Peptide stability assay

The overall procedures used to assess peptide stability are based on those described previously by Chan et al.¹⁸ and Ji et al.¹⁹. A peptide concentration of 300 μM was used, and time points taken at 0, 2, 4, 8, 16, and 24 h. The stability of sunitinib was also examined using this method, except an additional step was added after the final centrifugation step, whereby the pellet was dissolved in 8 M guanidine hydrochloride (300 μL) prior to analysis with RP-HPLC; this additional step was adapted from Ji et al.¹⁹. Supernantants were analyzed on an Agilent RP-HPLC using a linear 1%/min gradient of 0–50% solvent B with a 0.3 mL/min Phenomenex column. Peak height was used for integration of data at 215 nm and each experiment was performed in triplicate.