Role of S100 protein in CRC initiation

Tumour initiation is the initial stage of tumourigenesis. At this stage, irreversible genetic changes caused by oncogenic factors transform normal cells into malignant cells (Ref. Reference Testa, Pelosi and Castelli128). S100A1, S100A8 and S100A9 stimulate the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) (Refs. Reference Yu, Lu, Li, Xiao, Xing, Li and Wu26, Reference Simard, Cesaro, Chapeton-Montes, Tardif, Antoine, Girard and Tessier29). The increase in these factors may lead to the activation of oxidative stress, resulting in damage to different biological macromolecules, including proteins, nucleic acids, and lipids (Ref. Reference Pizzino, Irrera, Cucinotta, Pallio, Mannino, Arcoraci and Bitto129). The most sensitive target of oxidative stress is DNA, in which case ROS and RNS can cause DNA damage and mutations by incusing oxidation, halogenation, deamination, lipid peroxidation-derived adducts, and single- or double-strand breaks (Ref. Reference Kay, Thadhani, Samson and Engelward130). In addition, the binding of extracellular S100A1, S100A4, S100A6, S100A8/S100A9, S100A11, S100A12, S100A14, S100B, and S100P to TLRs and RAGE and activation of cellular signalling pathways resulting in the release of cytokines from inflammatory cells leads to ROS generation (Refs. Reference Duan, Wu, Zou, Wang, Ye, Li and Zhou15, Reference Simard, Cesaro, Chapeton-Montes, Tardif, Antoine, Girard and Tessier29, Reference Piazza, Leggiero, De Benedictis, Pastore, Salvatore, Tufano and De Robertis31, Reference Seguella, Rinaldi, Marianecci, Capuano, Pesce, Annunziata and Sarnelli82, Reference Cerezo, Remáková, Tomčik, Gay, Neidhart, Lukanidin and Šenolt131) and may contribute to the induction of mutagenesis in premalignant cells (Figure 3B). In summary, S100 proteins are implicated in cancer initiation by stimulating oxidative stress and inducing the expression of inflammatory cytokines.

Role of S100 proteins in CRC progression

The influence of pro-tumour factors and other specific conditions on damaged cells subsequently leads to the development of pre-malignant cells, which is known as the tumour promotion stage (Ref. Reference Testa, Pelosi and Castelli128). At this stage, cells undergo malignant conversion, resulting in aberrant proliferation to form the primary tumour and enter the stage of tumour progression (including tumour infiltration, invasion, and metastasis) (Figure 3C) (Refs. Reference Koveitypour, Panahi, Vakilian, Peymani, Seyed Forootan, Nasr Esfahani and Ghaedi105, Reference Hibino, Kawazoe, Kasahara, Itoh, Ishimoto, Sakata-Yanagimoto and Taniguchi132). S100A2, S100A4, S100A6, S100A7, S100A8/S100A9 and S100B, either as intracellular or extracellular factors, may exhibit malignancy-promoting effects and may be associated with the regulation of cell cycle progression, proliferation, migration, and local invasion in cancers (Refs. Reference Duan, Wu, Zou, Wang, Ye, Li and Zhou15, Reference Naz, Bashir, Ranganathan, Bodapati, Santosh and Kondaiah33, Reference Liu, Bunston, Hodson, Resaul, Sun, Cai and Ye51, Reference Duan, Wu, Ye, Wang, Yang, Zhang and Zhou95, Reference Sack, Walther, Scudiero, Selby, Aumann, Lemos and Stein107, Reference Seguella, Rinaldi, Marianecci, Capuano, Pesce, Annunziata and Sarnelli133).

The effects of S100 proteins on CRC progression have been investigated, with a focus on S100A4, S100A8, S100A9 and S100A8/S100A9 (Figure 3D). S100A4 plays a role in different cancer stages, including cell motility, adhesion, proliferation, angiogenesis, invasion, cell survival and metastasis. It is associated with CRC progression by modulating the signalling pathways of NF-κB, MAPKs, PI3K/AKT/mTOR and EGFR (Refs. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28, Reference Wang, Duan, Zou, Li, Yuan, Chen and Zhou32). The interaction of S100A4 with p53 may contribute to tumour growth and metastatic progression (Ref. Reference Orre, Panizza, Kaminskyy, Vernet, Gräslund, Zhivotovsky and Lehtiö114). S100A8 and S100A9, as homodimers or heterodimers, may affect tumour cell growth depending on their concentrations (Refs. Reference Duan, Wu, Ye, Wang, Yang, Zhang and Zhou95, Reference Li, Chen, Ding, Zhang, Luo, Wang and Liu101). Low concentrations of extracellular S100A8/S100A9 can promote cell growth by interacting with RAGE or TLR4 and subsequently activating MAPKs and the NF-κB signalling pathway, whereas high concentrations of S100A8/S100A9 can activate p53 transcriptional activity, presumably inducing p53-dependent cellular apoptosis (Ref. Reference Li, Chen, Ding, Zhang, Luo, Wang and Liu101). Notably, overexpression of S100A8/S100A9 in certain tissues correlates with inflammation and appears to be an initial step in the transformation of neoplastic lesions during CRC progression (Ref. Reference Peterova, Bures, Moravkova and Kohoutova79), suggesting a biological association between inflammation and neoplastic transformation in CRC.

Roles for other S100 proteins in CRC development have been demonstrated in several studies. For example, S100A2 activates the PI3K/AKT signalling pathway and upregulates glucose transporter 1 (GLUT1) expression in CRC, which induces glycolytic reprogramming and consequently increases tumour proliferation (Ref. Reference Li, Chen, Zhou, Niu, Wang, Li and Gao134). S100A3 appears to play a role in the occurrence and progression of various cancers; S100A3 overexpression may be linked to tumourigenesis and progression of CRC (Ref. Reference Liu, Sun, Zhi, Lu, Gao and Zhou41). S100A6 is overexpressed in CRC tissue and may play a role in tumour promotion (Ref. Reference Duan, Wu, Zou, Wang, Ye, Li and Zhou15). S100A14 is overexpressed in colon tissue (Ref. Reference Hashida and Coffey135) and may play roles in different cellular processes, including cell growth, motility and adhesion in CRC (Ref. Reference Diamantopoulou, Mantas, Kostakis, Agrogiannis, Garoufalia, Kavantzas and Kouraklis11). Low concentrations of extracellular S100A14 are involved in cell proliferation by binding to RAGE; however, S100A14 expression is inversely correlated with CRC progression (Refs. Reference Diamantopoulou, Mantas, Kostakis, Agrogiannis, Garoufalia, Kavantzas and Kouraklis11, Reference Jin, Chen, Luo, Ding and Liu136). Notably, S100A14 expression appears to be related to the expression of S100A1, S100A13 and S100A16, which are closely mapped to the 1q21 chromosomal region (Ref. Reference Hashida and Coffey135). S100P inactivates p53 and promotes cell proliferation in CRC, contributing to cytotoxic therapy resistance (Ref. Reference Gibadulinova, Pastorek, Filipcik, Radvak, Csaderova, Vojtesek and Pastorekova137). S100P expression is also correlated with clinical staging, recurrence and lymph node metastasis (Ref. Reference Dong, Wang, Yin, Chen, Li, Lin and Jiang75). However, the specific mechanisms underlying the expression of these proteins in CRC have not been fully elucidated.

Role of S100 proteins in TME formation in CRC

S100 proteins impact not only tumour promotion but are also closely related to the formation of tumour microenvironment (TME) by activating various immune cells (e.g., macrophages, T cells, B cells, etc.), cytokines, and chemokines, further supporting the role of these proteins in tumour progression (Refs. Reference Tanigawa, Tsukamoto, Koma, Kitamura, Urakami, Shimizu and Yokozaki53, Reference Bao, Wang, Dai, Liu, Zhang, Jin and Fang138, Reference Grum-Schwensen, Klingelhöfer, Beck, Bonefeld, Hamerlik, Guldberg and Ambartsumian139). The TME is formed as sites where cancer cells are in a network of stromal cells, including inflammatory immune cells, vascular cells and fibroblasts altogether (Ref. Reference Anderson and Simon140). These proteins can affect TME formation by excessive production of pro-inflammatory cytokines and chemokines, recruitment of immune cells and angiogenesis induction (Refs. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28, Reference Chen, Shu, Zhang, Ye, Tian and Shen30, Reference Anderson and Simon140). Among the S100 family proteins, S100A4, S100A8 and S100A9 are closely related to the TME by upregulating cytokines and chemokines and inducing immune cell infiltration in tumours (Refs. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28, Reference Ichikawa, Williams, Wang, Vogl and Srikrishna99, Reference Bao, Wang, Dai, Liu, Zhang, Jin and Fang138, Reference Grum-Schwensen, Klingelhöfer, Beck, Bonefeld, Hamerlik, Guldberg and Ambartsumian139). These proteins can directly or indirectly activate the NF-κB signalling pathway, which is always present in the TME. In addition, these proteins may play crucial roles in the inactivation of tumour suppressors, such as TP53, which regulates cellular homeostasis and exhibits transcriptional antagonism with NF-κB. This process increases the expression of NF-κB-dependent inflammatory genes (Ref. Reference Carrà, Lingua, Maffeo, Taulli and Morotti141).

S100 proteins may also play a decisive role in immune cell infiltration in TME. For example, Hatthakarnkul et al. (Ref. Reference Hatthakarnkul, Ammar, Pennel, Officer-Jones, Cusumano, Quinn and Edwards142) found that S100A2 expression was correlated with increased infiltration of CD163 M2-like macrophages in the tumour, suggesting that S100A2 contributes to immune activation (Ref. Reference Hatthakarnkul, Ammar, Pennel, Officer-Jones, Cusumano, Quinn and Edwards142). In another study, Kazakova et al. (Ref. Reference Kazakova, Rakina, Sudarskikh, Iamshchikov, Tarasova, Tashireva and Larionova143) analysed human CRC tissues and revealed that S100A4 was expressed by stromal compartments, particularly tumour-associated macrophages (TAMs) and showed a strong correlation with macrophage infiltration in CRC tumours (Ref. Reference Kazakova, Rakina, Sudarskikh, Iamshchikov, Tarasova, Tashireva and Larionova143). In addition, TAMs can be characterised by the upregulation of chemokine genes, such as IL-1β, IL-6 and IL-8, and S100 genes such as S100A8/S100A9 and S100A9 in primary CRC, resulting in the recruitment and regulation of immune cells (Ref. Reference Che, Liu, Huo, Luo, Xu, He, Li, Zhou, Huang, Chen, Ni, Zhou, Liu, Li, Zhou, Mo and Li144). Notably, the increased levels of IL-6 and IL-8 in the TME can upregulate the expression of S100A8/S100A9 in tumour-infiltrated myeloid cells, the differentiation of myeloid cells into S100A8/S100A9-expressing myeloid-derived suppressor cells (MDSCs) or M2 macrophages in the TME of CRC (Ref. Reference Kim, Oh, Kim, Park, Hong, Cheon and Kim145). Further studies are needed to determine the role of S100 proteins in the CRC microenvironment.

Role of S100 proteins in CRC metastasis

Metastasis is a complicated process, and different factors exert effects on the progression of metastasis (Ref. Reference Simon6). Recent studies have supported the involvement of different S100 proteins in CRC metastasis (Refs. Reference Destek and Gul45, Reference Li, Zhang, Qian, Wu, Sun, Ling and Xu52, Reference Fang, Zhang, Xu, Liu, Mo, Sun and Lan71, Reference Lin, Fang, Li, Li, Feng, Zhan and Deng146). The involvement of S100A4, S100A8 and S100A9 has been investigated in tumourigenesis, epithelial-mesenchymal transition (EMT), invasion and cell migration of CRC (Refs. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28, Reference Li, Zhang, Qian, Wu, Sun, Ling and Xu52, Reference Zhang, Wei, Wang, Qin, Wang, Lu and Ma147). It is well documented that S100A4 overexpression is associated with increased metastatic potential in patients with CRC (Ref. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28), as S100A4 knockdown limits metastasis formation in CRC xenograft mouse models (Ref. Reference Dahlmann148). This protein can induce production of cytokines TNF-α and IL-1β, which regulate the expression of transcription factors, such as Twist and Slug, that induce EMT (Ref. Reference Chattopadhyay, Ambati and Gundamaraju149). Moreover, S100A4 contributes to the recruitment of TGF-β-driven and -producing fibroblasts, leading to immune escape and tumour invasion in cancer (Ref. Reference Li, shi, Xu, Yao, Mou, yu and Li104). Extracellular S100A8 and/or S100A9 are also involved in the formation of the pre-metastatic niche by upregulating chemokine expression, such as CXC motif chemokine ligand 1 (CXCL1) and C-C motif ligand 5 (CCL5) (Refs. Reference Chen, Shu, Zhang, Ye, Tian and Shen30, Reference Wang, Sun, Wei, Cen and DuBois150). At low concentrations, they may induce CRC cell invasion. In addition, these proteins upregulate the expression of different cytokines and may be involved in EMT formation (Refs. Reference Chen, Shu, Zhang, Ye, Tian and Shen30, Reference Duan, Wu, Ye, Wang, Yang, Zhang and Zhou95). S100A8 promotes TGF-β-induced EMT and metastasis in CRC mouse models (Ref. Reference Li, Zhang, Qian, Wu, Sun, Ling and Xu52), suggesting that S100A8 and upstream transcription factor 2 (USF2) expression is upregulated during TGF-β-induced EMT and cell migration and invasion in CRC cells.

Among other S100 proteins, S100A2 is involved in metastasis through the formation of the S100A2/ Karyopherin alpha 2 (KPNA2) cotransport complex, which promotes cell metastasis by modulating the tumour-associated nuclear transcription factor y subunit alpha (NFYA) (Ref. Reference Han, Zhang, Liao, Zhang, Qian, Hou and Zhang151). S100A6 may contribute to invasion and metastasis in CRC cells by activating MAPK pathways (Ref. Reference Duan, Wu, Zou, Wang, Ye, Li and Zhou15). S100A11 can interact with LIM and SH3 protein 1 (LASP1) and enhance its expression in CRC. The LASP1-S100A11 axis can activate of TGF-β1/SMAD pathway, which mediates EMT and CRC progression (Ref. Reference Niu, Shao, Wang, Yang, Zhang, Luo and Zhao62). S100B is overexpressed in metastatic CRC and stimulates cell growth, invasion, and migration through interaction with thioredoxin-1 (Trx-1) and β-tubulin (Ref. Reference Zuo, Zhang, Lin, Shang, Bi, Lu and Jiang152). S100P is a transcriptional target gene for the transcriptional regulator of metastasis associated in colon cancer 1 (MACC1), which is a well-known driver of metastasis formation in CRC (Refs. Reference Lin, Fang, Li, Li, Feng, Zhan and Deng146, Reference Schmid, Dahlmann, Röhrich, Kobelt, Hoffmann, Burock and Stein153). Schmid et al. (Ref. Reference Schmid, Dahlmann, Röhrich, Kobelt, Hoffmann, Burock and Stein153) reported that S100P boosts the metastatic potential of CRC cells in vitro and in vivo via MACC1 (Ref. Reference Schmid, Dahlmann, Röhrich, Kobelt, Hoffmann, Burock and Stein153). Although different studies have confirmed the role of S100 proteins in the development of metastasis in CRC, the specific functions of most S100 proteins have not yet been fully characterised.

Roles of S100 proteins in drug resistance

Drug resistance is a complex process in which malignant cells become insensitive to anticancer drugs (Ref. Reference Emran, Shahriar, Mahmud, Rahman, Abir, Siddiquee and Hassan154). S100 proteins are differentially expressed in drug-resistant tumours (Ref. Reference Hua, Zhang, Jia, Chen, Sun and Zhu155) and may be involved in drug resistance in cancers. Intracellular S100 proteins intensify drug resistance by regulating different signalling pathways involved in cancer, such as reducing Ca²⁺ levels, inactivating p53, promoting annexin A2 (ANXA2) phosphorylation, regulating apoptosis and autophagy, elevating the expression of drug transporters (MDR-1, MRP-1 and LRP), activating cancer stem cells (CSCs) and interacting with non-coding RNAs (Refs. Reference Gonzalez, Garrie and Turner17, Reference Hua, Zhang, Jia, Chen, Sun and Zhu155). In addition, the binding of extracellular S100 proteins to RAGE or TLR4 can activate NF-κB signalling pathways and promote EMT, and the activation of these processes plays a critical role in the induction of chemo-drug resistance (Refs. Reference Hua, Zhang, Jia, Chen, Sun and Zhu155–Reference Harada, Ikeda, Kawabe, Oguri, Hashimura, Yokoi and Saegusa157).

Roles for different S100 proteins in inducing resistance in CRC cells to various chemotherapeutic drugs have been proposed. Chemotherapeutics may cause differential expression of S100 proteins; the expression levels of S100A2, S100A3, S100A4 and S100A10, notably upregulated in CRC tissues compared with healthy controls, are over 2-fold lower in 5-FU-resistant colon cancer cells (Ref. Reference Schmidt, Kalipciyan, Dornstauder, Rizovski, Steger, Sedivy and Mader158). S100A4 expression is upregulated in different drug-resistant colon cancer cells, including those resistant to methotrexate (Ref. Reference Mencía, Selga, Rico, de Almagro, Villalobos, Ramirez and Ciudad85) and cisplatin (DDP) (Ref. Reference Liu, Yang, Zhao, Chi, Wang and Sun159). Boye et al. (Ref. Reference Boye, Jacob, Frikstad, Nesland, Maelandsmo, Dahl and Flatmark160) reported that 5-FU sensitivity is not significantly correlated with S100A4 levels, since no difference in 5-FU sensitivity was observed among different groups, including overexpressed S100A4, S100A4-knockdown, and control CRC cells (Ref. Reference Boye, Jacob, Frikstad, Nesland, Maelandsmo, Dahl and Flatmark160). A strong correlation between S100A10 expression and oxaliplatin resistance was reported. Suzuki et al. (Ref. Reference Suzuki, Yamayoshi, Nishimuta and Tanigawara161) found that S100A10 in combination with ANXA2 can mediate oxaliplatin resistance in in vitro CRC models (Ref. Reference Suzuki, Yamayoshi, Nishimuta and Tanigawara161). Notably, S100A10 expression levels were not correlated with 5-FU-sensitive CRC cells, demonstrating that deregulated S100A10 expression is more specific to oxaliplatin than to 5-FU. Additionally, Fenouille et al. (Ref. Reference Fenouille, Grosso, Yunchao, Mary, Pontier-Bres, Imbert and Lagadec162) found that the expression levels of S100A10, ANXA2, and calpain 2 may be involved in irinotecan resistance, since their expression levels are significantly higher in irinotecan-resistant HT-29 CRC cells compared to irinotecan-sensitive cells (Ref. Reference Fenouille, Grosso, Yunchao, Mary, Pontier-Bres, Imbert and Lagadec162). S100P was upregulated in an oxaliplatin-resistant cell line (Ref. Reference Tang, Liu, Liu and Li163), whereas it was downregulated in a doxorubicin-resistant cell line (Ref. Reference Bertram, Palfner, Hiddemann and Kneba84). Previous studies have demonstrated that S100P interferes with the interaction between p53 and its corresponding repressor HDM2, disrupting the normal regulatory mechanisms of p53-HDM2 interaction, which may facilitate chemotherapy resistance. Further studies are needed to explore the precise roles of S100 proteins in processes involved in drug resistance.

Natural and synthetic molecules

Natural molecule inhibitors are classified as low-molecular-weight organic compounds that target important cancer-promoting proteins (Ref. Reference Li and Kang198). The inhibition of S100 proteins by small molecules has been previously reported. For CRC, it is documented that the interaction between S100A2 and KPNA2 mediates the transportation of the tumour-associated transcription factor NFYA, inhibits E-cadherin transcriptional activity, and subsequently facilitates metastasis. Han et al. reported that the use of a natural molecule, i.e., delanzomib, inhibits the S100A2-KPNA2 interaction and prevents CRC metastasis (Ref. Reference Han, Zhang, Liao, Zhang, Qian, Hou and Zhang151). Accordingly, delanzomib is a promising treatment option for preventing the progression of CRC.

In recent years, different synthetic molecules with inhibitory activity against S100A4 have been introduced to suppress cancer progression. For example, niclosamide, an FDA-approved anti-parasitic drug, has shown promising results for the treatment of various cancers and is being examined in clinical trials for different solid tumours (Refs. Reference Lee, Chen, Hsu and Lin176–Reference Kortüm, Radhakrishnan, Zincke, Sachse, Burock, Keilholz and Stein179). Niclosamide modulates β-catenin signalling and induces β-catenin degradation by inhibiting S100A4 transcription (Ref. Reference Stein, Arlt, Smith, Sack, Herrmann, Walther and Schlag108). The safety and efficacy of niclosamide for patients with metastatic CRC are currently being evaluated in a phase II clinical trial (Ref. Reference Burock, Daum, Keilholz, Neumann, Walther and Stein199). Kortum et al. (Ref. Reference Kortüm, Radhakrishnan, Zincke, Sachse, Burock, Keilholz and Stein179) showed that the inhibition of S100A4 by niclosamide reduced cell proliferation, motility and migration in vitro, supporting the therapeutic value of targeting S100A4 as an anti-metastatic approach for CRC (Ref. Reference Kortüm, Radhakrishnan, Zincke, Sachse, Burock, Keilholz and Stein179). Another S100A4 inhibitor, sulindac, an FDA-approved nonsteroidal anti-inflammatory drug (NSAID), significantly downregulated the mRNA and protein levels of β-catenin and S100A4 in tumours and reduced tumour growth and metastasis formation in an animal model compared with controls. Additionally, sulindac treatment reduced β-catenin and S100A4 levels in liver metastases (Ref. Reference Stein, Arlt, Smith, Sack, Herrmann, Walther and Schlag108). Calcimycin is an antibiotic drug that can inhibit the activity of S100A4. Sack et al. (Ref. Reference Sack, Walther, Scudiero, Selby, Aumann, Lemos and Stein107) found that calcimycin dysregulated the Wnt/β-catenin pathway and restricted cell motility and metastasis induced by S100A4 in colon cancer cells (Ref. Reference Sack, Walther, Scudiero, Selby, Aumann, Lemos and Stein107). These findings support S100A4 targeting as an effective approach for inhibiting the Wnt signalling pathway and demonstrate anti-tumour and anti-metastatic effects (Ref. Reference Schmid, Dahlmann, Röhrich, Kobelt, Hoffmann, Burock and Stein153). Trifluoperazine (TFP) is an FDA-approved antipsychotic drug and acts as an S100 protein inhibitor that disrupts the S100A4/myosin-IIA interaction. Qian et al. (Ref. Reference Qian, Sun, Zhou, Ge, Meng and Li184) demonstrated that the administration of TFP reduced tumour growth and proliferation and inhibited the EMT phenotype in a CRC mouse model, suggesting the potential antitumour activity of TFP in CRC (Ref. Reference Qian, Sun, Zhou, Ge, Meng and Li184).

Paquinimod and tasquinimod have been introduced as S100A8/S100A9 inhibitors that suppress RAGE and TLR4 signalling, respectively (Refs. Reference Talley, Valiauga, Anderson, Cannon, Choudhry and Campbell200, Reference Fan, Satilmis, Vandewalle, Verheye, Vlummens, Maes and De Veirman201). A single-cell RNA sequencing analysis revealed the involvement of S100A9+ macrophages in patients with MSI-H (C3 subtype) that show resistance to anti-programmed death 1 (PD-1) antibody (Ref. Reference Bao, Wang, Dai, Liu, Zhang, Jin and Fang138). Interestingly, administration of PD-1 blockade and tasquinimod reversed dysfunctional immunotherapy response and enhanced immunotherapy efficacy by depleting S100A9+ macrophages in vivo (Ref. Reference Bao, Wang, Dai, Liu, Zhang, Jin and Fang138). These results support the potential value of targeting S100A9 as a therapeutic strategy for treating patients with PD-1-resistant MSI-H CRC.

Inhibition of S100B by pentamidine (PTM) disrupts the S100B/p53 interaction (Ref. Reference Katte, Dowarha, Chou and Yu202), which promotes the expression of wtp53 and recovers p53-dependent cellular apoptosis in an in vitro colon cancer model (Ref. Reference Seguella, Rinaldi, Marianecci, Capuano, Pesce, Annunziata and Sarnelli133). Inhibition of S100P by cromolyn suppressed cell proliferation in CRC cell lines and attenuated tumour morphometric outcomes in an in vivo model of CRC by reducing tumour volume and weight compared with the control group. This suggests that the blockade of S00P by cromolyn may be a relevant anticancer approach for future therapeutic development (Ref. Reference Aliabadi, Haghshenas, Kiani, Panjehshahin and Erfani192). However, this inhibitor binds other S100 proteins, such as S100A1, S10012 and S100A13 due to the high structural similarity of these proteins, and the consequences of the lack of S100 protein specificity have not been investigated.

Neutralising antibodies

Neutralising anti-S100 antibodies have been introduced as novel therapeutic strategies for modulating different cellular processes, with S100A4, S100A8, S100A9 and S100P targeting by specific antibodies having been studied (Refs. Reference Raeisi, Azimirad, Schiopu, Zarnani, Asadzadeh Aghdaei, Abdemohamadi and Yadegar20, Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28, Reference Zhang, Wei, Wang, Qin, Wang, Lu and Ma147, Reference Dakhel, Padilla, Adan, Masa, Martinez, Roque and Hernández203). However, few studies have investigated the application of anti-S100 antibodies against CRC. For instance, Zhang et al. (Ref. Reference Zhang, Wei, Wang, Qin, Wang, Lu and Ma147) used an anti-S100A9 antibody to suppress colitis-associated colon cancer in mice. This study indicated that treatment of CRC mouse models with anti-S100A9 antibody may suppress key pathways involved in CRC development, such as the Wnt and PI3K/AKT signalling pathways. It has been suggested that an anti-S100A9 antibody could decrease the risk of CRC development (Ref. Reference Zhang, Wei, Wang, Qin, Wang, Lu and Ma147). Additionally, Zhang et al. (Ref. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28) reported that an anti-S100A4 neutralising antibody reduced tumour incidence in a mouse model, suggesting that it may serve as an approach for the prevention and treatment of colon cancer (Ref. Reference Zhang, Hou, Gu, Tian, Yuan, Jia and Chen28).

Peptide inhibitors

In addition to antibodies, specific S100-blocking peptides have been introduced in an attempt to develop cancer therapies. For example, Deguchi et al. (Ref. Reference Deguchi, Watanabe-Takahashi, Mishima, Omori, Ohto, Arashiki and Maru189) generated a multivalent peptide to inhibit the activity of S100A8 (divalent peptide3A5). Treatment of human colorectal tumour SW480 cells with this peptide diminished tumour progression and metastasis by preventing the activation of the TLR4-dependent pathway and suppressing VEGF production. Interestingly, administration of this peptide in a CRC mouse model improved the efficacy of bevacizumab (an anti-VEGF antibody) and attenuated lung metastasis (Ref. Reference Deguchi, Watanabe-Takahashi, Mishima, Omori, Ohto, Arashiki and Maru189). Therefore, this peptide may be a treatment option for aggressive cancer. In another study, the application of an S100A8/S100A9-targeting specific peptide suppressed tumour growth and downregulated the expression of EMT-associated markers in CRC mouse models (Ref. Reference Cho, Mun, Kim, Ham, Gil and Yang190).

MicroRNA (miRNA) mimics

miRNAs belong to a class of small RNA molecules (approximately 18–24 nucleotides) that play critical roles in the regulation of different signalling pathways related to cancers, and miRNA mimics have been introduced as a pharmaceutical strategy for treating cancers (Ref. Reference Menon, Abd-Aziz, Khalid, Poh and Naidu204). Furthermore, miRNAs are involved in the expression of different S100 proteins (Refs. Reference Chengling, Yulin, Xiaoyu, Xingchen, Sen, Ziming and Xianming187, Reference Mudduluru, Ilm, Fuchs and Stein205, Reference Xiao, Zhao, Du, Chen and Zhou206). Several studies have suggested that miRNA mimics may serve as effective agents for blocking S100 expression, most of which focus on targeting S100A4 as an effective strategy for preventing CRC. Two miRNAs, i.e., miR-187-3p and miR-149-3p, have been shown to decrease S100A4 expression and inhibit tumour cell proliferation, invasion and migration by blocking S100A4 (Refs. Reference Xiao, Zhao, Du, Chen and Zhou206, Reference Yang, Du, Xu, Xi and Li207). In addition, the miR-149 − 3p–S100A4–p53 axis contributes to induced drug resistance, since lower expression of miR-149 − 3p was observed in DDP-resistant colon cancer cells than in DDP-sensitive cells (Ref. Reference Liu, Yang, Zhao, Chi, Wang and Sun159).

In CRC cells, miR-325-3p/S100A4, miR-520c-3p/S100A4 and miR-296/S100A4 play important roles in carcinogenesis. Chengling et al. (Ref. Reference Chengling, Yulin, Xiaoyu, Xingchen, Sen, Ziming and Xianming187) indicated that miR-325-3p can target S100A4, and overexpression of miR-325-3p efficiently attenuated bone resorption in bone metastasis of CRC (Ref. Reference Chengling, Yulin, Xiaoyu, Xingchen, Sen, Ziming and Xianming187). He et al. (Ref. Reference He, Yu, Luo, Li, Li, Li and Wang188) found that miR-296 inhibited EMT, migration and invasion of CRC cells by mediating S100A4, demonstrating that miR-296 can be a potential target against CRC metastasis (Ref. Reference He, Yu, Luo, Li, Li, Li and Wang188). There are no data available on the application of miR-520c-3p to suppress S100A4 expression, but Mudduluru et al. (Ref. Reference Mudduluru, Ilm, Fuchs and Stein205) demonstrated that epigenetic silencing of miR-520c induced the expression of S100A4 and subsequently promoted CRC progression, suggesting that miR-520c regulated S100A4 expression (Ref. Reference Mudduluru, Ilm, Fuchs and Stein205). Although miRNAs have shown high effectiveness in targeting S100 proteins, systems with high efficacy for the miRNA delivery needs to be explored to reach an effective therapy in a clinical context. Further studies are needed to explore an effective approach for targeting S100 proteins with high efficacy for therapeutic interventions in CRC.