Folate-mediated tumor cell uptake of quantum dots entrapped in lipid nanoparticles.

Quantum dots (QDs) are fluorescent semiconductor nanocrystals with superior optical properties compared to organic dyes currently undergoing rapid development for biological applications, particularly in fluorescence imaging. The folate receptor, overexpressed in a broad spectrum of malignant tumors, is an attractive target for selective delivery of imaging agents to tumor cells. This study examines nanoparticles containing QDs entrapped in a lipid shell, and post-loaded with a folate-lipid conjugate for targeting to mouse and human tumor cells expressing the folate receptor. Hydrophobic QDs were mixed with 1,2 dipalmitoyl-sn-glycero-3 phosphocholine and methoxy-polyethylene-glycol-distearoyl-phosphatidyl-ethanolamine (mPEG-DSPE) generating a nanoparticle referred to as lipodot, with a mean diameter size of approximately 100 nm. Folate-derivatized PEG-DSPE was post-loaded into the lipodots at 0.5% lipid molar concentration. Mouse J6456 lymphoma cells (J6456-FR) and human head and neck KB cancer cells (KB-FR), up-regulated for their folate receptors, were incubated with folate-targeted and non-targeted lipodots in vitro. Using fluorescence microscopy, it was found that only folate-targeted lipodots were taken up by tumor cells. Confocal depth scanning showed substantial internalization. Confirming the specificity of folate-targeted lipodots, binding and internalization were inhibited by free folate, and no uptake was found in a folate-receptor negative cell line. Selective binding and uptake of folate-targeted lipodots by J6456-FR cells was also observed in vivo after intra-peritoneal injection in mice bearing ascitic J6456-FR tumors based on FACS analysis and confocal imaging of harvested cells from the peritoneal cavity. Folate-targeted lipodots represent an attractive approach for tumor cell labeling both in vitro and in vivo.

Phase I study of doxil-cisplatin combination chemotherapy in patients with advanced malignancies.

PURPOSE: Our first objective was to evaluate the feasibility of administering a combination of Doxil, a pegylated liposome formulation of doxorubicin, and cisplatin and to determine the maximum tolerated dose of the combination. A secondary objective was to examine Doxil peak and 7-day postinjection plasma levels at the various dose levels tested. METHODS: Patients with advanced solid tumors were treated every 4 weeks with cisplatin on day 1 and Doxil on day 2. In the first three dose levels, the dose of Doxil was fixed at 40 mg/m(2), whereas the dose of cisplatin was escalated from 40 to 50 and 60 mg/m(2). At the fourth and fifth dose levels, the dose of cisplatin was fixed at 60 mg/m(2), whereas the dose of Doxil was escalated to 50 and to 60 mg/m(2). Plasma Doxil (doxorubicin-equivalent) levels were measured by a high-performance liquid chromatography assay with fluorescence detection at 1 h and 7 days after infusion of Doxil. RESULTS: Twenty-six patients entered the study. Twenty-four patients completed a minimum of 2 courses and were fully assessable for toxicity and efficacy. Eighteen patients had received prior chemotherapy, 11 of them with anthracycline-containing regimens. A total of 177 courses were administered within the study. In 12 patients, cisplatin was discontinued after 1 to 13 courses, and Doxil was continued alone for 1-22 courses. All other patients received both drugs until discontinuation of therapy. The dose-limiting toxicities were neutropenia and mucositis. Grade 4 neutropenia was seen in 3 patients (one with neutropenic fever) at dose levels 4 and 5. Grade 3 mucositis was observed in 4 patients at dose levels 3, 4, and 5. In contrast, the most severe palmar-plantar erythrodysesthesia manifestation was grade 2 seen in 1 patient only. Tumor responses included seven partial responses, of which three were in ovarian cancer patients. In four of seven responders, the time to disease progression exceeded 1 year. Doxil 1-h (C(max) equivalent) levels were assessed in 20 patients. The mean Doxil C(max) (mg/l plasma) increased gradually with dose escalation from 14.7 +/- 1.9 for 40 mg/m(2), to 17.3 +/- 3.0 for 50 mg/m(2), and 23.3 +/- 5.5 for 60 mg/m(2). The 60 mg/m(2) C(max) was similar to data obtained in parallel clinical studies at our institution with single-agent Doxil at 60 mg/m(2). However, the 7-day Doxil postinfusion levels were significantly lower in patients receiving the Doxil-cisplatin combination than in those receiving single-agent Doxil. CONCLUSION: Doxil can be administered at full maximum tolerated dose (50 mg/m(2) every 4 weeks) in combination with 60 mg/m(2) cisplatin, with no evidence of major overlapping toxicities. Palmar-plantar erythrodysesthesia incidence and severity appears to be diminished, in comparison with data available for single-agent Doxil. Plasma concentration data point to an accelerated clearance of Doxil when administered after cisplatin.

Pegylated liposomal doxorubicin: metamorphosis of an old drug into a new form of chemotherapy.

Pegylated liposomal doxorubicin (Doxil, Caelyx) is a formulation of doxorubicin in poly(ethylene glycol)-coated (stealth) liposomes with a prolonged circulation time and unique toxicity profile. We review the preclinical and clinical pharmacology as well as recent clinical data obtained in specific cancer types. Doxil liposomes retain the drug payload during circulation and accumulate preferentially in tissues with increased microvascular permeability, as often is the case of tumors. Doxil toxicity profile is drastically different from that of doxorubicin, and is characterized by dominant and dose-limiting mucocutaneous toxicities, mild myelosuppression, minimal alopecia, and no apparent cardiac toxicity. Although the single maximum tolerated dose (MTD) of Doxil is actually lower than that of conventionally administered doxorubicin, the cumulative MTD dose of Doxil may be substantially greater than that of free doxorubicin. Doxil is probably one of the most active agents in AIDS-related Kaposi's sarcoma and has a definite role in management of recurrent ovarian cancer. The potential of Doxil in the treatment of other cancer types and the opportunities it offers in combination with other drugs and therapeutic modalities are under active investigation.

Skin toxic effects of polyethylene glycol-coated liposomal doxorubicin.

OBJECTIVES: To record the profile of toxic effects of polyethylene glycol-coated liposomal doxorubicin hydrochloride (Doxil) to the skin, and to evaluate whether the long circulation pattern and enhanced accumulation of liposomes in specific skin sites will result in any unique presentations. DESIGN: Patients were accrued in the frame of dose-range-finding studies that examine the toxic effects and antitumor activity of Doxil therapy in metastatic breast and prostate cancers. All patients receiving Doxil were instructed to report any skin eruption or discomfort. Skin examination was performed on a regular basis at every cycle of Doxil therapy and after specific complaints. SETTING: Outpatient day care unit of the oncology institute of a secondary-referral medical center. PATIENTS: Sixty patients (45 women and 15 men). MAIN OUTCOME MEASURES: A basic severity scale of I through IV was adopted for toxic effects to the skin, based on National Cancer Institute common toxicity criteria. RESULTS: The following 4 patterns of skin eruptions were encountered: hand-foot syndrome (n = 24), diffuse follicular rash (n = 6), intertrigolike eruption (n = 5), and new formation of melanotic macules (n = 3). Another major toxic effect of Doxil was stomatitis, which was found to be the dose-limiting factor for the maximal single dose. Alopecia and extravasation injuries did not occur. CONCLUSIONS: The profile of toxic effects of Doxil to the skin reflects its unique pharmacokinetics and tissue distribution. These skin reactions vary significantly from those associated with doxorubicin in non-liposome-encapsulated form.

Pegylated liposomal doxorubicin (doxil): reduced clinical cardiotoxicity in patients reaching or exceeding cumulative doses of 500 mg/m2.

BACKGROUND: The indications for pegylated liposomal doxorubicin (doxil) are expanding. We, therefore, wished to assess the safety of delivering doses exceeding 500 mg/m2 of doxil to patients with solid tumors. PATIENTS AND METHODS: Subjects accrued to eight phase I and II protocol studies conducted at two institutions, were assessed for cardiac function at baseline and at specified intervals by MUGA scans. In this retrospective analysis, the findings of 42 patients, from the total of 237 entered, who had reached or exceeded cumulative doses of 500 mg/m2 (range 500-1500 mg/m2) were reviewed. Changes in left ventricular ejection fraction (LVEF), and in clinical cardiac status were analyzed. Six patients, three who had received prior doxorubicin, also underwent endomyocardial biopsies after cumulative doses of 490-1320 mg/m2. RESULTS: None of the 42 patients had clinical congestive heart failure (CHF) secondary to cardiomyopathy. Post doxil MUGA scans were available for 41 of the 42 patients. Five had a drop of 10% or more in LVEF; three of these had received prior doxorubicin. Billingham endomyocardial biopsy scores ranged from 0-1 in five patients, while the sixth had a score of 1.5 after both 900 mg/m2 and 1320 mg/m2 doxil. Of a remaining 195 patients, 1 episode of CHF was recorded in a patient who had received 312 mg/m2 doxil over 120 mg/m2 of mitoxantrone and chest radiation. CONCLUSIONS: Cumulative doses in excess of 500 mg/m2 of doxil appear to carry a considerably lesser risk of cardiomyopathy as judged by serial LVEF's and clinical follow-up, than is generally associated with free doxorubicin. Heart biopsies have provided reassuring data in a small number of patients, even if pretreated with doxorubicin. However, since three doxorubicin pretreated patients were among the five experiencing drops in LVEF, more data are warranted on such patients.

Correlation of toxicity with pharmacokinetics of pegylated liposomal doxorubicin (Doxil) in metastatic breast carcinoma.

BACKGROUND: Doxil (ALZA Corp., Mountain View, CA) is a formulation of doxorubicin in polyethylene-glycol coated liposomes with a prolonged circulation time and unique toxicity profile. As yet, the effect of the dose schedule on toxicity and the correlation of toxicity with pharmacokinetics have not been directly addressed. METHODS: The objectives of this study were to examine the toxicity profile and pharmacokinetics of various dose schedules of Doxil in a group of patients with metastatic breast carcinoma (MBC) previously treated with chemotherapy. Forty-five patients received a total of 268 courses of Doxil (median per patient, 5; range, 1-19). Six dose schedules were investigated: 35 mg/m2 every 3 weeks (11 patients), 45 mg/m(2) every 3 weeks (5 patients), 50 mg/m(2) every 4 weeks (5 patients), 60 mg/m(2) every 4 weeks (6 patients), 65 mg/m(2) every 5 weeks (6 patients), and 70 mg/m(2) every 6 weeks (12 patients). Doxil pharmacokinetics was examined in 24 of these patients at the dose levels of 35, 45, 60, and 70 mg/m(2). RESULTS: Stomatitis was dose related, with higher incidence and severity at doses of 60-70 mg/m(2). Skin toxicity in the form of palmar-plantar erythrodysesthesia (PPE) developed usually after two or more courses of treatment and was schedule dependent with shorter dosing intervals leading to increased frequency and severity of skin manifestations. Myelosuppression, mainly as leukopenia/neutropenia, was dose dependent but mild and uncomplicated in most cases. Hair loss was infrequent (< 7%) and always of limited extent. Despite high cumulative doses up to 1500 mg/m(2), cardiac toxicity was observed in only 1 patient who received prior mitoxantrone and mediastinal radiotherapy. Objective responses, improvements, and durable stabilizations were observed in 9, 6, and 14 patients, respectively, indicating significant antitumor activity of Doxil in previously treated MBC patients. Doxil pharmacokinetics was well described by a monoexponential elimination curve with a long T(1/2) (median, 79 hours), a slow clearance (median, 40 mL/hour), and a small volume of distribution (median, 3.9 L). Cmax (peak plasma concentration) and AUC (area under the concentration*time curve) increased linearly with dose with a statistically significant correlation. Correlation analysis of dose and pharmacokinetic parameters with Doxil toxicites revealed that stomatitis grade and leukocyte nadir were correlated strongly with dose and Cmax, and weakly with AUC, whereas PPE grade was correlated significantly with only 1 parameter, T(1/2). CONCLUSIONS: The toxicity of Doxil is dose and schedule dependent and well correlated with pharmacokinetic parameters. Pharmacokinetic guidance of Doxil dosing may be a useful tool.

Doxil (Caelyx): an exploratory study with pharmacokinetics in patients with hormone-refractory prostate cancer.

Doxil, a doxorubicin formulation of polyethylene glycol-coated liposomes, has anti-tumor activity against Kaposi's sarcoma and other solid tumors with mild myelosuppression, minimal hair loss and a low risk of cardiotoxicity. Non-liposomal doxorubicin has modest activity in hormone-refractory prostate cancer (HRPC) with considerable toxicity. A pilot study of Doxil was conducted in 15 patients with HRPC. Doxil was administered i.v. using two regimes of equal dose intensity, either 45 mg/m2 every 3 weeks or 60 mg/m2 every 4 weeks. Plasma levels of doxorubicin were analyzed in 10 patients. The most common side effect was stomatitis with a higher incidence at the 60 mg/m2 dose level. In contrast, hand-foot syndrome was more frequent and severe in patients treated with the 3 week schedule of 45 mg/m2. Three patients responded to treatment (based on objective response in one patient and reduction of PSA level greater than 50% in the other two) and two patients had stable disease, all of them receiving 60 mg/m2. Pharmacokinetic analysis shows a proportional increase of plasma drug levels with dose and the characteristic long circulation time of Doxil with half-lives in the range of 3 days, somewhat longer than previously reported. In conclusion, Doxil at 60 mg/m2 every 4 weeks appears to be active against HRPC, but severe mucocutaneous toxicities prevented further investigation of this regime.

Nuclear delivery of doxorubicin via folate-targeted liposomes with bypass of multidrug-resistance efflux pump.

Folic acid, attached to polyethyleneglycol-derivatized, distearoyl-phosphatidylethanolamine, was used to target in vitro liposomes to folate receptor (FR)-overexpressing tumor cells. Confocal fluorescence microscopic observations demonstrated binding and subsequent internalization of rhodamine-labeled liposomes by a high FR-expressing, murine lung carcinoma line (M109-HiFR cells), with inhibition by free folic acid. Additional experiments tracking doxorubicin (DOX) fluorescence with DOX-loaded, folate-targeted liposomes (FTLs) indicate that liposomal DOX is rapidly internalized, released in the cytoplasmic compartment, and, shortly thereafter, detected in the nucleus, the entire process lasting 1-2 h. FR-mediated cell uptake of targeted liposomal DOX into a multidrug-resistant subline of M109-HiFR cells (M109R-HiFR) was unaffected by P-glycoprotein-mediated drug efflux, in sharp contrast to uptake of free DOX, based on verapamil-blockade experiments with quantitation of cell-associated DOX and flow cytometry analysis. Delivery of DOX by FTLs to M109R-HiFR cells increased continuously with time of exposure, reaching higher drug concentrations in whole cells and nuclei compared with exposure to free DOX. The in vitro cytotoxic activity obtained with DOX-loaded FTLs was 10-fold greater than that of the nontargeted liposome formulation, but was not improved over that of free DOX despite the higher cellular drug levels obtained with the targeted liposomes in M109R-HiFR cells. However, if M109R-HiFR cells were exposed to drugs in vitro and tested in an in vivo adoptive assay for tumor growth in syngeneic mice along a 5-week time span, FTL DOX was significantly more tumor inhibitory than free DOX. It is suggested that the biological activity of liposomal DOX released inside the cellular compartment is reduced in vitro due to the aggregated state of DOX, resulting from the liposome drug-loading process, and requires a long period of time and/or an in vivo environment for full expression.

Reduced UV-induced degradation of doxorubicin encapsulated in polyethyleneglycol-coated liposomes.

PURPOSE: The aim of this study was to investigate the stability of doxorubicin encapsulated in polyethyleneglycol-coated liposomes (Doxil) under UV-A light. METHODS: High performance liquid chromatography and a fluorimetric method were used to quantify doxorubicin in bulk solution and doxorubicin in Doxil formulation. RESULTS: The photodegradation of Doxil was significantly lower in comparison to the photodegradation of the free drug and showed no concentration dependency at the measured concentration range of 5-50 microg/ml. During and after UV-A irradiation, there was no leakage of the drug from liposomes to the medium. After induced leakage of doxorubicin from the liposomes by the ionophore nigericin, the degradation kinetics of Doxil were identical to that of free doxorubicin. CONCLUSIONS: High intraliposomal doxorubicin concentration and intraliposomal acidic pH are the two critical factors that protect DXR in Doxil from UV-A degradation.

Selective delivery of doxorubicin to patients with breast carcinoma metastases by stealth liposomes.

BACKGROUND: Stealth liposomes hold promise as a mode of delivering cytotoxic agents selectively to tumors in cancer patients. The objective of this study was to determine whether stealth liposomal doxorubicin accumulates selectively in bone metastases based on clinical material obtained from two patients with breast carcinoma. METHODS: Tumor tissue was obtained from two women (ages 33 years and 41 years, respectively) with metastatic breast carcinoma who responded to treatment with stealth liposomal doxorubicin and later underwent a surgical fixation procedure to treat a pathologic fracture of the femur. Drug levels in the tumor and adjacent muscle were examined by high performance liquid chromatography analysis in both patients and by fluorescence microscopy in one of the patients. RESULTS: Bone tumor fragments obtained during surgery performed 6 days after the administration of the 12th course of stealth liposomal doxorubicin in 1 patient and 12 days after the administration of the 16th course of stealth liposomal doxorubicin in the second patient had a 10-fold greater concentration of liposomal doxorubicin than tumor free muscle. Doxorubicin fluorescence and specific nuclear staining showed good colocalization, thus confirming the presence of the liposome-delivered drug in the nuclei of tumor cells. CONCLUSIONS: Using skeletal muscle as a comparator, stealth liposomal doxorubicin accumulates selectively in metastatic breast carcinoma cells within bone.

Enhancement of antitumor activity of polyethylene glycol-coated liposomal doxorubicin with soluble and liposomal interleukin 2.

Polyethylene glycol-coated liposomal doxorubicin (Doxil) has a sustained release profile and a mild myelosuppressive effect that may enable a beneficial interaction with lymphocyte-activating cytokines, such as interleukin 2 (IL-2). Previous studies have shown that liposome entrapment of IL-2 potentiates its immunomodulatory effects and reduces the need for frequent dosing. We assessed the therapeutic effect of Doxil (8 mg/kg) followed by free or liposomal IL-2 (50,000 Cetus Units x 3) in mice bearing M109 lung adenocarcinoma transplanted i.v. or i.p. Doxil was always administered i.v., whereas IL-2 was given i.v. in the i.v. M109 model and i.p. in the i.p. M109 model. The optimal combined treatment was significantly more effective than liposomal chemotherapy alone, producing tumor-free, long-term survivors in 100% (i.v. M109) and 94% (i.p. M109) of the mice, compared with 50% and 56%, respectively, for Doxil alone. The efficacy boost of IL-2 appeared to be formulation dependent, with free IL-2 and IL-2 in small unilamellar vesicles most active in the i.v. tumor model, and IL-2 in multilamellar vesicles most active in the i.p. tumor model. The combination of Doxil with free or liposomal IL-2 was devoid of any conspicuous toxicity. Cytokine treatment without chemotherapy was completely ineffective. Liposome-based chemoimmunotherapy is a synergistic and highly efficacious approach to eradicate metastatic and regionally spread tumors.

Targeting folate receptor with folate linked to extremities of poly(ethylene glycol)-grafted liposomes: in vitro studies.

Conjugates of three components, folic acid-poly(ethylene glycol)-distearoylphosphatidylethanolamine (FA-PEG-DSPE), derived from PEG with molecular masses of 2000 and 3350 Da were synthesized by a carbodiimide-mediated coupling of FA to H2N-PEG-DSPE. The conjugates were characterized by 1H NMR, MALDI-TOF, and HPLC analysis of enzymatic cleavage with carboxypeptidase G. As a prototype of a folate receptor (FR)-targeted system, the conjugates were formulated at 0.5 mol % phospholipid in hydrogenated phosphatidylcholine/cholesterol liposomes with or without additional methoxyPEG2000-DSPE. In vitro binding studies were performed with sublines of M109 (murine lung carcinoma) and KB (human epidermal carcinoma) cells each containing high and low densities of FR. FA-PEG-DSPE significantly enhanced liposome binding to tumor cells. The best binding was observed when FA-PEG liposomes contained no additional mPEG-lipid. In fact, our experiments showed that the presence of mPEG on liposomal surfaces significantly inhibited FA-PEG-liposome binding to FR. Increasing the molecular mass of the PEG tether from 2000 to 3350 Da improved the FR binding, particularly in the case of mPEG-coated liposomes. The FA-PEG liposomes bound to M109-HiFR cells very avidly as demonstrated by the inability of free FA (used in a 700-fold excess either at the beginning or at the end of the incubation) to prevent the cell binding. This is in contrast to the 5-10-fold lower cell binding activity of mPEG-FA compared to that of free FA, and likely to be related to the multivalent nature of the liposome-bound FA. Only 22% of FA-PEG3350 and 32% of FA-PEG3350/mPEG cell-associated liposomes could be removed by exposure to pH 3, conditions that dissociate FA-FR, suggesting that more than two-thirds of the bound liposomes were internalized during incubation for 24 h at 37 degrees C. FA-targeted liposomes also show enhanced nonspecific binding to extracellular tissue culture components, a phenomenon especially relevant in short incubation time experiments.

Pharmacological studies of cisplatin encapsulated in long-circulating liposomes in mouse tumor models.

We investigated the pharmacokinetics and therapeutic efficacy of cisplatin encapsulated in polyethyleneglycol-coated long-circulating liposomes in a formulation referred to as SPI-077, in three mouse tumor models (M-109 lung carcinoma inoculated s.c., J-6456 lymphoma inoculated i.p. and A-375 melanoma inoculated s.c.). Tumor-bearing mice were injected i.v. with single doses of SPI-077 and cisplatin. For pharmacokinetic experiments, mice were sacrificed at different timepoints post-treatment. Platinum levels were determined in plasma, spleen, liver, kidneys and tumors using flameless atomic absorption spectrophotometry. Survival times and/or tumor size were recorded for therapeutic studies. The pharmacokinetic studies revealed a prolonged circulation time and enhanced tumor uptake for SPI-077. In contrast to these results, no superior antitumor activity of SPI-077 over cisplatin could be observed in all tumor models. In vitro release experiments showed a negligible release (below 10%) of platinum from the liposomes. An in vitro cytotoxicity assay indicated a reduced cytotoxic activity of SPI-077 in comparison to cisplatin. We concluded that SPI-077 is being delivered to the tumor sites in a low bioavailability form, with extremely slow release kinetics. This explains the discrepant results of high platinum concentrations in tumors and reduced therapeutic activity after administration of SPI-077.

Development of liposomal anthracyclines: from basics to clinical applications.

The pharmacokinetics of liposome-encapsulated drugs are controlled by the interplay of two variables: the rate of plasma clearance of the liposome carrier, and the stability of the liposome-drug association in the blood stream. The pharmacokinetic properties of the liposomal drug, the vesicle size of the liposome carrier and the vascular permeability of individual tissues will determine the extravasation and biodistribution profile. The pharmacokinetics of polyethylene-glycol-(PEG)-liposomal doxorubicin are characterized by an extremely long circulating half-life, slow plasma clearance and reduced volume of distribution compared to free doxorubicin. These carrier systems show an improved extravasation profile with enhanced localization in tumors and superior therapeutic efficacy in comparison to doxorubicin in free form. These properties are the result of an optimized liposome composition and of a special drug-loading method which produces stable and long-circulating carriers. In clinical studies, doxorubicin encapsulated in PEG-coated liposomes shows a unique pharmacokinetic-toxicity profile and promising antitumor activity.

Comparative study of the antitumor activity of free doxorubicin and polyethylene glycol-coated liposomal doxorubicin in a mouse lymphoma model.

Here, we investigate various factors affecting the therapeutic efficacy of free doxorubicin (Free-Dox) and polyethylene glycol (PEG)-coated (PEGylated) liposomal doxorubicin (referred to as Doxil) in the ascitic J6456 lymphoma model of BALB/c mice. Free drug and liposomal drug were affected differently by the tumor burden and route of treatment administration. A delay in start of treatment from day 1 to day 5 almost completely abolished the efficacy of Free-Dox, whereas that of Doxil was only minimally reduced. Contrasting effects on the therapeutic efficacy of Free-Dox and Doxil were obtained by changing treatment administration from the i.v. to the i.p. route; the efficacy of free drug was relatively enhanced, whereas that of liposomal drug was relatively diminished. Overall, Doxil given by the systemic i.v. route was the most effective treatment in prolonging median survival and obtaining cures. Variations in the dose-schedule treatment regime confirm the superior therapeutic profile and reduced dependence on tumor burden of the PEGylated liposomal formulation over free drug. In addition, these experiments indicate that, at equal dose intensity, the dose level is more important than the frequency of administration for therapeutic activity.

Polyethylene glycol-coated (pegylated) liposomal doxorubicin. Rationale for use in solid tumours.

Polyethylene glycol (PEG)-coated (pegylated; Stealth) liposomes are stable, long-circulating drug carriers useful for delivering doxorubicin to the sites of solid tumours. Compared with conventional liposomes, pegylated liposomes are less extensively taken up by cells of the reticuloendothelial system (RES) and have a reduced tendency to leak drug while in circulation. The pharmacokinetics of PEG-liposome encapsulated doxorubicin are characterised by an extremely long circulating half-life, slow plasma clearance and a reduced volume of distribution compared with conventional liposomal doxorubicin or free doxorubicin. The long circulation and ability of pegylated liposomes to extravasate through 'leaky' tumour vasculature results in localisation of doxorubicin in tumour tissue. In a number of animal and human tumours, including breast, prostate, pancreatic and ovarian xenografts, pegylated liposomal doxorubicin produced higher intratumoural drug concentrations and better therapeutic responses than equivalent doses of conventional (nonpegylated)-liposome encapsulated doxorubicin or free doxorubicin. Low peak plasma concentrations of free doxorubicin after administration of pegylated liposomal doxorubicin and the reduced tendency of the liposomal drug to accumulate in myocardium suggest that a reduction in cardiac toxicity compared with free doxorubicin may be observed. Thus, the rationale for the use of pegylated liposomal doxorubicin in solid tumours may be summarised as follows: change in the toxicity profile with a decrease in acute adverse effects (such as nausea and vomiting) and reduced incidence of alopecia, greater activity in highly angiogenic tumours (such as Kaposi's sarcoma) and effective treatment of tumours moderately sensitive to doxorubicin (such as breast and ovarian carcinomas), with the possibility of increased tumour response because of enhanced drug accumulation. In addition, although no comparative study yet exists, there is a suggestion from early human studies with pegylated liposomal doxorubicin that cardiotoxicity may be reduced compared with the free drug.

Targeting of stealth liposomes to erbB-2 (Her/2) receptor: in vitro and in vivo studies.

Long-circulating (stealth) liposomes coated with polyethylene glycol (PEG), which show reduced uptake by the reticuloendothelial system (RES) and enhanced accumulation in tumours, were used for conjugation to monoclonal antibodies (MAbs) as a drug-targeting device. A MAb (N-12A5) directed against erbB-2 oncoprotein, a functional surface antigen, was used. Amplification and overexpression of the erbB-2 gene product, being unique to malignancy, confer onto this antibody-mediated therapy high tumour specificity. In vitro binding of [3H]cholesteryl ether ([3H]Chol ether) labelled anti-erbB-2 conjugated liposomes to N-87 cells (erbB-2-positive human gastric carcinoma) was compared with the binding of non-targeted liposomes and indicated a 16-fold increase in binding for the targeted liposomes. No difference in binding to OV1063 cells (erbB-2-negative human ovary carcinoma) was observed. These results indicate highly selective binding of antibody-targeted liposomes to erbB-2-overexpressing cells. Despite increased cell binding, doxorubicin (DOX) loaded in anti-erbB-2-conjugated liposomes did not cause increased in vitro cytotoxicity against N-87 cells, suggesting lack of liposome internalisation. In vivo, the critical factor needed to decrease the non-specific RES uptake and prolong the circulation time of antibody-conjugated liposomes is a low protein to phospholipid ratio ( < 60 micrograms mumol-1). Using these optimised liposome preparations loaded with DOX and by monitoring the drug levels and the [3H]Chol ether label, biodistribution studies in nude mice bearing subcutaneous implants of N-87 tumours were carried out. No significant differences in liver and spleen uptake between antibody-conjugated and plain liposomes were observed. Nevertheless, there was no enhancement of tumour liposome levels over plain liposomes. Both liposome preparations considerably enhanced DOX concentration in the tumour compared with free drug administration. Therapeutic experiments with N-87 tumour-bearing nude mice indicated that anti-tumour activity of targeted and non-targeted liposomes was similar, although both preparations had an increased therapeutic efficacy compared with the free drug. These studies suggest that efficacy is dependent on drug delivery to the tumour and that the rate-limiting factor of liposome accumulation in tumours is the liposome extravasation process, irrespective of liposome affinity or targeting to tumour cells.

Liposome longevity and stability in circulation: effects on the in vivo delivery to tumors and therapeutic efficacy of encapsulated anthracyclines.

The effect of liposome composition on drug delivery to tumors and therapeutic efficacy of liposome-encapsulated anthracyclines was investigated in two murine tumor models: an ascitic tumor (J6456 lymphoma) and a solid carcinoma (M-109). Longevity in circulation correlated positively with high drug levels in the extracellular (ascitic) tumor fluid and with delayed peak tumor levels. Using polyethylene-glycol(PEG)-coated liposomes, liposome stability (drug retention) was found to be an important determinant of therapeutic efficacy, as indicated by the superior survival conferred by high Tm phosphatidylcholines (hydrogenated, dipalmitoyl) over low Tm (egg phosphatidyl-choline). Replacing PEG with another negatively-charged surface headgroup (phosphatidyl-glycerol, phosphatidyl-inositol) resulted in relatively shorter longevity in circulation of the liposome-associated drug, but no detectable differences in anti-tumor efficacy. When neither the surface charged headgroup nor the PEG coating are present, the resulting drug formulation was significantly less effective than PEG and phosphatidylinositol-based formulations in both tumor models. In conclusion, longevity in circulation, as obtained with PEG coating, tends to improve the therapeutic efficacy of liposome-encapsulated anthracyclines. The current therapeutic models were however unable to detect differences between the therapeutic activity of PEG and other liposome formulations with relatively small differences in circulation longevity.

Hepatic arterial bolus chemotherapy for colorectal metastases using an implantable port.

Twenty-one patients with isolated colorectal liver metastases underwent hepatic artery infusion (HAI) port implantation for regional chemotherapy with bolus injections of 5-FU, LV and fast drip of cisplatin. Ten of the 21 patients had previously failed systemic chemotherapy before HAI. Toxicity was moderate and no need for modulation of the chemotherapeutic dose was required. The objective response rate of the whole group was 52.4%. The patients, who had not previously received systemic chemotherapy, had a significantly higher response rate of 81.8% compared to patients treated previously by systemic chemotherapy, who had a response rate of 20% (p=0.0089). In addition, there was a difference in cumulative survival between these two groups. The HAI combined chemotherapy with 5-FU, LV and cisplatin given by bolus injection through an implantable port is effective therapy with similar response rate but considerable reduced toxicity compared to continuous HAI with FUdR. We assume that this therapy might prolong survival significantly especially in patients not treated before by systemic chemotherapy.