Evaluating Maleic Anhydride Derivatives as Linkers for Ph-Sensitive Drug Release

Cancer remains a persistent global health challenge. Current therapeutic strategies often fall short due to the adaptive nature of tumor cells, highlighting the urgent need for innovative drug delivery approaches. Recent advances emphasize improved drug selectivity through platforms that combine active targeting ligands with stimuli-responsive release mechanisms. Among these, pH-sensitive systems are particularly promising, exploiting the characteristic acidic microenvironment of tumor tissues to trigger the cleavage of pH-labile linkers and ensure site-specific drug release in its active form. In this study, we explored the potential of maleic anhydride derivatives as pH-sensitive linkers for drug delivery applications. Three cyclic anhydrides were selected for evaluation: cis-aconitic anhydride, 2-(2’-carboxyethyl)maleic anhydride, and 1-methyl-2-(2’-carboxyethyl)maleic anhydride. These compounds differ in the length of the aliphatic spacer between the carboxyl group and the ring, as well as in substitution patterns at the double bond. To avoid the use of cytotoxic agents, monodansylcadaverine (DCV) was employed as a fluorescent drug analogue. Its amine functionality and measurable fluorescence enabled efficient model studies of conjugation and release. Amide coupling reactions were carried out in anhydrous organic solvents, and reaction conditions were optimized with respect to base selection. Conjugate stability and pH-responsive release profiles were assessed in buffered solutions mimicking physiological and acidic tumor conditions. As a result we successfully synthesized a series of maleic anhydride-based conjugates and characterized their stability and hydrolysis behavior. Side-product formation was observed and attributed to either known isomerization processes or potential double bond substitution. Notably, approximately 60% of DCV was released from the 1-methyl-2-(2’-carboxyethyl)maleic anhydride conjugate at pH 4, confirming the promise of this approach for further development of pH-triggered drug delivery systems. The presented work is a part of the project 2024/ABM/05/KPO/KPOD.07.07-IW.07-0249/24 granted by Polish Medical Research Agency.