Modakafusp Alfa (TAK-573), an Immunocytokine, Shows Clinical Activity in Patients with Relapsed/Refractory Multiple Myeloma; Updated Results from a First-in-Human Phase 1 Study

Background:

Modakafusp alfa (previously known as TAK-573) is a first-in-class immunocytokine designed to deliver interferon alpha-2b (IFNα2b) to CD38+ cells. It consists of two attenuated IFNα2b molecules genetically fused to the Fc portion of a humanized, anti-CD38, IgG4 monoclonal antibody (mAb). The specificity for CD38 and reduced IFN receptor binding affinity of the attenuated IFNα2b molecules significantly reduces the potential for off-target binding and toxicity. Furthermore, modakafusp alfa binds to a different epitope on CD38 than the currently approved anti-CD38 therapeutic mAbs, daratumumab and isatuximab. Preclinical evaluation of modakafusp alfa supports activation of type I IFN signaling in CD38+ cells, inducing direct anti-proliferative effects on myeloma cells, as well as direct and indirect immune cell activation. We have previously reported preliminary results from the first 59 patients (pts) in our first-in-human phase 1 trial of modakafusp alfa in pts with relapsed/refractory multiple myeloma (RRMM; NCT03215030), showing responses to single-agent therapy with doses starting at 0.1 mg/kg weekly; thrombocytopenia and neutropenia were dose-limiting toxicities when modakafusp alfa was administered weekly (QW), every 2 weeks (Q2W), and every 3 weeks (Q3W) (Vogl, Blood 2020). Here we report updated results from this trial, focusing on results from an expansion cohort with dosing every 4 weeks (Q4W).

Methods:

Eligible pts with RRMM who had received at least three previous lines of treatment received modakafusp alfa as a 1- to 4-hour intravenous infusion at 11 dose levels from 0.001 to 6 mg/kg following a 3+3 dose-escalation design. The initial dosing schedule was QW for 8 doses, then Q2W for 8 doses, and then monthly; subsequent cohorts evaluated dosing Q2W, Q3W or Q4W. Expansion cohorts were planned using modakafusp alfa at protocol-defined, biologically active doses that did not exceed the maximum tolerated dose (MTD).

Results:

As of May 2021, 83 pts had been treated across all planned dosing schedules. With Q4W dosing, the MTD was exceeded at the 6 mg/kg dose due to DLTs: a grade 3 infusion reaction and prolonged thrombocytopenia and neutropenia, which delayed the start of cycle 2 by >14 days. In total, 24 pts were treated with 1.5 mg/kg modakafusp alfa Q4W (5 pts during dose escalation and 19 pts in an expansion cohort). Analyses include data from all 24 pts. The median number of prior lines of therapy received was 6 (range 4-16); 21 pts (88%) were refractory to an anti-CD38 mAb, and 20 (83%) were triple class-refractory (to a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 mAb). Grade 3 or higher treatment-emergent adverse events (TEAEs) were reported in 18 pts (75%). The most frequent grade 3-4 TEAEs were neutropenia in 12 pts (50%; grade 4 in 6 [25%]), leukopenia in 9 (38%), decreased lymphocyte count in 9 (38%), anemia in 8 (33%), and thrombocytopenia in 8 (33%; grade 4 in 3 [13%]). One pt (4%) had a grade 3 bleeding event and continues on study treatment; 3 pts (13%) had infections (grade 3 in 2 [8%]); and 8 (33%) had infusion reactions (grade 3 in 1 [4%]). The overall response rate (ORR, ≥partial response [PR]) was 42% (complete response [CR], n=2; very good partial response [VGPR], n=5; PR, n=3), and the clinical benefit rate (ORR + minimal response [MR]) was 54% (MR, n=3). Median progression-free survival was 5.7 months (95% confidence interval [CI], 1.9-not reached [NR]), median time to response was 1.9 months (95% CI, 0.95-NR), and median duration of response was 7.4 months (95% CI, 2.3-NR). Among the 21 anti-CD38 mAb-refractory pts, the ORR was 43%, while among the 4 pts who received an anti-CD38 mAb in their most recent line of therapy prior to enrollment, the ORR was 75% (CR, n=1; VGPR, n=2). Correlative studies show evidence of T-cell and natural killer-cell activation, as well as activation of IFN signaling in CD38+ cells, including upregulation of CD38 expression.

Conclusion:

Modakafusp alfa (TAK-573) is a novel candidate for the treatment of RRMM, which has shown promising anti-myeloma activity in heavily pretreated pts, including anti-CD38 mAb-refractory pts and those who have received an anti-CD38 mAb in their most recent line of treatment. A Q4W dosing schedule of modakafusp alfa is feasible and the optimal dose and potential combinations are being explored.