Use of Individual Pharmacokinetically (PK)-Guided Sunitinib Dosing: A Feasibility Study in Patients With Advanced Solid Tumors

The purpose of this prospective study is to determine the safety and feasibility of pharmacokinetically (PK) guided dosing of sunitinib in 30 patients. At day 15 ± 1day, day 29 ± 1day and after 8 weeks ± 1day of sunitinib treatment sunitinib and SU12662 trough levels will be measured. Depending on the sunitinib and SU12662 trough levels (and toxicity) dose adjustments will be made.

Sunitinib is an orally available inhibitor of vascular endothelial growth factor (VEGFR), platelet-derived growth factor (PDGF), cytokine receptor (c-KIT), and receptor tyrosine kinase (FLT-3) activity. Sunitinib is proven effective as single agent in several solid tumor types and is approved for use in advanced renal cell cancer (RCC) and imatinib-resistant or -intolerant gastrointestinal stromal tumors (GISTs). However, in a large percentage of patients (30 and 50%), dose reductions are required because of multiple grade 2 toxicities or due to grade 3 or 4 toxicities. Therefore, the currently used dosing schedule is not optimal. Recently, a dose-efficacy relation was established for sunitinib treatment. This large meta-analysis of pharmacokinetic/pharmacodynamic data from studies performed in mRCC patients, GIST patients and patients with solid tumors, clearly showed a relationship between sunitinib exposure and efficacy and tolerability. Both time to progression (TTP) and overall survival (OS) were significantly better for mRCC patients with high area under the curve (AUC) compared to low AUC. This was not only observed for sunitinib exposure but also for its active metabolite SU12662. In addition, there was a significant relationship between exposure and probability of partial response (PR) or complete response (CR) in mRCC patients (p=0.00001), indicating that a dose intensity in patients should be as high as possible. Target plasma concentrations of sunitinib plus metabolite (N-desethyl sunitinib) are in the range of 50 to 100 ng/mL, as deduced from pharmacokinetic (PK) / pharmacodynamic (PD) preclinical data. Since the dose-efficacy relation for sunitinib treatment is solely established in a retrospective (meta-) analysis from patients treated in several studies, we propose to perform a prospective feasibility study in 30 patients with PK guided dosing of sunitinib. If PK guided once-daily continuous sunitinib dosing is feasible, a RCT in mRCC patients will be performed comparing PK guided dosing with a standard sunitinib dosing schedule.