Rapid
insulin release plays an essential role in maintaining
blood-glucose homeostasis in mammalians. Patients diagnosed with type-I
diabetes mellitus experience chronic and remarkably high
blood-sugar levels, and require lifelong
insulin injection
therapy, so there is a need for more convenient and less invasive
insulin delivery systems to increase patients' compliance and also to enhance their quality of life. Here, an endoplasmic-reticulum-localized split sec-
tobacco etch virus protease (TEVp)-based
rapamycin-actuated
protein-induction device (RAPID) is engineered, which is composed of the
rapamycin-inducible dimerization domains
FK506 binding protein (
FKBP) and
FKBP-
rapamycin binding protein fused with modified split sec-TEVp components.
Insulin accumulation inside the endoplasmic reticulum (ER) is achieved through tagging its C-terminus with KDEL, an ER-retention signal, spaced by a TEVp cleavage site. In the presence of
rapamycin, the split sec-TEVp-based RAPID components dimerize, regain their proteolytic activity, and remove the KDEL retention signal from
insulin. This leads to rapid secretion of accumulated
insulin from cells within few minutes. Using liver hydrodynamic transfection methodology, it is shown that RAPID quickly restores
glucose homeostasis in type-1-diabetic (T1DM) mice treated with an oral dose of clinically licensed
rapamycin. This rapid-release technology may become the foundation for other cell-based
therapies requiring instantaneous biopharmaceutical availability.