Synthesis and release studies of a bioreductively cleavable integrin ligand nintedanib conjugate

The development of selective anticancer therapies remains a major challenge in modern medicinal chemistry, with tumour hypoxia emerging as an attractive therapeutic target. The altered oxygenation of the tumour microenvironment leads to the overexpression of reductive enzymes such as nitroreductases, which catalyse the conversion of nitro groups into the corresponding amines. In this context, bioreductive triggers can be exploited for the development of conjugates designed to selectively release their payload at the tumour site. This work describes the synthesis and preliminary release evaluation of a cleavable integrin-targeted conjugate for the selective delivery and release of the anticancer drug nintedanib. The conjugate incorporates both an integrin ligand to direct the conjugate to tumour tissues overexpressing integrin αVβ6, and a cleavable linker based on a nitro-pyrrolyl scaffold capable of releasing the drug upon bioreduction of the nitro group. The conjugate was synthesized through SPPS and solution-phase synthesis. The final molecule was purified by HPLC and characterized by NMR and MS. Release studies are being performed in aqueous solutions containing nitroreductase and NADH, followed by metabolite detection by HPLC-UV-MS. The synthesis was carried out through a modular approach involving the separate preparation of the linker-nintedanib moiety and the peptide sequence, which were subsequently coupled through a final click reaction. This strategy enabled the efficient assembly of the final conjugate in a limited number of steps. Release studies under nitroreductase-mediated conditions are currently ongoing to evaluate the selective release of the drug. The proposed nitro-pyrrolyl platform represents a promising strategy for the development of hypoxia-responsive targeted therapeutics. Ongoing release studies under nitroreductase-mediated conditions will evaluate the ability of the linker to selectively trigger drug release. Further in vitro studies will be performed to assess the activity of the conjugate in tumour models