Hydra-Elastin-like Polypeptides Increase Rapamycin Potency When Targeting Cell Surface GRP78

Area of Science:

• Biotechnology
• Cancer Therapeutics
• Drug Delivery Systems

Background:

• Rapalogues are effective breast cancer treatments but have poor solubility and dose-limiting toxicities.
• Existing drug carriers often lack targeted delivery, limiting their efficacy and increasing side effects.

Purpose of the Study:

• To develop a long-circulating, targeted drug carrier for enhanced breast cancer therapy.
• To improve rapamycin delivery and efficacy by conjugating it to elastin-like polypeptides (ELPs) and targeting cell surface GRP78 (csGRP78).

Main Methods:

• Development of a multiheaded drug carrier (5FA) using ELPs and rapamycin-binding domains.
• Conjugation of 5FA with peptides targeting csGRP78 to create targeted carriers.
• Characterization using light scattering and mass spectrometry.
• In vitro evaluation in BT474 breast cancer cells, including cellular uptake (flow cytometry), proteolysis susceptibility (SubA), and mTORC1 inhibition (Western blot for pS6K).
• Visualization of carrier localization using super-resolution confocal laser scanning microscopy.

Main Results:

• Targeted carriers demonstrated enhanced cellular uptake and susceptibility to csGRP78-specific proteolysis (SubA).
• The best carrier, L-5FA, reduced mTOR activity by 3-fold compared to non-targeted carriers or free rapamycin.
• Targeting increased carrier exposure by approximately 8-fold, as visualized by microscopy.

Conclusions:

• Peptide ligands for GRP78 can be effectively incorporated into protein-based drug carriers to enhance targeted delivery in breast cancer.
• This approach offers a promising strategy to overcome the limitations of solubility and side effects associated with rapamycin therapy.