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Biomedical subjects

K K Sidhu

Publications and source records attributed to K K Sidhu.

8 recordsLinked to original sources
PubMed2005

Exogenous expression of glucagon-like peptide 1 receptor and human insulin in AtT-20 corticotrophs confers cAMP-mediated gene transcription and insulin secretion.

The insulinotrophic effects of glucagon-like peptide 1 (GLP-1) are mediated by its seven-transmembrane receptor (GLP-1R) in pancreatic beta-cells. We have transiently transfected the GLP-1R and a proopiomelanocortin (POMC) promoter-driven human preproinsulin gene vector (pIRES) into the AtT-20 pituitary corticotrophic cell line, to investigate the possibility of creating a regulated, insulin-expressing cell line. Receptor expression was confirmed by RT-PCR and functionality was demonstrated by measuring changes in cAMP levels in response to GLP-1. Rapid (5 min) stimulation of cAMP production was observed with 100 nM GLP-1, 24 h after transfection of 2 microg GLP-1R DNA. AtT-20 cells co-transfected with GLP-1R and human glycoprotein hormone alpha-subunit or rat POMC promoters revealed GLP-1-stimulated cAMP activation of transcription. Co-transfection of the pIRES vector with the GLP-1R resulted in GLP-1-stimulated activation of POMC promoter-driven preproinsulin gene transcription but insulin secretion was not detected. However, using an adenoviral expression system to infect AtT-20 cells with GLP-1R and the preproinsulin gene (including 120 bp of its own promoter) resulted in a 6.4 +/- 0.6-fold increase in cAMP and a 4.9 +/- 0.8-fold increase in insulin secretion in response to 100 nM GLP-1. These results demonstrate, for the first time, functional GLP-1R-mediated preproinsulin gene transcription and secretion in a transplantable cell line.

Cell Line↗
PubMed2003

Absence of pituitary adenylate cyclase-activating polypeptide-stimulated transcription of the human glycoprotein alpha-subunit gene in LbetaT2 gonadotrophs reveals disrupted cAMP-mediated gene transcription.

Hormone regulation of anterior pituitary expression of the common glycoprotein hormone alpha-subunit (alphaGSU) is mediated by multiple response elements residing in the first -435 bp of the human promoter. In rat pituitary cells and mouse alphaT3-1 precursor gonadotrophs, the human alphaGSU promoter is strongly responsive to activators of the adenylyl cyclase/cAMP pathway, such as the hypothalamic releasing hormone, pituitary adenylate cyclase-activating polypeptide (PACAP) and forskolin (an adenylyl cyclase activator). However, the role of PACAP and cAMP in regulating alphaGSU transcription in the more differentiated LbetaT2 gonadotroph is unclear. Here, we investigate the regulation of the human alphaGSU promoter by PACAP and forskolin in LbetaT2 and alphaT3-1 gonadotrophs. PACAP failed to stimulate alphaGSU promoter activity or cAMP production in LbetaT2 cells, in marked contrast to alphaT3-1 cells. LbetaT2 gonadotrophs expressed extremely low levels of any PACAP type 1 receptors (PAC(1)-R) isoform by RT-PCR and lacked PAC(1)-R by radioligand binding. Forskolin stimulated the alphaGSU promoter in LbetaT2 cells, but by less than 30% of the response seen in alphaT3-1 gonadotrophs. This blunted cAMP transcriptional effect was not due to different levels of cAMP generation, or altered expression of the cAMP target proteins CREB, Akt, CBP or ICER. However, only LbetaT2 cells showed detectable expression of the protein kinase A type IIalpha regulatory subunit. Binding of activating transcription factor-2 and phosphorylated CREB to the consensus CRE was observed in both LbetaT2 and alphaT3-1 gonadotrophs, yet forskolin failed to stimulate either CRE- or CREB-mediated transcription in LbetaT2 cells. Collectively, these data demonstrate the lack of functional PACAP receptors in LbetaT2 gonadotrophs, and a pronounced attenuation in the responsiveness of this differentiated gonadotroph cell line to cAMP stimulus.

Animals↗
PubMed1994

Synthesis and cytotoxic evaluation of some cyclic arylidene ketones and related oximes, oxime esters, and analogs.

A number of arylidene derivatives of alicyclic ketones and some corresponding oximes, oxime esters, and related compounds were prepared as candidate cytotoxic agents. All of the compounds were evaluated against murine L1210 lymphoid leukemia cells. In general, cytotoxicity was greatest with the alpha,beta-unsaturated ketones and diminished with the oximes, and the oxime esters had little or no activity in this screen. When the same compounds were examined in both the in vitro L1210 and P388 leukemia screens, in the majority of cases the L1210 cells were more sensitive to these derivatives. Over half of the compounds prepared were evaluated against approximately 55 human tumors in vitro and showed selective toxicity toward one or more groups of neoplastic diseases, particularly leukemia. Some correlations between structure and bioactivity were discerned. The cytotoxicity screening and stability studies of representative compounds suggested that the ketones, oximes, and oxime esters were stable under the conditions of bioevaluation. X-ray crystallography of four representative compounds revealed structural features associated with cytotoxicity which may be considered in the design of future candidate cytotoxins.

Animals↗
PubMed1993

Anticonvulsant activities of some arylsemicarbazones displaying potent oral activity in the maximal electroshock screen in rats accompanied by high protection indices.

Various semicarbazones derived from aryl aldehydes, phenylalkyl aldehydes, and phenylalkyl ketones as well as some related compounds were evaluated for anticonvulsant activity. Most of the compounds displayed anticonvulsant activity in the maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) screens accompanied by neurotoxicity when given to mice by the intraperitoneal route. However quantitative data revealed protection indices (TD50/ED50) of less than 4 in general. Oral administration of the compounds to rats led to excellent potency in the MES screen accompanied by high protection indices while virtually no activity in the scPTZ test was displayed. These observations support the theory that one large hydrophobic group (in this case the aryl ring) and two electron donor atoms (present in the semicarbazono group) are requirements for protection in the MES screen. In general, the semicarbazones had rapid onsets of action, and one of the ways in which these compounds displayed their anticonvulsant activity is likely to be interaction with chloride channels. Empirical and semiempirical conformational calculations indicated that certain molecular fragments and hydrophobicity of these molecules affect bioactivity.

Administration, Oral↗
PubMed1992

Synthesis and cytotoxic evaluation of some 6-arylidene-2-(alpha-hydroxyamino-alpha-arylmethyl)cyclohexanone oximes and related compounds.

Reaction of 2,6-bis-(phenylmethylene)cyclohexanone (1) with a 4-molar excess of hydroxylamine hydrochloride and sodium acetate to produce the corresponding oxime 2 gave rise to 2-(alpha-hydroxyamino-alpha-phenylmethyl)-6-phenylmethylenecyclohexan one oxime (5a), whose structure was deduced from high-resolution proton nuclear magnetic resonance spectroscopy and confirmed by X-ray analysis. Compound 2 was eventually prepared from 1 with hydroxylamine per se and not with a mixture of hydroxylamine hydrochloride and sodium acetate. Ten analogues of 5a, namely 5b-5k, were prepared and evaluated for cytotoxicity. Six of the 11 compounds in series 5, as well as 1, showed activity in the 240-950 microM range against murine mammary EMT6 cells. Series 5 was also examined for cytotoxicity in an in vitro screen conducted by the National Cancer Institute with approximately 54 cell lines, and four compounds demonstrated selective toxicity toward various groups of tumors.

Animals↗
PubMed1990

Charge densities of atoms of conjugated styryl ketones having activity against L1210 leukemia cells.

Electron density calculations were undertaken on several atoms in a series of 3-substituted-4-phenyl-3-buten-2-ones in order to gain insight into the molecular features which affect charge densities. The results indicate that substituents at position 3 alter the electron densities of the olefinic group but have little effect on the acetyl function. The compounds were tested against L1210 cells in vitro, and the results suggest that electronic--but not steric--factors are important in affecting cytotoxicity. The most active compound was 3-phenylmethylene-2,4-pentanedione (1c) with an ED50 value of 1.06 x 10(-8) M.

Animals↗