Study design and patients
This was a phase II multi-center study (NCT00798213) of dinaciclib that was originally designed as a randomized study for relapsed and/or refractory AML patients comparing the efficacy of dinaciclib versus gemtuzumab ozogamicin (GO, Mylotarg) and a single-arm study of dinaciclib in patients with ALL. AML patients treated with GO could cross over to dinaciclib at the time of disease progression. The study was approved by the Institutional Review Board (IRB) at each participating institution and was conducted in accordance with the Declaration of Helsinki and in compliance with International Conference on Harmonization Good Clinical Practice Guidelines. Written informed consent was obtained from all patients before study enrollment.
Patients with CD33-expressing AML (≥60 years old) or with ALL (≥18 years old) in first or second relapse or having primary refractory disease or refractory disease after first salvage and not considered candidates for hematopoietic stem cell transplantation (HSCT) were eligible for the study, provided they had an Eastern Cooperative Oncology Group (ECOG) performance status of ≤1, white blood cell (WBC) count ≤30 × 109/L, serum creatinine ≤2 mg/dL, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤2.5 X upper limit of normal and normal bilirubin. Patients were ineligible if they had active central nervous system disease, a second malignancy requiring treatment, known HIV, hepatitis B or hepatitis C infection, previous GO or CDK inhibitor treatment, or previous HSCT.
This study was initiated on March 10, 2009. Results were analyzed as of June 21, 2011. The study was terminated after enrollment of 26 patients due to change in the study sponsor; however, a total of 20 patients received dinaciclib (2 patients crossed over from GO), and the clinical experience with dinaciclib in these patients is presented below.
Study objectives and treatment plan
The primary objective was to determine the overall response rate (ORR), and secondary objectives included time to progression (TTP), safety, dinaciclib PKs, and exploratory biomarker studies.
Dinaciclib 50 mg/m
2 was given as a 2-h intravenous (IV) infusion in cycle 1, and if well tolerated, intra-patient dose escalation to 70 mg/m
2 was allowed in cycle 2. Each cycle lasted 21 days. Patient could continue treatment on the study in the absence of disease progression or unacceptable toxicity. The next cycle of therapy could start if non-hematologic toxicity from previous cycle recovered to ≤grade 1, and dose delay of up to 3 weeks was allowed for recovery. Permanent dose reduction was required for any ≥grade 3 clinically significant non-hematologic adverse event (70 mg/m
2 → 50 mg/m
2; 50 mg/m
2 → 40 mg/m
2; 40 mg/m
2 → 30 mg/m
2; 30 mg/m
2 → discontinue). To allow for continued treatment of subjects whose cytopenias were due to leukemia and not due to drug toxicity, subsequent cycles of treatment were allowed if absolute neutrophil count (ANC) ≥0.5 × 10
9/L or for ANC <0.5 × 10
9/L but no more than 20 % below the baseline pretreatment levels and platelet count ≥20 × 10
9/L or platelets <20 × 10
9/L but no more than 20 % below the baseline pretreatment levels. Anti-emetic prophylaxis including serotonin-receptor antagonist, metoclopramide, or prochloperazine with or without dexamethasone was allowed. After 10 patients had been treated with dinaciclib, the protocol was amended to require hospitalization for cycle 1 treatment, with administration of pre-treatment rasburicase, allopurinol, hydration, phosphate binders, and early administration of Kayexalate (sodium polystyrene sulfonate) for hyperkalemia, including pre-treatment for potassium ≥4 mmol/L. Intense monitoring of laboratory parameters for evidence of tumor lysis syndrome was required, including repeat measurements of serum potassium at 1, 2, 3, 6, and 24 h after start of dinaciclib infusion or more frequently if needed. Dexamethasone 20 mg IV was given early if symptoms of cytokine release syndrome were observed [
19].
Pharmacokinetic analysis
Blood samples for PK evaluations (3 mL each) were collected into prechilled K2 EDTA tubes at 0, 0.25–0.5, 1–2, and 4 h after the end of the 2-h infusion on day 1 of cycles 1, 2, and 3. Samples were kept on ice and centrifuged within 1 h of collection at 2,700g/4 °C for 10 min; separated plasma was immediately frozen on dry ice and then stored at −20 °C or below.
Dinaciclib plasma concentrations were determined using a validated high-performance liquid chromatography assay with tandem mass spectrometry detection [
34]. The internal standard was [13C3]-dinaciclib. The lower limit of quantitation (LLOQ) was 0.0250 ng/mL and the upper limit of quantitation was 10.0 ng/mL. The accuracy at the LLOQ was −1.0 and the precision coefficient of variation (CV) was 10.6 %. The accuracy at low, medium, and high quality control (QC) concentration was 5.8, 5.7, and 2.7, respectively, and precision at low, medium, and high QC concentrations was 4.9, 4.0, and 4.2, respectively. Dilution integrity was demonstrated at 10,000 ng/mL.
Plasma concentration versus time profiles and systemic exposure of dinaciclib in this study were estimated using a population pharmacokinetic (PPK) model-based approach. A 2-compartment PPK model was developed with data from two phase I studies in solid tumors [
31,
32]. The model fits were conducted using NONMEM V, level 1.1 (GloboMax LLC), and a first-order conditional estimation method was employed for all model runs. The model included between-subject variability on clearance and volume of distribution, and mixed error terms.
In vitro studies on primary leukemia cells and human leukemia cell lines
Primary leukemia cells for in vitro studies were isolated from BM or PB obtained from AML or ALL patients enrolled on a separate University of Maryland, Baltimore, IRB-approved protocol for tissue collection and not treated on this clinical study. The cells were isolated by gradient centrifugation using LSM (Mediatech) according to the manufacturer’s protocol. Cells were used either fresh or after viable freezing (FBS/10 % DMSO). Primary leukemia cells were cultured in RPMI 1640 (Invitrogen, Grand Island, NY, USA) supplemented with 15 % heat-inactivated FBS (HyClone Laboratories Inc., Red Bank, NJ, USA) and 200 mM l-Glutamine (Invitrogen). Leukemia cell lines HL-60 (AML), MOLT-4 (T cell ALL), and K562 (chronic myelogenous leukemia [CML] in erythroid blast transformation) were purchased from American Type Culture Collection (ATCC, Manassas, VA, USA) and cultured in RPMI 1640 (Invitrogen) supplemented with 10 % heat-inactivated FBS (HyClone Laboratories Inc.) and 200 mM l-Glutamine (Invitrogen).
Dinaciclib (SCH727965) was obtained from Merck & Co. Inc., Whitehouse Station, NJ, USA (originally Schering-Plough, Kenilworth, NJ, USA). The drug was dissolved in DMSO at 20 mM, aliquoted, and stored at −20 °C until use. Z-VAD-FMK (BD Parmingen, San Diego, CA, USA), a pancaspase inhibitor, was dissolved in DMSO at 20–60 mM and stored in aliquots at −20 °C until use.
Cell proliferation after dinaciclib treatment was assessed using the WST-1 cell proliferation assay (Roche, Indianapolis, IN, USA). Primary leukemia cells were cultured in the presence of increasing concentrations of the dinaciclib (0.0004–10 μM) for 24 h. Leukemia cells lines (HL-60, MOLT-4, K562) were cultured in the presence of increasing concentrations of the dinaciclib (0.0004–10 μM) for 2–72 h. Cells cultured in the presence of an equivalent volume of DMSO served as a treatment control. 4–8 replicates were plated for each drug dilution or control. The IC50 values for the WST-1 assay were calculated using GraphPad Prism 5 software (La Jolla, CA, USA).
Apoptosis assay was performed on fresh primary leukemia cells and leukemia cell lines (HL-60 and K562) treated with dinaciclib (2–200 nM) or an equivalent volume of DMSO (control) for different lengths of time (2–24 h). After treatment, cells were washed twice with cold PBS, resuspended in 1X binding buffer, and stained with propidium iodide (PI) and Annexin V using a FITC Annexin V Apoptosis Detection Kit I (BD Pharmingen) according to the manufacturer’s instructions. The stained cells were evaluated within 1 h on a FACScan (BD Biosciences, San Jose, CA, USA) and analyzed using FlowJo software (Tree Star, Ashland, OR, USA).
For cell cycle analysis, leukemia cells (HL-60 and K562) were treated with dinaciclib (20 and 200 nM) for 2–24 h, pelleted, fixed in 70 % ethanol at −20 °C, stained with 500 μl PI/RNase staining buffer (BD Pharmingen), and analyzed using a FACScan (BD Bioscience) and FlowJo software (Tree Star).
For Western blot analysis, leukemia cell pellets (primary leukemia cells, HL-60, MOLT-4, K562) were washed with PBS and lysed with RIPA buffer (Sigma-Aldrich, St. Louis, MO, USA) supplemented with Complete Mini™ protease inhibitor and PHOStop™ phosphatase inhibitors (Roche). Equal amounts of proteins up to 25 μg were separated on 4–12 % NuPAGE precast gels in 1X MOPS or 1X MES buffer (Invitrogen) and electro-blotted to PVDF membranes (Millipore, Billerica, MA, USA). The membranes were blocked with 5 % dry milk in 1X TBS/0.1 % Tween 20 for at least 1 h at room temperature. Blots were incubated with primary antibody (Ab) overnight at 4 °C, washed 3 times in TBS/0.1 % Tween 20, and then incubated with secondary Ab for 1 h at room temperature. Blots were washed three times, and the signal was detected with Amersham™ ECL™ detection systems (GE Healthcare, Pittsburgh, PA, USA). The following primary Abs were used: mouse anti-PARP (BD Pharmingen), rabbit anti-phospho-Rb (Ser807/811) and rabbit anti-Mcl-1 (both from Santa Cruz, Santa Cruz, CA, USA), rabbit anti-caspase 9 p35 and anti-caspase 3 (both from Cell Signaling, Danvers, MA, USA), and mouse anti-β-actin (Sigma-Aldrich). Commercially available HL-60 cell extract, non-induced SW-101 and etoposide-induced SW-102, were used as negative and positive controls for PARP cleavage (Enzo Life Sciences, Plymouth Meeting, PA, USA). Secondary horseradish peroxidase-conjugated anti-mouse or anti-rabbit Abs were from Cell Signaling (Beverly, MA, USA). The Western blot signals were measured by densitometry using ImageJ 1.45I software (NIH, Bethesda, USA).