Overhauser Enhanced Magnetic Resonance Imaging (OMRI)

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a) Serial imaging of tumor pO2 and metabolic profile in tumor bearing mice exposed to radiotherapy: The tumor microenvironment is characterized its unique physiology and metabolic profile which is characterized by hypoxia (low pO2) and acidotic (low pH) as a result of poor perfusion and aerobic glycolysis. These features provide imaging biomarkers such as tumor pO2 and glycolysis (pyruvate to lactate flux) which can be monitored to assess treatment response. Two tumor models were chosen for this study: SCCVII tumor implanted in C3H mice and HT29 tumor in nude mice. We first demonstrated using phantom objects, the capability to sequentially image pO2 and glycolysis and co-registering these two maps with anatomic images. After this, we chose two different tumor models based on their differing tumor microenvironment and imaged sequentially the pO2 maps and the conversion of the injeccted pyruvate being converted to lactate through glycolysis and co-registered with anatomic images. Tis enabled examining the dependence of tumor glycolysis on tumor pO2. Of the two tumors studied, SCCVII tumor was more glycolytic compared to HT29 tumors, consistent with the more hypoxic nature of the former. Further there was a spatial match between hypoxia and elevated glycolysis in SCCVII tumor. Upon irradiation (5 Gy) fractional hypoxia increased in these tumors. This was supported by measuring the extracellular acidification rates measured in tumors excised and studied in vitro my monitoring the lactate production. These studies suggest that the two imaging biomarkers can become useful in planning radiation therapy where the dose can be planned based on the spatial features of tumor pO2 status. b) Novel 13C labeled tracers for hyperpolarized MRI: The following features are necessary in a 13C labeled tracer to be implemented in in vivo applications: i) The molecule should be non-toxic at the levels administered for in vivo metabolic imaging; ii) it should have a carbon site which has a long T1; iii) It should participate in metabolic reactions or reactions of interest such as scavenging reactive oxygen species and form products which are specific to the reactions being monitored. Along these lines, we have narrowed on a list of candidate molecules, tested their ability to be polarized, and tested them in vivo. The following molecules have been tested successfully and currently synthetic efforts to scale up synthesis to have adequate quantities for the planned experiments is underway. The following tracers have been synthesized for their ability to participate in the Kreb's cycle: diethyl succinate; monoethyl succinate, a-ketoglutarate. The molecule dimethyl pyrroline N-oxide is a candidate we have successfully synthesized and tested in vivo for use as a reporter of in vivo reactive oxygen species indicator.