Pharmacokinetically stabilized cystine knot peptides that bind Alpha-v-Beta-6 integrin with single-digit nanomolar affinities for detection of pancreatic cancer

Richard H. Kimura, Robert Teed, Benjamin J. Hackel, Marybeth A. Pysz, Courtney Z. Chuang, Ataya Sathirachinda, Jürgen K. Willmann, Sanjiv S. Gambhir

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

Purpose: Detection of pancreatic cancer remains a high priority and effective diagnostic tools are needed for clinical applications. Many cancer cells overexpress integrin α vβ 6, a cell surface receptor being evaluated as a novel clinical biomarker. Experimental Design: To validate this molecular target, several highly stable cystine knot peptides were engineered by directed evolution to bind specifically and with high affinity (3-6 nmol/L) to integrin α vβ 6. The binders do not cross-react with related integrin α vβ 5, integrin α 5β 1, or tumor-angiogenesis-associated integrin, α vβ 3. Results: Positron emission tomography showed that these disulfide-stabilized peptides rapidly accumulate at tumors expressing integrin α vβ 6. Clinically relevant tumor-to-muscle ratios of 7.7 ± 2.4 to 11.3 ± 3.0 were achieved within 1 hour after radiotracer injection. Minimization of off-target dosing was achieved by reformatting α vβ 6-binding activities across various natural and pharmacokinetically stabilized cystine knot scaffolds with different amino acid content. We show that the primary sequence of a peptide scaffold directs its pharmacokinetics. Scaffolds with high arginine or glutamic acid content suffered high renal retention of more than 75% injected dose per gram (%ID/g). Substitution of these amino acids with renally cleared amino acids, notably serine, led to significant decreases in renal accumulation of less than 20%ID/g 1 hour postinjection (P < 0.05, n = 3). Conclusions: We have engineered highly stable cystine knot peptides with potent and specific integrin avb6-binding activities for cancer detection. Pharmacokinetic engineering of scaffold primary sequence led to significant decreases in off-target radiotracer accumulation. Optimization of binding affinity, specificity, stability, and pharmacokinetics will facilitate translation of cystine knots for cancer molecular imaging.

Original languageEnglish (US)
Pages (from-to)839-849
Number of pages11
JournalClinical Cancer Research
Volume18
Issue number3
DOIs
StatePublished - Feb 1 2012

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