Development and Evaluation of Liposomal Celastrol-PROTACs for Treating Triple-Negative Breast Cancer

<b>Background:</b> Based on our previous study, <i>Celastrol</i>-based proteolysis-targeting chimeras (<i>Celastrol</i>-PROTACs) were shown to induce apoptosis in 4T1 cells by selectively degrading GRP94 and CDK1/4 through the endogenous ubiquitin-proteasome system. However, their clinical translation is limited by poor solubility, low targeting efficiency, and liver and kidney toxicity. <b>Methods:</b> To address these limitations, we developed a pegylated liposomal formulation of <i>Celastrol</i>-PROTACs (Lip-<i>Celastrol</i>-PROTACs) and evaluated its therapeutic efficacy and safety profile. <b>Results:</b> The tumor volume of the mice in the <i>Celastrol</i>-PROTACs solution group (286 ± 79 mm³) was significantly larger than that of those in the Lip-<i>Celastrol</i>-PROTACs group (229 ± 49 mm³) on day 18 after intravenous administration (<i>p</i> < 0.01). This difference between the two groups was statistically significant (<i>p</i> < 0.01). Notably, the <i>Celastrol</i>-PROTACs group exhibited significantly greater weight loss compared to the Lip-<i>Celastrol</i>-PROTACs group (<i>p</i> < 0.001). In vivo toxicity assessments revealed that the levels of AST and BUN in the <i>Celastrol</i>-PROTACs group were 27.93 ± 4.88 U/L and 12.36 ± 1.33 μmol/L, respectively, whereas those in the Lip-<i>Celastrol</i>-PROTACs group were found to be 7.92 ± 0.94 U/L and 8.19 ± 0.67 μmol/L, respectively. These findings indicate a statistically significant difference between the two formulations (<i>p</i> < 0.01). <b>Conclusions:</b> Our research demonstrated that pegylated liposomes could improve the targeting efficiency and minimize the toxicity of PROTACs, thereby improving overall therapeutic efficacy. These findings indicated that Lip-<i>Celastrol</i>-PROTACs represent a promising strategy for future clinical applications.