Magnetic Resonance Spectroscopy for Detection of Choline Kinase Inhibition in the Treatment of Brain Tumors

Abstract

Abnormal choline metabolism is a hallmark of cancer and is associated with oncogenesis and tumor progression. Increased choline is consistently observed in both pre-clinical tumor models and in human brain tumors by proton magnetic resonance spectroscopy (MRS). Thus, inhibition of choline metabolism using specific choline kinase inhibitors such as MN58b may be a promising new strategy for treatment of brain tumors. We demonstrate the efficacy of MN58b in suppressing phosphocholine production in three brain tumor cell lines. In vivo MRS studies of rats with intra-cranial F98-derived brain tumors showed a significant decrease in tumor total choline concentration after treatment with MN58b. High resolution MRS of tissue extracts confirmed that this decrease was due to a significant reduction in phosphocholine. Concomitantly, a significant increase in poly-unsaturated lipid resonances was also observed in treated tumors, indicating apoptotic cell death. Magnetic resonance imaging (MRI) based volume measurements demonstrated a significant growth arrest in the MN58b-treated tumors in comparison to saline-treated controls. Histologically, MN58b-treated tumors showed decreased cell density, as well as increased apoptotic cells. These results suggest that inhibition of choline kinase can be used as an adjuvant to chemotherapy in the treatment of brain tumors and that decreases in total choline observed by MRS can be used as an effective phamacodynamic biomarker of treatment response.

Near infrared fluorescent imaging of choline kinase alpha expression and inhibition in breast tumors

“…An optimized bis-pyridinium ChoKα inhibitor was recently shown effective at 10 mg/kg daily for 3 days, and body weight measurements indicated no adverse toxicities [50]. Both JAS239 and MN58b were capable of significantly reducing intratumoral tCho and increasing PUFA resonances associated with apoptosis [23, 45]. However, JAS239 was more effective at reducing tumor tCho, decreasing the levels down to baseline noise.…”

“…After 1 h, cells were spiked for 1 h with 0.5 μCi/mL [methyl- 14 C]-choline (PerkinElmer) and fixed with trichloroacetic acid. Aqueous cellular extracts were separated by thin layer chromatography (TLC) and the 14 C-PC production measured by autoradiography on a Fujifilm FLA-7000 using previously described methods [4, 23]. …”

“…MN58b, a bis -cationic ChoKα inhibitor, has been demonstrated to be lethal to lymphoma cells, but causes a reversible cell cycle arrest in normal cells [17]. Although the mechanism by which ChoKα inhibition causes cell death may involve scaffolding in addition to enzymatic functions [21], measurement of total choline-containing metabolite (tCho) levels by MRS is still the primary method of validating ChoK inhibitors in vivo [22, 23]. A limitation of this approach is that metabolite levels are also affected by the contributions of phospholipases, organic cation transporters, and sphingomyelinases [3, 24, 25].…”

Choline kinase alpha—Putting the ChoK-hold on tumor metabolism

“…7a–c). In vivo tCho measurement by MRS was recently shown to be feasible for validation of the ChoKα inhibitor MN58b in rat models of glioma [113]. …”

“…The most promising of these compounds, MN58b (Fig. 5), is effective against a variety of cancer cell lines, significantly retards xenograft growth [112,113], and most importantly, is more specific for ChoKα than HC-3 [114]. Improved activity was found when the 4,4′-biphenyl linker of HC-3 was replaced by a 1,2-ethylene(bisbenzyl) fragment [115].…”