An open-label phase I dose-finding study of APR-246 in hematological malignancies

Mutations in the TP53 tumor suppressor gene occur at different frequencies in a variety of human malignancies. TP53 encodes a DNA-binding transcription factor that induces cell growth arrest, senescence and cell death by apoptosis upon cellular stress, including oncogenic stress and DNA damage. In hematological malignancies TP53 mutations are common in relapsed/refractory disease and confers a dismal prognosis. PRIMA-1 and the analog APR-246 (PRIMA-1) can restore wild-type conformation of mutant p53 and induce apoptosis in tumor cells of various origin. APR-246 is the first compound targeting mutant p53 to enter into a clinical trial. In the first in-man study APR-246 was given daily as a 2 h intravenous infusion for 4 consecutive days. The maximum tolerable dose using this schedule was defined as 60 mg/kg daily and the most common adverse effects were neurological. This is an extension of the first in-man study aiming at optimizing the dose regimen to obtain better antitumor response with less toxicity. The primary objective was to evaluate safety and tolerability of APR-246 with the new dosing schedule. Secondary objectives were to determine the pharmacokinetic (PK) profile and assess antitumor effects of APR-246. Main inclusion criteria were: relapsed/refractory non-M3 acute myeloid leukemia (AML) or chronic lymphatic leukemia (CLL) with deletion of 17p not eligible for other therapies, age ⩾ 18 years, ECOG performance status 0–2 and life expectancy of at least 2 months. Main exclusion criteria were hepatic transferase ⩾ 5 upper limit of normal (ULN), creatinine ⩾ 1.5 ULN, severe cardiac or respiratory disease. The trial was conducted in accordance to the Declaration of Helsinki and ICH-GCP guidelines and was registered at ClinicalTrials.gov, identifier NCT00900614. The dosing schedule was designed to maximize drug exposure without increasing peak concentrations. Four daily infusions were given using a boosting infusion of 50 mg/kg during 45min followed by a 85mg/kg as a 5 h and 15min infusion, in total 135 mg/kg, with an option to repeat the treatment in 21 day cycles. Interim analyses were scheduled at completion of every three patients or whenever necessary at any occasion. Dose limiting toxicity (DLT) was defined as study drug–related Common Terminology Criteria for Adverse Events (CTCAE) grade 1 for ataxia/incoordination, tremor and confusion; CTCAE grade 2 for somnolence, depressed level of consciousness and seizures; and other CTCAE grade 2, 3 or 4. Dose de-escalation was made twice by decision from the study board due to toxicity. After treating three patients on the starting dose of 135 mg/kg, there was a dose reduction to 105mg/kg (45 mg/kg bolus+60 mg/kg infusion). This schedule was given to five patients when a second de-escalation was made to 67.5 mg/kg (25 mg/kg +42.5 mg/kg). Efficacy was assessed by blood and bone marrow sampling at baseline, on day 4 and on day 21 for AML, and by lymph node evaluation manually; and with computed tomography (CT) scans at baseline and on day 21 for CLL. Predefined response criteria for AML was a reduction of blast cell count of ⩾ 25% in peripheral blood and/or bone marrow, and for CLL a reduction of lymphocytes in peripheral blood of ⩾25% and/or a ⩾ 25% reduction of tumor size assessed by CT scan or palpation of peripheral lymph nodules and/or disappearance of B symptoms. A Mini Mental Test was performed before and after infusion at day 1 and day 4. Safety visits twice weekly were made until day 21. PK samples were collected at baseline, 45 and 90 min after start and 2 h after completed infusion. PK calculations were performed by non-compartmental analysis. Plasma concentrations of APR-246 were determined using a validated LC-MS/MS method. Eleven patients were screened and ten were included at four centers, eight with AML and two with CLL. One patient failed screening due to an ongoing systemic infection and was not included. All patients had relapsed or refractory disease with a median of two previous lines of therapy (range 1–3). Three out of eight patients analyzed (exon 2–11) had TP53 mutations. Patient demographics are summarized in Table 1. Using the 6 h infusion administration, the PK of APR-246 was characterized by a low clearance (151± 35 ml/h per kg) and a large distribution volume (824± 219ml/kg; mean± s.d., n=10) indicating a distribution of APR-246 throughout the whole body. APR-246 concentrations declined in plasma with a t1/2 of about 3.8 ± 0.8 h. At steady state (day 4), no accumulation of APR-246 was observed with the adopted 6 h infusion schedule or after repeated cycles. Plasma clearance and distribution volume were similar at day 1 and day 4, suggesting time-independent kinetics, and in line with the PK parameters previously obtained in the range of doses 2–90 mg/kg after a 2 h infusion. This suggests dose-independent kinetics also up to a daily dose of 135 mg/kg per day given as a 6 h infusion. In total, 41 adverse events (AE) were considered to have probable or possible relationship to study treatment. There was a relation between the dose and the number of AE:s probably associated with study medication: 16, 11 and 1 AE:s were reported at dose levels 135, 105 and 67.5 mg/kg, respectively (Table 2). The most commonly reported AE were vomiting, constipation and dizziness,