Polyethylene Glycol-Liposomal Doxorubicin

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Abstract
Doxorubicin is an antineoplastic drug which has in vitro and in vivo activity against a number of malignancies including Kaposi’s sarcoma. Incorporation of doxorubicin into polyethylene glycol— coated (pegylated) liposomes alters the pharmacokinetics of the drug. Liposomal doxorubicin has a smaller volume of distribution and slower plasma clearance than standard free doxorubicin. The liposomal formulation achieves higher concentrations in the highly vascularised lesions of Kaposi’s sarcoma than in normal tissue. Liposomal doxorubicin monotherapy in patients with AIDS-related Kaposi’s sarcoma produced overall response rates (complete plus partial) of 43 and 59% in large comparative studies and 67 to 100% in noncomparative studies which included ≥ 20 patients. In comparative studies, liposomal doxorubicin was significantly more effective than the combination of standard doxorubicin, bleomycin and vincristine (overall response rates of 43 and 25%, respectively) and bleomycin and vincristine (BV) [overall response rates of 59 and 23%, respectively]. In addition, overall response rates to the liposomal drug were higher in both treatment arms of 2 smaller comparative studies which compared liposomal doxorubicin with BV, but significant between-treatment differences were not detected. Patient numbers in these 2 studies, however, may have been too small to detect significant differences. Liposomal doxorubicin is generally well tolerated. Myelosuppression is the most common dose-limiting adverse effect in patients with AIDS and Kaposi’s sarcoma. Neutropenia occurs most often; anaemia and thrombocytopenia occur less frequently, as do nausea and vomiting and stomatitis. Palmar-plantar erythrodysaesthesia occurs in some patients, most commonly after 6 to 8 weeks of chemotherapy. Although symptoms may occasionally be severe, the syndrome usually does not require dosage reduction or treatment delay. Limited data suggest that the incidence of cardiotoxicity may be lower after liposomal doxorubicin than after equivalent doses of standard doxorubicin. Overall, liposomal doxorubicin appears to be one of the most active single agents available for treating patients with AIDS-related Kaposi’s sarcoma. The therapeutic potential of liposomal doxorubicin administered in combination with other active agents to patients with Kaposi’s sarcoma is, as yet, unknown. However, administered alone, the drug seems to be more effective than the best available combination chemotherapy regimens. Doxorubicin is an anthracycline cytostatic antibiotic with activity against a variety of malignancies including Kaposi’s sarcoma. In vitro and in vivo, polyethylene glycol-coated (pegylated) liposomal doxorubicin inhibits the growth of Kaposi’s sarcoma cells. Kaposi’s sarcoma spindle cell cultures were more sensitive to liposomal doxorubicin than cultures of normal monocytes, or normal endothelial or smooth muscle cells. Tumour cell DNA fragmentation induced by doxorubicin is a result of topoisomerase II inhibition which occurs when the drug intercalates between DNA strands. Antitumour activity and drug toxicity may also relate to the formation of intracellular oxygen free radicals, which are produced by reduction of the doxorubicin molecule. In addition, liposomal doxorubicin induces expression of monocyte chemoattractant protein-1, which results in intralesional recruitment of phagocytic cells in patients with Kaposi’s sarcoma. The pharmacokinetic profile of liposomal doxorubicin is substantially different from that of standard free doxorubicin. Compared with standard doxorubicin, the liposomal product distributes in a smaller volume (254 vs 4.1L), has a larger area under the plasma concentration-time curve and is cleared from the body more slowly (total plasma clearance 45.3 vs 0.08 L/h). In biopsy specimens obtained 48 and 96 hours after administration of liposomal doxorubicin to patients with AIDS-related Kaposi’s sarcoma, higher drug concentrations were present in Kaposi’s sarcoma lesions than in normal skin tissue. The distribution half-life of liposomal doxorubicin is approximately 45 to 56 hours. Metabolites, including doxorubicinol, were detected in the urine, but not the plasma, of liposomal doxorubicin-treated patients, indicating that the metabolism of liposomal doxorubicin is similar to that of the free drug but that the rate of metabolite excretion is higher than the rate of metabolism. The effect of hepatic dysfunction on the clearance of liposomal doxorubicin is unclear; however, volume of distribution, clearance and elimination half-life in patients with mild to moderate hepatic dysfunction did not appear to be altered compared with values from historical controls. Clinical studies of liposomal doxorubicin in Kaposi’s sarcoma predominantly included men with AIDS, CD4+ counts 2 administered at 2- or 3-week intervals, overall response rates of 67 to 100% were reported. In the largest noncomparative study (n=238; overall response rate 81 %), no correlation was detected between response and CD4+ cell count, neutrophil count or ACTG risk category. Median quality-of-life scores improved during treatment in 2 studies which included prospective quality-of-life analysis. Liposomal doxorubicin produced better response rates than bleomycin and vincristine (BV) or standard doxorubicin plus bleomycin and vincristine (ABV) in 4 studies. In the 2 largest studies (n=218 and 225), liposomal doxorubicin was significantly more effective than ABV (response rates of 43 and 25%, respectively) or BV (59 and 23%, respectively). Extensive and progressive baseline disease in patients in these studies and/or more rigorously applied response criteria may have contributed to the low overall response rates observed in both treatment arms. More liposomal doxorubicin-than BV-treated patients completed 6 cycles of chemotherapy. Compared with these 2 large studies, response rates in 2 smaller studies which compared liposomal doxorubicin with BV chemotherapy in patients with Kaposi’s sarcoma were higher, but significant between-treatment differences were not observed. Patient numbers in the latter 2 studies may have been too small to detect significant differences. The reported duration of response to liposomal doxorubicin in the 2 largest comparative studies was 15 and 20 weeks. Between-treatment differences in response duration were not detected in any study. Liposomal doxorubicin is generally well tolerated. The most common dose-limiting adverse effect of the drug in patients with AIDS and Kaposi’s sarcoma is myelosuppression. At recommended dosages, neutropenia occurred in 50% of patients; severe neutropenia (9 cells/L) occurred in 14%. However, pre-existing immune system compromise complicates assessment of neutropenia and infectious events in patients with AIDS. Anaemia occurred in 19% of patients. Palmar-plantar erythrodysaesthesia, characterised by ulceration, erythema and desquamation on the palms of the hands and soles of the feet with pain and inflammation, occurs in some patients, most commonly after 6 to 8 weeks of treatment. At recommended dosages of liposomal doxorubicin, the incidence of this syndrome is 2 every 3 weeks as long as response continues. In several large clinical studies, liposomal doxorubicin was administered at 2-week intervals. Dosage reduction is suggested for patients with treatment-limiting neutropenia, stomatitis or palmar-plantar erythrodysaesthesia.