Bifunctional PAMAM dendrimer conjugates of folic acid and methotrexate with defined ratio

Biomacromolecules. 2012 Apr 9;13(4):982-91. doi: 10.1021/bm201639c. Epub 2012 Mar 30.

Abstract

Our group previously developed a multifunctional, targeted cancer therapeutic based on Generation 5 (G5) polyamidoamine (PAMAM) dendrimers. In those studies we conjugated the targeting molecule folic acid (FA) and the chemotherapeutic drug methotrexate (MTX) sequentially. This complex macromolecule was shown to selectively bind and kill KB tumor cells that overexpress folate receptor (FR) in vitro and in vivo. However, the multistep conjugation strategy employed in the synthesis of the molecule resulted in heterogeneous populations having differing numbers and ratios of the functionally antagonistic FA and MTX. This led to inconsistent and sometimes biologically inactive batches of molecules, especially during large-scale synthesis. We here resolved this issue by using a novel triazine scaffold approach that reduces the number of dendrimer conjugation steps required and allows for the synthesis of G5 conjugates with defined ratios of FA and MTX. Although an unoccupied γ-glutamyl carboxylate of FA has been previously suggested to be nonessential for FR binding, the functional requirement of an open α-carboxylate still remains unclear. In an attempt to also address this question, we have synthesized isomeric FA dendrimer conjugates (α-carboxyl or γ-carboxyl linked). Competitive binding studies revealed that both linkages have virtually identical affinity toward FR on KB cells. Our studies show that a novel bifunctional triazine-based conjugate G5-Triazine-γMTX-αFA with identical numbers of FA and MTX binds to FR through a polyvalent interaction and induces cytotoxicity in KB cells through FR-mediated cellular internalization, inducing higher toxicity as compared to conjugates synthesized by the multistep strategy. This work serves as a proof of concept for the development of bifunctional dendrimer conjugates that require a defined ratio of two functional molecules.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology*
  • Cell Proliferation / drug effects
  • Dendrimers / chemistry*
  • Dendrimers / pharmacology*
  • Drug Screening Assays, Antitumor
  • Folic Acid / chemistry
  • Folic Acid / pharmacology*
  • Humans
  • KB Cells
  • Macromolecular Substances / chemical synthesis
  • Macromolecular Substances / chemistry
  • Macromolecular Substances / pharmacology
  • Methotrexate / chemistry
  • Methotrexate / pharmacology*
  • Molecular Structure
  • Structure-Activity Relationship
  • Tumor Cells, Cultured

Substances

  • Antineoplastic Agents
  • Dendrimers
  • Macromolecular Substances
  • PAMAM Starburst
  • Folic Acid
  • Methotrexate