Labelling of I2B-imidazoline receptors by [3H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) in rat brain and liver: characterization, regulation and relation to monoamine oxidase enzymes

The novel selective imidazoline radioligand [3H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) was used to characterize and assess further the nature of I2-imidazoline receptors in rat brain and liver. In the cerebral cortex, 2-BFI displayed high affinity (Ki = 9.8 nM) for a single class of [3H]2-BFI binding sites. Other imidazoline/guanidine compounds (e.g. aganodine, cirazoline and idazoxan) displayed biphasic competition curves, indicating the existence of high (KiH = 2.9-78 nM; R(H) = 61-83%) and low (KiL = 4.7-158 microM) affinity sites. The pharmacological profile for [3H]2-BFI binding (aganodine > cirazoline > 2-BFI >> clonidine > amiloride >> efaroxan) was typical of that for I2-sites. This profile was almost identical to that obtained against [3H]idazoxan (correlation between pKi values, r = 0.97) which indicated that the sites characterized with [3H]2-BFI in brain corresponded to I2-imidazoline receptors. The low affinity of amiloride against [3H]2-BFI (Ki = 900 nM) further indicated that these brain I2-sites belong to the I2B-subtype. [3H]2-BFI binding sites (Bmax = 72 fmol/mg protein) in brain were differentially modulated by treatment (7 days) with cirazoline (up-regulation: 25%) and the MAO inhibitor phenelzine (down-regulation: 31%), indicating that these I2-sites are regulated in vivo, as is the case for those labelled by [3H]idazoxan. Chronic treatment with 2-phenylethylamine, a phenelzine metabolite and endogenous amine, did not alter the density of brain of I2-imidazoline receptors labelled by [3H]idazoxan. Preincubation of liver membranes with the MAO inhibitor clorgyline (10(-7) M) abolished the binding of [3H]Ro 41-1049 (N-(2-aminoethyl)-5-(m-fluorophenyl)-4-thiazole carboxamide) to MAO-A, but it did not alter the binding of [3H]Ro 19-6327 (N-(2-aminoethyl)-5-chloro-2-pyridine carboxamide) to MAO-B or that of [3H]2-BFI to I2-sites. At 10(-4) M it also abolished MAO-B sites, but a substantial proportion of I2-sites (40%) remained intact. Preincubation of liver membranes at 60 degrees C also abolished MAO-A/B sites, whereas still 22% of I2-sites remained. The results indicate that [3H]2-BFI is a good tool for the identification of I2-imidazoline receptors and suggest further that certain I2-sites and MAO are different proteins.

Pharmacological and molecular discrimination of brain I2-imidazoline receptor subtypes

I2-imidazoline receptors labelled with [3H]-idazoxan in the rabbit and rat brains displayed high and low affinity, respectively, for the guanidide amiloride; reinforcing the previous definition of I2A-imidazoline receptors expressed in the rabbit brain and I2B-imidazoline receptors expressed in the rat brain. Other drugs tested displayed biphasic curves in competition experiments, indicating the existence of high and low affinity sites for both subtypes of I2-imidazoline receptors. Among the drugs studied, bromoxidine, moxonidine, (+)- and (-)-medetomidine and clorgyline were more potent on the high and/or low affinity sites of I2B-than on their corresponding of I2A-imidazoline receptors (KiH ratios 20 to 65). No correlation was found for the potencies of the drugs tested at the low affinity sites of both I2-imidazoline receptor subtypes. Preincubation (30 min at 25 degrees C) with 10(-6) M clorgyline reduced by 60% the Bmax of [3H]-idazoxan binding to I2B-imidazoline receptors in the rat brain, but it did not affect the binding parameters of the radioligand saturation curves to I2A-imidazoline receptors in the rabbit brain. These results indicated that I2A- and I2B-imidazoline receptor subtypes differ in the pharmacological profiles of their high and low affinity sites and in the ability to irreversibly bind clorgyline. In rat cortical membranes western blot detection of immunoreactive imidazoline receptors proteins revealed a double band of approximately 29/30 kDa and two less intense bands of approximately 45 and approximately 66 kDa. In rabbit cortical membranes the antibody used detected proteins of approximately 30, approximately 57 and approximately 66 kDa. It is suggested that different imidazoline receptor proteins (approximately 45 vs approximately 57 kDa) may account for the different pharmacological profiles of I2-imidazoline receptor subtypes.

Adenovirus-mediated transfer of HPV 16 E6/E7 antisense RNA to human cervical cancer cells

To explore the potential of an adenoviral antisense RNA transcript for gene therapy of cervical cancer, we introduced the antisense RNA transcript of E6 and E7 genes of human papillomavirus (HPV) 16 into cervical cancer cells harboring HPV 16 via a recombinant adenoviral vector, Ad5CMV-HPV 16 AS and analyzed the effects of expression of these genes on cell growth and tumor growth. Ad5CMV-HPV 16 AS contains the cytomegalovirus-promoter, E6 and E7 genes of HPV 16 in antisense orientation, and the SV40 polyadenylation signal in a mini-gene cassette, which is inserted into the E1-deleted region of modified adenovirus 5. The entire E6/E7 region of HPV 16 was amplified by polymerase chain reaction (PCR) before cloning into the mini-gene cassette. By reverse transcriptase-PCR, HPV 16 E6/E7 antisense RNA was detected in SiHa cells infected with Ad5CMV-HPV 16 AS. The growth of the Ad5CMV-HPV 16 AS-infected cells was greatly suppressed, as evidenced by a decrease in cell count. The growth inhibitory effect of Ad5CMV-HPV 16 AS was significantly enhanced by an adenoviral p53 construct, Ad5CMV-p53. In an ex vivo study in nude mice, tumorigenicity was completely inhibited in mice injected with Ad5CMV-HPV 16 AS-infected SiHa cells. These data suggest that transfection of cervical cancer cells with HPV 16 E6/E7 antisense RNA in a form such as Ad5CMV-HPV 16 AS is a potential novel approach to the therapy of HPV 16-positive cervical cancer.

Growth inhibitory effect of anti-K-ras adenovirus on lung cancer cells

An adenoviral vector carrying a 2-Kb fragment of the K-ras proto-oncogene inserted in antisense orientation with respect to the cytomegalovirus promoter was constructed and used to infect H460a lung cancer cells (codon 61 K-ras mutation). The gene was efficiently transferred, and a high level of expression of antisense K-ras was achieved. At a multiplicity of infection to achieve 65% transduction of cells, the expression of K-ras protein was reduced by 70% in the lung cancer cell line H460a as compared with cells infected with control vectors or noninfected cells. This reduction produced a 47% inhibition of monolayer growth and a 90% inhibition of colony formation. At a similar level of transduction in the cell line H358 (codon 12 K-ras mutation), a 59% inhibition of monolayer growth compared with control vectors occurred; however the inhibition of H322 cells (wild-type k-ras) growth was no different than control vector infected cells. These data suggest that the adenoviral K-ras H322a antisense vector may have therapeutic potential in tumors in which K-ras is mutated.

Pharmacological modulation of immunoreactive imidazoline receptor proteins in rat brain: relationship with non-adrenoceptor [3H]-idazoxan binding sites

1. The densities of various imidazoline receptor proteins (with apparent molecular masses of approximately 29/30-45- and 66-kDa) were quantitated by immunoblotting in the rat cerebral cortex after various drug treatments. The modulation of these imidazoline receptor proteins was then compared with the changes in the density of non-adrenoceptor [3H]-idazoxan binding sites (I2-sites) induced by the same drug treatments. 2. Chronic treatment (7 days) with the I2-selective imidazol(in)e drugs idazoxan (10 mg kg-1), cirazoline (1 mg kg-1) and LSL 60101 (10 mg kg-1) differentially increased the immunoreactivity of imidazoline receptor proteins. The levels of the 29/30-kDa protein were increased by idazoxan and LSL 60101 (23%), the levels of the 45-kDa protein only by cirazoline (44%) and those of the 66-kDa protein only by idazoxan (50%). These drug treatments also increased the density of I2-sites (32-42%). 3. Chronic treatment (7 days) with efaroxan (10 mg kg-1), RX821002 (10 mg kg-1) and yohimbine (10 mg kg-1), which possess very low affinity for I2-imidazoline receptors, did not alter either the immunoreactivity of imidazoline receptor proteins or the density of I2-sites. 4. Chronic treatment (7 days) with the monoamine oxidase (MAO) inhibitors clorgyline (10 mg kg-1) and phenelzine (10 mg kg-1) decreased the immunoreactivity of the 29/30-kDa (17-24%), 45-kDa (19%) and 66-kDa (23-31%) imidazoline receptor proteins. The alkylating agent N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (1.6 mg kg-1, 6 h) also decreased the levels of the three imidazoline receptor proteins (20-47%). These drug treatments consistently decreased the density of I2-sites (31-57%). 5. Significant correlations were found when the mean percentage changes in immunoreactivity of imidazoline receptor proteins were related to the mean percentage changes in the density of I2-sites after the various drug treatments (r = 0.92 for the 29/30-kDa protein, r = 0.69 for the 45-kDa protein and r = 0.75 for the 66-kDa protein). 6. In the rat cerebral cortex the I2-imidazoline receptor labelled by [3H]-idazoxan is heterogeneous in nature and the related imidazoline receptor proteins (29/30-, 45- and 66-kDa) detected by immunoblotting contribute differentially to the modulation of I2-sites after drug treatment.

Adenovirus-mediated transfer of a wild-type p53 gene and induction of apoptosis in cervical cancer

In most cervical cancers, the function of p53 is down regulated. To explore the potential use of p53 in gene therapy for cervical cancer, we introduced wild-type p53 into cervical cancer cell lines via a recombinant adenoviral vector, Ad5CMV-p53, and analyzed its effects on cell and tumor growth. The transduction efficiencies of all cell lines were 100% at a multiplicity of infection of 100 or greater. The p53 protein was detected in Ad5CMV-p53-infected cells. Protein expression peaked at day 3 after infection and lasted 15 days. The Ad5CMV-p53-infected cells underwent apoptosis, and cell growth was greatly suppressed. The Ad5CMV-p53 treatment significantly reduced the volumes of established s.c. tumors in vivo. These results indicate that transfection of cervical cancer cells with the wild-type p53 gene via Ad5CMV-p53 is a potential novel approach to the therapy of cervical cancer.

Growth inhibition of human cervical cancer cells with the recombinant adenovirus p53 in vitro

Human papillomavirus (HPV) has been identified in the majority of invasive cancers of the uterine cervix sampled and has been found to contribute in a significant way to the genesis of human cervical cancer. HPV has two transforming genes that encode the oncoproteins E6 and E7. E6 can form complexes with p53 and promote p53 degradation. We introduced wild-type p53 into a cervical cancer cell line via a recombinant adenoviral vector, Ad5CMV-p53. Human cervical cancer cell line HeLa, which has HPV type 18 and wild-type p53, was used in this study. Cells were grown in RPMI medium supplemented with 10% heat-inactivated fetal bovine serum. Ad5CMV-p53 was created by inserting the cytomegalovirus promoter, wild-type p53 cDNA, and SV40 polyadenylation signal in a minigene cassette into the E1-deleted region of the modified Ad5 adenovirus. The transduction efficiency was 100% when a dose ensuring a multiplicity of infection of 100 or greater was used. The p53 protein was detected in Ad5CMV-p53-infected cells by immunohistochemical and Western blot analyses. The growth of the Ad5CMV-p53-infected cells was greatly suppressed as detected by both cell count and [3H]thymidine incorporation assay. These data suggest that transfection of HPV-positive cervical cancer cells with a wild-type p53 gene in a form such as Ad5CMV-p53 is a potential novel therapy for cervical cancer.

LSL 60101, a selective ligand for imidazoline I2 receptors, on glial fibrillary acidic protein concentration

The concentration of the astrocytic marker, glial fibrillary acidic protein (GFAP) was quantitated by immunoblotting (Western blotting) in the rat brain after treatment with the novel ligand for imidazoline I2 receptors LSL 60101 [2-(2-benzofuranyl)imidazole] and its 6-methoxy derivative LSL 60125. Chronic (7-21 days), but not acute (1 day) or short-term (3 days), treatment with LSL 60101 (10 mg/kg i.p.) markedly increased (44-49%) GFAP immunoreactivity in the rat cerebral cortex. In contrast, chronic (7 days) treatment with LSL 60125 (10 mg/kg i.p.) did not significantly modify GFAP concentrations. In vitro, both drugs displayed moderate high affinity and high selectivity for imidazoline I2 receptors versus alpha 2-adrenoceptors; however, only chronic treatment with LSL 60101 (10 mg/kg i.p.) but not with LSL 60125 (10 mg/kg i.p.) was associated with an up-regulation of imidazoline I2 receptors. These data indicate that glial imidazoline I2 receptors may have a direct physiological function related to GFAP expression and that LSL 60101 could be a good tool for the study of the implication of these receptors on astrocyte activation and neuronal regeneration.

Safety evaluation of Ad5CMV-p53 in vitro and in vivo

In preparation for a clinical trial of the recombinant p53 adenovirus Ad5CMV-p53 for the treatment of lung cancer, the potential adverse effects of Ad5CMV-p53 were assessed in vitro and in vivo. No infectious replication of Ad5CMV-p53 was detectable in HeLa cells infected with extracts from HeLa cells previously infected with Ad5CMV-p53. No Ad5CMV-p53 DNA replication was detected by 32Pi labeling in lung cancer cells infected with Ad5CMV-p53 at multiplicities of infection (moi) up to 1,000 pfu/cell (total of 5 x 10(9) pfu viruses). The infectivity and cytotoxicity of Ad5CMV-p53 were examined in vitro in normal human bronchial epithelial (NHBE) cells. At a moi of 50 pfu/cell, Ad5CMV-p53 infection and expression were detectable in 80% of the treated cells. The exogenous p53 protein was first detected by western blotting at 8 hr and peaked at 48 hr after infection. Growth of NHBE cells was not affected by Ad5CMV-p53 infection at a moi of 100 pfu/cell. The pathogenicity of Ad5CMV-p53 was assessed in BALB/c mice. The virus was given to four groups of mice by intratracheal injection at dosages from 10(7) to 10(10) pfu; a fifth group received phosphate-buffered saline alone. None of the viral injections proved to be lethal. Mild to moderate peribronchiolar and perivascular infiltration by mononuclear cells and lymphocytes, with patches of pneumonitis, was the most acute toxic effect detected by histologic analysis in the two high-dose groups. Immunohistochemical analysis of the same paraffin-embedded sections showed that infectivity and level of expression of p53 in lung tissue were dose-dependent. Our results demonstrate that Ad5CMV-p53 is a replication-defective virus that yields a relatively low degree of acute toxicity in mice; these data document a safety profile encouraging for clinical trials of Ad5CMV-p53 in the therapy of lung cancer.

The effects of phenelzine and other monoamine oxidase inhibitor antidepressants on brain and liver I2 imidazoline-preferring receptors

1. The binding of [3H]-idazoxan in the presence of 10(-6) M (-)-adrenaline was used to quantitate I2 imidazoline-preferring receptors in the rat brain and liver after chronic treatment with various irreversible and reversible monoamine oxidase (MAO) inhibitors. 2. Chronic treatment (7-14 days) with the irreversible MAO inhibitors, phenelzine (1-20 mg kg-1, i.p.), isocarboxazid (10 mg kg-1, i.p.), clorgyline (3 mg kg-1, i.p.) and tranylcypromine (10 mg kg-1, i.p.) markedly decreased (21-71%) the density of I2 imidazoline-preferring receptors in the rat brain and liver. In contrast, chronic treatment (7 days) with the reversible MAO-A inhibitors, moclobemide (1 and 10 mg kg-1, i.p.) or chlordimeform (10 mg kg-1, i.p.) or with the reversible MAO-B inhibitor Ro 16-6491 (1 and 10 mg kg-1, i.p.) did not alter the density of I2 imidazoline-preferring receptors in the rat brain and liver; except for the higher dose of Ro 16-6491 which only decreased the density of these putative receptors in the liver (38%). 3. In vitro, phenelzine, clorgyline, 3-phenylpropargylamine, tranylcypromine and chlordimeform displaced the binding of [3H]-idazoxan to brain and liver I2 imidazoline-preferring receptors from two distinct binding sites. Phenelzine, 3-phenylpropargylamine and tranylcypromine displayed moderate affinity (KiH = 0.3-6 microM) for brain and liver I2 imidazoline-preferring receptors; whereas chlordimeform displayed high affinity (KiH = 6 nM) for these receptors in the two tissues studied, Clorgyline displayed very high affinity for rat brain (KiH = 40 pM) but not for rat liver I2 imidazoline-preferring receptors (KiH = 169 nM). 4. Preincubation of cortical or liver membranes with phenelzine (10-4 M for 30 min) did not alter the total density of I2 imidazoline-preferring receptors, indicating that this irreversible MAO inhibitor does not irreversibly bind to I2 imidazoline-preferring receptors. In contrast, preincubation with 10-6 Mclorgyline reduced by 40% the Bmax of [3H]-idazoxan to brain and liver I2 imidazoline-preferring receptors.5. Chronic treatment (7 days) with the inducers of cytochrome P-450 enzymes phenobarbitone (40 or 80 mg kg-1, i.p.), 3-methylcholanthrene (20 mg kg-1, i.p.) or 2-methylimidazole (40 mg kg-1, i.p.) did not alter the binding parameters of [3H]-idazoxan to brain and liver 12 imidazoline-preferring receptors.The compound SKF 525A, a potent inhibitor of cytochrome P-450 enzymes which forms a tight but reversible complex with the haemoprotein, completely displaced with moderate affinity (KiH = 2-10 microM)the specific binding of [3H]-idazoxan to brain and liver 12 imidazoline-preferring receptors. Preincubation of total liver homogenates with 3 x 10-4 M phenelzine in the presence of 10-3 M NADH, a treatment that irreversibly inactivates the haeme group of cytochrome P-450, did not reduce the density of liver I2 imidazoline-preferring receptors. These results discounted a possible interaction of [3H]-idazoxan with the haeme group of cytochrome P-450 enzymes.6. Together the results indicate that the down-regulation of I2 imidazoline-preferring receptors is associated with an irreversible inactivation of MAO (at least in the brain) that is not related either to the affinity of the MAO inhibitors for I2 imidazoline-preferring receptors or to an irreversible binding to these putative receptors. These findings indicate a novel effect of irreversible MAO inhibitors in the brain and suggest a new target for these compounds that could be of relevance in the treatment of depression, a disease in which an increased density of brain I2 imidazoline-preferring receptors has been reported.

The effects of chronic imidazoline drug treatment on glial fibrillary acidic protein concentrations in rat brain

1. The concentration of the astrocytic marker, glial fibrillary acidic protein (GFAP) was quantitated by immunoblotting (western blotting) in the rat brain after treatment with various imidazoline drugs and other agents. 2. Chronic (7 days) but not acute (1 day) treatment with the imidazoline drugs, cirazoline (1 mg kg-1, i.p.) and idazoxan (10 mg kg-1, i.p.), but not with the structurally related alpha 2-adrenoceptor antagonists, RX821002 (2-methoxy idazoxan) (10 mg kg-1, i.p.) and efaroxan (10 mg kg-1, i.p.), markedly increased (45%) GFAP immunoreactivity in the rat cerebral cortex. Chronic treatment (7 days) with yohimbine (10 mg kg-1, i.p.), a non-imidazoline alpha 2-adrenoceptor antagonist, did not significantly modify GFAP immunoreactivity in the cerebral cortex. 3. Chronic treatment (7 days) with cirazoline and idazoxan did not alter the density of brain monoamine oxidase (MAO)-B sites labelled by [3H]-Ro 19-6327 (lazabemide), another relevant astroglial marker. Moreover, these imidazoline drug treatments did not modify the levels of alpha-tubulin in the cerebral cortex. These negative results reinforced the specificity of the effects of imidazoline drugs on GFAP. 4. Irreversible inactivation of brain alpha 2-adrenoceptors (and other neurotransmitters receptors) after treatment with an optimal dose of the peptide-coupling agent EEDQ (1.6 mg kg-1, i.p., for 6-24 h) did not alter GFAP immunoreactivity in the cerebral cortex. These results further disproved the involvement of these receptors on astroglial cells in the tonic control of GFAP levels.5. The binding of [3H]-idazoxan in the presence of 10-6 M (-)-adrenaline was used to quantitate in parallel 12-imidazoline preferring sites in the rat brain after the same treatments. Chronic treatment (7 days) with cirazoline and idazoxan, but not with RX821002, efaroxan or yohimbine, significantly increased (25%) the density of I2-sites in the cerebral cortex. The up-regulation of I2-sites induced by cirazoline was not observed in the liver, a tissue that also expresses 12-sites but lacks glial cells.6. A strong correlation (r = 0.97) was found when the mean percentage changes in GFAP immuno reactivity were related to the mean percentage changes in 12 imidazoline sites after the various drug treatments.7. Together the results suggest a direct physiological function of glial I2-imidazoline preferring sites in the regulation of GFAP levels.

Glycosyl phosphatidylinositol membrane anchoring of melanotransferrin (p97): apical compartmentalization in intestinal epithelial cells

Melanotransferrin (p97) is an iron-binding membrane glycoprotein with 40% homology to transferrin and lactoferrin. It was first identified on the basis of its high level of expression in melanoma cells, as compared to normal melanocytes. It is also present in many cultured cell types. In normal tissues, p97 is expressed in fetal intestine, umbilical cord, sweat gland ducts and liver sinusoidal lining cells. Kinetic studies in melanoma cells have suggested that p97 plays a role in iron metabolism. We have examined expression of p97 in cell lines derived from human colorectal carcinomas which express a differentiated phenotype. When polarized, these cells showed a preferred apical distribution of p97, as demonstrated by immunohistochemistry, immune electron microscopy and domain-selective biotinylation. Correspondingly, p97 was only found on the apical brush border of epithelial cells in the fetal intestine. p97 was shown to be anchored to the membrane through a glycosyl phosphatidylinositol moiety by treatment with phophatidylinositol-specific phospholipase C (PI-PLC) and labeling with [14C]ethanolamine. These observations provide a basis for the elucidation of the physiological role of p97 in iron metabolism and its possible role in cell proliferation and malignant cell transformation.