Michael Amantea

Doxorubicin Encapsulated in Liposomes Containing Surface‐Bound Polyethylene Glycol: Pharmacokinetics, Tumor Localization, and Safety in Patients with AIDS‐Related Kaposi's Sarcoma

A study of the plasma pharmacokinetics, tumor localization, and safety of a single dose of doxorubicin encapsulated in liposomes containing surface‐bound polyethylene glycol (PEG‐liposomal doxorubicin) was conducted in patients with Kaposis sarcoma (KS) as a manifestation of acquired immune deficiency syndrome (AIDS). Eighteen patients with AIDS‐KS diagnosed by examination of biopsy specimens were randomly assigned to receive either standard doxorubicin or PEG‐liposomal doxorubicin. Consecutive participants were entered at three dose levels (10, 20, and 40 mg/m2) in ascending fashion. Clearance of PEG‐liposomal doxorubicin was 0.034 L/h/m2 to 0.108 L/h/m2, volume of distribution (Vd) was 2.2 L/m2 to 4.4 L/m2, and half‐lives (t1/2) of the initial decline in the plasma concentration—time curve and of the terminal decline were 3.77 hours and 41.3 hours, respectively. Seventy‐two hours after administration, doxorubicin levels observed in lesions of patients receiving PEG‐liposomal doxorubicin were 5.2 to 11.4 times greater than those found in patients given comparable doses of standard doxorubicin. PEG‐liposomal doxorubicin and standard doxorubicin were roughly equipotent in producing toxicity. Encapsulation in liposomes containing surface‐bound PEG significantly limits the distribution and elimination of doxorubicin, results in greater accumulation of the drug in KS lesions 72 hours after dosing than does standard doxorubicin, and may improve drug efficacy and therapeutic index in the treatment of AIDS‐KS.

Comparative pharmacokinetics, tissue distribution, and therapeutic effectiveness of cisplatin encapsulated in long-circulating, pegylated liposomes (SPI-077) in tumor-bearing mice

Purpose: The pharmacokinetics (PK), biodistribution and therapeutic efficacy of cisplatin encapsulated in long-circulating pegylated (Stealth®) liposomes (SPI-077) were compared with those of nonliposomal cisplatin in two murine (C26 colon carcinoma and Lewis lung) tumor models. Methods: In therapeutic effectiveness studies, mice bearing murine C26 or Lewis lung tumors received multiple intravenous doses of SPI-077 or cisplatin in a variety of treatment schedules and cumulative doses. In the PK and biodistribution study, mice received a single intravenous bolus injection of 3 mg/kg of either SPI-077 or cisplatin 14 days after inoculation with 106 C26 tumor cells. Plasma and tissues were analyzed for total platinum (Pt) content by graphite furnace (flameless) atomic absorption spectrophotometery (GF-AAS). Results: Efficacy studies showed that SPI-077 had superior antitumor activity compared to the same cumulative dose of cisplatin. When lower doses of SPI-077 were compared to cisplatin at its maximally tolerated dose in Lewis lung tumors, equivalent SPI-077 antitumor activity was seen at only half the cisplatin dose. Higher cumulative doses of SPI-077 were well tolerated and had increased antitumor effect. SPI-077 PK were characterized by a one-compartment model with nonlinear (saturable) elimination, whereas cisplatin PK were described by a two-compartment model with linear elimination. SPI-077 had a 55-fold higher volume of distribution, 3-fold higher peak plasma levels, and a 60-fold larger plasma AUC compared with cisplatin. In addition, SPI-077-treated animals displayed a 4-fold reduction in Pt delivered to the kidneys (primary target organ of toxicity) relative to cisplatin, but a 28-fold higher tumor AUC than cisplatin. Conclusions: Based on the results of our studies, encapsulation of cisplatin in long-circulating pegylated liposomes has overcome limitations experienced with other liposomal cisplatin formulations. SPI-077 has a prolonged circulation time and increased tumor Pt disposition, and its antitumor effect is significantly improved compared to cisplatin in murine colon and lung cancer models.

A Population Pharmacokinetic Meta-analysis of Sunitinib Malate (SU11248) and Its Primary Metabolite (SU12662) in Healthy Volunteers and Oncology Patients

Purpose: Sunitinib malate is an oral multitargeted tyrosine kinase inhibitor approved for advanced renal cell carcinoma and imatinib-resistant or imatinib-intolerant gastrointestinal stromal tumor. Following administration, sunitinib is metabolized by cytochrome P450 3A4 to an active metabolite (SU12662). The objective of this analysis was to assess sunitinib and SU12662 pharmacokinetics and to identify covariates that might explain variability in exposure following oral administration. Experimental Design: Data from 590 subjects (73 volunteers and 517 patients) in 14 studies were analyzed. Plasma concentration-time data were analyzed using nonlinear mixed-effects modeling to estimate population pharmacokinetic parameters, as well as relationships between these parameters and gender, race, age, weight, creatinine clearance, Eastern Cooperative Oncology Group score, and tumor type. Simulations were done to determine the predicted effect of these covariates on exposure. Results: Separate models were developed for sunitinib and SU12662 (each a two-compartment model with first-order absorption and elimination). Sunitinib parameters were estimated as CL/F, 51.8 L/h and Vd/Fcentral, 2,030 liters. SU12662 parameters were estimated as CL/F, 29.6 L/h and Vd/Fcentral, 3,080 liters. Tumor type (except acute myeloid leukemia), Asian race, gender, body weight, and elevated Eastern Cooperative Oncology Group score described a portion of the variability in CL/F for sunitinib and metabolite; gender and body weight explained some of the variability in Vd/Fcentral for sunitinib and metabolite. Among patients, the predicted changes in sunitinib and metabolite AUC and Cmax as a result of the individual covariates ranged up to 17%. Conclusion: The magnitude of the predicted changes in exposure with the covariates studied minimizes the necessity for dose adjustment in any of these subpopulations.

PKPD Modeling of VEGF, sVEGFR‐2, sVEGFR‐3, and sKIT as Predictors of Tumor Dynamics and Overall Survival Following Sunitinib Treatment in GIST

The predictive value of longitudinal biomarker data (vascular endothelial growth factor (VEGF), soluble VEGF receptor (sVEGFR)‐2, sVEGFR‐3, and soluble stem cell factor receptor (sKIT)) for tumor response and survival was assessed based on data from 303 patients with imatinib‐resistant gastrointestinal stromal tumors (GIST) receiving sunitinib and/or placebo treatment. The longitudinal tumor size data were well characterized by a tumor growth inhibition model, which included, as significant descriptors of tumor size change, the model‐predicted relative changes from baseline over time for sKIT (most significant) and sVEGFR‐3, in addition to sunitinib exposure. Survival time was best described by a parametric time‐to‐event model with baseline tumor size and relative change in sVEGFR‐3 over time as predictive factors. Based on the proposed modeling framework to link longitudinal biomarker data with overall survival using pharmacokinetic–pharmacodynamic models, sVEGFR‐3 demonstrated the greatest predictive potential for overall survival following sunitinib treatment in GIST.

PKPD Modeling of Predictors for Adverse Effects and Overall Survival in Sunitinib‐Treated Patients With GIST

A modeling framework relating exposure, biomarkers (vascular endothelial growth factor (VEGF), soluble vascular endothelial growth factor receptor (sVEGFR)‐2, ‐3, soluble stem cell factor receptor (sKIT)), and tumor growth to overall survival (OS) was extended to include adverse effects (myelosuppression, hypertension, fatigue, and hand–foot syndrome (HFS)). Longitudinal pharmacokinetic–pharmacodynamic models of sunitinib were developed based on data from 303 patients with gastrointestinal stromal tumor. Myelosuppression was characterized by a semiphysiological model and hypertension with an indirect response model. Proportional odds models with a first‐order Markov model described the incidence and severity of fatigue and HFS. Relative change in sVEGFR‐3 was the most effective predictor of the occurrence and severity of myelosuppression, fatigue, and HFS. Hypertension was correlated best with sunitinib exposure. Baseline tumor size, time courses of neutropenia, and relative increase of diastolic blood pressure were identified as predictors of OS. The framework has potential to be used for early monitoring of adverse effects and clinical response, thereby facilitating dose individualization to maximize OS.

Population Pharmacokinetic and Pharmacodynamic Analysis of Bosutinib

Bosutinib is an orally active, competitive inhibitor of Src/Abl tyrosine kinases. A population pharmacokinetic model was developed using data pooled from 3 studies of patients (n = 870) with solid tumors or Philadelphia chromosome-positive leukemia. Patients (aged 18-91 y, weighing 35-221 kg) who received bosutinib 50 to 600 mg orally with food each contributed 6-9 pharmacokinetic samples. The final pharmacokinetic model was a linear two-compartment model with first-order absorption, an absorption lag-time, and dose-dependent bioavailability. Oral absorption was relatively slow, with a half-time of 1.14 h and a lag-time of 0.87 h; time to peak concentration was 5-6 h. Apparent clearance was 120 L/h. The apparent volume of the peripheral compartment was large with a slow turnover; alpha and beta half-lives were 19 h and 290 days, respectively. All parameters were estimated with acceptable precision (standard error <30%). No tested covariate (protocol, baseline demographic/clinical characteristics, or laboratory results) explained the high inter-individual variability of bosutinib pharmacokinetics. Therefore, adjusting bosutinib dose for body size (weight, surface area) would not provide benefit over fixed dosing. Using this exposure model in pharmacodynamic assessment of one study, adverse event incidence was shown to be similar in overall and bosutinib-responsive populations.

Population pharmacokinetic analysis of axitinib in healthy volunteers

AIMS Axitinib is a potent and selective second generation inhibitor of vascular endothelial growth factor receptors 1, 2 and 3 approved for second line treatment of advanced renal cell carcinoma. The objectives of this analysis were to assess plasma pharmacokinetics and identify covariates that may explain variability in axitinib disposition following single dose administration in healthy volunteers. METHODS Plasma concentration-time data from 337 healthy volunteers in 10 phase I studies were analyzed, using non-linear mixed effects modelling (nonmem) to estimate population pharmacokinetic parameters and evaluate relationships between parameters and food, formulation, demographic factors, measures of renal and hepatic function and metabolic genotypes (UGT1A1*28 and CYP2C19). RESULTS A two compartment structural model with first order absorption and lag time best described axitinib pharmacokinetics. Population estimates for systemic clearance (CL), central volume of distribution (Vc ), absorption rate constant (ka ) and absolute bioavailability (F) were 17.0 l h(-1) , 45.3 l, 0.523 h(-1) and 46.5%, respectively. With axitinib Form IV, ka and F increased in the fasted state by 207% and 33.8%, respectively. For Form XLI (marketed formulation), F was 15% lower compared with Form IV. CL was not significantly influenced by any of the covariates studied. Body weight significantly affected Vc , but the effect was within the estimated interindividual variability for Vc . CONCLUSIONS The analysis established a model that adequately characterizes axitinib pharmacokinetics in healthy volunteers. Vc was found to increase with body weight. However, no change in plasma exposures is expected with change in body weight; hence no dose adjustment is warranted.

PK-PD modeling of individual lesion FDG-PET response to predict overall survival in patients with sunitinib-treated gastrointestinal stromal tumor

Pharmacometric models were developed to characterize the relationships between lesion‐level tumor metabolic activity, as assessed by the maximum standardized uptake value (SUVmax) obtained on [18F]‐fluorodeoxyglucose (FDG) positron emission tomography (PET), tumor size, and overall survival (OS) in 66 patients with gastrointestinal stromal tumor (GIST) treated with intermittent sunitinib. An indirect response model in which sunitinib stimulates tumor loss best described the typically rapid decrease in SUVmax during on‐treatment periods and the recovery during off‐treatment periods. Substantial interindividual and interlesion variability were identified in SUVmax baseline and drug sensitivity. A parametric time‐to‐event model identified the relative change in SUVmax at one week for the lesion with the most pronounced response as a better predictor of OS than tumor size. Based on the proposed modeling framework, early changes in FDG‐PET response may serve as predictor for long‐term outcome in sunitinib‐treated GIST.

Clinical Implications of the Pharmacokinetics of Crizotinib in Populations of Patients with Non-Small Cell Lung Cancer

Purpose: We assessed the effect of baseline patient demographic and disease characteristics on the crizotinib pharmacokinetic parameters oral clearance (CL/F), volume of distribution (V2/F), and area under the curve at steady state (AUCss) following multiple crizotinib 250-mg twice-daily dosing in patients with ALK-positive cancer. Experimental Design: A pharmacokinetic model was fit to data from 1,214 patients. We identified statistically significant covariates (P ≤ 0.001) by evaluating their effects on CL/F and V2/F and estimated their magnitudes. Results: Age, Eastern Cooperative Oncology Group performance status, aspartate aminotransferase (AST) levels, albumin levels, and smoking status had no effect on CL/F or V2/F. Statistically significant covariates were Asian race and female sex for CL/F and V2/F and body weight, creatinine clearance (CLcr), and total bilirubin for CL/F only. The model predicted that CL/F would be 9% lower or higher in a 40-kg or a 100-kg patient, respectively; 16% lower in patients with CLcr 30 mL/minute; 23% lower in Asians; and 11% lower in females than the reference patient (65-kg non-Asian male; baseline CLcr, 91.6 mL/minute; total bilirubin, 0.41 mg/dL). The effect of total bilirubin on CL/F was small. V2/F was 23% lower in Asians than non-Asians and females than males. Effects of all significant covariates on AUCss were not predicted to be clinically relevant. Conclusions: Crizotinib at a 250-mg twice-daily starting dose appears to be appropriate for all patients irrespective of age, sex, race, body weight, mild or moderate renal impairment, or hepatic function (in the range evaluated: bilirubin ≤ 2.1 mg/dL or AST ≤124 U/L). Clin Cancer Res; 22(23); 5722–8. ©2016 AACR.

A Pharmacometric Framework for Axitinib Exposure, Efficacy, and Safety in Metastatic Renal Cell Carcinoma Patients

The relationships between exposure, biomarkers (vascular endothelial growth factor (VEGF), soluble VEGF receptors (sVEGFR)‐1, ‐2, ‐3, and soluble stem cell factor receptor (sKIT)), tumor sum of longest diameters (SLD), diastolic blood pressure (dBP), and overall survival (OS) were investigated in a modeling framework. The dataset included 64 metastatic renal cell carcinoma patients (mRCC) treated with oral axitinib. Biomarker timecourses were described by indirect response (IDR) models where axitinib inhibits sVEGFR‐1, ‐2, and ‐3 production, and VEGF degradation. No effect was identified on sKIT. A tumor model using sVEGFR‐3 dynamics as driver predicted SLD data well. An IDR model, with axitinib exposure stimulating the response, characterized dBP increase. In a time‐to‐event model the SLD timecourse predicted OS better than exposure, biomarker‐ or dBP‐related metrics. This type of framework can be used to relate pharmacokinetics, efficacy, and safety to long‐term clinical outcome in mRCC patients treated with VEGFR inhibitors. (ClinicalTrial.gov identifier NCT00569946.)