Growth factors are proteins that stimulate the growth of specific tissues. They bind to cells by growth factor receptors, activating cellular proliferation and differentiation. This activation of growth factor receptors creates a short, time-limited signal, which causes different parts of cellular proliferation and differentiation such as mitosis, clonal expansion, gene regulation, and cell apoptosis. While growth factor receptors operate on different cell types, their signal pathways often overlap, which makes them important targets for oncology research.
Growth Factors in Oncology
Growth factor receptors are important targets in oncology because mutations that lead to constitutive activation of these signal pathways result in the progression of various types of cancers. Overexpression of receptor tyrosine kinases (RTK), which include the epidermal growth factor receptor (EGFR) family and the vascular endothelial growth factor receptor (VEGFR) family, among others, have been found in many tumors. Mutations in serine/threonine-specific protein kinase receptors such as transforming growth factor-beta (TGFβ) have also been linked to growth of many tumors due to defects in the cellular growth inhibition response to TGFβ. For these reasons growth factors and growth factor signaling pathways have become promising targets in the development of oncologic therapeutics.
Therapies That Target Growth Factor Receptors
To combat various cancers, researchers are exploring numerous small molecules that can act as potential inhibitors targeting growth factor receptors. One therapeutic route is through stopping the proliferation of the cancerous cells themselves through cancer growth inhibitors. Cancer growth inhibitors block growth factors from triggering the intracellular signaling pathways that cause cancer cells to divide and grow. By blocking the signals, these compounds may stop cancer cells from developing or dividing, causing tumor growth to slow or stop. Epidermal growth factor receptor (EGFR) is a key factor in epithelial malignancies, and its activity enhances tumor growth, invasion, and metastasis. Considering the receptors significant role in rapid cell proliferation, and its involvement in the progression of many types of cancers, EFGR continues to command much interest as a target for cancer growth inhibitors.
Another route to inhibit tumor growth is through depriving tumors of oxygen and nutrients. Like normal cells, cancer cells need oxygen and nutrients to survive and grow. To do that, tumors need a constant blood supply. To slow or stop tumor growth, researchers can target a tumor’s angiogenic, vasculogenic, or lymphangiogenic abilities through angiogenesis inhibitors. Angiogenesis inhibitors are compounds that block the chemical signals that cells use to make blood vessels grow. A specific growth factor receptor family that is a target for angiogenesis inhibitors are vascular endothelial growth factor receptors (VEGFRs). There are several isoforms of the physiological signaling molecule VEGF. VEGFR2 in particular is highly expressed in vascular endothelial cells and is a known regulator of vasculogenesis, angiogenesis and lymphangiogenesis, making it an excellent target for angiogenesis inhibitors.
Researchers also are targeting growth factor receptors with monoclonal antibodies as oncologic therapies. Monoclonal antibodies are antibodies produced by a single clone of cells or cell line and consists of identical antibody molecules. When applied in oncology, monoclonal antibodies are designed to target a specific receptor on a cancer cell to either kill the cancer cell or stop it from growing. One of the first anticancer therapies approved by the FDA was for a monoclonal antibody targeting the overexpression of an EGF receptor, HER2. Monoclonal antibodies can also be designed to supplement or boost a person’s natural immune response against cancer cells.
Testing Targeted Therapies In Vitro
Growth factor receptors continue to command much interest as targets for the development of novel, specific small molecule inhibitory drugs and antibodies for oncology. Understanding the bioactivity of possible oncologic therapeutics in vitro as antagonists of growth factor receptors can assist researchers by providing critical data on receptor functioning prior to moving on to in vivo trials. Using cell-based assays like those used in INDIGO’s kits and services can help researchers understand receptor functioning for making important drug development decisions.
