Elena V. Batrakova

Pluronic® block copolymers as novel polymer therapeutics for drug and gene delivery

Pluronic block copolymers are found to be an efficient drug delivery system with multiple effects. The incorporation of drugs into the core of the micelles formed by Pluronic results in increased solubility, metabolic stability and circulation time for the drug. The interactions of the Pluronic unimers with multidrug-resistant cancer cells result in sensitization of these cells with respect to various anticancer agents. Furthermore, the single molecular chains of copolymer, unimers, inhibit drug efflux transporters in both the blood-brain barrier and in the small intestine, which provides for the enhanced transport of select drugs to the brain and increases oral bioavailability. These and other applications of Pluronic block copolymers in various drug delivery and gene delivery systems are considered.

Pluronic Block Copolymers: Evolution of Drug Delivery Concept from Inert Nanocarriers to Biological Response Modifiers

Polymer nanomaterials have sparked a considerable interest as vehicles used for diagnostic and therapeutic agents; research in nanomedicine has not only become a frontier movement but is also a revolutionizing drug delivery field. A common approach for building a drug delivery system is to incorporate the drug within the nanocarrier that results in increased solubility, metabolic stability, and improved circulation time. With this foundation, nanoparticles with stealth properties that can circumvent RES and other clearance and defense mechanisms are the most promising. However, recent developments indicate that select polymer nanomaterials can implement more than only inert carrier functions by being biological response modifiers. One representative of such materials is Pluronic block copolymers that cause various functional alterations in cells. The key attribute for the biological activity of Pluronics is their ability to incorporate into membranes followed by subsequent translocation into the cells and affecting various cellular functions, such as mitochondrial respiration, ATP synthesis, activity of drug efflux transporters, apoptotic signal transduction, and gene expression. As a result, Pluronics cause drastic sensitization of MDR tumors to various anticancer agents, enhance drug transport across the blood brain and intestinal barriers, and causes transcriptional activation of gene expression both in vitro and in vivo. Collectively, these studies suggest that Pluronics have a broad spectrum of biological response modifying activities which make it one of the most potent drug targeting systems available, resulting in a remarkable impact on the emergent field of nanomedicine.

Pluronic® block copolymers for overcoming drug resistance in cancer

Pluronic block copolymers have been used extensively in a variety of pharmaceutical formulations including delivery of low molecular mass drugs and polypeptides. This review describes novel applications of Pluronic block copolymers in the treatment of drug-resistant tumors. It has been discovered that Pluronic block copolymers interact with multidrug-resistant cancer (MDR) tumors resulting in drastic sensitization of these tumors with respect to various anticancer agents, particularly, anthracycline antibiotics. Furthermore, Pluronic affects several distinct drug resistance mechanisms including inhibition of drug efflux transporters, abolishing drug sequestration in acidic vesicles as well as inhibiting the glutathione/glutathione S-transferase detoxification system. All these mechanisms of drug resistance are energy-dependent and therefore ATP depletion induced by Pluronic block copolymers in MDR cells is considered as one potential reason for chemosensitization of these cells. Following validation using in vitro and in vivo models, a formulation containing doxorubicin and Pluronic mixture (L61 and F127), SP1049C, has been evaluated in phase I clinical trials. Further mechanistic studies and clinical evaluations of these systems are in progress.

The neuroleptic activity of haloperidol increases after its solubilization in surfactant micelles: Micelles as microcontainers for drug targeting

It has been suggested to use surfactant micelles as microcontainers for increasing the efficiency of neuroleptic targeting from blood flow into the brain. The neuroleptic action of haloperidol, intraperitoneally injected into mice in micellar solution of non‐ionic block copolymer surfactant (pluronic P‐85) in water, increased several‐fold if compared with that observed for haloperidol aqueous solution. Incorporation of brain‐specific antibodies into haloperidol‐containing micelles resulted in additional drastic increase (more than by 2 orders of magnitude) in the drug effect.

Pluronic® block copolymers as modulators of drug efflux transporter activity in the blood-brain barrier

Drug efflux transporters can influence the absorption, tissue distribution and elimination of many therapeutic agents. Modulation of drug efflux transporter activity is being explored as a means for improving the pharmacokinetic and pharmacodynamic properties of various drugs. In this regard, several polymer formulations have been shown to inhibit drug efflux transporters such as P-glycoprotein (P-gp). The current review will focus on Pluronic block copolymers in particular, the mechanisms involved in the effects of Pluronic on drug efflux transporters, and the optimal polymer compositions required for inhibition of drug efflux transporters. Special emphasis will be placed on the potential applications of Pluronic in enhancing the blood-brain barrier (BBB) penetration of drugs.

A new class of drug carriers: micelles of poly(oxyethylene)-poly(oxypropylene) block copolymers as microcontainers for drug targeting from blood in brain☆

Abstract A new concept of design of drug delivery systems based on using self-assembling supramacromolecular complexes is formulated. Microcontainers for drug targeting were prepared using polymeric surfactant poly(oxyethylene)-poly(oxypropylene) block copolymer (pluronic). Molecules of a drug are solubilized in a pluronic micelle being incorporated into its inner hydrophobic core, formed by poly(oxypropylene) chain blocks. The outer hydrophilic shell of such micelles is formed by nontoxic and nonimmunogenic poly(oxyethylene) blocks. Solubilization of low molecular weight compounds (fluorescein isotbiocyanate (FITC), haloperidol etc.) in pluronic micelles was studied using fluorescence and ultracentrifugation. The dimensions of the aggregates formed in the solutions of various pluronics (P85, F64, L68, L101) and its mixtures were determined using quasielastic light-scattering technique. In a majority of cases the diameter of pluronic micelles (including those containing solubilized compounds) was in the range of 12–36 nm. For targeting of such microcontainers to a certain cell the pluronic molecules were conjugated with antibodies against a target-specific antigen or with protein ligands selectively interacting with target cell receptors. The obtained conjugates were then incorporated into the drug-containing micelles by simple mixing of the corresponding components. It was found that solubilization of FITC in pluronic micelles considerably influences its distribution in animal (mouse) tissues resulting, in particular, in the drastic increase of FITC fluorescence in lung. Conjugation of FITC-containing micelles with insulin vector results in increase of FITC penetration in all tissues including the brain. The specific targeting of the solubilized FITC in brain was observed in the case when the pluronic conjugate with antibodies to the antigen of brain glial cells ( α 2 -glycoprotein) was incorporated into micelles. Under these conditions the considerable increase of FITC fluorescence in the brain and decrease of its fluorescence in the lungs has been registered. Possibility of using micellar microcontainers for targeting of solubilized neuroleptics (haloperidol) in brain was studied. Incorporation of antibodies to α 2 glycoprotein into haloperidol-containing micelles results in a drastic increase of drug effect. This result indicates that vector-containing pluronic micelles provide an effective transport of solubilized neuroleptics across blood-brain barrier.

Block copolymer-based formulation of doxorubicin. From cell screen to clinical trials

Abstract A new doxorubicin formulation (SP1049C) has been developed using a combination of two polyethylene oxide polypropylene oxide block copolymers, in particular Pluronic L61 and Pluronic F127. The analysis of cytotoxic activity of this product on the cell screen panel has shown that SP1049C is highly effective against multidrug resistant cells that are normally not susceptible to doxorubicin and most other cytotoxic drugs. Further mechanistic studies have revealed that SP1049C has higher activity than doxorubicin due to: (i) increase in the drug uptake; (ii) inhibition of the energy-dependent drug efflux; and (iii) changes in intracellular drug trafficking. The experiments on in vivo tumour models have confirmed high efficacy of SP1049C against drug-resistant tumours, as well as suggested that this product has considerably broader efficacy than doxorubicin. The analysis of pharmacokinetics and biodistribution of SP1049C has shown that it accumulates in tumour tissue more effectively than doxorubicin, while distribution of the formulation in normal tissues is similar to that of doxorubicin. The toxicity studies of the copolymer composition used in SP1049C and of the product itself have demonstrated that the carrier has high safety margin, while toxicity of SP1049C is similar to that of doxorubicin suggesting that no additional adverse effects should be expected in clinical trials of SP1049C.

Exosomes as drug delivery vehicles for Parkinson's disease therapy

Exosomes are naturally occurring nanosized vesicles that have attracted considerable attention as drug delivery vehicles in the past few years. Exosomes are comprised of natural lipid bilayers with the abundance of adhesive proteins that readily interact with cellular membranes. We posit that exosomes secreted by monocytes and macrophages can provide an unprecedented opportunity to avoid entrapment in mononuclear phagocytes (as a part of the host immune system), and at the same time enhance delivery of incorporated drugs to target cells ultimately increasing drug therapeutic efficacy. In light of this, we developed a new exosomal-based delivery system for a potent antioxidant, catalase, to treat Parkinsons disease (PD). Catalase was loaded into exosomes ex vivo using different methods: the incubation at room temperature, permeabilization with saponin, freeze-thaw cycles, sonication, or extrusion. The size of the obtained catalase-loaded exosomes (exoCAT) was in the range of 100-200nm. A reformation of exosomes upon sonication and extrusion, or permeabilization with saponin resulted in high loading efficiency, sustained release, and catalase preservation against proteases degradation. Exosomes were readily taken up by neuronal cells in vitro. A considerable amount of exosomes was detected in PD mouse brain following intranasal administration. ExoCAT provided significant neuroprotective effects in in vitro and in vivo models of PD. Overall, exosome-based catalase formulations have a potential to be a versatile strategy to treat inflammatory and neurodegenerative disorders.

Pluronic P85 Increases Permeability of a Broad Spectrum of Drugs in Polarized BBMEC and Caco-2 Cell Monolayers

AbstractPurpose. Previous studies demonstrated that inhibition of P glycoprotein (P-gp) by Pluronic P85 (P85) block copolymer increases apical (AP) to basolateral (BL) transport of rhodamine 123 (R123) in the polarized monolayers of bovine brain microvessel endothelial cells (BBMEC) and Caco-2 cells. The present work examines the effects of P85 on the transport of fluorescein (Flu), doxorubicin (Dox), etoposide (Et), taxol (Tax), 3′-azido-3′-deoxythymidine (AZT), valproic acid (VPA) and loperamide (Lo) using BBMEC and Caco-2 monolayers as in vitro models of the blood brain barrier and intestinal epithelium respectively. Methods. Drug permeability studies were performed on the confluent BBMEC and Caco-2 cell monolayers mounted in Side-Bi-Side diffusion cells. Results. Exposure of the cells to P85 significantly enhanced AP to BL permeability coefficients of Flu, Tax, Dox and AZT in both cell models. Further, P85 enhanced AP to BL transport of Et, VPA and Lo in Caco-2 monolayers. No changes in the permeability coefficients of the paracellular marker mannitol were observed in the presence of the copolymer. Conclusions. P85 increases AP to BL permeability in BBMEC and Caco-2 monolayers with respect to a broad panel of structurally diverse compounds, that were previously shown to be affected by P-gp and/ or multidrug resistance associated protein (MRP) efflux systems. Broad specificity of the block copolymer effects with respect to drugs and efflux systems appears to be a valuable property in view of developing pharmaceutical formulations to increase drug accumulation in selected organs and overcome both acquired and intrinsic drug resistance that limits the effectiveness of many chemotherapeutic agents.

Mechanism of sensitization of MDR cancer cells by Pluronic block copolymers: Selective energy depletion

This paper, for the first time, demonstrates that exposure of cells to the poly(ethylene oxide)-poly(propylene oxide) block copolymer, Pluronic P85, results in a substantial decrease in ATP levels selectively in MDR cells. Cells expressing high levels of functional P-glycoprotein (MCF-7/ADR, KBv; LLC-MDR1; Caco-2, bovine brain microvessel endothelial cells [BBMECs]) are highly responsive to Pluronic treatment, while cells with low levels of P-glycoprotein expression (MCF-7, KB, LLC-PK1, human umbilical vein endothelial cells [HUVECs] C2C12 myoblasts) are much less responsive to such treatment. Cytotoxicity studies suggest that Pluronic acts as a chemosensitizer and potentiates cytotoxic effects of doxorubicin in MDR cells. The ability of Pluronic to inhibit P-glycoprotein and sensitize MDR cells appears to be a result of ATP depletion. Because many mechanisms of drug resistance are energy dependent, a successful strategy for treating MDR cancer could be based on selective energy depletion in MDR cells. Therefore, the finding of the energy-depleting effects of Pluronic P85, in combination with its sensitization effects is of considerable theoretical and practical significance.