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It was recently shown that several new synthetic 2-alkylsulfanyl-6-benzyl-3, 4-dihydropyrimidin-4(3H)-one (S-DABO) derivatives demonstrated anti-HIV-1 activity. Three of the derivatives namely RZK-4, RZK-5 and RZK-6 were used in this study to explore their inhibitory effects on a variety of HIV strains. These compounds at a concentration of 200 microg mL(-1) almost completely inhibited the activity of recombinant HIV-1 reverse transcriptase. All of the three compounds reduced replication of HIV-1 laboratory-derived strains, low-passage clinical isolated strain, and the drug resistant strain. In particular RZK-6 showed potent activity against the HIV-1 drug resistant strain. In general, the antiviral activities are similar in magnitude to nevirapine (NVP), which is a non-nucleoside reverse transcriptase inhibitor approved by FDA. The therapeutic indexes of these compounds were remarkable, ranging from 3704 to 38462 indicating extremely low cytotoxicity. These results suggest that the three S-DABO derivatives in this study have good potential for further development in anti-HIV-1 therapy. It may be particularly useful to target at the non-nucleoside reverse transcriptase inhibitors resistant HIV-1 strain.

Trichosanthin (TCS) is a type I ribosome-inactivating protein possessing multiple biological and pharmacological activities. One of its major actions is inhibition of human immunodeficiency virus (HIV) replication. The mechanism is still not clear. It is generally believed that this action is mediated via ribosome inactivation. Recently, we found that some TCS mutants with full ribosome inactivating activity were devoid of anti-HIV-1 effect. This suggested that there might be other mechanisms contributing to the anti-HIV-1 action. This study showed that a commonly used c-Jun N-terminal kinases inhibitor (CEP-11004) could counteract the antiviral action of TCS in C8166 cells. CEP-11004 alone had no effect on HIV-1 replication and TCS alone significantly inhibited this process. When CEP-11004 was used together with TCS, the antiviral action of TCS was much reduced. Two methods were used to assess viral replication. (1) By measuring the HIV-1 reverse transcriptase, TCS on the average reduced viral replication to 52+/-4%. With CEP-11004 pretreatment, TCS appeared to lose the HIV-1 inhibitory activity with viral replication stood at 101+/-7%. (2) By measuring HIV-1 p24, TCS reduced viral replication to 68+/-4%. With CEP-11004 pretreatment, TCS again seemed to lose its anti-HIV-1 activity with HIV-1 replication rose back to 101+/-4%. Both indexes indicated that CEP-11004 counteracted the antiviral action of TCS. Phosphorylation of JNK on the other hand was only slightly elevated by 1.5-fold by TCS and CEP-11004 inhibited this elevation. These results suggested that the anti-HIV-1 effect of TCS may be related to the MAPK signal process downstream from the point of CEP inhibition.

Trichosanthin (TCS) is a type 1 ribosome-inactivating protein (RIP) effective against HIV-1 replication. The mechanism is not clear. Present results suggested that the antiviral action may be partly mediated through enhanced apoptosis on infected cells. TCS induced apoptosis in normal H9 cells and this action was more potent in those infected with HIV-1. In flow cytometry study, TCS induced larger population of apoptotic H9 cells chronically infected with HIV-1 in a dose-dependent manner. At TCS concentration of 25 microg/ml, 8.4% of normal H9 cells were found to be apoptotic whereas the same concentration induced 24.5% in HIV-1 chronically infected cells. Such difference was not found in the control experiments without TCS treatment. Two other studies supported this action. Cytotoxic study showed that cell viability was always lower in HIV-1 infected cells after TCS treatment, and DNA fragmentation study confirmed more laddering in infected cells. The mechanism of TCS induced apoptosis in normal or infected H9 cells is not clear. Results in this study demonstrated that TCS is more effective in inducing apoptosis in HIV-1 infected cells. This may explain in part the antiviral action of TCS.

Trichosanthin (TCS) is a type I ribosome-inactivating (RI) protein possessing multiple biological and pharmacological activities. Its major action is inhibition of human immunodeficiency virus (HIV) replication but the mechanism is still elusive. All evidences showed that this action is related to its RI activity. Previous studies found that TCS mutants with reduced RI activity simultaneously lost some anti-HIV activity. In this study, an exception was demonstrated by two TCS mutants retaining almost all RI activity but were devoid of anti-HIV-1 activity. Five mutants were constructed by using site-directed mutagenesis with either deletion or addition of amino acids to the C-terminal sequence. Results showed that the RI activity of mutants with C-terminal deletion mutants (TCS(C2), TCS(C4), and TCS(C14)) decreased by 1.2-3.3-fold with parallel downshifting of its anti-HIV-1 activity (1.4-4.8-fold). Another two mutants, TCS(C19aa) and TCS(KDEL) having 19 amino acid extension and a KDEL signal sequence added to the C-terminal sequence, retained all RI activity but subsequently lost most of the anti-HIV-1 activity. These findings suggested that ribosome inactivation alone might not be adequate to explain the anti-HIV action of TCS.

Trichosanthin (TCS) is a type I ribosome inactivating (RI) protein possessing anti-tumor and antiviral activity, including human immunodeficiency virus (HIV). The mechanism of these actions is not entirely clear, but is generally attributed to its RI property. In order to study the relationship between the anti-HIV-1 activity of TCS and its RI activity, three TCS mutants with different RI activities were constructed by using site-directed mutagenesis. The anti-HIV-1 activities of the three mutants were tested in vitro. Results showed that two TCS mutants, namely TCS(M(120-123)), TCS(E160A/E189A), with the greatest decrease in RI activity, lost almost all of the anti-HIV activity and cytopathic effect. Another mutant TCS(R122G), which exhibited a 160-fold decrease in RI activity, retained some anti-HIV activity. The results from this study suggested that RI activity of TCS may have significant contribution to its anti-HIV-1 property.