|LETTER TO THE EDITOR
|Ahead of print publication
Refined cancer stem cells-enriched lung cancer model systems: Cross-talk and fine-tuning Notch1 inhibition
Department of Biomedical Sciences, School of Biosciences and Technology VIT, Vellore, Tamil Nadu, India
|Date of Submission||17-Jun-2020|
|Date of Acceptance||30-Sep-2020|
|Date of Web Publication||23-Jul-2021|
Department of Biomedical Sciences School of Biosciences and Technology VIT, Vellore, Tamil Nadu
Source of Support: None, Conflict of Interest: None
The paper, in response to a paper in your journal, underscores the importance of targeting lung cancer stem cells (LCSCs), since these cells have the unique property of being relatively recalcitrant to chemo- and/or radio-therapy. The goal of this letter is to underscore the fact that the proportion of LCSCs varies in A549 cells (a model cell line for non-small cell lung cancer-[NSCLC]), depending on the markers used. For example, the side population cells were found to be 18.1% of the stem cells; CD44+/CD24– cells were 27.92%, while the ALDH1+ cells were only 4.2%. In addition, differences in culture conditions (media-related and hypoxia) including variations in the temporal aspects may also be important determinants of the extent/loss of stemness in the lung cancer cell lines used to model NSCLC. Hence, this calls for an inter-laboratory validation of harmonized protocols for reproducibility and reliable data comparison. This aspect is also significant, since the stoichiometry of cancer stem and tumorigenic nonstem cells in different regions of the same tumor as well as in various lung cancers are also different. This heterogeneity may be due to the varying rate of conversion of stem to tumorigenic nonstem cells and the relative expression of epithelial versus mesenchymal traits. Furthermore, the propensity of these cells to metastasize would be expected to be different. All these aberrant phenomena need to be faithfully modeled/replicated for an accurate assessment of Notch1 inhibition than would be possible with the three dimensional spheroidal cultures (used by the authors of the paper). In the development and refinement of these models, the role of the vasculature is important with Notch1 expression playing an important role. In this regard, the introduction of OCT3/4, SOX2 and KLF4 in a KRAS-mutated A549 cells resulted in the creation of a lung cancer organoid-like tissue with the capabilities of forming the vasculature and mesenchymal stem cells (a better mimic of the tumor microenvironment providing opportunities to evaluate paracrine and autocrine Notch Ligand-based signaling). These models, once developed and thoroughly validated, in terms of Notch1 expression can be used to better assess its role in regulating the behavior of cancer stem cells. The paper compares the role of nonspecific chemical inhibition of Notch signaling A5 -tert-Butyl (2S)-2-[[(2S)-2-[[2-(3,5-difluorophenyl)acetyl]amino]propanoyl]amino]-2-phenylacetate (DAPT) with siRNA-based blockade of Notch1 signaling. However, stability, selectivity and efficacy of siRNA-based inhibition can be improved by their encapsulation in nanovesicles either singly or in combination with chemical inhibitors (to lower the dose of the drug needed to eliminate the LCSCs), and needs to be strongly considered. There are other reports documenting Notch3 overexpression in 40% of neural stem-like cells (NSLC) stem cells; cross-talk with the epidermal growth factor receptor (EGFR) pathway and their combined inhibition resulting in cell death and growth inhibition. Hence, this calls for a combined evaluation of Notch3, apart from the involvement of the EGFR and other pathways (e.g., involving beta-catenin). Furthermore, refinement of the NSLC model systems can aid in the evaluation of other epigenetic regulators of Notch1 (like microRNA-582–5p) – a strategy to fine-tune the regulation of Notch1.
The author would like to profusely thank the management of VIT for creating the scientific ambience that made this manuscript possible. Also, the author would like to thank the students and research scholars for their support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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