As a lethal disease, cancer poses a challenge to the entire human race. Despite the progress made in modern medicine, cancer continues to be a leading cause of mortality worldwide. Moreover, the number of oncological diseases exhibits a steady growth rate due to poor ecology worldwide, particularly when considering the effect of microplastics on the epithelial barrier of mucous membranes (1), as well as the negative impact of agricultural pesticides (2), the nitrate poisoning of air (3)and drinking water (4), the consumption of red meat (5), and residing in proximity to industrial facilities (6).

Research is focused on socially important forms of cancer, including lung cancer, breast cancer and colorectal cancer (CRC), which is one of the most prevalent oncological diseases (7). Colonoscopy (8) with a subsequent morphological analysis of colon biopsy samples does not always suffice for the effective prevention of CRC (9-11). Additional pathomorphological tests on colon biopsy samples, involving molecular medicine methods, can significantly enhance the scope of diagnostics. However, the removal of precancerous lesions only does not solve the issue of effectively preventing CRC in high-risk patients. One of the possible solutions could be the development of pharmacological treatment protocols to regulate molecular mechanisms, responsible for the regeneration of cellular elements of the colon mucous membrane. In this context, special focus could be placed on decreasing β-catenin level that is one of the most critical indicators of the functional activity of neoplastic cells.

The present review discusses the methods of the pharmacological regulation of β-catenin in patients with precancerous colorectal lesions who are at a high risk of developing CRC.

Among the socially significant types of cancer, CRC stands out. At 60-70 years of age, the risk of developing the disease is highest and increases as one ages (12). The risk factors include hereditary genetic syndromes (Table I), communicable and non-communicable diseases, lifestyle risk factors (Table II) and inflammatory bowel disease (IBD).

A family history of CRC is one of the key risk factors, as well as the presence of syndromes, such as familial adenomatous polyposis (FAP), mismatch repair (MMR) gene mutations, Lynch, Muir-Torre, Peutz-Jeghers, Cowden, juvenile polyposis with autosomal dominant type of inheritance, serrated polyposis syndrome and Cronkhite-Canada syndrome with an unknown type of inheritance (Table I).

The results of multiple studies have demonstrated that patients with a positive family history have a lower risk of mortality due to CRC. A possible explanation for the link between a family history of CRC and improved survival rates is that those with a cancer-related family may make more conscious lifestyle choices, such as quitting smoking and increasing their physical activity. Another contributor could be more frequent and thorough screening that allows for the discovery of cancer at the early stages and, therefore, improves the chances of survival. Genetic differences between patients with CRC and those with no family history may be one more explanation for the existing contrast in survival rates. Studies have shown that patients with CRC and a positive family history are more likely to have heightened levels of microsatellite instability, which may lead to improved survival rates. Determining the influence, that family history has on the prognosis of CRC, is not an easy feat, since both genetic and environmental factors are to be considered; therefore, further research is required (13).

Among individuals aged 20-49 years, the incidence of CRC has increased in nine countries (Germany, USA, Australia, Canada, New Zealand, Great Britain, Denmark, Slovenia and Sweden), while only three countries have exhibited a decrease in its incidence (Italy, Austria and Lithuania) (14), and more than half of patients do not have the disease in their family history (15).

There is a consistent rate of morbidity among the elderly in North America, Europe and Oceania. A growing trend of the prevalence of CRC has been observed among young individuals with a high income in nine different countries on three different continents (14).

At the same time, the frequency of right-sided CRC makes it objectively more difficult to make a diagnosis during the endoscopic examination (16), as is the case with late-developing symptoms of colon obstruction due to a larger diameter of the right portion of the colon (16).

Colonoscopy is a gold standard for the diagnosis of colorectal neoplasms (16). Precancerous lesions are frequently discovered in patients aged ≥50 years during colorectal screening. The overwhelming majority of cases exhibit no symptoms, apart from occasional stomach aches and other signs of dyspepsia (17).

The diagnosis of precancerous lesions during colonoscopy is relatively easy; however, neoplasms in the proximal regions of the colon are poorly visible in a routine endoscopy (16) due to the larger diameter of the right-sided segments of the colon. This results in the later manifestation of intestinal obstruction and other CRC symptoms (16). The removal of such precancerous lesions is a crucial step in preventing CRC.

The European Society of Gastrointestinal Endoscopy recommends the cold snare method for the removal of polyps ≤9 mm in size. Diathermocoagulation together with mucous membrane lifting are used to remove sessile polyps ≤20 mm in size. If a polyp is pedunculated and >20 mm in size, those with a large head or a stem with >10 mm in diameter should be treated with a combination of diathermocoagulation and adrenaline injection into the stem or with one of the preventive mechanical techniques of hemostasis. However, larger size, visual signs of invasion and diagnostic extent of endoscopic ultrasonography are not always conclusive enough to select the only right method of polyp elimination (10); thus, an urgent morphological analysis may be required.

The World Health Organization (2019) (18) distinguishes CRC with serrated histoarchitecture, tubular and tubulovillous adenomas, focal intraepithelial neoplasia with underlying chronic inflammation (Table III). Moreover, as demonstrated in clinical practice, precancerous colorectal lesions often have mixed histological patterns with both serrated and tubular components, and there are no data either on what type of adenoma they should be classified as, or their molecular nature. Precancerous lesions with a serrated architecture appear due to the impaired proliferation in the cambium layer of intestinal epithelium in the crypt base, resulting in relocation of proliferating cells into the apical sections and development of serrated pattern (Fig. 1A) due to the competition for a place on a basal lamina (18).

The localization of proliferation zones in basal sections of colonic crypt without dysplasia indicators is typical for hyperplastic polyp, in contrast to which serrated adenoma is characterized by the horizontal displacement of a proliferative zone along its own muscularis mucosae, spread of serrated pattern into the crypt base, dilatation of its basal parts, asymmetric proliferation with dysplasia signs, formation of slit-like serrated structures and ectopic crypts similar to intussusception (Fig. 1B) (18).

The morphology of tubular adenomas shows the presence of glandular crypts, having mostly a typical architecture, exhibiting elongation, and increase in their number. The epithelium has enlarged hyperchromatic nuclei with varying degrees of stratification, spindle formation and loss of polarity, as well as a further overall decrease in the number of goblet cells. The specific feature of tubulovillous adenoma is the presence of finger-like projections, appearing as a result of crypt elongation (Fig. 1C).

A separate subtype of precancerous colorectal lesions is intraepithelial neoplasia in the case of IBD that creates additional complications for the differential diagnosis of serrated and conventional adenomas that are not IBD-related. The primary pathomorphological variation between IBD dysplasia and other precancerous lesions is considered to be the unique localization of dysplastic cells, which typically occurs in the upper crypts during sporadic adenomas and in the entire crypts during colitis (18,19) (Fig. 1D). In reality, morphologists usually cannot assess the exact localization of dysplastic cells due to the nature of tangential section, the incorrect placement of the sample in paraffin-embedded blocks, etc. One of the ways to solve this issue is using molecular genetic diagnostics.

Reduced DNA methylation and associated epigenetic disorders of gene expression (20,21) play a particularly critical pathophysiological role in the development of CRC. The disruption of DNA methylation is caused by mutations in DNA methyltransferase (DNMT) genes responsible for the genome-wide methylation patterns (22); in particular, the methylation status of the promoter regions of the methylguanine-DNA-methyltransferase gene (23,24) he disruption of which is predominantly associated with mutations in the KRAS and BRAF genes (25), which are found in 22% of hyperplastic polyps, 25% of sessile serrated adenomas, and 50% of serrated adenocarcinomas (24).

The proteins, bone morphogenetic protein 3, N-myc downstream-regulated gene 4, annexin A10 (25-27), Runt-related transcription factor 3, suppressor of cytokine signaling 1, neurogenin 1, calcium channel, voltage-dependent, T type, alpha 1G subunit, insulin-like growth factor 2, p16, human mutL homolog 1 and MSX2-interacting nuclear target protein (28-30) have been described as markers of impaired genomic methylation status for CRC. The impairment of the DNA methylation status is typical for right-sided location of CRC, female patients, individuals of an advanced age (31), and high levels of genomic instability (32-34).

Genomic instability is a natural result of mutation accumulation and a driving force of the neoplastic process. A central role in the development of this phenomenon belongs to epigenetic failures in the expression of MMR genes, which function as a system of correcting improperly paired nucleotides, deletions or inclusions of incorrect bases, occurring during DNA replication. The proliferation of cells with an unstable genome is accompanied by the development of aneuploidy, which is observed in 65-85% of sporadic colorectal tumors (35-38), and is often accompanied by mutations in the adenomatous polyposis coli (APC), tumor protein p53 (TP53), catenin beta-1 and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha genes, in 20% of cases (39). APC gene mutation can initiate both tubulovillous (40-42) and serrated adenomas (43,44).

Among the first markers to exhibit an increase in expression, are the non-coding RNAs, CCAT1 and HOTAIR, in the plasma of patients with CRC; their expression was found to be significantly higher in patients with CRC than in those of the healthy controls. Other circulating IncRNAs that have been described as potential biomarkers for CRC detection include LOC285194, RP11-462C24.1 and Nbla12061, 91H, PVT-1 and MEG3, NEAT1 and NEAT2(45).

The serum levels of insulin-like growth factor binding protein-2 are elevated in patients with colon cancer, which is associated with neoplastic changes in the colon and carcinoembryonic antigen concentrations (45), as well as the overactivation of pyruvate kinase M2.

Dbf4-dependent kinase genes, which inhibit the Wnt-signaling pathway, are epigenetically silenced in CRC cells due to promoter hypermethylation. The activation of DKKS through small interfering RNA promotes the growth and invasion of cancer cells in vitro (45).

When precancerous lesions transform into CRC, a number of molecular mechanisms are activated, resulting in an increased level of β-catenin in pathologically altered cells. The Wnt signaling pathway plays a crucial role in this process.

β-catenin plays a crucial role in the Wnt signaling pathway, which regulates the balance between the symmetric and asymmetric division of both normal stem cells and cancer stem cells. β-catenin binds to the multiprotein destruction complex, which includes APC, Axin, casein kinase 1 and glycogen synthase kinase (GSK)-3, without the presence of a Wnt ligand. The secondary consequence is that GSK-3 phosphorylates β-catenin, leading to its ultimate degradation in the proteasome.

Wnt-ligands uses the transmembrane receptors, Frizzled and low-density lipoprotein receptor-related protein 4/5, to affect the cells. This complex activates the cytoplasmic protein Dishevelled, stops β-catenin degradation and inactivates GSK-3β, leading to accumulation of β-catenin in the cytoplasm and creation of conditions, allowing β-catenin to enter the nucleus, activate T-cell factor/lymphoid enhancer-binding factor and triggers the expression of C-MYC, cyclin-dependent kinase 4, WNT1-inducible signaling pathway protein-1, peroxisome proliferator-activated receptor γ (PPAR-γ) and other genes.

As an alternative mechanism for increasing β-catenin synthesis in precancerous lesions cells, both the direct activation of the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway, which is the predominant signaling pathway that inhibits apoptosis, and the direct activation of intracellular AKT have been described.

PI3Ks are intracellular lipid kinases involved in the regulation of cell proliferation, differentiation and survival, that promote cell growth by inhibiting apoptosis in colorectal cancer cells and influences the effectiveness of chemotherapeutic agents (46).

AKT (AKT proto-oncogene), which plays a key role in several types of cell death, as well as in the destruction of extracellular signaling molecules, oxidation, osmotic stress and ischemic shock, phosphorylates GSK-3Β and increases the content of β-catenin in the cancer stem cells. In turn, mTOR forms two multiprotein complexes: mTorc1 and mTorc2, which are capable of antagonistically regulating each other's activity, while the first reduces and the second increases the content of β-catenin (Fig. 2).

A higher β-catenin level activates telomerases (tert), causing their elongation, the immortalization of pathologically altered cells and the increased production of transforming growth factor β (TGFβ), that uses the SMAD and DAXX, death-associated protein 6 signaling pathways to activate the PI3K/AKT/mTOR axis. This results in the accumulation of β-catenin (47) and the triggering of epithelial-mesenchymal transition (EMT) in precancerous lesion cells (48-50), accompanied by activation of Snail, Twist, Slug, zinc finger E-box binding homeobox (ZEB)1, ZEB2, lymphoid enhancer-binding factor 1 and other transcription factors.

The most critical part of EMT is the suppression of E-cadherin synthesis, involved in the formation of tight junctions between epitheliocytes, the increased expression of vimentin, smooth muscle actin, fibronectin and genes, responsible for the mesenchymal phenotype of epitheliocytes. The increased synthesis of extracellular matrix metalloproteinases completes the transformation of precancerous lesions into CRC and distinguishes the cells, capable of invasion into surrounding tissues and penetration into distant organs. In this respect, β-catenin accumulation in the cells of precancerous lesions gives a strong indication that transformation into CRC has been activated (51); however, the existing methods for diagnosing precancerous lesions and CRC, as aforementioned, do not include a standardized immunohistochemical assessment of the nuclear expression of β-catenin, despite the fact that the literature data on chemoprevention of colorectal cancer focuses on reducing the level of β-catenin.

Certain difficulties in the differential diagnosis of precancerous lesions and CRC are associated with IBD, involving mucous damage due to infection, allergic reactions or medication, that adversely affects the ability of goblet cells to produce mucin, functioning as a physical and chemical barrier between gut microbiota and mucous membrane (51).

Neutrophils and monocytes are the first to react to the disruption by migrating towards the damaged area with help of chemotactic gradients, formed by interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α cytokines, chemokine (C-C motif) ligand 8, C-X-C motif chemokine ligand 10 chemokines, macrophage inflammatory protein 2, granulocyte-macrophage colony-stimulating factor (GM-CSF), and granulocyte colony-stimulating factor (52).

Neutrophils provide the elimination of pathogens via phagocytosis, the formation of reactive oxygen species and the release of matrix metalloproteinases, elastase and neutrophil extracellular traps. It is generally accepted that once neutrophils complete their task, they should immediately undergo apoptosis, reducing inflammation, promoting the restoration of surrounding tissues and the return to normal tissue homeostasis. Normally, the regulation of local neutrophil activity is performed by immunosuppressive cytokines, in particular, IL-10 and TGF-β, that are produced by M2-activated macrophages, a result of transformation, undergone by monocytes that migrated to the phlogogenic area. In the case of IBD, this does not take place due to excessive phlogogenic stimulation (52).

The accumulation of activated neutrophils, macrophages and dendritic cells promotes changes in the crypt structure, the disruption of intercellular contacts and integrity of the basal lamina, that leads to the formation of crypt abscesses and is characterized by the increased synthesis of the pro-inflammatory cytokines, TNF-α and IL-1β, and the secretion of non-cytokine inflammatory molecules, attracting T-cells and neutrophils to the area of inflammation (Fig. 3). In turn, M1-activated macrophages in collaboration with intestinal fibroblasts induce fibrotic process, which is a disproportionate synthesis and the accumulation of extracellular matrix components, causing the disruption of mucosal histological architecture, the formation of ulcers and scars of the colonic wall, which significantly complicates endoscopic and morphological diagnosis of CRC (52).

In light of the above, molecular markers indicating the systemic nature of the pathological process are of particular diagnostic value. There is no consensus on such markers, but it is known that neutrophils, monocytes and, to a certain extent, dendritic cells are formed in the bone marrow from a common multipotent progenitor cell of the megakaryocytic lineage that is a direct descendant of a hematopoietic stem cell. It is reasonable to assume that genetic mutations in the stem cell or progenitor cell may prevent immunocytes from performing their regulatory functions, lead to their immortalization and cause disease progression.

A similar scenario was described (53) as one of the possible manifestations of the phenomenon, known as the clonal hematopoiesis of indeterminate potential (CHIP) that is frequently observed during the normal process of ageing (54). The phenomenon is based on the fact that in by the age of 70, hematopoietic stem cells of bone marrow accumulate from 350,000 to 1,400,000 mutations, including DNMT3A, Tet methylcytosine dioxygenase 2 (TET2), additional sex combs like-1, protein phosphatase 1D, Janus kinase 2 (JAK2), splicing factor 3b subunit 1, serine/arginine-rich splicing factor 2, TP53, guanine nucleotide binding protein, alpha stimulating activity polypeptide and guanine nucleotide-binding protein. If even one of the mutations appears to be able to guarantee the dominance of corresponding hematopoietic stem cell clone over other clones, a state of clonal expansion appears, which, on the one hand, significantly increases the risk of hematological cancer and, on the other hand, promotes the appearance of mutant immunocyte clones, responsible for a number of chronic inflammatory diseases (54).

Mutations, typical for CHIP, are found in hematopoietic stem cells, monocytes and granulocytes. Individuals with the DNMT3A mutation have a high level of IL-6 in their blood; mouse macrophages with TET2 mutation, when stimulated by bacterial endotoxin, exhibit a significantly increased production of IL-1β, -2, -6 and -8. The JAK2 mutation is always accompanied by a much stronger activation of granulocytes and the intensified production of IL-6 and -18, without an increase in the C-reactive protein level. Based on this, it is possible to make an accurate assessment of the local processes in the colon, taking into consideration the existing molecular and genetic damage, found in the stem cells and immunocytes (53).

IBD is an unmodifiable risk factor for the development of CRC (54). One of the significant causes of CRC in IBD-associated individuals is chronic inflammation, which is widely acknowledged to promote CRC. The mechanisms responsible for this are not yet fully understood (55). While the suppression of inflammation could potentially lower the risk of IBD-related CRC, there is limited evidence to suggest that anti-inflammatory agents, which are commonly used to treat IBD, have chemopreventive effects on patients with cancer (55).

Decreasing the level of β-catenin, as a key component of the Wnt signaling pathway, plays a crucial role in the prevention of precancerous lesions that are not associated with chronic inflammation. Genes, proteins involved in the signaling pathways of CRC and inhibitors are listed in Table IV (56-58).

Despite the advances of modern pharmacological industry, the chemoprophylaxis of CRC for patients with precancerous lesions remains rather ineffective. Precancerous colorectal lesions are detected daily via endoscopic methods and are confirmed pathomorphologically. Patients with IBD are also left to constantly balance between the remission and exacerbation stages. The key to success may be the local reduction of nuclear β-catenin that is the main initiator of oncogenic transformation of precancerous lesions into CRC. The immunohistochemical evaluation of nuclear β-catenin hyperexpression in precancerous cells may aid in the differential diagnosis of early-stage cancer and dysplasia, and may improve the assessment of the treatment efficacy in IBD itself and IBD-associated lesions.

Multiple data on the effectiveness of chemoprevention remain conflicting; there are no reliable data on the reduction of nuclear β-catenin expression in studies on most pharmacological drugs, and in some cases, the supposed benefit is overshadowed by existing side-effects, particularly as regards GCs and thiopurines. There is also an issue with the cross-inhibition of drugs. Therefore, further studies are warranted to investigate the phenomenon of clonal hematopoiesis with uncertain potential, which is probably a decisive factor in the progression of IBD, and further studies of repurposed drugs are also required.