Mechanism and consequences of RAF kinase activation by small-molecule inhibitors.

Despite the clinical success of RAF inhibitors in BRAF-mutated melanomas, attempts to target RAF kinases in the context of RAS-driven or otherwise RAF wild-type tumours have not only been ineffective, but RAF inhibitors appear to aggravate tumorigenesis in these settings. Subsequent preclinical investigation has revealed several regulatory mechanisms, feedback pathways and unexpected enzymatic quirks in the MAPK pathway, which may explain this paradox. In this review, we cover the various proposed molecular mechanisms for the RAF paradox, the clinical consequences and strategies to overcome it.

A novel, long-circulating, and functional liposomal formulation of antisense oligodeoxynucleotides targeted against MDR1.

The goal of this study was to develop a small, stable liposomal carrier for antisense oligodeoxynucleotides (asODN) that would have high trapping efficiencies and long circulation times in vivo. Traditional cationic liposomes aggregate to large complexes and, when injected intravenously, rapidly accumulate in the liver and lung. We produced charge-neutralized liposome-asODN particles by optimizing the charge interaction between a cationic lipid and negatively charged asODN, followed by a procedure in which a layer of neutral lipids coated the exterior of the cationic lipid-asODN particle. The coated cationic liposomes had an average diameter of 188 nm and entrapped 85-95% of the asODN. The biodistribution and pharmacokinetics of an 18-mer 125I-labeled phosphorothioate ODN formulated by this method were determined after tail vein injection in mice. The majority of the asODN was cleared from blood, with a half-life of >10 hours compared with <1 hour for free asODN. When coupled with an anti-CD19 targeted antibody, this formulation was also effective at delivering an MDR1 asODN to a multidrug-resistant human B-lymphoma cell line in vitro, decreasing the activity of P-glycoprotein. No inhibition was found for nontargeted formulations or for free asODN. A number of therapeutic opportunities exist for the use of small, stable, long-circulating, and targetable liposomal carriers such as this, with high trapping efficiencies for asODN.

A new liposomal formulation for antisense oligodeoxynucleotides with small size, high incorporation efficiency and good stability.

Antisense oligodeoxynucleotides (asODN) are therapeutic agents that are designed to inhibit the expression of disease-related genes. However, their therapeutic use may be hindered due to their rapid clearance from blood and their inefficiency at crossing cell membranes. Cationic liposome complexes have been used to enhance the intracellular delivery of asODN in vitro; however, this type of carrier has unfavorable pharmacokinetics for most in vivo applications. Significant therapeutic activity of cationic liposomal asODN following systemic administration has not been demonstrated. In an effort to develop improved liposomal carriers for asODN for in vivo applications, we have evaluated the physical characteristics of two formulations which represent alternatives to cationic liposome-asODN complexes: asODN passively entrapped within neutral liposomes (PELA) and asODN formulated in a novel coated cationic liposomal formulation (CCL). Our results confirm that PELA can be extruded to small diameters that are suitable for intravenous administration. PELA are stable in human plasma; however, the incorporation efficiency is relatively low ( approximately 20%). The CCL formulation can also be extruded to small diameters (<200 nm), with significantly higher (80-100%) incorporation efficiency and are stable in 50% human plasma at 37 degrees C. A liposomal carrier for asODN with these characteristics may provide a significant therapeutic advantage over free asODN for some therapeutic applications.

Delivery of c-myb antisense oligodeoxynucleotides to human neuroblastoma cells via disialoganglioside GD(2)-targeted immunoliposomes: antitumor effects.

BACKGROUND: Advanced-stage neuroblastoma resists conventional treatment; hence, novel therapeutic approaches are required. We evaluated the use of c-myb antisense oligodeoxynucleotides (asODNs) delivered to cells via targeted immunoliposomes to inhibit c-Myb protein expression and neuroblastoma cell proliferation in vitro. METHODS: Phosphorothioate asODNs and control sequences were encapsulated in cationic lipid, and the resulting particles were coated with neutral lipids to produce coated cationic liposomes (CCLs). Monoclonal antibodies directed against the disialoganglioside GD(2) were covalently coupled to the CCLs. (3)H-labeled liposomes were used to measure cellular binding, and cellular uptake of asODNs was evaluated by dot-blot analysis. Growth inhibition was quantified by counting trypan blue dye-stained cells. Expression of c-Myb protein was examined by western blot analysis. RESULTS: Our methods produced GD(2)-targeted liposomes that stably entrapped 80%-90% of added c-myb asODNs. These liposomes showed concentration-dependent binding to GD(2)-positive neuroblastoma cells that could be blocked by soluble anti-GD(2) monoclonal antibodies. GD(2)-targeted liposomes increased the uptake of asODNs by neuroblastoma cells by a factor of fourfold to 10-fold over that obtained with free asODNs. Neuroblastoma cell proliferation was inhibited to a greater extent by GD(2)-targeted liposomes containing c-myb asODNs than by nontargeted liposomes or free asODNs. GD(2)-targeted liposomes containing c-myb asODNs specifically reduced expression of c-Myb protein by neuroblastoma cells. Enhanced liposome binding and asODN uptake, as well as the antiproliferative effect, were not evident in GD(2)-negative cells. CONCLUSIONS: Encapsulation of asODNs into immunoliposomes appears to enhance their toxicity toward targeted cells while shielding nontargeted cells from antisense effects and may be efficacious for the delivery of drugs with broad therapeutic applications to tumor cells.

In vitro UVB irradiation of bovine crystalline lens causes cell damage and reduction in leucine aminopeptidase activity in lens epithelium.

Past studies in our laboratory have shown that low levels of UVB can cause changes in the optical properties of organ cultured ocular lenses, while other research has shown that in vitro UV radiation causes decreases in leucine aminopeptidase activity in homogenates of crystalline lens material. Therefore we have investigated whether there is a relationship between such decreases in enzyme activity and changes in lens optics and structure. Organ cultured bovine lenses were irradiated with low doses of UVB, and lens optics, histology and leucine aminopeptidase activity (leucine beta-naphthylamide hydrolysis at pH 7.5) were assessed daily. Lenses irradiated with 0.1 J cm-2 UVB showed a decrease of about 30% in leucine aminopeptidase activity 1 h after irradiation, while changes in lens optics were not observed until at least 24 h after irradiation. Histological examination of the lens anterior epithelium revealed changes in epithelial cells ranging from pyknotic nuclei to large areas of cell fragmentation. The results of this study suggest that a decrease in soluble aminopeptidase activity in lens epithelial cells may be a direct result of the epithelial cell damage rather than an effect of UVB on the enzyme per se.

Optical effects of UV-A and UV-B radiation on the cultured bovine lens.

The effects of repeated exposures to UV-A (335 nm) and UV-B (305 nm) radiation on the crystalline lens were studied by treating cultured bovine lenses daily or weekly. The effects of irradiation on lens optical quality were monitored using an automated scanning laser system that records both relative transmittance and focal length across the lens. Relatively low radiant exposures of UV-B were used (0.06, 0.03, 0.01 J/cm2) compared to UV-A (1.44 J/cm2). In total, 38 treated lenses and 32 controls were cultured for times ranging from 400-1000 hours. Results indicate that this range of UV-B exposure may represent the threshold for in vitro UV-B induced opacification. Lenses treated weekly with 0.06 J/cm2 UV-B showed a significant decrease in transmittance compared to controls 69 hours after the first treatment and an increase in focal length variability. The ability of the lens to repair itself, as found in a previous single dose study, was absent after repeated doses. Lenses exposed daily to 0.03 and 0.01 J/cm2 UV-B showed no significant change in transmittance or focal length variability compared to controls. Daily exposure to 1.44 J/cm2 UV-A resulted in no significant change in transmittance or focal length variability compared to controls.

Methionine intake in rainbow trout (Oncorhynchus mykiss), relationship to cataract formation and the metabolism of methionine.

Young rainbow trout were given diets containing graded levels of methionine for 16 wk. Analysis of the weight gain and food efficiency data showed the methionine requirement to be not more than 0.76% of the diet (1.9% of dietary protein). Activities of regulatory enzymes of the transulfuration pathway, methionine adenosyltransferase and cystathionine synthase in trout liver were not altered by changes in methionine intake. Concentrations of free serine in liver and plasma of the trout were high at low levels of methionine intake but fell as dietary methionine increased. This implied decreased flux through cystathionine synthase at low methionine intakes. Large increases in liver and plasma taurine occurred at high methionine intakes, implying enhanced transulfuration activity. Liver ornithine decarboxylase activity was reduced at the lowest level of dietary methionine used but the activity of S-adenosylmethionine decarboxylase was unchanged. Eye lenses of the trout given these diets were examined by a scanning lens monitor. Analysis of focal length variability with this equipment demonstrated that, if abnormality of the lens is to be avoided, a higher concentration of dietary methionine (0.96% or 0.6% methionine + 0.36% cystine) is needed than that required to maximize growth.

Optical performance of the bovine lens before and after cold cataract.

Cold cataracts were induced in ten bovine lenses and then removed by warming. Cataracts first appeared at an average temperature of 11.7 degrees C. The cataracts appeared to be densest at an average temperature of 1.2 degrees C, while warming caused them to disappear completely at an average temperature of 16.4 degrees C. A computer-operated scanning laser system was used to measure the equivalent focal length and changes in relative transmittance before, during, and after the cataract was induced. In general the focal length profile (spherical aberration) that existed before cooling was recaptured on warming. Scatter values indicate that transmittance is not affected by the temporary cold cataract. Thus the optical performance of the bovine lens appears to be identical before and after cold cataracts are induced. We believe that these results indicate that the cataract has a supramolecular origin.

UV-B radiation and the optical properties of cultured bovine lenses.

The effect of UV-B radiation on the crystalline lens was examined by subjecting bovine lenses in culture to varying low exposures at 300 nm. Lens optical quality was monitored on a long-term basis (to 1000 hrs.) with an automated scanning laser system that recorded both change in relative scatter and focal length across each lens. Data were collected for 20 lens positions at each scan. Radiant exposure levels consisted of 0.5, 0.25, 0.125, 0.06 and 0.03 Jcm-2. Twenty irradiated lenses were compared to twelve untreated controls. All of the irradiated lenses showed changes in scatter and focal length relative to the controls. Most (about 75%) of the treated lenses showed significant increases in scatter (200-400%) and focal length (10-20%) at 40 to 60 hours after exposure. A similar time frame for lens damage was noted by visual inspection. Exposure to UV-B at the above doses did not affect culture longevity.

An improved radiolabeling technique of ivalon and its use for dynamic monitoring of complications during therapeutic transcatheter embolization.

Transcatheter embolization by Ivalon particles for treatment of arteriovenous malformations has been an accepted therapeutic technique for many years. We describe a new and efficient radiolabeling technique of Ivalon particles using [99mTc]sulfur colloid. Continuous and dynamic monitoring of injected radiolabeled Ivalon particles is made possible by viewing the persistence scope of a portable gamma camera whose head is positioned over the patient undergoing therapeutic embolization. Therefore, if inadvertent pulmonary embolism or reflux migration of radiolabeled Ivalon particles has occurred, the angiographer is immediately aware of this potentially serious or fatal complication and can take corrective action. We describe two patients, each with an arteriovenous malformation, who had therapeutic embolization with radiolabeled Ivalon particles, one resulting in reflux migration and the other resulting in inadvertent pulmonary embolism.