Synthesis, biological activity, and conformational analysis of four seco-D-15,19-bisnor-1alpha,25-dihydroxyvitamin D analogues, diastereomeric at C17 and C20.

The synthesis of four CD-ring-modified 19-nor-1alpha, 25-dihydroxyvitamin D(3) derivatives lacking C15, referred to as 6C analogues, and diastereomeric at C17 and C20 is described. The synthesis involves an Ireland-Claisen rearrangement of a 3-methyl-substituted ester of (1R)-3-methyl-2-cyclohexen-1-ol as the key step, followed by elaboration of the side chain, transformation into a C8 cyclohexanone derivative, and final Wittig-Horner coupling with the 19-nor A-ring phosphine oxide. Despite possessing a more flexible side chain than the parent hormone, biological evaluation showed an unexpected superagonistic antiproliferative and prodifferentiating activity (10-50 times higher as compared to that of 1alpha,25(OH)(2)D(3)) for the diastereomer with the "natural" configuration at C17 and C20. The other diastereomers exhibit a 25-90% decrease in activity. All four analogues show a decreased binding affinity (45% or less), and their calcemic activity is 4-400 times less than that of 1alpha,25(OH)(2)D(3). The conformational behavior of their side chain was studied using molecular mechanics calculations, and the result is presented as volume maps. A relative activity volume was determined by subtraction of the volume map of the least active analogue from the volume map of the most active one. This shows three regions corresponding to preferred orientations in space of the side chain of the active analogue. One of these regions was found to overlap with the region that is preferentially occupied by the most active of the four diastereomeric 22-methyl-substituted 1alpha,25(OH)(2)D(3) analogues.     

Characterization of the activation pathway of phosphoramidate triester prodrugs of stavudine and zidovudine.

The phosphoramidate triester prodrugs of anti-human HIV 2', 3'-dideoxynucleoside analogs (ddN) represent a convenient approach to bypass the first phosphorylation to ddN 5'-monophosphate (ddNMP), resulting in an improved formation of ddN 5'-triphosphate and, hence, higher antiviral efficacy. Although phosphoramidate derivatization markedly increases the anti-HIV activity of 2',3'-didehydro-2', 3'-dideoxythymidine (d4T) in both wild-type and thymidine kinase-deficient CEM cells, the concept is far less successful for the 3'-azido-2',3'-dideoxythymidine (AZT) triesters. We now investigated the metabolism of triester prodrugs of d4T and AZT using pure enzymes or different biological media. The efficiency of the first activation step, mediated by carboxylesterases, consists of the formation of the amino acyl ddNMP metabolite. The efficiency of this step was shown to be dependent on the amino acid, alkyl ester, and ddN moiety. Triesters that showed no conversion to the amino acyl ddNMP accumulated as the phenyl-containing intermediate and had poor, if any, anti-HIV activity. In contrast to the relative stability of the triesters in human serum, carboxylesterase-mediated cleavage of the prodrugs was found to be remarkably high in mouse serum. The subsequent conversion of the amino acyl ddNMP metabolite to ddNMP or ddN was highest in rat liver cytosolic enzyme preparations. Although L-alaninyl-d4TMP was efficiently converted to d4TMP, the main metabolite formed from L-alaninyl-AZTMP was the free nucleoside (AZT), thus explaining why d4T prodrugs, but not AZT prodrugs, retain anti-HIV activity in HIV-infected thymidine kinase-deficient cell cultures. The rat liver phosphoramidase responsible for the formation of ddNMP was shown to be distinct from creatine kinase, alkaline phosphatase, and phosphodiesterase.     

Inhibitory activity of diarylamidine derivatives on murine leukemia L1210 cell growth

Summary A series of 96 diarylamidine (and diarylimidazoline) derivatives were evaluated for their inhibitory effects on the growth and DNA synthesis of murine leukemia L1210 cells. The amidino- and imidazolino-substituted aryl moieties of the compounds consisted of phenyl, indole, indene, benzofuran, benzo[b]thiophene or benzimidazole. Several of these compounds were found to inhibit L1210 cell proliferation with an ID₅₀ (50% inhibitory dose) of 1 g/ml or lower. Structure-function analysis revealed that the antitumor cell activity of the diarylamidines depended on the planarity of the molecule, the presence of amidino- (or, preferably, imidazolino-) groups on both aryl moieties, the nature of the bridge connecting the two aryl moieties (preferably no bridge at all, phenoxy or ethene) and, finally, the nature of the aryl moieties (preferably, benzofuran or benzo[b]thiophene). Hence, compound 20 (6-(2-imidazolin-2-yl)-2-[4-(2-imidazolin-2-yl)phenyl] benzo[b]thiophene) emerged as the most potent inhibitor of L1210 cell growth (ID₅₀: 0.21 g/ml). Its inhibitory potency was similar to that of the well-known trypanocidal drug ethidium bromide (compound 98). For all diarylamidine derivatives taken together, some correlation (r = 0.612) was noted between the log ID₅₀ for L1210 cell proliferation and the log ID₅₀ for L1210 cell DNA synthesis (as monitored by [methyl ³H]dThd incorporation). These findings suggest that the inhibitory effects of the diarylamidines on L1210 cell proliferation may at least partially reside in an inhibition of DNA synthesis. Compound 41 (2,2-vinylenedi-1-benzofuran-5-carboxamidine), that exhibited a potent antitumor activity in vitro (ID₅₀: 1.5 g/ml), was further evaluated for its antitumor efficacy in vivo and found to increase the median survival time of L1210 cell-inoculated BDF₁ mice up to 204%, if administered at a dose of 200 mg/kg.     

Influence of (E)-5-(2-Bromovinyl)-2′-deoxyuridine on corneal epithelium healing

When applied as 0.1% or 0.5% eye drops 9 times a day at hourly intervals, BVDU [(E)-5-(2-bromovinyl)-2-deoxy-uridine] did not retard the regeneration of rabbit corneal epithelium. Nor did it exert any toxic effects on the cells. Likewise, IDU (5-iodo-2-deoxyuridine) 0.1% eye drops did not significantly reduce the rate of epithelium wound closure. However, IDU produced toxic alterations in the cells.     

Epidemiology of Travelers— Diarrhea: Details of a Global Survey

Background Recent epidemiologic data on travelers— diarrhea (TD) are essential for the evaluation of conventional and future prophylactic and therapeutic measures.
Methods To determine the epidemiology, including risk factors, impact and quality-of-life evaluation of TD, a cross-sectional survey was conducted over 12 months at the airports of Mombasa (Kenya), Goa (India), Montego Bay (Jamaica) and Fortaleza (Brazil) by distributing questionnaires to visitors just prior to their flying home. The study period was March 1996 to July 1998.
Results Overall, 73,630 short-term visitors completed a questionnaire. The total diarrhea attack rate varied between a high of 54.6% in Mombasa and a low of 13.6% in Fortaleza, but only between 31.5% and 5.4% of all travelers had classic TD. The 14-day incidence rates varied between 19.5% and 65.7%. Few travelers meticulously avoided potentially dangerous food items, although in India and Kenya most travelers avoided those considered most dangerous. Risk factors were stays exceeding 1 week, age between 15 and 30 years, and residence in the UK. The impact, measured as incapacity or quality-of-life scores, was very considerable.
Conclusions TD continues to affect vacationers and business travelers as frequently as it did some 20 years ago. Compliance with recommendations to reduce exposure to pathogens by avoiding dangerous food items is poor among travelers from all countries. Implementation of food safety education programs may be difficult to achieve.     

Synthesis and antiviral activity of novel N-substituted derivatives of acyclovir

Novel N-substituted derivatives of acyclovir (1a) were synthesized and evaluated for their antiviral, antimetabolic, and antitumor cell properties in vitro. Monomethylation of 1a at positions 1, 7, and N-2 gave compounds 2-4, respectively. When positions 1 and N-2 were linked together by an isopropeno group, the tricyclic 9-[(2-hydroxyethoxy)methyl]-1,N-2-isopropenoguanine (5) was obtained. Compound 5 was then further methylated at positions N-2 and 7 to give 6 and 7, respectively. None of the new acyclovir derivatives showed any appreciable antimetabolic or antitumor cell activity. However, compounds 2 and 5 exhibited a marked antiherpetic activity. Their activity spectrum was similar to that of acyclovir, and their selectivity as inhibitors of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) was at least as great as, if not greater than, that of acyclovir.     

Recombinant LSDV Strains in Asia: Vaccine Spillover or Natural Emergence?

From 2017 to 2019, several vaccine-like recombinant strains of lumpy skin disease virus (LSDV) were discovered in Kazakhstan and neighbouring regions of Russia and China. Shortly before their emergence, the authorities in Kazakhstan launched a mass vaccination campaign with the Neethling-based Lumpivax vaccine. Since none of the other countries in the affected region had used a homologous LSDV vaccine, it was soon suspected that the Lumpivax vaccine was the cause of these unusual LSDV strains. In this study, we performed a genome-wide molecular analysis to investigate the composition of two Lumpivax vaccine batches and to establish a possible link between the vaccine and the recent outbreaks. Although labelled as a pure Neethling-based LSDV vaccine, the Lumpivax vaccine appears to be a complex mixture of multiple CaPVs. Using an iterative enrichment/assembly strategy, we obtained the complete genomes of a Neethling-like LSDV vaccine strain, a KSGP-like LSDV vaccine strain and a Sudan-like GTPV strain. The same analysis also revealed the presence of several recombinant LSDV strains that were (almost) identical to the recently described vaccine-like LSDV strains. Based on their InDel/SNP signatures, the vaccine-like recombinant strains can be divided into four groups. Each group has a distinct breakpoint pattern resulting from multiple recombination events, with the number of genetic exchanges ranging from 126 to 146. The enormous divergence of the recombinant strains suggests that they arose during seed production. The recent emergence of vaccine-like LSDV strains in large parts of Asia is, therefore, most likely the result of a spillover from animals vaccinated with the Lumpivax vaccine.     

Interval Colorectal Cancers: What and Why

An increasing number of studies now indicate that colonoscopic examination is not perfect in preventing colorectal cancer (CRC), especially of the proximal colon. Several factors can be implicated in the occurrence of interval CRCs—further referred to as postcolonoscopy CRCs-, such as missed, incompletely resected lesions and newly developed cancers. Missed lesions represent by far the dominant cause of postcolonoscopy CRCs, with nonpolypoid (flat or depressed) neoplasms and sessile serrated polyps playing a significant role. Molecular events underlying progression of such lesions may further augment the cancer risk. In this article, we review the literature about postcolonoscopy CRC risk and the most common explanations. We discuss potential implications, paying special attention to improvements required in education and training.