Pluronic mixed micelles overcoming methotrexate multidrug resistance: in vitro and in vivo evaluation

Natural and Synthetic Micelles for Delivery of Small Molecule Drugs, Imaging Agents and Nucleic Acids

The poor solubility, lack of targetability, quick renal clearance, and degradability of many therapeutic and imaging agents strongly limit their applications inside the human body. Amphiphilic copolymers having self-assembling properties can form core-shell structures called micelles, a promising nanocarrier for hydrophobic drugs, plasmid DNA, oligonucleotides, small interfering RNAs (siRNAs) and imaging agents. Fabrication of micelles loaded with different pharmaceutical agents provides numerous advantages including therapeutic efficacy, diagnostic sensitivity, and controlled release to the desired tissues. Moreover, due to their smaller particle size (10-100 nm) and modified surfaces with different functional groups (such as ligands) help them to accumulate easily in the target location, enhancing cellular uptake and reducing unwanted side effects. Furthermore, the release of the encapsulated agents may also be triggered from stimuli-sensitive micelles at different physiological conditions or by an external stimulus. In this review article, we discuss the recent advancement in formulating and targeting different natural and synthetic micelles including block copolymer micelles, cationic micelles, and dendrimers-, polysaccharide- and protein-based micelles for the delivery of different therapeutic and diagnostic agents. Finally, their applications, outcomes, and future perspectives have been summarized.

Drug delivery carriers with therapeutic functions

Design of micro- or nanocarriers for drug delivery has primarily been focused on properties such as hydrophobicity, biodegradability, size, shape, surface charge, and toxicity, so that they can achieve optimal delivery with respect to drug loading, release kinetics, biodistribution, cellular uptake, and biocompatibility. Incorporation of stimulus-sensitive moieties into the carriers would lead to "smart" delivery systems. A further evolution would be to endow the carrier with a therapeutic function such that it no longer serves as a mere passive entity to release the drug at the target tissue but can be viewed as a therapeutic agent in itself. In this review, we will discuss recent and ongoing efforts over the past decade to design therapeutic drug carriers that confer a biological benefit, including ROS scavenging or generating, pro- or anti-inflammatory, and immuno-evasive properties, to enhance the overall therapeutic efficacy of the delivery systems.

Drug reformulation for a neglected disease. The NANOHAT project to develop a safer more effective sleeping sickness drug

Background

Human African trypanosomiasis (HAT or sleeping sickness) is caused by the parasite Trypanosoma brucei sspp. The disease has two stages, a haemolymphatic stage after the bite of an infected tsetse fly, followed by a central nervous system stage where the parasite penetrates the brain, causing death if untreated. Treatment is stage-specific, due to the blood-brain barrier, with less toxic drugs such as pentamidine used to treat stage 1. The objective of our research programme was to develop an intravenous formulation of pentamidine which increases CNS exposure by some 10–100 fold, leading to efficacy against a model of stage 2 HAT. This target candidate profile is in line with drugs for neglected diseases inititative recommendations.

Methodology

To do this, we evaluated the physicochemical and structural characteristics of formulations of pentamidine with Pluronic micelles (triblock-copolymers of polyethylene-oxide and polypropylene oxide), selected candidates for efficacy and toxicity evaluation in vitro, quantified pentamidine CNS delivery of a sub-set of formulations in vitro and in vivo, and progressed one pentamidine-Pluronic formulation for further evaluation using an in vivo single dose brain penetration study.

Principal Findings

Screening pentamidine against 40 CNS targets did not reveal any major neurotoxicity concerns, however, pentamidine had a high affinity for the imidazoline₂ receptor. The reduction in insulin secretion in MIN6 β-cells by pentamidine may be secondary to pentamidine-mediated activation of β-cell imidazoline receptors and impairment of cell viability. Pluronic F68 (0.01%w/v)-pentamidine formulation had a similar inhibitory effect on insulin secretion as pentamidine alone and an additive trypanocidal effect in vitro. However, all Pluronics tested (P85, P105 and F68) did not significantly enhance brain exposure of pentamidine.

Significance

These results are relevant to further developing block-copolymers as nanocarriers, improving BBB drug penetration and understanding the side effects of pentamidine.

Sleeping sickness or human African Trypanosomiasis (HAT) is a disease caused by a parasite, which is transferred to humans by the bite of an infected tsetse fly. There are two disease stages: the first stage is the blood-based stage of the disease and the second stage affects the brain. It is fatal if left untreated. The blood-brain barrier (BBB) makes the brain stage difficult to treat because it prevents 99% of all drugs from entering the brain from the blood. Those anti-HAT drugs that do enter the brain are toxic and have serious side effects. Pentamidine is a less toxic blood stage drug, which our research has shown has a limited ability to cross the BBB due to its removal by proteins called transporters. The objective of this study was to use Pluronic to improve pentamidine delivery to target sites, whilst reducing its side effects. Pluronic is a polymer, which can assemble into micelles and encapsulate the drug. Thus, prolonging its circulation time and protecting it. Our study indicated that the selected Pluronics did not increase the brain delivery of pentamidine. However. Pluronic-pentamidine formulations were identified that harboured trypanocidal activity and did not increase safety concerns compared to unformulated pentamidine.

pH-responsive polymer micelles for methotrexate delivery at tumor microenvironments

Methotrexate (MTX) anticancer drug was successfully loaded and released in a controlled manner from polymer micelles made of a diblock copolymer of poly(monomethoxy ethylene glycol)-b-poly(ε-caprolactone) (mPEG-PCL). The empty and MTX-loaded micelles (MTX/mPEG-PCL) were characterized by electron microscopy. The drug release dependence upon pH 5.4, 6.5, and 7.4 for 30 days was proven and characterized by UV-Vis spectroscopy. The cytotoxic effect of MTX/mPEG-PCL micelles on MCF-7 breast cancer cells was evaluated through an MTT assay. The morphological analysis indicated the successful formation of micelles of 76 and 131 nm for empty and MTX-loaded micelles, respectively. An encapsulation efficiency of 70.2% and a loading capacity of 8.8% were obtained. The in vitro release of MTX showed a gradual and sustained profile over 22 days, with a clear trend to much higher release at acidic pH (80 and 90% for pH 6.7 and 5.5, respectively). The MTX/mPEG-PCL micelles showed an IC50 of MCF-7 cells at 30 µg mL−1. The results suggested that MTX/mPEG-PCL could be a promising drug delivery system for cancer treatment.

Doxorubicin Loaded Poloxamer Thermosensitive Hydrogels: Chemical, Pharmacological and Biological Evaluation

(1) Background: doxorubicin is a potent chemotherapeutic agent, but it has limitations regarding its side effects and therapy resistance. Hydrogels potentially deal with these problems, but several characterizations need to be optimized to better understand how hydrogel assisted chemotherapy works. Poloxamer 407 (P407) hydrogels were mixed with doxorubicin and physico-chemical, biological, and pharmacological characterizations were considered. (2) Methods: hydrogels were prepared by mixing P407 in PBS at 4 °C. Doxorubicin was added upon solutions became clear. Time-to-gelation, hydrogel morphology, and micelles were studied first. The effects of P407-doxorubicin were evaluated on MC-38 colon cancer cells. Furthermore, doxorubicin release was assessed and contrasted with non-invasive in vivo whole body fluorescence imaging. (3) Results: 25% P407 had favorable gelation properties with pore sizes of 30–180 µm. P407 micelles were approximately 5 nm in size. Doxorubicin was fully released in vitro from 25% P407 hydrogel within 120 h. Furthermore, P407 micelles strongly enhanced the anti-neoplastic effects of doxorubicin on MC-38 cells. In vivo fluorescence imaging revealed that hydrogels retained fluorescence signals at the injection site for 168 h. (4) Conclusions: non-invasive imaging showed how P407 gels retained drug at the injection site. Doxorubicin P407 micelles strongly enhanced the anti-tumor effects.

Tumor- and mitochondria-targeted nanoparticles eradicate drug resistant lung cancer through mitochondrial pathway of apoptosis

Chemotherapeutic drugs frequently encounter multidrug resistance. ATP from mitochondria helps overexpression of drug efflux pumps to induce multidrug resistance, so mitochondrial delivery as a means of "repurposing'' chemotherapeutic drugs currently used in the clinic appears to be a worthwhile strategy to pursue for the development of new anti-drug-resistant cancer agents. TPP-Pluronic F127-hyaluronic acid (HA) (TPH), with a mitochondria-targeting triphenylphosphine (TPP) head group, was first synthesized through ester bond formation. Paclitaxel (PTX)-loaded TPH (TPH/PTX) nanomicelles exhibited excellent physical properties and significantly inhibited A549/ADR cells. After TPH/PTX nanomicelles entered acidic lysosomes through macropinocytosis, the positively charged TP/PTX nanomicelles that resulted from degradation of HA by hyaluronidase (HAase) in acidic lysosomes were exposed and completed lysosomal escape at 12 h, finally localizing to mitochondria over a period of 24 h in A549/ADR cells. Subsequently, TPH/PTX caused mitochondrial outer membrane permeabilization (MOMP) by inhibiting antiapoptotic Bcl-2, leading to cytochrome C release and activation of caspase-3 and caspase-9. In an A549/ADR xenograft tumor model and a drug-resistant breast cancer-bearing mouse model with lung metastasis, TPH/PTX nanomicelles exhibited obvious tumor targeting and significant antitumor efficacy. This work presents the potential of a single, nontoxic nanoparticle (NP) platform for mitochondria-targeted delivery of therapeutics for diverse drug-resistant cancers.

Methotrexate-induced apoptosis in human ovarian adenocarcinoma SKOV-3 cells via ROS-mediated bax/bcl-2-cyt-c release cascading

Introduction

The communication between a substance and a cell may depend on whether the cell is normal or pathological. The disease cells and drug interaction may occasionally overcome beneficial action of the drug; subsequently, it is important to investigate the effect of the drug in both the normal and target cells. This study aimed to evaluate the methotrexate (MTX) antiproliferative effect and explore the mechanistic approach to investigate the cell death index in SKOV-3 ovarian cells during treatment with MTX.

Methods

In vitro studies of SKOV-3 cells were examined by tetrazolium assay after exposure to various concentrations of MTX. Moreover, reactive oxygen species (ROS) generation, mitochondrial membrane potential, DNA damage, and AO/EtBr staining morphological analysis of necrotic/apoptotic cells were detected; cellular impairment in mitochondria and DNA was confirmed by JC-1 mitotracker/DAPI, respectively, and cell death pathway markers; bax/bcl-2 were analyzed.

Results

A dose-dependent antiproliferative effect of MTX treatment was observed in SKOV-3 cells; the prominent inhibitory concentration was 40 µM of MTX (P<0.01). The growth inhibition rates of the cancer cells reached 24.07% in MTX. The MTX showed increase in ROS generation and mitochondrial depolarization, and DNA integrity cells collectively advocated the apoptotic cell death at higher concentration. In addition, the results of reverse transcription polymerase chain reaction also supported the apoptosis by upregulating the bax and downregulating the bcl-2 (P<0.01). Thus the MTX moderately provokes apoptosis.

Conclusion

Our findings suggest that MTX acts on SKOV-3 cancer cells by increasing intracellular ROS levels, leading to DNA damage and altering the MMP along with apoptotic gene upregulation. This mechanism may provide new therapeutic targets to improve tumor treatment.

Enhancement of dissolution and oral bioavailability of lacidipine via pluronic P123/F127 mixed polymeric micelles: formulation, optimization using central composite design and in vivo bioavailability study

This study aims at preparing and optimizing lacidipine (LCDP) polymeric micelles using thin film hydration technique in order to overcome LCDP solubility-limited oral bioavailability. A two-factor three-level central composite face-centered design (CCFD) was employed to optimize the formulation variables to obtain LCDP polymeric micelles of high entrapment efficiency and small and uniform particle size (PS). Formulation variables were: Pluronic to drug ratio (A) and Pluronic P123 percentage (B). LCDP polymeric micelles were assessed for entrapment efficiency (EE%), PS and polydispersity index (PDI). The formula with the highest desirability (0.959) was chosen as the optimized formula. The values of the formulation variables (A and B) in the optimized polymeric micelles formula were 45% and 80%, respectively. Optimum LCDP polymeric micelles had entrapment efficiency of 99.23%, PS of 21.08 nm and PDI of 0.11. Optimum LCDP polymeric micelles formula was physically characterized using transmission electron microscopy. LCDP polymeric micelles showed saturation solubility approximately 450 times that of raw LCDP in addition to significantly enhanced dissolution rate. Bioavailability study of optimum LCDP polymeric micelles formula in rabbits revealed a 6.85-fold increase in LCDP bioavailability compared to LCDP oral suspension.

Fullerenol-Based Intracellular Delivery of Methotrexate: A Water-Soluble Nanoconjugate for Enhanced Cytotoxicity and Improved Pharmacokinetics

Derivatization of fullerenes to polyhydroxylated fullerenes, i.e., fullerenols (FLU), dramatically decreases their toxicity and has been reported to enhance the solubility as well as cellular permeability. In this paper, we report synthesis of FLU as nanocarrier and subsequent chemical conjugation of Methotrexate (MTX) to FLU with a serum-stable and intracellularly hydrolysable ester bond between FLU and MTX. The conjugate was characterized for physiochemical attributes, micromeritics, drug-loading, and drug-release and evaluated for cancer cell-toxicity, cellular-uptake, hemocompatibility, protein binding, and pharmacokinetics. The developed hemocompatible FL-MTX offered lower protein binding vis-à-vis naïve drug and substantially higher drug loading. The conjugate offered pH-dependent release of 38.20 ± 1.19% at systemic pH and 85.67 ± 3.39% at the cancer cell pH. FLU-MTX-treated cells showed significant reduction in IC₅₀ value vis-à-vis the cells treated with pure MTX. Analogously, the results from confocal scanning laser microscopy also confirmed the easy access of the dye-tagged FLU-MTX conjugate to the cell interiors. In pharmacokinetics, the AUC of MTX was enhanced by approx. 6.15 times and plasma half-life was enhanced by 2.45 times, after parenteral administration of single equivalent dose in rodents. FLU-MTX offered enhanced availability of drug to the biological system, meanwhile improved the cancer-cell cytotoxicity, sustained the effective plasma drug concentrations, and offered substantial compatibility to erythrocytes.

Absence of Albumin Improves in Vitro Cellular Uptake and Disruption of Poloxamer 407-Based Nanoparticles inside Cancer Cells

Novel nanoparticles based on Poloxamer 407 and vegetable oil were produced by high pressure homogenization. Functionalization of those nanoparticles was made by incorporation of folic acid (FA)-Poloxamer 407 conjugate. These nanoparticles showed suitable characteristics for intravenous therapeutic applications similarly to PEGylated albumin-based nanoparticles, previously described by our research group. Here, we found that the absence of albumin at the interface of Poloxamer 407-based nanoparticles improves the overall process of in vitro cellular uptake and nanoparticle disruption inside cancer cells (folate receptor, FR, positive cells). The results presented here suggest that interfacial composition of those nanoparticles is of paramount importance for drug trafficking inside cancer cells.

Ginsenoside Rg3 micelles mitigate doxorubicin-induced cardiotoxicity and enhance its anticancer efficacy

Doxorubicin (DOX) is one of the most effective chemotherapy agents used in the treatment of hematological and solid tumors, however, it causes dose-related cardiotoxicity that may lead to heart failure in patients. One of the major reasons was increased reactive oxygen species (ROS) production. Ginsenoside Rg3 (Rg3), was powerful free radical scavengers and possessed cardioprotective effects. Nevertheless, Rg3 has low aqueous solubility and oral bioavailability, limiting its effects. Herein, we encapsulated Rg3 through spontaneous self-assembly of Pluronic F127 to improve its solubility and oral bioavailability. Moreover, co-administering Rg3 in Pluronic F127 micelles with doxorubicin can mitigate the cardiotoxicity, with ameliorating mitochondrial and metabolic function, improving calcium handling, and decreasing ROS production. In addition, it can improve the anticancer efficacy of doxorubicin. Therefore, our study provides a rational strategy for further developing a potentially viable adjunct-supportive treatment for reducing toxicity and increasing efficiency on chemotherapy.

c(RGDyK)-decorated Pluronic micelles for enhanced doxorubicin and paclitaxel delivery to brain glioma

Brain glioma therapy is an important challenge in oncology. Here, doxorubicin (DOX) and paclitaxel (PTX)-loaded cyclic arginine-glycine-aspartic acid peptide (c(RGDyK))-decorated Pluronic micelles (cyclic arginine-glycine-aspartic acid peptide-decorated Pluronic micelles loaded with doxorubicin and paclitaxel [RGD-PF-DP]) were designed as a potential targeted delivery system to enhance blood–brain barrier penetration and improve drug accumulation via integrin-mediated transcytosis/endocytosis and based on integrin overexpression in blood–brain barrier and glioma cells. The physicochemical characterization of RGD-PF-DP revealed a satisfactory size of 28.5±0.12 nm with uniform distribution and core-shell structure. The transport rates across the in vitro blood–brain barrier model, cellular uptake, cytotoxicity, and apoptosis of U87 malignant glioblastoma cells of RGD-PF-DP were significantly greater than those of non-c(RGDyK)-decorated Pluronic micelles. In vivo fluorescence imaging demonstrated the specificity and efficacy of intracranial tumor accumulation of RGD-PF-DP. RGD-PF-DP displayed an extended median survival time of 39 days, with no serious body weight loss during the regimen. No acute toxicity to major organs was observed in mice receiving treatment doses via intravenous administration. In conclusion, RGD-PF-DP could be a promising vehicle for enhanced doxorubicin and paclitaxel delivery in patients with brain glioma.

In Vivo Biodistribution and Anti-Tumor Efficacy Evaluation of Doxorubicin and Paclitaxel-Loaded Pluronic Micelles Decorated with c(RGDyK) Peptide

The treatment of squamous carcinoma, especially multidrug resistance (MDR) tumors, represents one of the most formidable challenges in oncology. In this study, integrin-mediated Pluronic-based micellar system (c(RGDyK)-FP-DP) was proposed as a drug delivery system to enhance the in vivo anti-tumor efficacy in MDR human squamous carcinoma (KBv)-bearing. Following the recognition by integrin proteins express on the cell surface, cellular uptake and in vitro anti-tumor efficacy of c(RGDyK)-FP-DP were better than conventional PF-DP in KBv cells. The tumor homing specificity and further in vivo anticancer efficacy of c(RGDyK)-FP-DP were performed using subcutaneous KBv tumor-bearing mice model, respectively. Compared with PF-DP, c(RGDyK)-FP-DP demonstrated more drug accumulation in tumor and relatively less drug accumulation in heart, and an extended median survival time in the KBv tumor-bearing mice model. Furthermore, preliminary in vivo subacute toxicity evaluation was also conducted by the measurement of histopathology, blood cell counts and clinical biochemistry parameters. Results showed that no obvious toxicity was observed to the hematological system or heart after a series of intravenous administration of c(RGDyK)-FP-DP. In conclusion, our results suggested that c(RGDyK) peptide conjugated Pluronic micelles could be a promising vehicle for enhancing the treatment of MDR human squamous carcinoma.

Dual-functional c(RGDyK)-decorated Pluronic micelles designed for antiangiogenesis and the treatment of drug-resistant tumor

Dual-functional drug delivery system was developed by decorating c(RGDyK) (cyclic RGD [arginine-glycine-aspartic acid] peptide) with Pluronic polymeric micelles (c[RGDyK]-FP-DP) to overcome the drawbacks of low transport of chemotherapeutics across the blood–tumor barrier and poor multidrug-resistant (MDR) tumor therapy. c(RGDyK) that can bind to the integrin protein richly expressed at the site of tumor vascular endothelial cells and tumor cells with high affinity and specificity was conjugated to the N-hydroxysuccinimide-activated PEO terminus of the Pluronic F127 block copolymer. In this study, decreased tumor angiogenic and increased apoptotic activity in MDR cancer cells were observed after the treatment with c(RGDyK)-FP-DP. c(RGDyK)-FP-DP was fully characterized in terms of morphology, particle size, zeta potential, and drug release. Importantly, in vitro antiangiogenesis results demonstrated that c(RGDyK)-FP-DP had a significant inhibition effect on the tubular formation of human umbilical vein endothelial cells and promoted cellular apoptotic activity in MDR KBv cells. In addition, the growth inhibition efficacy of KBv tumor spheroids after crossing the blood–tumor barrier was obviously increased by c(RGDyK)-FP-DP compared to other control groups. Results suggested that c(RGDyK)-decorated Pluronic polymeric micelles can take pharmacological action on both human umbilical vein endothelial cells and KBv MDR cancer cells, resulting in a dual-functional anticancer effect similar to that observed in our in vitro cellular studies.

The therapeutic effect of methotrexate-conjugated Pluronic-based polymeric micelles on the folate receptor-rich tumors treatment

The therapeutic effect of methotrexate (MTX)-conjugated Pluronic-based polymeric mixed micelles (F127/P105-MTX) on the folate receptor-overexpressing tumors treatment was investigated in this study. Due to its high structural similarity to folic acid and the high expression of folate receptor in most solid tumors, MTX serves as not only a cytotoxic agent but also a homing ligand. Cellular uptake and the endocytic mechanism studies of MTX-conjugated mixed micelles were performed in folate receptor-rich KBv and folate receptor-deficient A-549 cancer cells. Additionally, the efficacy and safety studies of F127/P105-MTX in KBv tumor-bearing mice were evaluated. Results indicate that F127/P105-MTX significantly enhanced the cellular uptake in KBv cells as compared to that of conventional non-MTX-conjugated mixed micelles. Moreover, the results showed that F127/P105-MTX can be internalized by both caveolae- and clathrin-mediated endocytosis in energy-dependent and folate receptor-dependent manners. The in vitro and in vivo antitumor efficacies of F127/P105-MTX were significantly enhanced in comparison with MTX-entrapped mixed micelles. Furthermore, no acute toxicities to hematological system and major organs have been observed after intravenous administration during the regimen. Therefore, our results suggest that F127/P105-MTX could be an effective and safe nano-drug delivery system for cancer therapy, especially for the folate receptor-rich cancer treatment.

Pluronics and MDR reversal: an update

Multidrug resistance (MDR) remains one of the biggest obstacles for effective cancer therapy. Currently there are only few methods that are available clinically that are used to bypass MDR with very limited success. In this review we describe how MDR can be overcome by a simple yet effective approach of using amphiphilic block copolymers. Triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), arranged in a triblock structure PEO-PPO-PEO, Pluronics or “poloxamers”, raised a considerable interest in the drug delivery field. Previous studies demonstrated that Pluronics sensitize MDR cancer cells resulting in increased cytotoxic activity of Dox, paclitaxel, and other drugs by 2–3 orders of magnitude. Pluronics can also prevent the development of MDR in vitro and in vivo. Additionally, promising results of clinical studies of Dox/Pluronic formulation reinforced the need to ascertain a thorough understanding of Pluronic effects in tumors. These effects are extremely comprehensive and appear on the level of plasma membranes, mitochondria, and regulation of gene expression selectively in MDR cancer cells. Moreover, it has been demonstrated recently that Pluronics can effectively deplete tumorigenic intrinsically drug-resistant cancer stem cells (CSC). Interestingly, sensitization of MDR and inhibition of drug efflux transporters is not specific or selective to Pluronics. Other amphiphilic polymers have shown similar activities in various experimental models. This review summarizes recent advances of understanding the Pluronic effects in sensitization and prevention of MDR.