Tumour Progression and Spontaneous Regression in the Lewis Rat Sarcoma Model.

Spontaneous regression of tumours is a fascinating phenomenon rarely observed in oncological patients. We used a Lewis rat sarcoma model in which subcutaneous tumours developed after inoculation of the R5-28/clone C4 cells. Rats with tumour progression showed splenomegaly and anaemia. Tumour growth was associated with leucocytosis, granulocytosis, decrease in lymphocyte and CD161(+) population in peripheral blood and increase in serum MCP1 concentration. Animals with spontaneous regression of tumours initially showed an increase in white blood cells number and proportion of granulocytes. Between the 42nd and 49th day, however, values of these parameters dropped in correlation with reduction of tumour size. In spontaneously regressed tumours, vascularization was higher and on the contrary, progressive tumours had more necrotic areas with a high number of infiltrating granulocytes. In conclusion, progression and spontaneous regression of tumours in the Lewis rat sarcoma model is associated with distinct changes in populations of blood cells and immune cells which participate in these completely different processes of tumourigenesis.

DNA hypomethylation and oxidative stress-mediated increase in genomic instability in equine sarcoid-derived fibroblasts.

It is widely accepted that equine sarcoid disease, the most common skin associated neoplasm in equids, is induced by bovine papillomavirus (BPV-1). Although BPV-1 DNA has been found in almost all examined sarcoids so far, its detailed impact on the horse's host cell metabolism is largely unknown. We used equine fibroblast cell lines originating from sarcoid biopsies to study BPV-1-associated changes on DNA methylation status and oxidative stress parameters. Sarcoid-derived fibroblasts manifested increased proliferation in vitro, transcriptional rDNA activity (NORs expression) and DNA hypomethylation compared to control cells. Cells isolated from equine sarcoids suffered from oxidative stress: the expression of antioxidant enzymes was decreased and the superoxide production was increased. Moreover, increased ploidy, oxidative DNA damage and micronuclei formation was monitored in sarcoid cells. We postulate that both altered DNA methylation status and redox milieu may affect genomic stability in BPV-1-infected cells and in turn contribute to sarcoid pathology.