In Vivo Assessment of Ovarian Tumor Response to Tyrosine Kinase Inhibitor Pazopanib by Using Hyperpolarized 13C-Pyruvate MR Spectroscopy and 18F-FDG PET/CT Imaging in a Mouse Model.

Purpose To assess in a mouse model whether early or late components of glucose metabolism, exemplified by fluorine 18 (18F) fluorodeoxyglucose (FDG) positron emission tomography (PET) and hyperpolarized carbon 13 (13C)-pyruvate magnetic resonance (MR) spectroscopy, can serve as indicators of response in ovarian cancer to multityrosine kinase inhibitor pazopanib. Materials and Methods In this Animal Care and Use Committee approved study, 17 days after the injection of 2 × 106 human ovarian SKOV3 tumors cells into 14 female nude mice, treatment with vehicle or pazopanib (2.5 mg per mouse peroral every other day) was initiated. Longitudinal T2-weighted MR imaging, dynamic MR spectroscopy of hyperpolarized pyruvate, and 18F-FDG PET/computed tomographic (CT) imaging were performed before treatment, 2 days after treatment, and 2 weeks after treatment. Results Pazopanib inhibited ovarian tumor growth compared with control (0.054 g ± 0.041 vs 0.223 g ± 0.112, respectively; six mice were treated with pazopanib and seven were control mice; P < .05). Significantly higher pyruvate-to-lactate conversion (lactate/pyruvate + lactate ratio) was found 2 days after treatment with pazopanib than before treatment (0.46 ± 0.07 vs 0.31 ± 0.14, respectively; P < .05; six tumors after treatment, seven tumors before treatment). This was not observed with the control group or with 18F-FDG PET/CT imaging. Conclusion The findings suggest that hyperpolarized 13C-pyruvate MR spectroscopy may serve as an early indicator of response to tyrosine kinase (angiogenesis) inhibitors such as pazopanib in ovarian cancer even when 18F-FDG PET/CT does not indicate a response. © RSNA, 2017 Online supplemental material is available for this article.

Tumor T1 Relaxation Time for Assessing Response to Bevacizumab Anti-Angiogenic Therapy in a Mouse Ovarian Cancer Model.

PURPOSE: To assess whether T1 relaxation time of tumors may be used to assess response to bevacizumab anti-angiogenic therapy. PROCEDURES: 12 female nude mice bearing subcutaneous SKOV3ip1-LC ovarian tumors were administered bevacizumab (6.25ug/g, n=6) or PBS (control, n=6) therapy twice a week for two weeks. T1 maps of tumors were generated before, two days, and 2 weeks after initiating therapy. Tumor weight was assessed by MR and at necropsy. Histology for microvessel density, proliferation, and apoptosis was performed. RESULTS: Bevacizumab treatment resulted in tumor growth inhibition (p<0.04, n=6), confirming therapeutic efficacy. Tumor T1 relaxation times increased in bevacizumab treated mice 2 days and 2 weeks after initiating therapy (p<.05, n=6). Microvessel density decreased 59% and cell proliferation (Ki67+) decreased 50% in the bevacizumab treatment group (p<.001, n=6), but not apoptosis. CONCLUSIONS: Findings suggest that increased tumor T1 relaxation time is associated with response to bevacizumab therapy in ovarian cancer model and might serve as an early indicator of response.