Mithramycin Depletes Specificity Protein 1 and Activates p53 to Mediate Senescence and Apoptosis of Malignant Pleural Mesothelioma Cells

Clinical Cancer Research 2015 October 12 [Epub ahead of print] [Link]

Rao M, Atay S, Shukla V, Hong Y, Upham T, Ripley T, Hong JA, Zhang M, Reardon E, Fetsch P, Miettinen M, Li X, Peer CJ, Sissung TM, Figg WD, De Rienzo A, Bueno R, Schrump D.



Specificity protein 1 (SP1) is an oncogenic transcription factor over-expressed in various human malignancies. This study sought to examine SP1 expression in malignant pleural mesotheliomas (MPM), and ascertain the potential efficacy of targeting SP1 in these neoplasms.

Experimental Design

qRT-PCR, immunoblot and immunohistochemistry techniques were used to evaluate SP1 expression in cultured MPM cells and MPM specimens and normal mesothelial cells/pleura. MTS, chemotaxis, soft agar, ß-galactosidase and Apo-BrdU techniques were used to assess proliferation, migration, clonogenicity, senescence and apoptosis in MPM cells following SP1 knockdown, p53 over-expression, or mithramycin treatment. Murine subcutaneous and intraperitoneal (IP) xenograft models were used to examine effects of mithramycin on MPM growth in vivo. Microarray, qRT-PCR, immunoblot and chromatin immunoprecipitation techniques were used to examine gene expression profiles mediated by mithramycin and combined SP1 knockdown/p53 over-expression, and correlate these changes with SP1 and p53 levels within target gene promoters.


MPM cells and tumors exhibited higher SP1 mRNA and protein levels relative to control cells/tissues. SP1 knockdown significantly inhibited proliferation, migration and clonogenicity of MPM cells. Mithramycin depleted SP1 and activated p53, dramatically inhibiting proliferation and clonogenicity of MPM cells. IP mithramycin significantly inhibited growth of subcutaneous MPM xenografts, and completely eradicated mesothelioma carcinomatosis in 75% of mice. Mithramycin modulated genes mediating oncogene signaling, cell cycle regulation, senescence and apoptosis in-vitro and in-vivo. The growth inhibitory effects of mithramycin in MPM cells were recapitulated by combined SP1 knockdown/p53 overexpression.


These findings provide preclinical rationale for phase II evaluation of mithramycin in mesothelioma patients.