For most cancers, the combination of chemotherapy drugs is a promising approach. The combination of DNA damage agent Exatecan and proteolysis targeting chimera (PROTAC) agent ARV-825, which is a selective bromodomain-containing protein 4 degrader, can further improve efficacy through the DNA damage-repair mechanism. The Cathepsin B-sensitive prodrug with high albumin affinity of Exatecan (C14-VC-PAB-Exa) was introduced and co-encapsulated with ARV-825 into the nano-drug delivery system for improving the physicochemical properties of the two drugs. To promote the translation of Exatecan and the PROTAC into the clinics, it is important to develop a reliable and high-throughput bioanalytical method for the simultaneous determination of Exatecan, C14-VC-PAB-Exa, and ARV-825 that can evaluate the pharmacokinetic behaviors of the analytes. In this study, an HPLC-MS/MS method after preparation by one-step protein precipitation was developed and fully validated. The analytes were eluted completely on a ZORBAX SB-C18 column by gradient elution. Multiple reaction monitoring mode with positive electrospray ionization was applied to quantify the analytes. The validated method on selectivity, linearity (r ≥ 0.995), precision and accuracy (<
15 %), extraction recovery (>
88.0 %), matrix effect (<
9.1 %), carry-over, and stability were within the predefined acceptance criteria. The method was successfully applied to the pharmacokinetic study of Exatecan, C14-VC-PAB-Exa, and ARV-825 in rats for the first time. The proposed robust and economical method will be an alternative bioanalytical procedure for Exatecan and ARV-825 in the future. What is more, the present work could provide a reference for the clinical combination of the two drugs.