Plasma and cellular pharmacokinetic considerations for the development and optimization of antitumor block copolymer micelles

Complex Factors and Challenges that Affect the Pharmacology, Safety and Efficacy of Nanocarrier Drug Delivery Systems

Major developments in nanomedicines, such as nanoparticles (NPs), nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past four decades. Although nanocarrier agents provide numerous advantages (e.g., greater solubility and duration of systemic exposure) compared to their small-molecule counterparts, there is considerable inter-patient variability seen in the systemic disposition, tumor delivery and overall pharmacological effects (i.e., anti-tumor efficacy and unwanted toxicity) of NP agents. This review aims to provide a summary of fundamental factors that affect the disposition of NPs in the treatment of cancer and why they should be evaluated during preclinical and clinical development. Furthermore, this chapter will highlight some of the translational challenges associated with elements of NPs and how these issues can only be addressed by detailed and novel pharmacology studies.

Nanoscale Self-Assembly for Therapeutic Delivery

Self-assembly is the process of association of individual units of a material into highly arranged/ordered structures/patterns. It imparts unique properties to both inorganic and organic structures, so generated, via non-covalent interactions. Currently, self-assembled nanomaterials are finding a wide variety of applications in the area of nanotechnology, imaging techniques, biosensors, biomedical sciences, etc., due to its simplicity, spontaneity, scalability, versatility, and inexpensiveness. Self-assembly of amphiphiles into nanostructures (micelles, vesicles, and hydrogels) happens due to various physical interactions. Recent advancements in the area of drug delivery have opened up newer avenues to develop novel drug delivery systems (DDSs) and self-assembled nanostructures have shown their tremendous potential to be used as facile and efficient materials for this purpose. The main objective of the projected review is to provide readers a concise and straightforward knowledge of basic concepts of supramolecular self-assembly process and how these highly functionalized and efficient nanomaterials can be useful in biomedical applications. Approaches for the self-assembly have been discussed for the fabrication of nanostructures. Advantages and limitations of these systems along with the parameters that are to be taken into consideration while designing a therapeutic delivery vehicle have also been outlined. In this review, various macro- and small-molecule-based systems have been elaborated. Besides, a section on DNA nanostructures as intelligent materials for future applications is also included.

Topical application of polymeric nanomicelles in ophthalmology: a review on research efforts for the noninvasive delivery of ocular therapeutics

INTRODUCTION

Polymeric micelles represent nowadays an interesting formulative approach for ocular drug delivery, as they act as solubility enhancers of poorly soluble drugs and promote drug transport across cornea and sclera. In particular, in the last 5 years polymeric nanomicelles have been increasingly investigated to overcome some of the important challenges of the topical treatment of ocular diseases.

AREAS COVERED

The aim of this review was to gather up-to-date information on the different roles that polymeric micelles (commonly in the nanosize scale) can play in ocular delivery. Thus, after a general description of ocular barriers and micelles features, the attention is focused on those properties that are relevant for ophthalmic application. Finally, their efficacy in improving the ocular delivery of different classes of therapeutics (anti-inflammatory, immunosuppressant, antiglaucoma, antifungal, and antiviral drugs) are reported.

EXPERT OPINION

Although still a few, in vivo experiments have clearly demonstrated the capability of polymeric nanomicelles to overcome a variety of hurdles associated to ocular therapy, notably increasing drug bioavailability. However, there are still some very important issues to be solved, such as tolerability and stability; additionally, the role of micelles in drug uptake by the ocular tissues and their potential for the treatment of posterior eye diseases still need to be clarified/verified.

Biodegradable organosilica magnetic micelles for magnetically targeted MRI and GSH-triggered tumor chemotherapy

A GSH-responsive Fe₃O₄/DOX co-loaded PEGylated organosilica-based biodegradable nanosystem was developed for magnetically targeted magnetic resonance imaging and tumor chemotherapy.

Matrix metalloproteinase 2/9-triggered-release micelles for inhaled drug delivery to treat lung cancer: preparation and in vitro/in vivo studies

Background

Improvement in drug accumulation in the lungs through inhalation administration and high expression of MMP2 and MMP9 in lung tumors have both been widely reported.

Methods

MMP2/9-triggered-release micelles were constructed and in vitro and in vivo studies of inhalation administration against lung tumor carried out. Pluronic P123 (P123) was modified with GPLGIAGQ-NH2 (GQ8) peptide to obtain P123-GQ8 (PG). MMP2/9-triggered-release micelles were constructed using PG and succinylated gelatin (SG) and loading paclitaxel (Ptx). To study biodistribution of micelles, DiR encapsulated in micelles was dosed to rats via intravenous injection or inhalation before ex vivo imaging for detecting DiR quantity in lungs. And B16F10 lung cancer-bearing nude mice were chosen as animal models to evaluate in vivo efficacy of MMP2/9-triggered-release micelles.

Results

Ptx-release efficiency from PG-SG-Ptx micelles was MMP2/9-concentration-dependent. For A549 cells, PG-SG-Ptx cytotoxicity was significantly greater (P<0.001) compared to P123-Ptx. Aerosol inhalation was chosen as the method of administration. In biodistribution experiment, DiR quantity in lungs was 5.8%±0.4% of that in major organs, while the ratio was 38.8%±0.5% for inhalation. For B16F10 lung cancer-bearing nude mice, the efficacy of inhalation of PG-SG-Ptx was significantly higher (P<0.001) than Taxol inhalation and injected PG-SG-Ptx. Inhaled PG-SG-Ptx also significantly inhibited the expression of Pgp in lung cancer.

Conclusion

Inhalation of MMP2/9-triggered-release micelles increased tumor sensitivity to chemotherapeutics and reduced the toxicity of chemotherapy to healthy lung cells, which has great potential in lung cancer therapy.

Synthesis of a Block Copolymer Exhibiting Cell-Responsive Phytochemical Release for Cancer Therapy

Phytochemicals constitute a promising class of therapeutics for the treatment of various diseases, but their delivery poses significant challenges. In this work, a nanoscale polyactive emulsion was designed for smart, cell-responsive delivery of a curcumin prodrug (curcumin dicarboxylate, CDA) that was chemically conjugated to enzymatically labile oligo-peptides with polycaprolactone (PCL) as the carrier. Matrix metalloproteinase (MMP)-sensitive (PLGLYAL) or nonsensitive (GPYYPLG) peptides were used as spacers for conjugating CDA and PCL. This CDA nanoemulsion incorporating the MMP-sensitive sequence exhibited markedly higher anti-cancer activity, cell internalization, and generation of reactive oxygen species in cancer cells in vitro than the control with the nonsensitive oligopeptide. Moreover, the nanopolyactives induced minimal cytotoxicity in noncancerous cell line. This work presents a unique strategy to engineer smart nano-polyactives for efficient and targeted delivery of phytochemicals.

Factors relating to the biodistribution & clearance of nanoparticles & their effects on in vivo application

Nanoparticles have promising biomedical applications for drug delivery, tumor imaging and tumor treatment. Pharmacokinetics are important for the in vivo application of nanoparticles. Biodistribution and clearance are largely defined as the key points of pharmacokinetics to maximize therapeutic efficacy and to minimize side effects. Different engineered nanoparticles have different biodistribution and clearance processes. The interactions of organs with nanoparticles, which are determined by the characteristics of the organs and the biochemical/physical properties of the nanoparticles, are a major factor influencing biodistribution and clearance. In this review, the clearance functions of organs and the properties related to pharmacokinetics, including nanoparticle size, shape, biodegradation and surface modifications are discussed.

An implantable depot capable of in situ generation of micelles to achieve controlled and targeted tumor chemotherapy

Camptothecin (CPT)-containing promicelle polymers (PM_CPT) based on 4-armed poly(ethylene glycol) (PEG) were developed previously to self-assemble into folate-targeted and glutathione (GSH)-sensitive micelles (M_CPT). To address severe systemic toxicity and lack of tumor specificity implicated in the intravenous administration of M_CPT, a micelle-generating depot has been developed by blend electrospinning of PEG-poly(lactide) (PELA) copolymers, PM_CPT and polyethylene oxide (PEO). Upon implantation of the depot onto a tumor, PM_CPT are sustainably released to self-assemble into M_CPT on the tumor site. The release of PM_CPT is adjusted by varying PEO/PELA ratios and reaches in the range of 23-92% after 30 days of incubation. By making use of the aggregation-induced emission (AIE) features of tetraphenylethylene (TPE) derivatives, the release process of TPE-containing promicelle polymers (PM_TPE) from the depot and the spontaneous formation of micelles (M_TPE) have been monitored from the self-assembly-induced fluorescence light-up both in vitro and in vivo. Compared with intravenous injection of M_CPT, the micelle-generating depot has significantly enhanced micelle accumulation in the tumor for an extended period of time and resulted in stronger tumor inhibitory efficacy, reduced systemic toxicity and more effective inhibition of tumor metastasis, demonstrating great potential for targeted cancer therapy with sustained efficacy.

STATEMENT OF SIGNIFICANCE

The promicelle polymer-co-electrospun fibers are developed to form a micelle-generating depot after implantation onto the tumor. The promicelle polymers are continuously released and simultaneously self-assemble into folate-targeted and glutathione-sensitive micelles, ensuring sustained micelle delivery for more than 30 days. The process of micelle formation in the tumor tissue is visualized in vivo for the first time based on the mechanism of aggregation-induced emission. This in situ micelle formation also prevents premature drug release and rapid clearance from the bloodstream. In addition, these fibers deliver anti-cancer agents directly within tumor cells via dual selectivity (i.e. spatially selective accumulation in tumor tissues via implantation and selective internalization into tumor cells via folate receptor-mediated endocytosis) and on-demand drug release in response to cytosol GSH. They exhibit superior tumor inhibitory efficacy with minimal systemic toxicity, and prevent from malignant metastasis of cancer cells.

A novel individual-cell-based mathematical model based on multicellular tumour spheroids for evaluating doxorubicin-related delivery in avascular regions

BACKGROUND AND PURPOSE

Effective drug delivery in the avascular regions of tumours, which is crucial for the promising antitumour activity of doxorubicin-related therapy, is governed by two inseparable processes: intercellular diffusion and intracellular retention. To accurately evaluate doxorubicin-related delivery in the avascular regions, these two processes should be assessed together. Here we describe a new approach to such an assessment.

EXPERIMENTAL APPROACH

An individual-cell-based mathematical model based on multicellular tumour spheroids was developed that describes the different intercellular diffusion and intracellular retention kinetics of doxorubicin in each cell layer. The different effects of a P-glycoprotein inhibitor (LY335979) and a hypoxia inhibitor (YC-1) were quantitatively evaluated and compared, in vitro (tumour spheroids) and in vivo (HepG2 tumours in mice). This approach was further tested by evaluating in these models, an experimental doxorubicin derivative, INNO 206, which is in Phase II clinical trials.

KEY RESULTS

Inhomogeneous, hypoxia-induced, P-glycoprotein expression compromised active transport of doxorubicin in the central area, that is, far from the vasculature. LY335979 inhibited efflux due to P-glycoprotein but limited levels of doxorubicin outside the inner cells, whereas YC-1 co-administration specifically increased doxorubicin accumulation in the inner cells without affecting the extracellular levels. INNO 206 exhibited a more effective distribution profile than doxorubicin.

CONCLUSIONS AND IMPLICATIONS

The individual-cell-based mathematical model accurately evaluated and predicted doxorubicin-related delivery and regulation in the avascular regions of tumours. The described framework provides a mechanistic basis for the proper development of doxorubicin-related drug co-administration profiles and nanoparticle development and could avoid unnecessary clinical trials.

A pH-responsive glycolipid-like nanocarrier for optimising the time-dependent distribution of free chemical drugs in focal cells

Though Drug delivery systems have achieved accumulation at tumor sites via passive targeting and active targeting, the therapeutic effects are far from perfect. The unsatisfactory results are mainly due to limited drug release from the nanocarriers at tumor sites, while the pharmacological activities of the drug are attributed to the concentration of the free drug and the time maintained at the pharmacological targets. A pH-responsive chitosan based glycolipid-like nanocarrier (CSO-FBA-SA) was fabricated by conjugating stearyl alcohol (SA) to chitosan oligosaccharide (CSO) with the linkage of 4-formylbenzoic acid (FBA). FBA was a kind of aromatic aldehyde carbonyl compounds, which can form the benzoic-imine bond. In the presence of a Schiff's base structure, the carrier showed improved properties and could be quickly degraded in an acidic environment. In order to explore the process and mechanism of the nanocarriers in focal cells, the method for determining the intracellular concentration of released free doxorubicin was established, and the time-dependent change of the DOX-loaded micelles was revealed. The sight of drug release was also obtained with CLSM. The cytotoxicity of the CSO-FBA-SA/DOX against human breast cancer MCF-7 cells increased by 2.75-fold and 3.77-fold in comparison with the CSO-SA/DOX and DOX, respectively. Furthermore, the CSO-FBA-SA/DOX showed a 2.12-fold higher cytotoxicity against the MCF-7 cells than that treated against human ovarian cancer SKOV-3 cells with lower intracellular pH value, which indicated that the cellular inhibition positively correlated with the intracellular pH value. High tumor accumulation and fast drug release of the CSO-FBA-SA/DOX in tumor was responsible for the remarkable tumor growth inhibitory effect. Moreover, the CSO-FBA-SA/DOX could selectively respond to the acidic environment and release DOX in tumor only, which had relatively minimal cytotoxicity towards normal tissues. The results showed that this newly developed glycolipid-like nanocarrier could act as a potential vector for delivering the drug effectively with a low systemic toxicity.

Matrix metalloproteinases-2/9-sensitive peptide-conjugated polymer micelles for site-specific release of drugs and enhancing tumor accumulation: preparation and in vitro and in vivo evaluation

Since elevated expression of matrix metalloproteinase (MMP)-2 and MMP-9 is commonly observed in several malignant tumors, MMPs have been widely reported as key factors in the design of drug delivery systems. Several strategies have been proposed to develop MMPs-responsive nanoparticles to deliver chemotherapeutics to malignant solid tumors. A stimuli-responsive drug delivery system, which could be cleaved by MMPs, was proposed in this study. By inserting an MMP-2/9 cleavable oligopeptide GPVGLIGK-NH₂ (GK8) as spacer between α-tocopherol succinate (α-TOS) and methoxy-polyethylene glycol molecular weight (MW 2000 Da) activated by N-hydroxysuccinimide (mPEG2K-NHS), mPEG2K-GK8-α-TOS (TGK) was synthesized as the primary ingredient for MMP-2/9-sensitive micelles composed of d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) and TGK (n:n =40:60, TGK micelles). mPEG2K-α-TOS (T2K) was similarly synthesized as nonsensitive control. The TGK micelles showed better stability than nonsensitive micelles composed of TPGS and T2K (n:n =40:60, T2K micelles) owing to the inserted peptide. Fluorescence resonance energy transfer results indicated that TGK micelles could be successfully cleaved by MMP-2/9. Effective drug release was demonstrated in the presence of collagenase type IV, a mixture of MMP-2 and MMP-9. Compared with nonsensitive micelles, docetaxel (DTX)-loaded TGK micelles showed a fold higher cellular uptake in HT1080 cells. While the half-maximal inhibitory concentration (IC₅₀) of TGK and T2K micelles were similar (P>0.05) in MCF-7 cells (MMP-2/9 underexpression), the IC₅₀ values of the aforementioned micelles were 0.064±0.006 and 0.122±0.009 μg/mL, respectively, in HT1080 cells (MMP-2/9 overexpression). The MMP-2/9-sensitive micelles also demonstrated desired tumor targeting and accumulation ability in vivo. The results of in vivo antitumor effect evaluation indicate that TGK micelles are potent against solid tumors while maintaining minimum systemic toxicity compared with T2K micelles and DTX.