A folate receptor-α-specific ligand that targets cancer tissue and not sites of inflammation

Balasubramanian Vaitilingam, Venkatesh Chelvam, Sumith A. Kularatne, Scott Poh, Wilfredo Ayala-Lopez, Philip S. Low

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Folic acid has been frequently exploited to target attached drugs to cells that overexpress a folate receptor (FR). Unfortunately, folic acid and folate-linked drugs bind equally well to both major isoforms of the FR-that is, FR-α, which is primarily expressed on malignant cells, and FR-β, which is upregulated on activated monocytes and macrophages. Because both major isoforms of FR can be expressed simultaneously in the same organism, folic acid cannot enable selective targeting of therapeutic and imaging agents to either tumor masses or sites of inflammation. In an effort to develop a targeting ligand that can selectively deliver attached imaging and therapeutic agents to tumor cells, we constructed a reduced and alkylated form of folic acid, N 5, N10-dimethyl tetrahydrofolate (DMTHF) that exhibits selectivity for FR-α. Methods: DMTHF-99mTc was injected into mice bearing FR-α-expressing tumor xenografts and imaged by γ-scintigraphy. The selectivity for FR-α over FR-β in vivo was examined by γ-scintigraphic images of animal models of various inflammatory diseases such as apolipoprotein E-deficient mice with atherosclerosis, DBA/1 LacJ mice with induced arthritis, C57BL/6J mice with muscle injury, and BALB/C mice with both FR-α tumor and ulcerative colitis, by administration of equal doses of DMTHF-99mTc and EC20-99mTc. The uptake of radiochelates in various organs was quantified by biodistribution studies. DMTHF-near-infrared dye conjugate and DMTHF-Oregon green dye conjugates were synthesized and evaluated for FR-α selectivity over FR-β in rat peritoneal macrophages and human peripheral blood monocytes, respectively, by flow cytometry. Fluorescence-guided imaging was also performed using folate and DMTHF dye conjugates. Results: The new targeting ligand was found to bind malignant cells in mice with solid tumor xenografts but not peripheral blood monocytes or inflammatory macrophages in animal models of atherosclerosis, rheumatoid arthritis, muscle injury, or ulcerative colitis. Results from optical and radioimaging studies and biodistribution experiments confirm the differential specificity of this new ligand for malignant masses. Conclusion: The new targeting ligand DMTHF enables selective noninvasive imaging and therapy of tumor tissues in the presence of inflammation.

Original languageEnglish (US)
Pages (from-to)1127-1134
Number of pages8
JournalJournal of Nuclear Medicine
Volume53
Issue number7
DOIs
StatePublished - Jul 1 2012

Keywords

  • Folate receptor alpha specific ligand
  • Optical and radioimaging of tumors
  • Tumor-targeted therapy

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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