Free doxorubicin

Figure 7 Release profiles of doxorubicin from the two nanoparticles free doxorubicin encapsulated nanoparticles and PLGA-doxorubicin loaded nanoparticles (adapted with permission from the publisher [24]).

Mickisch GH, Rahman A, Pastan I, et al. Increased effectiveness of liposome-encapsulated doxorubicin in multidrug-resistant-transgenic mice compared with free doxorubicin. J Natl Cancer Inst 1992 84(10) 804-805. 

In phase I clinical trials children with recurrent or refractory tumors previously treated with free doxorubicin were administered i.v. Doxil in various doses (40-70mg/m2) in order to determine the best tolerated one [391], It was concluded that the maximum tolerated dose was 60mg/m2 because at the highest, 70mg/m2, some patients developed mucositis, so dose adjustment was necessary. 

The superiority of doxorubicin targeted with the aid of poly(alkylcyanoacrylate) nanospheres was later confirmed in a murine hepatic metastases model (M5076 reticulosarcoma). Irrespective of the dose and the administration schedule, the reduction in the number of metastases was much greater with doxorubicin-loaded nanospheres than with free doxorubicin, particularly if treatment was given only when the metastases were... 

No significant difference was observed in the survival rate of MCF7 treated with free-Doxorubicin or NP-doxorubicin. In contrast, for doxorubicin R MCF7, the IC50 for doxorubicin was 130-fold lower when NP-doxorubicin were used instead of free-doxorubicin. These results indicated that nanospheres provided an effective carrier for introducing a cytotoxic dose of doxorubicin into the pleiotropic resistant human cancer cell line Doxorubicin R MCF7. 

Nemati, F. Dubernet, C. Colin de Verdifere, A. Poupon, M.F. Treupel Acar, L. Puisieux, F. Couvreur, P. Some parameters influencing cytotoxicity of free doxorubicin loaded nanoparticles in sensitive and multidrug resistant leucemic murine cells incubation time, number of particles per cell. Int. J. Pharm. 1994, 102, 55-62. 

Caelyx has linear pharmacokinetics and its disposition occurs in two phases, the first relatively short (5 hours) and the second prolonged (55 hours). Unlike free doxorubicin, most of the pegylated liposomal doxorubicin is... 

Myocet (75 mg/m ) causes significantly less vomiting (11 versus 23%) than conventional free doxorubicin (75 mg/m ) (20). It also leads to lower peak-free doxorubicin... 

Harris L, Winer E, Batist G, Rovira D, Navari R, Lee L the TLC D-99 Study Group. Phase III study of TLC D-99 (liposome encapsulated doxorubicin) vs. free doxorubicin in patients with metastatic breast cancer (Abstract 26). Proc Am Soc Clin Oncol 1998 17 A474. 

However, the administration of free doxorubicin often leads to dose-limiting side effects such as cardiotoxicity and myelosu-pression. This toxicity can be reduced by liposomal encapsulation of doxorubicin because of the modified biodistribution of the drug (1). Additionally, the efficiency of the drug is improved due to the passive targeting effect of liposomes. 

Liposomes have emerged as efficient drug delivery systems for anticancer agents. A liposomal formulation of doxorubicin, Caelyx , is used in routine clinical use for cancer treatment (1,2). Compared with free doxorubicin, Caelyx provides preferred accumulation in tumors and consequently reduced side effects. Caelyx is a non-targeted stealth liposome formulation of encapsulated doxorubicin. Due to a long circulation half-life, Caelyx accumulates in tumors by the EPR (enhanced permeability and... 

Different doxorubicin liposome samples including a commercially available doxorubicin liposome (Caelyx ) and free doxorubicin are added to result in a final doxorubicin concentration of 50pM in the cell culture supernatant. 

The amount of doxorubicin is calculated using a pre-determined standard curve derived from a serial dilution of free doxorubicin. 

The medium is replaced with serially diluted liposome samples and free doxorubicin (from 0.7 to 50pM doxorubicin) in 200 pi fresh media. 

Laurand, A. Laroche-Clary, A. Larrue, A. Huet, S. Soma, E. Bonnet, J. Robert, J. Quantification of the expression of multidrug resistance-related genes in human tumour ceU lines grown with free doxorubicin or doxorubicin encapsulated in polyisohexylcyanoacrylate nanospheres. Anticancer Res. 2004, 24, 3781-3788. 

Next, in order to determine whether a self-immolative connector was essential or not when the enzyme specifier was linked at NH2-3 on the daunosamine unit of an anthracycline, we decided to prepare the prodrug 48. Enzymatic cleavage of 48, if it occured, would give rise to a carbamic acid, unstable at physiological pH, which would immediately release free doxorubicin [63]. 

Hydrolysis of the galactosyl unit of 52 would produce a bis-carbamate intermediate. After release of C02, the resulting para-aminobenzylcarbamate, known to undergo spontaneous 1,6-elimination (52) under mild conditions, should lead to free doxorubicin (2) and another molecule of C02. Synthesis of prodrug 52 involved initial condensation of 2,3,4,6-tetra-O-acetyl-a-D-galactopyranose (49) with para-tolyl isocyanate in DMF to afford carbamate 53. Benzylic bromination of 53 to 54 was followed by solvolysis into primary alcohol 55. Activation of 55 to 56 was achieved by use of 4-nitrophenyl chloroformate. Further condensation of 56 with doxorubicin (2) in DMF gave 57 which was finally deprotected by transesterification to yield prodrug 52 [63]. 

As for the previous prodrugs, compound 52 displayed very low cytoxicity when compared to the parent compound, and it was fairly stable in plasma for 24 hours. In contrast with the simple carbamate 48, prodrug 52 was readily hydrolyzed by green coffee bean a-D-galactosidase to afford free doxorubicin [63],... 

In vitro cleavage of 73 by the fusion protein consisting of the humanized anti-carcinoembryogenic monoclonal antibody and the human (3-D-glucuronidase (48) was investigated (69). About 50 per cent of the prodrug was converted into free doxorubicin within 5 hours at pH 7.2 and... 

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