title: Aberrant Apoptotic Response of Colorectal Cancer Cells to Novel Nucleoside Analogues.
abstract: Despite the increased understanding of colorectal cancer and the introduction of targeted drug therapy, the metastatic phase of the disease remains refractory to treatment. Since the deregulation of normal apoptosis contributes to the pathogenesis of colorectal cancer, novel nucleoside analogues were synthesized here and evaluated for their ability to induce apoptosis and cause cell death in two colorectal adeno-carcinoma cell lines, Caco-2 and HT-29. Three novel nucleoside analogues assessed here showed cytotoxic activity, as measured by the MTT assay against both cell lines: the IC50 values ranged between 3 and 37 μM, with Caco-2 cells being more sensitive than HT-29 cells. Compared to camptothecin, the positive control, the nucleoside analogues were significantly less toxic to normal unstimulated leukocytes (p>0.05). Moreover, the nucleosides were able to induce apoptosis as measured by an increase in caspase 8 and caspase 3 activity above that of the control. This was additionally supported by data derived from Annexin V-FITC assays. Despite marginal changes to the mitochondrial membrane potential, all three nucleosides caused a significant increase in cytosolic cytochrome c (p>0.05), with a corresponding decrease in mitochondrial cytochrome c. Morphological analysis of both cell lines showed the rapid appearance of vacuoles following exposure to two of the nucleosides, while a third caused cellular detachment, delayed cytoplasmic vacuolisation and nuclear abnormalities. Preliminary investigations, using the autophagic indicator monodansylcadaverine and chloroquine as positive control, showed that two of the nucleosides induced the formation of autophagic vacuoles. In summary, the novel nucleoside analogues showed selective cytotoxicity towards both cancer cell lines and are effective initiators of an unusual apoptotic response, demonstrating their potential to serve as structural scaffolds for more potent analogues.
authors.affiliation: Division of Pharmacology, Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, South Africa.
authors.forename: Leonie
authors.initials: L
authors.lastname: Harmse
authors.affiliation: Division of Pharmacology, Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, South Africa.
authors.forename: Nurit
authors.initials: N
authors.lastname: Dahan-Farkas
authors.affiliation: Molecular Sciences Institute, School of Chemistry, Faculty of Science, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa.
authors.forename: Jenny-Lee
authors.initials: JL
authors.lastname: Panayides
authors.affiliation: Molecular Sciences Institute, School of Chemistry, Faculty of Science, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa; Department of Chemistry and Polymer Sciences, Stellenbosch University, Private Bag XI, Matieland 7602, South Africa.
authors.forename: Willem
authors.initials: W
authors.lastname: van Otterlo
authors.affiliation: Department of Internal Medicine, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, South Africa.
authors.forename: Clement
authors.initials: C
authors.lastname: Penny
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D018938:Caco-2 Cells; D002166:Camptothecin / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D019073:HT29 Cells; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009705:Nucleosides / Q000494:pharmacology*
chemical_list: D017304:Annexin A5; D009705:Nucleosides; D053148:Caspase 3; D053181:Caspase 8; D002166:Camptothecin