Electrostatics of PEGylated micelles and liposomes containing charged and neutral lipopolymers

Liposomes with Low Levels of Grafted Poly(ethylene glycol) Remain Susceptible to Destabilization by Anti-Poly(ethylene glycol) Antibodies

Binding of anti-PEG antibodies to poly(ethylene glycol) (PEG) on the surface of PEGylated liposomal doxorubicin (PLD) in vitro and in rats can activate complement and cause the rapid release of doxorubicin from the liposome interior. Here, we find that irinotecan liposomes (IL) and L-PLD, which have 16-fold lower levels of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE)-PEG2000 in their liposome membrane as compared to PLD, generate less complement activation but remain sensitive to destabilization and drug release by anti-PEG antibodies. Complement activation and liposome destabilization correlated with the theoretically estimated number of antibody molecules bound per liposome. Drug release from liposomes proceeded through the alternative complement pathway but was accelerated by the classical complement pathway. In contrast to PLD destabilization by anti-PEG immunoglobulin G (IgG), which proceeded by the insertion of membrane attack complexes in the lipid bilayer of otherwise intact PLD, anti-PEG IgG promoted the fusion of L-PLD, and IL to form unilamellar and oligo-vesicular liposomes. Anti-PEG immunoglobulin M (IgM) induced drug release from all liposomes (PLD, L-PLD, and IL) via the formation of unilamellar and oligo-vesicular liposomes. Anti-PEG IgG destabilized both PLD and L-PLD in rats, indicating that the reduction of PEG levels on liposomes is not an effective approach to prevent liposome destabilization by anti-PEG antibodies.

Design, optimization, characterization, and in vitro evaluation of metformin-loaded liposomes for triple negative breast cancer treatment

Recently, metformin (Met) has shown to have antineoplastic properties in cancer treatment by improving hypoxic tumor conditions, and causing reduction in the synthesis of biomolecules, which are vital for cancer growth. However, as an orally administered drug, Met has low bioavailability and rapid renal clearance. Thus, the goal of this study was to vectorize Met inside liposomes in the context of triple negative breast cancer (TNBC), which currently lacks treatment options when compared to other types of breast cancer. Vectorization of Met inside liposomes was done using Bangham method by implementing double design of experiment methodology to increase Met drug loading (minimum-run resolution V characterization design and Box-Behnken design), as it is generally extremely low for hydrophilic molecules. Optimization of Met-loaded liposome synthesis was successfully achieved with drug loading of 190 mg/g (19% w/w). The optimal Met-liposomes were 170 nm in diameter with low PdI (< 0.1) and negative surface charge (-20 mV), exhibiting sustained Met release at pH 7.4. The liposomal Met delivery system was stable over several months, and successfully reduced TNBC cell proliferation due to the encapsulated drug. This study is one the first reports addressing liposome formulation through thin-film hydration using two design of experiment methods aiming to increase drug loading of Met.

Anti-PEG antibodies before and after a first dose of Comirnaty® (mRNA-LNP-based SARS-CoV-2 vaccine)

The early and massive vaccination campaign in Israel with the mRNA-LNP Comirnaty® (Pfizer-BioNTech) vaccine against the SARS-CoV-2 virus made available large amounts of data regarding the efficacy and safety of this vaccine. Adverse reactions to mRNA-based SARS-CoV-2 vaccines are rare events, but due to large mediatic coverage they became feared and acted as a potential source of delay for the vaccination of the Israeli population. The experience with the reactogenicity of the polyethylene glycol (PEG) moiety of PEGylated liposomes, PEGylated proteins and other PEGylated drugs raised the fear that similar adverse effects can be associated with the PEG lipid which is an essential component of currently used mRNA-LNP vaccines against COVID-19. In this study we quantified the levels of anti-PEG IgG, IgM and IgE present in the blood of 79 volunteers immediately before and 3 weeks after receiving a first dose of Comirnaty® vaccine. Our in vitro results show that different humanized anti-PEG antibodies bind the PEGylated nano-liposomes in a concentration-dependent manner, but they bind with a lower affinity to the Comirnaty vaccine, despite it having a high mole% of neutral PEG₂₀₀₀-lipid on its surface. We found an increase in IgG concentration in the blood 3 weeks after the first vaccine administration, but no increase in IgM or IgE. In addition, no severe signs of adverse reactions to the Comirnaty vaccine were observed in the population studied despite the significant pre-existing high titers of IgG before the first dose of vaccine in 2 donors.

Irinotecan-Loaded Polymeric Micelles as a Promising Alternative to Enhance Antitumor Efficacy in Colorectal Cancer Therapy

Colorectal cancer has been considered a worldwide public health problem since current treatments are often ineffective. Irinotecan is a frontline chemotherapeutic agent that has dose-limiting side effects that compromise its therapeutic potential. Therefore, it is necessary to develop a novel, targeted drug delivery system with high therapeutic efficacy and an improved safety profile. Here, micellar formulations composed of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] (DSPE-mPEG_2k) containing irinotecan were proposed as a strategy for colorectal cancer therapy. Firstly, the irinotecan-loaded micelles were prepared using the solvent evaporation method. Then, micelles were characterized in terms of size, polydispersity, zeta potential, entrapment efficiency, and release kinetics. Cytotoxicity and in vivo antitumor activity were evaluated. The micelles showed size around 13 nm, zeta potential near neutral (-0.5 mV), and encapsulation efficiency around 68.5% (irinotecan 3 mg/mL) with a sustained drug release within the first 8 h. The micelles were evaluated in a CT26 tumor animal model showing inhibition of tumor growth (89%) higher than free drug (68.7%). Body weight variation, hemolytic activity, hematological, and biochemical data showed that, at the dose of 7.5 mg/kg, the irinotecan-loaded micelles have low toxicity. In summary, our findings provide evidence that DSPE-mPEG_2k micelles could be considered potential carriers for future irinotecan delivery and their possible therapeutic application against colorectal cancer.

Microfluidic formulation of lipid/polymer hybrid nanoparticles for plasmid DNA (pDNA) delivery

Lipid/polymer hybrid nanoparticles loaded with red fluorescent protein (RFP) encoded plasmid DNA (pDNA) was formulated using poly-lactic-co-glycolic acid (PLGA), cationic lipid DC-cholesterol and surfactant mPEG₂₀₀₀- DSPE. A lipid/ polymer ratio of 1: 10 at 1 mg/mL surfactant concentration was found to be optimal for producing nanoparticles with diameters of 100-120 nm that remained stable upon ultracentrifugation. The production of lipid/ polymer hybrid nanoparticles was investigated using microfluidics with a toroidal mixer design. Our results showed that the flow parameters significantly influenced the physicochemical characteristics of nanoparticles and loading of pDNA was only achieved at flow rate ratio (FRR) of 3: 1. The pDNA associated with nanoparticles was demonstrated to be structurally intact using gel electrophoresis, and the encapsulation efficiency (EE) was measured to be ∼65%. The prepared hybrid nanoparticles resulted in 20% of transfection efficacy in human embryonic kidney cells (HEK293T). This study demonstrated the potential of microfluidics in the development of hybrid nanoparticles for pDNA delivery, thus facilitating the clinical translation of DNA therapeutics.

Engineering biosafe cisplatin loaded nanostructured lipid carrier: optimisation, synthesis, pharmacokinetics and biodistribution

Low aqueous solubility, adverse effects of Cisplatin includes hepatotoxicity and nephrotoxicity necessitates development of nanoparticulate drug delivery. The study pertains to development of CisNLC (Cisplatin loaded Nanostructured Lipid Carrier) by ultrasonication. Physical characterisation includes particle size, zeta potential, TEM, SEM-EDX, DSC. Its ex vivo biocompatibility, pharmacokinetics and biodistribution along with acute toxicity induced oxidative stress in Balb/c mice were evaluated. The mean particle diameter of CisNLC was observed to be 141.5 ± 3.86 nm with zeta potential of -41.5 ± 1.62 mV. In vitro release studies at pH 7.4 and 5.8 showed burst release following a sustained release pattern post-72 h. CisNLC showed anticancer efficacy against PA-1. Negligible ex vivo haemolysis indicated bio-compatibility. Improved pharmacokinetics of CisNLC was observed. Acute toxicity and oxidative stress evaluation proved negligible toxicity by CisNLC. The formulated CisNLC had a good physical stability, biocompatible, indicated enhanced circulation and caused negligible toxicity on liver and kidney as compared to pure Cis.

Liposomal formulations of anticancer copper(II) thiosemicarbazone complexes

α-N-Heterocyclic thiosemicarbazones such as triapine and COTI-2 are currently investigated as anticancer therapeutics in clinical trials. However, triapine was widely inactive against solid tumor types. A likely explanation is the short plasma half-life time and fast metabolism. One promising approach to overcome these drawbacks is the encapsulation of the drug into nanoparticles (passive drug-targeting). In a previous work we showed that it was not possible to stably encapsulate free triapine into liposomes. Hence, in this manuscript we present the successful preparation of liposomal formulations of the copper(II) complexes of triapine and COTI-2. To this end, various drug-loading strategies were examined and the resulting liposomes were physico-chemically characterized. Especially for liposomal Cu-triapine, a decent encapsulation efficacy and a slow drug release behavior could be observed. In contrast, for COTI-2 and its copper(II) complex no stable loading could be achieved. Subsequent in vitro studies in different cell lines with liposomal Cu-triapine showed the expected strongly reduced cytotoxicity and DNA damage induction. Also in vivo distinctly higher copper plasma levels and a continuous release could be observed for the liposomal formulation compared to free Cu-triapine. Taken together, the here presented nanoformulation of Cu-triapine is an important step further to increase the plasma half-life time and tumor targeting properties of anticancer thiosemicarbazones.

Poly(Ethylene Glycol) Interacts with Hyaluronan in Aqueous Media

We report here the first evidence for the interaction of poly(ethylene glycol) (PEG) with hyaluronan (HA) in aqueous solutions. PEG-HA complexes (K_app = 45,000 ± 8000 M^-1) contained about 3.3 ± 0.1 of ethylene glycol units per disaccharide of HA. The carboxyl of the D-glucuronic acid and the amide of the N-acetyl-D-glucosamine did not participate in PEG binding. Similar experiments performed with dextran and monosaccharides showed that multiple free primary hydroxyls regularly distributed along the polysaccharide chain are necessary for PEG binding. Another novelty of our study is contraction of HA upon PEG binding. The effect was observed with HA in solution or adsorbed on positively charged liposomes. The thickness of the HA layer on the liposomes decreased 2-fold upon PEG addition. HA compaction induced by PEG may underlie the changes in the plasma membrane properties and resealing of mechanical injuries induced by Pluronics.

Premature Drug Release from Polyethylene Glycol (PEG)-Coated Liposomal Doxorubicin via Formation of the Membrane Attack Complex

Anti-polyethylene glycol (PEG) antibodies are present in many healthy individuals as well as in patients receiving polyethylene glycol-functionalized drugs. Antibodies against PEG-coated nanocarriers can accelerate their clearance, but their impact on nanodrug properties including nanocarrier integrity is unclear. Here, we show that anti-PEG IgG and IgM antibodies bind to PEG molecules on the surface of PEG-coated liposomal doxorubicin (Doxil, Doxisome, LC-101, and Lipo-Dox), resulting in complement activation, formation of the membrane attack complex (C5b-9) in the liposomal membrane, and rapid release of encapsulated doxorubicin from the liposomes. Drug release depended on both classical and alternative pathways of complement activation. Doxorubicin release of up to 40% was also observed in rats treated with anti-PEG IgG and PEG-coated liposomal doxorubicin. Our results demonstrate that anti-PEG antibodies can disrupt the membrane integrity of PEG-coated liposomal doxorubicin through activation of complement, which may alter therapeutic efficacy and safety in patients with high levels of pre-existing antibodies against PEG.

Symbiotic Self-Assembly Strategy toward Lipid-Encased Cross-Linked Polymer Nanoparticles for Efficient Gene Silencing

A novel "symbiotic self-assembly" strategy that integrates the advantages of biocompatible lipids with a structurally robust polymer to efficiently encapsulate and deliver siRNAs is reported. The assembly process is considered to be symbiotic because none of the assembling components are capable of self-assembly but can form well-defined nanostructures in the presence of others. The conditions of the self-assembly process are simple but have been chosen such that it offers the ability to arrive at a system that is noncationic for mitigating carrier-based cytotoxicity, efficiently encapsulate siRNA to minimize cargo loss, be effectively camouflaged to protect the siRNA from nuclease degradation, and efficiently escape the endosome to cause gene knockdown. The lipid-siRNA-polymer (L-siP) nanoassembly formation and its disassembly in the presence of an intracellular trigger have been extensively characterized experimentally and through computational modeling. The complexes have been evaluated for the delivery of four different siRNA molecules in six different cell lines, where an efficient gene knockdown is demonstrated. The reported generalized strategy has the potential to make an impact on the development of a safe and effective delivery agent for RNAi-mediated gene therapy that holds the promise of targeting several hard-to-cure diseases.

Involvement of complement activation in the pulmonary vasoactivity of polystyrene nanoparticles in pigs: unique surface properties underlying alternative pathway activation and instant opsonization

Background

It has been proposed that many hypersensitivity reactions to nanopharmaceuticals represent complement (C)-activation-related pseudoallergy (CARPA), and that pigs provide a sensitive animal model to study the phenomenon. However, a recent study suggested that pulmonary hypertension, the pivotal symptom of porcine CARPA, is not mediated by C in cases of polystyrene nanoparticle (PS-NP)-induced reactions.

Goals

To characterize PS-NPs and reexamine the contribution of CARPA to their pulmonary reactivity in pigs.

Study design

C activation by 200, 500, and 750 nm (diameter) PS-NPs and their opsonization were measured in human and pig sera, respectively, and correlated with hemodynamic effects of the same NPs in pigs in vivo.

Methods

Physicochemical characterization of PS-NPs included size, ζ-potential, cryo-transmission electron microscopy, and hydrophobicity analyses. C activation in human serum was measured by ELISA and opsonization of PS-NPs in pig serum by Western blot and flow cytometry. Pulmonary vasoactivity of PS-NPs was quantified in the porcine CARPA model.

Results

PS-NPs are monodisperse, highly hydrophobic spheres with strong negative surface charge. In human serum, they caused size-dependent, significant rises in C3a, Bb, and sC5b-9, but not C4d. Exposure to pig serum led within minutes to deposition of C5b-9 and opsonic iC3b on the NPs, and opsonic iC3b fragments (C3dg, C3d) also appeared in serum. PS-NPs caused major hemodynamic changes in pigs, primarily pulmonary hypertension, on the same time scale (minutes) as iC3b fragmentation and opsonization proceeded. There was significant correlation between C activation by different PS-NPs in human serum and pulmonary hypertension in pigs.

Conclusion

PS-NPs have extreme surface properties with no relevance to clinically used nanomedicines. They can activate C via the alternative pathway, entailing instantaneous opsonization of NPs in pig serum. Therefore, rather than being solely C-independent reactivity, the mechanism of PS-NP-induced hypersensitivity in pigs may involve C activation. These data are consistent with the “double-hit” concept of nanoparticle-induced hypersensitivity reactions involving both CARPA and C-independent pseudoallergy.

Nanoformulations of anticancer FGFR inhibitors with improved therapeutic index

Fibroblast growth factor receptor (FGFR) inhibitors like ponatinib and nintedanib are clinically approved for defined cancer patient cohorts but often exert dose-limiting adverse effects. Hence, we encapsulated the FGFR inhibitors ponatinib, PD173074, and nintedanib into polylactic acid nanoparticles and liposomes to enable increased tumor accumulation/specificity and reduce side effects. Different methods of drug loading were tested and the resulting formulations compared regarding average size distribution as well as encapsulation efficiency. Appropriate encapsulation levels were achieved for liposomal preparations only. Nanoencapsulation resulted in significantly decelerated uptake kinetics in vitro with clearly decreased short-term (up to 72 h) cytotoxicity at higher concentrations. However, in long-term clonogenic assays liposomal formations were equally or even more active as compared to the free drugs. Accordingly, in an FGFR inhibitor-sensitive murine osteosarcoma transplantation model (K7M2), only liposomal but not free ponatinib resulted in significant tumor growth inhibition (by 60.4%) at markedly reduced side effects.

In Vitro and In Vivo evaluation of a novel folate-targeted theranostic nanoemulsion of docetaxel for imaging and improved anticancer activity against ovarian cancers

Ovarian cancer ranks fifth in cancer related deaths for women in USA. The high mortality rate associated with ovarian cancer is due to diagnosis at later stages of disease and the high recurrence rate of 60-80%. Recurrent ovarian cancers are more likely to present as multidrug resistance (MDR) leading to unfavorable response from 2^nd and 3^rd line chemotherapy. Nanoemulsions (NEs) are emerging as an attractive drug delivery system to overcome MDR challenges. NEs can also minimize exposure of therapeutic cargo to normal tissues potentially reducing side effects. In >80% of ovarian cancers, Folate Receptor-α (FR-α) is expressed at 10- to 100-fold higher levels than on non-pathological tissues. Therefore, folate (FA) is being evaluated as an active targeting moiety for FR-α⁺ ovarian cancer. To improve therapeutic outcome with reduced toxicity, we developed NMI-500, a FA targeted gadolinium (Gd) annotated NE loaded with docetaxel (DTX). NMI-500 has been developed as theranostic agents as Gd will enable physician to acquire real time pharmacodynamics data on NE + DTX accumulation in target lesions. In present study, characterization for key translational metrics of NMI-500 showed size distribution in range of 120 to 150 nm and zeta potential around -45 mV. Active targeting of FA was evaluated against FR-α⁺ KB cells and results demonstrated significant improvement in cell association which was surface ligand density dependent. We found that NMI-500 was able to inhibit tumor growth in a spontaneous transgenic ovarian cancer model with improved safety profile and this growth inhibition could be longitudinally followed by MRI. These results indicate NMI-500 warrants advancement to clinical trials.

E-selectin targeted immunoliposomes for rapamycin delivery to activated endothelial cells

Activated endothelial cells play a pivotal role in the pathology of inflammatory disorders and thus present a target for therapeutic intervention by drugs that intervene in inflammatory signaling cascades, such as rapamycin (mammalian target of rapamycin (mTOR) inhibitor). In this study we developed anti-E-selectin immunoliposomes for targeted delivery to E-selectin over-expressing tumor necrosis factor-α (TNF-α) activated endothelial cells. Liposomes composed of 1,2-dipalmitoyl-sn-glycero-3.;hosphocholine (DPPC), Cholesterol, and 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000]-maleimide (DSPE-PEG-Mal) were loaded with rapamycin via lipid film hydration, after which they were further functionalized by coupling N-succinimidyl-S-acetylthioacetate (SATA)-modified mouse anti human E-selectin antibodies to the distal ends of the maleimidyl (Mal)-PEG groups. In cell binding assays, these immunoliposomes bound specifically to TNF-α activated endothelial cells. Upon internalization, rapamycin loaded immunoliposomes inhibited proliferation and migration of endothelial cells, as well as expression of inflammatory mediators. Our findings demonstrate that rapamycin-loaded immunoliposomes can specifically inhibit inflammatory responses in inflamed endothelial cells.

'Nano-in-nano' hybrid liposomes increase target specificity and gene silencing efficiency in breast cancer induced SCID mice

Gene silencing has immense potential in the treatment of cancer. However, enhancement of its efficiency requires the development of specifically targeted and safe carrier systems. Cationic carriers are generally limited by their immunogenicity. Hence, in this study, we report hybrid liposomes encapsulating Poly (L-lysine)-siRNA complex to silence epithelial cell adhesion molecule (EpCAM), highly expressed in epithelial cancers. The hybrid liposomes LL1 (Egg PC:DSPE-PEG, 10:0) and hybrid immunoliposomes LL2 (Egg PC:DSPE-PEG, 8:2) linked with EpCAM antibody as the targeting ligand showed an encapsulation efficiency of 70% and 86%, respectively. LL2 liposomes with a zeta potential of -26mV exhibited good colloidal stability in phosphate buffered saline containing bovine serum albumin and fetal bovine serum at 37°C. Cell uptake studies showed increased uptake of the LL2 when compared to LL1 liposomes. Finally, the hybrid immunoliposomes were evaluated for their efficacy in regressing the tumor volume in SCID mice. Eight doses each of 0.15mg/kg, which is among the lowest reported siRNA concentrations, were administered to the animals. About 45% reduction in tumor volume was achieved after 28days in the mice treated with LL2 when compared with the positive control and LL1 treated groups. Thus, our results demonstrate that the 'nano-in-nano' concept of encapsulating poly (l-Lysine) complexed EpCAM siRNA in immunoliposomes may be a promising strategy to treat EpCAM-positive epithelial cancers, especially as an adjuvant therapy.

Characterization of pegylated and non-pegylated liposomal formulation for the delivery of hypoxia activated vinblastine-N-oxide for the treatment of solid tumors

Solid tumors often contain hypoxic regions which are resistant to standard chemotherapy and radiotherapy. We have developed a liposomal delivery system for a prodrug of vinblastine (CPD100) which converts to the parent compound only in the presence of lower oxygen levels. As a part of this work we have developed and optimized two formulations of CPD100: one composed of sphingomyelin/cholesterol (55/45; mol/mol) (CPD100Li) and the other composed of sphingomyelin/cholesterol/PEG (55/40/5; mol/mol) (CPD100 PEGLi). We evaluated the antiproliferative effect of CPD100 and the two formulations against A549 non-small lung cancer cell. A549 cell line showed to be sensitive to CPD100 and the two formulations displayed a higher hypoxic: air cytotoxicity ratio compared to the pro-drug. CPD100 elimination from the circulation after injection in mouse was characterized by a very short circulation time (~0.44h), lower area under the curve (AUC) (33μgh/mL) and high clearance (916mL/h/kg) and lower volume of distribution (17.4mL/kg).Total drug elimination from the circulation after the administration of liposomal formulation was characterized by prolonged circulation time (5.5h) along with increase in the AUC (56μgh/mL) for CPD100 Li and (9.5h) with AUC (170μgh/mL) for CPD100PEGLi. This was observed along with increase in volume of distribution and decrease in clearance for the liposomes. The systemic exposure of the free drug was much lower than that achieved with the liposomes. When evaluated for the efficacy in A549 xenograft model in mice, both the liposomes demonstrated excellent tumor suppression and reduction for 3months. The blood chemistry panel and the comprehensive blood analysis showed no increase or decrease in the markers and blood count. In summary, the pharmacokinetic analysis along with the efficacy data emphasis on how the delivery vehicle modifies and enhances the accumulation of the drug and at the same time the increased systemic exposure is not related to toxicity.

Therapeutic efficacy of combined PEGylated liposomal doxorubicin and radiofrequency ablation: Comparing single and combined therapy in young and old mice

Antitumor therapy in the elderly is particularly challenging due to multiple, often chronic diseases, poly-therapy, and age-related physiological changes that affect drug efficacy and safety. Furthermore, tumors may become more aggressive and drug-resistant with advanced age, leading to poor patient prognosis. In this study, we evaluated in mice bearing medulloblastoma xenografts the effect of age on tumor progression and tumor therapy. We focused on therapeutic efficacy of two treatment modalities alone radiofrequency ablation therapy (RFA), PEGylated liposomal doxorubicin (PLD) equivalent to Doxil, and their combination. We demonstrated that tumor growth rate was higher and survival was lower in old versus young mice (p<0.05). Likewise, tumors in old mice were less susceptible to either PLD or RFA monotherapy. However, combined therapy of PLD and RFA succeeded to eliminate the age-related differences in anti-cancer treatment efficacy (p>0.05) by the two monotherapies. The results on PLD therapy are supported by preferable PEGylated nano-liposomes accumulation in tumors of young mice compared to old mice, as determined by near-infrared imaging with indocyanine green (ICG)-labeled PEGylated nano-liposomes. Taken together, our findings suggest that age effects on tumor progression and tumor monotherapy outcome may potentially be related to changes in tumor microenvironment, and that these changes can be overcome by RFA as this technique abolishes these differences and significantly improves success of PLD treatment.

Direct Pharmacological Inhibition of β-Catenin by RNA Interference in Tumors of Diverse Origin

The Wnt/β-catenin pathway is among the most frequently altered signaling networks in human cancers. Despite decades of preclinical and clinical research, efficient therapeutic targeting of Wnt/β-catenin has been elusive. RNA interference (RNAi) technology silences genes at the mRNA level and therefore can be applied to previously undruggable targets. Lipid nanoparticles (LNP) represent an elegant solution for the delivery of RNAi-triggering oligonucleotides to disease-relevant tissues, but have been mostly restricted to applications in the liver. In this study, we systematically tuned the composition of a prototype LNP to enable tumor-selective delivery of a Dicer-substrate siRNA (DsiRNA) targeting CTNNB1, the gene encoding β-catenin. This formulation, termed EnCore-R, demonstrated pharmacodynamic activity in subcutaneous human tumor xenografts, orthotopic patient-derived xenograft (PDX) tumors, disseminated hematopoietic tumors, genetically induced primary liver tumors, metastatic colorectal tumors, and murine metastatic melanoma. DsiRNA delivery was homogeneous in tumor sections, selective over normal liver and independent of apolipoprotein-E binding. Significant tumor growth inhibition was achieved in Wnt-dependent colorectal and hepatocellular carcinoma models, but not in Wnt-independent tumors. Finally, no evidence of accelerated blood clearance or sustained liver transaminase elevation was observed after repeated dosing in nonhuman primates. These data support further investigation to gain mechanistic insight, optimize dose regimens, and identify efficacious combinations with standard-of-care therapeutics. Mol Cancer Ther; 15(9); 2143-54. ©2016 AACR.

Insights into composition/structure/function relationships of Doxil® gained from "high-sensitivity" differential scanning calorimetry

Thermotropic behavior of Doxil® and its generic, Lipodox®, was characterized using "high-sensitivity" differential scanning calorimetry (DSC). This is the first report that two distinct endotherms were observed in Doxil and Lipodox upon heating. The first (Tm at 51±2°C) is broad and of low enthalpy, representing the membrane lipid phase transition, which occurs despite having high (38mole%) cholesterol. The second (Tm at ∼70°C) is narrow, representing melting of the intraliposomal doxorubicin-sulfate nanocrystals. The thermograms of Doxil and Lipodox are practically identical. The membrane phase transition is similar to that of drug-free nanoliposomes of the same size and lipid composition as Doxil, suggesting lack of significant drug-membrane interaction. The melting endotherm of the intraliposomal nanocrystals is 2.0-2.5-fold narrower than that of the crystals formed in a solution of 250mM ammonium sulfate and >60mg/ml doxorubicin. This suggests that nanovolume of liposomes improves doxorubicin-sulfate crystallinity. Moreover, both phase transitions are reversible in cycled DSC scanning (15-90-15°C). This indicates an unexpected "non-leaky" phospholipid phase transition and excellent physical and chemical stabilities of Doxil after short exposure to high temperature. Reducing mole% of cholesterol results in a "leaky" membrane phase transition of higher enthalpy. Namely, high mole% cholesterol is essential for the resistance to drug leakage during phase transition. Pegylated liposomal doxorubicin in which HSPC was replaced by DPPC shows the same non-leaky phase transition but at a lower temperature, indicating this type of phase transition is not unique to Doxil. The presence of DSPE-PEG2k increases the cooperativity of the phase transition. High-sensitivity DSC helps illuminate composition/structure/function relationships of Doxil, and is useful for the equivalence/similarity studies.

Nucleolin overexpression in breast cancer cell sub-populations with different stem-like phenotype enables targeted intracellular delivery of synergistic drug combination

Breast cancer stem cells (CSC) are thought responsible for tumor growth and relapse, metastization and active evasion to standard chemotherapy. The recognition that CSC may originate from non-stem cancer cells (non-SCC) through plastic epithelial-to-mesenchymal transition turned these into relevant cell targets. Of crucial importance for successful therapeutic intervention is the identification of surface receptors overexpressed in both CSC and non-SCC. Cell surface nucleolin has been described as overexpressed in cancer cells as well as a tumor angiogenic marker. Herein we have addressed the questions on whether nucleolin was a common receptor among breast CSC and non-SCC and whether it could be exploited for targeting purposes. Liposomes functionalized with the nucleolin-binding F3 peptide, targeted simultaneously, nucleolin-overexpressing putative breast CSC and non-SCC, which was paralleled by OCT4 and NANOG mRNA levels in cells from triple negative breast cancer (TNBC) origin. In murine embryonic stem cells, both nucleolin mRNA levels and F3 peptide-targeted liposomes cellular association were dependent on the stemness status. An in vivo tumorigenic assay suggested that surface nucleolin overexpression per se, could be associated with the identification of highly tumorigenic TNBC cells. This proposed link between nucleolin expression and the stem-like phenotype in TNBC, enabled 100% cell death mediated by F3 peptide-targeted synergistic drug combination, suggesting the potential to abrogate the plasticity and adaptability associated with CSC and non-SCC. Ultimately, nucleolin-specific therapeutic tools capable of simultaneous debulk multiple cellular compartments of the tumor microenvironment may pave the way towards a specific treatment for TNBC patient care.

Targeting brain cells with glutathione-modulated nanoliposomes: in vitro and in vivo study

Background

The blood–brain barrier prevents many drug moieties from reaching the central nervous system. Therefore, glutathione-modulated nanoliposomes have been engineered to enhance the targeting of flucytosine to the brain.

Methods

Glutathione-modulated nanoliposomes were prepared by thin-film hydration technique and evaluated in the primary brain cells of rats. Lecithin, cholesterol, and span 65 were mixed at 1:1:1 molar ratio. The molar percentage of PEGylated glutathione varied from 0 mol% to 0.75 mol%. The cellular binding and the uptake of the targeted liposomes were both monitored by epifluorescent microscope and flow cytometry techniques. A biodistribution and a pharmacokinetic study of flucytosine and flucytosine-loaded glutathione–modulated liposomes was carried out to evaluate the in vivo brain-targeting efficiency.

Results

The size of glutathione-modulated nanoliposomes was <100 nm and the zeta potential was more than −65 mV. The cumulative release reached 70% for certain formulations. The cellular uptake increased as molar percent of glutathione increased to reach the maximum at 0.75 mol%. The uptake of the targeted liposomes by brain cells of the rats was three times greater than that of the nontargeted liposomes. An in vivo study showed that the relative efficiency was 2.632±0.089 and the concentration efficiency was 1.590±0.049, and also, the drug-targeting index was 3.670±0.824.

Conclusion

Overall, these results revealed that glutathione-PEGylated nanoliposomes enhance the effective delivery of flucytosine to brain and could become a promising new therapeutic option for the treatment of the brain infections.

Complement activation as a bioequivalence issue relevant to the development of generic liposomes and other nanoparticulate drugs

Liposomes are known to activate the complement (C) system, which can lead in vivo to a hypersensitivity syndrome called C activation-related pseudoallergy (CARPA). CARPA has been getting increasing attention as a safety risk of i.v. therapy with liposomes, whose testing is now recommended in bioequivalence evaluations of generic liposomal drug candidates. This review highlights the adverse consequences of C activation, the unique symptoms of CARPA triggered by essentially all i.v. administered liposomal drugs, and the various features of vesicles influencing this adverse immune effect. For the case of Doxil, we also address the mechanism of C activation and the opsonization vs. long circulation (stealth) paradox. In reviewing the methods of assessing C activation and CARPA, we delineate the most sensitive porcine model and an algorithm for stepwise evaluation of the CARPA risk of i.v. liposomes, which are proposed for standardization for preclinical toxicology evaluation of liposomal and other nanoparticulate drug candidates.

Evaluation of drug loading, pharmacokinetic behavior, and toxicity of a cisplatin-containing hydrogel nanoparticle

Cisplatin is a cytotoxic drug used as a first-line therapy for a wide variety of cancers. However, significant renal and neurological toxicities limit its clinical use. It has been documented that drug toxicities can be mitigated through nanoparticle formulation, while simultaneously increasing tumor accumulation through the enhanced permeation and retention effect. Circulation persistence is a key characteristic for exploiting this effect, and to that end we have developed long-circulating, PEGylated, polymeric hydrogels using the Particle Replication In Non-wetting Templates (PRINT®) platform and complexed cisplatin into the particles (PRINT-Platin). Sustained release was demonstrated, and drug loading correlated to surface PEG density. A PEG Mushroom conformation showed the best compromise between particle pharmacokinetic (PK) parameters and drug loading (16wt.%). While the PK profile of PEG Brush was superior, the loading was poor (2wt.%). Conversely, the drug loading in non-PEGylated particles was better (20wt.%), but the PK was not desirable. We also showed comparable cytotoxicity to cisplatin in several cancer cell lines (non-small cell lung, A549; ovarian, SKOV-3; breast, MDA-MB-468) and a higher MTD in mice (10mg/kg versus 5mg/kg). The pharmacokinetic profiles of drug in plasma, tumor, and kidney indicate improved exposure in the blood and tumor accumulation, with concurrent renal protection, when cisplatin was formulated in a nanoparticle. PK parameters were markedly improved: a 16.4-times higher area-under-the-curve (AUC), a reduction in clearance (CL) by a factor of 11.2, and a 4.20-times increase in the volume of distribution (Vd). Additionally, non-small cell lung and ovarian tumor AUC was at least twice that of cisplatin in both models. These findings suggest the potential for PRINT-Platin to improve efficacy and reduce toxicity compared to current cisplatin therapies.

The effects of oil-in-water nanoemulsion polyethylene glycol surface density on intracellular stability, pharmacokinetics, and biodistribution in tumor bearing mice

PURPOSE

Lipid-based nanoparticles are extensively studied for drug delivery. These nanoparticles are often surface-coated with polyethylene glycol (PEG) to improve their biodistribution. Until now, the effects of varying PEG surface density have been studied in a narrow and low range. Here, the effects of high and a broad range of PEG surface densities on the in vivo performance of lipid-based nanoparticles were studied.

METHODS

Oil-in-water nanoemulsions were prepared with PEG surface densities of 5-50 mol%. Confocal microscopy was used to assess intracellular disintegration in vitro. In vivo pharmacokinetics and biodistribution in tumor bearing mice were studied using a small animal optical imager.

RESULTS

PEG surface density did not affect intracellular nanoemulsion stability. Surprisingly, circulation half-lives decreased with increasing PEG surface density. A plausible explanation was that nanoemulsion with high (50 mol%) PEG surface density activated the complement in a whole blood assay, whereas nanoemulsion with low (5 mol%) PEG density did not. In vivo, nanoemulsion with low PEG surface density was mostly confined to the tumor and organs of the mononuclear phagocyte system, whereas nanoemulsion with high PEG density accumulated throughout the mouse.

CONCLUSIONS

Optimal PEG surface density of lipid-based nanoparticles for tumor targeting was found to be below 10 mol%.

Therapeutic efficacy of combining pegylated liposomal doxorubicin and radiofrequency (RF) ablation: comparison between slow-drug-releasing, non-thermosensitive and fast-drug-releasing, thermosensitive nano-liposomes

AIMS

To determine how the accumulation of drug in mice bearing an extra-hepatic tumor and its therapeutic efficacy are affected by the type of PEGylated liposomal doxorubicin used, treatment modality, and rate of drug release from the liposomes, when combined with radiofrequency (RF) ablation.

MATERIALS AND METHODS

Two nano-drugs, both long-circulating PEGylated doxorubicin liposomes, were formulated: (1) PEGylated doxorubicin in thermosensitive liposomes (PLDTS), having a burst-type fast drug release above the liposomes' solid ordered to liquid disordered phase transition (at 42°C), and (2) non-thermosensitive PEGylated doxorubicin liposomes (PLDs), having a slow and continuous drug release. Both were administered intravenously at 8 mg/kg doxorubicin dose to tumor-bearing mice. Animals were divided into 6 groups: no treatment, PLD, RF, RF+PLD, PLDTS, and PLDTS+RF, for intra-tumor doxorubicin deposition at 1, 24, and 72 h post-injection (in total 41, mice), and 31 mice were used for randomized survival studies.

RESULTS

Non-thermosensitive PLD combined with RF had the least tumor growth and the best end-point survival, better than PLDTS+RF (p<0.005) or all individual therapies (p<0.001). Although at 1 h post-treatment the greatest amount of intra-tumoral doxorubicin was seen following PLDTS+RF (p<0.05), by 24 and 72 h the greatest doxorubicin amount was seen for PLD+RF (p<0.05); in this group the tumor also has the longest exposure to doxorubicin.

CONCLUSION

Optimizing therapeutic efficacy of PLD requires a better understanding of the relationship between the effect of RF on tumor microenvironment and liposome drug release profile. If drug release is too fast, the benefit of changing the microenvironment by RF on tumor drug localization and therapeutic efficacy may be much smaller than for PLDs having slow and temperature-independent drug release. Thus the much longer circulation time of doxorubicin from PLD than from PLDTS may be beneficial in many therapeutic instances, especially in extra-hepatic tumors.

Inhalation treatment of lung cancer: the influence of composition, size and shape of nanocarriers on their lung accumulation and retention

Objective

Various nanoparticles have been designed and tested in order to select optimal carriers for the inhalation delivery of anticancer drugs to the lungs.

Methods

The following nanocarriers were studied: micelles, liposomes, mesoporous silica nanoparticles (MSNs), poly propyleneimine (PPI) dendrimer-siRNA complexes nanoparticles, quantum dots (QDs), and poly (ethylene glycol) polymers. All particles were characterized using the following methods: dynamic light scattering, zeta potential, atomic force microscopy, in vitro cyto- and genotoxicity. In vivo organ distribution of all nanoparticles, retention in the lungs, and anticancer effects of liposomes loaded with doxorubicin were examined in nude mice after the pulmonary or intravenous delivery.

Results

Significant differences in lung uptake were found after the inhalation delivery of lipid-based and non-lipid-based nanoparticles. The accumulation of liposomes and micelles in lungs remained relatively high even 24 h after inhalation when compared with MSNs, QDs, and PPI dendrimers. There were notable differences between nanoparticle accumulation in the lungs and other organs 1 and 3 h after inhalation or intravenous administrations, but 24 h after intravenous injection all nanoparticles were mainly accumulated in the liver, kidneys, and spleen. Inhalation delivery of doxorubicin by liposomes significantly enhanced its anticancer effect and prevented severe adverse side effects of the treatment in mice bearing the orthotopic model of lung cancer.

Conclusion

The results of the study demonstrate that lipid-based nanocarriers had considerably higher accumulation and longer retention time in the lungs when compared with non-lipid-based carriers after the inhalation delivery. These particles are most suitable for effective inhalation treatment of lung cancer.

Bacteriophage Associated Silicon Particles: Design and Characterization of a Novel Theranostic Vector with Improved Payload Carrying Potential

There has been extensive research on the use of nanovectors for cancer therapy. Targeted delivery of nanotherapeutics necessitates two important characteristics; the ability to accumulate at the disease locus after overcoming sequential biological barriers and the ability to carry a substantial therapeutic payload. Successful combination of the above two features is challenging, especially in solid porous materials where chemical conjugation of targeting entities on the particle surface will generally prevent successful loading of the therapeutic substance. In this study, we propose a novel strategy for decorating the surface of mesoporous silicon particles with targeting entities (bacteriophage) and gold nanoparticles (AuNP) while maintaining their payload carrying potential. The resulting Bacteriophage Associated Silicon Particles (BASP) demonstrates efficient encapsulation of macromolecules and therapeutic nanoparticles into the porous structures. In vitro targeting data show enhanced targeting efficiency with about four orders of magnitude lower concentration of bacteriophage. In vivo targeting data suggest that BASP maintain their integrity following intravenous administration in mice and display up to three fold higher accumulation in the tumor.

Decationized crosslinked polyplexes for redox-triggered gene delivery

The clinical applicability of polymers as gene delivery systems depends not only on their efficiency, but also on their safety. The cytotoxicity of these systems remains a major issue, mainly due to their cationic nature. Therefore, it is highly preferable to have a system based on biocompatible neutral polymers, lacking polycations, without compromising the DNA condensing and protecting capacities. Here, we introduce a concept to obtain a neutral polymeric gene delivery system, through a 3-step process (charge-driven condensation; stabilization through disulfide crosslinking; polyplex decationization) to generate polyplexes with a core of disulfide crosslinked poly(hydroxypropyl methacrylamide) (pHPMA) in which plasmid DNA (pDNA) is entrapped and a shell of poly(ethylene glycol) (PEG). The resulting polyplexes combine beneficial features of high and stable DNA loading capacity, stealth behavior and reduced toxicity. The nanoparticles are designed to release the pDNA after cellular uptake through cleavage of disulfide crosslinks within the intracellular reducing environment. This was shown by forced introduction of the polyplexes into the cytosol of HeLa cells by electroporation, which resulted in a high level of expression of the reporter gene. Additionally, the decationized polyplexes showed no interference on the cellular cell viability or metabolic activity (even at high dose) and no complex-induced membrane destabilization. Furthermore, decationized polyplexes showed a low degree of non-specific uptake, which is a highly favorable property for targeted therapy. Summarizing, the stabilized, decationized polyplexes presented here contribute to solve the high toxicity, low stability and lack of cellular/tissue specificity of cationic polymer based gene delivery systems.

Interactions of nanomaterials and biological systems: Implications to personalized nanomedicine

The application of nanotechnology to personalized medicine provides an unprecedented opportunity to improve the treatment of many diseases. Nanomaterials offer several advantages as therapeutic and diagnostic tools due to design flexibility, small sizes, large surface-to-volume ratio, and ease of surface modification with multivalent ligands to increase avidity for target molecules. Nanomaterials can be engineered to interact with specific biological components, allowing them to benefit from the insights provided by personalized medicine techniques. To tailor these interactions, a comprehensive knowledge of how nanomaterials interact with biological systems is critical. Herein, we discuss how the interactions of nanomaterials with biological systems can guide their design for diagnostic, imaging and drug delivery purposes. A general overview of nanomaterials under investigation is provided with an emphasis on systems that have reached clinical trials. Finally, considerations for the development of personalized nanomedicines are summarized such as the potential toxicity, scientific and technical challenges in fabricating them, and regulatory and ethical issues raised by the utilization of nanomaterials.

Doxil®--the first FDA-approved nano-drug: lessons learned

Doxil®, the first FDA-approved nano-drug (1995), is based on three unrelated principles: (i) prolonged drug circulation time and avoidance of the RES due to the use of PEGylated nano-liposomes; (ii) high and stable remote loading of doxorubicin driven by a transmembrane ammonium sulfate gradient, which also allows for drug release at the tumor; and (iii) having the liposome lipid bilayer in a "liquid ordered" phase composed of the high-T(m) (53 °C) phosphatidylcholine, and cholesterol. Due to the EPR effect, Doxil is "passively targeted" to tumors and its doxorubicin is released and becomes available to tumor cells by as yet unknown means. This review summarizes historical and scientific perspectives of Doxil development and lessons learned from its development and 20 years of its use. It demonstrates the obligatory need for applying an understanding of the cross talk between physicochemical, nano-technological, and biological principles. However, in spite of the large reward, ~2 years after Doxil-related patents expired, there is still no FDA-approved generic "Doxil" available.

Fabrication principles and their contribution to the superior in vivo therapeutic efficacy of nano-liposomes remote loaded with glucocorticoids

We report here the design, development and performance of a novel formulation of liposome- encapsulated glucocorticoids (GCs). A highly efficient (>90%) and stable GC encapsulation was obtained based on a transmembrane calcium acetate gradient driving the active accumulation of an amphipathic weak acid GC pro-drug into the intraliposome aqueous compartment, where it forms a GC-calcium precipitate. We demonstrate fabrication principles that derive from the physicochemical properties of the GC and the liposomal lipids, which play a crucial role in GC release rate and kinetics. These principles allow fabrication of formulations that exhibit either a fast, second-order (t(1/2) ~1 h), or a slow, zero-order release rate (t(1/2) ~ 50 h) kinetics. A high therapeutic efficacy was found in murine models of experimental autoimmune encephalomyelitis (EAE) and hematological malignancies.

Structure and dynamics of highly PEG-ylated sterically stabilized micelles in aqueous media

Molecular assemblies of highly PEG-ylated phospholipids are important in many biomedical applications. We have studied sterically stabilized micelles (SSMs) of self-assembled DSPE–PEG2000 in pure water and isotonic HEPES-buffered saline solution. The observed SSM sizes of 2–15 nm largely depend on the solvent and the lipid concentration used. The critical micelle concentration of DSPE–PEG2000 is 10 times higher in water than in buffer, and the viscosity of the dispersion dramatically increases with the lipid concentration. To explain the experimentally observed results, we performed atomistic molecular dynamics simulations of solvated SSMs. Our modeling revealed that the observed assemblies have very different aggregation numbers (N(agg) ≈ 90 in saline solution and N(agg) < 8 in water) because of very different screening of their charged PO4(–) groups. We also demonstrate that the micelle cores can inflate and their coronas can fluctuate strongly, thus allowing storage and delivery of molecules with different chemistries.

Polymyxin B self-associated with phospholipid nanomicelles

CONTEXT

Although Polymyxin B (PXB) is an effective antibiotic for Gram-negative bacterial infections, clinical use is hampered by toxicity and protein binding, which may be overcome by delivering PXB using a safe nanocarrier.

OBJECTIVE

To determine whether PXB self-associates with long-circulating biocompatible/biodegradable PEGylated phospholipid nanomicelles (SSM) and change the PXB in vitro bioactivity.

MATERIALS AND METHODS

PXB and SSM (15 nm) composed of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N [methoxy(polyethylene glycol)-2000] (DSPE-PEG(2000)) were prepared in 10 mM HEPES-buffered saline. Interactions between PXB and SSM were determined by dynamic light scattering and fluorescence spectroscopy. Anti-infective effects of PXB-SSM were tested against Pseudomonas aeruginosa strain PA01 in vitro.

RESULTS

Approximately four PXB molecules self-associated with each SSM. However, significant decrease in P. aeruginosa killing was observed with PXB-SSM relative to PXB alone (P < 0.05). Empty SSM had no significant effect on bacterial growth.

DISCUSSION

PXB's self-association with SSM resulted in mitigation of the in vitro antibacterial activity. This phenomenon could be attributed, in part, to PEG(2000) hindering electrostatic interactions between cationic PXB and anionic bacterial cell wall.

CONCLUSION

PXB association with SSM formed a stable nanomedicine, resulting in decreased bioactivity of the drug in vitro. Effectiveness of this nanomedicine in vivo is yet to be studied.

Development and characterization of new nanoscaled ultrasound active lipid dispersions as contrast agents

Ultrasound contrast agents are widely used in clinical diagnosis. In recent years, the use of ultrasound contrast agents as therapeutic agents has gained a lot of attention. Of special interest are ultrasound-enhanced gene delivery in various tissues (e.g. cardiac, vascular, skeletal muscle and tumor tissue), ultrasound-enhanced protein delivery (e.g. insulin delivery) and ultrasound-enhanced delivery of small chemicals (e.g. doxorubicin, vancomycin). Commercially available ultrasound contrast agents such as SonoVue® or Optison® are ranged in a size of 2-8 μm. These micronscaled agents show a good ultrasound contrast enhancement and thus they are used for diagnostic imaging. But they are not suitable for targeted drug delivery to tumor tissues or blood clots because for these applications particles smaller than 700 nm are needed. In the present study, we developed new nanoscaled ultrasound contrast agents with a size between 70 and 300 nm. The lipid formulations show excellent contrast intensities using diagnostic ultrasound of about 1.4 MHz. The negatively charged colloidal dispersions are long-time stable under physiological conditions without loss of ultrasound reflectivity. The adjustable supramolecular organization of the carriers depends on the composition and varies from micellar to liposomal structures. The small size and the circulation stability of these systems make them promising for novel diagnostics and controlled drug release applications.

Size control of arsenic trioxide nanocrystals grown in nanowells

This paper describes a new strategy to generate nanocrystalline drugs through the precipitation of drug molecules in attoliter nanowells. We controlled the size of arsenic trioxide (ATO) nanocrystals by simply changing the concentration of ATO solution in the nanowells; particles with sizes ranging from 55 to 175 nm were formed. This approach only requires the drugs to be soluble in a solvent and thus can be broadly applicable to produce other drugs in nanocrystalline form.

Twelve chromatically opponent ganglion cell types in turtle retina

The turtle retina has been extensively used for the study of chromatic processing mechanisms. Color opponency has been previously investigated with trichromatic paradigms, but behavioral studies show that the turtle has an ultraviolet (UV) channel and a tetrachromatic visual system. Our laboratory has been working in the characterization of neuronal responses in the retina of vertebrates using stimuli in the UV-visible range of the electromagnetic spectrum. In the present investigation, we recorded color-opponent responses from turtle amacrine and ganglion cells to UV and visible stimuli and extended our previous results that UV color-opponency is present at the level of the inner nuclear layer. We recorded from 181 neurons, 36 of which were spectrally opponent. Among these, there were 10 amacrine (5%), and 26 ganglion cells (15%). Morphological identification of color-opponent neurons was possible for two ganglion cell classes (G17 and G22) and two amacrine cell classes (A22 and A23b). There was a variety of cell response types and a potential for complex processing of chromatic stimuli, with intensity- and wavelength-dependent response components. Ten types of color opponency were found in ganglion cells and by adding previous results from our laboratory, 12 types of opponent responses have been found. The majority of the ganglion cells were R+UVBG- and RG+UVB-color-opponents but there were other less frequent types of chromatic opponency. This study confirms the participation of a UV channel in the processing of color opponency in the turtle inner retina and shows that the turtle visual system has the retinal mechanisms to allow many possible chromatic combinations.