Phase 1 Trial of K0706, a Novel Oral BCR-ABL1 Tyrosine Kinase Inhibitor (TKI): In Patients with Chronic Myelogenous Leukemia (CML) and Phildelphia Positive Acute Lymphoblastic Leukemia (Ph+ ALL) Failing ≥ 3 Prior TKI Therapies: Initial Safety and Efficacy

Introduction: Despite availability of several BCR-ABL1 TKIs for treatment of CML, some patients (pts) fail ≥3 TKIs and/or have co-morbidities that limit use of 2^nd generation TKIs (2GTKI: Nilotinib, Dasatinib and Ponatinib). K0706 is a novel third generation TKI effective against wild-type and mutated BCR-ABL1 isoforms with significantly less off-target activity compared to existing TKIs. We report Phase I results of K0706 in pts who were resistant and/or intolerant to ≥3 prior TKIs or who had co-morbidities precluding the use of 2GTKI (NCT02629692).

Methods: This was a multicentre, open-label, dose-escalation and expansion study of K0706 to evaluate the safety and anti-leukemic activity of K0706, and determine the MTD. Patients with CML or Ph+ ALL resistant and/or intolerant to ≥3 prior TKIs received escalating doses of K0706 capsules (single daily dose) in 28 day cycles. Treatment continued until unacceptable toxicity, disease progression, consent withdrawal or death.

Results: At data cut-off of 30 June 2019, 35pts (19 male) have been treated with K0706 at doses of 12mg (n=1), 24mg (n=1), 48mg (n=6), 66mg (n=7), 90mg (n=3), 126mg (n=5), 174mg (n=5), 204mg (n=4), and 240mg (n=3); median age 61.6 (range 23.5-85.6) years; median time from diagnosis 10.13 (range 0.7-22.9) years. Diagnoses included 27 chronic phase [CP], 3 accelerated phase [AP], 4 blast phase [BP] CML and 1 Ph+ ALL. Eleven and 19pts received ≥3 prior TKIs and ≥4 prior TKIs respectively (intolerant, n=11; resistant and intolerant, n=24). 13pts had BCR-ABL mutations detectable at study entry (F317L, n=2; E255V/K, n=2; T315I, n=2; 1pt each had: Y253H, Y253F, V299L, Q252H and G250E respectively; 1pt each had 2BCR-ABL mutations: E255V, F317L and F359V, E255V respectively). At a median follow-up of 6.9 months (range 0.5-26 months), 68.6% of pts remained on K0706 and 31.5% completed ≥12 months of therapy. 11pts (31.4%) discontinued [10 due to disease progression (with 2 deaths) and 1 with a possibly related AE of CNS bleed confounded by disease progression].

The most common K0706-related AEs included transient mild to moderate gastrointestinal disturbances (18.5%), general disorders [i.e.: myalgia, fatigue, asthenia] (15.7%), neutropenia (12%) and thrombocytopenia (10%). At 240mg, 2 of 3pts had dose-limiting toxicities (DLTs) of ≥25% of doses missed in Cycle 1 because of toxicity (dyspnoea (1x grade 2, 1x grade 3) and non-cardiac chest pain (1x grade 2) DLTs were reversible and pts resolved at 174 mg without recurrence.

Of 27 CML CP pts, 7pts achieved a complete cytogenetic remission (CCyR) and 4 maintained CCyR. 1pt achieved partial CyR (PCyR), 1pt had disease progression in Cycle 1 and 5pts are yet to complete post baseline assessments. Of the 12 CML CP cytogenetic responders, 11 remain on treatment [mean duration 6.9 (range 2.9 -26) months in major cytogenetic response (MCyR) while 1pt had disease progression at 9.5 months]. Cytogenetic responses were observed in 2 of 11 CML-CP pts with mutations [CCyR in 1 of 2 pts with F317L and in 1pt with G250E]. Pts with T315I mutations had disease progression in Cycle 1. Following this, protocol was amended to enrol subjects with T315I mutations only when target plasma concentrations required preclinically to inhibit T315I clone are achieved. Five of 27 pts achieved major molecular response (MMR), 2 pts in MR 4.5.

Of 8 pts with CML AP (n=3), BP (n=4) or Ph+ ALL (n=1), 4 achieved confirmed MaHR; 2 entered the study in MaHR; 3 had MCyR [2 had CCyR and 1 had PCyR] and 2 had disease progression. 1pt in CML BP had a confirmed MaHR for 12 months. 1pt in AP with chromosome 3 inversion, had CCyR at 3 months and maintaining for 13 months.

Conclusion:K0706 has acceptable safety profile with activity in heavily pre-treated patients who had failed at least ≥3 prior lines of TKIs. The study provides early proof of principle for the effectiveness of K0706 in a setting with few available treatment options.