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.
Transplanted bone marrow donor cells with tissue specific phenotypes have been found in the brain, liver, heart, skin, lung, kidney, and gut of transplanted humans and mice. Such observations have led to the controversial hypothesis that hematopoietic stem cells (HSC) might be intrinsically plastic, and through transdifferentiation or fusion lead to the repair of damaged tissues throughout the body. Alternately, it is suggested that fusion of macrophages to the recipient cells may explain this phenomenon. We have shown recently that purified HSC are the cells responsible for GFP positive donor-derived muscle fibers in the recipient mice post bone marrow transplantation. However, further studies sorting for macrophage markers Mac-1 and F4/80 also resulted in donor-derived muscle fibers in the host. To address this discrepancy, we investigated subpopulations of Mac-1 and F4/80 positive cells, in the presence or absence of stem cell markers (Sca-1 and C-kit). We demonstrate that only the subpopulations of Mac-1 and F4/80 positive cells harboring stem cell markers, Sca-1 or c-kit, were capable of contributing to the regenerating muscle post transplantation. Furthermore, these same subpopulations demonstrated single cell High Proliferative Potential (HPP) (6–26%) in a 7 factor cytokine cocktail, compared to the Mac-1 or F4/80 cells with no stem cell markers (0%). Additionally, they demonstrated long-term engraftment in all three lineages at 1-year (average chimerism of 55% versus 0% in stem cell marker negative groups). These subpopulations were also evaluated for morphology using Hematoxylin/Eosin (H/E), Wright-Giemsa, and Nonspecific Esterase staining. In the Mac-1 and F4/80 positive groups, those negative for stem cell markers resembled differentiated cells of the myeloid origin (macrophages, granulocytes), while those with positive stem cell markers demonstrated stem cell characteristics. We did not observe any engraftability, donor-derived muscle fibers, or HPP potential for CD14 or cfms positive cells coexpressing stem cell markers, indicating that these markers are more appropriate for identifying macrophages. In conclusion, our studies demonstrate that both Mac-1 and F4/80 surface markers are present on HSC and therefore caution must be taken in the interpretation of data using these macrophage markers. It is reasonable to believe that the use of Mac-1 and/or F4/80 surface markers in a lineage depletion process may result in the loss of a subpopulation of stem cells, and other markers such as CD14 or c-fms may be more appropriate for eliminating differentiated macrophages.
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