Purpose: To investigate the feasibility of adaptive dosing and the impact of pharmacogenetic variation on 13-cisRA disposition in high-risk neuroblastoma patients.
Experimental Design: 13cisRA (160mg/m2 or 5.33mg/kg/day) was administered to 103 patients ≤21 years and plasma concentrations of 13-cisRA and 4-oxo-13-cisRA quantitated on day 14 of treatment. 71 patients were recruited to a dose adjustment group, targeting a 13-cisRA Cmax of 2μM, with dose increases of 25-50% implemented for patients with Cmax values <2μM. A population pharmacokinetic model was applied and polymorphisms in relevant cytochrome P450 genes analyzed.
Results: 13-cisRA Cmax values ranged from 0.42–11.2μM, with 34⁄103 (33%) patients failing to achieve a Cmax >2μM. Dose increases carried out in 20 patients in the dose adjustment study group led to concentrations >2μM in 18 patients (90%). 8⁄11 (73%) patients <12kg, receiving a dose of 5.33mg/kg, failed to achieve a Cmax ≥2μM. Significantly lower Cmax values were observed for patients treated with 5.33mg/kg versus 160mg/m2 (1.9±1.2 versus 3.1±2.0μM; mean±SD; P=0.023). Cmax was higher in patients who swallowed 13-cisRA capsules as compared to receiving the drug extracted from capsules (4.0±2.2 versus 2.6±1.8μM; P=0.0012). The target Cmax was achieved by 93% (25⁄27) versus 55% (42⁄76) of patients in these two groups respectively. No clear relationships were found between genetic variants and 13-cisRA pharmacokinetic parameters.
Conclusions: Dosing regimen and method of administration have a marked influence on 13-cisRA plasma concentrations. Body weight-based dosing should not be implemented for children <12kg and pharmacological data support higher doses for children unable to swallow 13-cisRA capsules.