Peptides can be highly specific and potent drugs, but they have been particularly challenging to bring to market because they are quickly removed from circulation prior to administering therapeutic value. While half-life extension strategies such as PEGylation are available for protein therapeutics, it is well known that proteins experience a significant decrease in their functional activity when attached to PEG. Extend Biosciences is harnessing the biology of vitamin D to improve the pharmacokinetic properties of biologics. Vitamin D is covalently and site-specifically attached to the peptide or protein. The modification is small enough so that it does not interfere with the function of the peptide. When this conjugate is injected subcutaneously, it is recognized by the Vitamin D Binding Protein (VDBP), which naturally waits in the skin for sunlight to activate vitamin D. VDBP then actively transports the conjugate into circulation and carries it around for an extended period of time. This results in an extended half-life and improved absorption and bioavailability of the peptide. We have multiple peptides in preclinical development for a number of complex diseases, many of which address a significant unmet medical need for both large patient populations as well as rare diseases.