Profiling the Role of Deacylation-Reacylation in the Lymphatic Transport of a Triglyceride-Mimetic Prodrug

Nanoparticles Targeting Lymph Nodes for Cancer Immunotherapy: Strategies and Influencing Factors

Immunotherapy has emerged as a potent strategy in cancer treatment, with many approved drugs and modalities in the development stages. Despite its promise, immunotherapy is not without its limitations, including side effects and suboptimal efficacy. Using nanoparticles (NPs) as delivery vehicles to target immunotherapy to lymph nodes (LNs) can improve the efficacy of immunotherapy drugs and reduce side effects in patients. In this context, this paper reviews the development of LN-targeted immunotherapeutic NP strategies, the mechanisms of NP transport during LN targeting, and their related biosafety risks. NP targeting of LNs involves either passive targeting, influenced by NP physical properties, or active targeting, facilitated by affinity ligands on NP surfaces, while alternative methods, such as intranodal injection and high endothelial venule (HEV) targeting, have uncertain clinical applicability and require further research and validation. LN targeting of NPs for immunotherapy can reduce side effects and increase biocompatibility, but risks such as toxicity, organ accumulation, and oxidative stress remain, although strategies such as biodegradable biomacromolecules, polyethylene glycol (PEG) coating, and impurity addition can mitigate these risks. Additionally, this work concludes with a future-oriented discussion, offering critical insights into the field.

Increasing Linker Chain Length and Intestinal Stability Enhances Lymphatic Transport and Lymph Node Exposure of Triglyceride Mimetic Prodrugs of a Model Immunomodulator Mycophenolic Acid

Targeted delivery of immunomodulators to the lymphatic system has the potential to enhance therapeutic efficacy by increasing colocalization of drugs with immune targets such as lymphocytes. A triglyceride (TG)-mimetic prodrug strategy has been recently shown to enhance the lymphatic delivery of a model immunomodulator, mycophenolic acid (MPA), via incorporation into the intestinal TG deacylation-reacylation and lymph lipoprotein transport pathways. In the current study, a series of structurally related TG prodrugs of MPA were examined to optimize structure-lymphatic transport relationships for lymph-directing lipid-mimetic prodrugs. MPA was conjugated to the sn-2 position of the glyceride backbone of the prodrugs using linkers of different chain length (5-21 carbons) and the effect of methyl substitutions at the alpha and/or beta carbons to the glyceride end of the linker was examined. Lymphatic transport was assessed in mesenteric lymph duct cannulated rats, and drug exposure in lymph nodes was examined following oral administration to mice. Prodrug stability in simulated intestinal digestive fluid was also evaluated. Prodrugs with straight chain linkers were relatively unstable in simulated intestinal fluid; however, co-administration of lipase inhibitors (JZL184 and orlistat) was able to reduce instability and increase lymphatic transport (2-fold for a prodrug with a 6-carbon spacer, i.e., MPA-C6-TG). Methyl substitutions to the chain resulted in similar trends in improving intestinal stability and lymphatic transport. Medium- to long-chain spacers (C12, C15) between MPA and the glyceride backbone were most effective in promoting lymphatic transport, consistent with increases in lipophilicity. In contrast, short-chain (C6-C10) linkers appeared to be too unstable in the intestine and insufficiently lipophilic to associate with lymph lipid transport pathways, while very long-chain (C18, C21) linkers were also not preferred, likely as a result of increases in molecular weight reducing solubility or permeability. In addition to more effectively promoting drug transport into mesenteric lymph, TG-mimetic prodrugs based on a C12 linker resulted in marked increases (>40 fold) in the exposure of MPA in the mesenteric lymph nodes in mice when compared to administration of MPA alone, suggesting that optimizing prodrug design has the potential to provide benefit in targeting and modulating immune cells.

Multifunctional Lipid Bilayer Nanocarriers for Cancer Immunotherapy in Heterogeneous Tumor Microenvironments, Combining Immunogenic Cell Death Stimuli with Immune Modulatory Drugs

In addition to the contribution of cancer cells, the solid tumor microenvironment (TME) has a critical role in determining tumor expansion, antitumor immunity, and the response to immunotherapy. Understanding the details of the complex interplay between cancer cells and components of the TME provides an unprecedented opportunity to explore combination therapy for intervening in the immune landscape to improve immunotherapy outcome. One approach is the introduction of multifunctional nanocarriers, capable of delivering drug combinations that provide immunogenic stimuli for improvement of tumor antigen presentation, contemporaneous with the delivery of coformulated drug or synthetic molecules that provide immune danger signals or interfere in immune-escape, immune-suppressive, and T-cell exclusion pathways. This forward-looking review will discuss the use of lipid-bilayer-encapsulated liposomes and mesoporous silica nanoparticles for combination immunotherapy of the heterogeneous immune landscapes in pancreatic ductal adenocarcinoma and triple-negative breast cancer. We describe how the combination of remote drug loading and lipid bilayer encapsulation is used for the synthesis of synergistic drug combinations that induce immunogenic cell death, interfere in the PD-1/PD-L1 axis, inhibit the indoleamine-pyrrole 2,3-dioxygenase (IDO-1) immune metabolic pathway, restore spatial access to activated T-cells to the cancer site, or reduce the impact of immunosuppressive stromal components. We show how an integration of current knowledge and future discovery can be used for a rational approach to nanoenabled cancer immunotherapy.

Triglyceride-Mimetic Prodrugs of Buprenorphine Enhance Oral Bioavailability via Promotion of Lymphatic Transport

Buprenorphine (BUP) is a potent opioid analgesic that is widely used for severe pain management and opioid replacement therapy. The oral bioavailability of BUP, however, is significantly limited by first-pass metabolism. Previous studies have shown that triglyceride (TG) mimetic prodrugs of the steroid hormone testosterone circumvent first-pass metabolism by directing drug transport through the intestinal lymphatics, bypassing the liver. The current study expanded this prodrug strategy to BUP. Here different self-immolative (SI) linkers were evaluated to conjugate BUP to the 2 position of the TG backbone via the phenol group on BUP. The SI linkers were designed to promote drug release in plasma. Lipolysis of the prodrug in the intestinal tract was examined via incubation with simulated intestinal fluid (SIF), and potential for parent drug liberation in the systemic circulation was evaluated via incubation in rat plasma. Lymphatic transport and bioavailability studies were subsequently conducted in mesenteric lymph duct or carotid artery-cannulated rats, respectively. TG prodrug derivatives were efficiently transported into the lymphatics (up to 45% of the dose in anaesthetised rats, vs. less than 0.1% for BUP). Incorporation of the SI linkers facilitated BUP release from the prodrugs in the plasma and in concert with high lymphatic transport led to a marked enhancement in oral bioavailability (up to 22-fold) compared to BUP alone. These data suggest the potential to develop an orally bioavailable BUP product which may have advantages with respect to patient preference when compared to current sublingual, transdermal patch or parenteral formulations.

Engineering of small-molecule lipidic prodrugs as novel nanomedicines for enhanced drug delivery

A widely established prodrug strategy can effectively optimize the unappealing properties of therapeutic agents in cancer treatment. Among them, lipidic prodrugs extremely uplift the physicochemical properties, site-specificity, and antitumor activities of therapeutic agents while reducing systemic toxicity. Although great perspectives have been summarized in the progress of prodrug-based nanoplatforms, no attention has been paid to emphasizing the rational design of small-molecule lipidic prodrugs (SLPs). With the aim of outlining the prospect of the SLPs approach, the review will first provide an overview of conjugation strategies that are amenable to SLPs fabrication. Then, the rational design of SLPs in response to the physiological barriers of chemotherapeutic agents is highlighted. Finally, their biomedical applications are also emphasized with special functions, followed by a brief introduction of the promising opportunities and potential challenges of SLPs-based drug delivery systems (DDSs) in clinical application.

Graphical Abstract

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.

Multiple strategies with the synergistic approach for addressing colorectal cancer

Cancer treatment is improving widely over time, but finding a proper defender to beat them seems like a distant dream. The quest for identification and discovery of drugs with an effective action is still a vital work. The role of a membrane protein called P-glycoprotein, which functions as garbage chute that efflux the waste, xenobiotics, and toxins out of the cancer cells acts as a major reason behind the therapeutic failure of most chemotherapeutic drugs. In this review, we mainly focused on a multiple strategies by employing 5-Fluorouracil, curcumin, and lipids in Nano formulation for the possible treatment of colorectal cancer and its metastasis. Eventually, multidrug resistance and angiogenesis can be altered and it would be helpful in colorectal cancer targeting.We have depicted the possible way for the depletion of colorectal cancer cells without disturbing the normal cells. The concept of focusing on multiple pathways for marking the colorectal cancer cells could help in activating one among the pathways if the other one fails. The activity of the 5-Fluorouracil can be enhanced with the help of curcumin which acts as a chemosensitizer, chemotherapeutic agent, and even for altering the resistance. As we eat to survive, so do the cancer cells. The cancer cells utilize the energy source to stay alive and survive. Fatty acids can be used as the energy source and this concept can be employed for targeting the colorectal cancer cells and also for altering the resistant part.

Targeted delivery of mycophenolic acid to the mesenteric lymph node using a triglyceride mimetic prodrug approach enhances gut-specific immunomodulation in mice

The mesenteric lymph nodes (MLN) are a key site for the generation of adaptive immune responses to gut-derived antigenic material and immune cells within the MLN contribute to the pathophysiology of a range of conditions including inflammatory and autoimmune diseases, viral infections, graft versus host disease and cancer. Targeting immunomodulating drugs to the MLN may thus be beneficial in a range of conditions. This paper investigates the potential benefit of targeting a model immunosuppressant drug, mycophenolic acid (MPA), to T cells in the MLN, using a triglyceride (TG) mimetic prodrug approach. We confirmed that administration of MPA in the TG prodrug form (MPA-TG), increased lymphatic transport of MPA-related species 83-fold and increased MLN concentrations of MPA >20 fold, when compared to MPA alone, for up to 4 h in mice. At the same time, the plasma exposure of MPA and MPA-TG was similar, limiting the opportunity for systemic side effects. Confocal microscopy and flow cytometry studies with a fluorescent model prodrug (Bodipy-TG) revealed that the prodrug accumulated in the MLN cortex and paracortex at 5 and 10 h following administration and was highly associated with B cells and T cells that are found in these regions of the MLN. Finally, we demonstrated that MPA-TG was significantly more effective than MPA at inhibiting CD4⁺ and CD8⁺ T cell proliferation in the MLN of mice in response to an oral ovalbumin antigen challenge. In contrast, MPA-TG was no more effective than MPA at inhibiting T cell proliferation in peripheral LN when mice were challenged via SC administration of ovalbumin. This paper provides the first evidence of an in vivo pharmacodynamic benefit of targeting the MLN using a TG mimetic prodrug approach. The TG mimetic prodrug technology has the potential to benefit the treatment of a range of conditions where aberrant immune responses are initiated in gut-associated lymphoid tissues.

Intestinal delivery in a long-chain fatty acid formulation enables lymphatic transport and systemic exposure of orlistat

Orlistat is a pancreatic lipase (PL) inhibitor that inhibits dietary lipid absorption and is used to treat obesity. The oral bioavailability of orlistat is considered zero after administration in standard formulations. This is advantageous in the treatment of obesity. However, if orlistat absorption could be improved it has the potential to treat diseases such as acute and critical illnesses where PL transport to the systemic circulation via gut lymph promotes organ failure. Orlistat is highly lipophilic and may associate with intestinal lipid absorption pathways into lymph. Here we investigate the potential to improve orlistat lymph and systemic uptake through intestinal administration in lipid formulations (LFs). The effect of lipid type, lipid dose, orlistat dose, and infusion time on lymph and systemic availability of orlistat was investigated. After administration in all LFs, orlistat concentrations in lymph were greater than in plasma, suggesting direct transport via lymph. Lymph and plasma orlistat derivative concentrations were ~8-fold greater after administration in a long-chain fatty acid (LC-FA) compared to a lipid-free, LC triglyceride (LC-TG) or medium-chain FA (MC-FA) formulation. Overall, administration of orlistat in a LC-FA formulation promotes lymph and systemic uptake which may enable treatment of diseases associated with elevated systemic PL activity.

Inhibition of the Lipid Droplet-Peroxisome Proliferator-Activated Receptor α Axis Suppresses Cancer Stem Cell Properties

Cancer stem cells (CSCs), having both self-renewal and tumorigenic capacity, utilize an energy metabolism system different from that of non-CSCs. Lipid droplets (LDs) are organelles that store neutral lipids, including triacylglycerol. Previous studies demonstrated that LDs are formed and store lipids as an energy source in some CSCs. LDs play central roles not only in lipid storage, but also as a source of endogenous lipid ligands, which are involved in numerous signaling pathways, including the peroxisome proliferator-activated receptor (PPAR) signaling pathway. However, it remains unclear whether LD-derived signal transduction is involved in the maintenance of the properties of CSCs. We investigated the roles of LDs in cancer stemness using pancreatic and colorectal CSCs and isogenic non-CSCs. PPARα was activated in CSCs in which LDs accumulated, but not in non-CSCs, and pharmacological and genetic inhibition of PPARα suppressed cancer stemness. In addition, inhibition of both re-esterification and lipolysis pathways suppressed cancer stemness. Our study suggested that LD metabolic turnover accompanying PPARα activation is a promising anti-CSC therapeutic target.

Lymph-directed immunotherapy - Harnessing endogenous lymphatic distribution pathways for enhanced therapeutic outcomes in cancer

The advent of immunotherapy has revolutionised the treatment of some cancers. Harnessing the immune system to improve tumour cell killing is now standard clinical practice and immunotherapy is the first line of defence for many cancers that historically, were difficult to treat. A unifying concept in cancer immunotherapy is the activation of the immune system to mount an attack on malignant cells, allowing the body to recognise, and in some cases, eliminate cancer. However, in spite of a significant proportion of patients that respond well to treatment, there remains a subset who are non-responders and a number of cancers that cannot be treated with these therapies. These limitations highlight the need for targeted delivery of immunomodulators to both tumours and the effector cells of the immune system, the latter being highly concentrated in the lymphatic system. In this context, macromolecular therapies may provide a significant advantage. Macromolecules are too large to easily access blood capillaries and instead typically exhibit preferential uptake via the lymphatic system. In contexts where immune cells are the therapeutic target, particularly in cancer therapy, this may be advantageous. In this review, we examine in brief the current immunotherapy approaches in cancer and how macromolecular and nanomedicine strategies may improve the therapeutic profiles of these drugs. We subsequently discuss how therapeutics directed either by parenteral or mucosal administration, can be taken up by the lymphatics thereby accessing a larger proportion of the body's immune cells. Finally, we detail drug delivery strategies that have been successfully employed to target the lymphatics.

Development and Optimization of Lipase-Catalyzed Synthesis of Phospholipids Containing 3,4-Dimethoxycinnamic Acid by Response Surface Methodology

The interesterification reaction of egg-yolk phosphatidylcholine (PC) with ethyl ester of 3,4-dimethoxycinnamic acid (E3,4DMCA) catalyzed by Novozym 435 in hexane as a reaction medium was shown to be an effective method for the synthesis of corresponding structured O-methylated phenophospholipids. The effects of substrate molar ratios, time of the reaction and enzyme load on the process of incorporation of 3,4DMCA into PC were evaluated by using the experimental factorial design of three factors and three levels. The results showed that a substrate molar ratio is a crucial variable for the maximization of the synthesis of 3,4-dimethoxycinnamoylated phospholipids. Under optimized parameters of 1/10 substrate molar ratio PC/E3,4DMCA, enzyme load 30% (w/w), hexane as a medium and incubation time of 3 days, the incorporation of aromatic acid into phospholipid fraction reached 21 mol%. The modified phosphatidylcholine (3,4DMCA-PC) and modified lysophosphatidylcholine (3,4DMCA-LPC) were obtained in isolated yields of 3.5% and 27.5% (w/w), respectively. The developed method of phosphatidylcholine interesterification is the first described in the literature dealing with 3,4DMCA and allows us to obtain new O-methylated phenophospholipids with potential applications as food additives or nutraceuticals with pro-health activity.

Lysophosphatidylcholine Containing Anisic Acid Is Able to Stimulate Insulin Secretion Targeting G Protein Coupled Receptors

Diabetes mellitus is a worldwide health problem with high rates of mortality and morbidity. Management of diabetes mellitus by dietary components is achievable especially at the initial stage of the disease. Several studies confirmed the antidiabetic activities of simple phenolic acids and lysophosphatidylcholine (LPC). The main goal of this study was to identify new potential insulin secretion modulators obtained by combining the structures of two natural compounds, namely O-methyl derivatives of phenolic acids and phospholipids. LPC and phosphatidylcholine bearing methoxylated aromatic carboxylic acids were tested as potential agents able to improve glucose-stimulated insulin secretion (GSIS) and intracellular calcium mobilization in MIN6 β pancreatic cell line. Our results show that LPC with covalently bonded molecule of p-anisic acid at the sn-1 position was able to induce GSIS and intracellular calcium flux. Notably, 1-anisoyl-2-hydroxy-sn-glycero-3-phosphocholine did not affect the viability of MIN6 cells, suggesting its potential safe use. Furthermore, we have shown that three G protein coupled receptors, namely GPR40, GPR55, and GPR119, are targeted by this LPC derivative.

Metabolism of bioconjugate therapeutics: why, when, and how?

Bioconjugation of therapeutic agents has been used as a selective drug delivery platform for many therapeutic areas. Bioconjugates are prepared by the covalent linkage of active compounds (small or large molecule) to a carrier molecule (lipids, proteins, peptides, carbohydrates, and polymers) through a chemical linker. The linkage of the active component to a carrier molecule enhances the therapeutic window through a targeted delivery and by reducing toxicity. Bioconjugates also possess improved pharmacokinetic properties such as a long half-life, increased stability, and cleavage by intracellular enzymes/environment. However, premature cleavage of the bioconjugates and the resulting metabolites/catabolites may produce undesirable toxic effects and, hence, it is critical to understand cleavage mechanisms, metabolism of bioconjugates, and translatability to human in the discovery stages. This article provides a comprehensive overview of linker cleavage pathways and catabolism/metabolism of antibody-drug conjugates, glycoconjugates, polymer-drug conjugates, lipid-drug conjugates, folate-targeted small molecule-drug conjugates, and drug-drug conjugates.

Emerging Roles for Lymphatics in Chronic Liver Disease

Chronic liver disease (CLD) is a global health epidemic causing ∼2 million deaths annually worldwide. As the incidence of CLD is expected to rise over the next decade, understanding the cellular and molecular mediators of CLD is critical for developing novel therapeutics. Common characteristics of CLD include steatosis, inflammation, and cholesterol accumulation in the liver. While the lymphatic system in the liver has largely been overlooked, the liver lymphatics, as in other organs, are thought to play a critical role in maintaining normal hepatic function by assisting in the removal of protein, cholesterol, and immune infiltrate. Lymphatic growth, permeability, and/or hyperplasia in non-liver organs has been demonstrated to be caused by obesity or hypercholesterolemia in humans and animal models. While it is still unclear if changes in permeability occur in liver lymphatics, the lymphatics do expand in number and size in all disease etiologies tested. This is consistent with the lymphatic endothelial cells (LEC) upregulating proliferation specific genes, however, other transcriptional changes occur in liver LECs that are dependent on the inflammatory mediators that are specific to the disease etiology. Whether these changes induce lymphatic dysfunction or if they impact liver function has yet to be directly addressed. Here, we will review what is known about liver lymphatics in health and disease, what can be learned from recent work on the influence of obesity and hypercholesterolemia on the lymphatics in other organs, changes that occur in LECs in the liver during disease and outstanding questions in the field.

Drug-Lipid Conjugates for Enhanced Oral Drug Delivery

Oral drug delivery route is one of the most convenient and extensively utilised routes for drug administration. But there exists class of drugs which exhibit poor bioavailability on oral drug administration. Designing of drug-lipid conjugates (DLCs) is one of the rationale strategy utilised in overcoming this challenge. This review extensively covers the various dimensions of drug modification using lipids to attain improved oral drug delivery. DLCs help in improving oral delivery by providing benefits like improved permeability, stability in gastric environment, higher drug loading in carriers, formation of self-assembled nanostructures, etc. The clinical effectiveness of DLCs is highlighted from available marketed drug products along with many DLCs in phase of clinical trials. Conclusively, this drug modification strategy can potentially help in augmenting oral drug delivery in future.

Novel strategies for the treatment of acute pancreatitis based on the determinants of severity

Acute pancreatitis (AP) is a common disease for which a specific treatment remains elusive. The key determinants of the outcome from AP are persistent organ failure and infected pancreatic necrosis. The prevention and treatment of these determinants provides a framework for the development of specific treatment strategies. The gut-lymph concept provides a common mechanism for systemic inflammation and organ dysfunction. Acute and critical illness, including AP, is associated with intestinal ischemia and drastic changes in the composition of gut lymph, which bypasses the liver to drain into the systemic circulation immediately proximal to the major organ systems which fail. The external diversion of gut lymph and the targeting of treatments to counter the toxic elements in gut lymph offers novel approaches to the prevention and treatment of persistent organ failure. Infected pancreatic necrosis is increasingly treated with less invasive techniques, the mainstay of which is drainage, both endoscopic and percutaneous. Further improvements will occur with the strategies to accelerate liquefaction and through a fundamental re-design of drains, both of which will increase drainage efficacy. The determinants of severity and outcome in patients admitted with AP provide the basis for innovative treatment strategies. The priorities are to translate the gut-lymph concept to clinical practice and to improve the design and active use of drains for infected complications of AP.

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.

Lipophilicity in Drug Development: Too Much or Not Enough?

A round table discussion was held during the AAPS Annual Meeting on October 27, 2015, with the somewhat provocative topic of whether we need more or less lipophilic compounds in drug development. The session was attended by more than 250 participants, and the feedback was very positive as this round table became a forum for the exchange of ideas from scientists within the academia and industry. Most importantly, the discussion highlighted the difference in approaches to compound selection and development strategies in various companies and organizations. As moderators of this session, we are writing this report to highlight the points and counterpoints made at the session and to bring the importance of the dialogue and debate to the forefront of discussions on how to select the best drug development candidates to enable efficient delivery and, hence, treatment of diseases.

50years of oral lipid-based formulations: Provenance, progress and future perspectives

Lipid based formulations (LBF) provide well proven opportunities to enhance the oral absorption of drugs and drug candidates that sit close to, or beyond, the boundaries of Lipinski's 'rule-of-five' chemical space. Advantages in permeability, efflux and presystemic metabolism are evident; however, the primary benefit is in increases in dissolution and apparent intestinal solubility for lipophilic, poorly water soluble drugs. This review firstly details the inherent advantages of LBF, their general properties and classification, and provides a brief retrospective assessment of the development of LBF over the past fifty years. More detailed analysis of the ability of LBF to promote intestinal solubilisation, supersaturation and absorption is then provided alongside review of the methods employed to assess formulation performance. Critical review of the ability of simple dispersion and more complex in vitro digestion methods to predict formulation performance subsequently reveals marked differences in the correlative ability of in vitro tests, depending on the properties of the drug involved. Notably, for highly permeable low melting drugs e.g. fenofibrate, LBF appear to provide significant benefit in all cases, and sustained ongoing solubilisation may not be required. In other cases, and particularly for higher melting point drugs such as danazol, where re-dissolution of crystalline precipitate drug is likely to be slow, correlations with ongoing solubilisation and supersaturation are more evident. In spite of their potential benefits, one limitation to broader use of LBF is low drug solubility in the excipients employed to generate formulations. Techniques to increase drug lipophilicity and lipid solubility are therefore explored, and in particular those methods that provide for temporary enhancement including lipophilic ionic liquid and prodrug technologies. The transient nature of these lipophilicity increases enhances lipid solubility and LBF viability, but precludes enduring effects on receptor promiscuity and off target toxicity. Finally, recent efforts to generate solid LBF are briefly described as a means to circumvent the need to encapsulate in soft or hard gelatin capsules, although the latter remain popular with consumers and a proven means of LBF delivery.

Constitutive Triglyceride Turnover into the Mesenteric Lymph Is Unable to Support Efficient Lymphatic Transport of a Biomimetic Triglyceride Prodrug

The triglyceride (TG) mimetic prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) biochemically integrates into intestinal lipid transport and lipoprotein assembly pathways and thereby promotes the delivery of mycophenolic acid (MPA) into the lymphatic system. As lipoprotein (LP) formation occurs constitutively, even in the fasted state, the current study aimed to determine whether lymphatic transport of 2-MPA-TG was dependent on coadministered exogenous lipid. In vitro incubation of the prodrug with rat digestive fluid and in situ intestinal perfusion experiments revealed that hydrolysis and absorption of the prodrug were relatively unaffected by the quantity of lipid in formulations. In vivo studies in rats, however, showed that the lymphatic transport of TG and 2-MPA-TG was significantly higher following administration with higher quantities of lipid and that oleic acid (C18:1) was more effective in promoting prodrug transport than lipids with higher degrees of unsaturation. The recovery of 2-MPA-TG and TG in lymph correlated strongly (R(2) = 0.99) and more than 97% of the prodrug was associated with chylomicrons. Inhibition of LP assembly by Pluronic L81 simultaneously inhibited the lymphatic transport of 2-MPA-TG and TG. In conclusion, although the TG mimetic prodrug effectively incorporates into TG resynthetic pathways, lipid coadministration is still required to support efficient lymphatic transport.