Binding of hybrid molecules containing pyrrolo [2,1-c][1,4]benzodiazepine (PBD) and oligopyrrole carriers to the human immunodeficiency type 1 virus TAR-RNA

The binding properties of a set of four hybrids, prepared combining from one to four polypyrrole minor groove binders and pyrrolo [2,1-c][1,4]benzodiazepine (PBD), have been studied using as target molecule the HIV-1 TAR-RNA.We found that these hybrids bind to TAR RNA and inhibit TAR/protein(s) interactions. The anti-proliferative activity of the hybrids has been tested in vitro on HL3T1 cells and compared to the anti-proliferative effects of the natural product distamycin A and PBD. The effects on HIV-1 LTR directed transcription were studied using the chloramphenicol-acetyltransferase gene reporter system, and structure-activity relationships are discussed. The results obtained demonstrate that the hybrids 22-25 exhibit different TAR-RNA binding activity with respect to both distamycin A and PBD. In addition, a direct relationship was found between number of pyrrole rings present in the hybrids 22-25 and anti-proliferative effects. It was found that increased length of the polypyrrole backbone leads to an increased in vitro anti-proliferative effect, i.e. the hybrid 25, containing the four pyrroles distamycin analogous, is more active than 22, 23 and 24 against cell proliferation. With respect to inhibition of HIV-1 LTR-driven transcription, it was found that the hybrids 23-25 containing two-four pyrroles are active. Therefore, when anti-proliferative effects are considered together with the inhibitory effects of HIV-1 LTR driven transcription, our results suggest that the hybrid 23 is the more interesting, since it exhibits low anti-proliferative activity and inhibits HIV-1 LTR driven transcription both in vitro and in ex vivo experiments.