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Polymeric Tubulysin-Peptide Nanoparticles with Potent Antitumor Activity

Authors' Affiliations: ¹ Insert Therapeutics and ² Calando Pharmaceuticals, Pasadena, California; and ³ R&D Biopharmaceuticals, Martinsried, Germany

Requests for reprints: Thomas Schluep, Calando Pharmaceuticals, 129 N. Hill Avenue, Suite 104, Pasadena, CA 91106. Phone: 626-783-7200; Fax: 626-683-7220; E-mail: tschluep{at}calandopharma.com.

Purpose: Tubulysins are naturally occurring tetrapeptides with potent antiproliferative activity against multiple cancer cell lines. However, they are also highly toxic in animal models. In order to improve the therapeutic index of this class of compounds, a nanoparticle prodrug of tubulysin A (TubA) was synthesized and evaluated in vitro and in vivo.

Experimental Design: A thiol derivative of TubA was covalently attached to a linear, β-cyclodextrin based polymer through a disulfide linker (CDP-TubA). The polymer conjugate assembled into stable nanoparticles. Inhibition of tubulin polymerization and antiproliferative activity of the polymer conjugate were evaluated in vitro. The preclinical efficacy of CDP-TubA administered i.v. was evaluated in nude mice bearing s.c. implanted human HT29 colorectal and H460 non–small cell lung carcinoma tumors.

Results: The IC₅₀ of CDP-TubA (in Tub A equivalents) was 24, 5, and 10 nmol/L versus 3, 1, and 2 nmol/L for Tub A in NCI-H1299 (lung), HT-29 (colon), and A2780 (ovarian) cell lines, respectively. Tub A and the active thiol derivative were potent inhibitors of tubulin polymerization, whereas CDP-TubA showed minimal inhibition, indicating that target inhibition requires release of the peptide drug from the nanoparticles. The maximum tolerated dose of CDP-TubA was 6 mg/kg (in TubA equivalents) versus 0.05 mg/kg for TubA in nude mice. In vivo, a single treatment cycle of three weekly doses of CDP-TubA showed a potent antitumor effect and significantly prolonged survival compared with TubA alone.

Conclusions: Cyclodextrin polymerized nanoparticles are an enabling technology for the safe and effective delivery of tubulysins for the treatment of cancer.

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