A Phase I Open-Label, Multi-Dose Escalation Study of the Dual Syk/Jak Inhibitor PRT062070 (Cerdulatinib) in Patients with Relapsed/Refractory B Cell Malignancies

Introduction: Preclinical studies of the Syk-mediated B-cell receptor pathway and Jak-mediated cytokine pathways have demonstrated a potential therapeutic advantage for the dual inhibition of both Syk and Jak kinases in the treatment of B-cell malignancies. Cerdulatinib (PRT062070) was identified from a chemistry screen as a potent and selective inhibitor of Syk, Jak1, Jak3, and Tyk2, with minimal activity against Jak2. Cerdulatinib is efficacious in rodent models of B-cell lymphoma and autoimmune disease (Coffey et al., ASH 2012) and has demonstrated anti-tumor activity in genetically diverse B-cell lymphoma cell lines that is greater than that of Syk- or Jak- selective inhibitors alone (Ma et al., ASH 2013).

Methods: This Phase 1 3+3 dose escalation study is evaluating cerdulatinib, given continuously on either a once daily (QD) or twice daily (BID) schedule, for relapsed/refractory chronic lymphocytic leukemia (CLL) or B-cell non-Hodgkin lymphoma (NHL). The primary objective is to determine the maximum tolerated dose (MTD) of cerdulatinib in patients with CLL or NHL. Secondary objectives are to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of cerdulatinib and to make a preliminary assessment of antitumor activity. Toxicity is graded according to the National Cancer Institute - Common Terminology Criteria for Adverse Events (NCI-CTCAE) v4. Clinical response is evaluated according to published criteria (Hallek et al., Blood 2008:111:5446-5456; Cheson et al., J. Clin. Oncol. 2012: 25:579-586). The level of inhibition of Syk and Jak is determined using a variety of whole blood assays measuring signaling via receptors for the B-cell antigen, IL2, IL4, IL6, and GM-CSF. Serum markers of tumor burden, including CCL3, CCL4, and other markers of inflammation, are also being measured.

Results: As of 4 August 2014, twelve patients have been enrolled in once daily dose cohorts of 15 mg QD, 30 mg QD, and 45 mg QD. No dose-limiting toxicities have been reported. Grade ≥3 adverse events (AEs), regardless of causality, were: Grade 3 anemia (n=1), Grade 3 neutropenia (n=1), Grade 3 fatigue (n=1), Grade 3 hypotension (n=1), Grade 3 AST increased (n=1), Grade 3 hematochezia (n=1), and Grade 5 Pneumocystis pneumonia (PCP; n=1). The patient who experienced PCP pneumonia was a 76 year old male with CLL who had received prior therapy with bendamustine and rituximab.

Cerdulatinib is well-absorbed with an average terminal elimination half-life at steady state of 14 hours. Selective inhibition of Syk and Jak in whole blood assays was observed post-treatment, with IC₂₅-IC₅₀ (C_min to C_max at steady-state) against these targets achieved at the 15 mg dose level, and IC₅₀-IC₈₀ (C_min to C_max at steady-state) achieved at the 30 mg and 45 mg doses. Reductions of >50% in serum markers of inflammation, as well as in CCL3 and CCL4, were noted at all dose levels post-treatment. Two patients treated at the 15 mg dose (1 CLL, 1 follicular lymphoma [FL]) remained on study for >230 and >200 days, respectively, with stable disease (SD) prior to disease progression. One patient treated at the 30 mg dose (diffuse large B-cell lymphoma [DLBCL], who did not respond to prior R-CHOP therapy), remained on study with SD for 140 days. One patient treated at the 30 mg dose (CLL) experienced a >60% decrease in peripheral lymphocyte count prior to coming off study for PCP pneumonia. Another patient treated at the 30 mg dose (CLL) experienced early lymphocytosis and a 33% reduction in lymph node size at the end of Cycle 2 and remains on study in Cycle 3. One patient treated at the 45 mg dose (FL) experienced a 40% decrease in lymph node size at the end of Cycle 4 and remains on study in Cycle 5.

Conclusions: Cerdulatinib has been well tolerated in the initial cohorts of this Phase 1 study, with no dose-limiting toxicities and preliminary evidence of anti-tumor activity. Dose escalation continues and Phase 2 expansion cohorts are planned in CLL, DLBCL and FL.