Factors affecting the pharmacokinetics and pharmacodynamics of liposomal drugs

Unravelling the in vivo dynamics of liposomes: Insights into biodistribution and cellular membrane interactions

Liposomes, as a colloidal drug delivery system dating back to the 1960s, remain a focal point of extensive research and stand as a highly efficient drug delivery method. The amalgamation of technological and biological advancements has propelled their evolution, elevating them to their current status. The key attributes of biodegradability and biocompatibility have been instrumental in driving substantial progress in liposome development. Demonstrating a remarkable ability to surmount barriers in drug absorption, enhance stability, and achieve targeted distribution within the body, liposomes have become pivotal in pharmaceutical research. In this comprehensive review, we delve into the intricate details of liposomal drug delivery systems, focusing specifically on their pharmacokinetics and cell membrane interactions via fusion, lipid exchange, endocytosis etc. Emphasizing the nuanced impact of various liposomal characteristics, we explore factors such as lipid composition, particle size, surface modifications, charge, dosage, and administration routes. By dissecting the multifaceted interactions between liposomes and biological barriers, including the reticuloendothelial system (RES), opsonization, enhanced permeability and retention (EPR) effect, ATP-binding cassette (ABC) phenomenon, and Complement Activation-Related Pseudoallergy (CARPA) effect, we provide a deeper understanding of liposomal behaviour in vivo. Furthermore, this review addresses the intricate challenges associated with translating liposomal technology into practical applications, offering insights into overcoming these hurdles. Additionally, we provide a comprehensive analysis of the clinical adoption and patent landscape of liposomes across diverse biomedical domains, shedding light on their potential implications for future research and therapeutic developments.

Nanotechnology-Based Strategies in Parasitic Disease Management: From Prevention to Diagnosis and Treatment

Parasitic infections are a major global health issue causing significant mortality and morbidity. Despite substantial advances in the diagnostics and treatment of these diseases, the currently available options fall far short of expectations. From diagnosis and treatment to prevention and control, nanotechnology-based techniques show promise as an alternative approach. Nanoparticles can be designed with specific properties to target parasites and deliver antiparasitic medications and vaccines. Nanoparticles such as liposomes, nanosuspensions, polymer-based nanoparticles, and solid lipid nanoparticles have been shown to overcome limitations such as limited bioavailability, poor cellular permeability, nonspecific distribution, and rapid drug elimination from the body. These nanoparticles also serve as nanobiosensors for the early detection and treatment of these diseases. This review aims to summarize the potential applications of nanoparticles in the prevention, diagnosis, and treatment of parasitic diseases such as leishmaniasis, malaria, and trypanosomiasis. It also discusses the advantages and disadvantages of these applications and their market values and highlights the need for further research in this field.

Dose-Dependent Effect of Phenothiazines as Dynamin II Inhibitors on the Uptake of PEGylated Liposomes by Endocytic Cells and In Vivo Pharmacokinetics of PEGylated Liposomal Doxorubicin in Rats

Dynamin II (dynII) plays a significant role in the internalization pathways of endocytic cells, by allowing membrane invaginations to "bud off". An important class of dynII inhibitors that are used clinically are phenothiazines, such as prochlorperazine (PCZ). PCZ is an antipsychotic drug but is also currently in clinical trials at higher concentrations as an adjuvant in cancer patients that increases the efficacy of monoclonal antibodies at high intravenous doses. It is unknown, however, whether high-dose dynII inhibitors have the potential to alter the pharmacokinetics of co-administered chemotherapeutic nanomedicines that are largely cleared via the mononuclear phagocyte system. This work therefore sought to investigate the impact of clinically relevant concentrations of phenothiazines, PCZ and thioridazine, on in vitro liposome endocytosis and in vivo liposome pharmacokinetics after PCZ infusion in rats. The uptake of fluorescently labeled PEGylated liposomes into differentiated and undifferentiated THP-1 and RAW246.7 cells, and primary human peripheral white blood cells, was investigated via flow cytometry after co-incubation with dynII inhibitors. The IV pharmacokinetics of PEGylated liposomes were also investigated in rats after a 20 min infusion with PCZ. Phenothiazines and dyngo4a reduced the uptake of PEGylated liposomes by THP-1 and RAW264.7 cells in a concentration-dependent manner in vitro. However, dynII inhibitors did not alter the mean uptake of liposomes by human peripheral white blood cells, but endocytic white cells from some donors exhibited sensitivity to phenothiazine exposure. When a clinically relevant dose of PCZ was co-administered with PEGylated liposomal doxorubicin (Caelyx/Doxil) in rats, the pharmacokinetics and biodistribution of liposomes were unaltered. These data suggest that while clinically relevant doses of dynII inhibitors can inhibit the uptake of liposomes by endocytic cells in vitro, they are unlikely to significantly affect the pharmacokinetics of long-circulating, co-administered liposomes.

Evaluation of Anticancer Activity of Zhubech, a New 5-FU Analog Liposomal Formulation, against Pancreatic Cancer

Pancreatic cancer is projected to be the second leading cause of cancer-related death by 2030 in the US. The benefits of the most common systemic therapy for various pancreatic cancers have been masked by high drug toxicities, adverse reactions, and resistance. The use of nanocarriers such as liposomes to overcome these unwanted effects has become very popular. This study aims to formulate 1,3-bistertrahydrofuran-2yl-5FU (MFU)-loaded liposomal nanoparticles (Zhubech) and to evaluate itsstability, release kinetics, in vitro and in vivo anticancer activities, and biodistribution in different tissues. Particle size and zeta potential were determined using a particle size analyzer, while cellular uptake of rhodamine-entrapped liposomal nanoparticles (Rho-LnPs) was determined by confocal microscopy. Gadolinium hexanoate (Gd-Hex) was synthesized and entrapped into the liposomal nanoparticle (LnP) (Gd-Hex-LnP), as a model contrast agent, to evaluate gadolinium biodistribution and accumulation by LnPs in vivo using inductively coupled plasma mass spectrometry (ICP-MS). The mean hydrodynamic diameters of blank LnPs and Zhubech were 90.0 ± 0.65 nm and 124.9 ± 3.2 nm, respectively. The hydrodynamic diameter of Zhubech was found to be highly stable at 4 °C and 25 °C for 30 days in solution. In vitro drug release of MFU from Zhubech formulation exhibited the Higuchi model (R2 value = 0.95). Both Miapaca-2 and Panc-1 treated with Zhubech showed reduced viability, two- or four-fold lower than that of MFU-treated cells in 3D spheroid (IC50Zhubech = 3.4 ± 1.0 μM vs. IC50MFU = 6.8 ± 1.1 μM) and organoid (IC50Zhubech = 9.8 ± 1.4 μM vs. IC50MFU = 42.3 ± 1.0 μM) culture models. Confocal imaging confirmed a high uptake of rhodamine-entrapped LnP by Panc-1 cells in a time-dependent manner. Tumor-efficacy studies in a PDX bearing mouse model revealed a more than 9-fold decrease in mean tumor volumes in Zhubech-treated (108 ± 13.5 mm3) compared to 5-FU-treated (1107 ± 116.2 mm3) animals, respectively. This study demonstrates that Zhubech may be a potential candidate for delivering drugs for pancreatic cancer treatment.

Chemical and Biomolecular Strategies for STING Pathway Activation in Cancer Immunotherapy

The stimulator of interferon genes (STING) cellular signaling pathway is a promising target for cancer immunotherapy. Activation of the intracellular STING protein triggers the production of a multifaceted array of immunostimulatory molecules, which, in the proper context, can drive dendritic cell maturation, antitumor macrophage polarization, T cell priming and activation, natural killer cell activation, vascular reprogramming, and/or cancer cell death, resulting in immune-mediated tumor elimination and generation of antitumor immune memory. Accordingly, there is a significant amount of ongoing preclinical and clinical research toward further understanding the role of the STING pathway in cancer immune surveillance as well as the development of modulators of the pathway as a strategy to stimulate antitumor immunity. Yet, the efficacy of STING pathway agonists is limited by many drug delivery and pharmacological challenges. Depending on the class of STING agonist and the desired administration route, these may include poor drug stability, immunocellular toxicity, immune-related adverse events, limited tumor or lymph node targeting and/or retention, low cellular uptake and intracellular delivery, and a complex dependence on the magnitude and kinetics of STING signaling. This review provides a concise summary of the STING pathway, highlighting recent biological developments, immunological consequences, and implications for drug delivery. This review also offers a critical analysis of an expanding arsenal of chemical strategies that are being employed to enhance the efficacy, safety, and/or clinical utility of STING pathway agonists and lastly draws attention to several opportunities for therapeutic advancements.

The Value of Pharmacogenetics to Reduce Drug-Related Toxicity in Cancer Patients

Many anticancer drugs cause adverse drug reactions (ADRs) that negatively impact safety and reduce quality of life. The typical narrow therapeutic range and exposure-response relationships described for anticancer drugs make precision dosing critical to ensure safe and effective drug exposure. Germline mutations in pharmacogenes contribute to inter-patient variability in pharmacokinetics and pharmacodynamics of anticancer drugs. Patients carrying reduced-activity or loss-of-function alleles are at increased risk for ADRs. Pretreatment genotyping offers a proactive approach to identify these high-risk patients, administer an individualized dose, and minimize the risk of ADRs. In the field of oncology, the most well-studied gene-drug pairs for which pharmacogenetic dosing recommendations have been published to improve safety are DPYD-fluoropyrimidines, TPMT/NUDT15-thiopurines, and UGT1A1-irinotecan. Despite the presence of these guidelines, the scientific evidence showing the benefits of pharmacogenetic testing (e.g., improved safety and cost-effectiveness) and the development of efficient multi-gene genotyping panels, routine pretreatment testing for these gene-drug pairs has not been implemented widely in the clinic. Important considerations required for widespread clinical implementation include pharmacogenetic education of physicians, availability or allocation of institutional resources to build an efficient clinical infrastructure, international standardization of guidelines, uniform adoption of guidelines by regulatory agencies leading to genotyping requirements in drug labels, and development of cohesive reimbursement policies for pretreatment genotyping. Without clinical implementation, the potential of pharmacogenetics to improve patient safety remains unfulfilled.

Development of nanotechnology-mediated precision radiotherapy for anti-metastasis and radioprotection

Radiotherapy (RT), including external beam RT and internal radiation therapy, uses high-energy ionizing radiation to kill tumor cells.

Stimuli-Responsive Iron Oxide Nanotheranostics: A Versatile and Powerful Approach for Cancer Therapy

Recent advancements in unravelling elements of cancer biology involved in disease progression and treatment resistance have highlighted the need for a holistic approach to effectively tackle cancer. Stimuli-responsive nanotheranostics based on iron oxide nanoparticles are an emerging class of versatile nanomedicines with powerful capabilities to "seek, sense, and attack" multiple components of solid tumors. In this work, the rationale for using iron oxide nanoparticles and the basic physical principles that impact their function in biomedical applications are reviewed. Subsequently, recent advances in the integration of iron oxide nanoparticles with various stimulus mechanisms to facilitate the development of stimuli-responsive nanotheranostics for application in cancer therapy are summarized. The integration of an iron oxide core with various surface coating mechanisms results in the generation of hybrid nanoconstructs with capabilities to codeliver a wide variety of highly potent anticancer therapeutics and immune modulators. Finally, emerging future directions and considerations for their clinical translation are touched upon.

Liposome as drug delivery system enhance anticancer activity of iridium (III) complex

Herein an Ir(III) complex [Ir(Hppy)₂(HMNPIP)](PF₆) (Ir1, Hppy = 2-phenylpyridine, HMNPIP = 2-(1H-imidazo[4,5-f][1, 10]phenanthroline-3-yl)-6-methoxy-4-nitrophenol) was prepared and characterized. Due to the low anticancer activity of Ir1 when administered free drug, we prepared a liposome Ir1Lipo encapsulated form of Ir1 to improve the antitumor effect, furthermore, we explored the antitumor mechanism of both forms in vitro experiments on HepG2 cells. We investigated the inhibitory efficiency of Ir1 and Ir1Lipo on cell viability and proliferation using MTT (MTT = 3-(4,5-dimethylthiazole)-2,5-diphenltetraazolium bromide) and colony-forming assay. Intracellular accumulation of reactive oxygen species (ROS) was examined using a fluorescence microscope (High Content Screening System, ImageXpress Micro XLS System, Molecular Devices LLC, Sunnyvale, CA), programmed cell death cells stained with acridine orange/ethidium bromide (AO/EB) using flow cytometry detection and western blot have been performed. An in vivo study where HepG2 cells were transplanted into nude nice as xenografts. Tumour volume and body weight were monitored during the 10 days of administration. After encapsulation in liposomes Ir1Lipo displayed high potency against a variety of tumour cells in vitro, especially against HepG2 (IC₅₀ = 4.6 ± 0.5 μM). Mechanism studies indicated that Ir1Lipo initiated apoptosis by generating intracellular ROS that regulate lysosomal-mitochondrial dysfunction, followed by microtubule disruption that subsequently leads to a G0/G1 phase of cell cycle arrest. Additionally, Ir1Lipo significantly curbed tumour growth in nude mice. The tumour inhibitory rate was 51.2% (5.6 mg/kg). Therefore, liposome as a drug delivery system greatly enhances anticancer activity of Ir1 by a factor of relatively minor side effects.

Current developments in drug delivery with thermosensitive liposomes

Thermosensitive liposomes (TSLs) have been an important research area in the field of tumor targeted chemotherapy. Since the first TSLs appeared that using 1,2-dipalmitoyl-sn-glyce-ro-3-phosphocholine (DPPC) as the primary liposomal lipid, many studies have been done using this type of liposome from basic and practical aspects. While TSLs composed of DPPC enhance the cargo release near the phase transition temperature, it has been shown that many factors affect their temperature sensitivity. Thus numerous attempts have been undertaken to develop new TSLs for improving their thermal response performance. The main objective of this review is to introduce the development and recent update of innovative TSLs formulations, including combination of radiofrequency ablation (RFA), high-intensity focused ultrasound (HIFU), magnetic resonance imaging (MRI) and alternating magnetic field (AMF). In addition, various factors affecting the design of TSLs, such as lipid composition, surfactant, size and serum components are also discussed.

Pharmacokinetics and pharmacodynamics of liposomal chemophototherapy with short drug-light intervals

Chemophototherapy (CPT) merges photodynamic therapy with chemotherapy and can substantially enhance drug delivery. Using a singular liposomal formulation for CPT, we describe a semi-mechanistic pharmacokinetic-pharmacodynamic (PK/PD) model to investigate observed antitumor effects. Long-circulating, sterically-stabilized liposomes loaded with doxorubicin (Dox) stably incorporate small amounts of a porphyrin-phospholipid (PoP) photosensitizer in the bilayer. These were administered intravenously to mice bearing low-passage, patient-derived pancreatic cancer xenografts (PDX). Dox PK was described with a two-compartment model and tumor drug disposition kinetics were modeled with first-order influx and efflux rates. Tumor irradiation with 665 nm laser light (200 J/cm2) 1 h after liposome administration increased tumor vascular permeabilization and drug accumulation, which was accounted for in the PK/PD model with increased tumor influx and efflux rates by approximately 12- and 4- fold, respectively. This modeling approach provided an overall 7-fold increase in Dox area under the curve in the tumor, matching experimental data (7.4-fold). A signal transduction model based on nonlinear direct cell killing accounted for observed tumor growth patterns. This PK/PD model adequately describes the CPT anti-PDX tumor response based on enhanced drug delivery at the short drug-light interval used.

Radiolabeling of Preformed Niosomes with [99mTc]: In Vitro Stability, Biodistribution, and In Vivo Performance

Nanocarriers radiolabeled with [^99mTc] can be used for diagnostic imaging and radionuclide therapy, as well as tracking their pharmacokinetic and biodistribution characteristics. Due to the advantages of niosomes as an ideal drug delivery system, in this study, the radiolabeling procedure of niosomes by [^99mTc]-HMPAO complexes was investigated and optimized. Glutathione (GSH)-loaded niosomes were prepared using a thin-film hydration method. To label the niosomes with [^99mTc], the preformed GSH-loaded niosomes were incubated with the [^99mTc]-HMPAO complex and were characterized for particle size, size distribution, zeta potential, morphology, and radiolabeling efficiency (RE). The effects of GSH concentration, incubation time, incubation temperature, and niosomal composition on RE were investigated. The biodistribution profile and in vivo SPECT/CT imaging of the niosomes and free [^99mTc]-HMPAO were also studied. Based on the results, all vesicles had nano-sized structure (160-235 nm) and negative surface charge. Among the different experimental conditions that were tested, including various incubation times, incubation temperatures, and GSH concentrations, the optimum condition that resulted in a RE of 92% was 200-mM GSH and 15-min incubation at 40°C. The in vitro release study in plasma showed that about 20% of radioactivity was released after 24 h, indicating an acceptable radiolabeling stability in plasma. The biodistribution of niosomes was clearly different from the free radiolabel. Niosomes carrying radionuclide were successfully used for tracking the in vivo disposition of these carriers and SPECT/CT imaging in rats. Furthermore, biodistribution studies in tumor-bearing mice revealed higher tumor accumulation of the niosomal formulation as compared with [^99mTc]-HMPAO.

Mononuclear phagocyte system function and nanoparticle pharmacology in obese and normal weight ovarian and endometrial cancer patients

PURPOSE

Obesity may alter mononuclear phagocyte system (MPS) function and the pharmacology and efficacy of nanoparticles therapies, such as PEGylated liposomal doxorubicin (PLD). We aimed to evaluate the relationships between hormone and chemokine mediators of MPS function and the pharmacokinetic (PK) exposure of PLD in obese and normal weight patients with ovarian and endometrial cancer.

METHODS

Hormone and chemokine mediators in obese and normal weight ovarian and endometrial cancer patients were measured. A separate pharmacology study was performed that evaluated the relationship between serum hormone concentrations, MPS function, and PK disposition of PLD in refractory ovarian cancer patients.

RESULTS

Univariate analysis revealed a significant relationship between serum estradiol and body mass index (OR 8.64, 95% CI 2.67-28.0, p < 0.001). Estrone and testosterone concentrations were positively correlated with MPS function (ρ = 0.57 and 0.53, p = 0.14 and 0.18, respectively) and inversely correlated with PLD PK exposure (ρ = - 0.75 and - 0.76, respectively, p = 0.02 for both).

CONCLUSIONS

Higher MPS function resulting in reduced PLD exposure is a potential mechanism for reduced efficacy of PLD and other nanoparticles observed in obese patients with cancer. PK simulations suggest higher doses of PLD are required in obese patients to achieve similar exposures as standard dosing in normal weight patients.

Radiation and Heat Improve the Delivery and Efficacy of Nanotherapeutics by Modulating Intratumoral Fluid Dynamics

Nanomedicine drug delivery systems are capable of transporting significant payloads to solid tumors. However, only a modest increase in antitumor efficacy relative to the standard of care has been observed. In this study, we demonstrate that a single dose of radiation or mild hyperthermia can substantially improve tumor uptake and distribution of nanotherapeutics, resulting in improved treatment efficacy. The delivery of nanomedicine was driven by a reduction in interstitial fluid pressure (IFP) and small perturbation of steady-state fluid flow. The transient effects on fluid dynamics in tumors with high IFP was also shown to dominate over immune cell endocytic capacity, another mechanism suspected of improving drug delivery. Furthermore, we demonstrate the specificity of this mechanism by showing that delivery of nanotherapeutics to low IFP tumors with high leukocyte infiltration does not benefit from pretreatment with radiation or heat. These results demonstrate that focusing on small perturbations to steady-state fluid dynamics, rather than large sustained effects or uncertain immune cell recruitment strategies, can impart a vulnerability to tumors with high IFP and enhance nanotherapeutic drug delivery and treatment efficacy.

PEG-Benzaldehyde-Hydrazone-Lipid Based PEG-Sheddable pH-Sensitive Liposomes: Abilities for Endosomal Escape and Long Circulation

PURPOSE

To fabricate an acid-cleavable PEG polymer for the development of PEG-cleavable pH-sensitive liposomes (CL-pPSL), and to investigate their ability for endosomal escape and long circulation.

METHODS

PEG-benzaldehyde-hydrazone-cholesteryl hemisuccinate (PEG_B-Hz-CHEMS) containing hydrazone and ester bonds was synthesised and used to fabricate a dual pH-sensitive CL-pPSL. Non-cleavable PEGylated pH-sensitive liposome (pPSL) was used as a reference and gemcitabine as a model drug. The cell uptake and endosomal escape were investigated in pancreatic cancer Mia PaCa-2 cells and pharmacokinetics were studied in rats.

RESULTS

The CL-pPSL showed accelerated drug release at endosomal pH 5.0 compared to pPSL. Compared to pPSL, CL-pPSL released their fluorescent payload to cytosol more efficiently and showed a 1.4-fold increase in intracellular gemcitabine concentration and higher cytotoxicity. In rats, injection of gemcitabine loaded CL-pPSL resulted in a slightly smaller V_d (149 ± 27 ml/kg; 170 ± 30 ml/kg) and shorter terminal T_1/2 (5.4 ± 0.3 h; 5.8 ± 0.6 h) (both p > 0.05) but a significantly lower AUC (p < 0.01), than pPSL, due to the lower PEGylation degree (1.7 mol%) which means a 'mushroom' configuration of PEG. A five-time increase in the dose with CL-pPSL resulted in a 11-fold increase in AUC and a longer T_1/2 (8.2 ± 0.5 h).

CONCLUSION

The PEG-detachment from the CL-pPSL enhanced endosome escape efficiency compared with pPSL, without significantly compromising their stealth abilities.

Plectin-targeted liposomes enhance the therapeutic efficacy of a PARP inhibitor in the treatment of ovarian cancer

Advances in genomics and proteomics drive precision medicine by providing actionable genetic alterations and molecularly targeted therapies, respectively. While genomic analysis and medicinal chemistry have advanced patient stratification with treatments tailored to the genetic profile of a patient's tumor, proteomic targeting has the potential to enhance the therapeutic index of drugs like poly(ADP-ribose) polymerase (PARP) inhibitors. PARP inhibitors in breast and ovarian cancer patients with BRCA1/2 mutations have shown promise. About 10% of the patients who received Olaparib (PARP inhibitor) showed adverse side effects including neutropenia, thrombocytopenia and in some cases resulted in myelodysplastic syndrome, indicating that off-target effects were substantial in these patients. Through proteomic analysis, our lab previously identified plectin, a cytolinker protein that mislocalized onto the cell surface during malignant transformation of healthy ovarian tissue. This cancer specific phenotype allowed us to image pancreatic cancer successfully using plectin targeted peptide (PTP) conjugated to nanoparticles or displayed on capsid protein of adeno-associated virus (AAV) particles. Objective: The goal of this study was to integrate the available pharmacogenomics and proteomic data to develop effective anti-tumor therapies using a targeted drug delivery approach. Methods: Plectin expression and localization in human ovarian tumor specimens were analyzed followed by in vitro confirmation of cell surface plectin localization in healthy and ovarian cancer cell lines. PTP-conjugated liposomes were prepared and their specificity for plectin+ cells was determined in vitro and in vivo. A remote loading method was employed to encapsulate a PARP inhibitor (AZ7379) into liposomes. An ideal buffer exchange method and remote loading conditions were determined based on the amount of lipid and drug recovered at the end of a remote loading process. Finally, in vivo tumor growth studies were performed to determine the efficacy of PTP liposomes in preventing PARP activity in mice bearing OVCAR8 (high grade epithelial ovarian cancer (EOC)) tumors. Results: PTP liposomal AZ7379 delivery not only enhanced PARP inhibition but also resulted in decelerated tumor growth in mice bearing subcutaneous and intraperitoneal OVCAR8 tumors. In mice bearing subcutaneous or intraperitoneal tumors, treatment with PTP liposomes resulted in a 3- and 1.7-fold decrease in tumor volume, respectively, compared to systemic drug treatment. Conclusion: Targeted drug delivery assisted by genomic and proteomic data provides an adaptable model system that can be extended to effectively treat other cancers and diseases.

Platelet-inspired medicine for tumor therapy

As the number of patients with tumor increases dramatically recent years, traditional therapies expose more and more problems which can even lead to death. Many researchers and clinicians quest for an efficient drug delivery system to deal with tumor as a result. With the researches further develop, we find that platelet can interact with tumor cells through a variety of ways. So it can be used as a carrier broadly to deliver different anti-tumor drugs for tumor treatment. In the present review, we summarize the interaction of tumor cells and platelet. At the same time, we focus on recent progress on the application of platelet drug-loaded system in the anti-tumor prospects.

Mediating Passive Tumor Accumulation through Particle Size, Tumor Type, and Location

As the enhanced permeation and retention (EPR) effect continues to be a controversial topic in nanomedicine, we sought to examine EPR as a function of nanoparticle size, tumor model, and tumor location, while also evaluating tumors for EPR mediating factors such as microvessel density, vascular permeability, lymphatics, stromal content, and tumor-associated immune cells. Tumor accumulation was evaluated for 55 × 60, 80 × 180, and 80 × 320 nm PRINT particles in four subcutaneous flank tumor models (SKOV3 human ovarian, 344SQ murine nonsmall cell lung, A549 human nonsmall cell lung, and A431 human epidermoid cancer). Each tumor model revealed specific particle accumulation trends with evident particle size dependence. Immuno-histochemistry staining revealed differences in tumor microvessel densities that correlated with overall tumor accumulation. Immunofluorescence images displayed size-mediated tumor penetration with signal from the larger particles concentrated close to the blood vessels, while signal from the smaller particle was observed throughout the tissue. Differences were also observed for the 55 × 60 nm particle tumor penetration across flank tumor models as a function of stromal content. The 55 × 60 nm particles were further evaluated in three orthotopic, metastatic tumor models (344SQ, A549, and SKOV3), revealing preferential accumulation in primary tumors and metastases over healthy tissue. Moreover, we observed higher tumor accumulation in the orthotopic lung cancer models than in the flank lung cancer models, whereas tumor accumulation was constant for both orthotopic and flank ovarian cancer models, further demonstrating the variability in the EPR effect as a function of tumor model and location.

Radiation effects on the tumor microenvironment: Implications for nanomedicine delivery

The tumor microenvironment has an important influence on cancer biological and clinical behavior and radiation treatment (RT) response. However, RT also influences the tumor microenvironment in a complex and dynamic manner that can either reinforce or inhibit this response and the likelihood of long-term disease control in patients. It is increasingly evident that the interplay between RT and the tumor microenvironment can be exploited to enhance the accumulation and intra-tumoral distribution of nanoparticles, mediated by changes to the vasculature and stroma with secondary effects on hypoxia, interstitial fluid pressure (IFP), solid tissue pressure (STP), and the recruitment and activation of bone marrow-derived myeloid cells (BMDCs). The use of RT to modulate nanoparticle drug delivery offers an exciting opportunity to improve antitumor efficacy. This review explores the interplay between RT and the tumor microenvironment, and the integrated effects on nanoparticle drug delivery and efficacy.

Profiling the relationship between tumor-associated macrophages and pharmacokinetics of liposomal agents in preclinical murine models

The mononuclear phagocyte system (MPS) has previously been shown to significantly affect the clearance, tumor delivery, and efficacy of nanoparticles (NPs). This study profiled MPS cell infiltration in murine preclinical tumor models and evaluated how these differences may affect tumor disposition of PEGylated liposomal doxorubicin (PLD) in models sensitive and resistant to PLD. Significant differences in MPS presence existed between tumor types (e.g. ovarian versus endometrial), cell lines within the same tumor type, and location of tumor implantation (i.e. flank versus orthotopic xenografts). Further, the differences in MPS presence of SKOV-3 ovarian and HEC1A endometrial orthotopic cancer models may account for the 2.6-fold greater PLD tumor exposure in SKOV-3, despite similar plasma, liver and spleen exposures. These findings suggest that profiling the presence of MPS cells within and between tumor types is important in tumor model selection and in tumor types and patients likely to respond to NP treatment.

When Is It Important to Measure Unbound Drug in Evaluating Nanomedicine Pharmacokinetics?

Nanoformulations have become important tools for modifying drug disposition, be it from the perspective of enabling prolonged drug release, protecting the drug molecule from metabolism, or achieving targeted delivery. When examining the in vivo pharmacokinetic properties of these formulations, most investigations either focus on systemic concentrations of total (encapsulated plus unencapsulated) drug, or concentrations of encapsulated and unencapsulated drug. However, it is rare to find studies that differentiate between protein-bound and unbound (free) forms of the unencapsulated drug. In light of the unique attributes of these formulations, we cannot simply assume it appropriate to rely upon the protein-binding properties of the traditionally formulated or legacy drug when trying to define the pharmacokinetic or pharmacokinetic/pharmacodynamic characteristics of these nanoformulations. Therefore, this commentary explores reasons why it is important to consider not only unencapsulated drug, but also the portion of unencapsulated drug that is not bound to plasma proteins. Specifically, we highlight those situations when it may be necessary to include measurement of unencapsulated, unbound drug concentrations as part of the nanoformulation pharmacokinetic evaluation.

Gulp1 is associated with the pharmacokinetics of PEGylated liposomal doxorubicin (PLD) in inbred mouse strains

Nanoparticles (NP) including liposomes are cleared by phagocytes of the mononuclear phagocyte system. High inter-patient variability in pharmacokinetics of PEGylated liposomal doxorubicin (PLD) has been reported. We hypothesized that genetic factors may be associated with the variable disposition of PLD. We evaluated plasma and tissue disposition of doxorubicin after administration of PLD at 6mg/kg IV ×1 via tail vein in 23 different male inbred mouse strains. An approximately 13-fold difference in plasma clearance of PLD was observed among inbred strains. We identified a correlation between strain-specific differences in PLD clearance and genetic variation within a genomic region encoding GULP1 (PTB domain containing engulfment adapter 1) protein using haplotype associated mapping and the efficient mixed-model association algorithms. Our results also show that Gulp1 expression in adipose tissue was associated with PLD disposition in plasma. Our findings suggest that genetic variants may be associated with inter-individual pharmacokinetic differences in NP clearance.

Physiological and pharmacokinetic effects of multilevel caging on Sprague Dawley rats under ketamine-xylazine anesthesia

While the cage refinement is a necessary step towards improving the welfare of research rats, increasing the complexity and surface area of the living space of an animal may have physiological impacts that need to be taken into consideration. In this study, ketamine (80 mg/kg) and xylazine (10 mg/kg) caused a short duration anesthesia that was significantly decreased in Sprague-Dawley rats housed in multilevel cages (MLC), compared to rats housed in standard cages (SDC). The withdrawal reflex, the palpebral reflexes and the time-to-sternal all occurred earlier in MLC housed rats, suggesting an effect of housing on the physiology of the rats. In addition, during anesthesia, cardiac frequencies were increased in animals housed in the smaller SDC. Respiratory frequencies, the blood oxygen saturation and rectal temperatures during anesthesia did not vary between conditions during the anesthesia. While xylazine pharmacokinetics were unchanged with caging conditions, the clearance and half-lives of ketamine and its metabolite, norketamine, were altered in the rats housed in MLC. Finally, while no difference was ultimately seen in rat body weights, isolated liver and adrenal gland weights were significantly lighter in rats housed in the MLC. Increasing cage sizes, while having a positive impact on wellbeing in rats, can alter anesthetic drug metabolism and thus modify anesthesia parameters and associated physiological processes.

Current understanding of interactions between nanoparticles and the immune system

The delivery of drugs, antigens, and imaging agents benefits from using nanotechnology-based carriers. The successful translation of nanoformulations to the clinic involves thorough assessment of their safety profiles, which, among other end-points, includes evaluation of immunotoxicity. The past decade of research focusing on nanoparticle interaction with the immune system has been fruitful in terms of understanding the basics of nanoparticle immunocompatibility, developing a bioanalytical infrastructure to screen for nanoparticle-mediated immune reactions, beginning to uncover the mechanisms of nanoparticle immunotoxicity, and utilizing current knowledge about the structure-activity relationship between nanoparticles' physicochemical properties and their effects on the immune system to guide safe drug delivery. In the present review, we focus on the most prominent pieces of the nanoparticle-immune system puzzle and discuss the achievements, disappointments, and lessons learned over the past 15years of research on the immunotoxicity of engineered nanomaterials.

Smart blood cell and microvesicle-based Trojan horse drug delivery: Merging expertise in blood transfusion and biomedical engineering in the field of nanomedicine

Therapeutic and diagnostic applications of nanomedicine are playing increasingly important roles in human health. Various types of synthetic nanoparticles, including liposomes, micelles, and other nanotherapeutic platforms and conjugates, are being engineered to encapsulate or carry drugs for treating diseases such as cancer, cardiovascular disorders, neurodegeneration, and inflammations. Nanocarriers are designed to increase the half-life of drugs, decrease their toxicity and, ideally, target pathological sites. Developing smart carriers with the capacity to deliver drugs specifically to the microenvironment of diseased cells with minimum systemic toxicity is the goal. Blood cells, and potentially also the liposome-like micro- and nano-vesicles they generate, may be regarded as ideally suited to perform such specific targeting with minimum immunogenic risks. Blood cell membranes are "decorated" with complex physiological receptors capable of targeting and communicating with other cells and tissues and delivering their content to the surrounding pathological microenvironment. Blood cells, such as erythrocytes, have been developed as permeable carriers to release drugs to diseased tissues or act as biofactory allowing enzymatic degradation of a pathological substrate. Interestingly, attempts are also being made to improve the targeting capacity of synthetic nanoparticles by "decorating" their surface with blood cell membrane receptor-like biochemical structures. Research is needed to further explore the benefits that blood cell-derived microvesicles, as a Trojan horse delivery systems, can bring to the arsenal of therapeutic micro- and nanotechnologies. This short review focuses on the therapeutic roles that red blood cells and platelets can play as smart drug-delivery systems, and highlights the benefits that blood transfusion expertise can bring to this exciting and novel biomedical engineering field.

Pre-clinical immunotoxicity studies of nanotechnology-formulated drugs: Challenges, considerations and strategy

Assorted challenges in physicochemical characterization, sterilization, depyrogenation, and in the assessment of pharmacology, safety, and efficacy profiles accompany pre-clinical development of nanotechnology-formulated drugs. Some of these challenges are not unique to nanotechnology and are common in the development of other pharmaceutical products. However, nanoparticle-formulated drugs are biochemically sophisticated, which causes their translation into the clinic to be particularly complex. An understanding of both the immune compatibility of nanoformulations and their effects on hematological parameters is now recognized as an important step in the (pre)clinical development of nanomedicines. An evaluation of nanoparticle immunotoxicity is usually performed as a part of a traditional toxicological assessment; however, it often requires additional in vitro and in vivo specialized immuno- and hematotoxicity tests. Herein, I review literature examples and share the experience with the NCI Nanotechnology Characterization Laboratory assay cascade used in the early (discovery-level) phase of pre-clinical development to summarize common challenges in the immunotoxicological assessment of nanomaterials, highlight considerations and discuss solutions to overcome problems that commonly slow or halt the translation of nanoparticle-formulated drugs toward clinical trials. Special attention will be paid to the grand-challenge related to detection, quantification and removal of endotoxin from nanoformulations, and practical considerations related to this challenge.

Low Intensity Ultrasound Mediated Liposomal Doxorubicin Delivery Using Polymer Microbubbles

Cardiotoxicity is the major dose-limiting factor in the chemotherapeutic use of doxorubicin (Dox). A delivery vehicle that can be triggered to release its payload in the tumoral microvasculature but not in healthy tissue would help improve the therapeutic window of the drug. Delivery strategies combining liposomal encapsulated Dox (LDox), microbubbles (MBs), and ultrasound (US) have been shown to improve therapeutic efficacy of LDox, but much remains to be known about the mechanisms and the US conditions that maximize cytotoxicity using this approach. In this study, we compared different US pulses in terms of drug release and acute toxicity. Drug uptake and proliferation rates using low-intensity US were measured in squamous cell carcinoma cells exposed to LDox conjugated to or coinjected with polymer MBs. The aims of this study were: (1) to compare the effects of low- and high-pressure US on Dox release kinetics; (2) to evaluate whether conjugating the liposome to the MB surface (DoxLPX) is an important factor for drug release and cytotoxicity; and (3) to determine which US parameters most inhibit cell proliferation and whether this inhibition is mediated by drug release or the MB/US interaction with cells. Low-pressure US (170 kPa) at high duty cycle (stable cavitation) released up to ∼ 70% of the encapsulated Dox from the DoxLPX, thus improving Dox bioavailability and cellular uptake and leading to a significant reduction in cell proliferation at 48 h. Flow cytometry showed that US generating stable oscillations of DoxLPX significantly increased cellular Dox uptake at 4 h after US exposure compared to LDox. Drug uptake was correlated with cytotoxicity at 48 h. Our results demonstrate that Dox-containing liposomes conjugated to polymer MBs can be triggered to release ∼ 70% of their payload using noninertial US. Following release, Dox became bioavailable to the cells and induced significantly higher cytotoxicity compared to nonreleased encapsulated drug. Our findings show promise for targeted drug delivery using this theranostic delivery platform at low US intensities.

Clinical experiences with systemically administered siRNA-based therapeutics in cancer

Small interfering RNA (siRNA)-based therapies are emerging as a promising new anticancer approach, and a small number of Phase I clinical trials involving patients with solid tumours have now been completed. Encouraging results from these pioneering clinical studies show that these new therapeutics can successfully and safely inhibit targeted gene products in patients with cancer, and have taught us important lessons regarding appropriate dosages and schedules. In this Review, we critically assess these Phase I studies and discuss their implications for future clinical trial design. Key challenges and future directions in the development of siRNA-containing anticancer therapeutics are also considered.

Physiological, pharmacokinetic and liver metabolism comparisons between 3-, 6-, 12- and 18-month-old male Sprague Dawley rats under ketamine-xylazine anesthesia

The main objective of this study was to compare the physiological changes (withdrawal and corneal reflexes, respiratory and cardiac frequency, blood oxygen saturation, and rectal temperature) following intraperitoneal administration of ketamine (80 mg/kg) and xylazine (10 mg/kg) to 3-, 6-, 12- and 18-month-old male Sprague Dawley rats (n=6/age group). Plasma pharmacokinetics, liver metabolism, and blood biochemistry were examined for a limited number of animals to better explain anesthetic drug effects. Selected organs were collected for histopathology. The results for the withdrawal and corneal reflexes suggest a shorter duration and decreased depth of anesthesia with aging. Significant cardiac and respiratory depression, as well as decreased blood oxygen saturation, occurred in all age groups however, cardiac frequency was the most affected parameter with aging, since the 6-, 12-, and 18-month-old animals did not recuperate to normal values during recovery from anesthesia. Pharmacokinetic parameters (T_1/2 and AUC) increased and drug clearance decreased with aging, which strongly suggests that drug exposure is associated with the physiological results. The findings for liver S9 fractions of 18-month-old rats compared with the other age groups suggest that following a normal ketamine anesthetic dose (80 mg/kg), drug metabolism is impaired, leading to a significant increase of drug exposure. In conclusion, age and related factors have a substantial effect on ketamine and xylazine availability, which is reflected by significant changes in pharmacokinetics and liver metabolism of these drugs, and this translates into shorter and less effective anesthesia with increasing age.

Interleukin-4 receptor-targeted liposomal doxorubicin as a model for enhancing cellular uptake and antitumor efficacy in murine colorectal cancer

Our previous studies showed that colorectal tumor has high interleukin-4 receptor α (IL-4Rα) expression, whereas adjacent normal tissue has low or no IL-4Rα expression. We also observed that human atherosclerotic plaque-specific peptide-1 (AP1) can specifically target to IL-4Rα. In this study, we investigated the therapeutic efficacy and systemic toxicity of AP1-conjuagted liposomal doxorubicin. AP1 bound more strongly to and was more efficiently internalized into IL-4Rα-overexpressing CT26 cells than CT26 control cells. Selective cytotoxicity experiment revealed that AP1-conjugated liposomal doxorubicin preferentially killed IL-4Rα-overexpressing CT26 cells. AP1-conjugated liposomal doxorubicin administered intravenously into mice produced significant inhibition of tumor growth and showed decreased cardiotoxicity of doxorubicin. These results indicated that AP1-conjugated liposomal doxorubicin has a potent and selective anticancer potential against IL-4Rα-overexpressing colorectal cancer cells, thus providing a model for targeted anticancer therapy.

Strategy for selecting nanotechnology carriers to overcome immunological and hematological toxicities challenging clinical translation of nucleic acid-based therapeutics

INTRODUCTION

Clinical translation of nucleic acid-based therapeutics (NATs) is hampered by assorted challenges in immunotoxicity, hematotoxicity, pharmacokinetics, toxicology and formulation. Nanotechnology-based platforms are being considered to help address some of these challenges due to the nanoparticles' ability to change drug biodistribution, stability, circulation half-life, route of administration and dosage. Addressing toxicology and pharmacology concerns by various means including NATs reformulation using nanotechnology-based carriers has been reviewed before. However, little attention was given to the immunological and hematological issues associated with nanotechnology reformulation.

AREAS COVERED

This review focuses on application of nanotechnology carriers for delivery of various types of NATs, and how reformulation using nanoparticles affects immunological and hematological toxicities of this promising class of therapeutic agents.

EXPERT OPINION

NATs share several immunological and hematological toxicities with common nanotechnology carriers. In order to avoid synergy or exaggeration of undesirable immunological and hematological effects of NATs by a nanocarrier, it is critical to consider the immunological compatibility of the nanotechnology platform and its components. Since receptors sensing nucleic acids are located essentially in all cellular compartments, a strategy for developing a nanoformulation with reduced immunotoxicity should first focus on precise delivery to the target site/cells and then on optimizing intracellular distribution.

Anesthetic and pathological changes following high doses of ketamine and xylazine in Sprague Dawley rats

The main objective of this study was to compare the effects of ketamine and xylazine in aging rats when coadministered intraperitoneally at high anesthetic doses. Three groups (n=6 rats/group) consisting of rats at 3, 6 and 12 months of age were used. During anesthesia, animals were monitored for heart rate, respiratory frequency, blood oxygen saturation, and rectal temperature. The corneal and paw withdrawal reflex were also examined during anesthesia. During anesthesia, withdrawal and corneal reflexes were absent for progressively longer durations with increasing age. Significant decreases in cardiac and respiratory frequency and, blood oxygen saturation occurred for the 6- and 12-month-old animals. Respiratory frequency and blood oxygen saturation returned to normal at the end of the anesthesia; however, the significant decrease in cardiac frequency persisted in the 6- and 12-month-old animals. Rectal temperature was decreased significantly only in the 3-month-old animals. Pulmonary edema and effusion occurred in 50% of the 12-month-old animals. In conclusion, if ketamine-xylazine are used for anesthesia, the doses should be optimized for the age of the subjects prior to initiation of the research project.

Factors affecting the pharmacokinetics and pharmacodynamics of PEGylated liposomal irinotecan (IHL-305) in patients with advanced solid tumors

IHL-305 is a PEGylated liposomal formulation of irinotecan (CPT-11). The objective of this study was to evaluate the factors associated with interpatient variability in the pharmacokinetics and pharmacodynamics of IHL-305 in patients with advanced solid tumors. IHL-305 was administered intravenously once every 4 weeks as part of a Phase I study. Pharmacokinetic studies of the liposomal sum total CPT-11, released CPT-11, SN-38, SN-38G, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin, and 7-ethyl-10-[4-amino-1-piperidino]-carbonyloxycamptothecin in plasma were performed. Noncompartmental and compartmental pharmacokinetic analyses were conducted using pharmacokinetic data for sum total CPT-11. The pharmacokinetic variability of IHL-305 is associated with linear and nonlinear clearance. Patients whose age and body composition (ratio of total body weight to ideal body weight [TBW/IBW]) were greater than the median age and TBW/IBW of the study had a 1.7-fold to 2.6-fold higher ratio of released CPT-11 area under the concentration versus time curve (AUC) to sum total CPT-11 AUC. Patients aged <60 years had a 1.3-fold higher ratio of percent decrease in monocytes at nadir to percent decrease in absolute neutrophil count at nadir as compared with patients aged ≥60 years. There was an inverse relationship between patient age and percent decrease in monocytes at nadir, ie, younger patients have a higher percent decrease in monocytes. Patients with a higher percent decrease in monocytes at nadir have a decreased plasma exposure of sum total CPT-11. The pharmacokinetics and pharmacodynamics of IHL-305 are consistent with those of other PEGylated liposomal carriers. Interpatient variability in the pharmacokinetics and pharmacodynamics of IHL-305 was associated with age, body composition, and monocytes.

Lipid/detergent mixed micelles as a tool for transferring antioxidant power from hydrophobic natural extracts into bio-deliverable liposome carriers: the case of lycopene rich oleoresins

Lipid/detergent mixed micelles promote and modulate the incorporation of carotenoids from natural oleoresins into bio-deliverable liposome carriers.

Effects of tumor microenvironment heterogeneity on nanoparticle disposition and efficacy in breast cancer tumor models

PURPOSE

Tumor cells are surrounded by a complex microenvironment. The purpose of our study was to evaluate the role of heterogeneity of the tumor microenvironment in the variability of nanoparticle (NP) delivery and efficacy.

EXPERIMENTAL DESIGNS

C3(1)-T-Antigen genetically engineered mouse model (C3-TAg) and T11/TP53(Null) orthotopic syngeneic murine transplant model (T11) representing human breast tumor subtypes basal-like and claudin-low, respectively, were evaluated. For the pharmacokinetic studies, non-liposomal doxorubicin (NL-doxo) or polyethylene glycol tagged (PEGylated) liposomal doxorubicin (PLD) was administered at 6 mg/kg i.v. x1. Area under the concentration versus time curve (AUC) of doxorubicin was calculated. Macrophages, collagen, and the amount of vasculature were assessed by IHC. Chemokines and cytokines were measured by multiplex immunochemistry. NL-doxo or PLD was administered at 6 mg/kg i.v. weekly x6 in efficacy studies. Analyses of intermediary tumor response and overall survival were performed.

RESULTS

Plasma AUC of NL-doxo and PLD encapsulated and released doxorubicin was similar between two models. However, tumor sum total AUC of PLD was 2-fold greater in C3-TAg compared with T11 (P < 0.05). T11 tumors showed significantly higher expression of CC chemokine ligand (CCL) 2 and VEGF-a, greater vascular quantity, and decreased expression of VEGF-c compared with C3-TAg (P < 0.05). PLD was more efficacious compared with NL-doxo in both models.

CONCLUSION

The tumor microenvironment and/or tumor cell features of breast cancer affected NP tumor delivery and efficacy, but not the small-molecule drug. Our findings reveal the role of the tumor microenvironment in variability of NP delivery and therapeutic outcomes.

Liposomal drug products and recent advances in the synthesis of supercritical fluid-mediated liposomes

Since the pioneering research of Bangham et al. in 1965, liposomes have attracted a large amount of interest as potential carriers of various bioactive molecules for clinical applications. However, scaling-up conventional methods of liposome preparation has been proven to be challenging. Compared with conventional methods, processes that use supercritical fluid (SCF)-CO2 require a reduced amount of organic solvent, are relatively fast and simple to perform, and yield stable and more uniform liposomes. A number of studies have demonstrated that SCF-CO2 methods might be suitable for industrial-scale manufacturing of liposomes. In this review there are two topics being discussed. We provide an overview of liposomal drug products and aim to describe the physicochemical properties of liposomes prepared using various SCF methods. We review all of the available literature on SCF-CO2-based liposomes and focus on the future applications of these innovative technologies in industrial-scale liposome preparation.

Correlating preclinical animal studies and human clinical trials of a multifunctional, polymeric nanoparticle

Nanoparticles are currently being investigated in a number of human clinical trials. As information on how nanoparticles function in humans is difficult to obtain, animal studies that can be correlative to human behavior are needed to provide guidance for human clinical trials. Here, we report correlative studies on animals and humans for CRLX101, a 20- to 30-nm-diameter, multifunctional, polymeric nanoparticle containing camptothecin (CPT). CRLX101 is currently in phase 2 clinical trials, and human data from several of the clinical investigations are compared with results from multispecies animal studies. The pharmacokinetics of polymer-conjugated CPT (indicative of the CRLX101 nanoparticles) in mice, rats, dogs, and humans reveal that the area under the curve scales linearly with milligrams of CPT per square meter for all species. Plasma concentrations of unconjugated CPT released from CRLX101 in animals and humans are consistent with each other after accounting for differences in serum albumin binding of CPT. Urinary excretion of polymer-conjugated CPT occurs primarily within the initial 24 h after dosing in animals and humans. The urinary excretion dynamics of polymer-conjugated and unconjugated CPT appear similar between animals and humans. CRLX101 accumulates into solid tumors and releases CPT over a period of several days to give inhibition of its target in animal xenograft models of cancer and in the tumors of humans. Taken in total, the evidence provided from animal models on the CRLX101 mechanism of action suggests that the behavior of CRLX101 in animals is translatable to humans.

Meta-analysis of inter-patient pharmacokinetic variability of liposomal and non-liposomal anticancer agents

A meta-analysis was conducted to evaluate the inter-patient pharmacokinetic (PK) variability of liposomal and small molecule (SM) anticancer agents. Inter-patient PK variability of 9 liposomal and SM formulations of the same drug was evaluated. PK variability was measured as coefficient of variance (CV%) of area under the plasma concentration versus time curve (AUC) and the fold-difference between AUCmax and AUCmin (AUC range). CV% of AUC and AUC ranges were 2.7-fold (P<0.001) and 16.7-fold (P=0.13) greater, respectively, for liposomal compared with SM drugs. There was an inverse linear relationship between the clearance (CL) of liposomal agents and PK variability with a lower CL associated with greater PK variability (R(2)=0.39). PK variability of liposomal agents was greater when evaluated from 0-336 h compared with 0-24h. PK variability of liposomes is significantly greater than SM. The factors associated with the PK variability of liposomal agents need to be evaluated.

FROM THE CLINICAL EDITOR

In this meta-analysis, the inter-patient pharmacokinetic variability of 9 liposomal and small molecule anti-cancer agents was studied. The authors determined that several parameters are in favor of the liposomal formulation; however, the PK variability of the formulation was higher compared with small molecule agents, the reason for which remains to be determined in future studies.

Recent trends in multifunctional liposomal nanocarriers for enhanced tumor targeting

Liposomes are delivery systems that have been used to formulate a vast variety of therapeutic and imaging agents for the past several decades. They have significant advantages over their free forms in terms of pharmacokinetics, sensitivity for cancer diagnosis and therapeutic efficacy. The multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers. Multifunctional liposomal nanocarriers should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor lesion relative to healthy tissues, remote-controlled or tumor stimuli-sensitive extravasation from blood at the tumor's vicinity, internalization motifs to move from tumor bounds and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing. This review will focus on current strategies used for cancer detection and therapy using liposomes with special attention to combination therapies.