Abstract 3402: Knockdown of TWIST1 increases chemosensitivity of osteosarcoma cells

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Abstract Knock-down of TWIST1 increases chemosensitivity of osteosarcoma cells Texas Children's Cancer Center; Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030 TWIST1, a basic helix-loop-helix (bHLH) transcription factor, has previously been reported to be involved in cancer metastasis, invasion, drug response, and osteoblast differentiation induced by bone morphogenic protein. Based on expression profiling, we have previously identified a chemoresistance signature in osteosarcoma that could predict at the time of diagnosis the response to neoadjuvant chemotherapy. One of the 45 genes in the chemoresistance signature is TWIST1 whose expression level was significantly higher in osteosarcomas that were subsequently found to be more chemoresistant. To investigate the involvement of TWIST1 in chemoresistance of osteosarcoma at the cellular level, we first demonstrated that the IC50 of doxorubicin but not cisplatin treatment in eight osteosarcoma cell lines correlated with the endogenous TWIST1 expression level. We then tested the hypothesis that down-regulation of TWIST1 expression through RNAi in osteosarcoma cell lines with high TWIST1 expression could restore the chemosensitivity in these cells. Using two independent shRNAs to knock-down TWIST1 in HOS, SJSA-1 or 143B cells, we were able to show that the transduced cells became more sensitive to doxorubicin treatment as compared with the parental cells or control cells that were transduced with shRNAs with scrambled sequences. The results of the cytotoxicity assay were confirmed by the clonogenic assay using single colonies of stable transfectants with HOS cells. Based on these results, we concluded that TWIST1 is involved in chemoresistance of osteosarcoma cell lines and that down-regulation of its expression through RNAi would sensitize osteosarcoma cells to doxorubicin. However, we did not observe increased chemoresistance with overexpression of TWIST1 in osteosarcoma cell lines that have low levels of TWIST1 expression, suggesting that TWIST1 alone is not sufficient to cause chemoresistance in osteosarcoma cells. Identification of downstream targets of TWIST1 that could mediate chemoresistance by comparing expression profiles of TWIST1-knockdown clones with parental and scrambled controls is ongoing. In summary, these results validate our previous finding that TWIST1 can be used as a potential marker for predicting chemoresistance in osteosarcoma and suggest that modulating TWIST1 or its downstream targets could be considered as a novel strategy to overcome chemoresistance in osteosarcoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3402.