s From the 48th Congress of the International Society of Paediatric Oncology (SIOP) Dublin, Ireland October 19–22, 2016

BACKGROUND: Glutathione S-transferase (GST) enzymes are involved in detoxifying chemotherapy agents and clearing reactive oxygen species formed by radiation. In this study, we explored the relationship between the host GSTP1-105 polymorphism (rs1695), tumor GSTpi protein expression, and clinical outcomes in pediatric medulloblastoma. We hypothesized that the GSTP1-105 G-allele and increased tumor GSTpi expression would be associated with lower progression-free survival and fewer adverse events. METHODS: The study included 106 medulloblastoma/primitive neuroectodermal tumor (PNET) patients seen at Texas Children’s Cancer Center. Genotyping was performed using an Illumina HumanOmni1-Quad BeadChip and tumor GSTpi expression was assessed using immunohistochemistry. We used the Kaplan-Meier method for survival analyses and multivariable logistic regression for toxicity comparisons. RESULTS: Patients with a GSTP1-105 AG/GG genotype or who had received a higher dose of craniospinal radiation (median 36 Gy) had a greater risk of requiring hearing aids than their respective counterparts (OR 4.0, 95%CI 1.2 - 13.6, and OR 3.1, 95%CI 1.1 - 8.8, respectively). Additionally, there was a statistically significant interaction between the two variables. Compared with the lowest risk group (GSTP1-105 AA-lower dose radiation) patients with a GSTP1-105 AG/GG genotype who received a higher dose radiation were 8.4 times more likely to require hearing aids (95%CI 1.4 - 49.9, p-trend ¼ 0.005). When adjusted for age, gender, and amifostine use, the association remained. CONCLUSIONS: The GSTP1-105 G-allele is associated with permanent ototoxicity in pediatric medulloblastoma/PNET and strongly interacts with radiation dose. A possible mechanism for this finding is that the GSTP1-105 G-allele leads to reduced GSTpi free radical detoxification in the setting of multimodality therapy including cisplatin and radiation. Patients with this allele should be considered for clinical trials employing radiation dose modifications and more targeted cytoprotectant strategies than are currently being used with amifostine.

INTRODUCTION: Substituted indoles and related structures have been shown to exhibit potent anticancer activity against breast cancer cell lines. Here, the effects of structurally similar substituted indoles against the human glial cancer cell lines, 1321N1 and U87MG, have been investigated by comparing the effects of these compounds to conventional anti cancer drugs. METHODS: Cell viability in the presence of the test compounds was measured using an MTS assay and corroborated by an ATP cell proliferation assay as well as a Trypan blue exclusion test. The significance of reactive oxygen species (ROS) in the process was determined using an Image-iT® LIVE ROS kit from Invitrogen. RESULTS: Both cell lines were treated with four commercial anticancer drugs and IC50 values were only reached at concentrations of 20 µM for cisplatin and 50 µM for gemcitabine over 48hrs on the 1321N1 cell line. However, the more malignant U87MG cell line was resistant to all the drugs, except for cisplatin where the IC50 value was reached at 300 µM after treatment for 48hrs. Similar studies were carried out with various substituted indoles and the cytotoxicity results on both cell lines showed that the IC50 value was reached within 90 minutes for the most potent compound at a concentration of 600 µM (1321N1) and 800 µM (U87MG). The idea that the mechanism of action of these compounds may work through the generation of ROS was investigated and this was confirmed over a similar time course using a suitable fluorogenic marker. Moreover, it was shown that the addition of an antioxidant (ascorbic acid) abolished the potency of the most active compound. CONCLUSION: Here, it has been demonstrated that certain substituted indoles are able to have a rapid, deleterious effect on the viability of two glioma cell lines and indicated that ROS generation may induce cell death.