Core-matched encapsulation of an oleate prodrug into nanostructured lipid carriers with high drug loading capability to facilitate the oral delivery of docetaxel

Exploring the optimal chain length of modification module in disulfide bond bridged paclitaxel prodrug nanoassemblies for breast tumor treatment

In the prodrug-based self-assembled nanoassemblies, prodrugs usually consist of drug modules, response modules, and modification modules. Modification modules play a critical role in regulating the nano-assembly ability of the prodrugs. Herein, we carried out a "fatty alcoholization" strategy and chose various lengths of aliphatic alcohol chains (AC) as modification modules to construct disulfide bond bridged paclitaxel (PTX) prodrug nanoassemblies. The PTX-AC prodrugs would self-assemble into nanoassemblies (PTX-AC PNs) with higher drug loading, stability, and tumor selectivity than commercial preparations. After comprehensive exploration, we found the chain length (AC12, AC16, AC20, AC24) of modification modules affected the assembly of PTX-AC PNs, further leading to disparate in vivo fate and antitumor efficacy. With the increase of the chain length of the modification modules (from AC12 to AC20), the assembly ability of the nanoassemblies was improved, attributed to the appropriate enhancement of hydrophobic force. When the chain length was further increased to AC24, the excessive hydrophobic force will lead to the aggregation of prodrugs and weaken the assembly ability. Therefore, PTX-AC20 PNs with proper chain length may solve the paradox of efficacy and tolerance in 4 T1 breast tumor owing to their optimal nano-assembly stability and modest redox-sensitivity. In short, this work highlighted the importance of screening optimal modification modules in developing prodrug nanoassemblies.

A self-microemulsion enhances oral absorption of docetaxel by inhibiting P-glycoprotein and CYP metabolism

Oral absorption of docetaxel was limited by drug efflux pump p-glycoprotein (P-gp) and cytochrome P450 enzyme (CYP 450). Therefore, co-loading agent that inhibits P-gp and CYP450 in self-nanoemulsifying drug delivery systems (SMEs) is considered a promising strategy for oral delivery of docetaxel. In this study, curcumin was selected as an inhibitor of P-gp and CYP450, and it was co-encapsuled in SMEs to improve the oral bioavailability of docetaxel. SMEs quickly dispersed in water within 20 s, and the droplet size was 32.23 ± 2.21 nm. The release rate of curcumin from DC-SMEs was higher than that of docetaxel in vitro. Compared with free docetaxel, SMEs significantly increased the permeability of docetaxel by 4.6 times. And competitive experiments showed that the increased permeability was the result of inhibition of p-gp. The half-life and oral bioavailabilty of DC-SMEs increased about 1.7 times and 1.6 times than docetaxel SMEs, which indicated that its good pharmacokinetic behavior was related to the restriction of hepatic first-pass metabolism. In conclusion, DC-SME was an ideal platform to facilitate oral delivery of docetaxel through inhibited P-gp and CYP 450.

Incorporating a Lipophilic Disulfide-Bridged Linoleic Prodrug into a Self-Microemulsifying Drug Delivery System to Facilitate Oral Absorption of Paclitaxel

The oral absorption of paclitaxel (PTX) is restricted by poor solubility in the gastrointestinal tract (GIT), low permeability, and high first-pass metabolism. Lipid carriers, such as a self-microemulsifying drug delivery system (SMEDDS), have been deemed as promising vehicles for promoting oral delivery of PTX. Herein, a lipophilic disulfide-bridged linoleic prodrug (PTX-S-S-LA) was synthesized and efficiently incorporated into SMEDDS to facilitate the oral absorption of PTX. This study mainly aims to evaluate the usefulness of the disulfide-bridged linoleic prodrug incorporated with SMEDDS and provides a new strategy for efficient oral delivery of PTX. The prodrug SMEDDS showed a markedly higher drug loading efficiency (3-fold) compared to that of parent PTX. PTX-S-S-LA SMEDDS significantly increased the drug partition (about 1.9-fold) in the intestinal micellar aqueous phase compared to PTX in the in vitro lipolysis study. Additionally, the gastrointestinal (GI) biodistribution study demonstrated that SMEDDS could enhance the GI biological adhesion and go through the lymphatic system to transport. Moreover, it was found that the reduction-sensitive prodrug (PTX-S-S-LA) has good stability in the GIT, leading to an improved antitumor efficiency without significant GI toxicity. Overall, the PTX-linoleic prodrug (PTX-S-S-LA) in combination with SMEDDS provides a promising way to enable effective oral delivery of PTX.

Development of a long-acting tablet with ticagrelor high-loaded nanostructured lipid carriers

Ticagrelor (TCG), an antiplatelet agent, has low solubility and permeability; thus, there are many trials to apply the pharmaceutical technology for the enhancement of TCG solubility and permeability. Herein, we have developed the TCG high-loaded nanostructured lipid carrier (HL-NLC) and solidified the HL-NLC to develop the oral tablet. The HL-NLC was successfully fabricated and optimized with a particle size of 164.5 nm, a PDI of 0.199, an encapsulation efficiency of 98.5%, and a drug loading of 16.4%. For the solidification of HL-NLC (S-HL-NLC), the adsorbent was determined based on the physical properties of the S-HL-NLC, such as bulk density, tap density, angle of repose, Hausner ratio, Carr's index, and drug content. Florite R was chosen because of its excellent adsorption capacity, excellent physical properties, and solubility of the powder after manufacturing. Using an S-HL-NLC, the S-HL-NLC tablet with HPMC 4 K was prepared, which is showed a released extent of more than 90% at 24 h. Thus, we have developed the sustained release tablet containing the TCG-loaded HL-NLC. Moreover, the formulations have exhibited no cytotoxicity against Caco-2 cells and improved the cellular uptake of TCG. In pharmacokinetic study, compared with raw TCG, the bioavailability of HL-NLC and S-HL-NLC was increased by 293% and 323%, respectively. In conclusion, we successfully developed the TCG high-loaded NLC tablet, that exhibited a sustained release profile and enhanced oral bioavailability.

Nano-strategies as Oral Drug Delivery Platforms for Treatment of Cancer: Challenges and Future Perspectives

Oral drug administration is the oldest and widely used method for drug administration. The objectives behind developing an oral drug delivery for the treatment of cancer are to achieve low cost treatment by utilizing novel techniques to target cancer through gut-associated lymphoid tissue (GALT) and to enhance patient comfort and compliance through a hospital-free treatment leading to "Chemotherapy at Home." Unfortunately, due to the physiological environment of the GIT and physicochemical properties of drug candidate, the efficacy of oral drug delivery methods is limited in the treatment of cancer. Due to their low hydrophilicity, high P-gp efflux and restricted intestinal permeability most of the anti-cancer drugs fail to achieve oral bioavailability. The review focuses on the efforts, challenges, opportunities and studies conducted by scientists worldwide on the oral administration of anticancer medications via nanocarriers such as liposomes, SLNs and dendrimers, because of their potential to overcome the epithelial barrier associated with GALT, as well as the applications of different polymers in targeting the cancer. The oral delivery can set newer horizons in cancer therapy to make it more patient friendly.

Smart design approaches for orally administered lipophilic prodrugs to promote lymphatic transport

Challenges to effective delivery of drugs following oral administration has attracted growing interest over recent decades. Small molecule drugs (<1000 Da) are generally absorbed across the gastrointestinal tract into the portal blood and further transported to the systemic circulation via the liver. This can result in a significant reduction to the oral bioavailability of drugs that are metabolically labile and ultimately lead to ineffective exposure and treatment. Targeting drug delivery to the intestinal lymphatics is attracting increased attention as an alternative route of drug transportation providing multiple benefits. These include bypassing hepatic first-pass metabolism and selectively targeting disease reservoirs residing within the lymphatic system. The particular physicochemical requirements for drugs to be able to access the lymphatics after oral delivery include high lipophilicity (logP>5) and high long-chain triglyceride solubility (> 50 mg/g), properties required to enable drug association with the lipoprotein transport pathway. The majority of small molecule drugs, however, are not this lipophilic and therefore not substantially transported via the intestinal lymph. This has contributed to a growing body of investigation into prodrug approaches to deliver drugs to the lymphatic system by chemical manipulation. Optimised lipophilic prodrugs have the potential to increase lymphatic transport thereby improving oral pharmacokinetics via a reduction in first pass metabolism and may also target of disease-specific reservoirs within the lymphatics. This may provide advantages for current pharmacotherapy approaches for a wide array of pathological conditions, e.g. immune disease, cancer and metabolic disease, and also presents a promising approach for advanced vaccination strategies. In this review, specific emphasis is placed on medicinal chemistry strategies that have been successfully employed to design lipophilic prodrugs to deliberately enable lymphatic transport. Recent progress and opportunities in medicinal chemistry and drug delivery that enable new platforms for efficacious and safe delivery of drugs are critically evaluated.

Improved Bioavailability of Poorly Soluble Drugs through Gastrointestinal Muco-Adhesion of Lipid Nanoparticles

Gastrointestinal absorption remains indispensable in the systemic delivery of most drugs, even though it presents several challenges that, paradoxically, may also provide opportunities that can be exploited to achieve maximal bioavailability. Drug delivery systems made from nanoparticle carriers and especially, lipid carriers, have the potential to traverse gastrointestinal barriers and deploy in the lymphatic pathway, which aptly, is free from first pass via the liver. Several poorly soluble drugs have presented improved systemic bioavailability when couriered in lipid nanoparticle carriers. In this review, we propose an additional frontier to enhancing the bioavailability of poorly soluble drugs when encapsulated in lipid nano-carriers by imparting muco-adhesion to the particles through application of appropriate polymeric coating to the lipid carrier. The combined effect of gastrointestinal muco-adhesion followed by lymphatic absorption is a promising approach to improving systemic bioavailability of poorly soluble drugs following oral administration. Evidence to the potential of this approach is backed-up by recent studies within the review.

Oral delivery of solid lipid nanoparticles: underlining the physicochemical characteristics and physiological condition affecting the lipolysis rate

INTRODUCTION

Lipid-based nano-drug delivery systems (LBNDDSs) have gained widespread attention in oral drug delivery due to their tunable and versatile properties such as biocompatibility and biodegradability, which makes them promising delivery systems for a variety of therapeutics. Currently, different types of LBNDDSs including liposomes, micelles, nanoemulsions, and solid lipid nanoparticles (SLNs) are developed for drug delivery applications. SLNs can be used as a controlled drug delivery system for oral delivery applications. However, its lipidic context makes that susceptible to lipolysis. The lipolysis rate of SLNs is affected by many factors that raise many questions for developing a more efficient delivery system.

AREAS COVERED

In the present work, we highlighted different factors affecting the digestion rate/level of SLNs in the gastrointestinal tract. This paper can be most useful for those researchers who are keen to develop a properly controlled drug delivery system based on SLNs for oral delivery applications.

EXPERT OPINION

SLNs can be used as a controlled drug delivery system for oral delivery applications. However, its lipidic context makes that susceptible to lipolysis. The lipolysis rate of SLNs is affected by many factors that raise many questions for developing a more efficient delivery system.

Structured edible lipid-based particle systems for oral drug-delivery

Oral administration is the most popular and patient-compliant route for drug delivery, though it raises great challenges due to the involvement of the gastro-intestine (GI) system and the drug bioavailability. Drug bioavailability is directly related to its ability to dissolve, transport and/or absorb through the physiological environment. A great number of drugs are characterized with low water solubility due to their hydrophobic nature, thus limiting their oral bioavailability and clinical use. Therefore, new strategies aiming to provide a protective shell through the GI system and improve drug solubility and permeability in the intestine were developed to overcome this limitation. Lipid-based systems have been proposed as good candidates for such a task owing to their hydrophobic nature which allows high drug loading, drug micellization ability during intestinal digestion due to the lipid content, and the vehicle physical protective environment. The use of edible lipids with high biocompatibility paves the bench-to-bedside translation. Four main types of structured lipid-based drug delivery systems differing in the physical state of the lipid phase have been described in the literature, namely emulsions, solid lipid nanoparticles, nanostructured lipid carriers, and oleogel-based particles. The current review provides a comprehensive overview of the different structured edible lipid-based oral delivery systems investigated up to date and emphasizes the contribution of each system component to the delivery performance, and the oral delivery path of lipids.

Oral lipid nanomedicines: Current status and future perspectives in cancer treatment

Oral anticancer drugs have earned a seat at the table, as the need for homecare treatment in oncology has increased. Interest in this field is growing as a result of their proven efficacy, lower costs and positive patient uptake. However, the gastrointestinal barrier is still the main obstacle to surmount in chemotherapeutic oral delivery. Anticancer nanomedicines have been proposed to solve this quandary. Among these, lipid nanoparticles are described to be efficiently absorbed while protecting drugs from early degradation in hostile environments. Their intestinal lymphatic tropism or mucoadhesive/penetrative properties give them unique characteristics for oral administration. Considering that chronic cancer cases are increasing over time, it is important to be able to provide treatments with low toxicity and low prices. The challenges, opportunities and therapeutic perspectives of lipid nanoparticles in this area will be discussed in this review, taking into consideration the pre-clinical and clinical progress made in the last decade.

Opportunities and challenges of fatty acid conjugated therapeutics

Instability, poor cellular uptake and unfavorable pharmacokinetics and biodistribution of many therapeutic molecules require modification in their physicochemical properties. The conjugation of these APIs with fatty acids has demonstrated an enhancement in their lipophilicity and stability. The improvement in the formulations that resulted from the conjugation of a drug with a fatty acid includes increased half-life, enhanced cellular uptake and retention, targeted tumor delivery, reduced chemoresistance in cancer, and improved blood-brain-barrier (BBB) penetration. In this review, various therapeutic molecules, including small molecules, peptides and oligonucleotides, that have been conjugated with fatty acid have been thoroughly discussed along with various conjugation strategies. The application of nano-system based delivery is gaining a lot of attention due to its ability to provide controlled drug release, targeting and reducing the extent of side effects. This review also covers various nano-carriers that have been utilized for the delivery of fatty acid drug conjugates. The enhanced lipophilicity of the drug-fatty acid conjugate has shown to enhance the affinity of the drug towards these carriers, thereby increasing the entrapment efficiency and formulation performance.

Tailoring functional nanostructured lipid carriers for glioblastoma treatment with enhanced permeability through in-vitro 3D BBB/BBTB models

The blood-brain barrier (BBB) and blood-brain tumour barrier (BBTB) pose a significant challenge to drug delivery to brain tumours, including aggressive glioblastoma (GB). The present study rationally designed functional nanostructured lipid carriers (NLC) to tailor their BBB penetrating properties with high encapsulation of CNS negative chemotherapeutic drug docetaxel (DTX). We investigated the effect of four liquid lipids, propylene glycol monolaurate (Lauroglycol® 90), Capryol® propylene glycol monocaprylate, caprylocaproylmacrogol-8-glycerides (Labrasol®) and polyoxyl-15-hydroxystearate (Kolliphor® HS15) individually and in combination to develop NLCs with effective permeation across in-vitro 3D BBB model without alteration in the integrity of the barrier. With desirable spherical shape as revealed by TEM and an average particle size of 123.3 ± 0.642 nm and zeta potential of -32 mV, DTX-NLCs demonstrated excellent stability for six months in its freeze-dried form. The confocal microscopy along with flow cytometry data revealed higher internalisation of DTX-NLCs in U87MG over SVG P12 cells. Micropinocytosis was observed to be one of the dominant pathways for internalisation in U87MG cells while clathrin-mediated pathway was more predominat in patient-derived glioblastoma cells. The NLCs readily penetrated the actively proliferating peripheral cells on the surface of the 3D tumour spheroids as compared to the necrotic core. The DTX-NLCs induced cell arrest through G2/M phase with a significant decrease in the mitochondrial reserve capacity of cells. The NLCs circumvented BBTB with high permeability followed by accumulation in glioblastoma cells with patient-derived cells displaying ~2.4-fold higher uptake in comparison to U87MG when studied in a 3D in-vitro model of BBTB/GB. We envisage this simple and industrially feasible technology as a potential candidate to be developed as GB nanomedicine.

Lipid Drug Carriers for Cancer Therapeutics: An Insight into Lymphatic Targeting, P-gp, CYP3A4 Modulation and Bioavailability Enhancement

In the treatment of cancer, chemotherapy plays an important role though the efficacy of anti-cancer drug administered orally is limited, due to their poor solubility in physiological medium, inability to cross biological membrane, high Para-glycoprotein (P-gp) mediated drug efflux, and pre-systemic metabolism. These all factors cumulatively reduce drug exposure at the target site leading to multidrug resistance (MDR). Lipid based carriers systems has been explored to overcome solubility and permeability related issues of anti-cancer drugs. The lipid based formulations have also been reported to circumvent the effect of P-gp and CYP3A4. Further long chain triglycerides (LCT) has shown their ability to access Lymphatic route over Medium Chain Triglycerides, as the former has been extensively used for targeting anti-cancer drugs at proliferating cells through lymphatic route. Therefore this review tries to reflect the usefulness of lipid based drug carriers systems (viz. liposome, solid lipid nanoparticle, nano-lipid carriers, self-emulsifying, lipidic pro-drugs) in targeting lymphatic system and overcoming issues related to solubility and permeability of anti-cancer drugs. Moreover, we have also tried to reflect how critically lipid based carriers are important in maximizing therapeutic safety and efficacy of anti-cancer drugs.

Emerging insights on drug delivery by fatty acid mediated synthesis of lipophilic prodrugs as novel nanomedicines

Many drug molecules that are currently in the market suffer from short half-life, poor absorption, low specificity, rapid degradation, and resistance development. The design and development of lipophilic prodrugs can provide numerous benefits to overcome these challenges. Fatty acids (FAs), which are lipophilic biomolecules constituted of essential components of the living cells, carry out many necessary functions required for the development of efficient prodrugs. Chemical conjugation of FAs to drug molecules may change their pharmacodynamics/pharmacokinetics in vivo and even their toxicity profile. Well-designed FA-based prodrugs can also present other benefits, such as improved oral bioavailability, promoted tumor targeting efficiency, controlled drug release, and enhanced cellular penetration, leading to improved therapeutic efficacy. In this review, we discuss diverse drug molecules conjugated to various unsaturated FAs. Furthermore, various drug-FA conjugates loaded into various nanostructure delivery systems, including liposomes, solid lipid nanoparticles, emulsions, nano-assemblies, micelles, and polymeric nanoparticles, are reviewed. The present review aims to inspire readers to explore new avenues in prodrug design based on the various FAs with or without nanostructured delivery systems.

Muscone/RI7217 co-modified upward messenger DTX liposomes enhanced permeability of blood-brain barrier and targeting glioma

Rationale: The dual-targeted drug delivery system was designed for enhancing permeation of the blood-brain barrier (BBB) and providing an anti-glioma effect. As transferrin receptor (TfR) is over-expressed by the brain capillary endothelial (hCMEC/D3) and glioma cells, a mouse monoclonal antibody, RI7217, with high affinity and selectivity for TfR, was used to study the brain targeted drug delivery system. Muscone, an ingredient of traditional Chinese medicine (TCM) musk, was used as the "guide" drug to probe the permeability of the BBB for drug delivery into the cerebrospinal fluid. This study investigated the combined effects of TCM aromatic resuscitation and modern receptor-targeted technology by the use of muscone/RI7217 co-modified docetaxel (DTX) liposomes for enhanced drug delivery to the brain for anti-glioma effect. Methods: Cellular drug uptake from the formulations was determined using fluorescence microscopy and flow cytometry. The drug penetrating ability into tumor spheroids were visualized using confocal laser scanning microscopy (CLSM). In vivo glioma-targeting ability of formulations was evaluated using whole-body fluorescent imaging system. The survival curve study was performed to evaluate the anti-glioma effect of the formulations. Results: The results showed that muscone and RI7217 co-modified DTX liposomes enhanced uptake into both hCMEC/D3 and U87-MG cells, increased penetration to the deep region of U87-MG tumor spheroids, improved brain targeting in vivo and prolonged survival time of nude mice bearing tumor. Conclusion: Muscone and RI7217 co-modified DTX liposomes were found to show improved brain targeting and enhanced the efficacy of anti-glioma drug treatment in vivo.

Nanoformulation strategies for improving intestinal permeability of drugs: A more precise look at permeability assessment methods and pharmacokinetic properties changes

The therapeutic efficacy of orally administered drugs is often restricted by their inherent limited oral bioavailability. Low water solubility, limited permeability through the intestinal barrier, instability in harsh environment of the gastrointestinal (GI) tract and being substrate of the efflux pumps and the cytochrome P450 (CYP) can impair oral drug bioavailability resulting in erratic and variable plasma drug profile. As more drugs with low membrane permeability are developed, new interest is growing to enhance their intestinal permeability and bioavailability. A wide variety of nanosystems have been developed to improve drug transport and absorption. Sufficient evidence exists to suggest that nanoparticles are able to increase the transepithelial transport of drug molecules. However, key questions remained unanswered. What types of nanoparticles are more efficient? What are preclinical (or clinical) achievements of each type of nanoformulation in terms of pharmacokinetic (PK) parameters? Addressing this issue in this paper, we have reviewed the current literature regarding permeability enhancement, permeability assessment methods and changes in PK parameters following administration of various nanoformulations. Although permeability enhancement by various nanoformulations holds great promise for oral drug delivery, many challenges still need to be addressed before development of more clinically successful nanoproducts.

Repaglinide-loaded nanostructured lipid carriers with different particle sizes for improving oral absorption: preparation, characterization, pharmacokinetics, and in situ intestinal perfusion

Repaglinide-loaded nanostructured lipid carriers (REP-NLCs) with different particle sizes were successfully designed and prepared to investigate the permeation and absorption ability by in situ single-pass intestinal perfusion (SPIP) study and pharmacokinetics. Both of the formulations prepared by solvent diffusion method exhibited a spherical shape under transmission electron microscopy (TEM) and similar zeta potential value of –11 mV. The particles size, encapsulation efficiency (EE), drug loading (DL) of REP-NLCs-Small and REP-NLCs-Large size preparations were about 79 nm and 325 nm, 96.83% and 98.60%, 4.41% and 3.05%, respectively. Besides, both REP-NLCs showed good colloidal stability and had no burst release phenomenon compared with REP-Sol. SPIP demonstrated the improved membrane permeability for NLCs compared with REP-Sol, especially NLCs-Small size preparation. The bioavailability increased sequentially in REP-Sol, REP-NLCs-Large, and REP-NLCs-Small, and the difference between each other was statistical significant. Our investigations demonstrate that NLCs with small particles size of 50–100 nm, such as 79 nm, are able to enhance absorption performance of a poorly soluble repaglinide compared with large particles size, such as 325 nm, by significantly improving the absorption in jejunum, and colon of rats and thus well improving oral bioavailability.

Co-encapsulation of docetaxel and cyclosporin A into SNEDDS to promote oral cancer chemotherapy

Self-nanoemulsifying drug delivery system (SNEDDS) have been considered as a promising platform for oral delivery of many BCS (biopharmaceutics classification system) class IV drugs, such as docetaxel (DTX). However, oral chemotherapy with DTX is also restricted by its active P-glycoprotein (P-gp) efflux and hepatic first-pass metabolism. To address these challenges, we developed a novel SNEDDS co-loaded with DTX and cyclosporine A (CsA) to achieve effective inhibition of P-gp efflux and P450 enzyme metabolization, improving oral bioavailability of DTX. The SNEDDS showed uniform droplet size of about 30 nm. Additionally, the prepared SNEDDS exhibited a sequential drug release trend of CsA prior to DTX. The intestinal experiments confirmed that the membrane permeability of DTX was significantly increased in the whole intestinal tract, especially in the jejunum segment. Furthermore, the oral bioavailability of co-loaded SNEDDS was 9.2-fold and 3.4-fold higher than DTX solution and DTX SNEDDS, respectively. More importantly, it exhibited a remarkable antitumor efficacy with a reduced toxicity compared with intravenously administered DTX solution. In summary, DTX-CsA co-loaded SNEDDS is a promising platform to facilitate oral docetaxel-based chemotherapy.

Integration of phospholipid-drug complex into self-nanoemulsifying drug delivery system to facilitate oral delivery of paclitaxel

Self-nanoemulsifying drug delivery system (SNEDDS) has emerged as a promising platform to improve oral absorption of drugs with poor solubility and low permeability. However, large polarity molecules with insufficient lipid solubility, such as paclitaxel (PTX), would suffer from inferior formulation of SNEDDS due to poor compatibility. Herein, phospholipid-drug complex (PLDC) and SNEDDS were integrated into one system to facilitate oral delivery of PTX. First, PTX was formulated into PLDC in response to its inferior physicochemical properties. Then, the prepared PLDC was further formulated into SNEDDS by integrating these two drug delivery technologies into one system (PLDC-SNEDDS). After PLDC-SNEDDS dispersed in aqueous medium, nanoemulsion was formed immediately with an average particle size of ∼30 nm. Furthermore, the nanomulsion of PLDC-SNEDDS showed good colloidal stability in both HCl solution (0.1 mol/l, pH 1.0) and phosphate buffer solution (PBS, pH 6.8). In vivo, PTX-PLDC-SNEDDS showed distinct advantages in terms of oral absorption efficiency, with a 3.42-fold and 2.13-fold higher bioavailability than PTX-PLDC and PTX solution, respectively. Our results suggest that the integration of PLDC into SNEDDS could be utilized to facilitate the oral delivery of hydrophobic drugs with large polarity.

Prodrugs in combination with nanocarriers as a strategy for promoting antitumoral efficiency

Prodrug entrapment into nanocarriers for tumor delivery is a strategy to achieve a valid therapy with high efficiency. The prodrug contains anticancer agents conjugating with functional moieties or ligands so that the active component is released after metabolism in the body or tumor. The advantages of nanosystems for loading prodrugs include high loading, increased prodrug stability, improved bioavailability and enhanced targeting to tumor cells. In the present article, we introduce the prodrug delivery approaches according to nanomedicine and the recent advances in prodrug-loaded nanocarriers. First, we discuss the conceptional design of combined prodrugs and nanocarriers in response to the obstruction in anticancer therapy. Then we describe the cases of prodrug-loaded nanoparticles for cancer treatment during the past 5 years.

High Co-loading Capacity and Stimuli-Responsive Release Based on Cascade Reaction of Self-Destructive Polymer for Improved Chemo-Photodynamic Therapy

Photodynamic therapy (PDT) shows a promising synergy with chemotherapy in the therapeutic outcome of malignant cancers. The minimal invasiveness and nonsystemic toxicity are appealing advantages of PDT, but combination with chemotherapy brings in the nonselective toxicity. We designed a polymeric nanoparticle system that contains both a chemotherapeutic agent and a photosensitizer to seek improvement for chemo-photodynamic therapy. First, to address the challenge of efficient co-delivery, polymer-conjugated doxorubicin (PEG-PBC-TKDOX) was synthesized to load photosensitizer chlorin e6 (Ce6). Ce6 is retained with DOX by a π-π stacking interaction, with high loading (41.9 wt %) and the optimal nanoparticle size (50 nm). Second, light given in PDT treatment not only excites Ce6 to produce cytotoxic reactive oxygen species (ROS) but also spatiotemporally activates a cascade reaction to release the loaded drugs. Finally, we report a self-destructive polymeric carrier (PEG-PBC-TKDOX) that depolymerizes its backbone to facilitate drug release upon ROS stimulus. This is achieved by grafting the ROS-sensitive pendant thioketal to aliphatic polycarbonate. When DOX is covalently modified to this polymer via thioketal, target specificity is controlled by light, and off-target delivery toxicity is mostly avoided. An oral squamous cell carcinoma that is clinically relevant to PDT was used as the cancer model. We put forward a polymeric system with improved efficiency for chemo-photodynamic therapy and reduced off-target toxicity.

Formulating a single thioether-bridged oleate prodrug into a self-nanoemulsifying drug delivery system to facilitate oral absorption of docetaxel

Oral chemotherapy of docetaxel (DTX) is restricted by active P-glycoprotein (P-gp) efflux, hepatic first-pass metabolism and then poor oral absorption. Herein, a lipophilic thioether-bridged oleate prodrug (DTX-S-OA) and an ester-bond linked oleate prodrug of docetaxel (DTX-OA) were synthesized and efficiently incorporated into a self-nanoemulsifying drug delivery system (SNEDDS) using core-matching technology with a high drug-loading rate. DTX-S-OA SNEDDS produced a uniform droplet size of about 30 nm and a significantly high drug loading capability (60 mg mL-1), compared with DTX SNEDDS (20 mg mL-1). Additionally, DTX-S-OA SNEDDS exhibited a markedly slower drug release property and higher (>2-fold) drug solubilization in the aqueous phase after 60 min lipolysis compared with DTX SNEDDS. In situ single-pass intestinal perfusion and intestinal biodistribution studies demonstrated that the membrane permeability and intestinal bioadhesion of SNEDDS were significantly increased. Moreover, DTX-S-OA showed a comparable ability with verapamil in inhibiting P-gp efflux. Lymphatic transport studies confirmed that DTX-S-OA SNEDDS could significantly enhance intestinal lymphatic transport. Notably, the bioavailability of DTX-S-OA SNEDDS was 6.2-fold and 2.0-fold higher than that of the DTX solution and DTX SNEDDS, respectively. Furthermore, DTX-S-OA achieved a more rapid release of free DTX from the prodrug in systemic circulation than DTX-OA. Therefore, such a unique combination strategy of the single thioether-bridged DTX-oleate prodrug and SNEDDS is a promising platform to enable effective oral delivery of DTX.

Paclitaxel-loaded Nanolipidic Carriers with Improved Oral Bioavailability and Anticancer Activity against Human Liver Carcinoma

The poorly water-soluble chemotherapeutic agents, paclitaxel (PTX), exhibit serious clinical side effects upon oral administration due to poor aqueous solubility and a high degree of toxic effects due to non-specific distribution to healthy tissues. In our efforts, we formulated biocompatible dietary lipid-based nanostructured lipidic carriers (NLCs) to enhance the oral bioavailability of PTX for treatment of the liver cancer. A three-factor, three-level Box-Behnken design was employed for formulation and optimization of PTX-loaded NLC formulations. PTX-loaded NLC formulation prepared by melt-emulsification in which glyceryl monostearate (GMS) was used as solid lipid and soybean oil as liquid lipid, while poloxamer 188 and Tween 80 (1:1) incorporated as a surfactant. In vitro drug release investigation was executed by dialysis bag approach, which indicated initial burst effect with > 60% drug release within a 4-h time period. Moreover, PTX-NLCs indicated high entrapment (86.48%) and drug loading efficiency (16.54%). In vitro cytotoxicity study of PTX-NLCs performed on HepG2 cell line by MTT assay indicated that PTX-NLCs exhibited comparatively higher cytotoxicity than commercial formulation (Intaxel®). IC₅₀ values of PTX-NLCs and Intaxel® after 24-h exposure were found to be 4.19 μM and 11.2 μM. In vivo pharmacokinetic study in Wistar rats also indicated nearly 6.8-fold improvement in AUC and C_max of the drug from the PTX-NLCs over the PTX suspension. In a nutshell, the observed results construed significant enhancement in the biopharmaceutical attributes of PTX-NLCs as a potential therapy for the management of human liver carcinoma.

Advancements in the oral delivery of Docetaxel: challenges, current state-of-the-art and future trends

The oral delivery of cancer chemotherapeutic drugs is challenging due to low bioavailability, gastrointestinal side effects, first-pass metabolism and P-glycoprotein efflux pumps. Thus, chemotherapeutic drugs, including Docetaxel, are administered via an intravenous route, which poses many disadvantages of its own. Recent advances in pharmaceutical research have focused on designing new and efficient drug delivery systems for site-specific targeting, thus leading to improved bioavailability and pharmacokinetics. A decent number of studies have been reported for the safe and effective oral delivery of Docetaxel. These nanocarriers, including liposomes, polymeric nanoparticles, metallic nanoparticles, hybrid nanoparticles, dendrimers and so on, have shown promising results in research papers and clinical trials. The present article comprehensively reviews the research efforts made so far in designing various advancements in the oral delivery of Docetaxel. Different strategies to improve oral bioavailability, prevent first-pass metabolism and inhibition of efflux pumping leading to improved pharmacokinetics and anticancer activity are discussed. The final portion of this review article presents key issues such as safety of nanomaterials, regulatory approval and future trends in nanomedicine research.

PEG-lipid-PLGA hybrid nanoparticles loaded with berberine-phospholipid complex to facilitate the oral delivery efficiency

The natural product berberine (BBR), present in various plants, arouses great interests because of its numerous pharmacological effects. However, the further development and application of BBR had been hampered by its poor oral bioavailability. In this work, we report on polymer–lipid hybrid nanoparticles (PEG–lipid–PLGA NPs) loaded with BBR phospholipid complex using a solvent evaporation method for enhancing the oral BBR efficiency. The advantage of this new drug delivery system is that the BBR–soybean phosphatidylcholine complex (BBR–SPC) could be used to enhance the liposolubility of BBR and improve the affinity with the biodegradable polymer to increase the drug-loading capacity and controlled/sustained release. The entrapment efficiency of the PEG–lipid–PLGA NPs/BBR–SPC was observed to approach approximately 89% which is more than 2.4 times compared with that of the PEG–lipid–PLGA NPs/BBR. To the best of our knowledge, this is the first report on using polymer material for effective encapsulation of BBR to improve its oral bioavailability. The prepared BBR delivery systems demonstrated a uniform spherical shape, a well-dispersed core-shell structure and a small particle size (149.6 ± 5.1 nm). The crystallographic and thermal analysis has indicated that the BBR dispersed in the PEG–lipid–PLGA NPs matrix is in an amorphous form. More importantly, the enhancement in the oral relative bioavailability of the PEG–lipid–PLGA NPs/BBR–SPC was ∼343% compared with that of BBR. These positive results demonstrated that PEG–lipid–PLGA NPs/BBR–SPC may have the potential for facilitating the oral drug delivery of BBR.

Self-delivering prodrug-nanoassemblies fabricated by disulfide bond bridged oleate prodrug of docetaxel for breast cancer therapy

Breast cancer leads to high mortality of women in the world. Docetaxel (DTX) has been widely applied as one of the first-line chemotherapeutic drugs for breast cancer therapy. However, the clinical outcome of DTX is far from satisfaction due to its poor drug delivery efficiency. Herein, a novel disulfide bond bridged oleate prodrug of DTX was designed and synthesized to construct self-delivering prodrug-based nanosystem for improved anticancer efficacy of DTX. The uniquely engineered prodrug-nanoassemblies showed redox-responsive drug release, increased cellular uptake and comparable cytotoxicity against 4T1 breast cancer cells when compared with free DTX. In vivo, oleate prodrug-based nanoparticles (NPs) demonstrated significantly prolonged systemic circulation and increased accumulation in tumor site. As a result, prodrug NPs produced a notable antitumor activity in 4T1 breast cancer xenograft in BALB/c mice. This prodrug-based self-assembly and self-delivery strategy could be utilized to improve the delivery efficiency of DTX for breast cancer treatment.

Combination of using prodrug-modified cationic liposome nanocomplexes and a potentiating strategy via targeted co-delivery of gemcitabine and docetaxel for CD44-overexpressed triple negative breast cancer therapy

In this study, novel prodrug-modified cationic liposome nanocomplexes (Combo NCs) were reported for gemcitabine (GEM) and docetaxel (DTX) co-delivery. This nanoplatform exhibited multiple favorable characteristics, such as a 'green' fabrication with a one-step chemical reaction, appropriate size (∼200nm) and distribution (PDI<0.2), low zeta potential (-31.1mv), high drug-loading efficiency (9.3% GEM plus 3.1% DTX, wt%) and pH and enzymatic dual-stimulus-responsive release properties. Immunofluorescence and cellular uptake studies showed that Combo NCs efficiently targeted overexpressed CD44 in MDA-MB-231 carcinoma. In vitro studies revealed that Combo NCs played a critical role in the synergistic induction of cytotoxicity, apoptosis and inhibition of wound healing. Combo NCs were confirmed to exhibit great potency for increasing S phase arrest and remodeling the CDA and dCK balance by decreasing the mRNA expression of CDA down to 0.09-fold and increasing the mRNA expression of dCK by 1.36-fold, remarkably increasing the dCK/CDA ratio to 15.3-fold compared with the blank control. The biodistribution results obtained in vivo revealed an effective accumulation in tumor foci. All of these advantages of Combo NCs contributed to their remarkable anti-tumor efficacy without systemic toxicity as well as their apoptosis-enhancing and anti-proliferative capacities, as determined by TUNEL and Ki67 immunohistochemistry in vivo. Consequently, such a rationally contemplated co-delivery system demonstrated the promising potential of clinical applications for triple-negative breast cancer therapy.

STATE OF SIGNIFICANCE

The Combo NCs were innovatively applied for co-delivery of hydrophilic GEM and hydrophobic DTX. The ester bond linking and shielding effect of HA-GEM made the carriers achieve synchronous release properties, which was determined in in vitro release study. Due to the HA modification, the vectors own great potency for positive targeting to CD44 overexpressed triple-negative breast cancer cells MDA-MB-231. Cytotoxicity and apoptosis studies confirmed the targeting effect and synergism between two drugs. Interestingly, we found in cell cycle study, drug combinations (free combination or Combo NCs) didn't show a rise in G2M phase, which was significantly higher when treated DTX alone. We further discovered the role of DTX in combinations may involve in modulating GEM associated enzymes thus enhancing the efficacy of GEM. Consequently, this nanoplatform provided a novel solution for achieving targeted co-delivery and potentiating effect in cancer therapy.

Lipid-Drug Conjugate for Enhancing Drug Delivery

Lipid-drug conjugates (LDCs) are drug molecules that have been covalently modified with lipids. The conjugation of lipids to drug molecules increases lipophilicity and also changes other properties of drugs. The conjugates demonstrate several advantages including improved oral bioavailability, improved targeting to the lymphatic system, enhanced tumor targeting, and reduced toxicity. Based on the chemical nature of drugs and lipids, various conjugation strategies and chemical linkers can be utilized to synthesize LDCs. Linkers and/or conjugation methods determine how drugs are released from LDCs and are critical for the optimal performance of LDCs. In this review, different lipids used for preparing LDCs and various conjugation strategies are summarized. Although LDCs can be administered without a delivery carrier, most of them are loaded into appropriate delivery systems. The lipid moiety in the conjugates can significantly enhance drug loading into hydrophobic components of delivery carriers and thus generate formulations with high drug loading and superior stability. Different delivery carriers such as emulsions, liposomes, micelles, lipid nanoparticles, and polymer nanoparticles are also discussed in this review.

Nanostructured lipid carriers: versatile oral delivery vehicle

Oral delivery is the most accepted and economical route for drug administration and leads to substantial reduction in dosing frequency. However, this route still remains a challenge for the pharmaceutical industry due to poorly soluble and permeable drugs leading to poor oral bioavailability. Incorporating bioactives into nanostructured lipid carriers (NLCs) has helped in boosting their therapeutic functionality and prolonged release from these carrier systems thus providing improved pharmacokinetic parameters. The present review provides an overview of noteworthy studies reporting impending benefits of NLCs in oral delivery and highlights recent advancements for developing engineered NLCs either by conjugating polymers over their surface or modifying their charge to overcome the mucosal barrier of GI tract for active transport across intestinal membrane.

Lay abstract: Oral administration of drugs is considered to be a convenient route; however, various drugs that are insoluble in water or unable to permeate across GI tract membrane cannot be delivered by this route. To deliver them effectively, various lipid carriers have been widely explored by researchers. Lipid carriers encapsulate drug inside them and deliver them effectively via the oral route. Also, encapsulation of drug protects them from degradation inside GI tract and safely delivers them to the site of action. This review summarizes application of lipid carriers, in other words, nanostructured lipid carriers, in eradicating these problems, with suitable examples.