Over the last decade, three major advances have contributed in improving the response rates against cancer including, immunotherapy; greater understanding of the molecular, biochemical, and cellular mechanisms in carcinogenesis thereby providing drug targets; and identification of reliable biomarkers for early detection to facilitate the earlier stage treatment of disease. However, no single universal cancer cure has yet been found, although combinations from the above areas have steadily improved survival outcomes. Hence, chemotherapy remains a key component in the oncologist's arsenal for cancer therapy, despite frequent development of drug resistance and more aggressive cancers with onset of advanced stage metastases. The focus here is to explore the repurposing of old drugs that cause pro‐oxidative overload to overcome onset of resistance to chemotherapy and enhance chemotherapeutic responses, particularly against metastatic cancer. Excellent examples of US Food and Drug Administration approved drugs suitable for repurposing are the potent and specific thioreductase inhibitor auranofin and the nonsteroidal anti‐inflammatory drug, celecoxib. Recently, both drugs were shown to selectively target and kill metastatic cancer cells and cancer stem cells (CSCs), predominantly by promoting excessive mitochondrial reactive oxygen species. Thus, targeting intracellular redox systems of advanced stage metastatic cancer cells and CSCs can promote an overload of pro‐oxidative stress to activate the intrinsic pathway for programmed cell death. It is envisaged that more clinical studies will incorporate longer term use of repurposed drugs, such as auranofin or celecoxib, to target redox systems in cancer cells as part of common practice postcancer diagnosis, providing enhanced chemotherapeutic responses and increased cancer survival.

To date two questions that remain unanswered regarding cancer are the following: i) how is it initiated, and ii) what is the role that cancer stem cells (CSCs) play in the disease process? Understanding the biology of CSCs and how they are generated is pivotal for the development of successful treatment regimens. To date, the lack of a representative cell model has prevented the successful identification and eradication of CSCs in vivo. The current methods of CSC identification are dependent on the protocol used to generate these cells, which has introduced variation and made the identification process more complicated. Furthermore, the list of possible markers is increasing in complexity. This is further confounded by the fact that there is insufficient information to determine whether the cells these markers detect are truly self-renewing stem cells or, instead, progenitor cells. In the present study, we investigated a novel cell line model, CSC480, which can be employed to assess CSC markers and for testing novel therapeutic regimens. CSC480 cells have been revealed to express markers of CSCs such as CD44, ALDH1 and Sox2, that have lower expression in the SW480 cell line. CSC480 cells also expressed higher levels of the cancer resistance marker, ABCG2 and had higher proliferative and growth capacity than SW480 cells. In the present study, we also evaluated a novel approach to identify different cell types present in heterogeneous cancer cell populations according to their proliferative ability using the proliferation marker 5-ethynyl-2'-deoxyuridine (EdU). Furthermore, using EdU, we identified dormant cells with a modified label-retaining cell (LRC) protocol. Through this novel LRC method, we assessed newly discovered markers of stemness to ascertain their capability to identify quiescent from dividing CSCs. In conclusion, the CSC480 cell line was an important model to be used in unravelling the underlying mechanisms that control fast-dividing and partially self-renewing stem cells (SCs) that may give rise to cancer.

How to cite this article: ALHulais RA, Ralph SJ. Cancer stem cells, stemness markers and selected drug targeting: metastatic colorectal cancer and cyclooxygenase-2/prostaglandin E2 connection to WNT as a model system.