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Covalent cross-linking approaches for all-trans retinoic acid-loaded thermo-responsive hydrogels

Xueli Mei1, Robert C Stewart2, Xiao Zhen Zhou2,3,4

  • 1Department of Chemistry, The University of Western Ontario, 1151 Richmond St., London, Ontario N6A 5B7, Canada. egillie@uwo.ca.

Soft Matter
|May 23, 2025
PubMed

Insights

Researchers developed a new injectable hydrogel for controlled release of all-trans retinoic acid (ATRA), a cancer therapy. The azide-alkyne cross-linked hydrogel showed promising drug release and stability for cancer treatment applications.

Area of Science:

  • Biomaterials Science
  • Polymer Chemistry
  • Drug Delivery Systems

Background:

  • All-trans retinoic acid (ATRA) shows therapeutic potential for various cancers but faces limitations like poor solubility and short in vivo half-life.
  • Injectable controlled-release systems are crucial for overcoming ATRA's delivery challenges.
  • Thermo-responsive poly(caprolactone-co-lactide)-poly(ethylene glycol)-poly(caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers offer a basis for such systems.

Purpose of the Study:

  • To investigate and compare covalent cross-linking strategies for stabilizing thermo-responsive PCLA-PEG-PCLA hydrogels for ATRA delivery.
  • To evaluate the impact of different cross-linking methods on hydrogel properties and ATRA encapsulation/release.
  • To assess the in vitro efficacy of ATRA-loaded hydrogels in a cancer cell model.

Main Methods:

  • Synthesis of azide end-capped PCLA-PEG-PCLA and cross-linking via strain-promoted azide-alkyne cycloaddition with 4-arm-PEG-DIBAC.
  • Comparison of azide-alkyne hydrogels with methacrylate-based hydrogels (free radical and thiol-Michael addition) and non-covalently cross-linked systems.
  • Encapsulation of all-trans retinoic acid (ATRA) and evaluation of its release kinetics over two weeks.
  • Assessment of ATRA-loaded hydrogel's effect on MDA-MB-468 cell proliferation.

Main Results:

  • Thiol-Michael addition failed to form gels; azide-alkyne cycloaddition successfully formed stable hydrogels.
  • Azide-alkyne hydrogels demonstrated properties intermediate between free radical and non-covalently cross-linked gels.
  • ATRA incorporation moderately affected azide-alkyne hydrogel properties but significantly disrupted free radical cross-linking.
  • ATRA was released over approximately two weeks, and ATRA-loaded gels inhibited cancer cell proliferation.

Conclusions:

  • Strain-promoted azide-alkyne cycloaddition provides a viable method for creating stable, injectable ATRA-releasing hydrogels from PCLA-PEG-PCLA copolymers.
  • The developed hydrogel system offers controlled release of ATRA, maintaining its therapeutic activity.
  • This approach holds promise for improving cancer therapy through enhanced drug delivery.

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