Background: Competitive displacement of a weakly virulent pathogen strain by a more virulent strain is one route to disease emergence. However the mechanisms by which pathogens compete for access to hosts are poorly understood. Among vector-borne pathogens, variation in the ability to infect vectors may effect displacement. The current study focused on competitive displacement in dengue virus serotype 3 (DENV3), a mosquito-borne pathogen of humans. In Sri Lanka in the 1980's, a native DENV3 strain associated with relatively mild dengue disease was displaced by an invasive DENV3 strain associated with the most severe disease manifestations, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), resulting in an outbreak of DHF/DSS. Here we tested the hypothesis that differences between the invasive and native strain in their infectivity for Aedes aegypti mosquitoes, the primary vector of DENV, contributed to the competitive success of the invasive strain

A classic response to systemic hypoxia is the increased production of red blood cells due to hypoxia-inducible factor (HIF)-mediated induction of erythropoietin (EPO). EPO is a glycoprotein hormone that is essential for normal erythropoiesis and is predominantly synthesized by peritubular renal interstitial fibroblast-like cells, which express cellular markers characteristic of neuronal cells and pericytes. To investigate whether the ability to synthesize EPO is a general functional feature of pericytes, we used conditional gene targeting to examine the von Hippel-Lindau/prolyl-4-hydroxylase domain (PHD)/HIF axis in cell-expressing neural glial antigen 2, a known molecular marker of pericytes in multiple organs. We found that pericytes in the brain synthesized EPO in mice with genetic HIF activation and were capable of responding to systemic hypoxia with the induction of Epo. Using high-resolution multiplex in situ hybridization, we determined that brain pericytes represent an important cellular source of Epo in the hypoxic brain (up to 70% of all Epo-expressing cells). We furthermore determined that Epo transcription in brain pericytes was HIF-2 dependent and cocontrolled by PHD2 and PHD3, oxygen- and 2-oxoglutarate-dependent prolyl-4-hydroxylases that regulate HIF activity. In summary, our studies provide experimental evidence that pericytes in the brain have the ability to function as oxygen sensors and respond to hypoxia with EPO synthesis. Our findings furthermore suggest that the ability to synthesize EPO may represent a functional feature of pericytes in the brain and kidney.

Some DDT analogs are estrogenic, particularly o,p'-DDT, which comprises approximately 15-20% of the commercial DDT mixture. Whether this compound or its metabolites are active has not been established. In fact, the data obtained thus far are more confusing than enlightening. For example, CCl4 pretreatment of immature female rats has been reported to inhibit or enhance estrogenic activity of o,p'-DDT, and SKF-525A pretreatment has been reported to enhance or not alter the estrogenic effect. Although o,p'-DDT inhibits binding of estradiol to the estrogen receptor from rat or human at low levels (approximately 1-10 micrometer) in vitro, higher levels are required to inhibit nuclear binding of [3H] estradiol in incubated whole uteri. Futhermore, o,p'-DDT appears to be neither estrogenic nor antiestrogenic in an in vitro estrogen assay. Methoxychlor appears to be "activated" by metabolism, and it is probable that phenolic metabolites are responsible for its estrogenic activity. Since chlorinated hydrocarbons often enhance the metabolism of steroids and may reduce circulating levels of steroids, interactions of the exogenous hormonally active agents with steroid receptors may be self-potentiating in vivo.

The no observable effect level was greater than six biweekly bilateral 0.50 mg/eye doses or two biweekly bilateral 1.0 mg/eye doses. These pharmacokinetic and safety data support monthly 1 or 2 mg/eye dose regimens in human clinical trials.

DON (6-diazo-5-oxo-L-norleucine), a glutamine antagonist, has been subjected to limited clinical trials since 1957. Use of the drug in adults has been curtailed due to sparse reports of effectiveness as well as its dose-limiting toxicities, i.e., severe nausea, vomiting and mucositis. In earlier studies, children given DON orally in combination with 6-mercaptopurine had significant prolongation of remission of acute leukemias during maintenance therapy. As DON is acid-labile and relatively unstable in solution, oral administration does not appear to be ideal for DON. In the trial described in this report, i.v. DON therapy was studied, using i.v. chlorpromazine to control vomiting, in 20 children, 17 of whom were evaluable following treatment at DON dose levels ranging from 150 mg/m2 to 520 mg/m2. Nausea and vomiting, the dose-limiting toxicity for adults, was controlled with chlorpromazine. Mucositis, which has also been observed in adults, did not occur in the children given DON i.v. A maximum tolerated dose was not defined; however, the projected maximum tolerated dose appears to be in excess of 450 mg/m2. DON was measured in plasma using a rapid-sampling HPLC procedure. The total body clearance, plasma t1/2, and area under the plasma concentration curve (AUC) were calculated using a noncompartmental method. The drug is rapidly cleared from plasma (t 1/2 = 3 h), and its volume of distribution is approximately twice that of total body water in children. These pharmacokinetic data, differ from that of adults reported by others. Specifically, the plasma t 1/2 for children is longer: total body clearance (Cl), and volume of distribution at steady state (Vss) are greater. In addition, no dose dependency of t 1/2, Cl or Vss was observed in this study, and the DON pharmacokinetics were linear and predictable. Five of nine children with acute leukemia showed improvement, though insufficient for classification as partial response, and five of eight children with solid tumors also showed improvement. Further trials using DON in combination with thiopurines or other agents appear indicated.

N-(5,5-Diacetoxypent-1-yl)doxorubicin (1b) is an intensely cytotoxic doxorubicin analogue that retains full potency against tumor cells that express elevated levels of P-glycoprotein and are resistant to doxorubicin. 1b was designed to be hydrolyzed in the presence of carboxylate esterases to N-(5-oxypent-1-yl)doxorubicin, an aldehyde capable of existing in equilibrium with a cyclic carbinolamine. To investigate the structural determinants of potency for 1b, we have prepared a series of chemically related compounds in which various omega-[bis(acetoxy)]alkyl or omega-[bis(acetoxy)]alkoxyalkyl groups are substituted at the 3'-amino position of the daunosamine sugar. These groups were selected to assess the effect of chain length, oxygen substitution, and carbinolamine ring size on analogue potency. The compounds were evaluated for their ability to inhibit the in vitro growth of the following cell lines: (a) Chinese hamster ovary (CHO) cells, (b) a CHO cell mutant 100-fold resistant to doxorubicin that expresses elevated levels of P-glycoprotein, (c) a murine ductal cell pancreatic adenocarcinoma (Panc 02), and (d) a murine mammary carcinoma (CA 755). The most potent members of the series were those that could form a straight chain aldehyde intermediate after esterase-mediated hydrolysis of the omega-bis(acetoxy) groups and give rise to 5- or 6-membered ring carbinolamines. Analogues capable of forming 7-, 8-, or 9-membered carbinolamines were markedly less active. The N-methyl derivative of 1b, which cannot give rise to a cyclic carbinolamine, was 2 orders of magnitude less potent than 1b. A branched chain analogue, 1f, which contained a tertiary carbon atom adjacent to the omega-bis(acetoxy) groups, was also substantially less active than its nonbranched counterpart, 1a. These findings suggest that the chain length of the 3'-amino substituents and the ability of the derived aldehydes to form 5- or 6-membered carbinolamines are critical determinants of biologic potency.

Natalizumab is a monoclonal antibody to human alpha4 integrin indicated for treatment of multiple sclerosis and Crohn's disease that prevents extravasation of leukocytes into surrounding tissues and their involvement in inflammation. Because alpha4 integrins and their receptors are involved in hematopoiesis and immune cell trafficking, natalizumab may interfere with these processes. We evaluated the effects of natalizumab on immune function in monkeys using in vitro and in vivo studies. Consistent with the pharmacologic effects of natalizumab, dose-related increases in white blood cell counts and spleen weights were observed. Administration to monkeys did not result in statistically significant alterations in the percentages of circulating B-cells, T-cells, T-cell subsets (CD4, CD8), or stem cells (CD34). A modest and highly variable delay in the primary humoral response to T-cell-dependent antigens was observed. Ex vivo studies using cells from natalizumab-treated monkeys demonstrated that treatment did not alter immune regulatory or effector cell functions in blood lymphocytes or spleen cells. A similar lack of effect on these functions was observed in vitro following treatment of PBMC and monocytes from human donors. Overall, natalizumab was well tolerated in monkeys, demonstrated the expected pharmacologic effect on cell trafficking, and showed no adverse effect on immune cell function.

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