CYP24A1 and HIV-1 infection: As shown in Fig 8D and 8E and Table 5, the N6/NBD556 and IBP-CP24/C34 combinations showed antagonistic effect against HIV-1 infection with CI of 2.50 and 2.37, respectively, confirming that the combination of the two inhibitors with same target sites generally has no synergistic, but antagonistic effect.