177lu-Satetraxetan-Lilotomab in the Treatment of Patients with Indolent Non-Hodgkin B-Cell Lymphoma (NHL), Phase 1/2 Safety and Efficacy Data from Four Different Pre-Dosing Regimens

177Lu-Satetraxetan-lilotomab (Betalutin®) is a novel CD37-binding IgG1 antibody labelled with the beta-emitter lutetium-177, in a ready-to-use formulation currently in Phase 1/2 clinical development for the treatment of Non-Hodgkins lymphoma. CD37 is an internalizing transmembrane antigen highly expressed on most B-cell malignancies, and is a promising therapeutic target. The optimisation of the pre-dosing regimen prior to administration of 177Lu-Satetraxetan-lilotomab may result in an improved safety and efficacy profile. The phase 1 stage of this study is designed with 4 arms to test different pre-dosing regimens (no pre-dosing, rituximab and two doses of lilotomab) on the effect of 177Lu-Satetraxetan-lilotomab. Methods: Patients with relapsed incurable NHL of follicular grade I-IIIA, marginal zone, mantle cell, lymphoplasmacytic and small lymphocytic subtypes and with platelet counts ≥ 150 x109/l were eligible for inclusion in the study. All patients received pre-treatment with rituximab (375 mg/m2) to deplete peripheral B cells and improve biodistribution of the labelled antibody. Pre-dosing with lilotomab (cold anti-CD37 antibody) was given in arms 1 and 4 or rituximab in arm 3, within 4 hours of 177Lu-Satetraxetan-lilotomab to block binding in the non-tumour tissue. The pre-treatment and pre-dosing regimen used in each arm is summarised below: Arm 1: rituximab day1 and 8, lilotomab (40 mg) plus Betalutin day 29 Arm 2: rituximab day 1 and 8, Betalutin day 29 Arm 3: rituximab day 1, rituximab plus Betalutin day 15 Arm 4: rituximab day 1, lilotomab (100 mg/m2) plus Betalutin day 15 The starting dose for Arm 1 was10 MBq/kg and was 15 MBq/kg for arm 2, 3 and 4 and in phase 2. Response was assessed by FDG PET/CT scans at 3 and 6 months post-treatment and then by CT scan up to 5 years after treatment. The results of the protocol specified interim analysis will be presented. Results: A total of36 patients have been enrolled into study, of which 24 are currently evaluable. Patients enrolled into the study had either follicular (n=20), mantel cell (n=2) or marginal zone (n=2) lymphoma. The number of prior therapies ranged from 1 to 8. The efficacy and safety results from patients enrolled into Arms 3 and 4 and treated with two different pre-dosing regimens will be presented for the first time. The most common toxicities observed were hematologic with all dose limiting toxicities (DLTs) being reversible and manageable and related to thrombocytopenia and neutropenia. At a dose of 15 MBq/kg, pre-dosing with 40 mg of lilotomab (Arm 1 and phase 2) reduced the incidence of hematological DLTs to 14% (2/14 patients) compared with 100% (2/2 patients) with no pre-dosing in Arm 2. No DLTs have been reported at 10 MBq/kg in either Arm 1 or 2. Fourteen serious adverse events (SAEs) were reported by 8 patients: Atrial fibrillation (n=2) and platelet count decreased (n=2) were the only SAEs reported by more than one patient. There have been no deaths and no secondary malignancies or other long-term safety events. The overall tumor response rate observed in 23 patients evaluable for efficacy was 57%, comprising 7/23 complete responses, 6/23 partial responses, 5/23 stable disease and 5/23 with progressive disease. In addition, one patient had a confirmed transformed lymphoma at 3 months. One patient is still in remission more than 3 years after treatment and two further patients are still in remission more than 2 years after treatment. Conclusions: Betalutin has the potential to be a novel, safe and effective therapy for B-cell malignancies with durable responses. Betalutin, a single dose, ready-to-use formulation, has a predictable and manageable safety profile which is improved by pre-dosing. Most AEs were haematological, all transient and reversible. Disclosures Kolstad: Nordic Nanovector: Other: Membership of Scientific Advisory Board. Illidge:Nordic Nanovector: Consultancy. Dahle:Nordic Nanovector ASA: Employment, Equity Ownership. Baylor Curtis:Nordic Nanovector: Employment. Østengen:Nordic Nanovector: Employment. Turner:Nordic Nanovector: Employment. Hartvig Larsen:Nordic nanovector: Equity Ownership. Holte:Mundipharma: Research Funding; Amgen: Research Funding.