Lung cancer is the leading cause of cancer mortality in industrialized countries. Despite of extensive researches to optimize the available treatments, the overall survival at 5 years is around 16%.Consequently, research aimed to identify new therapies for this disease, is very active. The identification of the role of epidermal growth factor receptor (EGFR) in the processes leading to cell proliferation in lung cancer, for example, has allowed the development of EGFR inhibitors currently approved for clinical use (gefitinib and erlotinib).
Chemokines are small basic cytokines with chemotactic activity. In addition to controlling the recruitment of leukocytes in inflammatory processes, new roles have been attributed more recently to chemokines in other biological processes including, for example, angiogenesis and hematopoiesis. Chemokines have also been implicated in the pathogenesis of different diseases, such as bronchial asthma, multiple sclerosis, post-viral myocarditis, atherosclerosis.
In the recent years the potential role of chemokines in the cancer progression has been the subject of much research. Most tumors produce at least some chemokines and express chemokine receptors on the cell surface. Since chemokines are able to attract inflammatory leukocytes, the initial interpretation of this observation was that the role of these molecules was to stimulate the immune response. On the other hand, it should be noted that tumors are considered as 'Darwinian' systems in which the selection pressure favours features such as loss of contact inhibition, independence from growth factors produced by the host, the ability to induce angiogenesis. It 's so hard to imagine that the tumor cells retain their ability to produce chemokines if the role of these proteins was only to induce the host immune response. Based on these considerations it has been postulated that chemokines play a role in favoring the development of cancer. And it is possible to imagine that they can act either directly, through interaction with their receptors through an autocrine mechanism, and indirectly through the recruitment of leukocytes, which could provide growth factors and angiogenesis.
The potential role of interleukin-8 (IL-8) in the development and progression of lung cancer has been extensively investigated. Clinical studies have shown a positive correlation between the amount of mRNA for IL-8 and the microvessel count in samples of lung cancer, and a negative correlation between these markers and survival, suggesting that indeed IL-8 promotes tumor growth, at least in part through the stimulation of angiogenesis. More recent studies have also confirmed the presence of a correlation between the expression of IL-8 and prognosis in lung cancer. A direct role of IL-8 in the proliferation of cancer cells was also observed. Luppi et al. have shown that IL-8 acts as a growth factor on two cell lines of lung cancer, A549 and NCI-H292. The authors have shown that IL-8 acts through the transactivation of EGFR, a mechanism by which a soluble ligand, that is IL-8, through binding to its receptor on the cell surface, activates a metalloprotease which, after cutting a membrane-bound EGF, make it available to interact with EGFR and cause the subsequent release of intracellular signals downstream.
Monocyte chemotactic protein-1 (MCP-1) was initially identified for its chemotactic activity towards monocytes. MCP-1 is expressed by many tumors, and it is interesting to mention that one of its discoverers had originally named it “tumor derived chemotactic factor”. Considerations similar to those expressed about the chemokines can apply to this protein. Ueno et al. have divided a group of 135 patients with breast cancer into two groups based on the level of expression of MCP-1 in the surgical specimen, showing that patients with low levels of MCP-1 (values below the median calculated in that population) had a disease-free survival significantly longer than patients with high levels of MCP-1. This observation was correlated with the number of tumor-associated macrophages. A more recent study showed that MCP-1 is an autocrine growth factor for prostate cancer cells. Our knowledge of the possible role of MCP-1 in lung cancer is very limited.
The present study has been done ex vivo on samples of lung cancer in humans. We enrolled patients related to our Cardio-Thoracic and Vascular Department with primary lung cancer, regardless of the hystotype. During bronchoscopy performed for diagnostic purposes, biopsy sample of tumor tissue was taken and on this MCP-1 has been dosed with immunochemical techniques (ELISA). The amount of MCP-1 has been corrected for total protein content measured by the method of Bradford. For patients unsuitable for surgery this was the only material available. For patients brought to surgery, the specimen has been sent to the laboratories of Pathology for histological evaluation. On this piece expression of MCP-1 has been measured through an immunohistochemical method, leading to a semiquantitative score, measured as +1/+2/+3. The values of MCP-1 are then compared, after dividing patients by histologic type (small cell and non small cell) and stage with overall survival, to evaluate the any correlation between the presence of MCP-1 and evolution of disease.
As regards the first group of patients, we enrolled 50 patients with NSLC (male/female: 44/6, mean age: : 66.5) performed bronchoscopic evaluation, and because of an inoperable staging of the disease, they were treated with chemotherapy and followed in the progression of the disease. The histologic type of lung cancer was: adenocarcinoma and squamous. The mean duration of follow-up was 9.52 months (range: 2-20), and at the end of the follow-up 11 patients were still alive.
MCP-1 was detectable in all lung cancer samples taken by bronchoscopy (mean value: 33.04 pg/μg proteine totali). When patients were divided according to median of MCP-1 value, patients with high MCP-1 levels had a lower survival than patient with low levels of MCP-1 (5 vs 8 mts, respectively). The difference in the survival Kaplan-Meier curves of the two groups was statistically significant (p=00.2) after correction for the staging ??
In the second group of patients with operable lung cancer, we were able to obtain the analysis of MCP-1 on a fragment of lung cancer tissue in 40 patients (male/female 37/3, mean age 72.8,). The histologic type of lung cancer was adenocarcinoma and squamous. All these patients were followed in order to evaluate for the progression of the disease. The mean follow-up time was 16.9 months (range 4-27), and at the end of the follow-up 15 of them were died. MCP-1 was measurable in all tissue samples, with the following expression: + 1, +2, +3. When we divided the patients in three categories according to the expression of MCP-1 in the lung cancer tissue, there weren’t differences in term of survival among patients with difference immunohistochimical expression of MCP-1.
These results suggest that MCP-1 might contribute to the poor prognosis of the lung cancer, particularly in patients observed in the inoperable stage of the disease. The difference between the results we obtained in the two groups of patients may be due to the different method of measurement of MCP-1 in the inoperable and operable patients (50 vs 40) including the different methods of expression of the results, the different stages of the disease, and the different mortality observed during the follow-up in the two groups of patients.
Further analyses will be necessary in order to better define whether MCP-1 is significantly involved in NSCLC behavior. MCP-1 could be a novel target in cancer treatment once its role in immune regulation and angiogenesis is better understood.