Biomedical subjects

X Dai

Publications and source records attributed to X Dai.

131 records · Page 8Linked to original sources

PubMedDate not supplied

In vitro evolution of a ribozyme that contains 5-bromouridine.

The Tetrahymena group I ribozyme was modified by replacing all 99 component uridine residues with 5-bromouridine. This resulted in a 13-fold reduction in catalytic efficiency in the RNA-catalyzed phosphoester-transfer reaction compared to the behavior of the unmodified ribozyme. A population of 10(13) variant ribozymes was constructed, each containing 5-bromouridine in place of uridine. Five successive 'generations' of in vitro evolution were carried out, selecting for improved phosphoester transferase activity. The evolved molecules exhibited a 27-fold increase in catalytic efficiency compared to the wild-type bromouridine-containing ribozyme, even exceeding that of the wild-type ribozyme in the non-brominated form. Three specific mutations were found to be responsible for this altered behavior. These mutations enhanced activity in the context of 5-bromouridine, but were detrimental in the context of unmodified uridine. The evolved RNAs not only tolerated but came to exploit the presence of the nucleotide analogue in carrying out their catalytic function.

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PubMedDate not supplied

Microarray-based compendium of hepatic gene expression profiles for prototypical ADME gene-inducing compounds in rats and mice in vivo.

To examine species-specific aspects of the induction of absorption, distribution, metabolism and excretion (ADME)-related genes, we used 25 000 gene oligonucleotide microarrays to construct a rodent gene-response compendium that compared hepatic gene expression profiles and developed consensus aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR) and pregnane X-receptor (PXR) ligand signatures relevant to drug clearance. Twenty-six inducer compounds were chosen from the literature. Rats and mice received one of six dose levels (log2 dose escalation, 32-fold dose range) of each compound daily for 3 days. Animals were necropsied 6-9 h after the last dose, and tissues were collected for RNA analysis. Hepatic gene expression profiles were obtained using Rosetta Resolver expression analysis system, and ADME-related genes were extracted. Cross-talk among nuclear receptors or hepatoxicity at high dose levels resulted in large signatures (usually >1000 genes at p < 0.01) for most compounds. After ADME gene transcript enrichment, agglomerative clustering separated AhR ligands from CAR/PXR ligands, but it was difficult to distinguish CAR from PXR ligands. Consensus signatures were derived from groups of AhR, CAR and PXR ligands; and cross-talk among responding genes was determined. Many compounds had distinct log dose-response profiles, and relative potencies for ligands were established. Robust responses by CYP1A1, CYP2B10 (CAR responsive in mice) and CYP2B15 (CAR responsive in rats) and CYP3A1 (PXR responsive in rats) were used to benchmark the relative potency of different ligands and to determine the relative selectivity for AhR, CAR or PXR. By using a compendium of gene expression profiles, we defined species-specific induction patterns across the ADME transcriptome.

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PubMedDate not supplied

Compendium of gene expression profiles comprising a baseline model of the human liver drug metabolism transcriptome.

Oligonucleotide microarrays were used to study the variability of pharmacokinetics and drug metabolism (PKDM)-related gene expression in 75 normal human livers. The objective was to define and use absorption, distribution, metabolism and excretion (ADME) gene expression variability to discern co-regulated genes and potential surrogate biomarkers of inducible gene expression. RNA was prepared from donor tissue and hybridized on Agilent microarrays against an RNA mass balanced pool from all donors. Clustering of PKDM gene sets revealed donors with distinct patterns of gene expression that grouped genes known to be regulated by the nuclear receptor, pregnane X-receptor (PXR). Fold range metrics and frequency distributions from the heterogeneous human population were used to define the variability of individual PKDM genes in the 75 human livers and were placed in context by comparing expression data with basal ADME gene expression variability in an inbred and diet/environment controlled population of 27 Rhesus livers. The most variable genes in the hepatic transcriptome were mainly related to drug metabolism, intermediary metabolism, inflammation and cell cycle control. Unique patterns of expression across 75 individuals of inducible ADME gene expression allowed their expression to be correlated with the expression of many other genes. Correlated genes for AhR, CAR and PXR responsive genes (CYP1A2, CYP2B6 and CYP3A4) were identified that may be co-regulated and, therefore, provide clues to the identity of surrogate gene or protein markers for CYP induction. In conclusion, microarrays were used to define the variable expression of hepatic ADME genes in a diverse human population, the expression variability of ADME genes was compared with the expression variability in an inbred population of Rhesus monkeys, and genes were defined that may be co-regulated with important inducible CYP genes.

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PubMedDate not supplied

Targeting tumours by adoptive transfer of immune cells.

1. Surgery, radiotherapy and chemotherapy are the most widely used and well-established modalities for treating malignant diseases. Surgery is used to excise solid tumours and radiotherapy/chemotherapy are used for the treatment of liquid tumours and for solid tumours where there is a risk of micrometastases. A major drawback for both radiotherapy and chemotherapy is their lack of specificity for tumour cells. Both these treatments can destroy normal bone marrow cells and result in severe side-effects. 2. The impairment of haemapoiesis due to bone marrow destruction combined with the use of toxins in chemotherapy that inhibit the proliferation of immune cells leaves many patients immunocompromised. This complicates the development of prophylactic (vaccine) strategies for tumours where patients are undergoing conventional therapy. 3. An alternative approach is to expand and activate tumour-specific immune cells in vitro that can then be adoptively transferred back in large numbers. This is defined as adoptive immunotherapy and has the advantage of potentially bypassing the immuno-inhibitory effects of conventional therapies. 4. Transferred immune cells have been shown to mediate tumour regression in patients by both direct and indirect mechanisms. The immune cells used include tumour reactive T lymphocytes and dendritic cells, which elicit tumour specific responses. 5. Many novel cell-based immunotherapeutic strategies developed in murine tumour models are now being applied in human clinical trials. The malignancies targeted include melanoma, chronic myelogenous leukaemia and breast, ovarian, colon and kidney cancers. In the present review, we discuss these novel cell-based strategies and the implications they have for the future treatment of human malignancies.

Adoptive Transfer↗

PubMedDate not supplied

Initial characterization of an antineoplastic, polysaccharide-rich extract of Mycobacterium bovis BCG, Tice substrain.

A purified hot-water extract from Mycobacterium bovis (BCG vaccine) has been found to have significant antitumor activity against a murine sarcoma in vivo, but not in vitro, suggesting that the active compound is behaving as an immunostimulant. The material, termed PS1, has an average molecular weight of 22.4 kDa, is freely soluble in water, but has low solubility in acetone or ethanol, and is remarkably heat-stable, as is the parent BCG vaccine in terms of high-dose antitumor activity. PS1 contains at least 50% carbohydrate, consisting mainly of glucose, galactose and mannose, and about 10% lipid that may correspond to phosphatidylinositol. It shares chemical and biological properties with an arabinomannan isolated from M. tuberculosis, but it contains only trace quantities of lipoarabinomannan (LAM). Crossed immunoelectrophoresis indicated that PS1 contains the mycobacterial antigen 89, but only a single, non-migrating precipitin arc appeared on immunoelectrophoresis against a standard anti-BCG serum. PS1 appears to be non-toxic in mice up to a dose of 5 mg/kg, while as little as 70 micrograms/kg is sufficient to inhibit tumor formation significantly.

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