Multivalent Presentation of Peptide Targeting Groups Alters Polymer Biodistribution to Target Tissues

Area of Science:

• Biomaterials Science
• Drug Delivery
• Orthopedics

Background:

• Bone drug delivery faces challenges with low distribution (<1%) and poor localization to remodeling sites.
• Existing hydroxyapatite-targeted systems lack specificity for osteoclasts or osteoblasts within bone.
• Targeting bone-acting drugs to active bone remodeling sites is crucial for effective treatment.

Purpose of the Study:

• To synthesize and evaluate oligo(ethylene glycol) copolymers with TRAP-binding peptides for targeted bone delivery.
• To investigate the impact of peptide orientation (gradient vs. random) and polymer molecular weight on bone targeting.
• To enhance specificity for bone cell drugging by targeting tartrate-resistant acid phosphatase (TRAP).

Main Methods:

• Synthesis of oligo(ethylene glycol) copolymers with varying peptide orientations and molecular weights.
• In vivo evaluation of copolymer accumulation in bone remodeling sites (fractures).
• Quantification of drug distribution and residence time at fracture sites.

Main Results:

• High molecular weight (M_n) random copolymers demonstrated superior accumulation (14% of tissue distribution) in remodeling bone for over 1 week.
• Intermediate and low M_n random copolymers showed reduced accumulation, indicating M_n dependence of residence time.
• High M_n gradient polymers exhibited low accumulation (2% at fractures after 1 week), suggesting TRAP binding is sensitive to peptide density.

Conclusions:

• TRAP-targeted, high M_n random copolymers represent a promising platform for enhanced bone remodeling targeting.
• Polymer molecular weight and peptide density are critical, modifiable parameters for optimizing bone drug delivery.
• This versatile targeting strategy holds potential for various bone drug delivery applications.