**3.5 Chloride channels**

Anoctamin 1 (**ANO1**), the calcium-activated chloride channel, is highly expressed in BC cell lines and primary BCs [86] and the 11q13 region is frequently amplified in BC and it is associated with grading and unfavorable outcome [86].

ANO1 was also shown to play an important role in controlling PDAC cell proliferation [87]. It has been shown that chloride channel accessory 1 and 2 genes (*CLCA1* and *CLCA2*) transcripts show widespread downregulation in CRC patients [88]. Therefore CLCA proteins could be tumor suppressors in CRC in analogy with what occurs in BC. **CLC1** is expressed in GC cells where it impairs cell proliferation and stimulates apoptosis, invasion and migration *in vitro* [89]. CLC1 overexpression in primary GC correlates with clinico-pathological parameters (lymph node involvement, stage, lymphatic and perineural invasion) as well as with poor prognosis [90]. **CLIC3** is not expressed in healthy pancreas while it is expressed in PanIN lesions [91] and in PDAC where it has a negative impact on patient survival.

**49**

*Ion Channels and Transporters as Cancer Biomarkers and Targets for Diagnostics with Antibodies*

The ligand-gated nicotinic acethylcholine receptors (**nAChRs**) are the channel type mostly studied in LC [92]. NSCLC shows altered expression of nicotinic subunits (mainly α1, α5 ανδ α7) compared with normal tissue. Moreover in NSCLC cells, nicotine has mitogenic effects of nicotine, mediated by α7-containing nAChRs [93]. Multiple genome-wide association studies (GWAS) have implicated the 15q25 nAChR gene cluster *CHRNA5-A3-B4* in nicotine dependence and LC [94]. The expression of the *CHRNA5* gene which encodes the α5-nAchR was increased in LC tissue and that the p.Asp398Asn polymorphism in the *CHRNA5* gene is associated with LC risk [92] and altered receptor function [95]. Additionally, the p.Asp398Asn polymorphism may influence α5 (CHRNA5) expression as well [92]. A α5-nAChR/ HIF-1α/VEGF axis exists in LC and is involved in nicotine-induced tumor cell proliferation. This fact suggests that α5-nAChR may serve as a potential anticancer

**AQP1** is expressed in BC and positively correlates with grading, histology, CK14 expression, smooth muscle actin expression, basal-like group and poor outcome, whereas it has significant negative correlation with ER status [97]. AQP1, **AQP3** and **AQP5** are expressed in CRC cell lines. AQP1 and AQP5 are expressed the early steps of CRC progression but also in liver metastases [98]. Moreover, AQP5 expression is associated with grading, nodal involvement and TNM stage [99]. AQP5 is expressed at significant levels in Lauren's intestinal type-GC, where it shows an apical localization [100], whereas AQP3 and **AQP4** are not overexpressed in GC. Shen et al. [101] showed that both AQP3 and AQP5 were overexpressed in GC and were associated with lymph node involvement. Moreover, AQP3 expression was higher in well differentiated tumors. AQP3 is also over-expressed in primary CRC with respect to healthy tissue, and its expression is positively regulated by EGF and is associated with lymph node involvement, metastasis and differentiation [102]. AQP3 and AQP5 are expressed in ESCC, while absent in healthy esophagus [103, 104]: the presence of the two aquaporins is associated with clinico-pathological features and their co-expression represents an independent negative prognostic factor. A recent microarray-based study demonstrated that reduced *AQP9* gene expression is related

to absence of adjuvant chemotherapy response in CRC patients [38].

The monocarboxylate transporter **SLC16A1** (encoded by the *SLC16A1* gene) is associated to basal-like BC, high histological grade, CK5, CK14, vimentin and Ki67. AQP1 along with SLC16A1 were shown to be associated with tumor aggressiveness of BC [105]. The voltage-gated proton channel Hv1 (**HVCN1**) overexpression in metastatic BC is associated with progression and unfavorable outcome [106]. The same occurs in CRC in which it is associated also with tumor size, lymph node involvement and stage [107]. In stage CRC, a low expression of **SLC7A1** (cationic amino-acid transporters-1, encoded by *SLC7A1* gene) is associated with shorter metastases-free survival [108]. The sodium proton exchanger 1 (**NHE1**, SLC9A1) interacts with EGFR and is involved in PDAC cell invasiveness [109]. It was shown that the Glucose Transporter 1 (**SLC2A1**, GLUT1) is expressed in BE-derived tumors in the late events of tumor progression [110]. SLC2A1 expression described also occurs in ESCC, where it represents a marker of poor prognosis [111]. Moreover, SLC2A1 expression increased

*DOI: http://dx.doi.org/10.5772/intechopen.90401*

target in nicotine-associated LC [96].

**3.7 Aquaporins (AQP)**

**3.8 Transporters**

**3.6 Ligand-gated channels**

*Ion Channels and Transporters as Cancer Biomarkers and Targets for Diagnostics with Antibodies DOI: http://dx.doi.org/10.5772/intechopen.90401*

#### **3.6 Ligand-gated channels**

*Translational Research in Cancer*

target for ER-positive BCs [70].

**3.4 Transient receptor potential (TRP) channels**

high STIM1 and low STIM2 have unfavorable prognosis, suggesting that the SOC family has a role in aggressiveness and in the metastatic process [69]. **ORAI3** has recently been associated with ER-positive BC [65] and could represent a novel

TRP channels are non-selective cation channels that can be activated by different stimuli such as pH variations, temperature and pressure among others [71, 72]. Since TRP channels are involved in migration and invasiveness, they contribute to the metastatic process in different tumors [73]. Ca2+ influx through TRPCs also occurs and promotes either cell proliferation or apoptosis, depending on TRPC subtype. **TRPC1** whose levels are high in BCs with low proliferation capacity, may not be the optimal target for therapies against aggressive BCs [74]. Significantly elevated (up to 200-fold) mRNA levels of *TRPC6* were shown in BC samples compared with paired control samples [74, 75], but no correlations with clinicopathological features emerged [74]. A similar behavior characterizes TRPC1, whose expression levels decrease during the progression of PCa from androgen-dependent to androgen-independent phase [75]. TRPC6 is overexpressed in ESCC with respect to normal esophageal tissue at both protein and mRNA levels [76]. A recent report evidenced correlations of TRPC6 with T and staging and an association between *TRPC6* mRNA and poor prognosis [77]. **TRPV6** is up-regulated in PgR and ER-negative BCs [78]. Basal-like BCs with high TRPV6 mRNA levels are associated with poor survival [79]. *In vitro* data suggest that TRPV6 may be a potential therapeutic target [79]. TRPV6 is highly expressed in PCa and are associated with the Gleason score and metastatisation [80]. The expression of **TRPV4** is decreased by progesterone [81]. **TRPM7** is highly expressed in BC, and such over expression is associated with poor prognosis in terms of distant metastasis- and recurrence-free survival [82]. In accordance with these observation, *TRPM7* mRNA levels are higher in BC metastases with respect to primary tumors. Also, TRPM7 are overexpressed in pancreatic ductal adenocarcinomas and are associated with lymph node metastases [83]. TRPM7 mRNA and protein are also overexpressed in bladder cancer with respect to normal tissue and are associated with poor prognosis [84]. **TRPA1** is overexpressed also in SCLC patients compared with NSCLC and since it is associated with SCLC patients' survival representing a potential therapeutic target [85].

Anoctamin 1 (**ANO1**), the calcium-activated chloride channel, is highly expressed in BC cell lines and primary BCs [86] and the 11q13 region is frequently amplified in BC and it is associated with grading and unfavorable outcome [86]. ANO1 was also shown to play an important role in controlling PDAC cell proliferation [87]. It has been shown that chloride channel accessory 1 and 2 genes (*CLCA1* and *CLCA2*) transcripts show widespread downregulation in CRC patients [88]. Therefore CLCA proteins could be tumor suppressors in CRC in analogy with what occurs in BC. **CLC1** is expressed in GC cells where it impairs cell proliferation and stimulates apoptosis, invasion and migration *in vitro* [89]. CLC1 overexpression in primary GC correlates with clinico-pathological parameters (lymph node involvement, stage, lymphatic and perineural invasion) as well as with poor prognosis [90]. **CLIC3** is not expressed in healthy pancreas while it is expressed in PanIN lesions [91] and in PDAC where it has a negative impact on

**48**

patient survival.

**3.5 Chloride channels**

The ligand-gated nicotinic acethylcholine receptors (**nAChRs**) are the channel type mostly studied in LC [92]. NSCLC shows altered expression of nicotinic subunits (mainly α1, α5 ανδ α7) compared with normal tissue. Moreover in NSCLC cells, nicotine has mitogenic effects of nicotine, mediated by α7-containing nAChRs [93]. Multiple genome-wide association studies (GWAS) have implicated the 15q25 nAChR gene cluster *CHRNA5-A3-B4* in nicotine dependence and LC [94]. The expression of the *CHRNA5* gene which encodes the α5-nAchR was increased in LC tissue and that the p.Asp398Asn polymorphism in the *CHRNA5* gene is associated with LC risk [92] and altered receptor function [95]. Additionally, the p.Asp398Asn polymorphism may influence α5 (CHRNA5) expression as well [92]. A α5-nAChR/ HIF-1α/VEGF axis exists in LC and is involved in nicotine-induced tumor cell proliferation. This fact suggests that α5-nAChR may serve as a potential anticancer target in nicotine-associated LC [96].

#### **3.7 Aquaporins (AQP)**

**AQP1** is expressed in BC and positively correlates with grading, histology, CK14 expression, smooth muscle actin expression, basal-like group and poor outcome, whereas it has significant negative correlation with ER status [97]. AQP1, **AQP3** and **AQP5** are expressed in CRC cell lines. AQP1 and AQP5 are expressed the early steps of CRC progression but also in liver metastases [98]. Moreover, AQP5 expression is associated with grading, nodal involvement and TNM stage [99]. AQP5 is expressed at significant levels in Lauren's intestinal type-GC, where it shows an apical localization [100], whereas AQP3 and **AQP4** are not overexpressed in GC. Shen et al. [101] showed that both AQP3 and AQP5 were overexpressed in GC and were associated with lymph node involvement. Moreover, AQP3 expression was higher in well differentiated tumors. AQP3 is also over-expressed in primary CRC with respect to healthy tissue, and its expression is positively regulated by EGF and is associated with lymph node involvement, metastasis and differentiation [102]. AQP3 and AQP5 are expressed in ESCC, while absent in healthy esophagus [103, 104]: the presence of the two aquaporins is associated with clinico-pathological features and their co-expression represents an independent negative prognostic factor. A recent microarray-based study demonstrated that reduced *AQP9* gene expression is related to absence of adjuvant chemotherapy response in CRC patients [38].

#### **3.8 Transporters**

The monocarboxylate transporter **SLC16A1** (encoded by the *SLC16A1* gene) is associated to basal-like BC, high histological grade, CK5, CK14, vimentin and Ki67. AQP1 along with SLC16A1 were shown to be associated with tumor aggressiveness of BC [105]. The voltage-gated proton channel Hv1 (**HVCN1**) overexpression in metastatic BC is associated with progression and unfavorable outcome [106]. The same occurs in CRC in which it is associated also with tumor size, lymph node involvement and stage [107]. In stage CRC, a low expression of **SLC7A1** (cationic amino-acid transporters-1, encoded by *SLC7A1* gene) is associated with shorter metastases-free survival [108].

The sodium proton exchanger 1 (**NHE1**, SLC9A1) interacts with EGFR and is involved in PDAC cell invasiveness [109]. It was shown that the Glucose Transporter 1 (**SLC2A1**, GLUT1) is expressed in BE-derived tumors in the late events of tumor progression [110]. SLC2A1 expression described also occurs in ESCC, where it represents a marker of poor prognosis [111]. Moreover, SLC2A1 expression increased after radiotherapy in ESCC patients [112]. The apical sodium-dependent bile acid transporters (**SLC10A2**), which mediate bile acid transport [113], are not expressed in the normal squamous epithelium of the esophagus [114], whereas their expression increases in Barrett's Esophagus, to decline in EA [115]. Divalent metal transporter1 (DMT1, **SLC11A2**) overexpression was associated with metastatization in EC [116]. One of the main causes of chemotherapy failure is drug efflux mediated by ATP-binding cassette transporters (ABC) [117]. It was recently shown that **ABCG2** together with V-ATPase are overexpressed in ESCC and are associated with grading, TNM stage and metastatization. **ABCB1** and ABCG2 are expressed in primary GC and GC cell lines [118] in which their expression is associated with tumor differentiation. ABCB1 expression is higher in diffuse type GC [119]. ABCG2 represents a target for a several chemotherapy drugs [120]: for example, cisplatin increases *ABCG2* mRNA *in vitro* and this is associated with patients' outcome [121]. In PDAC, **ABCB4, ABCB11, ABCC1, ABCC3, ABCC5, ABCC10** and ABCG2 are up-regulated, while **ABCA3, ABCC6**, CFTR (**ABCC7**) and **ABCC8** are down-regulated: such deregulation contributes to PDAC poor response to therapy [122]. The Solute Carrier transporters (SLC) is a family of transporters frequently deregulated in PDAC. **SLC7A5** (the L-type aminoacid transporter 1) are overexpressed in PDAC and are associated with molecular and clinico-pathological features (such as Ki-67, p53, CD34, CD98, VEGF size, stage) and prognosis [122]. **SLC22A3** and **SLC22A18** are up-regulated in PDAC with respect to healthy pancreas while **SLC22A1**, **SLC22A2**, **SLC22A11**, **SLC28A1**, **SLC28A3** and **SLC29A1** are down-regulated [122]. In particular, SLC28A1 overexpression was associated with poor overall survival whereas SLC22A3 and SLC29A3 overexpression was observed in patients treated with Gemcitabine with longer overall survival. PC patients with low expression of SMCT1 (**SLC5A8**) have poorer survival with respect to patients with high SLC5A8 levels [123]. The human equilibrative nucleoside transporter 1 (**SLC29A1**) is associated to longer time to progression and it was shown that it could predict gemcitabine effects in non-resectable PDAC patients, if evaluated in samples obtained by fine-needle aspiration [124]. Different conclusions were drawn when analyzing SLC29A1 expression in patients treated with chemo-radiotherapy [125]. In GC, **SLC7A5** overexpression was detected and it was found to be associated with clinico-pathological features such as size, lymph node involvement, TNM stage and local invasion [126]. **SLC16A1** was found to be expressed both in healthy stomach and GC, and it could be hypothesized a role in gastric physiology for this transporter [119]. In metastatic GC, **SLC16A3** is downregulated [119] and is associated with intestinal type. 4F2hc (**SLC3A2**) was found to be over-expressed in GC cell lines and in primary GC, with no significant correlation with clinico-pathological features. Since the study was conducted on a small number of samples, it could not allow definitive conclusions [127].
