PARP inhibition can induce anti-neoplastic effects when used as monotherapy or in combination with chemo- or radiotherapy in various tumor settings; however, the basis for the anti-metastasic activities resulting from PARP inhibition remains unknown. PARP inhibitors may also act as modulators of tumor angiogenesis. Proteomic analysis of endothelial cells revealed that vimentin, an intermediary filament involved in angiogenesis and a specific hallmark of EndoMT (endothelial to mesenchymal transition) transformation, was down-regulated following loss of PARP-1 function in endothelial cells. VE-cadherin, an endothelial marker of vascular normalization, was up-regulated in HUVEC treated with PARP inhibitors or following PARP-1 silencing; vimentin over-expression was sufficient to drive to an EndoMT phenotype. In melanoma cells, PARP inhibition reduced pro-metastatic markers, including vasculogenic mimicry. We also demonstrated that vimentin expression was sufficient to induce increased mesenchymal/pro-metastasic phenotypic changes in melanoma cells, including ILK/GSK3-β-dependent E-cadherin down-regulation, Snail1 activation and increased cell motility and migration. In a murine model of metastatic melanoma, PARP inhibition counteracted the ability of melanoma cells to metastasize to the lung. These results suggest that inhibition of PARP interferes with key metastasis-promoting processes, leading to suppression of invasion and colonization of distal organs by aggressive metastatic cells.

This work was supported by Ministerio de Ciencia e Innovación SAF2006-01094, SAF2009-13281-C02-01, Fundación La Caixa BM06-219-0 and Junta de Andalucía P07-CTS-0239 and CTS-6602 to FJO, Ministerio de Educación y Ciencia SAF2007-64597; CICYT: SAF2009-13281-C02-02; Junta de Andalucía, P06-CTS-01385 to JMRdA and grants CEIC (P10-CTS5865) and FEDER-ISCIII (PI10/00883) to JCR-M. AGdH has been funded by grants from ‘‘Fundación Científica de la Asociación Española Contra el Cáncer’’, Ministerio de Ciencia y Tecnología SAF2010-16089, and ‘‘Fundación La Marató de TV3’’. JCR-M has been funded by Grants CEIC (P1=-CTS5865) and FEDER-ISCIII (PI10/00883). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Baulida and García de Herreros' labs is supported by the Instituto de Salud Carlos III (PI12/ 00257 and D012/0036/0005, part of the Plan Nacional I+D+ I and cofounded by the ISCIII-Subdirección General de Evaluación and Fondo Europeo de Desarrollo Regional-FEDER), the Fundación Científica Asociación Española Contra el Cáncer (Ayudas a grupos estables de investigación, 2010-1) and the Ministerio de Economía y Competitividad (SAF2013-4889-C2-1R).