Polyethylene-glycol Coated Liposomes Malignant Exudates of Doxorubicin Encapsulated in Prolonged Circulation Time and Enhanced Accumulation in Updated

In preclinical studies, a doxorubicin liposome formulation containing polyethylene-glycol (Doxil) shows a long circulation time in plasma, enhanced accumulation in murine tumors, and a superior therapeutic activity over free (unencapsulated) doxorubicin (DOX). The purpose of this study was to characterize the pharmacokinetics of Doxil in cancer patients in comparison with free DOX and examine its accumulation in malignant effusions. The pharmacokinetics of doxorubicin and/or liposome-associated doxorubicin were analyzed in seven patients after injections of equivalent doses of free DOX and Doxil and in an additional group of nine patients after injection of Doxil only. Two dose levels were examined, 25 and 50 mg/m 2. When possible, drug levels were also measured in malignant effusions. The plasma elimination of Doxil followed a biexponential curve with half-lives of 2 and 45 h (median values), most of the dose being cleared from plasma under the longer half-life. Nearly 100% of the drug detected in plasma after Doxil injection was in liposome-encapsulated form. A slow plasma clearance (0.1 iiter/h for Doxil v e r s u s 45 liters/h for free DOX) and a small volume of distribution (4 liters for Doxil v e r s u s 254 liters for free DOX) are characteristic of Doxil. Doxorubicin metabolites were detected in the urine of Doxil-treated patients with a pattern similar to that reported for free DOX, although the overall urinary excretion of drug and metabolites was significantly reduced. Doxil treatment resulted in a 4to 16-fold enhancement of drug levels in malignant effusions, peaking between 3 to 7 days after injection. Stomatitis related to Doxil occurred in 5 of 15 evaluable patients and appears to be the most significant side effect in heavily pretreated patients. The results of this study are consistent with preclinical findings indicating that the pharmacokinetics of doxorubicin are drastically altered using Doxil and follow a pattern dictated by the liposome carrier. The enhanced drug accumulation in malignant effusions is apparently related to iiposome longevity in circulation. Further clinical investigation is needed to establish the relevance of these findings with regard to the ability of liposomes to modify the delivery of doxorubicin to solid tumors and its pattern of antitumor activity. I N T R O D U C T I O N The adminis t ra t ion of doxorubic in in l iposome-associa ted fo rm has been advocated as a means to reduce the cardiotoxici ty of the drug. This is based on the reduced cardiac uptake of l iposome-encapsu la ted doxorubic in and on pathological observat ions in preclinical animal mode l s us ing a variety of l iposome formulat ions ( reviewed in 1). In recent years, the deve lopmen t of new formula t ions of long-circulat ing l iposomes (also referred to as Stealth 3 or sterically stabilized liposomes) wi th reduced uptake by the RES 4 and enhanced accumula t ion in tumors has b roadened the potential applicat ions of these carriers in Received 9/14/93; accepted 12/16/93. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. This work was supported by grants from Liposome Technology, Inc. (to A. G. and Y. B.). A. G. is the recipient of a research career development award from the Israel Cancer Research Fund. 2 To whom requests for reprints should be addressed, at Sharett Institute of Oncology, Hadassah Medical Center, P.O. Box 12000, Jerusalem 91120, Israel. 3 Stealth Liposomes and Doxil are registered trademark names of Liposome Technology, Inc. 4 The abbreviations used are: RES, reticuloendothelial system; DOX, doxorubicin; PEG, polyethylene-glycol; HPLC, high pressure liquid chromatography; TLC, thin layer chromatography; AUC, area under the concentration • time curve. cancer drug del ivery ( reviewed in 2 and 3). In studies in rodents and dogs with some of these new formula t ions , l iposome-associa ted doxorubicin has been shown to circulate with very long half-l ives in the range of 15 to 30 h (4, 5). An increased accumula t ion of drug in mur ine transplantable tumors and in ascitic tumor exudates has been reported using long-circulat ing l iposomes as doxorubic in carriers (6, 7). Doxorubic in encapsula ted in long-circulat ing l iposomes also shows a superior therapeut ic ant i tumor activity and decreased toxicity when compared to free D O X 5 in a variety of mouse mode l s (6, 7). Thus, long-circulat ing l iposomes appear to offer a double advantage as an ant icancer drug del ivery system: toxicity buffer ing as with other previous l iposome formula t ions and selective tumor accumula t ion leading to an enhanced ant i tumor activity. We have p roposed (8) that the latter p h e n o m e n o n is the result of l iposome longevi ty in circulat ion on the one hand and increased microvascular permeabi l i ty of tumors (9) on the other. As a preamble to Phase I/II studies, it was impor tant to de termine whether the pharmacokine t i c observat ions with doxorubic in liposomes in animals are extrapolable to humans . We thus under took a pilot clinical s tudy whose aims were to examine the pharmacokine t ics of doxorubic in adminis tered in free and l iposome-encapsu la ted fo rm at two dose levels (25 and 50 mg/m2). The drug levels were also de te rmined in mal ignant effusions in an a t tempt to est imate the putative drug levels in the tumor interstitial fluid. The l iposome formulation used in this study, referred to hereafter as Doxil , contains a PEG derivat ized phosphol ip id which has been shown to confer opt imal prolongat ion of vesicle circulation t ime in animal mode l s (10, 11). P A T I E N T S A N D M E T H O D S Patients. Sixteen cancer patients (male/female, 6/10) with a median Zubrod performance status of 2 (range, 1-3) and a median age of 59.5 years (range, 38-73) were entered into this study. The distribution by tumor type was: breast cancer (6 patients), non-small cell lung cancer (three patients), ovarian cancer (three patients), mesothelioma (two patients), soft tissue sarcoma (one patient), and pancreatic cancer (one patient). The criteria of eligibility included: bilirubin <35 /xM; creatinine <150 /xM; WBC >4,000//xl; neutrophils -> 1,500//xl; platelets --100,000/~1; normal prothrombin time; and left ventricle ejection fraction >55%. The study was carried out under the approval of the Institutional Review Board of the Hadassah University Hospital and Israel Ministry of Health, and written informed consent was obtained from all patients entered. Twelve of the 16 patients entered into the study had failed at least one line of chemotherapy. Four patients had not received prior chemotherapy. In 12 patients, malignant effusions (ascites and pleural effusion) were present. When technically feasible and clinically indicated, these effusions were tapped, and samples were processed to obtain information on drug levels. Study Design. To rule out the possibility that interpatient variability may affect the interpretation of the results, a group of seven patients received the drug in free form in the first course of treatment and in encapsulated form (Doxil) in a second course of treatment. In this group, free DOX and Doxil were given at the same dose: 25 mg/m 2 in three patients and 50 mg/m 2 in four patients. To further characterize the pharmacokinetics of Doxil, a second group 5 The abbreviation of DOX or free DOX is used to designate doxorubicin as the product used for injection only.