Keywords

Introduction

One of the most prevalent cancer in the world to cause mortality is colon cancer, which is also the most frequent type of cancer to spread. The death rate has similarly continued to increase for women’s breast, colon, and rectum cancers as well as for the three most common cancer sites in men such as the lung and bronchus, colon and rectum, and prostate (Jemal et al. 2006; Das et al. 2022; Palaniappan et al. 2016; Balaji et al. 2022; Prakash and Rajamanickam 2015; Girigoswami and Girigoswami 2021; Haribabu et al. 2019). CD133, CD44, ALDH1, and ALCAM are some of the common stem cell markers for colon cancer. Using an antibody against its epitope AC133, colon cancer stem cells (CCSCs) were first discovered when the CD133 glycoprotein expressed themselves. Cancer relapse following chemotherapy is thought to be mediated by cancer stem cells (CSCs) in addition to initiating and sustaining tumor development (Todaro et al. 2010; Ricci-Vitiani et al. 2009; Scatena et al. 2011). The notion that human tumors can be viewed as a stem cell illness is gaining more importance and support from the available data. According to the cancer stem cell paradigm, a small subset of cancer cells with the capacity to initiate and maintain tumor development, self-renew, and pluripotency is assumed to be the cause of malignancies (Ricci-Vitiani et al. 2009). One must first separate single-cell suspensions from human colon cancer tissue before working with these cells. With the use of flow cytometry, cell suspensions are divided into tumor-initiating and nontumor-initiating fractions. The fractionated cells must be functionally assessed to identify their capacity to form tumors using the in vivo xenograft test, which is regarded as the gold standard. Moreover, methods for in vitro sphere-forming assay growth of these cells have been developed (Szaryńska et al. 2017). Surgical excision is the most common treatment for colorectal cancer (CRC). Yet 50% of CRC patients will develop metastases over their lifetime, with stage IV cases (with distant metastases) accounting for roughly about 25% of all instances. Treatments impact tumor-mass-derived, proliferating cancer cells while sparing cancer stem cells. Several analyses have shown that cellular signaling pathways play an important role in embryonic development, as well as in the tissue homeostasis development, healing, and preservation. They also contribute significantly to the development and preservation of stemness in CCSCs (Ebrahimi et al. 2023). Therefore, this chapter focuses on the various roles of CSCs and CCSCs in initiation and progression of colon cancer as well as its therapeutic implications (Fig. 1).

Fig. 1
figure 1

Diagram representing few of the features of cancer stem cells

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Etiology of Colon Cancer

Colon cancer typically starts when healthy colonic cells experience genetic changes, inadequate DNA mismatch, or exposure to carcinogens. The DNA of a cell carries a collection of instructions that direct the cell for their specific function. The body functions normally because healthy cells divide and expand in an organized manner. By undergoing “gain-of-function” mutations, proto-oncogenes that support healthy cell proliferation can become oncogenes. “Loss-of-function” mutations can also have an impact on tumor suppressor genes, which typically control growth (Okugawa et al. 2015). Colon cancer develops as a result of disruption of the Wnt signaling pathway, which occurs in a range of tumor. Studies of transgenic and knockout mice, transgenic and knockout human tumor cell lines, genetic studies of other species, and human cancer biology have contributed to its acceptance (Oving and Clevers 2002; Fearon and Vogelstein 1990). The genetic model of CRC requires a number of gene mutations, which include tumor suppressor genes APC, DCC, p53, and MCC, and oncogenes K-RAS and NRAS. These gene variations have been found to play a direct role in the adenoma-carcinoma sequence of CRC (Fearon and Vogelstein 1990; Bhatt et al. 2015; Rathva and Desai 2020). To prevent primary cancer, it is important to identify and modify the etiologic factors that arise naturally within the body or from external environmental sources. The term “secondary prevention of cancer” refers to the recognition and treatment of precancerous conditions or the early diagnosis of cancer that allows for treatment and the avoidance of the disease’s numerous complications (Sherlock et al. 1980). Colon cancer is more prevalent in older persons, with most instances occurring in those over 50 years of age. An increased risk of the illness exists in those with a family history of colon cancer or certain inherited genetic abnormalities, such as Lynch syndrome or familial adenomatous polyposis (FAP). Colon cancer risk has also been linked to Western lifestyle such as smoking, eating a diet high in red and processed meats, consuming little fiber, being sedentary, and leading a sedentary lifestyle. Bowel illness with chronic inflammation (IBD), such as ulcerative colitis (UC) or Crohn’s disease (CD), increases the risk of colon cancer. The risk of colon cancer may be raised by exposure to specific environmental chemicals and pollutants, such as asbestos, benzene, and pesticides. Although the precise mechanisms are yet to be entirely understood, people with diabetes have an elevated chance of acquiring colon cancer. A higher incidence of colon cancer has also been associated with obesity, especially in males. Alcoholism has been associated with a higher risk of colon cancer. Individuals are more likely to get the disease having a history of specific illnesses, such as colorectal polyps or past history of colon cancer. It is crucial to remember that, while these risk factors have been linked to an increased risk of colon cancer, they do not always cause the illness on their own. A complex combination of hereditary and environmental variables is probably a factor in its development (Brenner et al. 2014; Fearon and Vogelstein 1990; Lao and Grady 2011).

CCSC Identification and Isolation

The development and maintenance of colon cancer are thought to be mediated by CCSCs. Cancer cells with features similar to stem cells, such as the capacity for self-renewal and differentiation, have been identified as CSCs. For the development of efficient cancer therapies, the identification and isolation of CCSCs is essential. CCSCs may be isolated using a variety of techniques, such as cell surface indicators, functional tests, and molecular markers (Vermeulen et al. 2008; O’Brien et al. 2007; Scatena et al. 2011; Rajasekhar and Vemuri 2009).

Cell Surface Markers

It is a common strategy for locating and isolating CCSCs based on particular cell surface markers. CCSCs have been found to exhibit several cell surface markers, including CD133, CD44, CD166, and EpCAM. Using fluorescence-activated cell sorting (FACS) or magnetic-activated cell sorting (MACS), these markers are utilized to separate CCSCs (Scatena et al. 2011).

CD133

This is one of the most commonly used markers for CSCs in various cancers, including colon cancer. It is a five-transmembrane glycoprotein expressed on the surface of a fraction of colon cancer cells with stem cell–like features. It was selected based on the positive sampling of AC133, which is an epitope for CD133. This marker can be used to detect clonogenic and tumorigenic populations (Dalerba et al. 2007; Scatena et al. 2011).

CD44

This is a cell surface receptor associated with cell adhesion and migration. It is found on the surface of multiple types of stem cells, including CCSCs. Additionally, CD44 displays high tumorigenicity when combined with CD133 positivity. This marker can also be used with mesenchymal stem cell marker CD166 as the positive combination of both showcase a better ability to form tumors in mice (Aigner et al. 1997; Scatena et al. 2011).

EpCAM

The epithelial cell surface expresses the transmembrane glycoprotein known as epithelial cell adhesion molecule (EpCAM). Given that it is overexpressed in several cancer types, including colon cancer, it is regarded to be a potential marker for CCSCs.

CD166

A cell surface glycoprotein called CD166 has a role in both cell adhesion and signaling. Several different kinds of stem cells, including CCSCs, are found to express it on their surface.

Other Markers

A CD44 positivity is associated with tumor initiation and the marker plays a role in cell-cell interaction, adhesion, and proliferation (Vermeulen et al. 2008). Many cancers including colon cancer are known for overexpressing CD24. Additionally, CD24 along with CD29 has been found helpful in identifying the colon cancer population (Dayan et al. 2008).

Functional Assays

Functional analysis is an additional technique for locating and separating CCSCs. These tests rely on the CCSCs’ stem cell–like characteristics, such as the capacity for self-renewal and differentiation. The sphere formation test is one of the most commonly used functional assays for locating CCSCs. In this test, cancer cells are cultivated in a non-adherent setting that promotes the development of CSCs as spheroids.

Molecular Markers

Another method for locating and isolating CCSCs is by using molecular markers. The gene expression profile of CCSCs served as the foundation for these indicators. The genes ALDH1, LGR5, and CD133 have all been identified as molecular markers of CCSCs. Quantitative PCR or immunohistochemistry can also be used to identify the expression of these genes. Hence, locating and isolating CCSCs is crucial for developing effective cancer therapies. A number of techniques, such as cell surface indicators, functional tests, and molecular markers, have been developed to achieve this goal. Each of these methods can be used separately or in combination to locate and identify CCSCs (Banerjee et al. 2023; Vermeulen et al. 2008; O’Brien et al. 2007; Dalerba et al. 2007; Dylla et al. 2008; Huang et al. 2009).

Molecular Mechanisms Underlying in the Maintenance of Stem Cells for Colonic Cancer

Several biological processes contribute in the accumulation of stem cells in the colon and also in their function in colon cancer. Few of the instances are:

Wnt/β-Catenin Signaling Pathway

One of the signaling mechanisms most thoroughly investigated in CCSCs is the Wnt/β-catenin pathway. When Wnt ligands bind to the LRP5/6 co-receptor and the Frizzled receptor in healthy cells, β-catenin is stabilized and translocated to the nucleus which activates the Wnt signaling. When the Wnt/β-catenin pathway is abnormally activated in CCSCs, it results in the accumulation of β-catenin in the nucleus, where it interacts with TCF/LEF transcription factors that promote the expression of target genes essential for CSC maintenance, such as LGR5 and CD44 (Vermeulen et al. 2010).

Notch Signaling Pathway

Notch signaling is also required for survival of CCSCs. To activate Notch receptors, Jagged and Delta-like ligands attach to them, causing the receptor to cleave and release its intracellular domain (NICD). Upon that, NICD translocated to the nucleus interacts with the transcription factor CSL to stimulate the production of Notch target genes involved in CSC self-renewal, specifically Hes1 and Hey1 (Radtke and Raj 2003; Rajasekhar and Vemuri 2009).

Hedgehog Signaling Pathway

Another significant signaling cascade involved in maintaining CCSCs is the Hedgehog (Hh) pathway. Hh ligands bind to the transmembrane receptor Patched (PTCH), releasing its inhibition of the G protein–coupled receptor-like protein Smoothened, to begin Hh signaling (SMO). The stimulation of subsequent signaling molecules, such as Gli transcription variables, which are triggered by active SMO, enhances the production of Hh target genes involved in CSC self-renewal, such as Bmi1 and Snail (Yauch et al. 2008; Nusse and Clevers 2017).

Epigenetic Regulation

The preservation of CCSCs is also greatly aided by epigenetic processes including DNA methylation and histone modification. For instance, DNA methylation of tumor suppressor genes like CDKN2A and MLH1 may cause their silence and aid in the maintenance of CSCs. EZH2, for example, has been demonstrated to be overexpressed in CCSCs and to contribute in the maintenance of these cells’ potential for self-renewal (Yauch et al. 2008).

Inflammatory Signaling

CSCs activity may be impacted by chronic inflammation, which is also a risk factor for colon cancer. Inflammatory cytokines are found to encourage the growth of stem cells and aid in the development of colon cancer. Knowing the molecular mechanisms that keep stem cells in the colon healthy, might help in identifying possible therapeutic targets and shed light on the mechanism of colon cancer development (Rajasekhar and Vemuri 2009).

Interactions Between Colon Cancer Stem Cells and the Tumor Environment

A tumor microenvironment shelters CSCs. CSCs are thought to be in charge of tumor initiation, growth, and treatment resistance. They are a very small population of self-renewing, differentiating cells that exist inside the tumor. CCSCs interactions with the tumor microenvironment play a crucial role in the initiation and progression of CRC (Rajasekhar and Vemuri 2009).

Microenvironment of a Tumor

The network of cells and extracellular matrix elements that surround and support the tumor is known as the tumor microenvironment (TME). The TME is composed of fibroblasts, immunological cells, endothelial cells, extracellular matrix components, and signaling molecules. It is well established that TME significantly contributes to the onset and spread of cancer, including CRC. Since hypoxia is a typical characteristic of the tumor microenvironment, it is the central target for cancer growth concerning TME. This happens by activation of the hypoxia-inducible factor which dictates multiple factors in TME such as pH levels, nutrient availability, tumor metabolism, and extracellular matrix (ECM) (Jahanafrooz et al. 2020).

Immune Cells and Its Interactions

Immune cells present in the tumor microenvironment (TME) interact with CSC and can support their survival and growth by releasing cytokines, chemokines, and growth factors. For example, tumor-associated macrophages (TAMs), regulatory T cells, and myeloid-derived suppressor cells (MDSCs) have been shown to release chemicals such as IL-6 and IL-8 that aid in the development and maintenance of CSCs in CRC. TAMs, in particular, are well known for their role in supporting the activity of CSCs in CRC (Leong et al. 2022).

Function of Fibroblasts

Fibroblasts within the TME are known to support the proliferation and survival of CRC cells. Cancer-associated fibroblasts (CAFs) produce and secrete a variety of molecules such as growth factors, cytokines, and components of the extracellular matrix that can help promote the survival and proliferation of CSCs (Leong et al. 2022). In addition, CAFs have been shown to stimulate tumor growth and metastasis by increasing angiogenesis, which is the formation of new blood vessels that supply nutrients and oxygen to the tumor. The ECM in the TME supports the tumor structurally and affects the behavior of cells. Collagen, fibronectin, and laminin are ECM components that support CSC survival and growth. The signaling pathways involved in CSC self-renewal and differentiation are also regulated by ECM components.

Role of Fibroblasts

It is known that fibroblasts in the TME promote the growth and survival of CRC cells. CAFs release growth factors, cytokines, and ECM components that support CSC survival and proliferation. CAFs also encourage angiogenesis, which is crucial for the growth and spread of tumors. The ECM in the TME supports the structural integrity of the tumor while also influencing how cells behave. Collagen, fibronectin, and laminin are ECM components that support CSC proliferation and survival. The signaling pathways involved in CSC self-renewal and differentiation are also regulated by ECM components.

The Generation of Targeted Therapies for Colon Cancer Stem Cells

Although chemotherapy and surgery can help cure cancer, the illness frequently returns, and patients with advanced or metastatic cancer have dismal survival rates. New therapies are thus required to enhance patient outcomes. One potential strategy for treating colon cancer involves targeting cancer stem cells (CSCs), as these cells are believed to play a critical role in cancer development, metastasis, and resistance to medication (Cai et al. 2017). One of the major reasons for targeting CCSCs is the lack of traditional therapy’s efficiency due to which the cancer relapses. Hence, stem cell therapies are more desirable for colon cancer treatment. CCSC preferably focuses on two major benefits: (i) reducing the toxic effects on normal stem cells and (ii) stopping the relapse of tumors in the future. The different mechanisms to target CCSCs include cell surface molecules, antibodies, CCSC signaling, and self-renewal pathways (Lu et al. 2011). A tiny group of cancer cells called CCSCs have the capability for self-renewal and the aptitude to differentiate into multiple cell types. These cells are assumed to be in charge of the development and spread of colon cancer as well as its refractoriness to treatment. Consequently, a possible approach to increase the effectiveness of cancer treatment is to create targeted medicines for CCSCs (Zhang et al. 2008; Rajasekhar and Vemuri 2009). Several approaches have been proposed to target CCSCs, including the following:

Suppression of Signaling Pathways

Several signaling pathways, including Wnt, Notch, and Hedgehog, are known to control CSC self-renewal and differentiation. It has been suggested that one technique to combat CCSCs is to block these pathways using small molecule inhibitors or monoclonal antibodies. With a Notch inhibitor, for instance, a phase I clinical trial in individuals with advanced colon cancer produced encouraging outcomes (Zhang et al. 2008; Leong et al. 2022). Several other molecules and compounds inhibit the targeted pathways. Pyrivin is known to inhibit LRP6-mediated axin degradation and destabilizes β-catenin through Wnt signaling (Amado et al. 2014). Other mechanisms used by different molecules include: (a) tankyrases inhibition and beta-catenin destruction; (b) inhibition of TCF4 interaction; (c) inhibition of Wnt protein production or blocks of the protein itself; and (d) promotion degradation of beta-catenin (Fang et al. 2016; Akbari et al. 2015; Shang et al. 2017). TGF-β signaling is another pathway to target using P144 to block the interaction of the protein with its receptor. Similarly, another compound SD-208 is also reported to inhibit receptor1 kinase inhibitor. On the other hand, cyclopamine targets Hedgehog signaling to downregulate the expression of the pathway and its downstream genes (Batsaikhan et al. 2014).

Targeting CSC-Specific Markers

CSCs express certain markers, including CD44, CD133, and Lgr5, that can be utilized to recognize and target the cells. CSC-targeted treatments have been designed using antibodies against these markers or small molecule inhibitors of their signaling pathways (Yang et al. 2020). Some of the CCSC markers are shown in Fig. 2.

Fig. 2
figure 2

Diagram representing few of the CCSCs markers and its associated characteristics

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Differentiation Induction

Non-CSCs, which could be more susceptible to chemotherapy, can develop from CSCs. As a result, it has been suggested that utilizing peptides or small compounds to induce CSC differentiation is a way to make them more sensitive to treatment (Orian-Rousseau and Ponta 2015).

Combination Therapy

Combining CSC-targeted medicines with standard chemotherapy or radiation therapy may increase the effectiveness of the course of treatment. For instance, a recent study showed that combining chemotherapy and a Notch inhibitor increased survival in a mouse model of colon cancer (Orian-Rousseau and Ponta 2015). Therefore, it is thought that to increase the effectiveness of colon cancer treatment, the development of targeted treatments for CCSCs might be a viable strategy. Further study is required to establish the most effective method to target CCSCs and enhance patient outcomes, even though various promising treatments have been put forward.

Identifying and Tracking Biomarkers for CCSCs

As it is believed that CSCs are essential for the development, spread, and recurrence of colon cancer, obtaining biomarkers for recognizing and tracking the growth of CCSCs is critical for early diagnosis, prognosis, and therapy. Several biomarkers for tracking and recognizing of CCSCs have been found (Dalerba et al. 2007; Vermeulen et al. 2010; Haraguchi et al. 2006; Zhang et al. 2008; Yanamoto et al. 2011). Some of these biomarkers are as follows:

CD44

It is a glycoprotein on the cell surface that cancer stem cells express. It takes involvement in cell communication, adhesion, migration, and interactions. CD44, which is overexpressed in CCSCs, is a potential biomarker for their identification and monitoring. The adhesion, motility, and intercellular communication of cells are all mediated by the transmembrane glycoprotein CD44. Owing to alternative splicing, CD44 has a large number of isoforms and is expressed more often in different malignancies, such as colon cancer. High CD44 expression in cancer patients was associated with poorer survival outcomes and high metastases (Wang et al. 2018; Wang and Scadden 2015).

CD133

CSCs frequently overexpress a transmembrane glycoprotein called CD133, also known as prominin. CD133 plays a key role in cell signaling, communication, and adhesion. Its overexpression in CSCs makes it a useful biomarker for identifying and tracking these cells, including in colon cancer. CD133’s potential involvement in regulating cell proliferation and differentiation also makes it a relevant target to study CSCs (Shmelkov et al. 2008; Scatena et al. 2011). When CD133 expression is present, several cancer types, including colon cancer, have a poor prognosis. Colon cancer cells that are CD133-positive are more tumorigenic, capable of self-renewal, and resistant to therapy than those that are CD133-negative. Hence, it has been proposed that using monoclonal antibodies or small molecule inhibitors to target CD133 is one method of eliminating CCSCs (Grosse-Gehling et al. 2013; Jaks et al. 2008).

Lgr5

Lgr5 is a G protein–coupled receptor with leucine-rich repeats that is expressed on intestinal stem cells. It has been demonstrated that CCSCs overexpress it, making it a possible biomarker for its diagnosis. The Lgr5 gene produces the transmembrane receptor protein Lgr5. Lgr5, a protein primarily expressed in stem cells of various organs such as the liver, stomach, intestinal crypts, and hair follicles, plays a key role in the regeneration and proliferation of these cells (Merlos-Suárez et al. 2011; Scatena et al. 2011). In the intestinal crypts, Lgr5 is expressed in the rapidly dividing stem cells that are responsible for the continuous renewal of the intestinal epithelium. Similarly, in hair follicles, Lgr5-expressing stem cells are crucial for hair growth and regeneration (Kahlert et al. 2011).

ALDH1

ALDH1 is an enzyme that helps the body eliminate aldehydes. It is a possible biomarker for the diagnosis and surveillance as it has been demonstrated that CCSCs overexpress it. The bone marrow, breast, prostate, liver, and lung are just a few of the tissues that have high levels of ALDH1 expression. ALDH1 has been proven to be a marker for both healthy and aggressive stem cells throughout multiple tissues. The expression of ALDH1 has been correlated with resistance to radiation and chemotherapy treatments across multiple cancers, including breast cancer and lung cancer (Charafe-Jauffret et al. 2010; Winter et al. 2003).

EpCAM

EpCAM is a cell surface glycoprotein expressed by epithelial cells, including CCSCs, where it is frequently overexpressed and therefore a potential biomarker for identifying and tracking these cells. It plays a crucial role in cell adhesion, signaling, differentiation, and is also expressed in several healthy tissues such as the liver, pancreas, and digestive system. Breast cancer, CRC, and ovarian cancer are only a few of the malignancies where EpCAM is overexpressed. EpCAM expression has been connected to tumor development, invasion, and metastasis. In several malignancies, EpCAM is employed as a marker for CSCs (Pevny and Lovell-Badge 1997).

Sox2

It is a transcription factor that contributes to the maintenance and development of stem cells. It is a possible biomarker for the identification and tracking because it has been demonstrated that CCSCs overexpress it. An essential transcription factor for maintaining pluripotency in neural stem cells and embryonic stem cells is SOX2 (Sarkar and Hochedlinger 2013; Pesce and Schöler 2001; Rajasekhar and Vemuri 2009).

BMI1

It is a transcriptional inhibitor that controls stem cell differentiation and self-renewal. It has been demonstrated that CCSCs overexpress it, making it a possible biomarker for their diagnosis (Rajasekhar and Vemuri 2009).

Nanog

It is a transcription factor that is involved in stem cell self-renewal and pluripotency. It is overexpressed in CCSCs and is a potential biomarker for their detection and monitoring (Rajasekhar and Vemuri 2009).

OCT4

OCT4, a transcription factor, is involved in the self-renewal and pluripotency of stem cells. Its overexpression has been demonstrated in CCSCs, making it a potential biomarker for the detection and monitoring. OCT4 plays a critical role in maintaining the pluripotency of embryonic and germ cells and serves as a marker for various stem cells, including CSCs. It has been found to be expressed in several cancer types, such as ovarian, bladder, and testicular, and high OCT4 levels have been linked to poor prognosis in different malignancies in cancers such as breast and lung cancer (Looijenga et al. 2003; Ma et al. 2020; Scatena et al. 2011).

KLF4

It is a transcription factor that regulates stem cell self-renewal and differentiation. It is elevated in CCSCs and might be used as a diagnostic factor, for the discovery of novel therapy and tracking the disease condition. KLF4 is widely recognized for acting as a tumor suppressor in many different forms of cancer and as a crucial regulator of stem cell differentiation. It has been demonstrated that KLF4 may have a therapeutic effect in the treatment of cancer by preventing the proliferation of cancer cells and encouraging their differentiation. Intestinal cells, keratinocytes, epithelial cells, and other cell types have all been identified to express KLF4. KLF4 in particular is a marker for intestinal stem cells, which is essential for their upregulation and development (Kemper et al. 2010; Scatena et al. 2011; Rajasekhar and Vemuri 2009).

Drug Resistance Mechanism in Colonic Cancer Stem Cells

Drug resistance in CSCs is a major challenge in the treatment of colon cancer. CSCs are a small population of cells within a tumor that can self-renew and differentiate into all the cell types that comprise the tumor. These cells are assumed to be in charge of the development, growth, and metastasis of tumors. CSCs are also known to be more resistant to chemotherapy and radiation therapy than the non-CSCs within the tumor. In CCSCs, overexpression of ATP-binding cassette (ABC) transporters is one among the several processes that lead to drug resistance. Drug efflux from cells is facilitated by a class of proteins known as ABC transporters. Amplification of ABC transporter genes in CSCs can result with decreased intracellular drug accumulation, leading in drug resistance. ABC transporters like as ABCB1 and ABCG2 have been shown to be elevated in CCSCs.

Altered Signaling Pathways

Signaling pathways such as the Wnt/β-catenin, Notch, and Hedgehog pathways are known to be involved in the maintenance of stem cell properties in CSCs. Dysregulation of these pathways can lead to drug resistance. For example, activation of the Wnt/β-catenin pathway has been shown to promote drug resistance in CCSCs.

Epigenetic Modifications

Epigenetic alterations, such as DNA methylation and histone modifications, can alter the expression of genes and increase a person’s susceptibility to medication. Epigenetic alterations have been demonstrated to control the expression of genes involved in drug metabolism and transport in CCSCs.

Cancer Stem Cell Niche

Drug resistance can also be influenced by the milieu known as the stem cell niche that surrounds CSCs. CSCs are given nutrients from the stem cell niche that help them survive and regenerate themselves. The stem cell niche is hypothesized to contribute to drug resistance in CCSCs by supplying protective signals that guard against chemotherapy-induced cell death. Many cell types, including stromal cells, immunological cells, and endothelial cells, may be found in the CSC niche. These cells interact with CSCs and supply the signals needed for their survival. The ECM, which offers CSCs structural support and signaling chemicals, is a crucial part of the niche. ECM abnormalities can encourage CSC growth and tumor development (Estrada-Meza et al. 2022; Batlle and Clevers 2017; de Sousa e Melo et al. 2017; Ricci-Vitiani et al. 2009).

Development of Combination Therapies Targeting CCSCs and Other Cancer Cells

A novel strategy to increase the effectiveness of cancer therapy is to use combination medicines that target CCSCs and other cancer cells. CCSCs, a tiny group of cells that can self-renew and differentiate inside colon cancers, are thought to be the cause of tumor genesis, progression, and therapeutic resistance. It has been demonstrated that targeting these cells with certain medicines increases overall survival and lowers the likelihood of recurrence (Chen et al. 2020). Surgery, chemotherapy, and radiation therapy are now used to treat colon cancer, but their effectiveness against CSCs is frequently hampered by their toxicity, resistance, and lack of potency. Consequently, new treatments are required to specifically target CSCs as well as other cancer cells. To increase the efficacy of cancer treatment, combination medications that focus on both CSCs and other cancer cells are being developed (Lin et al. 2011). These treatments may combine traditional chemotherapy with targeted therapy, immunotherapy, and stem cell–targeting drugs. Although CCSCs and other cancer cells have been targeted with conventional chemotherapy medicines like 5-fluorouracil (5-FU) and oxaliplatin, their effectiveness is constrained by their toxicity and drug resistance. It has been demonstrated that combination therapies use less chemotherapy and are focused on treatments with more efficiency. Targeted medicines have been designed to specifically target CCSCs and other cancer cells by inhibiting pathways associated with tumor growth and survival, such as EGFR, VEGF, and Wnt signaling. Preclinical studies have demonstrated the efficacy of combination medicines that include targeted therapy and immunotherapy. Checkpoint inhibitors are an example of an immunotherapy drug that has been designed to stimulate the immune system’s ability to identify and eradicate cancer cells, including CSCs. Preclinical studies have demonstrated the efficacy of combination treatments that combine immunotherapy with medicines that target stem cells (Le et al. 2014). Stem cell–targeting drugs have been created to specifically target CCSCs by preventing stem cell self-renewal and promoting differentiation. Examples of these medicines are salinomycin and napabucasin. In preclinical investigations, combination treatments that combine chemotherapy or immunotherapy with stem cell-targeting drugs have demonstrated encouraging outcomes. Current clinical trials are evaluating the efficacy and safety of combination medicines that target CCSCs and other cancer cells (Jang et al. 2007).

Opportunities and Challenges for Developing Personalized Therapies Targeting CCSCs

Developing personalized therapies targeting CCSCs is a promising approach to improving the outcomes of patients with colon cancer. However, this approach also presents several opportunities and challenges. Personalized therapies that specifically target CCSCs have the potential to improve patient outcomes by reducing tumor recurrence and increasing survival rates. More effective treatments suggested that CSCs are assumed to be responsible for tumor initiation, development, and metastasis, targeting CSCs may be more successful than targeting the main tumor mass. Minimizing treatment side effects, personalized therapies that target CSCs may be less toxic than traditional chemotherapy and radiation therapy, as CSCs are known to be more resistant to these treatments than non-CSCs (Crea et al. 2011). Personalized treatment plans and personalized therapies allow for the development of treatment plans tailored to the specific genetic and molecular characteristics of each patient’s tumor. Identification of novel targets and developing personalized therapies require a deep understanding of the genetic and molecular characteristics of CSCs. This process can lead to the identification of novel targets for therapy development (Dalerba and Clarke 2017; Dubey and Gupta 2017). The heterogeneity of CSCs is a heterogeneous population of cells with varying genetic and molecular characteristics. Developing personalized therapies that target all subtypes of CSCs can be challenging. Due to lack of reliable biomarkers, the development of biomarkers that can accurately detect CSCs is still ongoing. This poses a problem for the creation of tailored treatments that specifically target CSCs. A limited understanding of the biology of CSCs is still being investigated. Lack of understanding presents a challenge for the development of targeted therapies. In terms of resistance to therapy, CSCs are known to be more resistant to chemotherapy and radiation therapy than non-CSCs. Developing therapies that can effectively target CSCs and overcome their resistance to treatment is a major challenge. Developing personalized therapies can be time-consuming and costly. Ensuring that these therapies are available to every patient, irrespective of their financial means, presents an additional hurdle (Crea et al. 2011; Dalerba and Clarke 2017; Dubey and Gupta 2017; Ricci-Vitiani et al. 2009).

Identification of Novel Drug Delivery Approaches for CCSCs Targeting Drugs

CCSCs are a subset of cancer cells with the potential to self-renew. They are in charge of the development, growth, metastasis, and recurrence of tumors. A possible strategy to increase the effectiveness of colon cancer treatment is to target CCSCs. Yet, the complex milieu of the colon and the diversity of the CCSC population make it difficult to deliver medications directly to CCSCs. Here are a few possible medication delivery strategies for CCSCs. By surface functionalizing nanoparticles with ligands that bind precisely to CCSC surface indicators, CCSCs may be targeted with particular nanoparticles. For instance, it has been demonstrated that nanoparticles coated with antibodies against CD44, a hallmark of CCSCs, preferentially aggregate in colon cancers and inhibit CCSC activity (Singh and Lillard 2009). Stem cells, such as mesenchymal stem cells (MSCs), have been shown to migrate specifically to colon tumors and release anticancer drugs in response to tumor signals. MSCs can be engineered to express CCSC-targeting receptors, such as CD44 or EpCAM, to enhance their specificity for CCSCs. Gene therapy can be used to deliver therapeutic genes to CCSCs. For example, lentiviral vectors can be used to deliver shRNAs that target CCSC-specific genes, such as CD44 or Lgr5 (Gao et al. 2013). Alternatively, gene therapy can be used to express toxic genes specifically in CCSCs, such as diphtheria toxin, to selectively kill CCSCs. Drug conjugates can be designed to selectively target CCSCs by conjugating a drug to a ligand that binds to a CCSC-specific surface marker. For example, paclitaxel can be conjugated to an antibody against CD44 to selectively kill CCSCs. The microenvironment of colon tumors, including the hypoxic and acidic conditions, can be exploited to selectively deliver drugs to CCSCs. For example, hypoxia-activated prodrugs can be used to selectively kill CCSCs in hypoxic regions of the tumor (Todaro et al. 2007; Yan et al. 2020; Scatena et al. 2011).

The Future for CCSCs in Drug Development

The identification of CCSCs has opened up new avenues for the development of more effective cancer therapies, some of which are explained below:

Personalized Medicine

The goal of personalized medicine is to provide treatments that are specifically suited to each patient’s unique genetic and molecular profile. In the future, CCSCs may be examined for specific mutations or patterns of expression that might help determine the most tailored treatments (Estrada-Meza et al. 2022; Batlle and Clevers 2017; Todaro et al. 2007).

Immunotherapy

Immunotherapy has shown promising results in the treatment of various cancers, including colon cancer. Future studies could explore the use of immunotherapy to target CCSCs, potentially using novel targets that are specific to CCSCs (Topalian et al. 2012). Immunotherapy encompasses various treatment modalities, such as cancer vaccines, CAR-T cell therapy, and checkpoint inhibitors, that enable the immune system to fight cancer in distinct ways. Checkpoint inhibitors function by blocking proteins on cancer cells’ surface that would normally prevent the immune system from attacking them, thereby enhancing the immune system’s ability to recognize and eliminate cancer cells. CAR-T cell therapy involves modifying patients’ immune cells in a lab to target and fight cancer cells, which are then reinfused into the patient’s body. Cancer vaccines stimulate the immune system to recognize and attack cancer cells, prompting an immune response to combat the disease (Doudna and Charpentier 2014).

Gene Editing

Current developments in gene editing technologies, such as CRISPR-Cas9, might be utilized to target CCSCs specifically. Moreover, CCSCs might be altered through gene editing to make them more responsive to conventional treatments. CRISPR-Cas9 is the most popular gene editing technique since it employs a guide RNA to target a particular DNA region and a Cas9 enzyme to cut the DNA. This enables the replacement, insertion, or deletion of genetic material at the desired location (Komor et al. 2016). Many potential uses for gene editing exist in the fields of health, agriculture, and fundamental research. It might be applied to the treatment of genetic abnormalities, the creation of disease-resistant crops, and novel cancer medicines, among other things. Moreover, the use of germline editing to alter genes that can be handed down to future generations has generated ethical questions. Some are concerned that this may have unexpected repercussions or result in new inequalities (Joyce and Fearon 2015).

Microenvironment Targeting

The microenvironment of colon tumors, including the extracellular matrix, stromal cells, and immune cells, plays a crucial role in CCSC survival and function. Targeting the microenvironment of colon tumors could provide a new approach to eliminating CCSCs and preventing tumor recurrence (Bao et al. 2006).

Conclusion

The recent discovery of medications that precisely target CCSCs is an important field of study that offers significant possibilities for the development of more effective therapies for colon cancer. More study is needed to better understand the biology of CCSCs and to find novel therapeutic development targets. A potential area of study in the discovery of novel medications for the treatment of colon cancer is the discovery and targeting of CCSCs. The formation of tumors and their resistance to conventional chemotherapy and radiation therapies are considered to be caused by CSCs. Patients with colon cancer may be benefited from a more potent therapy option if certain medications are used to target these cells. Wnt signaling pathways, CSC markers, and metabolic pathways are a few examples of prospective therapeutic targets. Finding safe and efficient dosage regimens is one of the difficulties in developing medications that selectively target CSCs, but researchers are hopeful about the potential advantages of this strategy. To completely comprehend the biology of CCSCs and to find novel therapeutic targets, more in-depth analysis is required. Clinical studies are required to assess the security and effectiveness of new medicines. Nonetheless, there is optimism for the discovery of novel medications that can enhance outcomes for colon cancer patients with ongoing investment and innovation. Drug resistance in CCSCs is a multifaceted process involving several processes, including epigenetic alterations, quiescence, altered signaling pathways, and CSC niche. The discovery of CCSCs has opened up new possibilities for the discovery of more efficient and personalized cancer medicines. Personalized medicine, immunotherapy, gene editing, and microenvironment targeting may all play a role in future advancements in the development of drugs that target CCSCs. For the development of cutting-edge therapies that may effectively target CCSCs and improve the prognosis for colon cancer patients, it is crucial to understand these pathways. There are potential and difficulties in creating tailored treatments that target CCSCs. While this approach has the potential to improve patient outcomes and reduce treatment side effects, several challenges must be addressed, including the heterogeneity of CSCs, the lack of reliable biomarkers, and the resistance of CSCs to therapy. Addressing these challenges will require ongoing research and collaboration among researchers, clinicians.

Cross-References