Oliver, Katherine

7094 Background: Waldenström Macroglobulinemia (WM) remains incurable with current available therapeutic options. Treatment options for relapsed/refractory pts are limited and often continuous, underscoring the need for new agents with novel mechanisms of action and pt-centered, fixed duration therapy. Iopofosine I 131 is a novel radiopharmaceutical compound composed of a lipid raft-targeting phospholipid ether covalently bound to 131 I, a beta emitting radioisotope. Here, we report preliminary sub-group results of the CLOVER-WaM study [NCT02952508] in WM pts treated with a Bruton’s Tyrosine Kinase inhibitor (BTKi) immediately prior to iopofosine. Methods: Eligible WM pts had received >2 prior therapies and had symptomatic disease requiring therapy according to consensus recommendations for WM. Treatment consisted of 2 cycles of iopofosine I 131 administered at 15 mCi/m 2 on days 1 and 15 of each 57-day cycle. The primary efficacy endpoint was major response rate (MRR; partial response or better, as determined by the modified IWWM-VI). Secondary and exploratory endpoints included overall response rate (ORR), treatment-free survival (TFS), progression free survival (PFS), duration of response (DOR), and clinical benefit rate (CBR; stable disease or better). Herein, efficacy endpoints were assessed in the modified intent-to-treat (mITT) population (all pts who received ≥60 mCi total administered dose of iopofosine I 131), and whose treatment regimen prior to iopofosine included a BTKi. Safety was evaluated using CTCAE v4.03 in pts who received ≥1 dose of iopofosine. Data cut off for this analysis was Jan. 16, 2026. Results: As previously reported, 65 pts were dosed and 55 are included in the mITT population. Of those, 22 (40%) had received a BTKi containing regimen immediately prior to iopofosine; and 11 who previously received at least 2 regimens utilizing BTKis and 12 who were refractory to rituximab. In this subgroup, median age was 70.5 (range 55-88), 17 (77%) were male, and 5 (23%) were female. The median number of prior therapies was 3 (range 2-7), 15/22 (68%) were MYD88 mutated and 18/22 (82%) were TP53 wildtype. The MRR was 15/22 (68.2%), ORR was 19/22 (86.4%) and CBR was 100%, median PFS was 12 months (range 1.6 to 28.0) and median TFS was 19.1 months (range 2.5-34.4). Grade ≥ 3, related treatment emergent adverse events (TEAE) occurring in > 10% of pts included anemia (41%), leukopenia (41%), neutropenia (58%), and thrombocytopenia (86%). Conclusions: Iopofosine I 131 demonstrated significant efficacy; 100% CBR, 86.4% ORR and 68.2% MRR with a median PFS of 12 months (range: 1.6 – 28.0 months) in a pt population with no current standard of care therapy. The treatment was well-tolerated with a manageable toxicity profile with cytopenias as the only Grade 3 or greater TEAE. Based on the results of this pivotal trial, iopofosine I 131 could be a promising novel treatment for WM pts after BTKi therapy. Clinical trial information: NCT02952508 .

7561 Background: Phospholipid ethers (PLE) provide a novel mechanism to specifically target tumor cells leveraging high lipid raft content in their cell membranes. PLE/phospholipid drug conjugates are specifically designed to have high affinity to lipid rafts which upon binding results in trans-membrane flipping with the ability to deliver an attached warhead directly to the cytosol. CLR 131 (I-131-CLR1404) is a novel PLE molecule armed with I-131 resulting in targeted tumor cell radiotherapy which is being examined in relapsed or refractory WM through an open-label, Phase 2 trial, CLOVER-1 (NCT02952508). Methods: The primary objective of this study is to determine the efficacy and safety of CLR 131 in select B-cell malignancies. Eligibility criteria for WM pts include receipt of at least 2 prior treatment regimens unless ineligible to receive standard agents and have measurable disease: either IgM or extramedullary disease. CLR 131 is administered in up to 4 IV infusions (15-20 min) over 3 months. Adverse events (AEs) are graded by NCI-CTCAE v4.03; responses are assessed by the VIth WM Criteria for Response Assessment [Owen 2013]. Results: 6 pts with WM were enrolled in the study with data current as of 8 Jan 2021. The median age was 69 (range 54-81) with 4 females and 2 males who had a median of 2 prior regimens (range 1-5) and received a mean total body dose of 92.76 mCi CLR 131. 3 of 6 patients were MYD88 wild type (WT) of which 2 were dual WT (MYD88 WT & CXCR4 WT). The overall response rate (ORR) was 100% and the major response rate (MRR) was 83%, including 1 pt with a CR, 4 PR, and 1 MR. For those pts who were dual WT, the MRR was 100% and 1 pt who was MYD88 WT (CXCR4 is unknown) had a complete response. The median time to initial response was 48 days. Median duration of response (DOR) and treatment free remission (TFR) have not been reached; ongoing mean DOR is 335 days and mean TFR is 384 days. 100% of MYD88 WT patients have exceeded 6.5 months of follow up with average TFR of 18.1 months. The primary treatment emergent AEs in pts with WM included fatigue and cytopenias, in line with prior experience with CLR 131 in other B-cell malignancies. The most commonly observed cytopenias included Grade 3 or 4 thrombocytopenia (100%), neutropenia (83%), anaemia (66%) and decreased white blood cell count (33%). Of note, no cases of bleeding or febrile neutropenia were observed. Conclusions: Initial results for CLR 131 show efficacy across multiple WM patient genotypes including dual WT patients with durable DOR and TFR after 2 to 4 infusions. CLR 131 represents a novel and promising approach to the treatment of MYD88 WT patients who have a historical median time to progression of 1.3 years. These encouraging data led to the pivotal global CLOVER-WaM trial (N=50) in WM patients who have failed or had a suboptimal response to a Bruton Tyrosine Kinase inhibitor. CLOVER-WaM is currently enrolling. Clinical trial information: NCT02952508.

Abstract Background: I-131-CLR1404 is a novel radioiodinated therapeutic that exploits the selective uptake and retention of phospholipid ethers (PLEs) by malignant cells. Based on initial preclinical and clinical experience and the exquisite radiosensitivity of MM, I-131-CLR1404 is being examined in RRMM in an open-label, dose escalation Phase 1 trial (NCT02278315) evaluating up to 5 cohorts and a maximum of 37.5 mCi/m2. Methods: The primary objective is to determine safety and tolerability of I-131-CLR1404 with and without dexamethasone (dex) in RRMM. Secondary objectives are to determine the recommended Phase 2 dose (RP2D) and therapeutic activity in RRMM. Eligibility criteria include progressive, relapsed/refractory MM, and at least one previous exposure to proteasome inhibitor (PI) and immunomodulatory (IMiD) drugs. Prior autologous stem cell transplant (ASCT) and external beam radiation therapy are allowed (≤ 20% of total marrow irradiated). There is no limit to the number of prior therapies. I-131-CLR1404 is administered intravenously as a single 30 minute infusion on day 1 with 40 mg dex orally weekly for 12 weeks. Dose-escalation uses a minimally modified, standard 3+3 schema with dose-limiting toxicities (DLTs) assessed through day 85 post-infusion. Adverse events (AEs) are graded by NCI-CTCAE v4.03; responses are assessed by the International Myeloma Working Group Uniform Response Criteria. Results: Ten patients have been enrolled in the study with data presented as of 30 Jun 2016 for 8 patients. Accrual is ongoing in the additional cohorts. Five patients were enrolled to cohort 1 (12.5 mCi/m2 + dex); 4 were evaluable and 1 patient was taken off study for rapid disease progression. Five patients have been enrolled to cohort 2 (18.75 mCi/m2 + dex), with data presented on 3 enrolled prior to data cutoff. The median age was 68.5 (range 55-85) and included 5 males and 3 females. All patients were standard risk (karyotyping) and median bone marrow plasma cell involvement was 25% (range 4-50%). Median number of prior therapies was 4 (range 2-12) (Table 1). Four of 8 patients previously underwent ASCT and 25% were previously treated with radiation therapy. Hematologic AEs (grade 3+) and non-hematologic AEs (grade 2+) potentially related to study drug are shown in Table 1. No difference in the toxicity profile was noted for patients with previous radiation therapy. Two serious adverse events (SAEs) have been reported, both in patients treated with 18.75 mCi/m2 I-131-CLR1404. One patient was hospitalized for a seizure (Day 62), assessed as unrelated to study drug and another patient was hospitalized for a grade 1 upper GI bleed in the setting of grade 4 thrombocytopenia (Day 23). This is believed to be the result of rapidly progressive disease, however relationship to I-131-CLR1404 could not be ruled out. Stable disease was achieved in 100% of evaluable patients (n=7). One subject in cohort 1 demonstrated a > 30% reduction in serum m-protein. Figure 1 provides a summary of percent change in serum free light chain assay (FLC) from baseline. Three patients had a reduction in FLC > 50%, 2 in cohort 1 and 1, to date, in cohort 2. Three patients had a stable FLC response through at least 22 days following treatment and 1 subject was unresponsive with regard to FLC. Median follow-up is 6.8 months (range 1.2-14.2). Patients did not receive subsequent systemic therapy for a median of 3.5 months (range 0.6-4.7). Furthermore, 1 subject in cohort 2 maintains stable disease and has not initiated subsequent treatment. Median progression free survival (PFS) is 3 months and included 4 patients with stable disease at the end of the 85 day study follow-up. In patients with progression after I-131-CLR1404, treatment included daratumumab (n=4), ASCT (n=1), and bortezomib, lenalidomide, and dex (VRD) (n=1). Conclusions: I-131-CLR1404 represents a unique, first in class targeted radiotherapeutic for MM. Preliminary data from this trial show an acceptable and expected safety profile with an efficacy signal in the initial 2 of a potential 5 cohorts. All evaluable patients, despite extensive previous therapy and refractoriness to new therapies, achieved disease stabilization. The study is ongoing to determine the RP2D and long term efficacy. Disclosures Ailawadhi: Pharmacyclics: Consultancy; Novartis: Consultancy; Amgen Inc: Consultancy; Takeda Oncology: Consultancy. Oliver:Cellectar Biosciences: Employment.