Synthesis of water-soluble porphyrin-dendron conjugates for targeted photodynamic therapy

Bryden, Francesca

Abstract

The targeting of photosensitisers with tumour-associated biomolecules is widely used for improved photosensitiser tumour localisation during photodynamic therapy, allowing fewer side effects in comparison to conventional cancer treatments. In particular, conjugation to antibody fragments allows exploitation of their high affinity towards tumour-associated antigens; however current methods of conjugating porphyrins to antibody fragments represent a compromise between high binding ratios and good stoichiometric and site-specific control. The work presented herein addresses this problem through the synthesis of porphyrin-dendron conjugates and their attachment at the interchain disulfide bridge of antibody fragments, allowing improved binding ratios while maintaining good structural control.

Synthesis of a range of click-functionalised porphyrins and dendrons bearing complimentary peripheral functionalities was carried out, followed by click conjugation of these structures under microwave irradiation to produce a range of lipophilic and hydrophilic porphyrin-dendron conjugates with between two and four peripheral porphyrins. Photophysical evaluation demonstrated retention of UV-vis and fluorescent character of porphyrins after conjugation, with some quenching of UV-vis absorption observed due to the close proximity of the porphyrins. Singlet oxygen quantum yields showed some quenching in all conjugates, with more sterically hindered systems showing the greatest reduction in SOQY in comparison to control porphyrins.

Conjugation of porphyrins to a HER2-targeted Herceptin™ Fab fragment was carried out through pre-conjugation of an alkyne-dibromomaleimide heterobifunctional linker to the Fab fragment, with two examples of cationic porphyrins conjugated via a click chemistry strategy to yield conjugates with precise 1:1 stoichiometry. Preliminary cytotoxicity studies of the targeted photosensitisers showed that both conjugates exhibited limited dark toxicity, and excellent cell killing in the HER2+ BT-474 cell line.

Successful focal-point deprotection and azide functionalisation was carried out on a single porphyrin-dendron conjugate, with a successful model click reaction to an alkyne-functionalised sugar displaying the possibility of bioconjugation of porphyrindendron conjugates via a click methodology.

Citation

Bryden, F. (2013). Synthesis of water-soluble porphyrin-dendron conjugates for targeted photodynamic therapy. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4221329

• Thesis Type: Thesis
• Deposit Date: Mar 19, 2019
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4221329
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Oct 1, 2013