, Shambavi Richard, MD, an assistant professor in medicine, hematology, and medical oncology at The Mount Sinai Hospital in New York, New York, addressed the emerging therapeutic frontiers in multiple myeloma with a focus on chimeric antigen receptor (CAR) approaches and bispecific antibodies.¹ Richard explored updated results from the KarMMa trial (NCT03361748), which enrolled 149 patients with relapsed/refractory multiple myeloma (RRMM) and who were previously exposed to immunomodulatory agents, proteasome inhibitors (PIs), and CD38 antibodies (mAbs) and reported poor outcomes. Evaluable patients received idecabtagene vicleucel (ide-cel; n = 128).^2,3

At a median follow-up of 15.4 months, the objective response rate (ORR) was 73% and median progression-free survival (PFS) was 8.8 months for all treated patients (TABLE3 ). Investigators reported that at the highest targeted dose of 450 × 10⁶ CAR T cells, the overall response rate (ORR) was 81%, the complete response (CR) rate was 39%, and the median PFS increased by 12.2 months with longer follow-up. In a subgroup analysis of difficult-to-treat patients, the ORR for patients with extramedullary disease was 70%; patients with high-tumor burden, 71%; and patients with R-ISS stage III disease, 48%.

Regarding safety, 97% of patients had cytopenia and 89% had grade 3/4 neutropenia; 52% experienced thrombocytopenia and 60% developed anemia. Cytokine release syndrome (CRS) had a median onset of 1 day, with a median duration of 5 days. CRS was seen in 84% of patients but grade 3/4 was observed in only 6% of patients. Neurologic toxicity was observed in 18% of patients and 4% were grade 3/4.

Updated results from the CARTITUDE-1 trial (NCT03548207)4 showed that ciltacabtagene autoleucel (cilta-cel) yielded early, deep, and durable responses in heavily pretreated patients with multiple myeloma, with a manageable safety profile at the recommended phase 2 dose.

In the study, 97 patients with a median of 6 prior lines received cilta-cel. The overall response rate per independent review committee (primary end point) was 97% (95% CI, 91%-99%), with 67% of patients achieving stringent CR (sCR). The median time to first response was 1 month (range, 1-9), and median time to CR or better was 2 months (range, 1-15). Responses deepened over time, and the median duration of response was not reached. Of 57 patients evaluable for minimal residual disease (MRD) assessment, 93% were MRD-negative at 10-5. The 12-month PFS and overall survival (OS) rates (95% CI) were 77% (66%-84%) and 89% (80%-94%), respectively; the median PFS was not reached.

“In terms of adverse events, neutropenia was 94.8% grade 3/4, and 60.8% of patients had grade 3/4 anemia,” said Richard. “CRS was almost universal, with any-grade CRS seen in 94.8% of patients. This was a little different compared with ido-cel in terms of time of onset, which was 7 days with this product vs 1 day with the ido-cell product,” she said. In both of these trials, early death within the first 2 to 3 months was 2% or less.

When comparing ide-cel to conventional treatment, according to findings presented by Shah et al,5 the investigators observed that ide-cel was associated with a significantly higher ORR compared with conventional treatment (OR, 5.11; 95% CI, 2.92-8.94; P < .001). Similarly, ide-cel significantly extended PFS (HR, 0.55; 95% CI, 0.42-0.73; P < .001) and OS (HR, 0.36; 95% CI, 0.24-0.54; P < .001) vs conventional treatment. Richard said this analysis aimed to compare efficacy outcomes observed with ide-cel treatment in KarMMa and conventional treatment in the Monoclonal Antibodies in Multiple Myeloma: Outcomes After Therapy Failure (MAMMOTH) study.⁶ Investigators analyzed outcomes of 275 patients with multiple myeloma with disease refractory to CD38 monoclonal antibodies at 14 academic centers.

Overcoming Resistance

Turning to the challenge of resistance to therapies in multiple myeloma, Richard noted that there are 3 main strategies in play: multiple myeloma–cell directed, T-cell directed; and CAR construct.

Possible strategies employed that use multiple myeloma cell–directed treatments involve pooling CAR T products with different antigens; using dual CAR products that are constructed using 2 antigen specifi cities, such as B-cell maturation antigen (BCMA)/CD19; or taking a tandem CAR approach. Investigators also can focus on alternate antigens including SLAMF7, CD138, or integrin beta7.

Strategies that are T-cell directed can focus on those that are enriched for central or stem cell memory T cells or use combination approaches with checkpoint inhibitors or immunomodulatory imide drugs and cereblon E3 ligase modulators (CelMoD).

Efforts that tweak the CAR construct are also undergoing evaluation. These include FasTCAR, in which manufacturing takes 24 to 36 hours; next-generation CARs, which are armored CAR T cells that prevent T-cell exhaustion; CARs that use a safety switch to mitigate adverse effects; and allogeneic CARS.

Bispecific Antibodies

Richard highlighted results from a study evaluating teclistamab, a bispecific antibody that binds to BCMA and CD3 to redirect T cells to attack multiple myeloma cells.

Findings from MajesTEC-1 (NCT03145181) demonstrated that the ORR in response-evaluable patients treated at the recommended phase 2 dose (n = 40) was 65% (95% CI, 48%-79%); 58% achieved a very good partial response or better.⁷ At the recommended phase 2 dose, the median duration of response was not reached. After 7.1 months’ median follow-up, 22 (85%) of 26 responders were alive and continuing treatment. During the 2021 American Society of Clinical Oncology Annual Meeting, Krishnan et al presented updated findings showing 58% of evaluable patients had achieved a very good partial response or better and 30% had achieved a CR or better; the median time to first confirmed response was 1.0 month (range, 0.2-3.1).⁸

Another bispecific antibody, talquetamab, has continued to show promising clinical activity in patients with RRMM. Updated findings from a phase 1 trial (NCT03399799)⁹ showed the ORR at the recommended phase 2 dose (RP2D) in response-evaluable patients (n = 24) was 63%, with 50% reaching very good partial response or better; 9/17 (53%) evaluable patients with triple-class refractory disease and 3/3 (100%) patients who were penta-refractory had a response. Median time to first confirmed response at the RP2D was 1.0 month (range, 0.2-3.8). Overall, responses were durable and deepened over time (median follow-up, 6.2 months [range, 2.7-9.7+] for responders at the RP2D).

When comparing CAR T-cell therapy to bispecific antibodies, Richard noted that patients undergo CAR T-cell therapy once with no further therapy indicated. Additionally, patients can enjoy a long chemotherapy holiday, whereas bispecific antibodies require more frequent doses. Toxicities are similar for the 2 approaches, although Richard said that CRS can be slightly more profound and at a somewhat higher grade with the CAR T-cell approach compared with that of bispecific antibodies.

In conclusion, Richard also noted that the costs associated with both these approaches will have an impact, especially in high up-front costs. Bispecific c antibodies, however, due to their chronic recurrent administration, may also come with a long-term financial burden.

_REFERENCES:

_{1. Richard S. New therapeutic frontiers for RRMM: CAR T and bispecifi c antibodies. Presented at: 39th Annual CFS®. Chemotherapy Foundation Symposium. Innovative Cancer Therapy for Tomorrow®. November 3-5, 2021; New York, NY.}

_{2. Munshi NC, Anderson LD Jr, Shah N, et al. Idecabtagene Vicleucel in Relapsed and Refractory Multiple Myeloma. N Engl J Med. 2021;384(8):705-716. doi:10.1056/NEJMoa2024850}

_{3. Anderson LD, Munshi NC, Shah N, et al. Idecabtagene vicleucel (ide-cel, bb2121), a BCMA-directed CAR T cell therapy, in relapsed and refractory multiple myeloma: Updated KarMMa results. J Clin Oncol. 2021;39(suppl 15):8016-8016. doi: 10.1200/JCO.2021.39.15_suppl.8016}

_{4. Usmani SZ, Berdeja JG, Madduri D, et al. Ciltacabtagene autoleucel, a B-cell maturation antigen-directed chimeric antigen receptor T-cell therapy, in relapsed/refractory multiple myeloma: updated results from CARTITUDE-1. J Clin Oncol. 2021;39(suppl 15; abstr 8005). doi: 10.1200/JCO.2021.39.15_suppl.8005}

_{5. Shah N, Ayers D, Davies FE, et al. A matching-adjusted indirect comparison of efficacy outcomes for idecabtagene vicleucel (ide-cel, bb2121), a BCMA-directed CAR T cell therapy versus conventional care in triple-class-exposed relapsed and refractory multiple myeloma. Presented at: 62nd American Society of Hematology Meeting and Exposition, December 5-8, 2020. Abstract 1653. https://bit.ly/3nQb458}

_{6. Gandhi UH, Cornell RF, Lakshman A, et al. Outcomes of patients with multiple myeloma refractory to CD38-targeted monoclonal antibody therapy. Leukemia. 2019;33(9):2266-2275. doi:10.1038/ s41375-019-0435-7}

_{7. Usmani SZ, Garfall AL, van de Donk NWCJ, et al. Teclistamab, a B-cell maturation antigen × CD3 bispecific antibody, in patients with relapsed or refractory multiple myeloma (MajesTEC-1): a multicentre, open-label, single-arm, phase 1 study. Lancet. 2021;398(10301):665- 674. doi:10.1016/S0140-6736(21)01338-6}

_{8. Krishnan AY, Garfall Al, Mateos M-V, et al. J Clinical Oncol. 2021;39(suppl 15):8007-8007. doi: 10.1200/JCO.2021.39.15_suppl.8007}

_{9. Berdeja JG, Krishnan AY, Oriol A, et al. Updated results of a phase 1, first-in-human study of talquetamab, a G protein-coupled receptor family C group 5 member D (GPRC5D) × CD3 bispecific antibody, in relapsed/refractory multiple myeloma (MM). J Clin Oncol. 2021;39(suppl 15):8008. doi: 10.1200/JCO.2021.39.15_suppl.8008}