Identification of new therapeutic targets for undifferentiated pleomorphic sarcoma

Abstract

Undifferentiated pleomorphic sarcoma (UPS) is a rare and highly aggressive soft tissue sarcoma with vast unmet treatment needs, both in curative options and the prolongation of survival. The heterogeneity and limited understanding of the targetable alterations within UPS have proven to be significant challenges in the successful development of new therapeutic options and their translation to the clinic. High-throughput screening in well-annotated preclinical models is a promising approach to identifying novel compounds for further research.

This project aims to (i) develop and characterise novel models of UPS from patient-derived xenograft models, (ii) identify compounds and target classes efficacious in UPS, and (iii) explore the anti-cancer effects of lead compounds, using the models developed.

The discovery of new therapeutic options for UPS has been restricted by the lack of suitable models. The first results chapter addresses this gap by characterising existing patient-derived cell lines and xenograft models. These patient-derived xenograft models were subsequently used to establish a novel cell line and an ex vivo tumour slice model.

With established, well-characterised models, the project aimed to identify new therapeutic targets for UPS. The following chapter focused on validating results from two commercial library screens: Prestwick FDA Approved Chemical Library (1280 compounds) and Screen-Well PKE (176 compounds), previously screened on the existing patient-derived UPS cell lines. This led to the identification of histone deacetylase (HDAC) inhibitors as promising candidates, as they exhibited low IC50 values with a clear reduction in cell viability.

To investigate these findings, the final chapter details the results of a custom HDAC inhibitor library (53 compounds) screened on existing and novel UPS cell lines. Hit validation identified four lead compounds, with the lowest average IC50, which were subsequently prioritised for further testing. This included viability analysis in 3D spheroid models, and combination assays with the standard of care, doxorubicin, to assess potential synergistic effects. Quisinostat was the most promising compound, exhibiting the greatest synergistic effects with doxorubicin, and was selected to investigate its on-target and functional effects on proliferation and apoptosis. The results of quisinostat combined with doxorubicin were then explored in more complex models: ex vivo tumour slices, which showed high variability, and in vivo, where monotherapy and combination treatment significantly reduced tumour volume.

Overall, this work developed novel models of UPS, which were utilised to identify quisinostat as a potential therapeutic option for UPS, demonstrating potent anti-tumour activity as a monotherapy and in combination with doxorubicin.