An open-label multicenter Phase 1/2 trial of venetoclax-dexamethasone in Relapsed/Refractory t(11;14)-positive systemic AL amyloidosis

Abstract Background: The t(11;14) translocation occurs in 50-60% patients with systemic AL amyloidosis. Venetoclax, an oral BCL2 inhibitor, has shown promising efficacy across t(11;14)-positive plasma cell disorders. However, till date, there are no prospective data in patients with previously treated AL amyloidosis, including those with prior exposure to anti-CD38 monoclonal antibodies (mAbs). Methods: We conducted an investigator-initiated phase 1/2 multicenter open-label trial of venetoclax (± dexamethasone) in patients with relapsed/refractory AL amyloidosis. Key inclusion criteria were central-laboratory confirmed t(11;14) by FISH analysis in ≥5% of CD-138-selected cells on bone marrow aspirate, measurable hematologic disease (dFLC≥2 mg/dL and/or M-spike ≥0.5 g/dL), prior exposure to anti-CD38 mAb, and ≥1 prior line of therapy. Key exclusion criteria were NT-proBNP>8500 pg/mL, NYHA class IIIb/IV, and ECOG>2. Phase 1 dose escalation utilized Bayesian Optimal Interval Network (BOIN) design to determine maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) across four levels: DL1 (venetoclax 200mg), DL2 (400mg), DL3 (400mg + dexamethasone 10mg weekly), and DL4 (400mg + dexamethasone 20mg weekly). A maximum of 6 cycles of therapy on the protocol were planned, with dose limiting toxicities (DLTs) being evaluated in cycle 1. The design accommodated 12-15 patients with ~67% probability of selecting the dose closest to the 25% target toxicity rate. Here, we present the results of the Phase 1 portion of the study, which has completed enrollment. Accrual in Phase 2 portion is currently ongoing. Results: Of 16 patients screened, 12 were enrolled and evaluable for safety and efficacy. Screen failures were attributed to second malignancy (n=2), t(11;14) positivity in <5% CD-138-selected cells (n=1), and t(11;14) negativity (n=1). Enrolled patients had a median age of 64 years, with 25% female, and 17% Black representation. At screening, the median percentage of CD-138-selected cells with t(11;14)-positivity on FISH was 65%. All patients had prior anti-CD38 mAb-exposure by protocol design, with 11/12 patients also exposed to bortezomib. The median number of prior lines of therapy was 1 (range, 1-5). Disease markers at treatment initiation included median dFLC of 14.35 mg/dL (range, 2.13-186.28), median NT-proBNP of 712.5 pg/mL (range, 54-8831), and the median serum creatinine of 0.99 mg/dL (range, 0.69-3.01). Regarding safety, there were no DLTs encountered during the specified timeframe. One patient each received DLs 1, 2, and 3, with all remaining patients receiving DL 4 (400mg + dexamethasone 20mg weekly), which is the RP2D in this trial. There was only one patient that developed grade 3 infection (lung infection; COVID-19). No tumor-lysis syndrome, grade 3 or higher cytopenia, or treatment-emergent deaths occurred. Hematologic overall response (PR or better) was achieved in 11/12 patients (91.7%), with 9/12 (75%) attaining ≥VGPR [4/12 (33.3%) heme-CR, with the remaining being VGPR]. The median time from treatment initiation to best response was 29 days. Among 7 patients that were evaluable for cardiac response, one underwent heart transplant after 3 cycles of study treatment (while in heme-CR), hence was no longer evaluable for cardiac organ response. Of the remaining 6 patients, 2 have achieved cardiac response till date. Renal organ response was observed in 4/7 evaluable patients. At a median follow-up of 8.8 months, 4 out of 12 patients have completed 6 treatment cycles, with 2 receiving ongoing therapy. Six patients discontinued treatment early due to hematologic progression (n=1), suboptimal hematologic response (n=2), patient preference (n=2), and heart transplant (n=1). Patient-reported outcomes (assessed by PROMIS-29) showed no significant changes in Physical Functioning and Fatigue domains among 5 patients with paired baseline and end-of-treatment assessments. Updated follow-up data will be presented at the meeting. Conclusions: To our knowledge, this represents the first prospective evaluation of venetoclax-dexamethasone in relapsed/refractory t(11;14) AL amyloidosis. The combination demonstrated substantial hematologic efficacy (75% ≥VGPR rate) and a favorable safety profile without dose-limiting toxicities. Our results support investigation of venetoclax-based combinations in the frontline treatment of newly diagnosed t(11;14) AL amyloidosis.