Targeted Delivery of Navitoclax to Elimate Senescent Tubular Epithelial Cells

Abstract

Treatments for chronic kidney disorder (CKD) offer symptom management, but no cure is available. This highlights the importance of CKD prevention. The high population of senescent cells can be seen as a driver of CKD. Senescent kidney cells can be eliminated by senolytics, a class of drugs that target the anti-apoptotic pathways. Unfortunately, many senolytics are paired with severe side effects such as neutropenia and thrombocytopenia. These side effects could potentially be mitigated by linking a senolytic, navitoclax, to a small protein, lysozyme (LZM). In this study, we investigated the binding of navitoclax to LZM through the use of a platinum binder (Lx). This was done by first conjugating LZM to a methionine-ester to expose surface ligands. Next, navitoclax was linked to Lx through an S-donor bond. The last step was conjugating both pieces by linking Lx to LZM with another S-donor bond on the exposed methionine. Furthermore, we investigated whether the conditionally immortalized proximal tubule epithelial cell line overexpressing the organic anion transporter 1 (ciPTEC-OAT1), could be used as a valid in vitro model to study LZM-based delivery of a senolytic. Both binding of LZM to methionine and navitoclax to Lx were obtained of which the latter reached a 65-78% purity. Outcomes showed the complexes could not be conjugated to each other, possibly due to poor solubility, steric hindrance, or the novel binding method which uses two S-donor bonds on the Pt center. The ciPTEC-OAT1 model proved to have endocytosis-mediated uptake of LZM, and only senescent cells were susceptible to navitoclax. Therefore, the ciPTEC-OAT1 model was deemed suitable for investigating LZM-navitoclax conjugates targeted at senescent kidney cells.