Napthalimidobenzamide DB-51630: a novel DNA binding agent inducing p300 gene expression and exerting a potent anti-cancer activity

Control of gene expression by small molecule compounds is a novel therapeutic strategy for cancer and usually it requires the presence of specific molecular recognition. The development of the compounds preferentially binding to the specific DNA sequence is one of the potential but very difficult approaches in this strategy. We designed and synthesized novel napthalimidobenzamide derivatives and analyzed their binding preferences to oligonucleotides by EtBr-displacement assay with DNA sequences, being essential fragments of the genes. To test whether these compounds modify the expression of specific genes, we analyzed the effect on the gene expression in AZ521 cells by differential display analysis using the compounds showing different characteristics in the recognition of specific DNA sequence. Among them, DB-51630, which showed approximately 350 times higher preferential binding to GC-repeats than to the AT and AA-repeating oligomers, caused the induction of a specific mRNA. The genetic sequence was identified to be the p300 gene by sequencing of the cloned cDNA. The p300 is a transcriptional co-activator protein that acts with other nuclear proteins in various cell differentiation and signal transduction pathways. This protein has intrinsic historic acetyltransferase activity and may act on chromatin directly to facilitate transcription. The increase of the amount of p300 mRNA increased after DB-51630 treatment by real time RT-PCR and Northern blot analysis. DB-51630 inhibited cell growth in various cancer cell lines at nanomolar range of concentrations, whereas p300 mRNA induction was observed at sub-nanomolar concentrations and the maximal induction occurred 8 h after DB-51630 treatment. In contrast, anti-cancer drugs such as doxorubicin, vincristine, cisplatin, etoposide, and actinomycin D did not increase p300 transcription. DB-51630 revealed potent anti-cancer activity against human solid tumor xenografts. Thus, we demonstrated the anti-cancer activity of DB-51630, which interacts with a specific DNA sequence, thereby inducing p300 gene expression and exhibited significant anti-cancer activity in human tumor xenografts. Furthermore, such compounds that bind to specific DNA sequences may not only control the expression of specific genes but also exert other mechanisms in the anti-cancer effect than those of classical DNA binding drugs.