Pharmacodynamic study using FLT PET/CT in advanced solid malignancies treated with a sequential combination of X-82 and docetaxel

Background A sequential approach, synchronizing cell-cycle specific chemotherapy during VEGFR-TKI treatment breaks, may improve the therapeutic index of this combination therapy. In this study we investigate the safety/tolerability and pharmacodynamic effects of docetaxel used in sequential combination with the novel VEGFR-TKI X-82. Methods Patients with advanced solid malignancies underwent 21-day treatment cycles with X-82 administered daily on days 1–14, a treatment break on days 15–20, and docetaxel administered on day 21. Randomization was 1:1 to either a low-dose X-82 (200 mg) or high-dose X-82 (400 mg) arm. Patients were scheduled to undergo four 3′-deoxy-3′- 18 F-fluorothymidine (FLT) PET/CT scans to assess changes in tumor cell proliferation. PET standardized uptake values (SUV) were summarized for tumors and changes were assessed using mixed effects models. Results 14 patients were enrolled and treated with median 3.5 cycles (range 0–12). Three patients in the high-dose cohort (50%) and three patients in the low-dose cohort (38%) experienced at least one grade 3 adverse event during the study (infections, cytopenias, electrolyte abnormalities, and vascular complications). Four patients with 13 metastatic tumors underwent FLT PET/CT scanning. During the cycle 1 X-82 exposure period, tumor SUV max decreased by − 11% ( p = 0.04). After administration of docetaxel and the cycle 2 X-82 exposure period, tumor SUV max decreased − 44% ( p = 0.03). Conclusions The sequential combination of X-82 and docetaxel was safe and led to diminished FLT uptake. Further, decrease in FLT uptake during cycle 2 (X-82 plus docetaxel) was greater than in cycle 1 (X-82 alone), suggesting sequential chemotherapy enhances the pharmacodynamic effect of therapy.