Obstruction of BRAF transcription by complementary PNA oligomers as a means to inhibit BRAF-mutant melanoma growth.

Peptide nucleic acid (PNA) oligomers are DNA mimics, which are capable of binding gene sequences 1000-fold more avidly than complementary native DNA by strand invasion and effectively obstruct transcription. Irreversibly obstructing the transcription or replication of a gene sequence, such as BRAF, offers a potential route to specifically target the cancer cell itself. We have employed PNA oligomers to target BRAF in a sequence-specific complementary manner. These PNAs have been modified by appending configurationally stabilizing cationic peptides in order to improve their cellular delivery and target avidity. Our results indicate that exposure of the melanoma cell lines to a modified PNA-peptide conjugate complementary to BRAF mutation sequence results in a concentration-dependent and time-dependent inhibition of cell growth that is specific for the BRAF-mutant melanoma cell lines with inhibition of mRNA and protein expression. Xenograft mouse trials show increased tumor growth delay and necrosis with the BRAF-complementary PNA-peptide conjugates as compared with the saline and scrambled PNA sequence controls. Similarly, quantitative measurement shows a 2.5-fold decrease in Ki67 and a 3-fold increase in terminal deoxynucleotidyl transferase dUTP nick end labeling expression with this approach. PNA-delivery peptide conjugates represent a novel way to target BRAF and represent a new approach in targeting selective oncogenes that induce tumor growth.