Phase 2 Study Evaluating the Efficacy and Safety of Parsaclisib in Patients with Relapsed or Refractory Mantle Cell Lymphoma Not Previously Treated with a BTK Inhibitor (CITADEL-205)

Background: Mantle cell lymphoma (MCL) accounts for approximately 5–7% of non-Hodgkin lymphomas (NHL). A number of therapies are used for second- and later-line treatment including Bruton's tyrosine kinase inhibitors (BTKi). However, treatment failure and intolerance are common and alternative therapies are needed. Parsaclisib is a potent, highly-selective, next-generation PI3Kδ inhibitor that demonstrated clinical activity in patients (pts) with relapsed or refractory (R/R) NHL. We report preliminary results for a cohort of BTK inhibitor-naïve pts with R/R MCL treated with parsaclisib monotherapy in the open-label, phase 2 study CITADEL-205 (NCT03235544).

Methods: Pts must be ≥18 years of age with pathologically confirmed MCL, R/R to the most recent treatment, documented cyclin D1 overexpression or t(11;14) translocation, have Eastern Cooperative Oncology Group performance status (ECOG PS) ≤2, and received 1 to 3 prior systemic treatments. Prior treatment with BTKi and PI3Ki were prohibited. Pts were allocated to receive parsaclisib 20 mg once daily (QD) for 8 weeks followed by either 20 mg once weekly (weekly-dosing group [WG]) or 2.5 mg QD (daily-dosing group [DG]). Prophylaxis for Pneumocystis jirovecii pneumonia (PJP) was required. Objective response rate (ORR) was the primary endpoint; complete response rate (CRR), duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety and tolerability were secondary endpoints. All radiology-based endpoints were based on independent review.

Results: From October 2017 to January 17, 2020 (data cut-off), 104 pts were treated (WG, n = 31; DG, n = 73). Enrollment was ongoing (target:100 pts). At cut-off, a total of 50 (48%) pts had discontinued treatment, including 31 (30%) pts for disease progression. The median exposure (range) was 4.0 months (0.1–19.1). The median age was 72 years and 80% of pts were men. The median time since initial diagnosis was 3.6 years. The majority of pts (92%) had ECOG PS ≤1, and 57% had high-risk MCL International Prognostic Index. The median number of previous systemic therapies was 1; 31% of pts had prior hematopoietic stem cell transplant, and 44% were refractory to their most recent systemic therapy.

At the data cut-off, 92 pts were evaluable for efficacy including 31 in WG and 61 in DG (Table). The median follow-up duration (range) for this population was 11.8 months (1.9–24.0) overall and 9.1 (1.9–24.0) for DG. The ORR (95% confidence interval CI) and CRR were 66.3% (55.7–75.8) and 15.2%, respectively in all evaluable pts, and were 65.6% (52.3–77.3) and 11.5% for DG. The median time to response for pts with a complete or partial response was 7.9 weeks. The median DOR (95% CI) was 11.0 months (6.6–14.7) for all responders and 9.0 months (7.7–14.7) for DG. The median PFS (95% CI) was 11.1 (5.8–16.6) months overall, and 11.1 (5.6–16.6) months for DG.

Among 104 safety-evaluable pts, most common treatment-emergent AEs (TEAEs) occurring in >10% of pts were diarrhea (25.0%), pyrexia (16.3%), constipation (11.5%), and neutropenia (10.6%). Most common grade ≥3 TEAEs reported in ≥5% of pts were neutropenia (8.7%) and diarrhea (7.7%). TEAEs leading to dose interruption or dose reduction occurred in 31.7% and 1.9% of pts, respectively. TEAEs leading to discontinuation occurred in 16.3% of pts including diarrhea (5.8%) and colitis (2.9%). Serious TEAEs reported in ≥2 pts included diarrhea (5.8%), colitis (2.9%), pyrexia (2.9%) and cytomegalovirus infection (1.9%). Four pts experienced fatal TEAEs. The fatal TEAEs in one pt (monocytic acute myeloid leukemia, leukocytosis, and acute kidney injury) were considered related to treatment. TEAEs of clinical interest included neutropenia (10.6%), rash (8.7%), colitis (4.8%), pneumonia (1.9%), PJP and pneumonitis (1% each). New or worsening grade ≥3 laboratory test values of clinical interest included decreased neutrophils (8.7%), platelets (7.7%), and hemoglobin (1.9%), and increases in alanine/aspartate aminotransferase (2.9%/1.9%).

Conclusion: Parsaclisib demonstrated a high rate of rapid and durable response, and had an acceptable safely profile and was generally well tolerated. These preliminary results suggest that parsaclisib represents a potentially new drug class and treatment option for BTKi-naïve, R/R MCL. Updated study results will be presented.