The response of RIF-1 fibrosarcomas to the vascular-disrupting agent ZD6126 assessed by in vivo and ex vivo 1H magnetic resonance spectroscopy

Abstract

The response of radiation-induced fibrosarcoma 1 (RIF-1) tumors treated with the vascular-disrupting agent (VDA) ZD6126 was assessed by in vivo and ex vivo 1H magnetic resonance spectroscopy (MRS) methods. Tumors treated with 200 mg/kg ZD6126 showed a significant reduction in total choline (tCho) in vivo 24 hours after treatment, whereas control tumors showed a significant increase in tCho. This response was investigated further within both ex vivo unprocessed tumor tissues and tumor tissue metabolite extracts. Ex vivo high-resolution magic angle spinning (HRMAS) and 1H MRS of metabolite extracts revealed a significant reduction in phosphocholine and glycerophosphocholine in biopsies of ZD6126-treated tumors, confirming in vivo tCho response. ZD6126-induced reduction in choline compounds is consistent with a reduction in cell membrane turnover associated with necrosis and cell death following disruption of the tumor vasculature. In vivo tumor tissue water diffusion and lactate measurements showed no significant changes in response to ZD6126. Spin-spin relaxation times (T2) of water and metabolites also remained unchanged. Noninvasive 1H MRS measurement of tCho in vivo provides a potential biomarker of tumor response to VDAs in RIF-1 tumors.

Figure 1

In vivo PRESS-localized ¹H MRS spectra (T_E = 136 milliseconds) acquired from one RIF-1 tumor (a) before and (b) 24 hours posttreatment with 200 mg/kg ZD6126.

Figure 2

Line series of tCho concentration (mM) determined by in vivo ¹H MRS for each RIF-1 tumor (a) before and 24 hours after saline, and (b) before and 24 hours after 200 mg/kg ZD6126, i.p.

Figure 3

tCho concentration plotted as a function of tumor volume for each individual RIF-1 tumor investigated by in vivo ¹H MRS.

Figure 4

tCho concentrations (mM) determined by in vivo ¹H MRS of unprocessed tissues, by HRMAS ¹H MRS of extracts, and by HR ¹H MRS of tissue extracts of RIF-1 tumors 24 hours after treatment with saline or 200 mg/kg ZD6126. tCho determined in vivo and by HRMAS was significantly reduced (**P < .02).

Figure 5

tCho/tCr ratios of RIF-1 tumors determined by in vivo ¹H MRS, HRMAS ¹H MRS, and high-resolution ¹H MRS of tissue extracts 24 hours after treatment with either saline or 200 mg/kg ZD6126.