PDTB-05. DEVELOPING A NONINVASIVE IMAGING MARKER FOR ASSESSING THE RESPONSE OF DIFFUSE INTRINSIC PONTINE GLIOMA TO PANOBINOSTAT USING HYPERPOLARIZED CARBON-13 MR METABOLIC IMAGING

One of the challenges in managing children with diffuse intrinsic pontine glioma (DIPG) is the lack of non-invasive imaging biomarkers for monitoring response to therapy. This study aimed to develop noninvasive imaging markers for assessing the response of DIPG to histone deacetylase inhibitor, panobinostat, which has shown potent anti-tumor effect in a recent study (Grasso et al, Nat Med. 2015). We hypothesized that the down-regulation of HIF1α with panobinostat treatment and the consequent decrease in LDHA activity in DIPG can be monitored by evaluating pyruvate to lactate conversion using HP 13C metabolic imaging in responding DIPG. Vehicle- (n=3) and panobinostat-treated (4nM for 72hr, n=2) K27M.H3 mutant DIPG cells were imaged in a perfusion bioreactor system. Following an injection of [1-13C]-pyruvate that was pre-polarized using a HyperSense (Ardenkjaer-Larsen et al, PNAS. 2003), 13C spectra were acquired every 3s for a total of 5min in a 500 MHz spectrometer using a 30° flip angle. Lactate levels were estimated by normalizing the lactate area-under-the-curve (AUC) to the pyruvate AUC and the level of cell viability that was assessed by estimating β-NTP from 31P spectra. The levels of HIF1α and LDHA activity in vehicle- and panobinostat-treated DIPG cells were assessed by Western blotting and spectrophotometric assay, respectively. HP 13C pyruvate to lactate conversion was reduced in the treated cells compared to control. Normalized lactate for treated group (1.22 ± 0.44) was smaller than normalized lactate for control (4.02 ± 0.93, p=0.03). The reduced lactate signal observed in the treated cells was associated with decreased levels of HIF1α and LDHA activity compared to control. The results from this study suggest that the modulation in pyruvate metabolism induced by panobinostat treatment can be monitored by HP 13C imaging and this novel metabolic imaging method may provide a non-invasive biomarker of response to panobinostat in DIPG.