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Background: Medulloblastoma (MB) is one of most frequent malignant tumors that affect children. Despite the relatively good survival rate, long time sequels still represent a challenge for MB. Therefore, in an attempt to reduce treatment aftereffects, new therapeutic targets are constantly being explored. Polo like kinase 1 (PLK1) is a master cell cycle regulator that is increased in proliferative cells, while its depletion has been repeatedly proposed as an oncological therapeutic strategy. Objectives: Here, we evaluated and compared the effects of PLK1 inhibition alone and in combination with currently used radio- and chemotherapy in MB cells. Methods: UW402, UW473, ONS-76 and DAOY MB cell lines were treated with BI 2536, BI 6727, GW843682X, and GSK461364 PLK1 inhibitors and cell proliferation, apoptosis, clonogenicity, cell invasion, adhesion and cell cycle distribution were evaluated. In addition, the combinatorial effect with gamma irradiation or etoposide, cisplatin and temozolomide was evaluated. Results: We show that PLK1 inhibition causes a significant decrease on cell proliferation, clonogenic capacity, cell invasion and adhesion, with modest differences between inhibitors. Yet, the four drugs cause G2/M arrest followed by increased cell death. PLK1 inhibition proved to be efficient to sensitize MB cells to radiation irrespective of the inhibitor, even though it showed thrifty results when combined with chemotherapy. Conclusions: We proved that all PLK1 inhibitors have anti-mitotic effects on MB cells, supporting the idea of using them as radiosensitizers. Taken together, our results strengthen the potential of using PLK1 as a therapeutic target to improve treatment strategy for this tumor.

Medulloblastoma (MB) treatment is continuously evolving. Better treatment approaches, focused on particular molecular pathways involved in MB development and progression support new treatment strategies. This article explores the antiproliferative, proapoptotic and radiosensitizing effects of Methoxyamine (MX), a base excision repair (BER) inhibitor that has shown anticancer potential by sensitizing tumor cells to ionizing radiation and chemotherapy. The DAOY (a desmoplastic cerebellar-derived MB) and ONS-76 (classical MB) cell lines were treated with MX at different concentrations, either alone or combined with various chemotherapeutic compounds: cisplatin (CDDP), temozolomide (TMZ) and thiotepa (THIO). Additionally, cell lines were exposed to MX and treated at different ionizing radiation fractions. Measurement of cell growth by XTT assay, clonogenic assay and detection of apoptotic cell death through caspase activity was obtained. Exposure to MX significantly decreased cell proliferation (p<0.05) while increasing cell apoptosis (p<0.05). Growth reduction was concentration-dependent for both DAOY and ONS-76 cells lines. Conversely, MX failed to enhance the cytotoxicity of CDDP, TMZ, and THIO. Moreover, MX treatment radiosensitized both cell lines, with ONS-76 cells being more prone to radiation effects at higher doses of exposure. These data support the role of MX as a direct cytotoxic compound for pediatric MB cells by inhibiting the BER pathway. Nevertheless, an antagonism, rather than a synergic or additive effect of MX with different concentrations of CDDP, TMZ and THIO was observed. Likewise, the radiosensitizing effect on MB cell lines seems to depend on radiation doses and MB subtype. This information may be relevant for clinical study designs employing BER inhibitors for MB.

Xp11.2 translocation renal cell carcinoma (Xp11.2 RCC) is a subtype of RCC characterized by translocations involving a breakpoint at the TFE3gene (Xp11.2). Moderate to strong nuclear TFE3 immunoreactivity has been recognized as a specific diagnostic marker for this type of tumor. However, exclusive cytoplasmic localization of a TFE3 fusion protein was reported in UOK 145 cells, a cell line derived from an Xp11.2 RCC harboring the PSF-TFE3translocation. If reproducible using immunohistochemistry (IHC), this finding would have important implications for pathologists in the diagnosis of Xp11.2 RCC, calling into question the specificity of nuclear immunoreactivity for TFE3 in these tumors. The purpose of this study was to determine whether the above-noted cytoplasmic localization of the TFE3 fusion protein could be reproduced using IHC. UOK 145 cells and fresh frozen tissue from 2 clinical cases of Xp11.2 RCC found to harbor the PSF-TFE3gene rearrangement (by cytogenetic testing) were collected. All samples were subjected to histopathologic evaluation by board-certified pathologists, TFE3 IHC, reverse transcription polymerase chain reaction, and Sanger sequencing analysis. A strong nuclear TFE3 immunoreactivity was demonstrated in all samples including the UOK 145 cell line. No cytoplasmic immunoreactivity was seen. Reverse transcription polymerase chain reaction and Sanger sequencing confirmed the previously reported PSF-TFE3gene fusion between exon 9 of PSFand exon 6 of TFE3in the UOK 145 cell line and in one of 2 clinical cases of Xp11.2 RCC. A novel PSF-TFE3gene fusion between exon 9 of PSFand exon 5 of TFE3was detected in the second clinical case of Xp11.2 RCC.