Bioconjugate Chem. 2002, 13, 1093−1099
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A Novel 2′-(N-Methylpyridinium Acetate) Prodrug of Paclitaxel Induces Superior Antitumor Responses in Preclinical Cancer Models Wolfgang Wrasidlo,† Gerhard Gaedicke,† Rodney Kiplin Guy,‡ Johanne Renaud,‡ Emmanuel Pitsinos,‡ Kyriaco C. Nicolaou,‡ Ralph A. Reisfeld,§ and Holger N. Lode*,† Charite´ Children's Hospital, Humboldt University, Berlin, Germany, and The Scripps Research Institute, Departments of Chemistry and Immunology, La Jolla, California 92037. Received April 1, 2002; Revised Manuscript Received July 30, 2002
The development of novel strategies for the treatment of malignancies by successful intervention in advanced stage disease is a major challenge in oncology. We tested the hypothesis that this can be achieved by the rational design of taxoid onium salts modified at C-7 and C-2′ positions. The characterization of these molecules revealed a dramatically improved water solubility and prodrug behavior in plasma. Specifically, all compounds released parental paclitaxel with half-lives ranging from 0.9 to 180 min. In the absence of plasma, only the 2′-(N-methylpyridinium acetate) derivative of paclitaxel (2′-MPA-paclitaxel) revealed a complete abrogation of paclitaxel specific microtubule assembly disassembly dynamics and a 3 log reduction in cellular binding, indicating that reversible blockage of the C-2′ position by methylpyridinium acetate yields a true paclitaxel prodrug. Structure/ activity profiles of all compounds in tissue culture revealed cytotoxicity effective at picomolar concentrations with a panel of 16 cancer cell lines in contrast to 4 nonmalignant cell lines. Importantly, the decisive cytotoxic potential observed in vitro for all compounds correlated only with in vivo findings for 2′-MPA-paclitaxel. Specifically, the 2′-MPA-paclitaxel prodrug induced regression of primary tumors in three xenograft models of nonsmall cell lung carcinoma, ovarian carcinoma and prostate cancer, in contrast to ineffective C-7 derivatives and parental paclitaxel. At the same time, a reduced systemic toxicity of 2′-MPA-paclitaxel was observed in contrast to a far more toxic parental paclitaxel. Taken together, these findings demonstrate that the 2′-MPA-paclitaxel prodrug is a promising new candidate for cancer therapy.
INTRODUCTION
Paclitaxel is an anticancer agent with established value for clinical application (1) including prostate, lung, breast, and ovarian cancer (2-11). However, limited response rates, significant side effects, and low solubility remain as major obstacles for more effective cancer therapy. Paclitaxel is a natural product gained from the bark of the pacific yew tree (Taxus brevifolia). Its chemical structure was first described by Wani at al. in 1971 (9). Unlike other anti-microtubule drugs, such as vinca alkaloids, colchicine, or podophyllotoxin, paclitaxel promotes the irreversible polymerization of tubulin (12-15). The presence of stable and dysfunctional microtubules causes disruption of the cell division and thus cell death or reversible cell cycle arrest. This arrest in the premitotic G2 and the mitotic phases, the so-called G2M-arrest, enhances the effect of irradiation and possibly the activity of other cytotoxic drugs (16). Paclitaxel also enhances the expression of tumor necrosis factor (TNF) R and IL-1 and downregulates TNF receptors, activities which are shared * To whom reprint requests should be addressed at Charite´ Children’s Hospital, Augustenburger Platz 1, 13353 Berlin, Germany. Phone: +49 30 450 559217; FAX: +49 30 450 559917; E-mail:
[email protected]. † Humboldt University. ‡ Scripps Research Institute, Department of Chemistry. § Scripps Research Institute, Department of Immunology.
by bacterial lipopolysaccharides. This cytokine stimulatory activity may also contribute to its antitumor properties and seems not to be related to the effect on microtubule assembly (17). Paclitaxel also induced internucleosomal DNA fragmentation associated with bcl-2 expression in leukemic cells, suggesting that its action triggers a gene-directed mechanism of programmed cell death (18). Toxicity consists mainly of hypersensitivity reactions, hematologic toxicity, and neurotoxicity. Hypersensitivity, despite proper premedication with dexametasone and/or histamine H2 antagonist diphenhydramine, is reported in 1-3% of patients (19-21). The clinical application of paclitaxel, which has a limited solubility in water (
