Cancer stem cells (CSC) are defined as cells with a tumor-initiating potential and are resistant to chemo-radiation therapy. Evasion of apoptosis is one of the hallmarks of human cancers attributed to CSCs. Human TRAIL/Apo-2L is a ligand of the TNF family that can trigger apoptotic cell death and has been demonstrated to induce apoptosis in a wide range of cancers. Interestingly, TRAIL receptor DR5 was found to be over-expressed in leukemic stem cells (LSCs). Inducing apoptosis in CSCs using TRAIL protein would be a novel and efficient strategy. We characterized and targeted the leukemic stem cells to induce self-death by TRAIL-based pathway. A fusion protein of IL2-TRAIL peptide was constructed to target leukemic cells over-expressing IL2 α receptor.
A chimeric recombinant construct was genetically engineered by fusing active peptide of human TRAIL with human IL2α gene. The LSCs were isolated from 13 leukemic patients using specific LSC markers by FACS sorting and was characterized using stem cell assays, flow cytometry and fluorescence microscopy. The cytotoxicity of isolated cells was evaluated with the recombinant TRAIL peptide in vitro by MTT assay.
LSCs isolated from leukemic patients showed presence of stem cell markers like CD123, CD45/CD34, CD96 and CD90. Further the LSCs showed stem cell characteristics like quiescent nature, drug efflux and expression of stem cell marker genes like ABCG2, CLL-1, Wnt3A, TERT, Notch1, Nanog, Sox2, Oct4, BMI1 and βCat. Recombinant immunotoxin of 12 kDa had an IC50 of 700 nM in vitro in leukemic cell lines. The immunotoxin showed ∼80 % efficacy, inducing apoptosis in LSCs derived from 11 patients in vitro.
Specific targeting of cancer stem cells using novel recombinant molecules is an efficient strategy in cancer therapy and could be explored in other types of cancer also to avoid recurrence due to chemo-resistance or radio-resistance.
The authors.
Department of Science and Technology, Government of India.
All authors have declared no conflicts of interest.