Rhabdomyosarcoma (RMS) is the most commonly diagnosed malignant soft tissue tumour in children and adolescents. Patients with metastatic or recurrent disease have a poor clinical outcome with a 5-year overall survival of about 30%. So, the identification of innovative therapies against advanced RMS represents an urgent clinical need. Aberrant epigenetic landscape is a hallmark of different malignancies due to alterations in the enzymes that modify DNA methylation and histone marks (acetylation/methylation). As a result, a number of therapeutic compounds against proteins involved in epigenetic modifications are regarded as promising anticancer epi-drugs. In this project, we plan to evaluate the antitumour activity in RMS preclinical models of OTX015, a bromodomain and extra terminal (BET) inhibitor, as well as of CPI-1205, targeting the histone methyltransferases EZH2, both of which have recently moved into phase I clinical trials for different haematological and solid tumours. Firstly, we will analyse the biological effects of these two drugs, as single agents or in combination, in alveolar and embryonal RMS cell lines, focusing on proliferation, survival, migration, DNA damage and cancer stem cell formation. We will also assess in vitro whether OTX015 and/or CPI-1205 treatments are able to synergize with ionizing radiations, a conventional therapeutic tool widely used in RMS patients, in order to understand if epigenetic reprogramming might be a useful approach to enhance selective cytotoxicity against RMS cells and to overcome possible radioresistance mechanisms. These preclinical findings on BET and EZH2 inhibitors should shed further light on RMS development and could have the potential to be translated into a more efficient and less toxic treatment for RMS patients.
Despite the overall cure rate has increased, the 5-year event-free survival for children or adolescents with non-metastatic ARMS or ERMS at unfavourable sites is about 65%, and it's about 30% for patients with metastatic or recurrent tumours. Conventional therapy, including cytotoxics and radiotherapy, still represents the conventional treatment for RMS tumours, but a subgroup of patients undergoes a rapid disease progression or eventually relapses shortly after treatment ends because of the appearance of resistant cancer cells. Furthermore, conventional chemo/radiotherapy is associated with significant acute and chronic toxicity (myelosuppression, nephrotoxicity, infertility, cardiomiopathy, etc) and with an increased risk of life threatening late events such as secondary malignancies. Consequently, the identification of novel sensitizing strategies in the treatment of RMS is urgently required.
Mutations of aberrant expression of epigenetic enzymes, specifically responsible of DNA methylation and histone acetylation/methylation at definite aminoacid residues, have been shown to contribute to the transformation of a "healthy" cell into a tumour cell. Indeed, the resultant epigenome imbalance, due to the inactivation of tumour suppressor genes and the activation of oncogenes, plays a central role in the development and progression of many tumours, including RMS. Current preclinical studies and phase-I/II clinical trials are focused on several epigenetic components, aiming at restoring the appropriate transcriptome and methylome patterns. Based on this evidence, we believe that the evaluation of the activity of OTX015, a pan BET inhibitor, and CPI-1205, able to block EZH2 enzyme, in ARMS and ERMS cell lines both as single agents or in combination between them or with ionizing radiation (IR) might provide an additional therapeutic approach in RMS patients and a deeper insight into the molecular mechanisms underlying tumorigenesis of this soft tissue sarcoma. Furthermore, the identification of the molecular targets and signal pathways modulated by these novel epi-drugs might help in finding novel tissue and serum biomarkers for an early diagnosis and a more appropriate stratification into risk classes. Of particular importance will be the information of the effects of OTX015 and CPI-1205 on the formation of rhabdospheres, associated with cancer stem cell (CSC) proliferation and maintenance, since the reduction in CSC metastatic potential should be a promising approach to improve the efficacy of cancer treatment and, in turn, patient survival. Finally, the assessment of the combined utilization of OTX015 and/or CPI-1205 with IR in RMS in vitro models will give a rationale to translate experiments in preclinical mouse models in the attempt of designing more effective and less toxic therapeutic protocols for the management of RMS patients. Ultimately this project might allow an improvement of the therapeutic index in terms of reducing the side effects and increasing the quality of life, especially in those patients with high-risk RMS.