Cell and Tissue Specific Metabolism of Nucleoside and Nucleotide Drugs: Case Studies and Implications for Precision Medicine.

Many clinically used antiviral drugs are nucleoside or nucleotide analog drugs, which have a unique mechanism of action that requires intracellular phosphorylation. This dependence on intracellular activation presents novel challenges for the discovery and development of nucleoside/nucleotide analog drugs. Contrary to many small molecule drug development programs that rely on plasma pharmacokinetics and systemic exposures, the precise mechanisms that result in efficacious intracellular nucleoside triphosphate concentrations must be understood in the process of nucleoside/nucleotide drug development. The importance is highlighted here, using the following as case studies: the herpes treatment acyclovir, the cytomegalovirus therapy ganciclovir, and human immunodeficiency virus (HIV) treatments based on tenofovir, which are also in use for HIV prophylaxis. For each drug, the specificity of metabolism that results in its activation in different cells or tissues is discussed, and the implications explored. Acyclovir's dependence on a viral enzyme for activation provides selective pressure for resistance mutations. Ganciclovir is also dependent on a viral enzyme for activation, and suicide gene therapy capitalizes on that for a novel oncology treatment. The tissue of most relevance for tenofovir activation depends on its use as treatment or as prophylaxis, and the pharmacogenomics and drug-drug interactions in those tissues must be considered. Finally, differential metabolism of different tenofovir prodrugs and its effects on toxicity risk are explored. Taken together, these examples highlight the importance of understanding tissue specific metabolism for optimal use of nucleoside/nucleotide drugs in the clinic. SIGNIFICANCE STATEMENT: Nucleoside and nucleotide analogue drugs are cornerstones in current antiviral therapy and prevention efforts that require intracellular phosphorylation for activity. Understanding their cell and tissue specific metabolism enables their rational, precision use for maximum efficacy.

Use of Virtual Reality Simulation to Identify Vision-Related Disability in Patients With Glaucoma.

Importance: Clinical assessment of vision-related disability is hampered by the lack of instruments to assess visual performance in real-world situations. Interactive virtual reality (VR) environments displayed in a binocular stereoscopic VR headset have been designed, presumably simulating day-to-day activities to evaluate vision-related disability. Objective: To investigate the application of VR to identify vision-related disability in patients with glaucoma. Design, Setting, and Participants: In a cross-sectional study, 98 patients with glaucoma and 50 healthy individuals were consecutively recruited from a university eye clinic; all participants were Chinese. The study was conducted between August 30, 2016, and July 31, 2017; data analysis was performed from December 1, 2017, to October 30, 2018. Exposures: Measurements of visual acuity, contrast sensitivity, visual field (VF), National Eye Institute 25-item Visual Function Questionnaire Rasch score, and VR disability scores determined from 5 VR simulations: supermarket shopping, stair and city navigations in daytime, and stair and city navigations in nighttime. Duration required to complete the simulation, number of items incorrectly identified, and number of collisions were measured to compute task-specific and overall VR disability scores. Vision-related disability was identified when the VR disability score was outside the normal age-adjusted 95% confidence region. Main Outcomes and Measures: Virtual reality disability score. Results: In the 98 patients with glaucoma, mean (SD) age was 49.8 (11.6) years and 60 were men (61.2%); in the 50 healthy individuals, mean (SD) age was 48.3 (14.8) years and 16 were men (32.0%). The patients with glaucoma had different degrees of VF loss (122 eyes [62.2%] had moderate or advanced VF defects). The time required to complete the activities by patients with glaucoma vs healthy individuals was longer by 15.2 seconds (95% CI, 5.5-24.9 seconds) or 34.1% (95% CI, 12.4%-55.7%) for the shopping simulation, 72.8 seconds (95% CI, 23.0-122.6 seconds) or 33.8% (95% CI, 10.7%-56.9%) for the nighttime stair navigation, and 38.1 seconds (95% CI, 10.9-65.2 seconds) or 30.8% (95% CI, 8.8%-52.8%) for the nighttime city navigation. The mean (SD) duration was not significantly different between the glaucoma and healthy groups in daytime stair (203.7 [93.7] vs 192.9 [89.1] seconds, P = .52) and city (118.7 [41.5] vs 117.0 [52.3] seconds, P = .85) navigation. For each decibel decrease in binocular VF sensitivity, the risk of collision increased by 15% in nighttime stair (hazard ratio [HR], 1.15; 95% CI, 1.08-1.22) and city (HR, 1.15; 95% CI, 1.08-1.23) navigations. Fifty-eight patients (59.1%) with glaucoma had vision-related disability in at least 1 simulated daily task; a higher proportion of patients had vision-related disability in nighttime city (27 of 88 [30.7%]) and stair (27 of 90 [30.0%]) navigation than in daytime city (7 of 88 [8.0%]) and stair (19 of 96 [19.8%]) navigation. The overall VR disability score was associated with the National Eye Institute 25-item Visual Function Questionnaire Rasch score (R2 = 0.207). Conclusions and Relevance: These findings suggest that vision-related disability is associated with lighting condition and task in patients with glaucoma. Virtual reality may allow eye care professionals to understand the patients' perspectives on how visual impairment imparts disability in daily living and provide a new paradigm to augment the assessment of vision-related disability.

Discovery of Genetic Variants of the Kinases That Activate Tenofovir in a Compartment-specific Manner.

Tenofovir (TFV) is used in combination with other antiretroviral drugs for human immunodeficiency virus (HIV) treatment and prevention. TFV requires two phosphorylation steps to become pharmacologically active; however, the kinases that activate TFV in cells and tissues susceptible to HIV infection have yet to be identified. Peripheral blood mononuclear cells (PBMC), vaginal, and colorectal tissues were transfected with siRNA targeting nucleotide kinases, incubated with TFV, and TFV-monophosphate (TFV-MP) and TFV-diphosphate (TFV-DP) were measured using mass spectrometry-liquid chromatography. Adenylate kinase 2 (AK2) performed the first TFV phosphorylation step in PBMC, vaginal, and colorectal tissues. Interestingly, both pyruvate kinase isozymes, muscle (PKM) or liver and red blood cell (PKLR), were able to phosphorylate TFV-MP to TFV-DP in PBMC and vaginal tissue, while creatine kinase, muscle (CKM) catalyzed this conversion in colorectal tissue. In addition, next-generation sequencing of the Microbicide Trials Network MTN-001 clinical samples detected 71 previously unreported genetic variants in the genes encoding these kinases. In conclusion, our results demonstrate that TFV is activated in a compartment-specific manner. Further, genetic variants have been identified that could negatively impact TFV activation, thereby compromising TFV efficacy in HIV treatment and prevention.

Dissimilarities in the metabolism of antiretroviral drugs used in HIV pre-exposure prophylaxis in colon and vagina tissues.

Attempts to prevent HIV infection through pre-exposure prophylaxis (PrEP) include topical application of anti-HIV drugs to the mucosal sites of infection; however, a potential role for local drug metabolizing enzymes in modulating the exposure of the mucosal tissues to these drugs has yet to be explored. Here we present the first report that enzymes belonging to the cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) families of drug metabolizing enzymes are expressed and active in vaginal and colorectal tissue using biopsies collected from healthy volunteers. In doing so, we discovered that dapivirine and maraviroc, a non-nucleoside reverse transcriptase inhibitor and an entry inhibitor currently in development as microbicides for HIV PrEP, are differentially metabolized in colorectal tissue and vaginal tissue. Taken together, these data should help to guide the optimization of small molecules being developed for HIV PrEP.

Comparison of retinal nerve fiber layer imaging by spectral domain optical coherence tomography and scanning laser ophthalmoscopy.

OBJECTIVE: To compare the area and the angular width of localized retinal nerve fiber layer (RNFL) defects imaged by confocal scanning laser ophthalmoscopy (CSLO) and optical coherence tomography (OCT) and to evaluate their agreement. DESIGN: Cross-sectional study. PARTICIPANTS: Fifty-one eyes of 41 glaucoma patients. METHODS: Sixty-one distinctive, localized RNFL defects (17 superior and 44 inferior RNFL defects) detected in RNFL photographs imaged by a CSLO were identified. These patients underwent RNFL imaging with a spectral-domain OCT. The RNFL thickness deviation maps (50×50 pixels) generated by the OCT revealed the locations of abnormal RNFL thicknesses with abnormal pixels denoted in red (RNFL thickness less than the lower 99% normal distribution) or yellow (RNFL thickness less than the lower 95% normal distribution). The RNFL thickness deviation maps were aligned and overlaid with the corresponding CSLO RNFL photographs. The area and the angular width of RNFL defects from the corresponding retinal regions in the CSLO RNFL photographs and the OCT RNFL thickness maps were measured and compared. Their agreement was analyzed with the Bland-Altman plot. MAIN OUTCOME MEASURES: The area and the angular width of RNFL defects and the agreement of RNFL defects measurements between OCT images and CSLO RNFL photographs. RESULTS: The area and the angular width of RNFL defects measured with the CSLO RNFL photographs were 1.11 ± 0.57 mm² and 23.80 ± 10.38°, respectively, which were significantly smaller than those measured by the OCT RNFL thickness deviation map when abnormal RNFL thickness was defined as less than the lower 95% centile ranges (2.27 ± 0.92 mm² and 74.16 ± 28.74°, respectively; both P < 0.001). When abnormal RNFL thickness was defined as less than the lower 99% centile ranges, a significant difference in angular width (42.11 ± 22.19°; P<0.001), but not in area (1.19 ± 0.68 mm²; P = 0.444) was found between the 2 imaging methods. Bland-Altman plots revealed that a larger RNFL defect was associated with a greater difference in angular width between OCT and CSLO RNFL photography measurements. CONCLUSIONS: The agreement of RNFL defect measurements between CSLO RNFL photography and OCT was poor. The OCT RNFL thickness deviation map could reveal additional RNFL abnormalities not detectable by CSLO RNFL photography. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Gastric cancer cell detection in peritoneal washing: cytology versus RT-PCR for CEA transcripts.

This study investigates the sensitivity and specificity of cytology, qualitative, and real-time RT-PCR methods in free cancer cell detection of peritoneal washing from gastric cancer patients. Peritoneal washings were collected from 65 gastric cancer patients for routine cytology and total RNA extraction for qualitative and real-time RT-PCR for CEA. The sensitivity and false-positive rate was 51.1%, 0% for cytology, 48.9% and 5% for qualitative RT-PCR for CEA, and 42.5% and 5% for real-time RT-PCR for CEA. The qualitative and real time RT-PCR results show high concordance rate (89.7%). The highest sensitivity was obtained by the combination of cytology with qualitative RT-PCR for CEA (70.2%). RT-PCR results were positive in 63.6% of cytologic "atypia" cases. Combination of cytology and either of the RT-PCR methods resulted in significantly higher sensitivity than any one of the three methods alone (P < 0.05). There was no definite advantage of the real-time RT-PCR over the conventional RT-PCR.