Ovatodiolide targets chronic myeloid leukemia stem cells by epigenetically upregulating hsa-miR-155, suppressing the BCR-ABL fusion gene and dysregulating the PI3K/AKT/mTOR pathway

Abstract

Chronic myeloid leukemia (CML) is a myeloproliferative pathology, originating from the hematopoietic cancer stem cells (hCSCs) due to the Bcl-Abl Philadelphia chromosome transformation. However, targeting these hCSCs as an effective anti-CML strategy is relatively less explored. Ovatodiolide (Ova) is a natural diterpenoid isolate of Anisomeles indica with broad anticancer activity. In this study, we investigated the anti-hCSCs potential of Ova against CD34⁺/CD38⁻, CD34⁺/CD38⁺, and unsorted K562 cell lines using flow cytometry, western blot, RT-PCR, genomic mapping, and tumorsphere formation assays. We demonstrated that compared to unsorted K562 and CD34⁺/CD38⁺, CD34⁺/CD38⁻ cells were significantly enriched with Oct4, Sox2, CD133, Bcr-Abl, p-CrkL and p-Stat5 protein and/or mRNA. Furthermore, we showed that Ova alone or by enhancing the therapeutic potential of Imatinib, reduced the viability of CML cell lines, dose-dependently, irrespective of the cancer stemness, as well as markedly inhibit the Bcr-Abl, p-CrkL, Stat5, and MDR protein expression levels in CD34⁺ cells. Mechanistic investigations revealed a significant up-regulation of hsa-miR-155, which resulted in the reduction of dysregulating the PIK3CA expression in Ova-treated K562 CD34⁺/CD38⁻ cells. Additionally, Ova alone or in combination with Imatinib suppressed the hCSC traits of the CD34⁺/CD38⁻ cells, resulting in loss of their ability to form tumorspheres, enhanced apoptosis, increase in the Bax/Bcl-2 ratio, and dysregulation of the PI3K/AKT/mTOR signaling pathway. Together, these results demonstrate the PI3K/AKT/mTOR signaling-mediated anti-hCSC effect of Ova in CML, as well as suggest a likely role for Ova as a small molecule PI3K/mTOR dual inhibitor, thus, extending its potential benefit to other mTOR-mediated pathologies.