This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Burkhart, D. J. Articles by Koch, T. H. Search for Related Content PubMed PubMed Citation Articles by Burkhart, D. J. Articles by Koch, T. H.

Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado

Requests for reprints: Tad H. Koch, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215. Phone: 303-492-6193; Fax: 303-492-5894. E-mail: tad.koch{at}colorado.edu

We have reported the synthesis and biological evaluation of a prodrug to a doxorubicin active metabolite. Under physiologic conditions, release of the active metabolite, a conjugate of doxorubicin with formaldehyde, occurs with a half-life of 1 hour. To direct this prodrug to tumor, we designed two conjugates of the prodrug, doxsaliform, with the _vß₃-targeting peptides, CDCRGDCFC (RGD-4C) and cyclic-(N-Me-VRGDf) (Cilengitide). We now report the synthesis of these doxsaliform-peptide conjugates and their evaluation using MDA-MB-435 cancer cells. A hydroxylamine ether tether was used to attach 5''-formyldoxsaliform to RGD-4C in its acyclic form via an oxime functional group. The construct acyclic-RGD-4C-doxsaliform showed good binding affinity for _vß₃ in the vitronection cell adhesion assay (IC₅₀ = 10 nmol/L) and good growth inhibition of MDA-MB-435 breast cancer cells (IC₅₀ = 50 nmol/L). In its bicyclic forms, RGD-4C showed less affinity for _vß₃ and significantly less water solubility. Cyclic-(N-Me-VRGDf) was modified by substitution of D-4-aminophenylalanine for D-phenylalanine to provide a novel attachment point for doxsaliform. The conjugate, cyclic-(N-Me-VRGDf-NH)-doxsaliform, maintained a high affinity for _vß₃ (IC₅₀ = 5 nmol/L) in the vitronectin cell adhesion assay relative to the peptide bearing only the tether (0.5 nmol/L). The IC₅₀ for growth inhibition of MDA-MB-435 cells was 90 nmol/L. Flow cytometry and growth inhibition experiments suggest that the complete drug construct does not penetrate through the plasma membrane, but the active metabolite does on release from the targeting group. These drug conjugates could have significantly reduced side effects and are promising candidates for in vivo evaluation in tumor-bearing mice.

Key Words: Doxorubicin • Doxsaliform • RGD peptide • _vß₃ • MDA-MB-435

Grant support: U.S. Army Prostate Cancer Research Program grant DAMD 17-01-1-0046; National Cancer Institute of the NIH grant CA-92107; and University of Colorado Council for Research and Creative Work faculty fellowship (T.H. Koch). The National Science Foundation helped with the purchase of NMR equipment (grant CHE-0131003).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 7/29/04; revised 9/ 4/04; accepted 9/29/04.