Second Generation Photoactivated Insulins
Date
2020Metadata
[+] Show full item recordAbstract
The photoactivated depot (PAD) is a minimally invasive approach developed for a continuously variable light stimulated release of insulin. In this approach, a protein depot that can last for days is injected under the skin. A light source placed on the skin above the site of injection can trigger protein release into the blood with a transcutaneous irradiation. Since the insulin photorelease is a photochemical reaction, the amount released can be tightly controlled by varying the duration of irradiation. PAD is beneficial for diabetics as it can deliver insulin in a continuously variable fashion and can be automated as an artificial pancreas to avoid dosing errors.
A first-generation material was constructed by covalently linking insulin to an insoluble polymer via a photocleavable group. Insolubility is a key requirement of the PAD material to allow retention at the site of injection, prior to irradiation. In vitro and in vivo experiments demonstrated its ability to deliver insulin on exposure to light. However, it needed further improvements due to the use of the polymer. Due to its large size, the material had low insulin density and was injected using a lower gauge needle. The polymer was not eliminated from the injection site after irradiation. Thus, alternative polymer-free approaches were explored to confer insolubility to insulin.
In this work, photocleavable small molecules (tags) were explored to lower protein solubility. Firstly, non-polar peptidic and unnatural photocleavable tags were designed that could render insulin less soluble in aqueous conditions. Protein solubility also depends on its net charge. As an alternative approach, insulin solubility was lowered by balancing its charges with tags to be zero at physiological pH. A series of positively charged photocleavable groups were designed to raise the pI of insulin from 5.4 to 7.2.
Two ideal materials, one chosen from each category of tags, were tested in diabetic rats. A PAD dose-response relationship was developed for the first time in living systems. These observations can assist in the development of an automated of the delivery system in response to blood glucose (with a continuous glucose monitor) for the diabetics.
Table of Contents
Introduction -- The tag approach -- The hydrophobic tags -- The charge tags -- Discrete photolysis -- In vivo studies -- Summary, scope, and conclusions -- Appendix
Degree
Ph.D. (Doctor of Philosophy)