Patients were enrolled after this study protocol was approved by the Committee on Human Research. All participants provided written informed consent. Patients had advanced solid tumor malignancies. There were no restrictions on prior number of therapies, and prior paclitaxel and EGFR- or HER2-targeted therapies were allowed. Evaluable disease was required, but measureable disease was not required. Inclusion criteria included age >18 years, ECOG performance status of 0-2, life expectancy > 3 months, adequate organ function, and at least one month since prior therapy of any kind. Exclusions included pre-existing grade 2 neuropathy, significant cardiac disease, and progressing brain metastases.
Pretreatment evaluation included hematologic and biochemical blood work, chest/abd/pelvis CT imaging, and EKG and MUGA evaluations within 5 weeks of enrollment.
Patients self-administered lapatinib orally on days 1 and 2 followed by the intravenous administration of nab-paclitaxel at a fixed standard dose of 100 mg/m2 on day 3 of weeks 1, 2, and 3 of a 4-week cycle. Lapatinib was the experimental therapy and was administered using a dose escalation design guided by toxicity evaluation (see below). Lapatinib was administered in twice-daily dosing because of the higher AUC and reduced pill burden experienced with this schedule (24
). Patients were instructed to take the lapatinib pills on an empty stomach to avoid any potential confounding effects caused by concomitant food intake. Patients continued on therapy as long as they remained free of progression and unacceptable toxicities. Treatment response was assessed both clinically and using Response Criteria to Treatment in Solid Tumors (RECIST) (25
) every 2 months. Clinical activity was determined using results from history and physical examinations, serum biomarkers, chest/abd/pelvis CT scans, and occasional bone scans.
Dose Escalation Design
The lapatinib dose was escalated according to an accelerated titration design1
starting with 1000 mg/day in twice daily dosing (dose level 0) (26
). Subsequent lapatinib dose levels were designated as the following: dose level 1 = 1500 mg/day, dose level 2 = 2000 mg/day, dose level 3 = 2750 mg/day, dose level 4 = 3750 mg/day, dose level 5 = 5250 mg/day, dose level 6 = 7500 mg/day. At least one month of treatment and toxicity data were required for all patients in order to determine tolerability. The accelerated phase continued in cohorts of one until a patient experienced a dose limiting toxicity (DLT), or two patients experienced ≥ grade 2 toxicity. When one of these criteria was met, the accelerated dose-escalation phase closed and the standard dose-escalation phase was initiated. The standard phase continued in cohorts of 3, expandable to 6, until the highest dose at which ≤1 of 6 patients experienced a DLT was determined. There was no intra-patient dose escalation. Toxicity was assessed according to the Common Toxicity Criteria (CTC) version 3.0. DLT was defined as toxicity that occurred during the first cycle of therapy and was attributable to treatment. Toxicities meeting criteria for a DLT include 1) grade 4 neutropenia (ANC <500) for ≥ 96 hours or grade 3 neutropenia with fever (ANC <1000 and T>38.5 °C); 2) grade 4 thrombocytopenia (<25,000) or a bleeding episode requiring platelet transfusion support; 3) any grade 3 or greater non-hematologic toxicity excluding fatigue and sensory neuropathy. Diarrhea and nausea/vomiting were graded in the setting of maximal anti-diarrheals and anti-emetics, respectively; 4) grade 3 or greater sensory neuropathy despite dose reduction of nab-paclitaxel; 5) grade 3 or greater fatigue lasting longer than 1 week; and 6) any lapatinib- or nab-paclitaxel-related toxicity causing treatment delay of greater than 2 weeks.
Toxicity Assessment, Toxicity Management and Dose Modifications
Toxicity assessments were made on days 3, 10, and 17 of the first two cycles and monthly thereafter. Complete blood counts were evaluated with each nab-paclitaxel infusion. Radiologic and cardiac imaging was done every 8 weeks. For patients with grade 3 diarrhea or rash despite maximal supportive care, or a second recurrence of intolerable grade 2 diarrhea or rash despite maximal supportive care, the lapatinib dose was decreased to one level lower and nab-paclitaxel was held until symptoms improved to a grade 1 toxicity level. GCSF support was added in the first instance of grade ≥2 neutropenia. Dose reduction of nab-paclitaxel was incurred in the second instance of grade ≥2 neutropenia despite GCSF, and in the first instance of grade ≥2 neuropathy after resolution to grade 1. For all other non-hematologic grade ≥3 toxicities, treatment was held until improvement to grade 1 and then resumed at the same dose of nab-paclitaxel and one dose level lower of lapatinib.
Plasma Lapatinib Levels and Paclitaxel Pharmacokinetics
Blood samples for assessment of lapatinib plasma concentration were obtained at baseline, 4 hours after the first dose of lapatinib (approximate Tmax), and 48 hours after the first lapatinib dose (highest trough concentration for this regimen) prior to the nab-paclitaxel infusion. Samples were analyzed for lapatinib plasma concentration using a previously described method (27
) with a sensitivity of 1ng/mL and precision and accuracy within 15%.
After the maximum tolerated dose (MTD) was defined, 3 additional patients were enrolled at the MTD for paclitaxel pharmacokinetic studies. In these three patients, the administration of lapatinib was omitted from the first week of nab-paclitaxel, but was given prior to the second and all the subsequent weekly infusions. Blood samples were drawn before and at ½, 1, 2, 4, 7, and 24 hours after the beginning of the nab-paclitaxel infusion on day 3 and again on day 10 of the first cycle. An additional sample was also collected 24 hours after the 3rd infusion of nab-paclitaxel on day 18 of the first cycle.
Paclitaxel concentration was measured using a liquid chromatography/ tandem mass spectrometry system consisting of a 717 plus autosampler (Waters Corporation, Milford, MA) and Quattro Ultima (Micromass, Manchester, UK) detector with electospray positive ionization mode. The multiple reaction monitor was set at: 854.4 – 509.2 m/z for paclitaxel and 859.4 – 509.2 m/z for internal standard (paclitaxel-d5). The sample cone voltage and collision energy for paclitaxel and internal standard were set at 35 V and 15 eV, respectively. Chromatography was performed on BDS C18 column (50 × 4.6 mm, 5mm particle size, Thermo Electron Corporation, Bellefonte, PA). The mobile phase was CH3CN: H2O: CH3COOH, (50: 50: 0.15) (v/v) containing 4 mM NH4CH3COO. The flow rate was 1.0 ml/min with 25% of the flow liquid split into the mass system. The plasma sample (0.2 ml) was extracted with 1 ml of methyl tert-butyl ether. The organic layer was then transferred to another tube, evaporated by N2 gas, reconstituted with 0.15 ml of mobile phase, and 10 μl was injected onto the column. The standard curve was from 20-5000 ng/ml. The relative standard deviations for low, medium, and high concentration QC samples were less than 15%. Pharmacokinetic analyses were performed using WinNonlin software Version 4.1.
MR Perfusion Studies
Dynamic contrast enhanced MRI (DCE-MRI) scans of measureable non-pulmonary and non-CNS metastases were obtained within 2 weeks of starting lapatinib therapy and again on day 3 of cycle 1 immediately following the 2-day lapatinib pulse (defined as scans 1 and 2, respectively) in a subset of eligible patients. DCE-MRI scans were also obtained on days 15 (pre-lapatinib) and 17 (post-lapatinib) of the first cycle during the standard phase of the protocol (defined as scans 3 and 4).
All scans were obtained on a 1.5 T scanner (General Electric Healthcare, Milwaukee, WI). Initial unenhanced MR images were obtained to localize a non-pulmonary non-CNS metastasis at least 2 cm in craniocaudad diameter. A solid portion of the tumor was designated as the indicator lesion at the discretion of the study radiologist. For the dynamic contrast technique, a three-dimensional (3D) fast spoiled gradient-recalled (SPGR) echo sequence (256 × 128 matrix; eight 5-mm slices acquired every 11 seconds for 5.53 minutes; 22-36 cm axial field of view) was used to acquire T1-weighted images before, during, and following intravenous administration of 0.1 mmol/kg gadopentetate dimeglumine injected at 3 cc/sec and followed by a 10 cc saline flush at 3 cc/sec. For each scan, the dynamic contrast enhanced images were transferred to a desktop computer (Dell Dimension 4700, Round Rock, TX) for post-processing using a commercially available image analysis software program (MIStar, Apollo Medical Imaging, Melbourne, Australia). All MR perfusion studies were analyzed by a single radiologist. Signal-intensity time curves were generated by averaging all voxels in each region of interest at each time point. Because signal intensity varies nearly linearly with tracer concentration, using the pulse sequences and concentrations expected in this study, it was determined that conversion to tracer concentration via T1 mapping would increase rather than decrease measurement variability. These data were fit to the Tofts model to determine tumor vascular permeability (Ktrans) and the fractional plasma volume (Vp) for each tumor.
The Wilcoxon signed-rank test for matched paired data was used to compare the Ktrans and Vp values between pre- and post-lapatinib DCE-MRI studies.