Synthesis and antitumor activity of 6-O-carboxymethyl chitin fixing 5-fluorouracils through pentamethylene, monomethylene spacer groups via amide, ester bonds

Macromolecular Prodrugs of 5-Fluorouracil. 1: Synthesis and Hydrolytic Stability

The hydroxyl groups of poly(ethylene glycol), dextran and poly-[N5-(2-hydroxy-ethyl-L-glutamineI were activated using the 4-nitrophenyl chloroformate method. The resulting phenyl carbonate groups reacted quantitatively with the primary amine groups of oligopeptides with 2-(5-fluorouracil-1-yl) glycine ethyl ester moiety as C-terminus. Following this procedure, 5-fluorouracil-polymer conjugates with peptide chains of different amino acid sequences and configurations were synthesized. The conjugates showed a good hydrolytic stability in buffer solutions of pH 7.4 and 5.5, as well as in calf serum, which indicated good stability of the polymer-drug linkage in the blood.

In Vivo and in Vitro Antitumor Activity of CM-Chitin Immobilized Doxorubicins by Lysosomal Digestible Tetrapeptide Spacer Groups

In vivo and in vitro antitumor activities of macromolecular prodrugs of doxorubicin (DXR) using 6- O-carboxymethylchitin (CM-chitin) as a carrier polymer were investigated. In order to determine the effect of a spacer group between a drug and a carrier polymer on the antitumor activity, we employed two different spacer groups, a lysosomal digestible tetrapeptide (Gly-Phe-Leu-Gly) and a simple hydrophobic pentamethylene to immobilize DXR molecules to CM-chitin. The cytotoxic activity of the conjugates obtained were investigated against four kinds of tumor cell lines, p388D1 lymphocytic leukemia, L1210 leukemia, HLE human hepatoma and Hela utrocervical carcinoma cell in vitra The CM-chitin/Gly-Phe-Leu-Gly/DXR conjugate 1 with lysosomal digestible tetrapeptide spacer groups showed slightly higher in vitro cytotoxic activity against these tumor cells than CM-chitin/C5/DXR conjugate 2 with a simple pentamethylene spacer group. However, the cytotoxic activity of these two conjugates was weaker than that of the free DXR. The survival effects of these conjugates were investigated against p388 lymphocytic leukemia bearing mice in vivo by intraperitoneal (i.p.) implantation and intravenous (i.v.) injection. Although these conjugates did not show very high cytotoxic activities in vitro compared with the free DXR, conjugate 1, with the lysosomal digestible tetrapeptide spacer groups, exhibited survival effects against p388 lymphocytic leukemia in mice i.p./i.v. However, conjugate 2, with the simple pentamethylene spacer group, did not show any survival effects under the same conditions. These conjugates did not display an acute toxicity in the high dose ranges.

Controlled hydrophobic/hydrophilicity of chitosan for spheres without specific processing technique

Chitosan is functionalized with phthalic anhydride at the amino group and poly(ethylene glycol) methyl ether at the hydroxyl group via homogeneous reaction. The product regenerated forms particles in either aqueous solution or organic solvents. The particles are spheres with the size of few micrometers as observed from scanning electronmicroscopy. The present work demonstrates that by simply adjusting the hydrophilicity and hydrophobicity, we can directly obtain spheres without a specific processing technique.

Macromolecular Therapeutics

Macromolecular drugs (also referred to as polymeric drugs) are a diverse group of drugs including polymer-conjugated drugs, polymeric micelles, liposomal drugs and solid phase depot formulations of various agents. In this review we will consider only water-soluble macromolecular drugs. In common, such drugs have high molecular weights, more than 40 kDa, which enables them to overcome renal excretion. Consequently, this group of drugs can attain prolonged plasma or local half-lives. The prolonged circulating time of these macromolecules enables them to utilise the vascular abnormalities of solid tumour tissues, a phenomenon called the enhanced permeability and retention (EPR) effect. The EPR effect facilitates extravasation of polymeric drugs more selectively at tumour tissues, and this selective targeting to solid tumour tissues may lead to superior therapeutic benefits with fewer systemic adverse effects. This contrasts with conventional low-molecular-weight drugs, where intratumour concentration diminishes rapidly in parallel with plasma concentration. The EPR effect is also operative in inflammatory tissues, which justifies the development and use of this class of drugs in infectious and inflammatory conditions. At the present time, several polymeric drugs have been approved by regulatory agencies. These include zinostatin stimalamer (copolymer styrene maleic acid-conjugated neocarzinostatin, or SMANCS) and polyethyleneglycol-conjugated interferon-alpha-2a. This article discusses these and other polymeric drugs in the setting of targeting to solid tumours.

Intracellularly biorecognizable derivatives of 5-fluorouracil. Implications for site-specific delivery in the human condition

The release of 5-fluorouracil from polymer-based conjugates can be influenced by the type of linkages used to bind the drug to the polymer carrier. The use of specific oligopeptide sequences designed to be biorecognizable by intracellular enzymes is a promising approach for increasing the site-specific release of 5-fluorouracil from polymer-based conjugates. In this study, we investigated the biorecognizability of specific oligopeptide sequences linking 5-fluorouracil to a water-soluble copolymer carrier based on N-(2-hydroxypropyl) methacrylamide by human cathepsin B (EC 3.4.22.1), cathepsin H(EC 3.4.22.6), and a homogenate of the human colon adenocarcinoma cell line SW 480. The cathepsins were chosen based on the hypothesis that they were two principal lysosomal enzymes responsible for the release of 5-fluorouracil from these conjugates. Our results support this hypothesis; however, these two enzymes may not be the only lysosomal enzymes responsible for the release kinetics observed. While the results for cathepsin B corresponded well to our hypothesis, the cleavage via cathepsin H was lower than predicted, suggesting the presence of additional lysosomal enzymes with catalytic activity toward these 5-fluorouracil derivatives.