Stable depletion of poly (ADP-ribose) polymerase-1 reduces in vivo melanoma growth and increases chemosensitivity

Poly(ADP-ribose) polymerase (PARP)-1, which plays a key role in DNA repair, inflammation and transcription, has recently been shown to be involved in angiogenesis. The aim of this study was to investigate PARP-1 role in melanoma aggressiveness and chemoresistance in vivo using clones stably silenced for PARP-1 expression. Whilst the growth characteristics of PARP-1-deficient melanoma cells were comparable to those of PARP-1-proficient cells in vitro, their tumourigenic potential in vivo was significantly compromised. In fact, mice challenged intra-muscle with PARP-1-deficient cells showed a delayed development of measurable tumour nodules, which were also significantly reduced in size with respect to those of mice inoculated with PARP-1-proficient cells. Moreover, animals challenged intra-cranially with PARP-1-deficient cells, a model that mimics CNS localisation of melanoma, showed an increased survival. Immunohistochemical analyses of PARP-1-depleted melanoma grafts indicated a reduced expression of the angiogenesis marker PECAM-1/CD31 and of the pro-inflammatory mediators TNF-α and GITR. Notably, PARP-1-silenced melanoma was extremely sensitive to temozolomide, an anticancer agent used for the treatment of metastatic melanoma. These results provide novel evidence for a direct role of PARP-1 in tumour aggressiveness and chemoresistance.