Role of interleukin-6 in cancer progression and therapeutic resistance

In the last several decades, the number of people dying from cancer-related deaths has not reduced significantly despite phenomenal advances in the technologies related to diagnosis and therapeutic modalities. The principal cause behind limitations in the curability of this disease is the reducing sensitivity of the cancer cells towards conventional anticancer therapeutic modalities, particularly in advance stages of the disease. Amongst several reasons, certain secretory factors released by the tumour cells into the microenvironment have been found to confer resistance towards chemo- and radiotherapy, besides promoting growth. Interleukin-6 (IL-6), one of the major cytokines in the tumour microenvironment, is an important factor which is found at high concentrations and known to be deregulated in cancer. Its overexpression has been reported in almost all types of tumours. The strong association between inflammation and cancer is reflected by the high IL-6 levels in the tumour microenvironment, where it promotes tumorigenesis by regulating all hallmarks of cancer and multiple signalling pathways, including apoptosis, survival, proliferation, angiogenesis, invasiveness and metastasis, and, most importantly, the metabolism. Moreover, IL-6 protects the cancer cells from therapy-induced DNA damage, oxidative stress and apoptosis by facilitating the repair and induction of countersignalling (antioxidant and anti-apoptotic/pro-survival) pathways. Therefore, blocking IL-6 or inhibiting its associated signalling independently or in combination with conventional anticancer therapies could be a potential therapeutic strategy for the treatment of cancers with IL-6-dominated signalling.