Background: Cyclin D has been shown to play an essential role in acute lymphoblastic leukemia (ALL) initiation and progression, providing rationale for targeting the CDK4/6-cyclin D complex that regulates cell cycle progression.
Procedure: The Children's Oncology Group AINV18P1 phase 1 trial evaluated the CDK4/6 inhibitor, palbociclib, in combination with standard four-drug re-induction chemotherapy in children and young adults with relapsed/refractory B- and T-cell lymphoblastic leukemia (ALL) and lymphoma. Palbociclib (50 mg/m2 /dose) was administered orally once daily for 21 consecutive days, first as a single agent (Days 1-3) and subsequently combined with re-induction chemotherapy. This two-part study was designed to determine the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D), followed by an expansion pharmacokinetic cohort.
Results: Twelve heavily pretreated patients enrolled, all of whom were evaluable for toxicity. One dose-limiting hematologic toxicity (DLT) occurred at the starting dose of 50 mg/m2 /dose orally for 21 days. No additional DLTs were observed in the dose determination or pharmacokinetic expansion cohorts, and overall rates of grade 3/4 nonhematologic toxicities were comparable to those observed with the chemotherapy platform alone. Five complete responses were observed, two among four patients with T-ALL and three among seven patients with B-ALL. Pharmacokinetic studies showed similar profiles with both liquid and capsule formulations of palbociclib.
Conclusions: Palbociclib in combination with re-induction chemotherapy was well tolerated with a RP2D of 50 mg/m2 /day for 21 days. Complete responses were observed among heavily pretreated patients.
Trial registration: ClinicalTrials.gov NCT02255461 NCT03792256.
Keywords: acute lymphoblastic leukemia; palbociclib; pediatric; relapse.
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