Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance
Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance the cytotoxic effects of ionizing radiation (IR). EGFR and PKC. PKC, in addition to MEK/ERK signaling, is usually required for the suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells treated with IR and erlotinib. In conclusion, we identify EGFR as a molecular target to overcome a novel mechanism of radioresistance in KRAS-mutant tumor cells, which stands in contrast hSPRY1 to the unresponsiveness of KRAS-mutant cancers TAK-242 S enantiomer manufacture to EGFR-directed brokers in monotherapy. Our findings may reposition EGFR-targeted brokers for combination with DSB-inducing therapies in KRAS-mutant NSCLC. Keywords: KRAS, EGFR, Lung Cancer, Radiation Introduction Exposure of cellular DNA to ionizing radiation (IR) generates various types of damage (1). A dose of 1 Gy produces 20C40 DNA double-strand breaks (DSB) in a mammalian cell (1, 2). Unrepaired or misrepaired DSB are the principal type of damage that may result in lethal chromosomal aberrations and cell death, or radiobiologically termed cell inactivation, within 1C3 division cycles (reviewed in ref. (3)). Molecular targeted anti-cancer brokers have been tested extensively pre-clinically, and increasingly so in the clinic, to enhance the cytotoxic effects of IR. Pre-clinical data suggest that radiosensitization is usually frequently achieved by interfering with DSB repair, thereby increasing the levels of residual, unrepaired DSB (4C6). Unrepaired DSB may induce cellular senescence or apoptosis, but the latter outcome is usually generally more desirable as senescent cells remain viable and can even escape senescence (7, 8). Non-small cell lung cancer (NSCLC) is usually difficult to control locally by IR due to the typically large tumor size at diagnosis and the proximity to critical normal organs, which limit the achievable dose of radiation (reviewed in ref. (9)). Therefore, radiation has been combined with radiosensitizing chemotherapeutics. However, this combination has yielded only a moderate survival benefit and at the cost of significant toxicity in many patients. The epidermal growth factor receptor (EGFR) is usually a member of the erbB multi-gene family. Receptor activation is usually associated with phosphorylation of the intracellular tyrosine kinase domain name and recruitment of signaling molecules that initiate the diverse signaling cascades that promote biological responses, including enhanced proliferation, cell survival, as well as radiation resistance (reviewed in ref. (10, 11)). As EGFR is usually expressed in up to ~80% of NSCLC, it constitutes a potentially important target in NSCLC therapy (12). Clinical trials have sought to integrate EGFR-targeted monoclonal antibodies (mAb) or selective tyrosine kinase inhibitors (TKI) into the treatment of NSCLC in order to achieve radiosensitization, with varying results (13C15). For NSCLC harboring wild-type EGFR, TAK-242 S enantiomer manufacture it is usually increasingly appreciated that these brokers should be selected based on the molecular profile of a given tumor rather than administered to all patients (16). However, predictive biomarkers of radiosensitization have been lacking. The KRAS gene encodes a GTPase involved in relaying signals from the cell membrane to the nucleus. Upon the introduction of point mutations, most commonly at codons 12 and 13, the K-Ras protein becomes constitutively active and acquires oncogenic properties. KRAS mutations are found in approximately 30% of NSCLC (17) and are associated with resistance to EGFR-targeted brokers in mono-therapy as well as poor prognosis (18C21). In KRAS-mutant cells, critical pro-survival and growth effector pathways are activated by K-Ras and consequently exhibit resistance to inhibition by TKIs such as erlotinib or mAbs such as cetuximab (22, 23). There is usually also evidence that KRAS mutations confer radioresistance, although this phenomenon is usually understudied in NSCLC (24C26). Large scale screening of annotated cancer cell lines has been successfully employed to identify cell line subsets sensitive to single agent treatments and associated biomarkers (27C30). There is usually a need to adapt such screening platforms for the study TAK-242 S enantiomer manufacture of IR in conjunction with potentially radiosensitizing targeted compounds. We recently reported that the radiosensitizing effects of erlotinib and cetuximab seen in a short-term survival assay as used in screening platforms correlate well with results of the standard clonogenic survival assay (6). The degree of radiosensitization for single doses of IR was relatively small, i.e., 1.02C1.17 for short-term survival and 1.15C1.46 for clonogenic survival, consistent with data reported by others (6, 31, 32). However, it is usually thought that a small radiosensitizing effect incurred by a single dose of IR could be amplified when doses are repeated (33), as would be the case during a several-week clinical course of radiation consisting of 30 or more.