The novel cyclohepta[d]pyrimidine derivatives targeting the non-nucleoside reverse transcriptase inhibitor (NNRTI) binding site have been rationally designed based on the structure of the NNRTI binding pocket. Although extensive SARs for non-cyclic analogues (such as MKC-442 and TNK-651) have been obtained, little or no information was available about the annelated series. The key point for the development of such compounds is the right size of the annelated rings, which should not only possess conformational flexibility, but also restrict effectively the rotation and position of the aromatic ring to the plane of the pyrimidine ring. According to structure-activity relationships (SARs), studies of the crystal structure of the RT complex with TNK-651 inhibitor suggest that cycloheptyl group would adjust the aromatic ring with an effective conformation to the plane of the pyrimidine ring, which could improve the activity.
Compared with the structures of APCP, BPCP and EPCP, BmPCP reserves the part of TNK-651and then was identified as a potential lead compound by the inhibition of viral infectivity in different cells. Selectivity Index reached to 84 on MT4 cell and 266 on TZM-bl cell respectively.
Here we tested the inhibitory activity of BmPCP on infection by laboratory-adapted HIV-1 strains, including HIV-1SF33 and HIV-1 1617-1 as well as HIV clinical isolates circulating in China. In China, CRF07_BC and B' have been the most commonly transmitted HIV-1 subtypes across the country. Therefore, we focused on the inhibitory activity of BmPCP on Chinese epidemic HIV-1 subtype strains. The result showed that BmPCP was effective against infection by a broad spectrum of HIV-1 strains, including both R5 and X4 viruses with IC50 at low μM levels. BmPCP has antiviral activity on laboratory-adapted HIV strains as well as clinical isolates from Chinese AIDS patients.
Also similar to NVP, BmPCP inhibits HIV-1 infection by targeting the post entry of the HIV-1 replication cycle by time-of-additional assay. Furthermore, in vitro HIV-1 reverse transcriptase activity assays corroborated that BmPCP directly targets the process of HIV reverse transcriptase. These results suggest that BmPCP may act as a NNRTI to inhibit HIV-1 replication. BmPCP exhibited low cytotoxicity to cells that were used for testing anti-HIV-1 activity, thus having selectivity index ranging from 60 to 360, suggesting a good potential for further development of BmPCP as a new anti-HIV-1 drug.
Like NVP, BmPCP was much less effective against NNRTI drug resistant strains. However, BmPCP with a novel structure acts as a NNRTI to inhibit HIV-1 replication and can serve as a lead compound for further development of new anti-HIV-1 drugs.