Magainin peptides, isolated from Xenopus skin, have broad spectra of antimicrobial activity and low toxicities to normal eukaryotic cells, thus being good candidates for therapeutic agents. The mechanism of action is considered to be the permeabilization of bacterial membranes. A number of studies using lipid vesicles have elucidated its molecular detail. However, their interactions with bacteria are not yet well understood. In this paper, we synthesized several magainin analogs with different charges (0 to +6) and hydrophobicities, and systematically studied their interactions with the outer and inner membranes of three species of Gram-negative bacteria (Escherichia coli, Acinetobacter calcoaceticus, Proteus vulgaris). The treatment of the E. coli cells with native magainin 2 (+4) immediately induced the efflux of the intracellular K+ ions and the cell death. A number of blebs were formed on the bacterial surface and the outer membrane became leaky. An increase in the peptide's positive charge enhanced the outer membrane permeabilization and the bactericidal activity. The cationic peptides also effectively permeabilized the inner membranes rich in acidic phospholipids, indicating the importance of electrostatic interactions. Substitution of Trp for Phe simultaneously increased the bactericidal activity and the hemolytic activity. A strategy to develop potent antimicrobial peptides was discussed on the basis of these results.

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Anthracyclines have long been considered to be among the most active agents clinically available for the treatment of breast cancer despite their toxicity. To improve their pharmacological profiles, a new macromolecular prodrug, denoted NC-6300, was synthesized. NC-6300 comprises epirubicin covalently bound to polyethyleneglycol polyaspartate block copolymer through an acid-labile hydrazone bond. The conjugate forms a micellar structure spontaneously in aqueous media with a diameter of 60-70 nm. The block copolymers are partially substituted with hydrophobic benzyl groups to stabilize the micellar structure. The present study was designed to confirm that polymeric micelles incorporating epirubicin through an acid-labile linker improve the therapeutic index and achieve a broad range of therapeutic doses. Pharmacokinetic studies in rats showed highly enhanced plasma retention of NC-6300 compared with native epirubicin. The maximal tolerated doses in mice of NC-6300 and native epirubicin were 25 and 9 mg/kg, respectively, when administered three times with a 4-day interval between each dose. NC-6300 at 15 and 20 mg/kg with the same administration schedule regressed a Hep3B human hepatic tumor with slight and transient bodyweight loss. Remarkably, NC-6300 also inhibited growth of an MDA-MB-231 human breast tumor at the same dosage. In contrast, native epirubicin at 7 mg/kg administered three times with a 4-day interval was only able to slow tumor growth. Tissue distribution studies of NC-6300 showed efficient free epirubicin released in the tumor at 74% by area under the concentration-time curve (AUC) evaluation, supporting the effectiveness of NC-6300. In conclusion, NC-6300 improved the potency of epirubicin, demonstrating the advantage of NC-6300 attributable to the efficient drug release in the tumor. (Cancer Sci 2011; 102: 192-199) A nthracyclines were first introduced for the treatment of metastatic breast cancer in the 1970s and are still among the most active single agents for the treatment of this disease despite their cardiotoxicity.(1) The aim of increasing their efficacy was first addressed using liposomes.(2) Efforts to design liposomes that are pH-sensitive, temperature-sensitive or antibody-targeted have all been pursued with various degrees of success.(3) However, current clinically approved liposomal formulations have still resulted in only modest increased efficacy for the treatment of cancer.(4) Its actual advantage is reduced toxicity rather than increased therapeutic effect. To increase the efficacy, polymer-based anthracyclines have also been studied extensively. (8,9) Recent strategies have been developed and successfully applied to attain desirable tumor localization through polymeric micelles composed of polyethylene glycol (PEG)-poly (amino acid) block copolymers.(10) These types of strategies involve drug release inside endosomes and lysosomes after cellular internalization, where the slightly acidic pH leads to cleavage of the acid-sensitive linkage.

Epirubicin is widely used to treat various human tumors. However, it is difficult to achieve a sufficient antitumor effect because of dosage limitation to prevent cardiotoxicity. We hypothesized that epirubicin-incorporating micelle would reduce cardiotoxicity and improve the antitumor effect. NC-6300 comprises epirubicin covalently bound to PEG polyaspartate block copolymer through an acid-labile hydrazone bond. The conjugate forms a micellar structure of 40-80 nm in diameter in an aqueous milieu. NC-6300 (10, 15 mg ⁄ kg) and epirubicin (10 mg ⁄ kg) were given i.v. three times to mice bearing s.c. or liver xenograft of human hepatocellular carcinoma Hep3B cells. Cardiotoxicity was evaluated by echocardiography in C57BL ⁄ 6 mice that were given NC-6300 (10 mg ⁄ kg) or epirubicin (10 mg ⁄ kg) in nine doses over 12 weeks. NC-6300 showed a significantly potent antitumor effect against Hep3B s.c. tumors compared with epirubicin. Moreover, NC-6300 also produced a significantly longer survival rate than epirubicin against the liver orthotopic tumor of Hep3B. With respect to cardiotoxicity, epirubicin-treated mice showed significant deteriorations in fractional shortening and ejection fraction. In contrast, cardiac functions of NC-6300 treated mice were no less well maintained than in control mice. This study warrants a clinical evaluation of NC-6300 in patients with hepatocellular carcinoma or other cancers. (Cancer Sci 2013; 104: 920-925) H epatocellular carcinoma (HCC) is the fifth most common cancer and the third largest cause of cancer mortality worldwide.(1,2) The range of available oncological treatment for HCC is sometimes limited due to poor liver function caused by concomitant chronic liver disease, especially liver cirrhosis, which is mainly the result of hepatitis virus infection. Surgical resection is widely considered the mainstay for curative treatment and yields a certain survival rate. However, <20% of patients with HCC can undergo surgical resection. (3,4) With the exception of patients at an early stage and with adequate liver function, recurrence rates after surgical resection are unfortunately high. High recurrence rates are also seen in patients treated by other local treatment options, such as ablation, percutaneous ethanol injection, and trans-arterial chemoembolization.(5) For advanced HCC, the only available option is sorafenib, a tyrosine kinase inhibitor, which was recently approved; however, the survival rate associated with its use is far from satisfactory.