**5. Advantages of Targeting EMT**

EMT is recognized as playing a key role in developing cancer, metastasis, and chemotherapy resistance, and its crucial roles throughout cancer progression have recently been

discovered and investigated. Although there is still debate about whether EMT causes cancer metastasis, its importance in cancer chemoresistance is becoming more widely recognized, with many EMT-related signaling pathways implicated in cancer cell chemoresistance [39]. Targeted cancer treatments have been an emerging field in the recent decade. Several monoclonal antibody therapies and small chemicals, particularly kinase inhibitors, have been discovered/synthesized and undergo clinical trials with improved anti-cancer effectiveness. While many targeted therapeutic medications demonstrated encouraging preliminary clinical outcomes, such as enhanced overall survival, a significant percentage of patients who received targeted therapy acquired drug resistance following long-term treatment [108]. As a result, cancer drug resistance will determine the success of forthcoming targeted treatment medications. Drug resistance can be caused by various mechanisms, including drug efflux, drug metabolism, and drug target mutations [1,109]. The function of EMT in cancer therapy resistance has recently been explored. In the early 1990s, a relationship between EMT and cancer cell treatment resistance was proposed. Heckford et al. discovered that EMT occurred in two Adriamycin-resistant MCF-7 cells and vinblastine-resistant ZR-75-B cells [110]. Attempts have been devoted to targeting the ABC transporters to overcome drug resistance [111,112]. When it became obvious that EMT plays a critical role in drug resistance, scientists began exploring drugs targeting EMT to overcome drug resistance. Gupta et al. created EMT cells using E-cadherin shRNA and used this cell line to develop CSC-selective small molecule inhibitors. Using highthroughput screening, they discovered an antibiotic named Salinomycin that eliminated breast CSCs preferentially [113]. Salinomycin also reduced EMT caused by doxorubicin exposure and improved doxorubicin sensitivity in HCC cells [114]. It inhibited the expression and operation of drug efflux pumps in BC cells, resulting in a considerable reduction in doxorubicin resistance [115]. In addition to Salinomycin, several minor pharmacologic inhibitors of EMT have been discovered and tested in vitro and in vivo cancer treatment resistance models. Mocetinostat, a histone deacetylase (HDAC) inhibitor that restored miR-203 and decreased ZEB1 (EMT-TF) expression, reversed EMT in drug-resistant cancer cells and sensitized them to the chemotherapeutic agent docetaxel [116]. Curcumin, a component of curry, was discovered to sensitize 5-fluorouracil-resistant colorectal cancer cells via inhibiting EMT via miRNA [117]. According to Namba et al., EMT mediated by the Akt/GSK3/Snail1 pathway was a critical signaling event in acquiring gemcitabine resistance in PC cells. The anti-viral zidovudine inhibited these signaling pathways, restoring gemcitabine sensitivity in cancer cells. Co-administered zidovudine with gemcitabine reduced tumor growth and prevented cancer cells from establishing the EMT phenotype in mice with a gemcitabine-resistant pancreatic tumor xenograft [118]. Oncologists have recently focused on metformin since it has anti-cancer and chemopreventive qualities independent of anti-hyperglycemic effects [119,120]. Hirsch et al. later discovered that metformin targets BCSCs [121]. According to follow-up studies, metformin lowers CSCs by targeting EMT Metformin triggered transcriptional re-programming of BCSCs by lowering major EMT-TFs such as SNAIL2, Twist1, and ZEB1, according to Vazquez-Martin and colleagues [121]. Metformin has been shown to prevent EMT in lung cancer by inhibiting the IL-6/STAT3 axis in lung adenocarcinoma [122]. Although the direct molecular target of metformin in suppressing EMT is unknown, the Stimulation of AMPK may play a significant role in the drug's anti-EMT activity [123,124]. Metformin is being studied in over 200 human clinical studies for cancer therapy because of its possible CSC, anti-cancer properties, and favorable safety profile [125]. As a result, targeting EMT has been viewed as a unique strategy for combating cancer treatment resistance. In addition to the small compounds that have been created, a lot of pharmacological screening is being done to find new EMT inhibitors. Chua et al. created an EMT spot migration recognition method that can be utilized for high-content screening to screen small molecule EMT inhibitors that target certain growth factors. Scientists could undertake high throughput screening of small compounds utilizing enhanced screening platforms thanks to advancements in EMT and CSC biology [126]. Aref et al. also created a microfluidic device that mimics the 3D

tumor microenvironment by including tumor cell spheroids and an adjacent endothelial monolayer. This approach is very beneficial in identifying EMT medicines active in a complex in vivo tumor microenvironment with several cell kinds interacting [127,128]. As a result, targeting EMTs with the natural chemical entity is viewed as a unique and innovative approach to combating cancer treatment resistance.
