Tunable DNA cleavage activity promoted by copper(ii) ternary complexes with N-donor heterocyclic ligands.

Several small molecules have the capacity to cleave DNA promptly at high yields, even under mild conditions. Usually, this activity has no constraints, occurring without external or user control. Here, we demonstrate that UV-light exposure can greatly enhance the DNA cleavage activity promoted by four ternary copper(ii) complexes. A remarkable photocontrolled activity was achieved, which may be interesting for chemical and biochemical applications.

Preparation and cytotoxicity of cisplatin-containing liposomes.

We encapsulated cisplatin into stealth pH-sensitive liposomes and studied their stability, cytotoxicity and accumulation in a human small-cell lung carcinoma cell line (GLC4) and its resistant subline (GLC4/CDDP). Since reduced cellular drug accumulation has been shown to be the main mechanism responsible for resistance in the GLC4/CDDP subline, we evaluated the ability of this new delivery system to improve cellular uptake. The liposomes were composed of dioleoylphosphatidylethanolamine (DOPE), cholesteryl hemisuccinate (CHEMS), and distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) and were characterized by determining the encapsulation percentage as a function of lipid concentration. Among the different formulations, DOPE/CHEMS/DSPE-PEG liposomes (lipid concentration equal to 40 mM) encapsulated cisplatin more efficiently than other concentrations of liposomes (about 20.0%, mean diameter of 174 nm). These liposomes presented good stability in mouse plasma which was obtained using a 0.24-M EDTA solution (70% cisplatin was retained inside the liposomes after 30 min of incubation). Concerning cytotoxic effects, they are more effective (1.34-fold) than free cisplatin for growth inhibition of the human lung cancer cell line A549. The study of cytotoxicity to GLC4 and GLC4/CDDP cell lines showed similar IC50 values (approximately 1.4 microM), i.e., cisplatin-resistant cells were sensitive to this cisplatin formulation. Platinum accumulation in both sensitive and resistant cell lines followed the same pattern, i.e., approximately the same intracellular platinum concentration (4.0 x 10-17 mol/cell) yielded the same cytotoxic effect. These results indicate that long-circulating pH-sensitive liposomes, also termed as stealth pH-sensitive liposomes, may present a promising delivery system for cisplatin-based cancer treatment. This liposome system proved to be able to circumvent the cisplatin resistance, whereas it was not observed when using non-long-circulating liposomes composed of phosphatidylcholine, phosphatidylserine, and cholesterol.

Preparation and cytotoxicity of cisplatin-containing liposomes

We encapsulated cisplatin into stealth pH-sensitive liposomes and studied their stability, cytotoxicity and accumulation in a human small-cell lung carcinoma cell line (GLC4) and its resistant subline (GLC4/CDDP). Since reduced cellular drug accumulation has been shown to be the main mechanism responsible for resistance in the GLC4/CDDP subline, we evaluated the ability of this new delivery system to improve cellular uptake. The liposomes were composed of dioleoylphosphatidylethanolamine (DOPE), cholesteryl hemisuccinate (CHEMS), and distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) and were characterized by determining the encapsulation percentage as a function of lipid concentration. Among the different formulations, DOPE/CHEMS/DSPE-PEG liposomes (lipid concentration equal to 40 mM) encapsulated cisplatin more efficiently than other concentrations of liposomes (about 20.0 percent, mean diameter of 174 nm). These liposomes presented good stability in mouse plasma which was obtained using a 0.24-M EDTA solution (70 percent cisplatin was retained inside the liposomes after 30 min of incubation). Concerning cytotoxic effects, they are more effective (1.34-fold) than free cisplatin for growth inhibition of the human lung cancer cell line A549. The study of cytotoxicity to GLC4 and GLC4/CDDP cell lines showed similar IC50 values (approximately 1.4 æM), i.e., cisplatin-resistant cells were sensitive to this cisplatin formulation. Platinum accumulation in both sensitive and resistant cell lines followed the same pattern, i.e., approximately the same intracellular platinum concentration (4.0 x 10-17 mol/cell) yielded the same cytotoxic effect. These results indicate that long-circulating pH-sensitive liposomes, also termed as stealth pH-sensitive liposomes, may present a promising delivery system for cisplatin-based cancer treatment. This liposome system proved to be able to circumvent the cisplatin resistance, whereas...

P-glycoprotein preferentially effluxes anthracyclines containing free basic versus charged amine.

The multidrug resistant (MDR) tumor phenotype, characterized by a decreased cellular drug accumulation is achieved by ATP-dependent extrusions of drugs from cells by P-glycoprotein (P-gp) and/or by multidrug resistance protein (MRP1). Despite the huge amount of research that has been performed on the mechanisms of P-gp-mediated efflux of drug, it is not yet known what the molecular parameters are required for a molecule to be recognized and pumped out by P-gp. Anthracyclines are weak bases and, depending on the pH, can exist either in the neutral or in the positively charged form. The aim of the work reported here was to determine which molecular form is actively pumped out by P-gp (the neutral form, the protonated form, or both), and if both, the relative efficiencies of pumping. We used spectrofluorometric methods to determine the efflux of anthracyclines in K562/Adr cells, at different intracellular and extracellular pH levels. Using 3'-deamino, 3'-hydroxyl doxorubicin (OH-DOX), which is permanently neutral, we first verified that our methodologies were accurate and that the P-gp-mediated efflux of OH-DOX would not depend on the pH being in the range 6.6--8.4. The P-gp-mediated efflux of daunorubicin (DNR) and 3'-hydroxy-4-amino (WP608) was determined at different pH values. These two drugs were chosen because: (a) the lipophilicity of the neutral forms of these two molecules is so similar that any difference in the P-gp-mediated efflux cannot be assigned to lipohilicity variation, and (b) their pKa values are different (8.4 and 7.7 for DNR and WP608, respectively), which makes it easy to obtain a large variation in the proportions of the neutral and positively charged forms. Our data show that both forms are recognized by P-gp but the neutral form is pumped about three times more efficiently than the charged form. This is corroborated by results showing the active efflux (checked at pH(i) 7.3 only) of five other anthracycline containing a basic center. We interpret these data to mean that: (a) the positive charge of anthracycline is not a necessary requirement for P-gp recognition, but that (b) the presence of a protonable basic nitrogen facilitates the processing of these compounds by MDR efflux system.

A physicochemical study of the tetracycline coordination to oxovanadium(IV).

The interaction of tetracycline and oxovanadium(IV) in aqueous solution was studied by potentiometric and spectrophotometric methods. Oxovanadium(IV) ions form both a positively charged 1:1 and a neutral 2:1 metal-ligand complex with tetracycline. When a 1:1 ligand-to-metal ratio mixture is used at about pH 4.5 the 1:1 species predominates, being replaced at pH 6 by the binuclear complex. The binuclear complex has been isolated and fully characterised. Infrared and EPR studies suggest the existence of two distinct vanadyl binding sites. Our results indicate that the first vanadium coordinates to the BCD-ring system and the second one to the A-ring. Biological implications of the existence of a neutral complex at physiological pH are briefly discussed.