An Acrolein-Based Drug Delivery System Enables Tumor-Specific Sphingosine-1-Phosphate Targeting in Breast Cancer without Lymphocytopenia.

We developed a novel FTY720 prodrug (pro-FTY) that specifically inhibits sphingosine-1-phosphate signaling in cancer cells using a novel drug delivery system that reacts with acrolein. Our objective was to evaluate the efficacy and safety of pro-FTY in preclinical experiments. Ten breast cancer cell lines, two multidrug-resistant cell lines, and one normal mammary cell line were used to compare the IC50 values of pro-FTY with those of other drugs. Patient-derived organoids (PDO) were established and utilized for IC50 value comparisons. Drug efficacy was tested in mice bearing either syngeneic 4T1 cell tumors or patient-derived xenograft tumors, and blood analysis (including mass spectrometry) was performed. FTY720 and pro-FTY inhibited the survival of all breast cancer cell lines, including multidrug-resistant cells resistant to paclitaxel or doxorubicin. Unlike pro-FTY, FTY720 inhibited the survival of normal breast cell lines, suggesting that pro-FTY does not affect normal breast cells. Pro-FTY showed reproducible activity against multidrug-resistant PDOs, whereas paclitaxel and doxorubicin did not. Mass spectrometric analysis of pro-FTY-treated mice showed that FTY720 accumulated in tumors but was barely detectable in blood. Importantly, lymphocytopenia occurred in FTY720-treated mice but not in pro-FTY-treated mice. Furthermore, intravenous pro-FTY treatment significantly suppressed tumor growth in mice bearing patient-derived xenograft tumors generated from multidrug-resistant PDOs. In conclusion, pro-FTY inhibited breast cancer, including multidrug-resistant breast cancer, while avoiding lymphocytopenia, highlighting its clinical potential. SIGNIFICANCE: Pro-FTY selectively inhibits sphingosine-1-phosphate signaling in cancer cells using a novel acrolein-responsive drug delivery system that reacts with acrolein. Pro-FTY does not inhibit normal cell growth, thus avoiding lymphocytopenia. Pro-FTY is effective against multidrug-resistant breast cancer with a unique mechanism of action, highlighting its translational and therapeutic potential.