Nuclear spin hyperpolarization can dramatically increase the sensitivity of the (13)C magnetic resonance experiment, allowing dynamic measurements of the metabolism of hyperpolarized (13)C-labeled substrates in vivo. Here, we report a preclinical study of the response of lymphoma tumors to the vascular disrupting agent (VDA), combretastatin-A4-phosphate (CA4P), as detected by measuring changes in tumor metabolism of hyperpolarized [1-(13)C]pyruvate and [1,4-(13)C(2)]fumarate. These measurements were compared with dynamic contrast agent-enhanced magnetic resonance imaging (DCE-MRI) measurements of tumor vascular function and diffusion-weighted MRI (DW-MRI) measurements of the tumor cell necrosis that resulted from subsequent loss of tumor perfusion. The rate constant describing flux of hyperpolarized (13)C label between [1-(13)C]pyruvate and lactate was decreased by 34% within 6 hours of CA4P treatment and remained at this lower level at 24 hours. The rate constant describing production of labeled malate from hyperpolarized [1,4-(13)C(2)]fumarate increased 1.6-fold and 2.5-fold at 6 and 24 hours after treatment, respectively, and correlated with the degree of necrosis detected in histologic sections. Although DCE-MRI measurements showed a substantial reduction in perfusion at 6 hours after treatment, which had recovered by 24 hours, DW-MRI showed no change in the apparent diffusion coefficient of tumor water at 6 hours after treatment, although there was a 32% increase at 24 hours (P <0.02) when regions of extensive necrosis were observed by histology. Measurements of hyperpolarized [1-(13)C]pyruvate and [1,4-(13)C(2)]fumarate metabolism may provide, therefore, a more sustained and sensitive indicator of response to a VDA than DCE-MRI or DW-MRI, respectively.
Bibliographical note©2010 AACR.
- angiogenesis inhibitors
- carbon isotopes
- contrast media
- diffusion magnetic resonance imaging
- injections, intravenous
- magnetic resonance spectroscopy
- neovascularization, pathologic
- pyruvic acid
- time factors