Osteosarcoma (OS) is the most common paediatric primary non-hematopoietic bone tumor. Survival of these young patients is related to the response to chemotherapy and development of metastases. Despite many advances in cancer research, chemotherapy regimens for OS are still based on non-selective cytotoxic drugs. It is essential to investigate new specific molecular therapies for osteosarcoma to increase the survival rate of these patients. From WES analysis performed on 8 osteosarcoma biopsies of patients at different stage of the disease (responder and non-responder to therapy and metastatic and non-metastatic), we identified KMT2C, a regulator of chromatin, that showed variations in most samples. Successively, we performed immunohistochemical (IHC) and gene expression analysis of KMT2C on the same OS samples. They showed positivity both in the nucleus and in the cytoplasm, so we noted that there was a nucleus/cytoplasmic trafficking in osteosarcoma cells, also patients with drugs resistance and development of metastasis showed an increase of nucleus/cytoplasmic trafficking and a higher cytoplasmic localization. The osteosarcoma sample that showed the highest value of gene and protein KMT2C expression showed a probably damaging variation on the catalytic domain of the protein (SET) that allows the addition of methyl groups to the specific lysine residues.
The aim will be to better understand the role of KMT2C in carcinogenesis and progression of osteosarcoma and we will perform the IHC and mRNA expression analysis on a large population of patients with conventional high grade OS with known clinical and pathological data, particularly to metastatic progression and responsiveness to therapy. Moreover, we will perform gene expression analysis of genes involved in metastatic pathway and western blot analysis, both before and after siRNA silencing assay, to understand how KMT2C could modulate the metastatic pathway and identify new therapeutic approach.
Although, the advances in understanding of the aetiology and biology of osteosarcoma, the recent clinical trials of osteosarcoma have shown only modest progress. This is due because the absence of pathognomonic mutations and the heterogeneity of the disease. For these reasons, molecular mechanisms related to carcinogenesis, progression and resistance to therapy are still largely unknown. Indeed, even now the osteosarcoma karyotype is considered complex.
The sequencing of the exome has become indispensable tools to study the aetiology of this tumor.
The knowledge of genetic variations in coding exon regions may result in an easier discovery of new molecular target therapy, indeed this approach is likely to uncover the contribution of a new set of rare disease-causating variants with larger effect sizes and involving until now unsuspected genes.
From our WES analysis performed on eight high-grade osteosarcomas, we got a plethora of data that after the correct interpretation using bioinformatic tools, led us to identify KMT2C as gene that may be involve in osteosarcoma carcinogenesis. Indeed, given the potential roles of mutations in enhancer regulators such as KMT2C in cancer pathogenesis, increasing our understanding of how enhancer-mediated process function in cellular growth should lead to future research efforts. From our data, we believe that the different mutations of KMT2C and the different intracellular localization of the protein could result in a specific signature characteristic for each patient. Therefore, the continuation of the study on ever larger groups of patients followed by the study of modulation of genes involved in metastatic pathway after the gene silencing of KMT2C on osteosarcoma cell cultures may have the potential to reveal the real role of KMT2C in osteosarcoma carcinogenesis and progression. Clinically, this information may be used to explore opportunities for risk-stratified screening and with the goal to provide new cancer therapy approach to improve survival rate and quality of life for osteosarcoma patients.