Castration-resistant prostate cancer bone metastasis response measured by 18F-fluoride PET after treatment with dasatinib and correlation with progression-free survival: Results from American College of Radiology Imaging Network 6687

¹⁸F-fluoride PET quantitatively images bone metabolism and may serve as a pharmacodynamic assessment for systemic therapy such as dasatinib, a potent SRC kinase inhibitor, with activity in bone. Methods: This was an imaging companion trial (American College of Radiology Imaging Network [ACRIN] 6687) to a multicenter metastatic castration-resistant prostate cancer (CRPC) tissue biomarker-guided therapeutic trial (NCT00918385). Men with bone metastatic CRPC underwent ¹⁸F-fluoride PET before and 12 weeks after initiation of dasatinib (100 mg daily). Dynamic imaging was performed over a 15-cm field of view for trial assessments. The primary endpoint was to determine whether changes in ¹⁸F-fluoride incorporation in tumor and normal bone occurred in response to dasatinib. Other endpoints included differential effect of dasatinib between ¹⁸F-fluoride incorporation in tumor and normal bone, ¹⁸F-fluoride transport in bone metastases, correlation with progression-free survival (PFS), prostate-specific antigen, and markers of bone turnover. Results: Eighteen participants enrolled, and 17 underwent interpretable baseline ¹⁸F-fluoride PET imaging before initiation of dasatinib. Twelve of 17 patients underwent on-treatment PET imaging. Statistically significant changes in response to dasatinib were identified by the SUV_maxavg (average of maximum standardized uptake value [SUV_max] for up to 5 tumors within the dynamic field of view) in bone metastases (P = 0.0002), with a significant differential ¹⁸F-fluoride PET response between tumor and normal bone (P < 0.0001). Changes in ¹⁸F-fluoride incorporation in bone metastases had borderline correlation with PFS by SUV_maxavg (hazard ratio, 0.91; 95% confidence interval, 0.82-1.00; P = 0.056). Changes by SUV_maxavg correlated with bone alkaline phosphatase ( P = 0.0014) but not prostate-specific antigen (P = 0.47). Conclusion: This trial provides evidence of the ability ¹⁸F-fluoride PET to delineate treatment response of dasatinib in CRPC bone metastases with borderline correlation with PFS.