Influence of interleukins on prognosis of patients with oral squamous cells carcinoma

1. Universidade Federal de Sergipe (UFS), Lagarto, Sergipe, Brazil
2. Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil
3. Universidade Federal de Uberlândia (UFU), Uberlândia, Minas Gerais, Brazil

INTRODUCTION

Squamous cell carcinoma (SCC) is a malignant neoplasm that affects the structures and tissues of the oral cavity⁽¹⁾. This condition may originate from a precancerous primary lesion that arises in the mouth or from metastasis⁽²⁾. Its etiology is multifactorial; smoking and alcohol consumption are the habits that most influence oral cancer^{(1, 3)}. Men are often more affected than women because they are more involved with risk factors⁽⁴⁾. According to the literature, oral cancer is the eighth leading cause of death, with oral squamous cell carcinoma (OSCC) representing the most common malignant neoplasm in the mucous membranes of the oral and oropharynx mucosa⁽⁵⁾.

Interleukins (IL) are a group of cytokines and are one of the main molecules that act in the immune system, transmitting signals among cells⁽⁶⁾. Interleukin 1 (IL-1) and 6 (IL-6) are produced in SCC and play a key role in the progression of the carcinogenesis process. IL-1 is produced in order to mediate the host defense system when there is an aggression, as well as to stimulate immune cells and fluids leakage. IL-6 production occurs through the activation of nuclear factor kappa B (NF-kB) by stimulating lymphoid cells; it acts similarly to IL-1, however with more specific activities, such as differentiation and growth factors for T and B cells⁽⁷⁾. IL-10 also favors tumor progression; this cytokine regulates immune cell differentiation and proliferation and contributes to immune evasion of anti-tumor immunity⁽⁸⁾.

Cytokines synthesized from a tumor may modulate a cascade reaction that will eventually act on the progression of the carcinogenesis process⁽⁷⁾. The production of IL-6 in high quantities is known to be present in pathological processes, constituting an important diagnostic biological marker⁽⁹⁾. Thus, in OSCC, salivary levels of IL-1, IL-6 and IL-8 are highly sensitive parameters to verify the progression of the neoplasia^{(9, 10)}. Moreover, IL-37, a member of the IL-1 family, has innate immunity inhibitory properties, with the potential to influence inflammatory tumors, and it is suggested as a new diagnostic biomarker⁽¹¹⁾.

In the absence of specific indications on the general role of IL in the carcinogenesis process, this systematic review aims to investigate the literature on IL as mediators that negatively or positively influence the prognosis of patients with OSCC.

MATERIAL AND METHODS

This is a systematic review study conducted according to the instructions of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (www.prisma-statement.org). PubMed (including MedLine), Scopus, Web of Science, SciELO and Latin American and Caribbean Health Sciences (LILACS) databases were used as primary sources for the study; OpenGrey and OpenThesis, used to search for “gray literature”. Additional information regarding the search strategy used is shown in Table 1.

The Medical Subject Headings (MeSH) feature selected the key words: oral cavity, mouth, carcinoma squamous cell, carcinoma, oral cavity, squamous cell, squamous cell carcinoma, squamous carcinoma, epidermoid carcinoma, planocellular carcinoma, interleukin, interleukin-1, interleukin-6, interleukin-8, IL-1, IL-6 and IL-8, connected together by the Boolean operators “and” and “or”.

The following were included: 1. observational studies without restriction of period, language and publication status; 2. studies that identified the relationship among the IL(s) analyzed and their influence on OSCC prognosis. The following were excluded: 1. studies that did not displayed as content the objective of the present systematic review; 2. in vitro studies; 3. animal studies; 4. case reports, letter to editor and/or editorials, literature review, books and book chapters, indexes and abstracts; 5. studies that analyzed IL levels but did not assess the relationship with prognosis in OSCC patients.

Data collection was performed in two phases: in the first, the titles and abstracts were systematically examined by the reviewer to check the eligibility criteria (with access to the names of the authors and journals). Those who presented titles according to the eligibility criteria, but the abstracts were not available were also obtained and analyzed in full. In the second phase, the preliminary eligible studies had the full text evaluated to verify if they met the eligibility criteria. In specific cases, when the study potentially eligible presented incomplete data, the authors were contacted by email to provide further information. After complete screening, the texts of the selected articles were reexamined and their data extracted in a standardized form, containing: authorship, year of publication and place of study, IL, type of study, sample, methods of disclosure of IL(s) levels and main outcome.

The selected studies were assessed for risk of bias and individual quality using the checklist obtained through the critical assessment tools from the Joanna Briggs Institute allowed for systematic reviews⁽¹²⁾. The reviewer assessed the risk of bias and the individual quality of the studies, which were classified as high, moderate or low risk of bias. At that point, the review was blinded to the authors and journals, avoiding any selection bias and possible conflicts of interest. The search was performed in August 2017. The results were exported to Mendeley 1.13.3 software desktop (Mendeley TM Ltd, London, UK), where duplicity was verified.

RESULTS

Study selection

The flowchart shown in Figure demonstrates our selection profile.

Characteristics of studies

All included studies were published in English. One study was conducted in Brazil⁽¹³⁾; one in China⁽¹⁴⁾; two in Croatia^{(15, 16)}; two in India^{(17, 18)}; one in England⁽¹⁹⁾; one in Iran⁽²⁰⁾; three in Japan^(21-23); one in Pakistan⁽²⁴⁾; one in the United Kingdom⁽²⁵⁾; and two in Taiwan^{(26, 27)}. A summary of the descriptive characteristics of the included articles can be found in Table 2.

Risk of individual bias of the studies

Among the 15 studies selected, eight showed low risk of bias^{(14-19, 25-27)}; four, moderate risk of bias^{(20, 22-24)}; and three, high risk of bias^{(13, 16, 21)}. Detailed information on the assessment of risk of individual bias of the studies is shown in Table 3.

Summary of results

There was a certain degree of heterogeneity between the included studies, which showed differences on the type of study, the types of IL evaluated, the methods of disclosure of IL, and the main outcome. Therefore, it was not possible to perform a meta-analysis.

IL-4 was evaluated in three studies^{(13, 20, 24)}. Only one of them presented results⁽²⁴⁾ showing that high levels of IL-4 in patients with OSCC seem to be related to poorer prognosis. IL-6 was evaluated in seven studies^{(13, 15, 16, 18, 21, 23, 26)}. Except in one study⁽¹³⁾, the results of others showed that high levels of IL-6 in patients with OSCC seem to be related to poorer prognosis. IL-8 was evaluated in three studies^{(13, 17, 22)}. Except for one study⁽¹³⁾, the results of others showed that high levels of IL-8 in patients with OSCC seem to be related to poorer prognosis. IL-10 was evaluated in six studies^{(14, 19, 20, 24, 25, 27)}. According to the results of half of them^{(14, 24, 27)}, increased levels of IL-10 in OSCC patients seem to be related to poorer prognosis. IL-12 was evaluated in two studies^{(13, 19)}. The results of these surveys showed that increased levels of IL-12 in patients with OSCC do not seem to be related to a poorer prognosis. IL-13 was evaluated in one study⁽²⁴⁾. High levels of IL-13 in patients with OSCC seem to be related to poorer prognosis.

DISCUSSION

We sought to verify the general role of IL in the carcinogenesis process, correlating its actions with the prognosis of patients with OSCC. According to the results of the studies included in the present review, it was noticeable that most of the analyzed IL is associated with poor prognosis in patients with OSCC.

Immunosuppression in cancer patients is a well-established phenomenon and may include changes in cytokines and in the balance of immune cell populations⁽²⁸⁾. Helper T lymphocytes play a key role in controlling the immune response and are subdivided into T-helper 1 (Th1) and T-helper 2 (Th2). Their differences lie in synthesized mediators and induced responses. The Th1 lineage is responsible for promoting cell-mediated immunity and acting in anti-tumor pathways, secreting mediators, such as interferon-γ (IFN-γ), which activates macrophages, cytotoxic T lymphocytes and natural killer cells (NK). The Th2 lineage induces humoral response and is responsible for IL secretion, such as IL-4, which favors tumor progression by inhibiting mediators secreted by a Th1 cells^{(29, 30)}. Functional imbalance between mediators secreted by Th1 and Th2, which favor IL secreted by Th2 cell lineages, was responsible for the progression of head and neck SCC⁽³¹⁾.

IL-4 presents antiangiogenic properties that may inhibit tumor progression⁽³²⁾. However, this same IL presents antiapoptotic property, which may help in the tumor’s immune protection, besides favoring tumor growth⁽³³⁾. This dual action of IL-4 has influenced the increase of its levels and the poorer prognosis of patients with OSCC⁽²⁴⁾.

According to the results of the present review, increased IL-6 levels seem to be related to unfavorable prognosis in patients with OSCC. The relationship between lymphatic metastases and IL-6 occurs by stimulating lymph vessel proliferation by signaling the expression of vascular endothelial growth factor C (VEGF-C), which is regulated by the PI3K-Akt pathway and stimulated by IL-6R signaling. IL-6 binding to IL-6R initiates gp130 homodimerization and triggers signaling cascades via the JAK-STAT, Ras-MAPK and PI3K-Akt pathways; which is essential for the regulation of VEGF-C messenger ribonucleic acid (RNAm) expression by IL-6 in tumor cells, favoring both the development of lymphatic metastases and the poorer prognosis of the disease⁽³⁴⁾. Gp130 homodimerization and activation of signaling cascades, in one sample study, were related to constitutive activation of signal transducers and activators of transcription (STAT3) as a contributing factor to the carcinogenesis process in a variety of malignancies. The authors also observed the association with IL-6, showing that STAT3 activation occurred between IL-6 and IL-6R in the tumor microenvironment, showing us that high cytokine expression was positively correlated with tumor progression and poorer prognosis⁽²³⁾.

A study⁽³⁵⁾ evaluated the polymorphisms expression of matrix metalloproteinase-1 (MMP-1) and IL-8 in tongue SCC; the data from this research suggest that these proteins are not strongly associated with the carcinogenesis process of this pathology, although they may contribute during the progression of this neoplastic lesion through positive regulation of the gene for MMP-1 and IL-8. Metalloproteinases act as a tool for tumor growth, either modulating the extracellular matrix, or regulating the release of growth factors and/or inducing angiogenesis⁽³⁶⁾. MMP-1 was involved in the degradation process of type I collagen, favoring tumor invasion and metastasis⁽³⁷⁾.

A study verified the presence of two receptors (IL-8A and IL-8B) for IL-8 in head and neck SCC, and receptor type A was related to poorer prognosis⁽³⁸⁾. Receptor A is specific for IL-8, whereas several cytokines also present affinity for receptor type B⁽³⁵⁾. Therefore, these authors suggest a positive relationship between IL-8 and tumor lesion progression together with the metastasis process.

In the research of one of the studies selected for this review⁽²²⁾, 27 out of 50 sample components were in an early stage (stage I/II) of OSCC, presented lower serum levels of IL-8 and tended to survive longer when compared to individuals at more advanced stages (stage III/IV) and with higher serum levels of this IL. It is possible that the presence of increased levels of IL-8 leads to poor prognosis through the generation and activation of M2 macrophages, which also secrete IL-8 and VEGF-C – proteins that enhance angiogenesis in the tumor environment and favor tumor expansion⁽³⁹⁾. Furthermore, the authors of this research⁽²²⁾, through in vitro results, assume that the increase in M2 macrophage generation may cause an unfavorable clinical outcome through the secretion of IL-10, an immunosuppressive cytokine.

The main source of IL-10 is tissue macrophages, as well as their synthesis may occur through T lymphocytes, B lymphocytes, mast cells, eosinophils and keratinocytes⁽⁴⁰⁾. This interleukin regulates the differentiation and proliferation of immune cells, as well as contributes to immune evasion of anti-tumor immunity by interfering with regulation of Class I major histocompatibility complex (MHC) expression or inhibition of T cell activation and function⁽⁷⁾. According to results from two studies^{(14, 27)}, high levels of IL-10 seem to be related to poorer prognosis of OSCC. IL-10 induces a polarized M2 phenotype and inhibits the synthesis of proinflammatory cytokines, such as IFN-γ and tumor necrotic factor alpha (TNF-α), which favor the emergence of local immunosuppression and allow tumor progression⁽⁴¹⁾.

Although evidence reinforces the role of IL-10 in tumor progression, studies^{(19, 25)} have shown results contrary to this statement. According to data from these studies, there was no significant difference in IL-10 levels between patients with OSCC and the control group, nor influence on prognosis and survival time. These results were opposite when the carcinoma site was located in another region of the head and neck. Thus, some authors suggest that there may be specificity in the profile of the tumor immune response correlated with the primary site of SCC development⁽¹⁹⁾.

Generally, tumor growth is associated with the ability to evade the attack instituted by the host immune system. In the carcinogenesis process, there is a change in immune function between Th1 and Th2 cells, which favors the immunosuppressive response Th2 cell-mediated, and stimulates tumor progression⁽³⁰⁾. One of the possible determinants for functional dysregulation between these two cell lineages involves the IL imbalance participating in the integration of their functions⁽⁴²⁾. A study found that after administration of IL-12 in the intratumoral region, there was increased expression of the immune response through Th1 cells⁽⁴³⁾. In addition, another study found longer survival time in patients with higher IL-12 expression in tumor tissue⁽⁴⁴⁾. Therefore, it is assumed that the performance of this IL in a tumor environment may increase the survival time⁽¹⁹⁾.

Among the studies included in this review, only one evaluated the role of IL-13 in the carcinogenesis process, which was associated with poorer prognosis in patients with OSCC⁽²⁴⁾. IL-13 may inhibit IFN-γ secretion and cytotoxic T lymphocyte activity, thus hindering the action of the anti-tumor immune response⁽⁴⁵⁾. IL-13 aids tumor cell defense against immune response, also acts as an autocrine growth factor and stimulates tumor progression, metastasis and antiapoptotic response in some malignant neoplasms⁽²⁴⁾.

CONCLUSION

According to the results of the studies selected for this systematic review, IL-4, IL-6, IL-8, IL-10 and IL-13 tend to present a response related to the intensification of the carcinogenesis process, whereas increased IL-12 levels were not associated with an unfavorable prognosis in patients with OSCC.

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