It is highly convincing that tumour recurrence can be prevented if CSCs are specifically targeted. Development of drugs to target and eradicate CSCs represents a major challenge due to the fact that they are resistant to conventional therapies. The slow replication rate of cancer stem cells compared to adult cancer cells and overexpression of ABC transporter proteins that are capable of eliminating the molecules
used in cancer therapies could be possible reasons for inherent resistance in CSCs. Regulation of CD44 or CD24 expression in various cancers seems to be effective in controlling tumour initiation and inhibition of CSC population.demonstrated reduction of leukemic stem cells in acutemyeloid leukaemia by targeting CD44 function.
Therefore, CD44 could be a potential therapeutic target in solid tumours that are expressing this molecule. However,the influence of alteration in CD44 function on normal stem cells has to be considered during experiments on a cancer patient.
Genetic manipulations of certain surface marker expression in CSCs and examining the effect on cancer progression have been under investigation. MicroRNA (miRNA) has
been used to downregulate specific gene functions in CSCs and repress their expression in order to understand their key functional activities. They are also being used to inhibit proliferation and induce apoptosis, senescence when transfected into cancer cells [64]. By using these approaches, inducing the differentiation of CSCs may transform them to mature cancer cells which can be more vulnerable to conventional therapies. This miRNA could be advantageous in treating malignant tumours by repressing specific genes of signalling pathways involved in CSCs.Previous studies demonstrated these strategies.work with let-7 miRNA in breast-cancer-induced CD44+/CD24−/low cell population to differentiate and consequently inhibited formation of tumours. Using mullerianinhibiting hormone,.demonstrated inhibition of stem/progenitor cell population in tumours. More recently, Liu et al.showed thatmiR-34a inhibits prostate
cancer stem cells and metastasis by directly repressing CD44 expression. However, widespread explorations of miR-34a functionalities are necessary for complete understanding and could be considered for further therapeutic implications. Recent studies on CD24 depletion using siRNA and NDRG2 regulation in hepatocellular carcinoma and shRNA methods in bladder cancer demonstrated the reduction of tumourigenesis and CD24 could be used as a prognostic marker. However, absence of CD24 expression in
breast and prostate cancer restricts its use as a potential target for controlling invasion and metastasis. This suggests that CD24 expression seems to be strictly tissue specific and more elucidations necessary to develop more obvious therapeutic
strategies. However, the miRNA application has to be viewed as a strategy to analyse the expression and regulato context, it may be helpful in understanding the role of a surface marker in driving tumour initiation and metastasis of different tumour types. Knock-down of CD44 or CD24 may enhance CSC differentiation to mature cells and reduce tumour progression. Targeting key regulatory genes in CSCs may control their critical signalling pathways, but it has to be specific to targeting genes expressed in only CSCs but not normal stem cells