Thiols contain a sulfur atom bonded to a hydrogen atom (-SH), the high electron density of the sulfur atom makes the thiol group a potent nucleophile. As a result, thiols can undergo a variety of reactions, including oxidation, reduction, and substitution reactions, making them an attractive target for electrophilic compounds-including the "thiol switch" mechanism. The thiol switch mechanism involves the reversible modification of thiol groups in biomolecules by electrophilic compounds. This mechanism is mediated by the formation of a covalent bond between the electrophile and the thiol group, which leads to changes in the biomolecule's activity and function. Thiol switches have emerged as a promising approach for modulating the pharmacological properties of drug candidates. Conjugation of drug molecules to thiol-containing biomolecules take advantage of thiol-sensitivity for enhancing drug bioavailability and efficacy. This approach involves the covalent attachment of drugs to thiol-containing biomolecules, through a cleavable linker that can act as a thiol switch. The thioester bond is a specific type of cleavable linker that has been shown to be particularly useful for thiol switch-based drug development. Thioester linkages are labile, and can be easily cleaved through a mechanism known as thiolysis. This cleavage releases the drug from the thiol-containing biomolecule, leading to increased drug bioavailability and efficacy. Aspirin is a well-known anti-inflammatory agent that has been used clinically for decades. However, its clinical use is limited by its gastrointestinal side effects and limited bioavailability. One approach to improve the solubility is to conjugate aspirin with a thiol-containing biomolecule, such as cysteine, through a thioester linker. In the body, the presence of a redox environment, which involves the interplay of oxidizing and reducing agents, can influence the behavior of the aspirin-cytosine conjugate. The conjugate's linker, designed to be sensitive to thiol-cysteine, reacts with the thiol groups of cysteine residues present in various biomolecules, such as proteins or glutathione, which act as reducing agents.This approach can take advantage of the thiol sensitivity of the conjugate, as well as cysteine's facile redox chemistry, which can enhance drug bioavailability and efficacy by increasing stability and cell permeability. In this study, we investigate the role of thiol-sensitivity in modulating the bioavailability and efficacy of drug candidates using an aspirin-cysteine conjugate with a thioester linkage. We synthesized the conjugate using a thiol-cleavable linker and evaluated its bioavailability and efficacy in vitro. Our results demonstrate the potential of thioester-based thiol switch approaches for drug development and provide insight into the molecular mechanisms underlying thiol-cysteine sensitivity.