**5. MicroRNAs in cancer therapies**

## **5.1 miRNA candidates used in preclinical trials**

Increasing the evidence has demonstrated that miRNA expression is modified in cancer, and restoring the level of cellular miRNA could underpin the development of miRNA-based therapies. Below we briefly describe miRNAs that are currently used in preclinical and clinical trials and also represent examples that affect the emerging hallmarks of cancer such as evasion from apoptosis (miR-15/16, miR-34 cluster) [48], enabling replicative immortality (miR-34a) [48], activating invasion and metastasis (miR-10b) [49], tumor-promoting inflammation (miR-155), and genome instability and mutation (miR-155) [50].

### *5.1.1 miR-10b*

Guessous et al. [51] observed that miR-10b is overexpressed in human glioblastoma and stem cell lines when compared to healthy tissues or astrocytes. After the modulation of miR-10b, they found out that the inhibition of miR-10b strongly reduced cell proliferation, invasion, and migration of glioblastoma and stem cell lines, whereas its overexpression caused cell migration and invasion. Moreover, in a previous study, Ma's group [52] has demonstrated that the use of miR-10b antagomiRs was correlated with reduced metastasis both in cell-culture lines and in animal model of breast tumor-bearing mice. Thus, miR-10b inhibition both *in vitro* and *in vivo* significantly decreased miR-10b levels and increased levels of Hoxd10 gene, an important miR-10b target. Curiously, the administration of miR-10b antagomiRs *in vivo* did not reduce primary mammary tumor growth but significantly suppressed the development of lung metastases, highlighting its antimetastatic role.

**39**

*MiRNA-Based Therapeutics in Oncology, Realities, and Challenges*

investigate the anti-miRNA-based therapy for liver cancer.

tumor-suppressor RECK gene as a direct target of miR-221.

Since miR-221 overexpression alters multiple cancer pathways, it becomes a potential target for miRNA-based therapy. In order to validate the role of miR-221 in tumorigenesis, Callegari et al.[53] showed that *in vivo* delivery of an AMO antimiR-221 caused a significant decrease in the size and number of tumor nodules. Based on the results from their study, it was highlighted the promoter role of miR-221 in liver carcinogenesis, being also established a valuable animal model to

Moreover, using a colorectal cancer model, Qin et al. [54] showed that miR-221 promotes cell migration and invasion *in vitro* and metastasis *in vivo,* identifying

With regard to the role of miR-221 in tumorigenesis combined with the need to limit its expression, Brognara's group demonstrated that a peptide nucleic acid conjugate targeted against miR-221 (Rpep-PNA-a221) caused a suppression of miR-221 expression and an upregulation of its target p27Kip1 in two breast cancer cell lines (MCF-7 and MDA-MB-231), respectively [55]. On the other hand, in a recent study, Gallo et al. [56] evaluated the pharmacokinetic and pharmacodynamic properties of a locked nucleic acid anti-miR-221 (LNA-i-miR-221) in the models of mice and monkeys. Their data highlighted that LNA-anti-miR-221 has a short half-life, optimal tissue bioavailability and minimal urine excretion in both species. A very important aspect of their study was that no toxicity was present in the pilot monkey study. This finding defines the potential application of LNA-anti-miRNAs in clinical studies.

Sometimes developing a miRNA-based therapy is difficult because the same miRNA can act both as an oncogene and as a tumor-suppressor gene, due to its multiple targets and mechanisms of action. Such an example in this way is represented by miR-222, which has a role of oncomiR in liver cancers, by targeting and suppressing the PTEN tumor-suppressor gene, or TS-miRNA, whose downregulation in erythroblastic leukemia leads to the overexpression of c-KIT oncogene [27].

miR-34 is one of the most important TS-miRs, being positively controlled by TP53 [57], repressed by MYC [58], and silenced by aberrant CpG methylation [59]. Overexpression of miR-34 was related to apoptosis and cell cycle arrest [60], while its underexpression was linked to different tumor types, including nonsmall-cell lung cancer (NSCLC) [61], breast cancer [62], or ovarian cancer [63]. Several studies have proved that ionizing radiation upregulates the levels of expression from different miR-34 family members in a variety of human cell types: miR-34b in lymphocytes [64], miR-34c in prostate cancer cell lines [65], and miR-34a in thyroid cells [66]. Consequently, to increase the therapeutic efficiency, some of the future studies should focus on the combined use of DNA damage response related to miRNAs and radio- or chemotherapy. By performing a miR-34 modulation, Trang et al. [47] have demonstrated that synthetic miR-34 mimics incorporated in a lipid-based particle was able to block tumor growth in a mouse model of nonsmall cell lung. Likewise, Daige et al. [67] have proved that the use of encapsulating miR-34a mimics into liposomes (MRX34) leads to increase the level of miR34a in liver tumors, followed by significantly reducing several of its mRNA targets, and consequently tumor regression.

*DOI: http://dx.doi.org/10.5772/intechopen.81847*

*5.1.2 miR-221*

*5.1.3 miR-222*

*5.1.4 miR-34*

*MiRNA-Based Therapeutics in Oncology, Realities, and Challenges DOI: http://dx.doi.org/10.5772/intechopen.81847*

#### *5.1.2 miR-221*

*Antisense Therapy*

in mouse models [46, 47].

**5. MicroRNAs in cancer therapies**

**5.1 miRNA candidates used in preclinical trials**

genome instability and mutation (miR-155) [50].

decrease the toxicity and increase the antitumor effect, in a model of colon carcinoma. Recent studies [43, 44] have proved that codelivery of miR-200c with chitosan, a cationic polymer with a high specificity for nucleic acid binding, decreased the angiogenesis, invasion, EMT, and metastasis and increased the apoptosis, highlighting the role of miRNA concentration in treatment effectiveness. Hao et al. [45] used miRNA (MiR-15a, miR16-1)/ATE-APT complex formed by atelocollagen (ATE), a type I collagen positively charged polymer, in combination with a RNA aptamer (APT) used as a ligand to target PCa cells that express prostate-specific membrane antigen (PSMA). Their study concluded that miRNA/ATE-APT complex was more efficient than an ATE-miRNA complex and that by using a PSMA-targeted system, the chances for selective killing of prostate cancer cells significantly would increase. Moreover, it is worth into consideration the administration methods used for synthetic miRNAs (miRNA mimics) delivery into cells. Previous studies of Trang et al. have shown that both intratumoral and intravenous administration of let-7a mimics lead to the diminishing of non-small-cell lung cancer (NSCLC) tumor size

As a future improvement in miRNA delivery systems, it is recommended to be synthetized proteins or peptides in order to be used as vector polymeric due to their low cytotoxicity and immunogenicity. Finding a suitable delivery system for a specific miR according to tumor cell type and the development of systems to target

Increasing the evidence has demonstrated that miRNA expression is modified in cancer, and restoring the level of cellular miRNA could underpin the development of miRNA-based therapies. Below we briefly describe miRNAs that are currently used in preclinical and clinical trials and also represent examples that affect the emerging hallmarks of cancer such as evasion from apoptosis (miR-15/16, miR-34 cluster) [48], enabling replicative immortality (miR-34a) [48], activating invasion and metastasis (miR-10b) [49], tumor-promoting inflammation (miR-155), and

Guessous et al. [51] observed that miR-10b is overexpressed in human glioblastoma and stem cell lines when compared to healthy tissues or astrocytes. After the modulation of miR-10b, they found out that the inhibition of miR-10b strongly reduced cell proliferation, invasion, and migration of glioblastoma and stem cell lines, whereas its overexpression caused cell migration and invasion. Moreover, in a previous study, Ma's group [52] has demonstrated that the use of miR-10b antagomiRs was correlated with reduced metastasis both in cell-culture lines and in animal model of breast tumor-bearing mice. Thus, miR-10b inhibition both *in vitro* and *in vivo* significantly decreased miR-10b levels and increased levels of Hoxd10 gene, an important miR-10b target. Curiously, the administration of miR-10b antagomiRs *in vivo* did not reduce primary mammary tumor growth but significantly suppressed the development of lung metastases, highlighting its antimeta-

specific cancer membrane antigens still represent major challenges.

**38**

static role.

*5.1.1 miR-10b*

Since miR-221 overexpression alters multiple cancer pathways, it becomes a potential target for miRNA-based therapy. In order to validate the role of miR-221 in tumorigenesis, Callegari et al.[53] showed that *in vivo* delivery of an AMO antimiR-221 caused a significant decrease in the size and number of tumor nodules. Based on the results from their study, it was highlighted the promoter role of miR-221 in liver carcinogenesis, being also established a valuable animal model to investigate the anti-miRNA-based therapy for liver cancer.

Moreover, using a colorectal cancer model, Qin et al. [54] showed that miR-221 promotes cell migration and invasion *in vitro* and metastasis *in vivo,* identifying tumor-suppressor RECK gene as a direct target of miR-221.

With regard to the role of miR-221 in tumorigenesis combined with the need to limit its expression, Brognara's group demonstrated that a peptide nucleic acid conjugate targeted against miR-221 (Rpep-PNA-a221) caused a suppression of miR-221 expression and an upregulation of its target p27Kip1 in two breast cancer cell lines (MCF-7 and MDA-MB-231), respectively [55]. On the other hand, in a recent study, Gallo et al. [56] evaluated the pharmacokinetic and pharmacodynamic properties of a locked nucleic acid anti-miR-221 (LNA-i-miR-221) in the models of mice and monkeys. Their data highlighted that LNA-anti-miR-221 has a short half-life, optimal tissue bioavailability and minimal urine excretion in both species. A very important aspect of their study was that no toxicity was present in the pilot monkey study. This finding defines the potential application of LNA-anti-miRNAs in clinical studies.

## *5.1.3 miR-222*

Sometimes developing a miRNA-based therapy is difficult because the same miRNA can act both as an oncogene and as a tumor-suppressor gene, due to its multiple targets and mechanisms of action. Such an example in this way is represented by miR-222, which has a role of oncomiR in liver cancers, by targeting and suppressing the PTEN tumor-suppressor gene, or TS-miRNA, whose downregulation in erythroblastic leukemia leads to the overexpression of c-KIT oncogene [27].
