New therapeutic and diagnostic strategies in glioblastoma: Cancer Stem Cells targeted by monoclonal antibody

Abstract

One of the most challenging objective in oncology is the identification of new specific tumor target to design effective therapies. At present it is widely accepted that the tumors are originated from a undifferentiated cell population able to trigger the cancer establishment and responsible for its maintenance. These undifferentiated cells are called Cancer Stem Cells (CSC) or tumor-initiating cells. A direct consequence of the CSC hierarchical model applied to clinic is that is currently taking place the idea that the traditional cancer treatment concern only the bulk tumor and the differentiated population without affecting the stem cell compartment. In that scenario the resistant cancer stem cells can proliferate and diffuse resulting in a temporary success of the treatment followed by a relapse. For this reason an effective therapy should be addressed to the eradication of CSCs that represent a gold target from the clinical treatment. CSCs are relatively slow proliferating in vivo, where they divide asymmetrically and are amplified few time with a massive duplications cycles of division made by progenitors. Therefore CSCs can be resistant to several available therapies which primarily affect actively duplicating cells. Despite to their relative quiescence, several mechanisms could account for this resistance such as the increased expression of drug pumps (Zhou, Schuetz et al. 2001), the expression of anti-apoptotic proteins, the higher efficiency in repairing DNA damage (Bao, Wu et al. 2006). The aim of this work was to specifically target CSCs of one of the most important causes of death for cancer, glioblastoma multiforme (GBM) by generating monoclonal antibodies (mAbs). Glioblastoma multiforme is the most common and most aggressive malignant primary brain tumor in humans. Even after treatments based on multiple approaches, as radiotherapy, surgical resection and chemotherapy, the prognosis of GBM patients remains unfavorable. The generation of mAbs against new surface markers against glioblastoma stem cells could have an impact as for the diagnostic as for therapeutic application. New mAbs could help to set up new diagnostic tests or to follow the effect of therapies. The mAbs generated could be employed as new therapeutic tools with selective toxicity against tumor cells, add efficacy to present therapies and represent an additional line of treatment for patients in advanced stages with multiresistant diseases. Moreover the discovery of a common stemness marker as antigen on glioblastoma stem cells may allow to select for cancer stem cells and this help to isolate and characterize them and possibly may be useful for defining novel diagnostic techniques and targeted therapies. The glioblastoma stem cells maintain the characteristics of tumor initiating cells after prolonged culture in vitro. We used these cells as immunogens in immunocompetent BALB/c mice to develop a hybridoma library. After the initial screening of the library was identified the 1.4A12 antibody that identified integriná7 (ITGA7) as antigen mostly expressed on brain tumor stem cells. The biological function of the integriná7 was evaluated the vitro and in vivo. ITGA7 silencing impairs the growth rate proliferation, clonogenicity, invasion in vitro and the tumor growth reduction in vivo. We analyzed the effect of 1.4A12 antibody and its role in counteracting the ITGA7 pathway. The 1.4 anti-integrin alpha7 antibody interferes with the integrin alpha 7 signaling and suppressed tumor invasion in vitro and tumour growth in vivo. All our data indicated that integrin alpha7 is involved in GBM pathogenesis and that 1.4A12 antibody could be of great help in defining new therapeutic options to increase glioblastoma eradication interfering with the tumor growth and with the invasion of cancer cells.