Rocaglamides are potent natural anticancer products that inhibit proliferation of various cancer cells at nanomolar concentrations. We have recently shown that these compounds prevent tumor growth and sensitize resistant cancer cells to apoptosis by blocking the MEK-ERK-eIF4 pathway. However, their direct molecular target(s) remain(s) unknown. In this study, using an affinity chromatography approach we discovered that prohibitin (PHB) 1 and 2 are the direct targets of rocaglamides. Binding of rocaglamides to PHB prevents interaction between PHB and CRaf and, thereby, inhibits CRaf activation and subsequently CRaf-MEK-ERK signaling. Moreover, knockdown of PHB mimicked the effects of rocaglamides on the CRaf-MEK-ERK pathway and cell cycle progression. Thus, our finding suggests that rocaglamides are a new type of anticancer agent and that they may serve as a small-molecular tool for studying PHB-mediated cellular processes.

The wogonin-containing herb Scutellaria baicalensis has successfully been used for curing various diseases in traditional Chinese medicine. Wogonin has been shown to induce apoptosis in different cancer cells and to suppress growth of human cancer xenografts in vivo. However, its direct targets remain unknown. In this study, we demonstrate for the first time that wogonin and structurally related natural flavones, for example, apigenin, chrysin and luteolin, are inhibitors of cyclin-dependent kinase 9 (CDK9) and block phosphorylation of the carboxy-terminal domain of RNA polymerase II at Ser2. This effect leads to reduced RNA synthesis and subsequently rapid downregulation of the short-lived anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1) resulting in apoptosis induction in cancer cells. We show that genetic inhibition of Mcl-1 or CDK9 expression by siRNA is sufficient to mimic flavone-induced apoptosis. Pull-down and in silico docking studies demonstrate that wogonin directly binds to CDK9, presumably to the ATP-binding pocket. In contrast, wogonin does not inhibit CDK2, CDK4 and CDK6 at doses that inhibit CDK9 activity. Furthermore, we show that wogonin preferentially inhibits CDK9 in malignant compared with normal lymphocytes. Thus, our study reveals a new mechanism of anti-cancer action of natural flavones and supports CDK9 as a therapeutic target in oncology.

Cutaneous T-cell lymphomas (CTCLs) are malignancies of skin-homing lymphoid cells, which have so far not been investigated thoroughly for common oncogenic mutations. We screened 90 biopsy specimens from CTCL patients (41 mycosis fungoides, 36 Sé zary syndrome, and 13 non-mycosis fungoides/Sé zary syndrome CTCL) for somatic mutations using OncoMap technology. We detected oncogenic mutations for the RAS pathway in 4 of 90 samples. One mycosis fungoides and one pleomorphic CTCL harbored a KRAS G13D mutation; one Séz-ary syndrome and one CD30 ؉ CTCL harbored a NRAS Q61K amino acid change. All mutations were found in stage IV patients (4 of 42) who showed significantly decreased overall survival compared with stage IV patients without mutations (P ‫؍‬ .04). In addition, we detected a NRAS Q61K IntroductionCutaneous T-cell lymphomas (CTCLs) are rare malignancies of skin-homing T lymphocytes. Curative modalities have thus far proven elusive. CTCL microarray studies have revealed natural clusters in association with prognosis. 1 Array-based comparative genomic hybridization (CGH) combined with gene expression profiling identified highly recurrent chromosomal alterations both in mycosis fungoides (MF) and Sézary syndrome (SS) patient specimens. 2,3 For example, FASTK and SKAP1 gene loci showed recurrent gains, and these genes also exhibited increased expression, whereas RB1 and DLEU tumor suppressor genes displayed diminished expression associated with loss. In another study, recurrent deletion of tumor suppressor genes BCL7A, SMAC/ DIABLO, and RHOF in MF was observed. 4 Genomic patterns characteristic of MF differ markedly from SS. 5 This might implicate discriminative molecular pathogenesis and different therapeutic requirements.The RAS-RAF-MEK-ERK signaling pathway regulates cell responses to environmental stimuli and plays a crucial role in many cancers. 6 Thus, RAF and MEK are attractive therapeutic targets. 7,8 RAS is a small guanine-nucleotide binding protein that is attached to the inner side of the plasma membrane. Activation of RAS causes RAF recruitment and activation by phosphorylation. Activated RAF kinase phosphorylates and activates MEK, which phosphorylates ERK. Three RAS (KRAS, NRAS, and HRAS), 3 RAF (ARAF, BRAF, and CRAF), 2 MEK (MEK1 and MEK2), and 2 ERK (ERK1 and ERK2) isoforms compose the "canonical" mitogen-activated protein kinase pathway. Somatic mutations that are found in many cancers, including colon carcinoma, melanoma, or pancreatic cancer, occur almost exclusively in BRAF, KRAS, or NRAS isoforms. 9-11 Typical mutations affect glycine 12 (G12), glycine 13 (G13), or glutamine 61 (Q61) and keep RAS in an activated form. The RAS pathway regulates survival, proliferation, senescence, and differentiation. However, in tumor cells, mutated (oncogenic) RAS preferentially promotes survival and proliferation. Thus, RAF and MEK kinases serve as suitable drug targets. RAF is targeted by inhibitors in preclinical or clinical development, including, for example, RAF265 and PLX4720. 12,13 However, target...