Identification and targeting of a unique NaV1.7 domain driving chronic pain

Small molecules directly targeting the voltage-gated sodium channel (VGSC) NaV1.7 have not been clinically successful. We reported that preventing the addition of a small ubiquitin-like modifier onto the NaV1.7-interacting cytosolic collapsin response mediator protein 2 (CRMP2) blocked NaV1.7 function and was antinociceptive in rodent models of neuropathic pain. Here, we discovered a CRMP2 regulatory sequence (CRS) unique to NaV1.7 that is essential for this regulatory coupling. CRMP2 preferentially bound to the NaV1.7 CRS over other NaV isoforms. Substitution of the NaV1.7 CRS with the homologous domains from the other eight VGSC isoforms decreased NaV1.7 currents. A cell-penetrant decoy peptide corresponding to the NaV1.7-CRS reduced NaV1.7 currents and trafficking, decreased presynaptic NaV1.7 expression, reduced spinal CGRP release, and reversed nerve injury-induced mechanical allodynia. Importantly, the NaV1.7-CRS peptide did not produce motor impairment, nor did it alter physiological pain sensation, which is essential for survival. As a proof-of-concept for a NaV1.7 -targeted gene therapy, we packaged a plasmid encoding the NaV1.7-CRS in an AAV virus. Treatment with this virus reduced NaV1.7 function in both rodent and rhesus macaque sensory neurons. This gene therapy reversed and prevented mechanical allodynia in a model of nerve injury and reversed mechanical and cold allodynia in a model of chemotherapy-induced peripheral neuropathy. These findings support the conclusion that the CRS domain is a targetable region for the treatment of chronic neuropathic pain.

Stereospecific Effects of Benzimidazolonepiperidine Compounds on T-Type Ca2+ Channels and Pain

T-type calcium channels activate in response to subthreshold membrane depolarizations and represent an important source of Ca²⁺ influx near the resting membrane potential. These channels regulate neuronal excitability and have been linked to pain. For this reason, T-type calcium channels are suitable molecular targets for the development of new non-opioid analgesics. Our previous work identified an analogue of benzimidazolonepiperidine, 5bk, that preferentially inhibited Ca_V3.2 channels and reversed mechanical allodynia. In this study, we synthesized and screened a small library of 47 compounds derived from 5bk. We found several compounds that inhibited the Ca²⁺ influx in DRG neurons of all sizes. After separating the enantiomers of each active compound, we found two compounds, 3-25-R and 3-14-3-S, that potently inhibited the Ca²⁺ influx. Whole-cell patch clamp recordings from small- to medium-sized DRG neurons revealed that both compounds decreased total Ca²⁺. Application of 3-14-3-S (but not 3-25-R) blocked transiently expressed Ca_V3.1-3.3 channels with a similar IC₅₀ value. 3-14-3-S decreased T-type, but not N-type, Ca²⁺ currents in DRG neurons. Furthermore, intrathecal delivery of 3-14-3-S relieved tonic, neuropathic, and inflammatory pain in preclinical models. 3-14-3-S did not exhibit any activity against G protein-coupled opioid receptors. Preliminary docking studies also suggest that 3-14-3-S can bind to the central pore domain of T-type channels. Together, our chemical characterization and functional and behavioral data identify a novel T-type calcium channel blocker with in vivo efficacy in experimental models of tonic, neuropathic, and inflammatory pain.

The ribonuclease H activity of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2 is modulated by residue 294 of the small subunit

Reverse transcriptases (RTs) exhibit DNA polymerase and ribonuclease H (RNase H) activities. The RTs of human immunodeficiency viruses type 1 and type 2 (HIV-1 and HIV-2) are composed of two subunits, both sharing the same N-terminus (which encompasses the DNA polymerase domain). The smaller subunit lacks the C-terminal segment of the larger one, which contains the RNase H domain. The DNA polymerase domain of RTs resembles a right hand linked to the RNase H domain by a connection subdomain. Despite the high homology between HIV-1 and HIV-2 RTs, the RNase H activity of the latter is substantially lower than that of HIV-1 RT. The thumb subdomain of the small subunit controls the level of RNase H activity. We show here that Gln294, located in this thumb, is responsible for this difference in activity. A HIV-2 RT mutant, where Gln294 in the small subunit was replaced by a proline (present in HIV-1 RT), has an activity almost 10-fold higher than that of the wild-type RT. A comparative in vitro study of the kinetic parameters of the RNase H activity suggests that residue 294 affects the K(m) rather than the kcat value, influencing the affinity for the RNA.DNA substrate.

Clathsterol, a novel anti-HIV-1 RT sulfated sterol from the sponge Clathria species

As part of a search for novel inhibitors of humandeficiency virus type 1 (HIV-1) reverse transcriptase (RT), the MeOH-EtOAc extract of a Red Sea sponge, Clathria sp., was shown to be active. Bioassay-guided fractionation of the extract yielded a novel sterol sulfate, clathsterol (1), which is responsible for the activity and is active at a concentration of 10 microM. The structure of 1 was established mainly by interpretation of spectral data and a chemical transformation.

The ribonuclease H activity of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2 is affected by the thumb subdomain of the small protein subunits

Retroviral reverse transcriptases (RTs) have both DNA polymerase and ribonuclease H (RNase H) activities. The RTs of HIV-1 and HIV-2 are heterodimers of p66/p51 and p68/p54 subunits, respectively. The smaller subunit lacks the C-terminal segment of the larger subunit (which is the RNase H domain). The structure of the DNA polymerase domain of HIV-1 RT resembles a right hand (with fingers, palm and thumb subdomains), linked to the RNase H domain via the connection subdomain. The RNase H activity of the Rod strain of HIV-2 RT is about tenfold lower than that of HIV-1 RT, while the DNA polymerase activity of these RTs is similar. A chimeric RT in which residues 227-427 (which constitute a small part of the palm and the entire thumb and connection subdomains) of the Rod strain of HIV-2 RT were replaced by the corresponding segment from HIV-1 RT, has an RNase H activity as high as HIV-1 RT (despite the fact that the RNase H domain is derived from HIV-2 RT). We analyzed the RNase H activity of wild-type HIV-2 RT from the D-194 strain and compared it with this activity of the RT from the Rod strain of HIV-2 and HIV-1 RT. The level of this activity of both HIV-2 RT strains was low; suggesting that low RNase H activity is a general property of HIV-2 isolates. The in vitro RNase H digestion pattern of the three wild-type RTs was indistinguishable, despite the difference in the level of RNase H activity. We constructed new chimeric HIV-1/HIV-2 RTs, in which protein segments and/or subunits were exchanged. The DNA polymerase activity of the parental HIV-1 and HIV-2 RTs was similar; as expected, the specific activity of the polymerases of all the hybrid RTs were also similar. However, the RNase H specific activity of the chimeric RTs was either high (like HIV-1 RT) or low (like HIV-2 RT). The origin of the thumb subdomain in the small subunit of the chimeric RTs (residues 244-322) determines the level of the RNase H activity. The strand-transfer activity of the chimeric RTs is also affected by the thumb subdomain of the small subunit; transfer was much more efficient if this subdomain was derived from HIV-1 RT. The data can be explained from the three-dimensional structure of HIV-1 RT. The thumb of the smaller subunit contacts the RNase H domain; it is through these contacts that the thumb affects the level of the RNase H activity of RT.

New co-metabolites of the streptazolin pathway

Variation of the culture conditions of Streptomyces sp. strain A1, which produces streptazolin (1), resulted in the isolation of four new co-metabolites: 5-O-(beta-D-xylopyranosyl)streptazolin (3), 9-hydroxystreptazolin (4), 13-hydroxystreptazolin (5), and streptenol E (6). Their structures were established by spectroscopic and chemical methods. The possible biosynthetic relationship between the streptazolins and the streptenols is discussed.

Polycitone A, a novel and potent general inhibitor of retroviral reverse transcriptases and cellular DNA polymerases

Polycitone A, an aromatic alkaloid isolated from the ascidian Polycitor sp. exhibits potent inhibitory capacity of both RNA- and DNA-directed DNA polymerases. The drug inhibits retroviral reverse transcriptase (RT) [i.e. of human immunodeficiency virus type 1 (HIV), murine leukaemia virus (MLV) and mouse mammary tumour virus (MMTV)] as efficiently as cellular DNA polymerases (i.e. of both DNA polymerases alpha and beta and Escherichia coli DNA polymerase I). The mode and mechanism of inhibition of the DNA-polymerase activity associated with HIV-1 RT by polycitone A have been studied. The results suggest that the inhibitory capacity of the DNA polymerase activity is independent of the template-primer used. The RNase H function, on the other hand, is hardly affected by this inhibitor. Polycitone A has been shown to interfere with DNA primer extension as well as with the formation of the RT-DNA complex. Steady-state kinetic studies demonstrate that this inhibitor can be considered as an allosteric inhibitor of HIV-1 RT. The target site on the enzyme may be also spatially related to the substrate binding site, since this inhibitor behaves competitively with respect to dTTP with poly(rA).oligo(dT) as template primer. Chemical transformations of the five phenol groups of polycitone A by methoxy groups have a determinant effect on the inhibitory potency. Thus, the pentamethoxy derivative which is devoid of all hydroxy moieties, loses significantly, by 40-fold, the ability to inhibit the DNA polymerase function. Furthermore, this analogue lacks the ability to inhibit DNA primer extension as well as the formation of the RT-DNA complex. Indeed, inhibition of the first step in DNA polymerization, the formation of the RT-DNA complex, and hence, of the overall process, could serve as a model for a universal inhibitor of the superfamily of DNA polymerases.

The inhibition of the reverse transcriptase of HIV-1 by the natural sulfoglycolipids from cyanobacteria: contribution of different moieties to their high potency

The potent in vitro inhibition of the enzymatic activity of the human immunodeficiency virus-1 (HIV-1) reverse transcriptase (RT) by the lipophilic extracts of cyanobacteria8 was primarily attributed to the sulfoquinovosylpranosyl lipids, compounds 1-4. These sulfolipids inhibit efficiently and selectively only the DNA polymerase activity of HIV-1 RT (and not the ribonuclease H function) with 50% inhibitory concentration value (IC50) as low as 24 nM exhibited by compound 1. The novel natural compound 4, in which two hydroxy groups on the sugar moiety are substituted by palmitoyl residues, exhibits a significant decrease in the maximal inhibition capacity. It is possible, therefore, that the contribution of acylated groups to the molecule at these positions interferes with inhibition, possibly, by steric hindrance. Both the sulfonic acid moiety and the fatty acid ester side chain have a substantial effect in potentiating the extent of inhibition. For one, the inhibitory effects of all the natural glycolipids tested (5-8) are markedly reduced, and the hydrolysis of the fatty acid side chain, as in derivative 9, has substantially abolished the inhibition of HIV RT.

Reverse transcriptase of mouse mammary tumour virus: expression in bacteria, purification and biochemical characterization

We have constructed a plasmid that induces in bacteria the synthesis of an enzymically active reverse transcriptase (RT) of mouse mammary tumour virus (MMTV), a retrovirus with a typical B-type morphology. The highest catalytic activity was detected only when 27 residues from the C-terminus of the protease were included in the N-terminus of the recombinant RT, after an extra deoxyadenosine was added between the pro and pol genes to overcome the -1 frameshift event (which occurs naturally in virus-infected cells). The recombinant protein with a six-histidine tag was purified to homogeneity by a two-column purification procedure, Ni2+ nitriloacetic acid/agarose followed by carboxymethyl-Sepharose chromatography. Unlike most RTs, the purified MMTV RT is enzymically active as a monomer even after binding a DNA substrate. Like all RTs studied, the recombinant MMTV RT possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity, all of which show a preference for Mg2+ over Mn2+ ions. Other features of these enzymic activities, such as extension of DNA primers, processivity of DNA synthesis, pH dependence, steady-state kinetic constants, effects of Na+ or K+ ions and sensitivity to a thiol-specific reagent and to a zinc chelator, have been evaluated. The catalytic properties of MMTV RT were compared with those of the well-studied RT of HIV-1, the causative agent of AIDS. Interestingly, MMTV RT exhibits a high sensitivity to nucleoside triphosphate analogues (which are known to be potent inhibitors of HIV RTs and are being used as the major anti-AIDS drugs), as high as that of HIV-1 and HIV-2 RTs. Furthermore the recombinant MMTV RT shows a processivity of DNA synthesis higher than that of HIV-1 RT.

New acylated sulfoglycolipids and digalactolipids and related known glycolipids from cyanobacteria with a potential to inhibit the reverse transcriptase of HIV-1

Five novel diacylated sulfoglycolipids (1-5) were isolated from the cyanobacterium Scytonema sp. (TAU strain SL-30-1-4) and four novel acylated diglycolipids (6-9) were isolated from the cyanobacterium Oscillatoria raoi (TAU strain IL-76-1-2). These two groups of glycolipids and related known glycolipids isolated from these two and three other strains of cyanobacteria, Phormidium tenue (TAU strain IL-144-1), O. trichoides (TAU strain IL-104-3-2), and O. limnetica (TAU strain NG-4-1-2), were found to inhibit HIV-1 RT enzymatic activity to different extents. The structure elucidation of the various compounds is based on the selective hydrolysis of the glycerol ester moieties, GCMS analysis of the methyl ester derivatives of the liberated fatty acids, homo- and heteronuclear-2D-NMR techniques, and MS. The use of negative-ion FABMS for analyzing the combination and distribution of the fatty acids in glycolipids is demonstrated.

Subunit-specific mutagenesis of the cysteine 280 residue of the reverse transcriptase of human immunodeficiency virus type 1: effects on sensitivity to a specific inhibitor of the RNase H activity

Treatment of human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) with N-ethylmaleimide (NEM) selectively inhibits the RNase H activity. The cysteine residue at position 280 (C280) is the target for NEM; HIV-1 RT carrying the mutation C280S is resistant to NEM. Since HIV-1 RT is composed of two related subunits (p66 and p51) that play distinct roles, we asked whether the C280 in p51 or the C280 in p66 is responsible for the sensitivity of the enzyme to NEM. HIV-1 RT versions were prepared that had one mutant and one wild-type subunit. When these chimeric enzymes were tested, both the p51 and p66 subunits were found to contribute to the sensitivity of the enzyme to NEM. The implications of these results are discussed in the context of the structure of the enzyme.

Mode of inhibition of HIV reverse transcriptase by 2-hexaprenylhydroquinone, a novel general inhibitor of RNA-and DNA-directed DNA polymerases

A natural compound from the Red Sea sponge Ircinia sp., 2-hexaprenylhydroquinone (HPH), has been shown to be a general inhibitor of retroviral reverse transcriptases (from HIV-1, HIV-2 and murine leukaemia virus) as well as of cellular DNA polymerases (Escherichia coli DNA polymerase I, and DNA polymerases alpha and beta). The pattern of inhibition was found to be similar for all DNA polymerases tested. Thus the mode of inhibition was studied in detail for HIV-1 reverse transcriptase. HPH is a non-competitive inhibitor and binds the enzyme irreversibly with high affinity (Ki=0. 62 microM). The polar hydroxy groups have been shown to be of key importance. A methylated derivative, mHPH, which is devoid of these polar moieties, showed a significantly decreased capacity to inhibit all DNA polymerases tested. Like the natural product, mHPH binds the enzyme independently at an allosteric site, but with reduced affinity (Ki=7.4 microM). We show that HPH does not interfere with the first step of the polymerization process, i.e. the physical formation of the reverse-transcriptase-DNA complex. Consequently, we suggest that the natural inhibitor interferes with the subsequent steps of the overall reaction. Since HPH seems not to affect the affinity of dNTP for the enzyme (the Km is unchanged under conditions where the HPH concentration is increased), we speculate that its inhibitory capacity is derived from its effect on the nucleotidyl-transfer catalytic reaction. We suggest that such a mechanism of inhibition is typical of an inhibitor whose mode of inhibition should be common to all RNA- and DNA-directed polymerases.

Mechanism of inhibition of HIV reverse transcriptase by toxiusol, a novel general inhibitor of retroviral and cellular DNA polymerases

Toxiusol, a natural product isolated from the Red Sea sponge Toxiclona toxius, has been shown to be a potent inhibitor of various viral reverse transcriptases (RT) [i.e., of human immunodeficiency virus (HIV-1), equine infectious anemia virus, and murine leukemia virus] and cellular DNA polymerases (i.e., of DNA polymerases alpha and beta and Escherichia coli DNA polymerase I). A thorough investigation of the mode of inhibition was conducted with HIV-1 RT-associated DNA polymerase activity. The inhibition is unaffected by the nature of template-primer used. The inhibitory active site of toxiusol is attributable to the polar moieties at the benzene ring. The presence of either sulfate groups in the natural lead compound or hydroxyl groups in the corresponding hydroquinone is critical, because both compounds are equally effective at low micromolar concentrations. Conversely, the presence of acetyl groups in the same position in the derivative toxiusol diacetate lowers significantly or abolishes the inhibitory activity. Toxiusol binds the HIV-1 RT irreversibly and in a noncompetitive way with high affinity (Ki = 1.2 microM), probably through polar groups. The replacement with acetyl moieties in the analog toxiusol diacetate hampers the binding of the inhibitor to the enzyme (Ki increases to about 26 microM). Still, the compound binds irreversibly, probably through its hydrophobic structure skeleton. Toxiusol diacetate loses its ability to inhibit the first step in the DNA polymerization process (that is, the formation of the DNA-enzyme complex as measured by a gel retardation assay), which contributes to its poor inhibitory capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Peyssonols A and B, two novel inhibitors of the reverse transcriptases of human immunodeficiency virus types 1 and 2

Two new sesquiterpene hydroquinones, peyssonol A and peyssonol B, of the Red Sea algae Peyssonelia sp., have been shown to be potent inhibitors of the RNA-directed DNA synthesis of the reverse transcriptases (RTs) of human immunodeficiency virus (HIV)-1 and HIV-2. The DNA-dependent DNA polymerase activity is inhibited to a lesser extent, whereas the RNase H activity is unaffected. The inhibition of the DNA polymerase activities is independent of the nature of the template primers used. Peyssonol A probably binds the RT at a site distinct from those occupied by the substrates of the RNA-directed DNA synthesis, since the mode of inhibition is noncompetitive with respect to both dNTP's and template primer. This is partially true for peyssonol B, which is noncompetitive with respect to only dNTP, but is competitive with respect to the template primer. We have speculated that, since peyssonol B and the template primer bear no apparent structural resemblance, the competitive pattern of inhibition can be explained by an indirect steric hindrance or by the overlap of the inhibitor and the substrate distinct binding sites of the enzyme. Alternatively, the binding of the inhibitor to a distinct site induces conformational changes that distort the binding of the template primer. Furthermore, we have shown that both peyssonol A and peyssonol B interfere with the direct binding of the RT to the template primer, offering an explanation for the mechanism of the enzyme inhibition. The insensitivity of DNA polymerase beta and the poor response of DNA polymerase alpha to peyssonol A make this inhibitor more attractive for the future development of a potent anti-HIV RT drug.

Synthesis of naphthalenesulfonic acid small molecules as selective inhibitors of the DNA polymerase and ribonuclease H activities of HIV-1 reverse transcriptase

Over 25 selected naphthalenesulfonic acid derivatives were evaluated for their inhibitory effect on two different functional domains of the HIV-1 reverse transcriptase (RT), namely the ribonuclease H and DNA polymerase activities. Most of the analogues were found to be either specific toward the DNA polymerase activity or showed nonselective inhibition of both catalytic functions. The most active compounds are either symmetrical derivatives or nonsymmetrical derivatives containing a lipophilic appendage consisting of a palmitoyl or cholesteryl moiety. The six most active compounds in the preliminary screen, derivatives 6, 16, 17, 23, 26, and 27, were subjected to experiments to determine their 50% inhibitory concentration (IC50) values in the assays that measure RNA-dependent DNA polymerase (RDDP), DNA-dependent DNA polymerase (DDDP), and ribonuclease H (RNase H) functions of HIV-1 RT. The most potent derivative was a nonsymmetric cholesterol-linked 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid analogue, compound 23, which demonstrated an IC50 value of 0.06 microM for inhibiting RDDP activity. Inhibition of DDDP and RNase H activity for this compound was demonstrated at concentrations that were over 100-fold of that for inhibiting RDDP activity. However, the potency of this active compound does not correlate in the whole virus assay, probably due to a lack of cellular entry. The cholesterol derivative, 23, also possesses HIV-1 protease inhibitory activity and belongs to a unique class of multifunctional HIV-1 inhibitors.

Enzymatic properties of two mutants of reverse transcriptase of human immunodeficiency virus type 1 (tyrosine 181-->isoleucine and tyrosine 188-->leucine), resistant to nonnucleoside inhibitors

A number of structurally diverse compounds have been shown to be potent inhibitors of the DNA polymerase activity of human immunodeficiency virus (HIV-1) reverse transcriptase (RT). The compounds can be grouped into two broad classes: nucleoside analogs and nonnucleoside inhibitors. The nonnucleoside inhibitors are quite specific for the polymerase activity of HIV-1 RT; they do not affect the polymerase activity of HIV-2 RT or the ribonuclease H (RNase H) activity of either HIV-1 RT or HIV-2 RT. Structural, biochemical, and genetic analyses showed that this group of inhibitors binds in a hydrophobic pocket near the polymerase active site. Mutations in amino acids that line this hydrophobic pocket, for example at tyrosine 181, tyrosine 188, or lysine 103, lead to enzymes that are resistant to the nonnucleoside inhibitors. We have investigated the enzymatic properties of two mutants of HIV-1 RT in which residues 181 and 188 were replaced by the corresponding amino acids in HIV-2 RT (tyrosine 181-->isoleucine and tyrosine 188-->leucine). The two tyrosine mutants closely resemble the wild-type HIV-1 RT in almost all the catalytic functions tested, including the heat stability, sensitivity of the DNA polymerase activity to inhibition by deoxynucleoside analogs, inhibition by the zinc chelator o-phenanthroline, and the Km values calculated for the DNA polymerase activity. There is, however, a slight difference in the effect of orthophenanthroline on the RNase H activity. In addition, there is a subtle disparity in the fidelity of DNA synthesis (analyzed by a mispair extension assay), thus indicating that these mutant RTs are not likely to confer any selective advantages or disadvantages to the variant virions over wild-type virus.

3,5,8-Trihydroxy-4-quinolone, a novel natural inhibitor of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2

The natural product of the Red Sea sponge Verongia sp., identified as 3,5,8-trihydroxy-4-quinolone, was found to be a potent inhibitor of the RNA-directed DNA synthesis of the reverse transcriptases (RTs) of human immunodeficiency viruses type 1 and type 2 (HIV-1 and HIV-2, respectively). This inhibition was unaffected by the nature of the primer template used for DNA synthesis. The DNA-dependent DNA polymerase activity was inhibited to a lesser extent, whereas the ribonuclease H (RNase H) function associated with both HIV RTs was only slightly inhibited. The inhibition by the trihydroxyquinolone is reversible and noncompetitive with respect to both substrates--dTTP and the template primer poly(rA)n.oligo(dT)12-18. The inhibitor binds HIV-1 RT with a high affinity (Ki = 0.46 microM). This compound was shown also to inhibit the catalytic activities of the RT of murine leukemia virus, establishing the general inhibitory effect on retroviral RTs. Introductions of acetyl or methoxy moieties at positions with potential activity have generated three synthetic analogs of the natural compound. Only one analog, 5,8-dimethoxy-4-quinolone, exhibited an inhibition potency similar to that of the unmodified compound. Analysis of the three analogs has led us to the conclusion that the hydroxyl group at the ortho position to the carbonyl group in the pyridinone ring is a key structural element for the inhibitory activity. Thus, it could well be that the inhibitor interacts with the enzyme through a hydrogen bond of this hydroxyl group. We hope that the identification of the inhibitory site of the compound might be an important step toward the rational design of new potent anti-HIV RT drugs.

The catalytic properties of the reverse transcriptase of the lentivirus equine infectious anemia virus

The reverse transcriptase (RT) of equine infectious anemia virus (EIAV) shares sequence similarity with the RTs of other lentiviruses, particularly with the RTs of human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2, respectively), the causative agents of acquired immunodeficiency syndrome (AIDS). There is a 41-42% sequence identity between EIAV RT and both HIV RTs (which have 61% sequence identity to each other). We have compared the enzymic properties of EIAV RT with those of HIV-1 RT. Several aspects of the activities of EIAV RT differ from the corresponding activities of HIV-1 RT. There are significant differences in the inhibition of the DNA polymerase activities by the deoxynucleoside triphosphate analogs, 3'-azido-2,3'-dideoxythymidine triphosphate, dideoxyTTP and dideoxyGTP and by the nonnucleoside inhibitor, tetrahydroimidazo[4,5,1-jk-1,4]benzodiazepin-2-(1H)-one and thione; in the dependence of DNA polymerase and RNase H activities on pH; in the inhibition of the DNA polymerase activities by the thiol-specific reagent N-ethylmaleimide; in the specific DNA polymerase activity; in the inhibition of the ribonuclease H activity by the zinc chelator orthophenanthroline. However, there are several cases in which EIAV RT and HIV-1 RT are more similar than was previously found for HIV-1 RT and HIV-2 RT. These include the Km values for the DNA polymerase activities, the heat stability of the DNA polymerase functions and the specific activity of the RNase H function.

Hexaprenoid hydroquinones, novel inhibitors of the reverse transcriptase of human immunodeficiency virus type 1

Activity against human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) in the organic extract of the Red Sea sponge Toxiclona toxius was traced by us to five novel natural compounds, namely toxiusol [1], shaagrockol B [3], shaagrockol C [4], toxicol A [6], all of which are sulfated hexaprenoid hydroquinones, and toxicol B [7], the p-hydroquinone derivative of compound 6. The hydrolysis of the two sulfated compounds 1 and 4 yielded the corresponding hydroquinones designated as compounds 2 and 5, and further oxidation of compound 7 afforded the corresponding p-quinone derivative, compound 8. All compounds exhibited inhibitory activity of both DNA polymerizing functions of HIV-1 RT but failed to inhibit the RT-associated ribonuclease H activity. Toxiusol [1] was found to be the most potent inhibitor of the RNA-dependent DNA polymerase function (with 50% inhibition obtained at 1.5 microM and 95% inhibition at 4.6 microM), whereas the DNA-dependent DNA polymerase was significantly less sensitive to the inhibitor (with 50% inhibition achieved at 6.6 microM and 95% inhibition only at 41.6 microM). The fact that compound 1 discriminates between the two DNA polymerase activities of the RT offers new prospects for developing potent and highly specific anti-RT compounds, since the RNA-dependent DNA polymerase activity of RT is the only unique function that is not expressed at significant levels in uninfected mammalian cells.

The interaction of illimaquinone, a selective inhibitor of the RNase H activity, with the reverse transcriptases of human immunodeficiency and murine leukemia retroviruses

Illimaquinone, a natural marine product, was shown by us to inhibit preferentially the ribonuclease H (RNase H) activity of the reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1). We have also shown that illimaquinone inhibits the RNase H activity of HIV-2 RT in addition to that of HIV-1 RT, murine leukemia virus RT, and Escherichia coli RNase H. Chemical modifications of HIV-1 RT by sulfhydryl-specific reagents, such as N-ethylmaleimide (NEM) have been demonstrated to specifically inhibit the RNase H activity of the enzyme. Since our previous studies have suggested that cysteine 280 in HIV-1 RT interacts with the sulfhydryl reagents, we have examined the possibility that illimaquinone interacts with the RT molecules via amino acid residues located in the vicinity of cysteine 280 in both HIV-1 and HIV-2 RTs. In the combined effect studies of illimaquinone and NEM, the two structurally unrelated compounds were shown to be mutually exclusive, exhibiting an antagonistic interaction with both HIV-1 and murine leukemia virus-associated RNase H activities. This implicates cysteine 280, in both HIV-1 and HIV-2 RTs, to be in close proximity to the putative binding site of the enzyme to illimaquinone. The above conclusion is further supported by the fact that the RNase H activity of an enzymatically active mutant of HIV-1 RT, in which cysteine 280 was replaced by serine, was substantially more resistant to illimaquinone than the corresponding activity of the wild-type enzyme. The fact that NEM failed to inhibit E. coli RNase H as opposed to illimaquinone highlights a major difference between the retroviral and bacterial RNase H.

The effects of cysteine mutations on the catalytic activities of the reverse transcriptase of human immunodeficiency virus type-1

The reverse transcriptase (RT) of the human immunodeficiency virus type 1 (HIV-1) has only 2 cysteine residues at positions 38 and 280. In order to investigate the role of these cysteines in the structure and function of the enzyme, we have previously modified each of the cysteines to serines employing site-directed mutagenesis. Two of the mutant forms of HIV-1 RT, the single mutant of cysteine 280 and a double mutant with both cysteines modified, were purified. In the present study we have compared the catalytic properties of the DNA-polymerizing and the ribonuclease H (RNase H) functions of the two mutant RTs to those of the native enzyme. The results indicate that the single mutant RT closely resembles the wild type enzyme in almost all the catalytic functions tested. The double cysteine mutant RT, on the other hand, exhibits several unique features. First, the specific activities of the RNA- and DNA-directed DNA synthesis are significantly lower than the corresponding activities of the other two enzymes. This probably results from the lower Vmax values exhibited by the double mutant RT, since the Km values calculated for all enzymes were similar. Second, the most outstanding differences are associated with the RNase H activity of the double mutant RT. The specific activity of RNase H is about 4-fold higher than the wild type and the single mutant RTs. Furthermore, the heat stability of the RNase H function of the double mutated RT is at least 15-fold higher than that of the other two RTs. The substantial resistance to heat denaturation is apparent only for the RNase H activity, since the DNA polymerizing function of the double mutant RT is as sensitive to heat denaturation as the other two proteins.

Inhibition of the reverse transcriptase activity and replication of human immunodeficiency virus type 1 by AS 101 in vitro

In a search for compounds active against human immunodeficiency virus type 1 (HIV-1), it was found that the novel low-molecular weight immunoenhancer ammonium trichloro(dioxyethylene-O,O'-) tellurate (AS101) suppresses production of HIV-1 in vitro. Treatment of HIV-1-infected peripheral blood mononuclear cells (PBMC) with increasing concentrations of AS101 resulted in substantial inhibition of virus production as measured by both reverse transcriptase (RT) activity and antigen presence in supernatants of treated cells. AS101 had no effect on PBMC viability, growth, or morphology up to a concentration of 15 microM for 14 days. To elucidate a possible mechanism for the inhibition of AS101, we have analyzed the effect of the drug on the catalytic functions associated with HIV RT, namely the RDDP, DDDP, and RNase H activities. RDDP and DDDP activities were impaired by the drug with calculated IC50 value of about 4 microM. On the other hand, the RNase H activity was less sensitive to AS101, with an apparent IC50 value of about 30 microM. The anti-HIV-1 activity of AS101 as reflected by inhibition of the different catalytic functions associated with viral RT, in the absence of drug-related toxicity to lymphocytes, together with its immunomodulating activity strongly argues in favor of its evaluation, as a therapeutic agent for patients with HIV infection.

The carotenoid halocynthiaxanthin: A novel inhibitor of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2

We have studied the effects of a natural carotenoid, identified as halocynthiaxanthin, on the enzymatic activities associated with the recombinant preparations of the reverse transcriptases (RTs) of human immunodeficiency viruses (HIV) types 1 and 2. The carotenoid was found to be a potent inhibitor of the RNA-dependent DNA polymerase activity (with 50% inhibition obtained at 5-7 microM halocynthiaxanthin), whereas the DNA-dependent DNA polymerase function of both RTs was significantly less sensitive to the inhibitor. Conversely, the ribonuclease H activity associated with the two HIV RTs was essentially insensitive to the carotenoid. The RNA-dependent DNA polymerase function of RT is the only unique activity found in this enzyme that is not expressed at significant levels in uninfected eukaryotic cells. Therefore, it is possible that this carotenoid may serve as a good candidate for the development of novel potent and specific inhibitors of HIV RT.

Catalytic properties of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2

The enzyme reverse transcriptase (RT) is crucial in the early steps of the life cycle of retroviruses. We have expressed in bacteria the RTs from human immunodeficiency viruses (HIV) types 1 and 2 in order to study the structural-functional relationships of these two multifunctional enzymes that share a relatively high degree of amino acid sequence homology. For comparison purposes, we have analyzed several catalytic functions of both enzymes. The two HIV RTs show a high similarity in many aspects studied but exhibit profound differences in several other properties. For instance, the specific RNase H activity of HIV-2 RT is about 10 times lower than the corresponding activity of HIV-1 RT. There are also significant dissimilarities between some of the apparent Km values calculated for the DNA polymerizing functions of both enzymes. Furthermore, the heat stability of the DNA polymerizing activity of HIV-2 RT is about 15-fold higher than that of HIV-1 RT. On the other hand, the susceptibility of the RNase H activities of the two enzymes to heat inactivation was found to be similar. Other treatments also enable discrimination between the RNase H and DNA polymerizing catalytic properties of the two enzymes (although both reverse transcriptases respond similarily). Thus, the RNase H activity was inactivated by N-ethylmaleimide, suggesting the possible involvement of cysteine residues in performing this activity, whereas the DNA polymerizing functions of the two enzymes were fully resistant to this chemical modification. The zinc chelator 1,10-phenanthroline affected the DNA polymerase activities of both enzymes to a significantly higher extent than the RNase H activity. In all, the two HIV RTs were shown to be substantially different one from the other in several of their properties and also distinct from other RTs thus far studied.

Illimaquinone, a selective inhibitor of the RNase H activity of human immunodeficiency virus type 1 reverse transcriptase

We studied the effect of the natural marine substance illimaquinone on the catalytic activities of reverse transcriptase from human immunodeficiency virus type 1. Illimaquinone inhibited the RNase H activity of the enzyme at concentrations of 5 to 10 microgram/ml, whereas RNA-dependent DNA polymerase and DNA-dependent DNA polymerase activities were considerably less susceptible to this inhibition. Two synthetic derivatives of illimaquinone, in which the 6'-hydroxyl group at the ortho position to one of carbonyl groups of the quinone ring was modified, proved ineffective in inhibiting the human immunodeficiency virus type 1 reverse transcriptase RNase H function, suggesting involvement of the 6'-hydroxyl group in blocking the enzymatic activity.

The inhibition of human immunodeficiency virus type 1 reverse transcriptase by avarol and avarone derivatives

We have analyzed the effects of several natural compounds related to avarols and avarones on the catalytic functions of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). The most potent substances, designated as avarone A,B and E and avarol F, inhibited indiscriminately the enzymatic activities of HIV-1 RT, namely the RNA-dependent and DNA-dependent DNA polymerase as well as the ribonuclease H. The inhibition of the DNA polymerase activity was found to be non-competitive with respect to either the template-primer or the deoxynucleotidetriphosphate. These studies suggest that the hydroxyl group at the ortho position to the carbonyl group at the quinone ring is involved in blocking the RT activity. The identification of the active site of the inhibitors will hopefully lead to the rational design of new potent anti-HIV drugs.