Folic Acid-Appended Hydroxypropyl-β-Cyclodextrin Exhibits Potent Antitumor Activity in Chronic Myeloid Leukemia Cells via Autophagic Cell Death

SIMPLE SUMMARY: 2-Hydroxypropyl-β-cyclodextrin (HP-β-CyD) is a cyclic oligosaccharide widely used as an excipient in pharmaceutical preparations, in addition to also being used as a cholesterol regulator. HP-β-CyD was used in clinical trials for patients with Niemann-Pick Type C disease to remove accumulated intracellular lipid. HP-β-CyD has anti-leukemia activity by inducing apoptosis and cell-cycle arrest; however, the antitumor activity of HP-β-CyD lacks tumor cell-selectivity. Taking advantage of the fact that folate receptors are highly expressed in many cancer cells, we synthesized folate-appended HP-β-CyD (FA-HP-β-CyD) to confer tumor cell-selectivity to HP-β-CyD. FA-HP-β-CyD inhibited the proliferation of chronic myeloid leukemia (CML) cells and the mechanism underlying the effect of FA-HP-β-CyD in inducing cell death may involve autophagy. The combination of FA-HP-β-CyD and ABL tyrosine kinase inhibitors (imatinib and ponatinib) had a synergistic inhibitory effect on CML cells. In a mouse model of BCR-ABL-induced leukemia, FA-HP-β-CyD had a stronger inhibitory effect on leukemia progression than HP-β-CyD or imatinib. ABSTRACT: 2-Hydroxypropyl-β-cyclodextrin (HP-β-CyD) is widely used as an enabling excipient in pharmaceutical formulations. We previously demonstrated that HP-β-CyD disrupted cholesterol homeostasis, and inhibited the proliferation of leukemia cells by inducing apoptosis and cell-cycle arrest. Recently developed drug delivery systems using folic acid (FA) and folic acid receptors (FR) are currently being used in cancer treatment. To confer tumor cell-selectivity to HP-β-CyD, we synthesized folate-appended HP-β-CyD (FA-HP-β-CyD) and evaluated the potential of FA-HP-β-CyD as an anticancer agent using chronic myeloid leukemia (CML) cells in vitro and in vivo. FA-HP-β-CyD inhibited the growth of FR-expressing cells but not that of FR-negative cells. FA-HP-β-CyD had stronger anti-leukemia and cell-binding activities than HP-β-CyD in CML cells. Unlike HP-β-CyD, FA-HP-β-CyD entered CML cells through endocytosis and induced both apoptosis and autophagy via mitophagy. FA-HP-β-CyD increased the inhibitory effects of the ABL tyrosine kinase inhibitors imatinib mesylate and ponatinib, which are commonly used in CML. In vivo experiments in a BCR-ABL leukemia mouse model showed that FA-HP-β-CyD was more effective than HP-β-CyD at a ten-fold lower dose. These results indicate that FA-HP-β-CyD may be a novel tumor-targeting agent for the treatment of leukemia.