Phase 1/2 Trial to Jointly Optimize Dose and Administration Schedule of Evomela in Newly Diagnosed Multiple Myeloma Patients Undergoing Autologous Hematopoietic Cell Transplantation

Background: Eligible patients with multiple myeloma (MM) are offered autologous hematopoietic cell transplantation (auto-HCT) in their first remission. The usual conditioning regimen consists of melphalan (Alkeran) 200 mg/m² infused over ~ 30 minutes due to its limited stability. Evomela is a newer formulation of melphalan, which is stable at room temperature for ~ 24 hours. The current trial studied the dose escalation and compared the short versus extended infusion time of evomela used as a conditioning regimen before auto-HCT.

Methods: Patients with newly diagnosed MM, age ≤ 70, were eligible. Two dose levels, 200 and 225 mg/m² were studied. Patients were randomized between two infusion schedules: 30-60 minutes (short) and an extended infusion of 8-9 hours. Disease response was measured using IMWG criteria. Minimal residual disease (MRD) was measured by flow cytometry at 10^-5.

Results: Sixty patients were enrolled. The first 3 patients in each arm were treated at evomela 200 mg/m². Since no dose-limiting toxicity (DLT) was observed, all subsequent patients (n=54; 27 in each arm) were treated at evomela 225 mg/m². The results are presented for patients treated at evomela 225 mg/m². Patient characteristics were evenly distributed (Table 1). The median age was 58.6 years (range: 42.6 -70.3). Twelve (22%) patients had high-risk cytogenetics (4 [15%] in the short infusion; 8 [30%] in the extended infusion arm), p-value 0.19.

There were no deaths, and no patient experienced grade > 3 adverse events (AE). Grade 2-3 AEs were seen in 53 (98%) patients (26 [96%] in the short infusion; 27 [100%] in the extended infusion). Twenty-four (44%) patients experience grade 2-3 diarrhea (16 [60%] in the short infusion; 8 [30%] in the extended infusion). Grade 2-3 esophagitis was seen in 3 (6%) patients overall (0 in the short infusion; 3 [11%] in the extended infusion). Atrial fibrillation was seen in one patient (grade 2, extended infusion).

Before transplant, six (22%) patients were in stringent complete remission (sCR) or CR in the short infusion arm vs. 4 (15%) patients in the extended infusion arm. At day-90 post-transplant, 13 (48%) patients in each arm were in sCR/CR, and 17 (63%) patients in each arm achieved MRD-negative status. Overall, 23 (43%) patients achieved MRD-negative plus sCR/CR status at day-90 (11 [41%] in short and 12 [50%] in the extended infusion arm).

The median follow-up was 14.5 (range: 6-40) months (13.8 months in the short infusion and 14.8 months in the extended infusion arm). The median progression-free survival (PFS) was not reached in the overall trial population (Figure). The median PFS in the short infusion arm was not reached vs. 28.2 months in the extended infusion arm. The 2-year progression-free survival (PFS) was 91% in the short infusion arm vs. 77% in the extended infusion arm (hazard ratio (HR)=9.5 with 95% CI: 1- 91.2), p-value=0.022. On multivariate analysis, controlling for age and cytogenetic risk category, the extended infusion arm was associated with a shorter PFS (HR 10.96; 95% CI 1.18 – 102.02), p-value 0.0355, although the range for HR was notably wide, which could be attributed to a small number of events in each arm.

Conclusions: Dose escalation of evomela to 225 mg/m² is safe and associated with an acceptable toxicity profile and a high response rate. Short and extended infusions of evomela are well-tolerated and associated with high response rates. The PFS is longer with the short infusion schedule, however, to affirm these preliminary observations, additional follow-up is needed.