Browsing by Author "Punger, Tatjana"

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma. It arises from skeletal muscle stem cells, which fail to differentiate. Multimodal treatment approach has improved the outcome of RMS during the recent years. However, in case of relapsed or metastatic disease, the prognosis is still very poor. This indicates a high demand for novel targeted therapy approach for RMS. Prox1 transcription factor has been shown to regulate myoblast differentiation into skeletal muscle fibers. Our unpublished observations indicate that Prox1 is highly expressed in RMS tumors and that it is essential for RMS cell growth. The aim of this study was to find novel drug candidates for RMS treatment depending on Prox1 and/or its downstream signaling. High-throughput drug screening with 528 oncology compounds was tested on wild-type and Prox1 silenced rhabdomyosarcoma cells (RD cell line). Gene silencing was performed via lentiviral vectors encoding shRNA for Prox1. In the screening results, we focused on the drugs, which were more potent in Prox1 silenced cells with nano- or micromolar concentrations compared to the wild-type cells. The results revealed 7 potential groups of inhibitors, which had superior suppressive effect on RMS cell viability specifically when Prox1 was silenced. In vitro validation of high-throughput screening results by MTT and luciferase assays confirmed the results. Based on the magnitude of their inhibitory effect and information available on these compounds, three drugs were chosen for further investigation. Two of these compounds also potently inhibited the growth of patient-derived primary RMS cells, which we obtained from the Helsinki University Hospital and named KLHEL1. These drugs were also less toxic to healthy myoblasts. In addition, these two compounds significantly decreased Prox1 mRNA and protein levels in wild-type cells, and completely inhibited the ability of both RD and KLHEL1 cells to form colonies. Combinational exposure to these inhibitors further enhanced the effect compared to a single agent treatment. The present findings demonstrate a potential for repurposing of these drugs for targeted treatment in rhabdomyosarcoma expressing high Prox1 levels.