A cationic derivative of amphotericin B as a novel delivery system for antisense oligonucleotides

Polyene-based cationic lipids as visually traceable siRNA transfer reagents

Cationic lipids are promising non-viral vectors for the cellular delivery of nucleic acids. Important considerations for the development of new delivery vectors are enhanced uptake efficiency, low toxicity and traceability. Traceable gene transfer systems however typically require the inclusion of a labeled excipient, and highly sensitive imaging instrumentation to detect the presence of the label. Recently, we reported the synthesis and characterization of colored, polyene cationic phospholipidoids composed of a rigid, polyenoic acid of predetermined dimension (C20:5 and C30:9) paired with flexible saturated alkyl chains of varying lengths (12:0, 14:0, 16:0, 18:0, 20:0 carbons). Herein, the potential of these cationic phospholipids as siRNA carriers was evaluated through standard liposomal formulations in combination with a neutral helper lipid DOPE. The polyene-based lipids were compared with a standard cationic lipid for siRNA-delivery into luciferase expressing HR5-CL11 cells. Within the series of lipids screened, knockdown results indicated that polyene cationic phospholipids paired with longer saturated alkyl chains are more effective as gene transfer agents, and perform comparably with the commercial lipid EPC. Furthermore, the chromophore associated with the polyene chain allowed tracking of the siRNA delivery using direct observation. The polyene lipoplexes were tracked on both a macroscopic and microscopic level either as a single-component or as a multi-component lipoplex formulation. When combined with a reference EPC, effective knockdown and tracking abilities were combined in a single preparation.

Overcoming endosomal barrier by amphotericin B-loaded dual pH-responsive PDMA-b-PDPA micelleplexes for siRNA delivery

The endosomal barrier is a major bottleneck for the effective intracellular delivery of siRNA by nonviral nanocarriers. Here, we report a novel amphotericin B (AmB)-loaded, dual pH-responsive micelleplex platform for siRNA delivery. Micelles were self-assembled from poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diisopropylamino)ethyl methacrylate) (PDMA-b-PDPA) diblock copolymers. At pH 7.4, AmB was loaded into the hydrophobic PDPA core, and siRNA was complexed with a positively charged PDMA shell to form the micelleplexes. After cellular uptake, the PDMA-b-PDPA/siRNA micelleplexes dissociated in early endosomes to release AmB. Live cell imaging studies demonstrated that released AmB significantly increased the ability of siRNA to overcome the endosomal barrier. Transfection studies showed that AmB-loaded micelleplexes resulted in significant increase in luciferase (Luc) knockdown efficiency over the AmB-free control. The enhanced Luc knockdown efficiency was abolished by bafilomycin A1, a vacuolar ATPase inhibitor that inhibits the acidification of the endocytic organelles. These data support the central hypothesis that membrane poration by AmB and increased endosomal swelling and membrane tension by a "proton sponge" polymer provided a synergistic strategy to disrupt endosomes for improved intracellular delivery of siRNA.

Changes of conductance and compressibility of bilayer lipid membranes induced by oligonucleotide-cationic polyene antibiotic complexes

The positively charged polyene molecule amphotericin B 3-dimethylaminopropylamide (AMA) is an efficient agent for the delivery of antisense oligodeoxyribonucleotides (ODN) into target cells. In the present study, bilayer lipid membrane (BLM) conductance, elasticity modulus perpendicular to the membrane plane, surface potential and electrical capacitance were measured by conductance and electrostriction methods in the presence of AMA, pure or complexed to 20-mer single stranded ODN at different ratios. Pure AMA did not induce changes in conductance of cholesterol-containing BLM, but did induce an increase in elasticity modulus and surface potential. ODN/AMA complexes changed BLM properties depending on the charge ratio. The most pronounced effect on membrane conductance was observed for positively charged ODN/AMA complexes (charge ratio rho-/+=0.1), while for negatively charged complexes these changes were less marked/apparent, correlating to substantially lower binding constants. The effect of ODN/AMA complexes on elasticity modulus and charge potential was biphasic. After an increase in both values, a decrease was observed for higher incubation times and ODN/AMA concentrations. These results are interpreted as indicating that the membrane property changes result from the large AMA aggregates induced by the presence of the negatively charged ODN, which condensate on these aggregates. It is suggested that the decrease of elasticity modulus and surface potential in the presence of increasing incubation time and AMA concentration result from desorption of the complexes in the complex-free compartment of the BLM cell, or appearance of a non-linear conductance of the lipid bilayer. The first alternative would explain the AMA-induced transmembrane transfer of ODN.

Transient permeability induced by alkyl derivatives of amphotericin B in lipid membranes

Individual ionic channels were shown to be formed in the brain cholesterol containing phospholipid membranes by two-sided addition of the amphotericin B alkyl derivatives. At concentrations between 10(-8) and 10(-7) M, the resulting conductance appeared to be transient. Existence of different antibiotic assemblies was justified by the kinetic analysis of the membrane conductance decline following the antibiotic washing out. In order to account for the transient characteristics of the induced conductance, it was proposed that the antibiotic oligomers incorporate into the membrane from the aqueous phase, form channels aggregating with cholesterol, and then dissociate in the bilayer into non-active degraded oligomeric or monomeric forms.

Intracellular uptake of modified oligonucleotide studied by two fluorescence techniques

Interaction, i.e., cellular uptake and intracellular distribution, of synthetic modified antisense oligonucleotide with the B16 melanoma cell line was studied using cationic polyene antibiotic, amphotericin B 3-dimethylaminopropyl amide, as a carrier vector. The antisense oligonucleotide--dT(15) oligomer analogue containing isopolar, nonisosteric, phosphonate-based internucleotide linkages 3'-O-P-CH(2)-O-5'--was labeled with fluorescent tetramethylrhodamine marker. The oligonucleotide itinerancy across the cell membrane and its distribution inside the cell was visualized using fluorescence microimaging. During the first several hours a strong preference staining of the cell nucleus was found. Fluorescence lifetime measurements from the intracellular environment (confocal laser microspectrofluorimeter, frequency domain phase/modulation technique in 1 to 200 MHz frequency region) yielded two spectral components of 4.9 and 1.4 ns lifetime, respectively. While the former component correlates with the previously characterized effect of the fluorophore binding to biomolecular targets in membranes and/or cytoplasm, the latter component is newly observed and its possible origin is discussed.

Complex formation and vectorization of a phosphorothioate oligonucleotide with an amphipathic leucine- and lysine-rich peptide: study at molecular and cellular levels

Optical spectroscopic techniques such as CD, Raman scattering, and fluorescence imaging allowed us to analyze the complex formation and vectorization of a single-stranded 20-mer phosphorothioate oligodeoxynucleotide with a 15-mer amphipathic peptide at molecular and cellular levels. Different solvent mixtures (methanol and water) and molecular ratios of peptide/oligodeoxynucleotide complexes were tested in order to overcome the problems related to solubility. Optimal conditions for both spectroscopic and cellular experiments were obtained with the molecular ratio peptide/oligodeoxynucleotide equal to 21:4, corresponding to a 7:5 ratio for their respective +/- charge ratio. At the molecular level, CD and Raman spectra were consistent with a alpha-helix conformation of the peptide in water or in a methanol-water mixture. The presence of methanol increased considerably the solubility of the peptide without altering its alpha-helix conformation, as evidenced by CD and Raman spectroscopies. UV absorption melting profile of the oligodeoxynucleotide gave rise to a flat melting profile, corresponding to its random structure in solution. Raman spectra of oligodeoxynucleotide/peptide complexes could only be studied in methanol/water mixture solutions. Drastic changes observed in Raman spectra have undoubtedly shown: (a) the perturbation occurred in the peptide secondary structure, and (b) possible interaction between the lysine residues of the peptide and the oligodeoxynucleotide. At the cellular level, the complex was prepared in a mixture of 10% methanol and 90% cell medium. Cellular uptake in optimal conditions for the oligodeoxynucleotide delivery with low cytotoxicity was controlled by fluorescence imaging allowing to specifically locate the compacted oligonucleotide labeled with fluorescein at its 5'-terminus with the peptide into human glioma cells after 1 h of incubation at 37 degrees C.

Effect of pH and sodium chloride on the strength and selectivity of the interaction of gamma [correction for tau] -cyclodextrin with some antisense nucleosides

The influence of pH and the concentration of sodium chloride on the strength and selectivity of the interaction of twelve 8-substituted-2'-deoxyadenosine and sixteen 5-substituted-2'-deoxyuridine derivatives with gamma-cyclodextrin (GCD) have been studied by the spectral mapping technique (SPM). The potency values of the spectral map were regarded as indicators of the capability of antisense nucleosides and GCD to interact simultaneously taking into consideration all relevant data. It has been established that the strength of interaction is highest in acetic and lowest in alkaline solutions, and the selectivities of acidic, alkaline and salt solutions are markedly different. The length of hydrophobic alkyl substituents in antisense molecules influenced both the strength and selectivity of the interaction. The character of the base structure affected only the selectivity.

Minimally modified phosphodiester antisense oligodeoxyribonucleotide directed against the multidrug resistance gene mdr1

In the perspective of reversing multidrug resistance through antisense strategy while avoiding non-antisense effects of all-phosphorothioate oligonucleotides which non-specifically bind to proteins, a minimally modified antisense phosphodiester oligodeoxyribonucleotide has been designed against mdr1, one of the multidrug resistance genes. Its stability in lysates prepared from NIH/3T3 cells transfected with the human mdr1 gene has already been demonstrated. Confocal microspectrofluorometry using a fluorescence resonance energy transfer technique allowed its stability inside living cells to be proven. Its internalization into the cells was achieved with different delivery agents (addition of a cholesteryl group, Superfect or an amphotericin B cationic derivative) and has been followed by fluorescence imaging. For each of the delivery systems, Western blotting allowed its antisense efficiency to be compared to that of an all-phosphorothioate antisense oligonucleotide. No antisense efficiency was demonstrated for the minimally modified ODN when internalized with Superfect. In both other cases, the best extinction of the P-glycoprotein expression has always been achieved with the all-phosphorothioate antisense. While the difference was significant in the case the amphotericin B derivative was used as delivery agent (20% remaining protein expression with the all-phosphorothioate vs. 40% with the minimally modified antisense), it was negligible for the cholesterol conjugates (2% vs. 6%). It is of great interest to prove that an almost all-phosphodiester oligonucleotide can be an efficient antisense against an overexpressed gene. The reduction of non-antisense effects as non-specific binding to proteins are of importance in the case relatively high ODN concentrations are used, which can prove to be necessary in the case of overexpressed genes.

Anthrapyridones, a novel group of antitumour non-cross resistant anthraquinone analogues. Synthesis and molecular basis of the cytotoxic activity towards K562/DOX cells

1. Multidrug resistance (MDR) to antitumour agents, structurally dissimilar and having different intracellular targets, is the major problem in cancer therapy. MDR phenomenon is associated with the presence of membrane proteins which belong to the ATP-binding cassette family transporters responsible for the active drug efflux leading to the decreased intracellular accumulation. 2. The search of new compounds able to overcome MDR is of prime importance. 3. Recently we have synthesized a new family of anthrapyridone compounds. The series contained derivatives modified with appropriate hydrophobic or hydrophylic substituents at the side chain. 4. The interaction of these derivatives with erythroleukemia K562 sensitive and K562/DOX resistant (overexpressing P-glycoprotein) cell lines has been examined. The study was performed using a spectrofluorometric method which allows to continuously follow the uptake and efflux of fluorescent molecules by living cells. 5. It was demonstrated that the increase in the lipophilicity of anthrapyridones favoured the very fast cellular uptake exceeding the rate of P-gp dependent efflux out of the cell. For these derivatives, very high accumulation (the same for sensitive and resistant cells) was observed and the in vitro biological data confirmed that these compounds exhibited comparable cytotoxic activity towards sensitive and P-gp resistant cell line. In contrast, anthrapyridones modified with hydrophylic substituents exhibited relatively low kinetics of cellular uptake. 6. For these derivatives decreased accumulation in resistant cells was observed and the in vitro biological data demonstrated that they were much less active against P-gp resistant cells in comparison to sensitive cells. 7. We also studied, using confocal microscopy, the intracellular distribution of anthrapyridones in NIH-3T3 cells. Our data showed that these compounds were strongly accumulated in the nucleus and lysosomes.