TKI258 (dovitinib lactate) in metastatic renal cell carcinoma (mRCC) patients refractory to approved targeted therapies: A phase I/II dose finding and biomarker study

Abstract

3563 Background: TKI258 is a potent receptor tyrosine kinase inhibitor (TKI) that selectively targets VEGFR, PDGFR, FGFR, CSF1R, c-KIT, RET, TrKA, and FLT3. Compared to other TKI agents, TKI258 additionally targets FGFR. FGF has been reported as an important escape mechanism of anti-VEGFR therapies. Methods: The primary objective of this phase I was to determine the maximum tolerated dose (MTD) of TKI258, administered orally on a 5 days on / 2 days off schedule in repeated 28 day cycles, in mRCC pts refractory to standard therapies. A two-parameter Bayesian logistic regression model and safety data for at least 21 pts will be used to determine MTD. Results: A phase I study is ongoing. As of December 2008, 11 pts (9 m, 2 f), median age: 55 (29–66 yrs) have been enrolled. Four pts have been treated at 500 mg/day (start dose): 2 are ongoing at cycle (C) 7; 1 pt discontinued due to PD and 1 due to sinus bradycardia. Five pts received 600 mg/day: 2 DLTs (G4 hypertension and G3 fatigue - pts discontinued) leading to dose reduction of all patients to 500mg/day; 2 pts in C5 and C4, 1 pt discontinued for PD. Two pts just entered the extension cohort at 500 mg. Other toxicities ≥G2 included fatigue, nausea, vomiting, diarrhea, neutropenia, folliculitis and dizziness. PK data showed CMax range (180–487 ng/mL, n = 8), and AUC range (2200–8251 ng/mL*h). Preliminary biomarker data indicated pts had high baseline VEGF (506 ± 203 pg/ml, n=6) and bFGF (220 ± 185 pg/ml, n = 6) levels, which may reflect failure of previous anti-VEGF agents. Induction of plasma FGF23 levels, a pharmacodynamic biomarker of FGFR1 inhibition, was observed in pts from the first 500 mg/day dosing cohort. Preliminary evidence of efficacy is observed with one minor response (-17% at C4), 4 stable disease and 1 dramatic shrinkage/necrosis of some target lesions (lymph node & suprarenal mass). Conclusions: TKI258 500mg/day seems a feasible schedule in heavily pre-treated mRCC patients with some indications of clinical benefit. These preliminary findings will be confirmed in the extension cohort. [Table: see text]