Abstract 2926: PNA as novel targeted cancer therapy for BRAFV600E mutant melanoma

Abstract

Abstract Our aim is to target tumor cells specifically by directly suppressing their oncogenes with peptide nucleic acid (PNA) oligonucleotide analogues. PNA oligonucleotides bind to DNA over 1000-fold more avidly than its native complement, are completely resistant to intra and extra cellular enzymatic degradation, show no nonspecific toxicity at therapeutic levels, and when conjugated to delivery peptides can be made nuclear and cell membrane permeable. We have employed these PNA oligomers to target BRAFV600E which is prevalent in cutaneous melanoma in a sequence-specific complementary manner so as to disrupt transcription by strand invasion. For these studies, we have developed a novel delivery peptide conjugated to PNA modified to increase both cellular delivery and PNA stability towards its target. Our results indicate that exposure of the melanoma cell lines to a modified PNA-peptide conjugate selective for BRAFV600E results in a concentration-dependent inhibition of cell growth that is specific for the BRAFV600E mutant melanoma cell lines with an IC50 range of 250 to 500 nM. Moreover, there is no inhibition of BRAFWT cell growth at these concentrations. This is associated with suppression of BRAFV600E protein over time with no effect on BRAFWT protein levels. Furthermore, BRAFV600E protein expression was suppressed for up to 6 days following initial exposure proving the durability of this type of inhibition. Exposure to this modified PNA-peptide down-regulates BRAFV600E mRNA transcription exclusively in the mutant cell lines. Live cell imaging of BRAFV600E mutant cells confirms localization of fluorescein-labeled PNA-delivery peptide specific to BRAFV600E to the nucleus within 3 hours of treatment. Our results indicate that these PNA-peptide derivatives could represent a novel and promising new therapy for patients with BRAFV600E mutant melanoma, and this technology could be applied to a multitude of other cancers either with specific translocations or mutations differing from wild-type cells even by only a single base pair. Citation Format: Jeffrey H. Rothman, Oliver Surriga, Shyamprasad D. Vasudeva, Grazia Ambrosini, Ouathek Ouerfelli, Gary K. Schwartz. PNA as novel targeted cancer therapy for BRAFV600E mutant melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2926. doi:10.1158/1538-7445.AM2014-2926