Publications

A conic pyroelectric detector is employed to measure the effective reflectances of powder beds of metals, SiC, WC, and graphite. The experimental results are compared with numerical solutions of the radiation transfer equation in a half-infinite homogeneous body with effective radiative properties. The effective albedo and phase function are theoretically estimated by the model of opaque particles with specularly or diffusely reflecting surfaces in the assumption of geometrical optics. The studied powder beds with particles of several tens of microns in diameter are generally described by the model where specular reflection by particle surfaces is assumed corresponding to refraction and extinction indices of materials in the dense form. The model does not apply to semitransparent particles of SiC. The powder beds of submicron particles of SiC and WC are highly agglomerated and consist of clusters of particles with diameters of several tens of microns. A submicron powder bed is found to be considerably less reflective than a micron-sized powder bed of the same material. This is described by the model where the agglomerates of submicron particles are treated as large particles with diffusely reflecting surfaces. The effective normal-hemispherical reflectance of a micron-sized powder bed correlates with the hemispherical reflectance of dense material. The observed differences between the experiment and the model can be explained by a systematic error at calibration, oxidation of materials, and diffraction effects.

The thymidine (dThd) kinase (TK) encoded by herpes simplex virus type 1 (HSV-1) is not only endowed with dThd kinase, but also with thymidylate (dTMP) kinase and 2'-deoxycytidine (dCyd) kinase (dCK) activity. HSV-1 TK also recognizes a variety of antiherpetic guanine nucleoside analogues such as acyclovir (ACV), ganciclovir (GCV), lobucavir (LBV), penciclovir (PCV), and others (i.e., A5021). Site-directed mutagenesis of the highly conserved Ala-167 to Tyr in HSV-1 TK completely abolished TK, dTMP-K, and dCK activity, but maintained ACV-, GCV-, LBV-, PCV-, and A5021-phosphorylating capacity. A variety of 5-substituted pyrimidine nucleoside substrates, but also a number of selective HSV-1 TK inhibitors structurally related to thymine lost significant binding affinity for the mutant enzyme and did not markedly compete with GCV phosphorylation by the mutant enzyme. These findings could be explained by computer-assisted modeling data that revealed steric hindrance of the pyrimidine ring in the HSV-1 TK active site by the large 4-hydroxybenzyl ring of 167-Tyr, while the positioning of the purine ring of guanine-based HIV-1 TK substrates in the active site was kept virtually unaltered. Surprisingly, the efficiency of conversion the antiherpetic 2'-deoxyguanosine analogues ACV, GCV, LBV, PCV, and A5021 to their phosphorylated forms by the A167Y mutant HSV-1 TK was far more pronounced than for the wild-type enzyme. Therefore, the single A167Y mutation converts the wild-type HSV-1 TK from a predominantly pyrimidine nucleos(t)ide kinase into a virtually exclusive purine (guanine) nucleoside analogue kinase.

The redesign of azamacrocyclic CXCR4 chemokine receptor antagonists resulted in the discovery of novel, small molecule, orally bioavailable compounds that retained T-tropic (CXCR4 using, X4) anti-HIV-1 activity. A structure-activity relationship (SAR) was determined on the basis of the inhibition of replication of X4 HIV-1 NL4.3 in MT-4 cells. As a result of lead optimization, we identified (S)-N'-((1H-benzo[d]imidazol-2-yl)methyl)-N'-(5,6,7,8-tetrahydroquinolin-8-yl)butane-1,4-diamine (AMD070) 2 as a potent and selective antagonist of CXCR4 with an IC(50) value of 13 nM in a CXCR4 125I-SDF inhibition binding assay. Compound 2 inhibited the replication of T-tropic HIV-1 (NL4.3 strain) in MT-4 cells and PBMCs with an IC(50) of 2 and 26 nM, respectively, while remaining noncytotoxic to cells at concentrations exceeding 23 microM. The pharmacokinetics of 2 was evaluated in rat and dog, and good oral bioavailability was observed in both species. This compound represents the first small molecule orally bioavailable CXCR4 antagonist that was developed for the treatment of HIV-1 infection.

We investigated and compared the reproducibility, accuracy, detection limits, and dynamic ranges of two commercial kits for quantification of RNA viral load using a titrated virus stock (laboratory strain HIV-1 IIIB) and 107 plasma samples of 25 HIV-1-infected patients. The high reproducibility of both methods (SD = 0.2-0.3 log for both methods) allowed reliable detection of a 0.5 log change in RNA viral load. Both methods had a similar detection limit (at least 10(3) RNA copies/ml plasma) and a dynamic range that extended over a 5 log (AMPLICOR) or a 6 log (NASBA) range of HIV-1 input. For HIV-1 IIIB, the viral load was compatible with measurements of virus-associated p24 antigen. For 21 patients (91 samples), the RNA viral load was similar with both methods differing by no more than 0.5 log. For four patients, the difference in viral load between the two methods was > 0.5 log for all 16 samples. For three of these patients, this could be explained by mismatches with primers or probes in the gag sequence: there was no correlation to the viral subtype. The RNA viral load determination was highly sensitive compared with p24 antigen measurement (> 95% of patients had a detectable viral load vs. 40% who had a detectable p24 level), but in the p24-positive samples the correlation between the antigen level and the RNA viral load was of only borderline significance. We also found that the viral RNA in whole blood was stable for at least 48 h during transport at room temperature. These observations show that both the NASBA HIV-1 RNA QT test and the AMPLICOR HIV monitor test are reliable parameters of the viral load, with great promise for their use as potential surrogate markers.