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Research Articles: Therapeutics, Targets, and Development

Anti-CD30 diabody-drug conjugates with potent antitumor activity

Seattle Genetics, Inc., Bothell, Washington

Requests for reprints: Kristine M. Kim, Seattle Genetics, Inc., 21823 30th Drive Southeast, Bothell, WA 98021. Phone: 425-527-4644; Fax: 425-527-4609. E-mail: kkim{at}seagen.com

Abstract

Anti-CD30 diabodies were engineered with two cysteine mutations for site-specific drug conjugation in each chain of these homodimeric antibody fragments. Diabodies were conjugated with 4 equivalents of the anti-tubulin drugs, monomethyl auristatin E or F, via a protease-cleavable dipeptide linker, to create the conjugates, diabody-vcE4 and diabody-vcF4, respectively. Diabody conjugation had only minor (<3-fold) effects on antigen binding. Diabody-vcF4 was potently cytotoxic against the antigen-positive cell lines, Karpas-299 (34 pmol/L IC₅₀) and L540cy (22 pmol/L IC₅₀), and was 8- and 21-fold more active than diabody-vcE4 against these cell lines, respectively. Clearance of diabody-vcF4 (99-134 mL/d/kg) was 5-fold slower than for the nonconjugated diabody in naive severe combined immunodeficient mice. Diabody-vcF4 had potent and dose-dependent antitumor activity against established Karpas-299 xenografts and gave durable complete responses at well-tolerated doses. Biodistribution experiments with diabody-[³H]-vcF4 (0.72-7.2 mg/kg) in tumor-bearing mice showed a dose-dependent increase in total auristatin accumulation in tumors (520 nmol/L) and decrease in relative auristatin accumulation (8.1 %ID/g), with peak localization at 4 to 24 h after dosing. Diabody-vcF4 had 4-fold lower cytotoxic activity than the corresponding IgG1-vcF4 conjugate in vitro. A similar potency difference was observed in vivo despite 25- to 34-fold faster clearance of diabody-vcF4 than IgG1-vcF4. This may reflect that dose-escalated diabody-vcF4 can surpass IgG1-vcF4 in auristatin delivery to tumors, albeit with higher auristatin exposure to some organs including kidney and liver. Diabody-drug conjugates can have potent antitumor activity at well-tolerated doses and warrant further optimization for cancer therapy. [Mol Cancer Ther 2008;7(8):2486–97]

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Note: K.M. Kim and C.F. McDonagh contributed equally to this work.

Current address for P.J. Carter: VLST, Inc., 307 Westlake Avenue North, Suite 300, Seattle, WA 98100.

Current address for C.F. McDonagh: Merrimack Pharmaceuticals, One Kendall Square, Cambridge, MA 02139.

¹ http://www.equinoxppu.com

² Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

Received 4/23/08; revised 6/ 4/08; accepted 6/ 6/08.