Cancer research
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In previous studies we have shown that the sensitivity of melanoma cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis was determined largely by the level of expression of death receptor TRAIL receptor 2 on the cells. However, approximately one-third of melanoma cell lines were resistant to TRAIL, despite expression of high levels of TRAIL receptor 2. The present studies show that these cell lines had similar levels of TRAIL-induced activated caspase-3 as the TRAIL-sensitive lines, but the activated caspase-3 did not degrade substrates downstream of caspase-3 [inhibitor of caspase-activated DNase and poly(ADP-ribose) polymerase]. ⋯ TRAIL was shown to cause release of Smac/DIABLO from mitochondria, but this release was greater in TRAIL-sensitive cell lines than in TRAIL-resistant cell lines and was associated with down-regulation of XIAP levels. Furthermore, inhibition of Smac/DIABLO release by overexpression of Bcl-2 inhibited down-regulation of XIAP levels. These results suggest that Smac/DIABLO release from mitochondria and its binding to XIAP are an alternative pathway by which TRAIL induces apoptosis of melanoma, and this pathway is dependent on the release of activated caspase-3 from inhibition by XIAP and possibly other inhibitor of apoptosis family members.
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Many oncogenes induce expression of vascular endothelial growth factor (VEGF), a key factor in tumor angiogenesis. Phosphatidylinositol 3'-kinase (PI3K)/Akt is a common signaling pathway for oncogenes and tumor suppressor genes and is involved in VEGF regulation. Because hypoxia is a major stimulus for VEGF production, we examined the effects of LY294002, a selective PI3K inhibitor, on hypoxia-inducible factor (HIF)-1alpha and HIF-2alpha expression and on endogenous VEGF responses to hypoxia. ⋯ This effect was blocked by PI3K inhibitor, demonstrating one mechanism for ras synergy with hypoxia-mediated induction of genes. The decreased HIF-1alpha expression was not dependent on VHL interaction because a renal carcinoma cell line with VHL mutation and constitutive high HIF-1alpha expression also showed down-regulation of HIF-1alpha after treatment with LY294002. These results have implications for the use of PI3K inhibitors to inhibit synergistic effects of hypoxia with a wide range of common oncogenes.
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Relevant drawbacks of the molecular structure and mechanism of the action of camptothecins are the instability of the E ring lactone and the reversibility of drug-target interaction. Such features are expected to limit the clinical efficacy of conventional camptothecins. In an attempt to overcome these limitations and to improve the pharmacological profile of camptothecins, a novel series of seven modified lipophilic analogues was synthesized based on the hypothesis that lipophilicity could promote a rapid cellular accumulation and stabilization of drug-target interaction. ⋯ The relevant liver accumulation may account for a marked effect of ST1481 against liver metastases induced by the ovarian carcinoma IGROV-1. In conclusion, the results support the hypothesis that a potent lipophilic camptothecin with a proper substituent at the position 7 may have therapeutic advantages likely related to a rapid intracellular uptake and tissue distribution, stabilization of the drug-target complex, and good oral bioavailability. Overall, the results support the preclinical interest of ST1481 in terms of efficacy, potency, toxicity profile, and ability to overcome multidrug resistance.
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The insulin-like growth factor I receptor (IGF-IR) is a ubiquitous and multifunctional tyrosine kinase that has been implicated in breast cancer development. In estrogen receptor (ER)-positive breast tumors, the levels of the IGF-IR and its substrate, insulin-receptor substrate 1 (IRS-1), are often elevated, and these characteristics have been linked with increased radioresistance and cancer recurrence. In vitro, activation of the IGF-IR/IRS-1 pathway in ER-positive cells improves growth and counteracts apoptosis induced by anticancer treatments. ⋯ However, a chronic (2-day) IGF-I exposure induced the PI-3K/Akt pathway only in MCF-7 cells. The reactivation of this pathway in ER-negative cells by overexpression of constitutively active Akt mutants was not sufficient to significantly improve proliferation or survival (with or without IGF-I), which indicated that other pathways are also required to support these functions. Our results suggest that in breast cancer cells, IGF-IR can control nonmitogenic processes regardless of the ER status, whereas IGF-IR growth-related functions may depend on ER expression.
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Comparative Study
Catechol-O-methyltransferase (COMT)-mediated metabolism of catechol estrogens: comparison of wild-type and variant COMT isoforms.
The oxidative metabolism of 17beta-estradiol (E2) and estrone (E1) to catechol estrogens (2-OHE2, 4-OHE2, 2-OHE1, and 4-OHE1) and estrogen quinones has been postulated to be a factor in mammary carcinogenesis. Catechol-O-methyltransferase (COMT) catalyzes the methylation of catechol estrogens to methoxy estrogens, which simultaneously lowers the potential for DNA damage and increases the concentration of 2-methoxyestradiol (2-MeOE2), an antiproliferative metabolite. We expressed two recombinant forms of COMT, the wild-type (108Val) and a common variant (108Met), to determine whether their catalytic efficiencies differ with respect to catechol estrogen inactivation. ⋯ The variant isoform differed from wild-type COMT by being thermolabile, leading to 2-3-fold lower levels of product formation. MCF-7 breast cancer cells with the variant COMT 108Met/Met genotype also displayed 2-3-fold lower catalytic activity than ZR-75 breast cancer cells with the wild-type COMT 108Val/Val genotype. Thus, inherited alterations in COMT catalytic activity are associated with significant differences in catechol estrogen and methoxy estrogen levels and, thereby, may contribute to interindividual differences in breast cancer risk associated with estrogen-mediated carcinogenicity.