A polymer-Triton X-100 conjugate capable of PH-dependent red blood cell lysis: a model system illustrating the possibility of drug delivery within acidic intracellular compartments

In vitro screening of topical formulation excipients for epithelial toxicity in cancerous and non-cancerous cell lines

Chemical excipients used in topical formulations may be toxic to living skin cells. Here, we compared the in vitro toxicity of some common solubilizing excipients against human melanoma cells, human keratinocytes (HaCaT) and primary skin fibroblasts (FB) as examples of cancerous, immortalized and primary human skin cells, often used as experimental models representative of in vivo conditions. Two distinct endpoint assays (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet (CV)) were used. The mechanism of cell death after excipient exposure was assessed through Reactive Oxygen Species (ROS) production, cell membrane integrity and cell cycle progression. Results showed that the surfactants, Labrasol®, Labrafil® and Transcutol®, were less toxic than Triton X-100 (a model irritant) in all cell types whereas the oil, Labrafac®, was non-toxic. The human melanoma WM164 cell line showed the greatest sensitivity toward cytotoxicity after chemical exposure, while the other cell lines were more resistant. The relative excipient cytotoxicity responses observed in the MTT and CV assays were comparable and similar trends were seen in their estimated 50 % inhibitory concentration (IC50) values. DNA fragmentation by flow cytometry after exposing the cells to IC50 concentrations of the excipients showed negligible apoptotic populations. ROS production was increased in all cell types after toxic exposure; however, ROS elevation did not lead to apoptosis. The toxicity profiles of each excipient are not only relevant to their use in formulating safe topical products but also in the potential synergistic efficacy in the topical treatment of melanoma.

Development of an Oil-in-Water Self-Emulsifying Microemulsion for Cutaneous Delivery of Rose Bengal: Investigation of Anti-Melanoma Properties

The topical delivery route is proposed as an alternative or adjunctive approach to melanoma treatment, since the target site for melanoma treatment-the epidermal basal layer-is potentially accessible by this route. Microemulsion systems are effective delivery vehicles for enhanced, targeted skin delivery. This work investigated the effect of Rose Bengal (RB) and RB-loaded self-emulsifying microemulsions (SEMEs) on growth inhibition of human melanoma and normal skin cell monolayers, the safety of the excipients incorporated in SEMEs on human cell lines, and the in-vitro human skin penetration of RB delivered in SEMEs and control solution. Cellular toxicity was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the growth inhibitory mechanism of RB was investigated by flow cytometry using PI staining. Unloaded SEMEs caused reduced cellular toxicity compared to the surfactant excipient, Labrasol^®. RB-loaded SEMEs increased cell growth inhibition compared to the RB aqueous solution. Flow cytometry revealed apoptotic cells after treatment with RB-loaded SEMEs, indicating that apoptosis may be one of the mechanisms of cell death. Preliminary results of multiphoton microscopy with fluorescence lifetime imaging (MPM-FLIM) analysis showed deeper penetration with greater skin concentrations of RB delivered from SEMEs compared to the RB aqueous solution. This study highlights the enhanced skin penetration and antimelanoma effects of RB loaded in a SEME system.

Synthesis, physicochemical characterization, toxicity and efficacy of a PEG conjugate and a hybrid PEG conjugate nanoparticle formulation of the antibiotic moxifloxacin

Moxifloxacin was conjugated to polyethylene glycol to segregate host cell toxicity from antimicrobial activity. The conjugate was then encapsulated into a polycaprolactone nanoparticle to assist the simultaneous delivery of multiple drugs to the site of microbial infection.

Phospholipid-Coated Hydrophobic Mesoporous Silica Nanoparticles Enhance Thrombectomy by High-Intensity Focused Ultrasound with Low Production of Embolism-Inducing Clot Debris

Here we report the efficacy of a nanoparticle-assisted high-intensity focused ultrasound (HIFU) treatment that selectively destroys blood clots while minimizing generation of microparticles, or microemboli, that can cause further complications postsurgery. Treatment of malignant blood clots (thrombi) and the resulting emboli are critical problems for numerous patients, and treatments addressing these conditions would benefit from advancements in noninvasive procedures such as HIFU. While recanalization of occlusive blood clots is currently addressed with surgical intervention that seeks to minimize formation of large emboli, there is a danger of microemboli (micrometer-size particles) that have been theorized to be responsible for the poor correlation between apparent surgical success and patient outcome. Here, the addition of phospholipid-coated hydrophobically modified silica nanoparticles (P@hMSNs) improved the efficacy of HIFU treatment by serving as cavitation nuclei for mechanical disruption of thrombi. This treatment was evaluated for the ability to clear the HIFU focal area of a thick and dense thrombus within 10 min. Moreover, it was found that the use of P@hMSN+HIFU treatment generated a significantly smaller microembolic load as compared to comparison techniques, including a HIFU + microbubble contrast agent, HIFU alone, and direct mechanical disruption. This reduction in the microembolic load can occur either with primary removal of the clot by P@hMSN+HIFU or by insonation of the clot fragments after mechanical thrombectomy. Lastly, this method was evaluated in a flow model, where nonocclusive model thrombi and model emboli were mechanically ablated within the focal area within 15 s. Together, these results represent a combination therapy capable of resolving thrombi and microembolisms resulting from thrombectomy through localized destruction of clotted material.

Final Report on the Safety Assessment of Octoxynol-1, Octoxynol-3, Octoxynol-5, Octoxynol- 6, Octoxynol-7, Octoxynol-8, Octoxynol-9, Octoxynol-10, Octoxynol-11, Octoxynol-12, Octoxynol-13, Octoxynol-16, Octoxynol-20, Octoxynol-25, Octoxynol-30, Octoxynol-33, Octoxynol-40, Octoxynol-70, Octoxynol-9 Carboxylic Acid, Octoxynol-20 Carboxylic Acid, Potassium Octoxynol-12 Phosphate, Sodium Octoxynol-2 Ethane Sulfonate, Sodium Octoxynol-2 Sulfate, Sodium Octoxynol-6 Sulfate, and Sodium Octoxynol-9 Sulfate1

Octoxynols are ethoxylated alkylphenols in which the size of the molecule is related to the number of moles of ethylene oxide used in synthesis. Reactions are performed at elevated temperature, under pressure, and in the presence of NaOH. It is possible that the synthesis may leave trace amounts of ethylene oxide, 1,4-dioxane, and unreacted C9 phenols. Octoxynols of various chain lengths as well as octoxynol salts and organic acids function in cosmetics either as surfactants—emulsifying agents, surfactants—cleansing agents, surfactant—solubilizing agents, or surfactants—hydrotropes in a wide variety of cosmetic products at concentrations ranging from 0.0008% to 25%, with most less than 5.0%. The octoxynols are chemically similar to nonoxynols, the safety of which were previously considered. Long-chain nonoxynols (9 and above) were considered safe as used, whereas short-chain nonoxynols (8 and below) were considered safe as used in rinse-off products and safe at concentrations less than 5% in leave-on formulations.

Enhanced anti-tumor activity and safety profile of targeted nano-scaled HPMA copolymer-alendronate-TNP-470 conjugate in the treatment of bone malignances

Bone neoplasms, such as osteosarcoma, exhibit a propensity for systemic metastases resulting in adverse clinical outcome. Traditional treatment consisting of aggressive chemotherapy combined with surgical resection, has been the mainstay of these malignances. Therefore, bone-targeted non-toxic therapies are required. We previously conjugated the aminobisphosphonate alendronate (ALN), and the potent anti-angiogenic agent TNP-470 with N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer. HPMA copolymer-ALN-TNP-470 conjugate exhibited improved anti-angiogenic and anti-tumor activity compared with the combination of free ALN and TNP-470 when evaluated in a xenogeneic model of human osteosarcoma. The immune system has major effect on toxicology studies and on tumor progression. Therefore, in this manuscript we examined the safety and efficacy profiles of the conjugate using murine osteosarcoma syngeneic model. Toxicity and efficacy evaluation revealed superior anti-tumor activity and decreased organ-related toxicities of the conjugate compared with the combination of free ALN plus TNP-470. Finally, comparative anti-angiogenic activity and specificity studies, using surrogate biomarkers of circulating endothelial cells (CEC), highlighted the advantage of the conjugate over the free agents. The therapeutic platform described here may have clinical translational relevance for the treatment of bone-related angiogenesis-dependent malignances.

Integrin-assisted drug delivery of nano-scaled polymer therapeutics bearing paclitaxel

Angiogenesis plays a prominent role in cancer progression. Anti-angiogenic therapy therefore, either alone or in combination with conventional cytotoxic therapy, offers a promising therapeutic approach. Paclitaxel (PTX) is a widely-used potent cytotoxic drug that also exhibits anti-angiogenic effects at low doses. However, its use, at its full potential, is limited by severe side effects. Here we designed and synthesized a targeted conjugate of PTX, a polymer and an integrin-targeted moiety resulting in a polyglutamic acid (PGA)-PTX-E-[c(RGDfK)(2)] nano-scaled conjugate. Polymer conjugation converted PTX to a macromolecule, which passively targets the tumor tissue exploiting the enhanced permeability and retention effect, while extravasating via the leaky tumor neovasculature. The cyclic RGD peptidomimetic enhanced the effects previously seen for PGA-PTX alone, utilizing the additional active targeting to the α(v)β(3) integrin overexpressed on tumor endothelial and epithelial cells. This strategy is particularly valuable when tumors are well-vascularized, but they present poor vascular permeability. We show that PGA is enzymatically-degradable leading to PTX release under lysosomal acidic pH. PGA-PTX-E-[c(RGDfK)(2)] inhibited the growth of proliferating α(v)β(3)-expressing endothelial cells and several cancer cells. We also showed that PGA-PTX-E-[c(RGDfK)(2)] blocked endothelial cells migration towards vascular endothelial growth factor; blocked capillary-like tube formation; and inhibited endothelial cells attachment to fibrinogen. Orthotopic studies in mice demonstrated preferential tumor accumulation of the RGD-bearing conjugate, leading to enhanced anti-tumor efficacy and a marked decrease in toxicity as compared with free PTX-treated mice.

Polymeric nanoparticles for gene delivery

Since the evolution of the concept of gene therapy, delivering therapeutic genes to the diseased cells has been a major challenge. Although viral vectors have been shown to be efficient in delivering genes, the issue of their safety is still to be solved. Meanwhile, the field of developing nonviral expression vectors has seen considerable progress. As compared with viruses, these are relatively safe but are confronted with the problem of poor transfection efficiency. With the growing understanding of the biology of gene transfection, and the continued efforts at enhancing the efficiency of nonviral expression vectors, it could soon become a preferred option for human gene therapy. In this review, the potential of polymeric nanoparticles as a gene expression vector is discussed. Furthermore, the importance of understanding the pathophysiology of disease conditions in developing gene expression vectors is discussed in Section 6.

Synthesis and preliminary evaluation of poly(amidoamine)–melittin conjugates as endosomolytic polymers and/or potential anticancer therapeutics

The pH-responsive poly(amidoamine)s (PAAs) have been previously described. Whereas ISA23 enhances transfection in vitro and ISA1 promotes the cytosolic delivery of the non-permeant toxins this process shows poor efficiency. The aim of this study was to prepare and evaluate PAA conjugates containing the membrane disrupting peptide melittin (MLT). It was hypothesised that PAA conjugation would reduce the haemolytic activity of MLT at pH 7.4, however, upon delivery to tumours by the EPR effect, the polymer would uncoil in an acidic environment exposing MLT and allowing it to interact with membranes. PAA-MLT conjugates were prepared using MLT as a comonomer together with bis-acryloylpiperazine, 2-methylpiperazine and bis-hydroxyethylethylenediamine (ISA1-like), or bis-acrylamidoacetic acid and 2-methylpiperazine (ISA23-like). The melittin content of the conjugates was 6-19% (w/w). Although ISA1-MLT improved gelonin delivery compared to the parent polymer ISA1 (alpha 13-fold increase) and showed pH-dependent haemolytic activity at a polymer concentration of 0.05 mg/ml, this conjugate also displayed high haemolytic activity at pH 7.4.In contrast, ISA23-MLT like the parent compound ISA23 did not deliver gelonin. However, this conjugate could have potential as a novel polymeric anticancer conjugate due to its lack of haemolytic activity at pH 7.4 and retention of cytotoxicity.

Understanding the Mechanism of Action of Poly(amidoamine)s as Endosomolytic Polymers: Correlation of Physicochemical and Biological Properties

Bioresponsive poly(amidoamine)s (PAA)s are currently under development as endosomolytic polymers for intracellular delivery of proteins and genes. Here for the first time, small-angle neutron scattering (SANS) is used to systematically investigate the pH-dependent conformational change of an endosomolytic polymer, the PAA ISA 23. The radius of gyration of the ISA23 was determined as a function of pH and counterion, the aim being to correlate changes in polymer conformation with membrane activity assessed using a rat red blood cell haemolysis assay. With decreasing pH, the ISA23 radius of gyration increased to a maximum (R(g) approximately 80 A) around pH = 3, before subsequently decreasing once more. At high pH and therefore high ionic strengths, the polymer is negatively charged and adopts a rather compact structure (R(g) approximately 20 A), presumably with the dissociated carboxylic groups on the exterior of the polymer coil. At low pH, the coil again collapses (R(g) < 20 A), presumably due to the effects of the high ionic strength. It is concluded that the nature of the salt form has no direct bearing on the size of the polymer coil, but it does indirectly determine the prevailing pH and, hence, polymer conformation. Pulsed-gradient spin-echo NMR measurements were in good agreement with the SANS estimates of the radius of gyration, although ISA23 polydispersity does complicate the data interpretation/comparison. These results support the proposed mode of action of PAAs, namely a coil expansion on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. The results do, however, suggest that the charge on the polymer shows a closer correlation with the haemolysis activity rather than the polymer conformation.

Adaptation of commercial immunoassays to analysis of complex biological substances

An Intracellular Adhesion Molecule I (ICAM-1) immunoassay from R and D Systems, and a Melanoma Inhibitory Activity (MIA) immunoassay from Roche Diagnostics were tested for accurate quantitation within complex biological substances such as cell lysates. Prior to assay, lysates of melanoma cells were treated with detergents to obtain soluble antigens. Maximum ICAM-1 and maximum MIA were detected after treatment using 0.8% Triton X-100. Two key aspects of assay accuracy were: 1) determining the dilutions of test sample that provided accurate quantitation (sample range), and 2) performing spiking experiments at these dilutions to determine absence or presence of a "matrix" effect due to biological complexity of the sample. A high degree of accuracy was found by diluting this particular cellular extract 50-fold prior to ICAM-1 assay, or only 5-fold prior to MIA assay. In addition, the bicinchoninic acid protein assay was analyzed to test the accuracy of protein quantitation of cellular lysates. Precision, limits of detection, and quantitation, robustness, linearity, and specificity also were tested for the immunoassays.

Poly(amidoamine)s as potential nonviral vectors: ability to form interpolyelectrolyte complexes and to mediate transfection in vitro

Poly(amidoamine)s (PAAs) are water-soluble polymers that display pH-dependent membrane activity. PAAs have the potential to act as a synthetic alternative to fusogenic peptides and thus promote endosomal escape. The purpose of this study was to investigate for the first time whether PAA have the ability to complex DNA, protect it from nuclease degradation and to promote transfection in vitro. PAAs ISA 1 (Mn 6900) and ISA 23 (Mn 10,500) and their 2-phenylethylamine containing analogues ISA 4 and ISA 22 (Mn approximately 8000) were studied. All PAAs retarded the electrophoretic mobility of lambda Hind III DNA demonstrating interpolyelectrolyte complex (IPEC) formation and toroids of 80-150 nm in diameter (10:1 polymer excess) were visible using TEM. DNase II inhibition was observed. At a polymer:DNA ratio of 10:1, this was ISA 1(89.6 +/- 6.1%), ISA 4 (92.2 +/- 11.2%), ISA 22 (69.4 +/- 3.7%), and ISA 23 (58.0 +/- 10.0%). PAAs demonstrated the ability to mediate pSV beta-galactosidase transfection of HepG2 cells. At a vector:DNA mass ratio of 5:1, ISA 23 showed equivalent transfection ability compared with polyethylenimine and LipofectIN and was more effective than LipofectACE. These properties suggest that PAAs warrant further development as endosomolytic vectors.

Poly(amidoamine)-mediated intracytoplasmic delivery of ricin A-chain and gelonin

Poly(amidoamine)s (PAAs) are water-soluble synthetic polymers designed to be biodegradable and biocompatible. Moreover, they display membrane disruptive properties in response to a decrease in pH. This attribute confers PAAs with endosomolytic properties in vitro and in vivo. A model system was developed to quantify their ability to promote the endosomal escape of macromolecules that may be interesting as therapeutic agents. Here, two PAAs (ISA 1 and 4) were incubated with B16F10 cells in vitro together with two non-permeant toxins: either ricin A-chain (RTA) or gelonin. The relatively non-toxic PAAs ISA 1 and 4 (IC50>1.5 mg/ml) restored activity to the inherently inert toxins. The IC50 values for the ISA 1/RTA and ISA 1/gelonin combinations were 0.65+/-0.05 and 0.55+/-0.12 mg/ml, respectively. Similarly, when ISA 4 was incubated with a non-toxic combination of RTA and gelonin the IC50 value decreased to 0.57+/-0.03 and 0.43+/-0.26 mg/ml, respectively. In contrast, the neutral polymer dextran and the PAA ISA 22 were unable to mediate this effect. These observations suggest that specific PAA-toxin combinations warrant further development as novel therapeutics.

Derivatives of monoglycerides as apoptotic agents in T-cells

Recently, lipids have received considerable attention for their potential to induce apoptosis when added exogenously to cells. In this study, we directly demonstrate that murine T-cells undergo rapid apoptosis following treatment with various forms of monoglycerides, which are a family of naturally occurring lipids consisting of a single fatty acid moiety attached to a glycerol backbone. The potency of these lipids varied depending on their chemical structure, whereas glycerol backbone or corresponding fatty acids alone were ineffective. Moreover, monoglyceride-mediated apoptosis was suppressed either by Bcl-2 overexpression, treatment with a broad inhibitor of caspases, or RNA and protein synthesis inhibitors. In addition, treatment of cells with derivatives of monoglycerides induced a calcium flux, which could be inhibited by both extracellular (EGTA) or intracellular (EGTA-AM) calcium chelators. To our knowledge, this is the first report demonstrating a role for derivatives of monoglycerides as inducers of apoptosis in mammalian cells.

Cyclodextrin as a potential drug carrier in salbutamol dry powder aerosols: the in-vitro deposition and toxicity studies of the complexes

This research was carried out to develop a new carrier in dry powder aerosols. Two types of cyclodextrin were chosen; gamma cyclodextrin (GCD) and dimethyl-beta-cyclodextrin (DMCD) as carriers in dry powder formulations. Salbutamol was used as a model drug and a control formulation containing lactose and the drug was included. A twin-stage impinger (TSI) was used to evaluate in delivery efficiency of those dry powder formulations. The toxicity of cyclodextrin complexes was investigated in the rat by monitoring blood urea nitrogen (BUN) and urinary creatinine, as well as determining haemolysis of human red blood cells. The release of salbutamol from dry powder formulations was also studied over a period of time. From the results obtained, it was found that the formulation containing GCD-enhanced drug delivery to the lower stage of the TSI (deposition = 65%) much greater than that of both formulations containing DMCD (50%) and the control formulation (40%) (P<0.05). After injecting the GCD complex BUN and creatinine levels in rats were similar to those obtained in the control while those receiving DMCD complex had higher BUN and creatinine. The haemolysis of red blood cells incubated with the DMCD complex was higher than that obtained in the GCD complex. The drug release in both formulations containing GCD and DMCD was fast (over 70% was released in 5 min) and nearly all the drug was released within 30 min. It can be concluded that GCD and DMCD are able to promote salbutamol delivery in dry powder inhaler compared to a formulation containing lactose. In addition, GCD is relatively safe in the rat if the amount of GCD in the formulation is similar to this experiment.

Increased vigabatrin entry into the brain by polysorbate 80 and sodium caprate

The effects of a non-ionic surfactant, polysorbate 80, and the sodium salt of the saturated fatty acid, sodium caprate (C10), as potential brain absorption enhancers for vigabatrin were studied. Vigabatrin is an enzyme-activated irreversible inhibitor of gamma-aminobutyric acid (GABA) transaminase that increases brain and cerebrospinal GABA concentrations in animals and man. Before intravenous administration, a range of concentrations of the surfactants were tested using erythrocyte lysis or the red blood cell lysis test to establish the non-toxic concentration range. Vigabatrin was dissolved in 0.1% polysorbate 80 and 0.1% sodium caprate and administered intravenously in doses of 4 mL kg(-1) to male Wistar rats (230-250 g; n = 3). Rats were killed 2 h after drug and surfactant administration and the brains were immediately removed and homogenized in 0.4 M perchloric acid. Selected ion monitoring electrospray mass spectrometry was used to determine the concentration of vigabatrin and GABA directly from the perchloric acid extract of the rat brain. This method was developed to increase the speed and efficiency of the analysis by removing the need for complex extraction and derivatization procedures while retaining the specificity of the mass spectrometer as a detector. The stability of both vigabatrin and GABA in perchloric acid was established by monitoring their pseudo molecular ions in standard solutions at timed intervals over 24 h. Although the detection level for vigabatrin and GABA was at least 50 pg, only GABA was detected in rat brain. Vigabatrin caused a small increase in whole brain GABA. However, GABA levels were higher in the samples with vigabatrin + enhancer than in the samples where vigabatrin alone was administered. One-way analysis of variance indicated a significant effect of the surfactants on GABA levels (F (5,17) = 11.86, P < 0.01) and vigabatrin absorption was presumed. The rectal temperature of the rats is lowered by the presence of vigabatrin in the brain. Vigabatrin alone decreased rectal temperature by 6%. When given with either polysorbate 80 or sodium caprate, the extent of temperature lowering was significantly greater (P < 0.001). There was no significant difference after 2 h between polysorbate 80 + vigabatrin, and sodium caprate + vigabatrin.

pH-responsive pseudo-peptides for cell membrane disruption

We describe pseudo-peptides obtained by the copolymerisation of L-lysine and L-lysine ethyl-ester with various hydrophobic dicarboxylic acid moieties. In aqueous solution, when the carboxylic acid groups are charged, the polymers dissolve. When they are fully neutralised the hydrophobic moieties cause the polymer to precipitate. The pH range over which reversible precipitation occurs can be adjusted by changing the intramolecular hydrophilic/hydrophobic balance, by using a carboxylic acid moiety with a different pK(a) value or by changing the apparent pK(a) value of the polymer through chemical modifications of the backbone. These bio-degradable materials are well tolerated by a range of mammalian cell lines at physiological pH but display an ability to associate with the outer membranes of these cells, which they rupture to varying degrees at pH 5.5. Relative to the degree of lysis displayed by poly(L-lysine iso-phthalamide), lysis was reduced by partial esterification and increased by replacing the aromatic iso-phthaloyl moiety with a long chain aliphatic dodecyl moiety. Similar behaviour was observed for the pH-dependent rupture of human erythrocytes, where poly(L-lysine dodecanamide) displayed enhanced cell lysis at pH values <7.0 relative to poly(L-lysine iso-phthalamide).

Poly(amidoamine)s as potential endosomolytic polymers: evaluation in vitro and body distribution in normal and tumour-bearing animals

Fusogenic peptides derived from viral coat proteins cause perturbation of the endosomal membrane and are often used to improve the transfection efficiency of non-viral vectors in vitro. However, fusogenic peptides have limited potential for use in vivo due to their inherent immunogenicity. Totally synthetic polymers that are endosomolytic should circumvent this problem and could be useful as components of non-viral delivery systems as long as they do not immediately localise in the liver after intravenous (i.v.) injection. Linear poly(amidoamine) polymers (PAAs) having amido- and tertiary amino-groups along the main polymer undergo pH-dependent conformational change and thus provide an ideal opportunity for design of polymers that display membrane activity at low pH. Here we describe four PAAs, ISA 1 (Mn = 6900 Da) and ISA 23 (Mn = 10,500 Da) and their analogues ISA 4 and ISA 22 (Mn approximately 8000 Da) containing approximately 1 mol% 2-p-hydroxyphenyl ethylamine to allow radioiodination and thus monitoring of their biodistribution. In vitro cytotoxicity was assessed by MTT assay after incubation of PAAs with B16F10 and Mewo cell lines. The IC50 values observed for all PAAs were > 2 mg/mL in comparison with poly(L-lysine) which displayed an IC50 in the range 0.01-0.1 mg/mL. At pH 7.4 none of the PAAs studied was haemolytic at 1 h at concentrations below 3 mg/mL. PAAs were subsequently incubated with rat red blood cells for 24 h (1 mg/mL) at different pHs. In contrast to poly(L-lysine) which was haemolytic at pH 7.4, 6.5 and 5.5, none of the PAAs was lytic at pH 7.4, but they became membrane active at lower pH (approximately 45% for ISA 4, 50% for ISA 22 and 90% for ISA 23). These observations were substantiated by SEM and confirm the pH-dependence of membrane activity. After i.v. injection to rats 125I-labelled ISA 4 was immediately taken up by the liver (> 80% recovered dose at 1 h) whereas 125I-labelled ISA 22 was not (liver uptake was < 10% recovered dose at 5 h). Furthermore, biodistribution studies in mice bearing subcutaneous B16F10 melanoma showed that 125I-labelled ISA 22 was still accumulating in tumour tissue after 5 h (2.5% dose/g). PAAs have potential as endosomolytic agents and quantitation of the endosome to cytoplasm transfer is warranted after i.v. administration.

In vitro cytotoxicity of poly(amidoamine)s: relevance to DNA delivery

We have examined the cytotoxicity of a number of poly(amidoamine) polymers which have been proposed for use as DNA delivery systems and compared them to the charged polyamino acid polylysine. Most of the poly(amidoamine)s tested were shown to be remarkably non-toxic to both HepG2 and HL60 cell lines. However, one of the structures (NG30, co-monomers methylene bisacrylamide, dimethylethylene diamine) did show cytotoxicity similar to that of polylysine. A second PAA structure (NG37, NG38, NG39, co-monomers bisacryloyl piperazine, 2-methyl piperazine) showed mild cytotoxicity towards both cell lines, related to the degree of polymerisation. The results support the idea that the cytotoxicity of polycations has a strong structural basis rather than being an effect due only to charge. As a consequence of their general reduced level of cytotoxicity, poly(amidoamine)s appear to have possible advantages for complexation with DNA over some other cationic polymers as a key component of DNA delivery systems.