Alberto Gabizon

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/m2 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/m2 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.

Challenges and Key Considerations of the Enhanced Permeability and Retention Effect for Nanomedicine Drug Delivery in Oncology

Enhanced permeability of the tumor vasculature allows macromolecules to enter the tumor interstitial space, whereas the suppressed lymphatic filtration allows them to stay there. This phenomenon, enhanced permeability and retention (EPR), has been the basis of nanotechnology platforms to deliver drugs to tumors. However, progress in developing effective drugs using this approach has been hampered by heterogeneity of EPR effect in different tumors and limited experimental data from patients on effectiveness of this mechanism as related to enhanced drug accumulation. This report summarizes the workshop discussions on key issues of the EPR effect and major gaps that need to be addressed to effectively advance nanoparticle-based drug delivery.

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 LVEFs 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.

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 myelosupression, 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 Kaposis 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.

Liposomal doxorubicin: antitumor activity and unique toxicities during two complementary phase I studies.

PURPOSE The purpose of our studies was to define the maximal-tolerated dose of liposomal doxorubicin (DOX-SL; Liposome Technology Inc, Menlo Park, CA), a doxorubicin formulation of polyethyleneglycol-coated liposomes, characterize the toxicities associated with this formulation, and evaluate any indication of antitumor activity within a phase I setting. PATIENTS AND METHODS Two separate phase I studies were conducted following the initial human pharmacokinetic testing at one of the sites (Hadassah). The starting dose of 20 mg/m2 at the University of Southern California was just below the dose without toxicity in the pharmacokinetic study. At Hadassah, the phase I starting dose was just above their earlier safe single doses, 60 mg/m2. Both studies involved cohorts of at least three patients and redosing every 3 to 4 weeks. To determine the recommended dose for phase II trials, an additional level of 50 mg/m2 every 3 weeks was explored, and the level of 60 mg/m2 every 4 weeks was expanded. RESULTS A total of 56 patients receiving 281 courses of DOX-SL was accrued and evaluated for toxicity. Hand-foot (H-F) syndrome and stomatitis are the two main dose-limiting factors of DOX-SL. Stomatitis was dose-limiting for high single doses of DOX-SL greater than 70 mg/m2. Skin toxicity manifested primarily as H-F syndrome was dose-limiting for repetitive dosing, but acceptable at either 50 mg/m2 every 3 weeks or 60 mg/m2 every 4 weeks. Attenuation of acute subjective symptoms and lack of alopecia were generally observed. Patients with carcinomas of the breast, ovary, prostate, and head and neck were among those showing objective antitumor responses or improvement based, in part, on blood levels of tumor markers. CONCLUSION The toxicity profile of DOX-SL differs prominently from that of the free drug administered by bolus or rapid infusion and with some differences, resembles that of prolonged continuous infusion. This finding, as well as the antitumor activity observed, supports wide phase II testing of DOX-SL in solid tumors.

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

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.

Liposome circulation time and tumor targeting: implications for cancer chemotherapy

Abstract The pharmacokinetics and biodistribution 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 circulation. Inhibition of the rapid uptake of liposomes by the reticuloendothelial system and reduction of the rate of drug leakage have resulted in long-circulating liposomal drug systems with valuable pharmacologic properties. These carrier systems show an improved extravasation profile with enhanced localization in tumors and possibly in other tissues, such as skin. An anticancer drug, doxorubicin, encapsulated in polyethyleneglycol-coated, long-circulating liposomes, shows a unique pharmacokinetic/toxicity pattern and promising antitumor activity in initial clinical studies.

Activation of complement by therapeutic liposomes and other lipid excipient-based therapeutic products: Prediction and prevention

Some therapeutic liposomes and lipid excipient-based anticancer drugs are recognized by the immune system as foreign, leading to a variety of adverse immune phenomena. One of them is complement (C) activation, the cause, or major contributing factor to a hypersensitivity syndrome called C activation-related pseudoallergy (CARPA). CARPA represents a novel subcategory of acute (type I) hypersensitivity reactions (HSR), which is mostly mild, transient, and preventable by appropriate precautions. However, in an occasional patient, it can be severe or even lethal. Because a main manifestation of C activation is cardiopulmonary distress, CARPA may be a safety issue primarily in cardiac patients. Along with an overview of the various types of liposome-immune system interactions, this review updates the experimental and clinical information on CARPA to different therapeutic liposomes and lipid excipient-based (micellar) anticancer drugs, including PEGylated liposomal doxorubicin sulfate (PLD, Doxil®) and paclitaxel (Taxol®). The substantial individual variation of in vitro and in vivo findings reflects an extremely complex immune phenomenon involving multiple, redundant pathways of C activation, signal transduction in allergy-mediating cells and vasoactive mediator actions at the effector cell level. The latest advances in this field include the proposal of doxorubicin-induced shape changes and aggregation of liposomes in Doxil as possible contributing factors to CARPA caused by PLD, and the finding that Doxil-induced immune suppression prevents HSR to co-administered carboplatin, a significant benefit of Doxil in combination chemotherapy with carboplatin. The review evaluates the use of in vitro C assays and the porcine liposome-induced cardiopulmonary distress model for predicting CARPA. It is concluded that CARPA may become a frequent safety issue in the upcoming era of nanomedicines, necessitating its prevention at an early stage of nanomedicine R&D.

Prolongation of the Circulation Time of Doxorubicin Encapsulated in Liposomes Containing a Polyethylene Glycol-Derivatized Phospholipid: Pharmacokinetic Studies in Rodents and Dogs

The pharmacokinetics of doxorubicin (DOX) encapsulated in liposomes containing polyethylene glycol-derivatized distearoylphosphatidylethanolamine (PEG/DSPE) were investigated in rodents and dogs. The plasma levels of DOX obtained with PEG/DSPE-containing liposomes were consistently higher than those without PEG/DSPE or when PEG/DSPE was replaced with hydrogenated phosphatidylinositol (HPI). Despite the inclusion of PEG/DSPE in liposomes, there was a significant drop in the plasma levels of DOX when the main phospholipid component, hydrogenated phosphatidylcholine, was replaced with lipids of lower phase transition temperature (dipalmitoylphosphatidylcholine, egg phosphatidylcholine), indicating that phase transition temperature affects the pharmacokinetics of liposome-encapsulated DOX. In beagle dogs, clearance was significantly slower for DOX encapsulated in PEG/ DSPE-containing liposomes than in HPI-containing liposomes, with distribution half-lives of 29 and 13 hr, respectively. In both instances, almost 100% of the drug measured in plasma was liposome-associated. The apparent volume of distribution was only slightly above the estimated plasma volume of the dogs, indicating that drug leakage from circulating liposomes is insignificant and that the distribution of liposomal drug is limited mostly to the intravascular compartment in healthy animals.

Pros and Cons of the Liposome Platform in Cancer Drug Targeting

Coating of liposomes with polyethylene-glycol (PEG) by incorporation in the liposome bilayer of PEG-derivatized lipids results in inhibition of liposome uptake by the reticulo-endothelial system and significant prolongation of liposome residence time in the blood stream. Parallel developments in drug loading technology have improved the efficiency and stability of drug entrapment in liposomes, particularly with regard to cationic amphiphiles such as anthracyclines. An example of this new generation of liposomes is a formulation of pegylated liposomal doxorubicin known as Doxil® or Caelyx®, whose clinical pharmacokinetic profile is characterized by slow plasma clearance and small volume of distribution. A hallmark of these long-circulating liposomal drug carriers is their enhanced accumulation in tumors. The mechanism underlying this passive targeting effect is the phenomenon known as enhanced permeability and retention (EPR) which has been described in a broad variety of experimental tumor types. Further to the passive targeting effect, the liposome drug delivery platform offers the possibility of grafting tumor-specific ligands on the liposome membrane for active targeting to tumor cells, and potentially intracellular drug delivery. The pros and cons of the liposome platform in cancer targeting are discussed vis-à-vis nontargeted drugs, using as an example a liposome drug delivery system targeted to the folate receptor.