Background: Malignant peripheral nerve sheath tumor (MPNST) is an aggressive form of soft-tissue sarcoma (STS) in children. Despite intensive therapy, relatively few children with metastatic and unresectable disease survive beyond three years. RAS pathway activation is common in MPNST, suggesting MEK pathway inhibition as a targeted therapy, but the impact on clinical outcome has been small to date. Procedure: We conducted preclinical pharmacokinetic (PK) and pharmacodynamic studies of two MEK inhibitors, trametinib and selumetinib, in two MPNST models and analyzed tumors for intratumor drug levels. We then investigated 3′-deoxy-3′-[ 18 F]fluorothymidine (18 F-FLT) PET imaging followed by 18 F-FDG PET/CT imaging of MPNST xenografts coupled to short-term or longer-term treatment with selumetinib focusing on PET-based imaging as a biomarker of MEK inhibition. Results: Trametinib decreased pERK expression in MPNST xenografts but did not prolong survival or decrease Ki67 expression. In contrast, selumetinib prolonged survival of animals bearing MPNST xenografts, and this correlated with decreased pERK and Ki67 staining. PK studies revealed a significantly higher fraction of unbound selumetinib within a responsive MPNST xenograft model. Thymidine uptake, assessed by 18 F-FLT PET/CT, positively correlated with Ki67 expression in different xenograft models and in response to selumetinib. Conclusion: The ability of MEK inhibitors to control MPNST growth cannot simply be predicted by serum drug levels or drug-induced changes in pERK expression. Tumor cell proliferation assessed by 18 F-FLT PET imaging might be useful as an early response marker to targeted therapies, including MEK inhibition, where a primary effect is cellcycle arrest.

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Brain tumor is considered as one of the most aggressive and incurable form of cancer. Majority of the brain tumors have a median survival rate of only 12%. Even though advanced treatments such as surgical removal, chemotherapy and radiotherapy are available, brain tumor persists to be lethal. Obstacles associated with the current treatment options are: recurrence, development of resistance and inability to cross blood brain barrier (BBB). BBB restricts majority of drugs to reach the brain thus resulting in an ineffective treatment. Pimozide (PMZ) is an antipsychotic drug used for the treatment of schizophrenia and chronic psychosis. In this study, pimozide has shown significant reduction in the viability of U-87MG, U-251MG, DAOY and T98G cell lines with an IC50 ranging from 11µM to 20µM after 24 h of treatment. Pimozide induced apoptosis in these cell lines as evaluated by FITC/Annexin assay and further validated by the cleavage of caspase 3 as well as PARP by western blot analysis. Pimozide treatment resulted in the concentration dependent decrease in the expression of GLI1, OCT4, SOX2 and NANOG in U87MG, U251MG, DAOY and T98G brain cancer cell lines, depicting a reduction in the stem cell like property of these cell lines. In addition, pimozide treatment inhibited the expression of proto-oncogene c-Myc. Inhibition of Gli1 and c-Myc demonstrates that pimozide might also inhibit the growth of cancer cells by targeting SHH signaling. Our results further demonstrated that oral administration of pimozide (25mg/kg) inhibits the brain tumors in intracranial tumor model with no significant difference in average weight of critical organs. It is important to note that pimozide is an FDA approved drug with no considerable toxicity. Overall, this study depicts that pimizode is a potential candidate to target brain tumors. Citation Format: Itishree Kaushik, Alok Ranjan, Blake Schwettmann, Sanjay Srivastava. Pimozide suppresses the growth of brain tumor by targeting oncogenic pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5452.

Brain tumor is considered as one of the most aggressive and incurable form of cancer. Majority of the brain tumors have a median survival rate of only 12%. Even though advanced treatments such as surgical removal, chemotherapy and radiotherapy are available, brain tumor persists to be lethal. Temozolomide (TMZ) is the main therapy for brain tumor but resistance to TMZ is the major cause of treatment failure. This resistance in tumor cells has frequently been linked to the expression of O6‐methylguanine‐DNA methyltransferase (MGMT). Pimozide (PMZ) is a neuroleptic drug used for the treatment of schizophrenia and chronic psychosis. In our study, we observed that pimozide significantly reduced the viability of U87MG, U251MG, DAOY and GBM28 cell lines with an IC50 ranging from 11μM to 20μM after 24 h of treatment. Pimozide induced apoptosis in these cell lines as evaluated by FITC/Annexin assay and further validated by the cleavage of caspase 3 as well as PARP. Western blot analysis resulted in the concentration dependent decrease in the expression of STAT3 signaling mainly targeting the anti‐apoptotic markers BCl‐XL, BCl‐2 and Survivin etc in U87MG, U251MG, DAOY and GBM28 brain cancer cell lines. PMZ alone suppressed the growth of U87MG cells with an IC50 of 10μM, after 96 hours of treatment. On the other hand, treatment of U87MG cells with 750 μM of TMZ in combination with 10μM PMZ for 96 hours increased the killing of U87MG cells by 50% as compared to 10% when treated with TMZ. In addition, PMZ treatment reduced the survival of TMZ resistant U251R cells with an IC50 ranging from 15–20 μM after 24 h of treatment. Our results further demonstrated that oral administration of PMZ (25mg/kg) significantly inhibits the growth of brain tumors in an intracranial tumor model without any apparent signs of toxicity. It is important to note that PMZ is an FDA approved drug with no considerable toxicity. Overall, this study depicts that PMZ is a potential candidate to target brain tumors. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Rhabdomyosarcoma (RMS) is a childhood sarcoma composed of myoblast-like cells, which suggests a defect in terminal skeletal muscle differentiation. To explore potential defects in the differentiation program, we searched for mRNA splicing variants in genes encoding transcription factors driving skeletal muscle lineage commitment and differentiation. We studied two RMS cases and identified altered splicing resulting in "skipping" the second of three exons in MYOD1. RNA-Seq data from 42 tumors and additional RMS cell lines revealed exon 2 skipping in both MYOD1 and MYF5 but not in MYF6 or MYOG. Complementary molecular analysis of MYOD1 mRNA found evidence for exon skipping in 5 additional RMS cases. Functional studies showed that so-called MYODΔEx2 protein failed to robustly induce muscle-specific genes, and its ectopic expression conferred a selective advantage in cultured fibroblasts and an RMS xenograft. In summary, we present previously unrecognized exon skipping within MYOD1 and MYF5 in RMS, and we propose that alternative splicing can represent a mechanism to alter the function of these two transcription factors in RMS.