EKI-785

Elevated epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) signaling are known to contribute to the malignant properties of glioblastoma multiforme (GBM), which include uncontrolled cell proliferation and evasion of apoptosis. Small molecule inhibitors that target these protein kinases have been evaluated in multiple clinical trials for cancer patients, including those with GBM. Here we have examined the cellular and molecular effects of a combined kinase inhibition of mTOR (rapamycin) and EGFR (EKI-785) in U87 and U251 GBM cells. Simultaneous treatment with rapamycin and EKI-785 results in synergistic antiproliferative as well as proapoptotic effects. At a molecular level, rapamycin alone significantly decreases S6 phosphorylation, whereas EKI-785 alone promotes substantially reduced signal transducer and activator of transcription (STAT3) phosphorylation. Treatment with rapamycin alone also increases Akt phosphorylation on Ser-473, but this effect is blocked by a simultaneous administration of EKI-785. Individually, EKI-785 diminishes while rapamycin promotes the binding of the translation inhibitor eukaryotic initiation factor 4E binding protein (4EBP1) to the eukaryotic translation initiation factor 4E (eIF4E). In spite of these opposing effects, the highest level of 4EBP1-eIF4E binding occurs with the combination of the two inhibitors. These results indicate that the inhibition of EGFR and mTOR has distinct as well as common signaling consequences and provides a molecular rationale for the synergistic antitumor effects of EKI-785 and rapamycin administration.

Colorectal cancer is one of the leading causes of cancer-related death in the western world, with surgical resection the only curative treatment. Screening programmes involving faecal occult blood tests with periodic endoscopic examination of the bowel can achieve a reduction in mortality of 15–33%. However, despite widely published recommendations for such screening programmes, compliance remains poor. Chemoprevention, defined as the prevention of cancer by the use of pharmacological agents that inhibit or reverse the process of carcinogenesis, might provide an alternative approach to reducing mortality from colorectal cancer. Moreover, therapeutic strategies that use a combination of chemopreventative drugs to target multiple alterations that result in tumour initiation or progression are highly attractive.Colorectal neoplasia is frequently associated with alterations in signalling through the epidermal growth factor (EGF)-family of receptors, as well as changes in the cyclooxygenase (Cox) pathway. Colorectal neoplasia results in increased cell proliferation and cell motility and helps stimulate tumour growth by promoting tumour-associated angiogenesis. Interactions between the EGF and Cox pathways are well documented: EGF induces Cox-2 and overexpression of Cox-2 increases EGF-receptor expression in intestinal epithelial cells. The targeting of their respective pathways by inhibitors has been shown to have potent anti-neoplastic effects, although tumour growth is not completely prevented and there is potential toxicity associated with their long-term use.Torrence et al.1xCombinatorial chemoprevention of intestinal neoplasia. Torrence, C.J. et al. Nat. Med. 2000; 6: 1024–1028Crossref | PubMed | Scopus (446)See all References used a combination therapy involving a newly developed inhibitor of the EGF receptor (EGFR) kinase (EKI-785) and a well-known cyclooxygenase inhibitor (sulindac) to prevent tumour development in the Min mouse model of colorectal cancer. These mice harbour an inactivated APC gene and normally develop multiple intestinal polyps. Mice were treated for 60 days with various combinations of drug–food formulations, after which their intestinal tracts were removed and the number of polyps counted. Individually, the compounds provided significant protection from polyp formation (approximately 50% and 70% reduction, respectively); in combination, they provided nearly complete protection (95–97%). Detailed histopathological staining revealed the presence of numerous microscopic adenomas in all treatment groups, suggesting that the main effect of the chemopreventative agents was on tumour progression rather than on initiation.Chemical modification of EKI-785 resulted in the development of EKI-569, which has improved pharmacokinetics, is better at reducing the number of polyps (87%) and can inhibit EGFR kinase activity in vivo at clinically relevant doses. Use of EKI-569 allowed less-toxic doses of sulindac to be used and, in combination, resulted in protection from tumour development in 95% of Min mice, with nearly 50% of mice having no tumours at all. Detailed histological examinations of the entire gastrointestinal tract revealed no evidence of overt toxicity.It is surprising that Torrence et al.1xCombinatorial chemoprevention of intestinal neoplasia. Torrence, C.J. et al. Nat. Med. 2000; 6: 1024–1028Crossref | PubMed | Scopus (446)See all References used sulindac, a nonselective NSAID inhibitor, rather than one of the readily available selective inhibitors. Nevertheless, it will be fascinating to unravel the molecular and biochemical mechanisms involved in growth suppression by the combination therapies. Most importantly, these results have direct practical implications and suggest that it should be possible to bypass the main toxicity associated with long-term, non-steroidal, anti-inflammatory drug treatment in patients.