A Phase 1/2, Dose and Schedule Evaluation Study to Investigate the Safety and Clinical Activity of Belantamab Mafodotin Administered in Combination with Lenalidomide and Dexamethasone in Transplant-Ineligible Patients with Newly Diagnosed Multiple Myeloma

Background: The combination of lenalidomide with dexamethasone (Rd) represents a preferred treatment backbone for newly diagnosed, transplant-ineligible patients (pts) with multiple myeloma (MM), while the addition of a third drug (i.e., daratumumab, bortezomib, carfilzomib or ixazomib) leads to higher response rates and deeper responses. Belantamab mafodotin (belamaf; GSK2857916) is a multi-modal antibody-drug conjugate that has demonstrated a clinically meaningful anti-myeloma activity with a manageable safety profile in heavily pre-treated pts with relapsed or refractory MM. Preclinical evidence suggest a potential synergy between belamaf and lenalidomide; at the same time, these drugs do not have overlapping toxicities. Thus, there is strong rationale for investigating the clinical activity of upfront belamaf in combination with Rd in transplant-ineligible MM pts.

Aims: The present analysis evaluates the safety profile of belamaf in 3 different dosing schemes in combination with Rd in treatment-naïve, transplant-ineligible MM pts.

Methods: BelaRd (study short title) is an open-label, single-center, phase 1/2 study conducted in Greece, aiming to enroll 66 newly diagnosed, transplant-ineligible MM pts. The study comprises 2 parts. Part 1 will evaluate 3 doses of belamaf (2.5, 1.9, and 1.4 mg/kg) in combination with Rd, each given in an individual cohort of pts, and will determine the recommended phase 2 dose (RP2D). In this part, belamaf will be administered q8w and, depending on toxicity, dosing may be rescheduled to q4w or q12w. In Part 2, a single cohort of pts will be treated with belamaf in the RP2D in combination with Rd to further evaluate the safety and clinical activity of this regimen. Part 2 will also evaluate 2 different sets of guidelines for ocular adverse events (AEs) in 2 separate groups of pts to identify the optimal method for the management of belamaf-related keratopathy. This is the initial safety analysis of Part 1 and includes pts who received ≥1 belamaf dose and were followed up for ≥8 weeks.

Results: Overall, as of 16 July 2021 (cut-off date), 18 pts completed the dose-limiting toxicity (DLT) observation period, defined as specific ≥ grade 3 AEs occurring during the first cycle of study treatment, and were included in the safety analysis. The median age was 72 years (range: 65-82), and the majority of pts were male (55.6%). Lytic bone lesions were present in 12 (66.7%) pts; no pts had extramedullary disease. Most pts (9, 50.0%) had Eastern Cooperative Oncology Group performance status 0 followed by those at 1 (8, 44.4%) and 2 (1, 5.6%). Regarding the revised International Staging System, most pts (13, 72.2%) were at stage II, followed by those at stages III (2, 11.1%) and I (3, 16.7%); 3 (16.7%) pts had high-risk cytogenetics, defined as del17p13, t(4;14) or t(14;16). By the cut-off date, pts had received a median of 4 treatment cycles, with 17 (94.4%) pts still being on treatment; 1 (5.6%) pt died due to pneumonia, unrelated to the study treatment. 16 (88.9%) pts experienced ≥1 treatment emergent adverse event (TEAE). In total, 11 (61.1%) pts had ≥1 TEAE grade 3/4, of which 1 was related to belamaf; 1 (5.6%) pt experienced a serious adverse event (SAE). There were 2 cases of dose reduction and 1 case of dose delay. The most common grade 3/4 TEAEs were fatigue (5 pts, 27.8%) and rash (4 pts, 22.7%), all related to lenalidomide. One SAE was reported: pneumonia grade 5 in the 2.5 mg/kg cohort. DLTs were noted in 3 (16.7%) pts: 1 pt with grade 3 fatigue in the 1.4 mg/kg cohort and 1 pt with grade 3 rash in each of the 1.9 and 1.4 mg/kg cohorts, all related to lenalidomide.

Regarding belamaf-related ocular AEs, there were 2 cases of superficial punctuate keratopathy (grade 1 and 2 each, both in the 2.5 mg/kg cohort), 10 cases of decreased visual acuity (grade 1 [8 pts, 44.4%]: 4 in the 1.9 mg/kg cohort and 4 in the 1.4 mg/kg cohort; grade 2 [2 pts, 11.1%] in the 2.5 mg/kg cohort), and 1 case of grade 1 blurred vision in 2.5 mg/kg cohort.

Conclusions: In the first safety analysis of the BelaRd study no new safety signals for the belamaf-Rd combination were observed. The frequency of ocular AEs was within the anticipated range. This early analysis shows that the triplet combination can be safely administered in treatment-naïve, transplant-ineligible MM pts. The enrollment in the study is ongoing, and more safety and efficacy data will become available with the inclusion of additional pts in an updated analysis.