Insulin-like Growth Factor-1 Receptor and ErbB Kinase Inhibitor Combinations Block Proliferation and Induce Apoptosis through Cyclin D1 Reduction and Bax Activation

Abstract

The insulin-like growth factor-1 receptor (IGF-1R) and ErbB family of receptors are receptor tyrosine kinases that play important roles in cancer. Lack of response and resistance to therapies targeting ErbB receptors occur and are often associated with activation of the IGF-1R pathway. Combinations of agents that inhibit IGF-1R and ErbB receptors have been shown to synergistically block cancer cell proliferation and xenograft tumor growth. To determine the mechanism by which targeting both IGF-1R and ErbB receptors causes synergistic effects on cell growth and survival, we investigated the effects of combinations of selective IGF-1R and ErbB kinase inhibitors on proliferative and apoptotic signaling. We identified A431 squamous cell carcinoma cells as most sensitive to combinations of ErbB and IGF-1R inhibitors. The inhibitor combinations resulted in not only blockade of A431 cell proliferation, but also induced apoptosis, which was not seen with either agent alone. Upon examining phosphorylation states and expression levels of proteins in the IGF-1R and ErbB signaling pathways, we found a correlation between the ability of combinations to inhibit proliferation and to decrease levels of phosphorylated Akt and cyclin D1. In addition, the massive cell death induced by combined IGF-1R/ErbB inhibition was associated with Mcl-1 reduction and Bax activation. Thus, targeting both IGF-1R and ErbB receptors simultaneously results in cell cycle arrest and apoptosis through combined effects on Akt, cyclin D1, and Bax activation. IGF-1R2 function is important for cellular processes that are activated in cancer cells, including cell proliferation, survival, metastasis, and invasion (1-4). Transformation of cells by several oncogenes has been shown to require IGF-1R function (2, 5), and anchorage-independent growth (3) and survival of cancer cells in response to cellular stress (5) can both be mediated by the IGF-1R. IGF-1R stimulates cell proliferation and survival through activation of the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) and Akt pathways. Upon binding of IGF-1 or IGF-2 to the IGF-1R, the receptor becomes autophosphorylated on several tyrosine residues. These phosphotyrosines serve as binding sites for adaptor proteins, including insulin receptor substrate (IRS)-1-4 and Shc, which are then phosphorylated by the activated receptor. Phosphorylated IRS and Shc in turn recruit Grb2/SOS, which leads to activation of the MAPK pathway, and the p85 subunit of phosphatidylinositol 3-kinase, resulting in phosphatidylinositol 3,4,5-trisphosphate production and Akt activation (3, 6, 7). The MAPK and Akt pathways regulate levels of cell cycle proteins like cyclin D1 and p27 to cause increased cell proliferation (8) and decrease apoptosis by phosphorylating the proapoptotic protein, Bad, which results in its sequestration by 14-3-3 (9). Antibodies that target IGF-1R and one small molecule IGF-1R inhibitor are undergoing clinical trials, and several other IGF-1R small molecule inhibitors ...

Differential induction of apoptosis in HER2 and EGFR addicted cancers following PI3K inhibition

“…Thus, we hypothesize that in EGFR mutant NSCLCs, high levels of Mcl-1 may directly sequester Bax and/or Bak to prevent their oligomerization or may bind preexisting BIM, thereby preventing BIM-mediated activation, or ''priming,'' of Bax/Bak. Indeed, interactions between Mcl-1 with BIM have been reported in the gefitinib-sensitive A431 cells (39). Furthermore, it may be the case that only when BIM levels become excessive, contingent upon both Mcl-1 degradation and BIM up-regulation, that BIM primes Bax/Bak, and commits cells to apoptosis as we observed.…”

BMS-754807, a small molecule inhibitor of insulin-like growth factor-1R/IR

“…Due to the wide expression of IGF-1R and the potential cross-talk between the IGF-1R pathway and other signaling pathways implicated in tumorigenesis (EGFR, HER-2/neu, and mammalian target of rapamycin), BMS-754807 has the potential to be combined with other therapies in a wide range of tumors (27)(28)(29). The reciprocity of inhibition of multiple signaling pathways is being tested in clinical studies by simultaneous inhibition of IGF-1R in combination with EGFR and HER2 antibodies and small molecule inhibitors (30)(31)(32). To explore the cross-talk with other signal transduction pathways, BMS-754807 was tested in combination with anticancer agents in multiple human tumor cell types in vitro.…”

MM-141, an IGF-IR– and ErbB3-Directed Bispecific Antibody, Overcomes Network Adaptations That Limit Activity of IGF-IR Inhibitors

“…Preclinical evidence supports a role for IGF-IR in reducing the effectiveness of anti-ErbB2 and anti-EGFR therapies, requiring coblockade of the PI3K/AKT/mTOR cascade (14)(15)(16). Addition of the IGF-I ligand has been shown to protect trastuzumab-sensitive cells from cell death (17), and patients treated with trastuzumab who also express IGF-IR have shorter progression-free survival (18).…”