Subcutaneous Daratumumab in Patients with Relapsed or Refractory Multiple Myeloma: Part 2 Safety and Efficacy Update of the Open-Label, Multicenter, Phase 1b Study (PAVO)

Introduction: Daratumumab (DARA) is a human IgGκ anti-CD38 monoclonal antibody with a direct on-tumor and immunomodulatory mechanism of action. DARA (16 mg/kg administered intravenously [IV]) is approved in many countries as monotherapy and in combination with standard of care (SOC) treatment regimens for patients with relapsed/refractory (RR) multiple myeloma (MM) and newly diagnosed MM. Three phase 3 studies have now demonstrated that DARA in combination with SOC treatment doubles complete response (CR) rates, triples minimal residual disease-negative rates, and reduces the risk of progression or death by at least 50% vs SOC alone. The median durations of the first, second, and subsequent DARA IV infusions are 7.0, 4.3, and 3.4 hours, respectively. To determine whether the duration of infusion can be shortened without compromising the safety or efficacy of daratumumab, an open-label, multicenter, phase 1b clinical trial (PAVO; NCT02519452) was conducted to evaluate a subcutaneous (SC) formulation of DARA with recombinant human hyaluronidase enzyme PH20 (rHuPH20; ENHANZE^® drug delivery technology, Halozyme, Inc.) in patients with RRMM. Part 1 of the study revealed that a mix-and-deliver SC administration was well tolerated, with low rates of infusion-related reactions (IRRs) and similar efficacy to DARA IV (Usmani et al. ASH 2016; abstract 1149). Here, we present updated safety and efficacy findings from Part 2 of the PAVO study, where a concentrated, pre-mixed SC co-formulation of DARA and rHuPH20 (DARA SC) was evaluated in patients with RRMM.

Methods: Eligible RRMM patients had received ≥2 prior lines of therapy, including a proteasome inhibitor (PI) and immunomodulatory drug (IMiD). In Part 2 of the study, a concentrated co-formulation of DARA (1,800 mg) and rHuPH20 (30,000 U; in 15 mL) in a single, pre-mixed vial was administered over 3 to 5 minutes by manual SC injection into the abdomen. DARA SC was given QW during Cycles 1-2, Q2W during Cycles 3-6, and Q4W thereafter in 28-day cycles. Pre- and/or post infusion medications included acetaminophen, diphenhydramine, montelukast, and methylprednisolone. Co-primary endpoints were safety and C_trough of DARA SC at the end of QW dosing. Secondary endpoints included the overall response rate (ORR) and CR rate according to the International Myeloma Working Group response criteria.

Results: At the clinical cut-off date of December 13, 2017, 25 patients were enrolled in Part 2 of the study. Patients received a median of 3 (range: 2-9) prior lines of therapy, with 56% double refractory to both PI and IMiD. No treatment discontinuations occurred due to treatment-emergent adverse events (TEAEs). The most common (≥20%) TEAEs included lymphopenia (32%), thrombocytopenia (24%), fatigue, asthenia, back pain, diarrhea, nausea, headache, and viral upper respiratory tract infection (20% each). The incidence (16%) and severity of IRRs (mostly grade 1-2) with DARA SC was low, the majority of which occurred on Cycle 1 Day 1, and no discontinuations due to IRRs were observed. Transient grade 3 hypertension was reported as an IRR in 2 patients. Grade 1 injection-site TEAEs were reported with DARA SC in 3 patients (induration, erythema, injection-site discoloration, and hematoma [n = 1 each]).

At 6.5 months of median follow-up, the ORR was 52% (28% very good partial response; 24% partial response). Median progression-free survival (PFS) was not reached among all-treated patients, including among patients who were double refractory. Updated data will be presented at the meeting based on longer follow-up.

Conclusions: DARA SC enabled dosing in 3-5 minutes and improves patient convenience. DARA SC was well-tolerated in patients with RRMM with low rates of IRRs and no new safety signals compared with DARA IV. Over 50% of patients responded to treatment and median PFS has not been reached after median follow-up of 6.5 months. These data inform ongoing phase 3 studies of DARA SC in RRMM (including a non-inferiority study of DARA SC vs DARA IV [COLUMBA; NCT03277105]), smoldering multiple myeloma, and AL amyloidosis.