Homeostasis under hypoxic conditions is maintained through a coordinated transcriptional response mediated by the hypoxia-inducible factor (HIF) pathway and requires coactivation by the CBP and p300 transcriptional coactivators. Through a target-based high-throughput screen, we identified chetomin as a disrupter of HIF binding to p300. At a molecular level, chetomin disrupts the structure of the CH1 domain of p300 and precludes its interaction with HIF, thereby attenuating hypoxia-inducible transcription. Systemic administration of chetomin inhibited hypoxia-inducible transcription within tumors and inhibited tumor growth. These results demonstrate a therapeutic window for pharmacological attenuation of HIF activity and further establish the feasibility of disrupting a signal transduction pathway by targeting the function of a transcriptional coactivator with a small molecule.

Ubiquitination controls the stability of most cellular proteins, and its deregulation contributes to human diseases including cancer. Deubiquitinases remove ubiquitin from proteins, and their inhibition can induce the degradation of selected proteins, potentially including otherwise 'undruggable' targets. For example, the inhibition of ubiquitin-specific protease 7 (USP7) results in the degradation of the oncogenic E3 ligase MDM2, and leads to re-activation of the tumour suppressor p53 in various cancers. Here we report that two compounds, FT671 and FT827, inhibit USP7 with high affinity and specificity in vitro and within human cells. Co-crystal structures reveal that both compounds target a dynamic pocket near the catalytic centre of the auto-inhibited apo form of USP7, which differs from other USP deubiquitinases. Consistent with USP7 target engagement in cells, FT671 destabilizes USP7 substrates including MDM2, increases levels of p53, and results in the transcription of p53 target genes, induction of the tumour suppressor p21, and inhibition of tumour growth in mice.

Four novel bisulfide bromotyrosine derivatives, psammaplins E (9), F (10), G (11), and H (12), and two new bromotyrosine derivatives, psammaplins I (13) and J (14), were isolated from the sponge Pseudoceratina purpurea, along with known psammaplins A (4), B (6), C (7), and D (8) and bisaprasin (5). The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis. Compounds 4, 5, and 10 are potent histone deacetylase inhibitors and also show mild cytotoxicity. Furthermore, compounds 4, 5, and 11 are potent DNA methyltransferase inhibitors. The biogenetic pathway previously proposed for the psammaplins class is also revisited.

Recent studies identified a short peptide motif that serves as a docking site for cyclin͞cyclin-dependent kinase (cdk) 2 complexes . Peptides containing this motif block the phosphorylation of substrates by cyclin A͞cdk2 or cyclin E͞cdk2. Here we report that cell membrane-permeable forms of such peptides preferentially induced transformed cells to undergo apoptosis relative to nontransformed cells. Deregulation of E2F family transcription factors is a common event during transformation and was sufficient to sensitize cells to the cyclin͞cdk2 inhibitory peptides. These results suggest that deregulation of E2F and inhibition of cdk2 are synthetically lethal and provide a rationale for the development of cdk2 antagonists as antineoplastic agents.Certain molecular pathways frequently are altered during human carcinogenesis. Therefore one approach to treating cancer, while minimizing host toxicity, would be to develop drugs that preferentially kill cells in which such pathways are altered.An example of a molecular pathway that is recurrently altered in cancer involves the retinoblastoma tumor suppressor protein (pRB) (1-3). Many tumors lack a wild-type RB-1 allele, thus depriving them of pRB. Furthermore, pRB is negatively regulated by cyclin-dependent kinases (cdks). These cdks are, in turn, negatively regulated by certain cdk inhibitors and positively regulated by certain cyclins. These upstream pRB regulators frequently are altered in tumors that retain a wild-type RB-1 allele. Thus, functional inactivation of pRB, a known inhibitor of cell growth, may be a necessary step in human carcinogenesis.Members of the E2F cell-cycle regulatory transcription factor family are critical downstream targets of pRB. Binding to pRB converts E2F from a transcriptional activator to a potent transcriptional repressor. Consequently, E2F-responsive genes are activated in cancer cells because of loss of pRB͞E2F repressor complexes and liberation of free, transcriptionally active E2F. Of note, at least some E2F family members, including E2F1, are themselves transcribed from E2F-responsive promoters (4-7). Thus, pathological activation of E2F responsive genes can establish a positive feedback loop. Paradoxically, forced activation of E2F-responsive genes, such as through the overproduction of E2F1, can induce both cellular proliferation and cell death (apoptosis) (8-11).E2F family members bind to DNA as heterodimers with members of the DP family. The DNA-binding capability of some of these heterodimers is negatively regulated by cyclin A͞cdk2 (12-15). For example, E2F1, E2F2, and E2F3 each contain a short, collinear cyclin A͞cdk2 binding motif that is required for the timely neutralization of E2F DNA-binding capability as cells traverse and prepare to exit S phase (13,16,17). Mutation of this motif in E2F1 enhances its ability to induce apoptosis (13). In summary, E2F is negatively regulated by both pRB and cyclin A͞cdk2. We therefore reasoned that pharmacologic inhibition of cyclin A͞cdk2 might preferentially kill cells in whic...

LAF389 is a synthetic analogue of bengamides, a class of marine natural products that produce inhibitory effects on tumor growth in vitro and in vivo. A proteomicsbased approach has been used to identify signaling pathways affected by bengamides. LAF389 treatment of cells resulted in altered mobility of a subset of proteins on two-dimensional gel electrophoresis. Detailed analysis of one of the proteins, 14-3-3␥, showed that bengamide treatment resulted in retention of the amino-terminal methionine, suggesting that bengamides directly or indirectly inhibited methionine aminopeptidases (MetAps). Both known MetAps are inhibited by LAF389. Short interfering RNA suppression of MetAp2 also altered amino-terminal processing of 14-3-3␥. A high resolution structure of human MetAp2 co-crystallized with a bengamide shows that the compound binds in a manner that mimics peptide substrates. Additionally, the structure reveals that three key hydroxyl groups on the inhibitor coordinate the di-cobalt center in the enzyme active site.

Following earlier work on cystine-bridged peptides, cyclic phosphopeptides containing nonreducible mimics of cystine were synthesized that show high affinity and specificity toward the Src homology (SH2) domain of the growth factor receptor-binding protein (Grb2). Replacement of the cystine in the cyclic heptapeptide cyclo(CYVNVPC) by D-alpha-acetylthialysine or D-alpha-lysine gave cyclo(YVNVP(D-alpha-acetyl-thiaK)) (22) and cyclo(YVNVP(D-alpha-acetyl-K)) (30), which showed improved binding 10-fold relative to that of the control peptide KPFYVNVEF (1). NMR spectroscopy and molecular modeling experiments indicate that a beta-turn conformation centered around YVNV is essential for high-affinity binding. X-ray structure analyses show that the linear peptide 1 and the cyclic compound 21 adopt a similar binding mode with a beta-turn conformation. Our data confirm the unique structural requirements of the ligand binding site of the SH2 domain of Grb2. Moreover, the potency of our cyclic lactams can be explained by the stabilization of the beta-turn conformation by three intramolecular hydrogen bonds (one mediated by an H2O molecule). These stable and easily accessible cyclic peptides can serve as templates for the evaluation of phosphotyrosine surrogates and further chemical elaboration.

We have synthesized a histone deacetylase inhibitor, NVP-LAQ824, a cinnamic hydroxamic acid, that inhibited in vitro enzymatic activities and transcriptionally activated the p21 promoter in reporter gene assays. NVP-LAQ824 selectively inhibited growth of cancer cell lines at submicromolar levels after 48 -72 h of exposure, whereas higher concentrations and longer exposure times were required to retard the growth of normal dermal human fibroblasts. Flow cytometry studies revealed that both tumor and normal cells arrested in the G 2 -M phase of the cell cycle after compound treatment. However, an increased sub-G 1 population at 48 h (reminiscent of apoptotic cells) was observed only in the cancer cell line. Annexin V staining data supported our hypothesis that NVP-LAQ824 induced apoptosis in tumor and transformed cells but not in normal cells. Western blotting experiments showed an increased histone H3 and H4 acetylation level in NVP-LAQ824-treated cancer cells, suggesting that the likely in vivo target of NVP-LAQ824 was histone deacetylase(s). Finally, NVP-LAQ824 exhibited antitumor effects in a xenograft animal model. Together, our data indicated that the activity of NVP-LAQ824 was consistent with its intended mechanism of action. This novel histone deacetylase inhibitor is currently in clinical trials as an anticancer agent.

Bengamide B, a novel sponge-derived marine natural product with broad spectrum antitumor activity, was not suitable for further preclinical development because of its difficult synthesis and very poor water solubility. Bengamide B produced a 31% T/C at its solubility-limited maximum intravenous dose of 33 micromol/kg in MDA-MB-435 breast carcinoma implanted subcutaneously as a xenograft in nude mice. Compound 8a, a bengamide B analogue with three structural changes (t-Bu alkene substituent, unsubstituted lactam nitrogen, and inverted lactam 5'-myristoyloxy group), was as potent as bengamide B in vitro and more efficacious than bengamide B in vivo. A series of ester-modified analogues based on 8a were synthesized and tested in vitro and in vivo (MDA-MB-435). The cyclohexyl- and phenethyl-substituted esters, 8c and 8g, respectively, had in vitro and in vivo activities similar to that of 8a and enhanced water solubility (ca. 1 mg/mL). Consequently, 8c and 8g were tested in the MDA-MB-435 xenograft model at 100 micromol/kg and produced 29% and 57% tumor regression, respectively.