Transfer of liposomal drug carriers from the blood to the peritoneal cavity of normal and ascitic tumor-bearing mice

Peritoneal B Cells Play a Role in the Production of Anti-polyethylene Glycol (PEG) IgM against Intravenously Injected siRNA-PEGylated Liposome Complexes

Polyethylene glycol (PEG)-modified (PEGylated) cationic liposomes are frequently used as delivery vehicles for small interfering RNA (siRNA)-based drugs because of their ability to encapsulate/complex with siRNA and prolong the circulation half-life in vivo. Nevertheless, we have reported that subsequent intravenous (IV) injections of siRNA complexed with PEGylated cationic liposomes (PLpx) induces the production of anti-PEG immunoglobulin M (IgM), which accelerates the blood clearance of subsequent doses of PLpx and other PEGylated products. In this study, it is interesting that splenectomy (removal of spleen) did not prevent anti-PEG IgM induction by IV injection of PLpx. This indicates that B cells other than the splenic version are involved in anti-PEG IgM production under these conditions. In vitro and in vivo studies have shown that peritoneal cells also secrete anti-PEG IgM in response to the administration of PLpx. Interleukin-6 (IL-6) is a glycoprotein that is secreted by peritoneal immune cells and has been detected in response to the in vivo administration of PLpx. These observations indicate that IV injection of PLpx stimulates the proliferation/differentiation of peritoneal PEG-specific B cells into plasma cells via IL-6 induction, which results in the production of anti-PEG IgM from the peritoneal cavity of mice. Our results suggest the mutual contribution of peritoneal B cells as a potent anti-PEG immune response against PLpx.

Plasmafiltration as an effective method in the removal of circulating pegylated liposomal doxorubicin (PLD) and the reduction of mucocutaneous toxicity during the treatment of advanced platinum-resistant ovarian cancer

PURPOSE

The present study evaluates the safety and efficacy of double-plasma filtration (PF) to remove the exceeding pegylated liposomal doxorubicin (PLD) in circulation, thus reducing mucocutaneous toxicity.

METHODS

A total of 16 patients with platinum-resistant ovarian cancer were treated with 50 mg/m² PLD applied in 1-h IV infusion every 28 days. PF was scheduled at 44-46 h post-infusion. The concentration of plasma PLD and non-liposomal doxorubicin (NLD) was monitored with high-performance liquid chromatography at 116 h post-infusion. A non-linear method for mixed-effects was used in the population pharmacokinetic model. The dose fraction of PLD eliminated by the patient prior to PF was compared with the fraction removed by PF. PLD-related toxicity was recorded according to CTCAE v4.0 criteria and compared to historical data. Anticancer effects were evaluated according to RECIST 1.1 criteria.

RESULTS

The patients received a median of 3 (2-6) chemotherapy cycles. A total of 53 cycles with PF were evaluated, which removed 31% (10) of the dose; on the other hand, the fraction eliminated prior to PF was of 34% (7). Exposure to NLD reached only 10% of exposure to the parent PLD. PLD-related toxicity was low, finding only one case of grade 3 hand-foot syndrome (6.7%) and grade 1 mucositis (6.7%). Other adverse effects were also mild (grade 1-2). PF-related adverse effects were low (7%). Median progression-free survival (PFS) and overall survival (OS) was of 3.6 (1.5-8.1) and 7.5 (1.7-26.7) months, respectively. Furthermore, 33% of the patients achieved stable disease (SD), whereas that 67% progressed.

CONCLUSION

PF can be considered as safe and effective for the extracorporeal removal of PLD, resulting in a lower incidence of mucocutaneous toxicity.

Heat-activated drug delivery increases tumor accumulation of synergistic chemotherapies

Doxorubicin is a clinically important anthracycline chemotherapeutic agent that is used to treat many cancers. Nanomedicine formulations including Doxil® and ThermoDox® have been developed to mitigate doxorubicin cardiotoxicity. Doxil is used clinically to treat ovarian cancer, AIDS-related Kaposi's sarcoma, and multiple myeloma, but there is evidence that therapeutic efficacy is hampered by lack of drug release. ThermoDox is a lipid-based heat-activated formulation of doxorubicin that relies on externally applied energy to increase tissue temperatures and efficiently trigger drug release, thereby affording therapeutic advantages compared to Doxil. However, elevating tissue temperatures is a complex treatment process requiring significant time, cost, and expertise compared to standard intravenous chemotherapy. This work endeavors to develop a companion therapeutic to ThermoDox that also relies on heat-triggered release in order to increase the therapeutic index of doxorubicin. To this end, a thermosensitive liposome formulation of the heat shock protein 90 inhibitor alvespimycin has been developed and characterized. This research demonstrates that both doxorubicin and alvespimycin are potent anti-cancer agents and that heat amplifies their cytotoxic effects. Furthermore, the two drugs are proven to act synergistically when cancer cells are treated with the drugs in combination. The formulation of alvespimycin was rationally designed to exhibit similar pharmacokinetics and drug release kinetics compared to ThermoDox, enabling the two drugs to be delivered to heated tumors at similar efficiencies resulting in control of a particular synergistic ratio of drugs. In vivo measurements demonstrated effective heat-mediated triggering of doxorubicin and alvespimycin release from thermosensitive liposomes within tumor vasculature. This treatment strategy resulted in a ~10-fold increase in drug concentration within tumors compared to free drug administered without tumor heating.

Distinct biodistribution of doxorubicin and the altered dispositions mediated by different liposomal formulations

The liposomal formulations of doxorubicin produced distinct efficacy and toxicity profiles compared to doxorubicin solution in cancer patients. This study aims to investigate the drug tissue distribution and the driving force for tissue distribution from doxorubicin solution and two liposomal delivery systems, Doxil and Myocet. These three formulations were intravenously administered to mice at a single dose of 5mg/kg. Eleven organs, plasma and blood were collected at different time points. Total doxorubicin concentrations in each specimen were measured with LC-MS/MS. Compared to doxorubicin solution, both Doxil and Myocet produced distinct doxorubicin tissue exposure in all 11 tissues. Interestingly, the tissue exposure by Myocet was drastically different from that of Doxil and showed a formulation-dependent pattern. Cmax of doxorubicin in heart tissue by Doxil and Myocet was approximately 60% and 50% respectively of that by doxorubicin solution. The predominant driving force for doxorubicin tissue distribution is liposomal-doxorubicin deposition for Doxil and free drug concentration for doxorubicin solution. For Myocet, the driving force for tissue distribution is predominately liposomal-doxorubicin deposition into tissues within the first 4h; as the non-PEGylated doxorubicin liposomal decomposes, the driving force for tissue distribution is gradually switched to the released free doxorubicin. Unique tissue distributions are correlated with their toxicity profiles.

Liposomal Doxorubicin in Breast Cancer

Drug-delivery carriers represent an important step in the development of targeted therapy. Encapsulation of drug into liposomes represents such a carrier, and helps to minimize side effects of conventional doxorubicin by improving the tumor-specific biodistribution profile. We review the development of the two liposomal doxorubicin formulations, pegylated liposomal doxorubicin and liposomal-encapsulated doxorubicin citrate from reconstitution and comparative pharmacokinetics to pivotal Phase III trials, with special emphasis in breast cancer. The relative differences in the toxicity profile can be attributed to their differences in the liposomal formulations. Areas of special interest include the reduction in cardiac toxicities and the improved efficacy, such as in the treatment of ovarian cancer. These improvements have also increased the potential of these liposomal formulations of doxorubicin for combination and sequencing with other biological and cytotoxic agents for clinical benefit.

Gene Therapy: Recent Advances and Applications in Dermatology

Background:

Gene therapy is an innovative and exciting new branch of medicine. Despite the fact that a human disease has yet to be cured using this therapeutic approach, numerous clinical trials are taking place around the world based on encouraging preclinical data.

Objective:

The aim of this review is to bring the reader up to date with this rapidly advancing field and to highlight the technical advances that must occur before gene therapy will become common practice in dermatology.

Methods:

The current level of gene delivery technology restricts the applications. The advantages and disadvantages of viral and nonviral gene delivery systems are discussed.

Results:

Considerable advances are being made in the areas of cancer immunotherapy and vaccines. Of particular importance to the treatment of skin diseases will be the isolation and ex vivo manipulation of epidermal stem cells, the development of skin-specific regulatory sequences for gene expression, and the formulation of gene delivery systems suitable for systemic administration.

Conclusions:

In general, skin and keratinocytes are considered to be good targets for gene transfer applications, and several diseases have been identified as potential candidates for treatment in the near future.

Evaluation of therapeutic effectiveness of 131I-antiEGFR-BSA-PCL in a mouse model of colorectal cancer

AIM: To investigate the biological effects of internal irradiation, and the therapeutic effectiveness was assessed of ¹³¹I-labeled anti-epidermal growth factor receptor (EGFR) liposomes, derived from cetuximab, when used as a tumor-targeting carrier in a colorectal cancer mouse model.

METHODS: We described the liposomes and characterized their EGFR-targeted binding and cellular uptake in EGFR-overexpressing LS180 colorectal cancer cells. After intra-tumor injections of 74 MBq (740 MBq/mL) ¹³¹I-antiEGFR-BSA-PCL, we investigated the biological effects of internal irradiation and the therapeutic efficacy of ¹³¹I-antiEGFR-BSA-PCL on colorectal cancer in a male BALB/c mouse model. Tumor size, body weight, histopathology, and SPECT imaging were monitored for 33 d post-therapy.

RESULTS: The rapid radioiodine uptake of ¹³¹I-antiEGFR-BSA-PCL and ¹³¹I-BSA-PCL reached maximum levels at 4 h after incubation, and the ¹³¹I uptake of ¹³¹I-antiEGFR-BSA-PCL was higher than that of ¹³¹I-BSA-PCL in vitro. The ¹³¹I tissue distribution assay revealed that ¹³¹I-antiEGFR-BSA-PCL was markedly taken up by the tumor. Furthermore, a tissue distribution assay revealed that ¹³¹I-antiEGFR-BSA-PCL was markedly taken up by the tumor and reached its maximal uptake value of 21.0 ± 1.01 %ID/g (%ID/g is the percentage injected dose per gram of tissue) at 72 h following therapy; the drug concentration in the tumor was higher than that in the liver, heart, colon, or spleen. Tumor size measurements showed that tumor development was significantly inhibited by treatments with ¹³¹I-antiEGFR-BSA-PCL and ¹³¹I-BSA-PCL. The volume of tumor increased, and treatment rate with ¹³¹I-antiEGFR-BSA-PCL was 124% ± 7%, lower than that with ¹³¹I-BSA-PCL (127% ± 9%), ¹³¹I (143% ± 7%), and normal saline (146% ± 10%). The percentage losses in original body weights were 39% ± 3%, 41% ± 4%, 49% ± 5%, and 55% ± 13%, respectively. The best survival and cure rates were obtained in the group treated with ¹³¹I-antiEGFR-BSA-PCL. The animals injected with ¹³¹I-antiEGFR-BSA-PCL and ¹³¹I-BSA-PCL showed more uniform focused liposome distribution within the tumor area.

CONCLUSION: This study demonstrated the potential beneficial application of ¹³¹I-antiEGFR-BSA-PCL for treating colorectal cancer. ¹³¹I-antiEGFR-BSA-PCL suppressed the development of xenografted colorectal cancer in nude mice, thereby providing a novel candidate for receptor-mediated targeted radiotherapy.

Brain tumor-targeted delivery and therapy by focused ultrasound introduced doxorubicin-loaded cationic liposomes

Brain tumor lacks effective delivery system for treatment. Focused ultrasound (FUS) can reversibly open BBB without impacts on normal tissues. As a potential drug carrier, cationic liposomes (CLs) have the ability to passively accumulate in tumor tissues for their positive charge. In this study, FUS introduced doxorubicin-loaded cationic liposomes (DOX-CLs) were applied to improve the efficiency of glioma-targeted delivery. Doxorubicin-loaded CLs (DOX-CLs) and quantum dot-loaded cationic liposomes (QD-CLs) were prepared using extrusion technology, and their characterizations were evaluated. With the advantage of QDs in tracing images, the glioma-targeted accumulation of FUS + CLs was evaluated by fluorescence imaging and flow cytometer. Cell survival rate, tumor volume, animal survival time, and brain histology in C6 glioma model were investigated to evaluate the glioma-targeted delivery of FUS + DOX-CLs. DOX-CLs and QD-CLs had suitable nanoscale sizes and high entrapment efficiency. The combined strategy of FUS introduced CLs significantly increased the glioma-targeted accumulation for load drugs. FUS + DOX-CLs showed the strongest inhibition on glioma based on glioma cell in vitro and glioma model in vivo experiments. From MRI and histological analysis, FUS + DOX-CLs group strongly suppressed the glioma progression and extended the animal survival time to 81.2 days. Among all the DOX treatment groups, FUS + DOX-CLs group showed the best cell viability and highest level of tumor apoptosis and necrosis. Combining the advantages of BBB reversible opening by FUS and glioma-targeted binding by CLs, ultrasound introduced cationic liposomes could achieve glioma-targeted delivery, which might be developed as a potential strategy for future brain tumor therapy.

Biodistribution and pharmacokinetics of 188Re-liposomes and their comparative therapeutic efficacy with 5-fluorouracil in C26 colonic peritoneal carcinomatosis mice

BACKGROUND

Nanoliposomes are designed as carriers capable of packaging drugs through passive targeting tumor sites by enhanced permeability and retention (EPR) effects. In the present study the biodistribution, pharmacokinetics, micro single-photon emission computed tomography (micro-SPECT/CT) image, dosimetry, and therapeutic efficacy of (188)Re-labeled nanoliposomes ((188)Re-liposomes) in a C26 colonic peritoneal carcinomatosis mouse model were evaluated.

METHODS

Colon carcinoma peritoneal metastatic BALB/c mice were intravenously administered (188)Re-liposomes. Biodistribution and micro-SPECT/CT imaging were performed to determine the drug profile and targeting efficiency of (188)Re-liposomes. Pharmacokinetics study was described by a noncompartmental model. The OLINDA|EXM computer program was used for the dosimetry evaluation. For therapeutic efficacy, the survival, tumor, and ascites inhibition of mice after treatment with (188)Re-liposomes and 5-fluorouracil (5-FU), respectively, were evaluated and compared.

RESULTS

In biodistribution, the highest uptake of (188)Re-liposomes in tumor tissues (7.91% ± 2.02% of the injected dose per gram of tissue [%ID/g]) and a high tumor to muscle ratio (25.8 ± 6.1) were observed at 24 hours after intravenous administration. The pharmacokinetics of (188)Re-liposomes showed high circulation time and high bioavailability (mean residence time [MRT] = 19.2 hours, area under the curve [AUC] = 820.4%ID/g*h). Micro-SPECT/CT imaging of (188)Re-liposomes showed a high uptake and targeting in ascites, liver, spleen, and tumor. The results were correlated with images from autoradiography and biodistribution data. Dosimetry study revealed that the (188)Re-liposomes did not cause high absorbed doses in normal tissue but did in small tumors. Radiotherapeutics with (188)Re-liposomes provided better survival time (increased by 34.6% of life span; P < 0.05), tumor and ascites inhibition (decreased by 63.4% and 83.3% at 7 days after treatment; P < 0.05) in mice compared with chemotherapeutics of 5-fluorouracil (5-FU).

CONCLUSION

The use of (188)Re-liposomes for passively targeted tumor therapy had greater therapeutic effect than the currently clinically applied chemotherapeutics drug 5-FU in a colonic peritoneal carcinomatosis mouse model. This result suggests that (188)Re-liposomes have potential benefit and are safe in treating peritoneal carcinomatasis of colon cancer.

Evaluation of pharmacokinetics of 111In-labeled VNB-PEGylated liposomes after intraperitoneal and intravenous administration in a tumor/ascites mouse model

Nanoliposomes are important drug carriers that can passively target tumor sites by the enhanced permeability and retention (EPR) effect in neoplasm lesions. This study evaluated the biodistribution and pharmacokinetics of 111In-labeled vinorelbine (VNB)-encapsulated PEGylated liposomes (IVNBPL) after intraperitoneal (i.p.) and intravenous (i.v.) administration in a C26/tk-luc colon carcinoma ascites mouse model. IVNBPL was prepared by labeling VNB-encapsulated PEGylated liposomes with 111In-oxine. BALB/c mice were i.p. inoculated with 2 x 10(5) C26/tk-luc cells in 500 muL of phosphate-buffered saline. Peritoneal tumor lesions were confirmed by 124I-FIAU/micro-PET (positron emission tomography) and bioluminescence imaging. Ascites production was examined by ultrasound imaging on day 10 after tumor cell inoculation. The pharmacokinetics and biodistribution studies of IVNBPL in a tumor/ascites mouse model were conducted. The labeling efficiency was more than 90%. The in vitro stability in human plasma at 37 degrees C for 72 hours was 83% +/- 3.5%. For i.p. administration, the areas under curves (AUCs) of ascites and tumor were 6.78- and 1.70-fold higher, whereas the AUCs of normal tissues were lower than those via the i.v. route. This study demonstrates that i.p. administration is a better approach than i.v. injection for IVNBPL, when applied to the treatment of i.p. malignant disease in a tumor/ascites mouse model.

Pharmacokinetics, micro-SPECT/CT imaging and therapeutic efficacy of (188)Re-DXR-liposome in C26 colon carcinoma ascites mice model

The pharmacokinetics and internal radionuclide therapy of intraperitoneally administrated (188)Re-N,N-bis(2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA)-labeled pegylated liposomal doxorubicin ((188)Re-DXR-liposome) were investigated in the C26 murine colon carcinoma ascites mouse model. After intraperitoneal administration of the nanotargeted bimodality (188)Re-DXR-liposome, the ascites and tumor accumulation of the radioactivity were observed, the levels of radioactivity within the ascites were maintained at relatively higher levels before 48 h and the levels of radioactivity in the tumor were maintained at steady levels after 4 h. The AUC((o-->infinity)) of (188)Re-DXR-liposome in blood, ascites and tumor was 9.3-, 4.2- and 4.7-fold larger than that of (188)Re-BMEDA, respectively. The maximum tolerated dose of intraperitoneally administrated (188)Re-DXR-liposome was determined in normal BALB/c mice. The survival, tumor and ascites inhibition of mice after (188)Re-DXR-liposome (22.2 MBq of (188)Re, 5 mg/kg of DXR) treatment were evaluated. Consequently, radiochemotherapeutics of (188)Re-DXR-liposome attained better survival time, tumor and ascites inhibition (decreased by 49% and 91% at 4 days after treatment; P<.05) in mice than radiotherapeutics of (188)Re-liposome or chemotherapeutics of Lipo-Dox did. Therefore, intraperitoneal administration of novel (188)Re-DXR-liposome could provide a benefit and promising strategy for delivery of passive nanotargeted bimodality radiochemotherapeutics in oncology applications.

Biodistribution, pharmacokinetics and imaging of 188Re-BMEDA-labeled pegylated liposomes after intraperitoneal injection in a C26 colon carcinoma ascites mouse model

Nanoliposomes are important carriers capable of packaging drugs for various delivery applications through passive targeting tumor sites by enhanced permeability and retention effect. Radiolabeled liposomes have potential applications in radiotherapy and diagnostic imaging. The purpose of this study was to investigate the biodistribution, pharmacokinetics and imaging of nanotargeted (188)Re-N,N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA)-labeled pegylated liposomes (RBLPL) and unencapsulated (188)Re-BMEDA after intraperitoneal (ip) injection in a C26 colon carcinoma ascites mouse model. The nanopegylated liposomes were labeled with (188)Re-BMEDA. The labeling efficiency of RBLPL was 82.3+/-4.5%. In vitro stability of RBLPL in normal saline at room temperature and in rat plasma at 37 degrees C for 72 h was 92.01+/-1.31% and 82.4+/-1.64%, respectively. The biodistribution studies indicated that the radioactivity in ascites was 69.96+/-14.08 percentage injected dose per gram (% ID/g) at 1h to 5.99+/-1.97% ID/g at 48 h after ip administration of RBLPL. The levels of radioactivity in tumor were progressive accumulation to a maximum of 6.57+/-1.7% ID/g at 24 h. The radioactivity of (188)Re-BMEDA in ascites reached the maximum level of 54.89+/-5.91% ID/g at 1 h and declined rapidly with time. Pharmacokinetic studies revealed that the terminal half-life, total body clearance and area under the curve of RBLPL were 5.3-, 9.5- and 9.4-fold higher than that of (188)Re-BMEDA in blood, respectively. These results suggested that the long circulation, bioavailability and localization of RBLPL in tumor and ascites sites, which also demonstrate that the ip administration of RBLPL is a potential multifunctional nanoradiotherapeutics and imaging agents on a C26 colon carcinoma ascites mouse model.

Improvement in 5-fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) concentration by 5-fluorouracil-polyethylene-glycol-liposomes in abdominal stop-flow: treatment of VX2 liver-tumor-bearing rabbits

The application of liposome-encapsulated cytostatics results in higher concentrations in tumor tissue. This effect can be further increased by blood flow retardation with longer retention time in the tumor and by arterial administration. In abdominal stop-flow therapy, a separate partial circulation with a defined flow is realized via a roller pump under hypoxic conditions. Forty chinchilla rabbits with VX-2 liver tumors were treated either intra-aortally (stop-flow therapy) or systemically with 50 mg 5-FU or 5-FU-PEG liposomes. During therapy, pH and pO2 were measured at regular intervals. After 20 minutes, concentrations of 5-FU and its metabolite FdUrd were determined by HPLC in different organs and the liver tumor. Compared to the i.v. application of monosubstances, the combination of i.a. 5-FU-PEG liposomes and flow retardation increased the concentration in tumor tissue by a factor of 44 and even 100-fold in the para-aortal lymph nodes (LN). The concentration of 5-FU and FdUrd was increased by flow reduction, intraaortal application and liposomal encapsulation of 5-FU.

Preparation, characterization, and stability of liposome-based formulations of mitoxantrone

The preparation, characterization, and stability of lyophilized liposome-based formulation of mitoxantrone was investigated. Mitoxantrone was entrapped inside small, unilamellar liposomes composed of dioleoylphosphocholine (DOPC), cholesterol, and cardiolipin. The mean vesicle size and drug entrapment efficiency of the liposomes were approximately 150 nm and approximately 99%, respectively. Less than 1% of drug was lost and mean vesicle size remained unchanged after sterile filtration. The pre-lyophilized (pre-lyo) formulations were characterized by a differential scanning calorimetric (DSC) method. Results showed that the glass transition temperatures (Tg) increased as the molar ratios of sucrose:lipid and trehalose:lipid in the formulations were increased. The maximum Tg' of the pre-lyo formulations containing 10:1 sucrose:lipid and trehalose:lipid molar ratios were -37C and -41C, respectively. After reconstitution of the lyophilized cake of the sucrose-containing formulation, the mean vesicle size was comparable to pre-lyo liposome size. In vitro release studies showed that less than 2% of mitoxantrone was released after an extensive dialysis against phosphate buffered saline (PBS) at 37C, indicating that the mitoxantrone was highly associated and retained inside the liposomes. Short-term stability studies of the sucrose-containing formulations revealed that the reconstituted and eight-fold diluted formulations were stable for up to 8 hours at room temperature. Long-term stability studies of lyophilized liposomal mitoxantrone showed that the lyophilized formulation was stable for up to 13 months after storage at refrigerated condition.

Pharmacokinetics of pegylated liposomal Doxorubicin: review of animal and human studies

Pegylated liposomal doxorubicin (doxorubicin HCl liposome injection; Doxil or Caelyx) is a liposomal formulation of doxorubicin, reducing uptake by the reticulo-endothelial system due to the attachment of polyethylene glycol polymers to a lipid anchor and stably retaining drug as a result of liposomal entrapment via an ammonium sulfate chemical gradient. These features result in a pharmacokinetic profile characterised by an extended circulation time and a reduced volume of distribution, thereby promoting tumour uptake. Preclinical studies demonstrated one- or two-phase plasma concentration-time profiles. Most of the drug is cleared with an elimination half-life of 20-30 hours. The volume of distribution is close to the blood volume, and the area under the concentration-time curve (AUC) is increased at least 60-fold compared with free doxorubicin. Studies of tissue distribution indicated preferential accumulation into various implanted tumours and human tumour xenografts, with an enhancement of drug concentrations in the tumour when compared with free drug. Clinical studies of pegylated liposomal doxorubicin in humans have included patients with AIDS-related Kaposi's sarcoma (ARKS) and with a variety of solid tumours, including ovarian, breast and prostate carcinomas. The pharmacokinetic profile in humans at doses between 10 and 80 mg/m(2) is similar to that in animals, with one or two distribution phases: an initial phase with a half-life of 1-3 hours and a second phase with a half-life of 30-90 hours. The AUC after a dose of 50 mg/m(2) is approximately 300-fold greater than that with free drug. Clearance and volume of distribution are drastically reduced (at least 250-fold and 60-fold, respectively). Preliminary observations indicate that utilising the distinct pharmacokinetic parameters of pegylated liposomal doxorubicin in dose scheduling is an attractive possibility. In agreement with the preclinical findings, the ability of pegylated liposomes to extravasate through the leaky vasculature of tumours, as well as their extended circulation time, results in enhanced delivery of liposomal drug and/or radiotracers to the tumour site in cancer patients. There is evidence of selective tumour uptake in malignant effusions, ARKS skin lesions and a variety of solid tumours. The toxicity profile of pegylated liposomal doxorubicin is characterised by dose-limiting mucosal and cutaneous toxicities, mild myelosuppression, decreased cardiotoxicity compared with free doxorubicin and minimal alopecia. The mucocutaneous toxicities are dose-limiting per injection; however, the reduced cardiotoxicity allows a larger cumulative dose than that acceptable for free doxorubicin. Thus, pegylated liposomal doxorubicin represents a new class of chemotherapy delivery system that may significantly improve the therapeutic index of doxorubicin.

Determination by liquid chromatography with fluorescence detection of total 7-ethyl-10-hydroxy-camptothecin (SN-38) in beagle dog plasma after intravenous administration of liposome-based SN-38 (LE-SN38)

An HPLC- fluorescence method to quantitate total 7-ethyl-10-hydroxy-camptothecin (SN-38) in beagle dog plasma spiked with liposome based formulation of SN-38 (LE-SN38) and using camptothecin (CPT) as the internal standard (I.S.) was developed and validated to support pharmacokinetics/toxicokinetics studies. Sample preparation was done by protein precipitation using acetonitrile with 0.5% acetic acid. The supernatant was evaporated, and reconstituted in acetonitrile-20 mM ammonium acetate, pH 3.5 (20:80, v/v). When injected onto a Zorbax SB-C(18) HPLC column SN-38 as well as I.S. were detected by fluorescence using an excitation at 368 nm and emission at 515 nm. The SN-38 concentrations in samples were calculated from a standard curve of peak area ratios of SN-38 to the I.S. using weighted linear regression. The sensitivity limit for SN-38 was 1.00 ng/ml in beagle dog plasma with a precision (expressed as relative standard deviation) of 12.4% and an accuracy (expressed as analytical recovery) of 104%. The assay was linear within the standard curve range of 1-750 ng/ml. Acceptable precision and accuracy were also obtained for concentrations over the balance of the standard curve range from between-run and within-run calculations.

Development of novel topical tranexamic acid liposome formulations

The aims of this study were to develop novel liposome formulations for tranexamic acid (TA) from various lipid compositions [neutral (hydrogenated soya phosphatidylcholine and cholesterol), positive (stearylamine) or negative (dicetyl phosphate) charged lipid], and to investigate the effects of concentrations of TA (5 and 10% in DI water) and charges on the physicochemical properties of liposomes. Liposomes were prepared by chloroform film method with sonication. The physical (appearance, pH, size, morphology) and chemical (drug encapsulation efficiency, transition temperature, enthalpy of transition) properties of liposomes were characterized. The TA contents were determined spectrophotometrically at 415 nm, following derivatization with 2,4,6-trinitrobenzosulfonic acid. The charged liposomes demonstrated better physical stability than the neutral liposomes. The percentages of TA entrapped in all liposome formulations varied between 13.2 and 15.6%, and were independent of TA concentrations and charges of liposomes. Charges affected the physical stability, pH and size of liposomes. The particle sizes of negative blank and positive liposomes (with and without the entrapped drug) were approximately 10 times larger than the negative liposome with the entrapped TA. The multilamellar 7:2:1 molar ratio of hydrogenated soy phosphatidylcholine/cholesterol/dicetyl phosphate entrapped with 10% TA liposome (10%TA,-) was selected for further release study, due to its high physical stability, small particle size and relatively high drug encapsulation efficiency.

Gadolinium-loaded nanoparticles engineered from microemulsion templates

Microemulsions (oil-in-water) have been used as templates to engineer stable emulsifying wax and Brij 72 (polyoxyl 2 stearyl ether) nanoparticles. The technique is simple, reproducible, and amenable to large-scale production of stable nanoparticles having diameters below 100 nm. Investigation of the process variables showed that the amount of surfactant used in the preparation of microemulsion templates had the greatest influence on the microemulsion window, as well as the properties and stability of the cured nanoparticles. Emulsifying wax and Brij 72 nanoparticles (2 mg/mL) made with 3 mM polyoxyl 20 stearyl ether and 2.3mM polysorbate 80, respectively, were the most stable based on retention of nanoparticle size over time. Gadolinium acetylacetonate (GdAcAc), a potential anticancer agent for neutron capture therapy (NCT), was entrapped in stable nanoparticles. The apparent water solubility of GdAcAc was increased more than 2000-fold by entrapment into nanoparticles. The entrapment efficiency of GdAcAc was about 100% for emulsifying wax nanoparticles and 86% for Brij 72 nanoparticles, as determined by gel permeation chromatography (GPC). Elution profiles were obtained with light scattering (counts per second) to detect nanoparticles and ultraviolet (UV) absorption of GdAcAc at 288 nm. Challenges of these cured nanoparticles in biologically relevant media such as 10% fetal bovine serum, 10 mM phosphate-buffered saline, 150 mM NaCl, and 10% lactose at 37 degrees C for 60 min demonstrated that these nanoparticles are stable. The ease of preparation of these very small and stable nanoparticles, and the ability to entrap lipophilic drugs such as GdAcAc with high efficiency, suggested that these systems may have potential in cell targeting, especially for specific delivery to tumor cells for NCT.

Efficient delivery of Antennapedia homeodomain fused to CTL epitope with liposomes into dendritic cells results in the activation of CD8+ T cells

The in vivo induction of a CTL response using Antennapedia homeodomain (AntpHD) fused to a poorly immunogenic CTL epitope requires that the Ag is given in presence of SDS, an unacceptable adjuvant for human use. In the present report, we developed a hybrid CTL epitope delivery system consisting of AntpHD peptide vector formulated in liposomes as an alternative approach to bypass the need for SDS. It is proposed that liposomes will prevent degradation of the Ag in vivo and will deliver AntpHD recombinant peptide to the cytosol of APCs. We show in this work that dendritic cells incubated with AntpHD-fused peptide in liposomes can present MHC class I-restricted peptide and induce CTL response with a minimal amount of Ag. Intracellular processing studies have shown that encapsulated AntpHD recombinant peptide is endocytized before entering the cytosol, where it is processed by the proteasome complex. The processed liposomal peptides are then transported to the endoplasmic reticulum. The increase of the CTL response induced by AntpHD-fused peptide in liposomes correlates with this active transport to the class I-processing pathway. In vivo studies demonstrated that positively charged liposomes increase the immunogenicity of AntpHD-Cw3 when injected s.c. in mice in comparison to SDS. Moreover, addition of CpG oligodeoxynucleotide immunostimulatory sequences further increase the CD8+ T cell response. This strategy combining lipid-based carriers with AntpHD peptide to target poorly immunogenic Ags into the MHC class I processing pathway represents a novel approach for CTL vaccines that may have important applications for development of cancer vaccines.

Pharmacokinetic/pharmacodynamic modeling of antitumor agents encapsulated into liposomes

Pharmacokinetic/pharmacodynamic (PK/PD) modeling of antitumor agents has been developed for doxorubicin (DOX) in order to predict the optimum conditions for a drug carrier to maximize the antitumor effect. A PK model was constructed for free and liposomal doxorubicin using a hybrid model wherein the disposition in the whole body is described by compartment models, which were linked to the tumor compartment via the blood flow rate. The PD model for doxorubicin was described by a cell-kill kinetic model, which represents the number of tumor cells quantitatively, as a function of the free concentration of doxorubicin in the tumor compartment. The influence of each parameter on the antitumor effects was examined by sensitivity analysis based on the PK/PD model, which clearly showed the importance of optimizing the release rate of DOX from liposomes. The validity of the model has been tested using animal experiments. Preliminary simulations were also performed for humans after scaling up the PK/PD model from rodents to humans. The optimum conditions in the rate of drug release from liposomes were different for rodents vis-a-vis humans, which indicates the limitations involved in extrapolating optimum conditions for experimental animals to those for humans.

Development of a pharmacokinetic/pharmacodynamic (PK/PD)-simulation system for doxorubicin in long circulating liposomes in mice using peritoneal P388

The objective of this study was to develop a simulation system that optimizes the pharmacokinetic parameters of drug carriers for anticancer agents in order to maximize their anticancer effects. The pharmacokinetic/pharmacodynamic (PK/PD) model of doxorubicin (DOX) encapsulated into liposomes has been developed for mice and each parameter required for simulations was obtained in the peritoneally inoculated P388 leukemia model in mice. PK parameters, which describe the dispositions of free and liposomally encapsulated DOX, were obtained by kinetic analysis of experimental data in this study, as well as from literature. PD parameters, which describe the growth and death rate of cancer cells in vivo, were also determined. The PK/PD model developed in this study is capable of simulating the time course of the number of cancer cells quantitatively and evaluating the significance of each parameter on the carrier system for DOX. Simulations based on the PK/PD model predict the optimum rate of drug release from long circulating liposomes as 0.06 h(-1) for maximum anticancer effect. Thus, this simulation system provides useful information relative to the optimization of drug carriers for DOX.

Controlled destabilization of a liposomal drug delivery system enhances mitoxantrone antitumor activity

Programmable fusogenic vesicles (PFVs) are lipid-based drug-delivery systems that exhibit time-dependent destabilization. The rate at which this destabilization occurs is determined by the exchange rate of a bilayer-stabilizing component, polyethylene glycol-phosphatidylethanolamine (PEG-PE) from the vesicle surface. This exchange rate is controlled, in turn, by the acyl chain composition of the PEG-PE. We describe in vitro and in vivo studies using PFVs as delivery vehicles for the anticancer drug mitoxantrone. We demonstrate that the PEG-PE acyl composition determined the rate at which PFVs are eliminated from plasma after intravenous administration, and the rate of mitoxantrone leakage from PFV. The nature of the PEG-PE component also determined the antitumor efficacy of mitoxantrone-loaded PFV in murine and human in murine and human xenograft tumor models. Increased circulation time and improved activity were obtained for PFV containing PEG-PE with an 18-carbon acyl chain length, as a result of slower vesicle destabilization.

Separation of liposomes from plasma components using fast protein liquid chromatography

We describe an efficient method for separating liposomes (large unilamellar vesicles, 120-150 nm diameter) from plasma lipoproteins employing fast protein liquid chromatography (FPLC). This method resolves very low density lipoprotein (VLDL), low-density lipoprotein, high-density lipoprotein, and other plasma components. Selective detection of liposomes (large unilamellar vesicles, 120-150 nm diameter) was achieved using either radiolabeled or fluorescent lipid probes. The liposomes were found to coelute with the earliest FPLC-eluting lipoprotein fraction, VLDL. The remaining plasma lipoprotein and protein components eluted at later times and were resolved from liposomes and VLDL. In order to separate VLDL from liposomes, we selectively precipitated the VLDL fraction from plasma using tungstophosphoric acid and magnesium chloride, prior to separation by FPLC. Furthermore, we demonstrate that this technique can be used to separate liposomes from lipoproteins in plasma samples collected after intravenous administration of liposomes to mice. This technique has wide application in studies of liposome stability in blood and, in particular, for the characterization of liposomal drug carrier systems.

Contact hypersensitivity: a simple model for the characterization of disease-site targeting by liposomes

A murine model of delayed-type hypersensitivity (DTH) is characterized with respect to liposome accumulation at a site of inflammation. Mice were sensitized by painting the abdominal region with a solution of 2,4-dinitrofluorobenzene (DNFB) and inflammation was induced 5 days later by challenging the ear with a dilute solution of DNFB. The inflammatory response was readily monitored by measuring ear thickness (edema) and radiolabeled leukocyte infiltration. Maximum ear swelling and cellular infiltration occurred 24 h after the epicutaneous challenge with the ear returning to normal size after approximately 72 h. We demonstrate that large unilamellar vesicles (LUV) accumulate at the site of inflammation to a level more than 20-fold higher than that measured in the untreated ear. Vesicle delivery to the ear correlated with increased vascular leakage resulting from endothelium remodeling in response to DNFB challenge, and was not a consequence of increased local tissue blood volume. Extravasation occurred only during the first 24 h after ear challenge; after this time the permeability of the endothelium to vesicles returned to normal. We further showed that LUV with a diameter of 120 nm exhibit maximum levels of accumulation, that a polyethylene glycol surface coating does not increase delivery, and that the process can be inhibited by the application of topical corticosteroids at the time of induction. These data and the inflammation model are discussed with respect to developing lipid-based drug delivery vehicles designed to accumulate at inflammatory disease sites.

Cationic lipids, phosphatidylethanolamine and the intracellular delivery of polymeric, nucleic acid-based drugs (review)

Polymeric, nucleic acid drugs must be protected from endogenous nucleases and delivered to target cell nuclei in order to maximize their activity. Constructs expressing therapeutic genes, antisense oligonucleotides and ribozymes can be delivered into cells by viral vectors, but concerns over safety and clinical utility have led to research into the development of alternative, non-viral delivery systems. Antisense and ribozyme drug development has focused upon modifications to the natural oligonucleotide chemistry which make the molecules resistant to nuclease degradation. These novel oligonucleotides cannot be generated by transgenes and must be administered in similar fashion to conventional drugs. However, oligonucleotides cannot cross membranes by passive diffusion and intracellular delivery for these drugs is very inefficient. Here we review the recent advances in forming lipid-DNA particles designed to mimic viral delivery of DNA. Most evidence now supports the hypothesis that lipid-DNA drugs enter target cells by endocytosis and disrupt the endosomal membrane, releasing nucleic acid into the cytoplasm. The mechanisms of particle formation and endosome disruption are not well understood. Cationic lipids are employed to provide an electrostatic interaction between the lipid carrier and polyanionic nucleic acids, and they are critical for efficient packaging of the drugs into a form suitable for systemic administration. However, their role in endosome disruption and other aspects of successful delivery leading to gene expression or inhibition of mRNA translation are less clear. We discuss the propensity of lipid-nucleic acid particles to undergo lipid mixing and fusion with adjacent membranes, and how phosphatidylethanolamine and other lipids may act as factors capable of disrupting bilayer structure and the endosomal pathway. Finally, we consider the challenges that remain in bringing nucleic acid based drugs into the realm of clinical reality.

Plasma clearance, biodistribution and therapeutic properties of mitoxantrone encapsulated in conventional and sterically stabilized liposomes after intravenous administration in BDF1 mice

Mitoxantrone can be efficiently loaded into large unilamellar vesicles using a transmembrane pH gradient. Release studies indicate that these drug-loaded carriers are highly stable and even after dissipation of the residual pH gradient retain more than 85% of encapsulated mitoxantrone following dialysis at 37 degrees C for 5 days. In murine studies we have compared the plasma clearance and biodistribution of both mitoxantrone and liposomal lipid following intravenous administration of free drug or mitoxantrone encapsulated in either conventional or sterically stabilized liposomes. In contrast to the rapid blood clearance observed for free mitoxantrone, both liposomal systems provided extended circulation lifetimes, with over 90% of the drug present 1 h after administration and 15-30% remaining at 24 h. In agreement with previous reports, longer plasma half-lives were observed for sterically stabilized liposomes than for conventional systems. In addition, a strong correlation between drug and carrier biodistribution was seen, with uptake occurring mainly in the liver and spleen and paralleling plasma clearance. This would suggest that tissue disposition reflects that of drug-loaded liposomes rather than the individual components. Liposomal encapsulation also significantly reduced mitoxantrone toxicity, allowing administration of higher, more efficacious drug doses. In a murine L1210 tumour model, for example, no long-term survivors were seen in animal groups treated with free drug, whereas at the maximum therapeutic dose of liposomal mitoxantrone survival rates of 40% were observed.

Sphingomyelin-cholesterol liposomes significantly enhance the pharmacokinetic and therapeutic properties of vincristine in murine and human tumour models

This study reports on the development of a liposomal formulation of vincristine with significantly enhanced stability and biological properties. The in vitro and in vivo pharmacokinetic, tumour delivery and efficacy properties of liposomal vincristine formulations based on sphingomyelin (SM) and cholesterol were compared with liposomes composed of distearoylphosphatidylcholine (DSPC) and cholesterol. SM/cholesterol liposomes had significantly greater in vitro stability than did similar DSPC/cholesterol liposomes. SM/cholesterol liposomes also had significantly improved biological properties compared with DSPC/cholesterol. Specifically, SM/cholesterol liposomes administered intravenously retained 25% of the entrapped vincristine after 72 h in the circulation, compared with 5% retention in DSPC/cholesterol liposomes. The improved retention properties of SM/cholesterol liposomes resulted in plasma vincristine levels 7-fold higher than in DSPC/cholesterol liposomes. The improved circulation lifetime of vincristine in SM/cholesterol liposomes correlated with increased vincristine accumulation in peritoneal ascitic murine P388 tumours and in subcutaneous solid A431 human xenograft tumours. Increased vincristine delivery to tumours was also accompanied by increased anti-tumour efficacy. Treatment with SM/cholesterol liposomal formulations of vincristine resulted in greater than 50% cures in mice bearing ascitic P388 tumours, an activity that could not be achieved with the DSPC/cholesterol formulation. Similarly, treatment of mice with severe combined immunodeficiency (SCID) bearing solid human A431 xenograft tumours with SM/cholesterol vincristine formulations delayed the time required for 100% increase in tumour mass to > 40 days, compared with 5 days, 7 days and 14 days for mice receiving no treatment or treatment with free vincristine or DSPC/cholesterol formulations of vincristine respectively.

A two-step targeting approach for delivery of doxorubicin-loaded liposomes to tumour cells in vivo

A two-step targeting approach was used to deliver doxorubicin-loaded liposomes to a murine tumour cell (P388 leukaemia) grown in culture and, more importantly, in vivo. Targeting was mediated through the use of an antibody specific for the Thy 1.2 antigen that is highly expressed on P388 cells. Briefly, the approach consists of prelabeling target cells with biotinylated anti-Thy 1.2 antibody prior to administration of drug-loaded liposomes that have streptavidin covalently attached to their surface. Results from in vitro studies demonstrate that a 30-fold increase in cell-associated lipid and a 20-fold increase in cell-associated doxorubicin can be achieved over control liposomes using this two-step procedure. Flow-cytometry and fluorescent-microscopy data were used to confirm that P388 cells can be stably labeled with the biotinylated anti-Thy 1.2 antibody in vivo. Subsequently, liposome-targeting studies were initiated in vivo, where target cell binding was assessed following i.p. or i.v. injection of doxorubicin-loaded liposomes into animals bearing P388 tumours prelabeled with biotinylated antibody. A streptavidin-mediated 3.7-fold increase in cell-associated lipid and drug was achieved when the liposomes were given i.p. When doxorubicin-loaded streptavidin liposomes were injected i.v., P388 cells located in the peritoneal cavity were specifically labeled, although the efficiency of this targeting reaction was low. Less than a 2-fold increase in cell-associated lipid was achieved through the use of target-specific (streptavidin-coated) liposomes. These studies demonstrate that the presence of a well-labeled target cell population within the peritoneal cavity will not promote accumulation of an i.v. injected, targeted liposomal drug. Furthermore, the importance of separating target-cell-specific binding from non-specific uptake by tumour-associated macrophages is discussed.

Pharmacology of liposomal vincristine in mice bearing L1210 ascitic and B16/BL6 solid tumours

Vincristine pharmacokinetic, tumour uptake and therapeutic characteristics were investigated here in order to elucidate the processes underlying the enhanced efficacy observed for vincristine entrapped in small (120 nm) distearoylphosphatidylcholine/cholesterol liposomes. Plasma vincristine levels after intravenous (i.v.) injection are elevated more than 100-fold in the liposomal formulation compared with free drug in tumour-bearing as well as non-tumour-bearing mice over 24 h. Biodistribution studies demonstrate that the extent and duration of tumour exposure to vincristine is dramatically improved when the drug is administered i.v. in liposomal form. Specifically, 72 h trapezoidal area under the curve values for liposomal vincristine in the murine L1210 ascitic and B16/BL6 solid tumours are 12.9- to 4.1-fold larger, respectively, than observed for free drug. Similar to previous results with the L1210 model, increased drug delivery to the B16 tumour results in significant inhibition of tumour growth, whereas no anti-tumour activity is observed with free vincristine. Comparisons of drug and liposomal lipid accumulation in tumour and muscle tissue indicate that the enhanced efficacy of liposomal vincristine is related predominantly to drug delivered by liposomes to the tumour site rather than drug released from liposomes in the circulation. Consequently, improvements in liposomal vincristine formulations must focus on factors that increase uptake of liposomes into tumour sites as well as enhance liposomal drug retention in the circulation.