Transferrin receptor (TfR) has been shown to be significantly overexpressed in different types of cancers. We discovered TfR as a target for gambogic acid (GA), used in traditional Chinese medicine and a previously undiscovered link between TfR and the rapid activation of apoptosis. The binding site of GA on TfR is independent of the transferrin binding site, and it appears that GA potentially inhibits TfR internalization. Down-regulation of TfR by RNA interference decreases sensitivity to GA-induced apoptosis, further supporting TfR as the primary GA receptor. In summary, GA binding to TfR induces a unique signal leading to rapid apoptosis of tumor cells. These results suggest that GA may provide an additional approach for targeting the TfR and its use in cancer therapy.rapid apoptosis ͉ caspases ͉ target identification

Imatinib inhibitsgatekeeper mutation ͉ imatinib resistance ͉ kinase inhibitor

IntroductionBreast cancer is among the most common human cancers, affecting one in every eight women and accounting for an estimated 192,000 cases and more than 40,000 deaths in the United States during 2001. One of the significant predictors of breast cancer prognosis is regional and distant metastasis; yet the mechanism of metastasis and the ability to predict it are far from being fully understood.From both a clinical and experimental perspective, a more detailed understanding of the mechanisms of metastasis is needed in order to identify better diagnostic markers and therapeutic approaches.In order to study breast cancer, many investigators have used human derived cell lines that have yielded significant insight into the biology of breast cancer; yet these models DMEM = Dulbecco's modified Eagle medium; EDTA = ethylenediamine tetraacetic acid; FBS = fetal bovine serum; H&E = hematoxylin and eosin; MAPK = mitogen-activated protein kinase; mT = middle T; OPN = osteopontin; PBS = phosphate-buffered saline; PCR = polymerase chain reaction; PI3-K = phosphatidylinositol-3-kinase; PyV = polyomavirus; SEM = scanning electron microscopy; SSH = suppression subtractive hybridization. AbstractIntroduction: In order to study metastatic disease, we employed the use of two related polyomavirus middle T transgenic mouse tumor transplant models of mammary carcinoma (termed Met and Db) that display significant differences in metastatic potential.

mTOR Ser/Thr protein kinase operates in two distinct multi-protein complexes, TORC1 and TORC2, which together regulate growth, metabolism, angiogenesis and survival by integrating nutrient and hormonal environmental signals. The activity of mTOR is frequently up-regulated in human cancer by constitutive mitogen stimuli or oncogenic mutations upstream of TORC1 and TORC2. Rapamycin provides mechanistic rationale and clinical proof of concept for the therapeutic value of targeting mTOR in human cancer, but it also provided insights into how ATP-competitive TORC1/2 inhibitors have the potential to demonstrate superior efficacy. Through rational drug design we have discovered INK128, a potent, selective TORC1/2 inhibitor with excellent drug-like properties. INK128 inhibits mTOR kinase (sub-nanomolar) in an ATP-dependent fashion and demonstrates a high degree of selectivity against closely related kinases as well as against a panel of more than 400 kinases. INK128 inhibits both the phosphorylation of S6 and 4EBP1, the downstream substrates of TORC1, and selectively inhibits AKT phosphorylation at Ser473, the downstream substrate of TORC2, in vitro and in vivo. Interestingly, potent inhibition was also observed in cell lines resistant to rapamycin and pan-PI3K inhibitors. Daily, oral administration of INK128 (alone or in combination) inhibited angiogenesis and tumor growth in multiple xenograft models with predicted dose:exposure PK/PD relationship. We attribute the superior activity of INK128 to the fact that it is a more effective inhibitor of TORC1 relative to rapamycin. We further demonstrated that TORC1/2 inhibitors cause death of murine and human leukemia cells in models of pre-B acute lymphoblastic leukemia. In vivo, oral daily treatment with TORC1/2 inhibitors delayed leukemia onset and augmented the effects of ABL kinase inhibitors. Unexpectedly, these novel TORC1/2 inhibitors had much weaker effects than rapamycin on proliferation and function of normal lymphocytes. These findings establish that transformed lymphocytes are selectively sensitive to active-site TORC1/2 inhibitors and further support the development of such compounds for leukemia therapy in addition to solid tumors. In summary, INK128 is a potent, selective, and orally active TORC1/2 dual inhibitor positioned to enter clinical development. TORC1/2 inhibitors are mechanistically distinct from rapamycin and offer a compelling approach to the treatment of cancer by targeting translational control, cell metabolism, growth and angiogenesis. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B148.

A novel series of 3,5-diaryl-oxadiazoles was identified as apoptosis-inducing agents through our cell and chemical genetics -based screening assay for compounds that induce apoptosis using a chemical genetics approach.