Measurement of tumor VEGF-A levels with 89Zr-bevacizumab PET as an early biomarker for the antiangiogenic effect of everolimus treatment in an ovarian cancer xenograft model.

PURPOSE: The mTOR pathway is frequently activated in ovarian cancers. mTOR inhibitors, such as everolimus, can reduce VEGF-A production by cancer cells. We investigated whether early everolimus treatment effects could be monitored by positron emission tomography (PET) with (89)Zr-bevacizumab.

EXPERIMENTAL DESIGN: The effect of everolimus on VEGF-A secretion was determined in a panel of human ovarian cancer cell lines and in A2780(luc+) ovarian cancer cells xenografted subcutaneously in BALB/c mice. Mice received daily 10 mg/kg everolimus intraperitoneally (i.p.) for 14 days. PET scans with the tracer (89)Zr-labeled bevacizumab were conducted before and after treatment. Ex vivo (89)Zr-bevacizumab biodistribution and correlative tissue analyses were conducted. Tumor VEGF-A levels were measured with ELISA and mean vascular density (MVD) was determined with immunohistochemistry.

RESULTS: Everolimus treatment reduced VEGF-A levels in the supernatant of all cell lines. Everolimus lowered (89)Zr-bevacizumab tumor uptake by 21.7% ± 4.0% [mean standardized uptake value (SUV(mean)) 2.3 ± 0.2 vs. 2.9 ± 0.2, P < 0.01]. Ex vivo biodistribution also showed lower tracer uptake in the tumors of treated as compared with control animals (7.8 ± 0.8%ID/g vs. 14.0 ± 1.7%ID/g, P < 0.01), whereas no differences were observed for other tissues. This coincided with lower VEGF-A protein levels in tumor lysates in treated versus untreated tumors (P = 0.04) and reduced MVD (P < 0.01).

CONCLUSION: Tumor VEGF-A levels are decreased by everolimus. (89)Zr-bevacizumab PET could be used to monitor tumor VEGF-A levels as an early biomarker of the antiangiogenic effect of mTOR inhibitor therapy.