Monitoring Mammary Tumor Progression and Effect of Tamoxifen Treatment in MMTV-PymT Using MRI and Magnetic Resonance Spectroscopy with Hyperpolarized [1-13C] pyruvate

PurposeTo use dynamic magnetic resonance spectroscopy (MRS) of hyperpolarized C-13-pyruvate to follow the progress over time in vivo of breast cancer metabolism in the MMTV-PymT model, and to follow the response to the anti-estrogen drug tamoxifen. MethodsTumor growth was monitored by anatomical MRI by measuring tumor volumes. Dynamic MRS of hyperpolarized C-13 was used to measure an apparent pyruvate-to-lactate rate constant (k(p)) of lactate dehydrogenase (LDH) in vivo. Further, ex vivo pathology and in vitro LDH initial reaction velocity were evaluated. ResultsTamoxifen significantly halted the tumor growth measured as tumor volume by MRI. In the untreated animals, k(p) correlated with tumor growth. The k(P) was somewhat but not significantly lower in the treated group. Studies in vitro confirmed the effects of tamoxifen on tumor growth, and here the LDH reaction velocity was reduced significantly in the treated group. ConclusionThese hyperpolarized C-13 MRS findings indicate that tumor metabolic changes affects k(P). The measured k(p) did not relate to treatment response to the same extent as did tumor growth, histological evaluation, and in vitro determination of LDH activity. Magn Reson Med 73:51-58, 2015. (c) 2014 Wiley Periodicals, Inc.