Metformin Plus TKI Use in Patients With Non-Small Cell Lung Carcinoma

Lung cancer is the first cause of death in men and women, representing 28% and 26% of registered deaths worldwide, respectively. Among patients with this disease, at least 80% has non-small cell lung cancer (NSCLC), and 60% of patients are diagnosed when they already have a locally advanced or metastatic disease. NSCLC therapy regimens depend on the stage of disease and may require surgery, chemotherapy, radiotherapy, or a combination of these. Survival rate at 5 years is low for patients with stage II and III of the disease, with variation from 30% to 5%, this means that an improvement in therapy are required.

Advances in molecular biology of cancer have led to discovering several molecular targets and developing new target therapies. Epidermal growth factor receptor (EGFR) is involved in the development and progression of several types of cancer, including NSCLC. However, despite clinical success with different tyrosine kinase specific domain inhibitors (TKIs), most of the patients respond to these drugs initially, but eventually develop resistance to these drugs after and average period of time of 10 months. Thus, innovative treatment strategies are required urgently to overcome therapeutic resistance to EGFR-TKIs and to improve survival of patients with NSCLC.

Recently, metformin has been associated with reduction in the global risk of incidence and mortality of different types of cancer, due to its anti-tumor properties. In specific types of cancer, retrospective studies have demonstrated a clinical benefit from the use of metformin combined with the treatment of cancer.

Patients with NSCLC with positive EGFR mutations are highly sensible to specific anti-EGFR tyrosine kinase inhibitors, however, most of the patients who initially respond to these target therapies, will present progression of the disease posteriorly during the treatment, this is known as acquired resistance. Acquired resistance to target therapies was first studied in patients with chronic myeloid leukemia with BCR-ABL translocation treated with Imitanib, an inhibitor of aberrant kinase BCR-ABL. Thanks to research, mutations associated with resistance to treatment with TKIs in NSCLC with positive EGFR mutations were discovered. By several studies, additional mutations were found in the kinase domain and in KRAS in those patients with acquired resistance to Gefitinib or Erlotinib. By PCR it was found that 50% of patients with resistance to TKI develop a specific mutation in exon 20 (T790M). However, the mechanism by which the other 50% of patients develop resistance to anti-EGFR TKI is yet unknown. Some studies have found focal amplification of MET proto-oncogen in 22% of the patients with acquired resistance to Gefitinib. The proposed mechanism is that MET amplification promotes resistance by activation of HER3 depending PI3K pathway. Nonetheless, there are few studies with few patients about MET amplification as a resistance mechanism.

On the other hand, there are patients who have this resistance mutation since the first presentation, or de novo. T790M mutation may be present before exposition to TKI and it's generally found with other activating mutations in EGFR (exon 19 deletion and punctual L858R mutation). A response rate of 8% has been reported in those patients treated with gefitinib or erlotinib whose T790M mutation was positive at the time of the diagnosis, with progression-free survival of 2 months and global survival median of 16 months.

Despite the advances in treatment have increased response rate and progression-free survival with anti-EGFR TKI in patients with presence of activating mutations, most of them will develop resistance mutations (T790M) and disease progression. There is no standard treatment in patients who progress from a first generation anti-EGFR TKI, such as erlotinib and gefitinib. Some studies have used afatinib as second line therapy in patients who had progression, finding a benefit in the progression-free survival, disease control rate up until 58% and delay in the development of lung cancer associate symptoms, thus improving quality of life in patients treated with afatinib.

Acquired resistance will develop in a mean time of 9 to 13 months and the 50% to 60% will be secondary to development of T790M resistance mutation.

The molecular mechanisms that generate acquired resistance to anti-EGFR TKI are not completely clear. We know that around 50% of cases are caused by an acquired mutation in the EGFR T790M and a lower percentage by MET oncogene amplification, nevertheless, there are other proposed molecular mechanisms, such as the activation of mesenchymal-epithelial transition. The latter, refers to changes in the phenotype of epithelial cells to cells with mesenchymal cells phenotype, resulting in increase in motility, proliferation and metastasis of tumor cells. It's been proposed that epithelial-mesenchymal (EMT) is associated with sensitivity to chemotherapy and TKI. Finding an effective therapy for patients who develop T790M resistance mutation is required to overcome resistance to first generation anti-EGFR TKI. Afatinib, as a second generation irreversible anti-EGFR TKI, has demonstrated in some studies to have certain effect in patients with resistance, however, the benefit is marginal. Studies have shown that the union of the tyrosine kinase portion of afatinib in patients with resistance mutation, is 100 times less strong that the union in cells with anti-EGFR activating mutations. Pre-clinical studies have demonstrated that inhibition of IL-6 receptor activation and activation of JAK1/STAT3 pathway overcomes resistance and sensitize again those cells with EGFR resistance mutation.

Metformin is a drug that has been used for several years to treat diabetes mellitus and metabolic syndrome, it's generally well tolerated. Several studies since 1910 have suggested that patients with diabetes are at increased risk to develop cancer. The American Diabetes Association and The American Cancer Society have come to a consensus that suggests a clear association for greater risk of cancer incidence in diabetic patients. The tumors that have been studied with more frequency are in: colon, endometrium, rectus and breast. On the other hand, several epidemiologic and cases and control studies have suggested that the use of metformin decreases risk to develop cancer up until 30% with a hazard ratio (HR) of 0.77 (0.64-0.92) and risk of cancer-specific death with a HR of 0.67 (0.53-0.85). Such protective effect has been seen in all kinds of cancer, but has been more studied in breast, gastrointestinal and lung cancer.

The effect of metformin as chemo-prevention is subject to debate, however, there's more information about its use as adjuvant in the treatment of lung cancer, in combination with chemotherapy or target molecular therapy. Pre-clinical studies in mice have demonstrated that use of metformin per os may decrease the necessary dosage of chemotherapy and may prolong tumor remission. Metformin, by inhibiting repairing and anti-apoptosis mechanisms, increases sensitivity to chemotherapy, especially to platinum. Studies that involve metformin, paclitaxel, carboplatin and doxorubicin, have demonstrated to have an effect in tumor regression and prevention of recurrences up until four times the effect of monotherapy in xenograft models in cellular lines of lung and prostate cancer. Retrospective studies have found a benefit in progression-free survival and global survival in diabetic patients with NSCLC, who also are treated with metformin.

T790M mutation and MET amplification are the main resistance mechanisms to anti-EGFR TKI, other mechanisms such as epithelial-mesenchymal transition (EMT) by TGF-β are resistance mechanisms. TGF-β also induces activation of IL-6 and paracrine activation of the receptor (IL-6R) and at the same time the activation of pathway JAK1/STAT3 and cell immortalization. Pre-clinical studies with cellular lines of lung cancer with anti-EGFR acquired-resistance treatment show that metformin prevents transcription of factors that activate epithelial-mesenchymal transition, inhibiting TGF-β, thus, inhibiting IL-6/JAK1/STAT3 pathway, overcoming anti-EGFR TKI resistance in patients with T790M resistance mutation, in vitro and in vivo. A recent study reports that use of metformin in combination with gefitinib may increase efficacy of the latter, showing anti-proliferative and pro-apoptotic effect in cellular lines of NSCLC. Other studies have shown, by Western-blot, a decrease in levels of phosphorylation and activation of growth pathways MAPK, AKT and mTOR with the use of metformin, found in pre-clinical studies. Currently, a phase I/II study is being carried out to determine effective dose, safety and posteriorly the activity of metformin in combination with erlotinib as second line therapy in patients with NSCLC without EGFR mutation.

The main objective of this study is to assess the progression-free survival period in patients with advanced non-small cell lung cancer in treatment with TKIs and metformin versus TKI alone. The secondary objectives are the response rate, global survival, quality of life, safety, as well as determining the alteration of nutrition parameters associated to the combined use of TKIs and metformin.

Besides the secondary objectives, we want to find new candidate markers in the tumor characteristics to predict anti-tumor activity, as well as the search for serum biomarkers; among which we will analyze EGFR mutations (exon 18-21 mutations), IL-6, IGF-1, as well as determination of LKB-1 molecule expression in tumor tissue. We will associate the prognostic and potential role as possible biomarkers.