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Many macromolecular drug conjugates have been developed for the purpose of optimizing the pharmacokinetic profile of anti-tumor drugs. The drugs are chemically coupled to these macromolecules, enabling them to be transported through the bloodstream and to be delivered to tumor tissues without being metabolized. Macromolecules are well known to accumulate in the tumor tissue through a mechanism known as the "enhanced permeability and retention (EPR) effect."1)The use of macromolecules for the delivery of doxorubicin (DXR) [2][3][4] to tumors was investigated in a previous study 5) and is believed to enhance efficacy and reduce systemic side effects. 6) Recently, the N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-DXR conjugate, called PK1, has entered clinical development in the UK 7,8) and its Phase 1 results 9) showed that by conjugating the drug with a macromolecule, its distribution properties could be altered depending on the properties of the carrier macromolecules. 10,11) Various macromolecules, such as immunoglobulins, 12) albumin, 13) polyaminoacids, [14][15][16][17][18][19] synthetic polymers, 20,21) and polysaccharides, [22][23][24][25] have traditionally been used as drug carriers; however, this approach does not always produce the desired results in vivo since the distribution characteristics of these drug carriers has so far not been characterized and, therefore, is not well known. In particular, there is not enough information about the distribution properties and physicochemical characteristics of polysaccharides to select suitable drug carriers for tumor targeting.The present study focused on the relationship between the tissue distribution of macromolecular carriers derived from naturally occurring polysaccharides, and their physicochemical characteristics, namely, molecular weight (MW) and electric charge, or as it is often called, degree of substitution (DS). These have been reported by Nishikawa et al. 26) to play an important role in tissue distribution. The macromolecules selected as drug carriers were polysaccharide derivatives: CMDex, CMMG, CMCh, HA, and DSH. The choice was based on the reasoning that: (a) these polysaccharide derivatives are potentially biocompatible; (b) they contain a large number of carboxyl groups for drug attachment and provide sufficient carrying capacity for the drug; and (c) the resulting drug conjugates promised to be water-soluble. Having previously investigated some of the characteristics of D-manno-Dglucan (MG) and its derivatives, 27,28) we decided to decrease their anticoagulant activity by selectively N-desulfating and then N-acetylating 29) heparin. To test the relationship between the molecular weight and anionic charge (MW and DS of CM groups) of these polysaccharide carriers to their tissue distribution, carrier-DXR conjugates were prepared by binding their components directly or via a GGFG spacer. Their respective antitumor effects were then tested in vivo on Walker 256 carcinosarcomabearing rats. It was shown that polymeric modification of DXR ...

Paclitaxel (Taxol ® ), an anti-microtubule agent isolated from the trunk bark of the Pacific Yew tree, Taxus brevifolia, 1) shows great promise as an anti-neoplastic agent for a variety of human cancers including breast, ovarian, non small cell lung, head and neck cancers, leukemia, and melanoma. [2][3][4][5][6] Its unique mechanism of action is related to its ability to promote microtubule assembly and inhibit cell replication in the late G2 or M phases of the cell cycle.7) A major problem associated with the administration of paclitaxel is its low solubility in water as well as in most pharmaceutically acceptable solvents. 21,22) and polymer-bound derivatives. 23,24) Although some of the dosage forms can be solubilized to release sufficient quantities of paclitaxel and have shown improved anti-tumor effects in animal models, problems-such as stability-have been observed.25) The use of macromolecules for the targeted delivery of anticancer agents has generated considerable interest regarding enhancing therapeutic efficacy and reducing systemic side effects, and some satisfactory results have been obtained. 26) We previously reported how to prepare carboxymethyldextran (CMDex) and doxorubicin (DXR) conjugates using a peptide linker, and in our evaluation we showed that CMDex with a suitable anionic nature and MW of more than 150 kDa increased retention of the conjugate in blood circulation and increased accumulation of DXR in tumors.27) Furthermore, CMDex-peptide-DXR conjugates containing a gly-gly-phegly spacer were more efficacious in a Walker-256 carcinoma rat model than a free DXR or a conjugate with no spacer. We chose CMDex as a candidate for a paclitaxel carrier since: CMDex is biocompatible; it contains a large number of carboxyl groups for the drug attachment and provides sufficient carrying capacity of the drug; and the resulting CMDex-drug conjugate has a high probability of being water-soluble.In this paper, we examine the synthesis and evaluation of CMDex-paclitaxel conjugates bound with an ester bond and using amino acid linkers, namely, gly, ala, leu, and ile. We also look at how polymeric modification of paclitaxel with CMDex significantly improves water solubility and antitumor activity. The gly linker was introduced into the 2Ј-hydroxyl group to form CMDex-2Ј-gly-paclitaxel and into the 7-hydroxyl group to form CMDex-7-gly-paclitaxel. All other amino acid linkers-ala, leu, and ile-were introduced only into the 2Ј-hydroxyl group of paclitaxel. These were all designed to be water-soluble. The amounts of paclitaxel released from the conjugates during incubation with a buffer and mouse plasma at 37°C were measured by HPLC. We compared this to their in vivo tumor distribution and in vivo anti-tumor effects in a paclitaxel resistant tumor mouse model (colon 26). The tumor and body weights of the mice were monitored after continuous intravenous administration. Paclitaxel was bound via its hydroxyl group to carboxymethyldextran (CMDex, 150 kDa) by means of an amino acid linker; the linker was intr...

Paclitaxel shows great promise as an anti-neoplastic agent for a variety of human cancers, including ovarian, breast, and non-small cell lung cancer and acquired immune deficiency syndrome (AIDS)-related Kaposi's sarcoma.1-6) Docetaxel and paclitaxel together form the drug category of taxanes. However, its low solubility in water is a major problem associated with the administration of paclitaxel. Side effects including nausea, vomiting, diarrhea, mucositis, myelosuppression, cardiotoxicity and neurotoxicity were reported. 7,8) Various alternative dosage forms for paclitaxel delivery have been developed to increase efficacy, decrease toxicity, and improve solubility of paclitaxel without using Cremophor ® EL, and many have entered phase I-III trials as intravenously injectable anticancer agents. For example, there are many on going phase II-III studies for polyglutamatepaclitaxel (CT-2103, XYOTAX) as well as phase I studies for polymeric micelle-formulated paclitaxel (Genexol-PM) and paclitaxel-incorporating micellar nanoparticle formulation (NK105). 9) Recently, an albumin-stabilized nanoparticle formulation of paclitaxel (Abraxane, ABI-007), 10) which was designed to overcome insolubility problems encountered with paclitaxel, has gained approval from the Food and Drug Administration (FDA) for treatment of metastatic breast cancer.These macromolecular prodrugs are thought to accumulate in tumors as a result of the enhanced permeability and retention (EPR) effect.11) This effect relies on the fact that tumors usually have hyperpermeable vasculatures, allowing longer circulating macromolecules to pass out through the leaky vessels into tumor tissue, from which there is no readily available returning lymphatic route.12) Long-circulating macromolecules-including albumin, polymer conjugates, polymeric micelles, and liposome-are well known to accumulate passively in solid tumors by the EPR effect. Therefore, intravenously administered drug-delivery systems would increase the concentration of antitumor drugs in tumor. For example, the polymer-protein conjugate styrene maleic anhydride-neocarzinostatin (SMANCS) was originally synthesized by Maeda H. and was subsequently approved in Japan as a treatment for hepatocellular carcinoma. 13)Molecular weight (MW) and electric charges of conjugates are critical to achieve effective tumor targeting.14) Macromolecules with MWs greater than roughly 70 kDa and weak anionic charges are known to circulate in blood for a long time due to small hepatic uptake and urinary excretion clearance.15) Such macromolecules are expected to accumulate in tumors effectively after intravenous administration. AZ10992 was thus designed to have the MW of approximately 150 kDa, weak anionic charges, and a peptidyl linker (GlyGlyPheGly) to provide an appropriate release rate of paclitaxel with time-dependent cytocidal activity. Our previous study demonstrated the proof of our design in terms of therapeutic efficacy. 16)However, further studies are required to provide crucial information about safety pr...