Synthesis, Biological Evaluation, and Binding Mode of a New Class of Oncogenic K-Ras4b Inhibitors.

Ras proteins are implicated in some of the most common life-threatening cancers. Despite intense research during the past three decades, progress towards small-molecule inhibitors of mutant Ras proteins still has been limited. Only recently has significant progress been made, in particular with ligands for binding sites located in the switch II and between the switch I and switch II region of K-Ras4B. However, the structural diversity of inhibitors identified for those sites to date is narrow. Herein, we show that hydrazones and oxime ethers of specific bis(het)aryl ketones represent structurally variable chemotypes for new GDP/GTP-exchange inhibitors with significant cellular activity.

Sequence-Selective Covalent CaaX-Box Receptors Prevent Farnesylation of Oncogenic Ras Proteins and Impact MAPK/PI3†K Signaling.

Oncogenic Ras proteins are implicated in the most common life-threatening cancers. Despite intense research over the past two decades, the progress towards small-molecule inhibitors has been limited. One reason for this failure is that Ras proteins interact with their effectors only via protein-protein interactions, which are notoriously difficult to address with small organic molecules. Herein we describe an alternative strategy, which prevents farnesylation and subsequent membrane insertion, a prerequisite for the activation of Ras proteins. Our approach is based on sequence-selective supramolecular receptors which bind to the C-terminal farnesyl transferase recognition unit of Ras and Rheb proteins and covalently modify the essential cysteine in the so-called CaaX-box.

Allosteric Activation of GDP-Bound Ras Isoforms by Bisphenol Derivative Plasticisers.

The protein family of small GTPases controls cellular processes by acting as a binary switch between an active and an inactive state. The most prominent family members are H-Ras, N-Ras, and K-Ras isoforms, which are highly related and frequently mutated in cancer. Bisphenols are widespread in modern life because of their industrial application as plasticisers. Bisphenol A (BPA) is the best-known member and has gained significant scientific as well as public attention as an endocrine disrupting chemical, a fact that eventually led to its replacement. However, compounds used to replace BPA still contain the molecular scaffold of bisphenols. BPA, BPAF, BPB, BPE, BPF, and an amine-substituted BPAF-derivate all interact with all GDP-bound Ras-Isoforms through binding to a common site on these proteins. NMR-, SOScat-, and GDI- assay-based data revealed a new bisphenol-induced, allosterically activated GDP-bound Ras conformation that define these plasticisers as Ras allosteric agonists.

Small Molecules Antagonise the MIA-Fibronectin Interaction in Malignant Melanoma.

Melanoma inhibitory activity (MIA), an extracellular protein highly expressed by malignant melanoma cells, plays an important functional role in melanoma development, progression, and metastasis. After its secretion, MIA directly interacts with extracellular matrix proteins, such as fibronectin (FN). By this mechanism, MIA actively facilitates focal cell detachment from surrounding structures and strongly promotes tumour cell invasion and migration. Hence, the molecular understanding of MIA's function provides a promising target for the development of new strategies in malignant melanoma therapy. Here, we describe for the first time the discovery of small molecules that are able to disrupt the MIA-FN complex by selectively binding to a new druggable pocket, which we could identify on MIA by structural analysis and fragment-based screening. Our findings may inspire novel drug discovery efforts aiming at a therapeutically effective treatment of melanoma by targeting MIA.

The Bisphenol A analogue Bisphenol S binds to K-Ras4B--implications for 'BPA-free' plastics.

K-Ras4B is a small GTPase that belongs to the Ras superfamily of guanine nucleotide-binding proteins. GTPases function as molecular switches in cells and are key players in intracellular signalling. Ras has been identified as an oncogene and is mutated in more than 20% of human cancers. Here, we report that Bisphenol S binds into a binding pocket of K-Ras4B previously identified for various low molecular weight compounds. Our results advocate for more comprehensive safety studies on the toxicity of Bisphenol S, as it is frequently used for Bisphenol A-free food containers.

Sequence-selective molecular recognition of the C-terminal CaaX-boxes of Rheb and related Ras-proteins by synthetic receptors.

Constitutive activation of Ras-proteins plays an important role in the development of aggressive colorectal carcinomas and several other types of cancer. Despite some progress in recent years in the case of K-Ras4B, until now not a single small molecule inhibitor has been identified that binds efficiently to Rheb and interrupts the protein-protein interactions with mTOR. We describe here a complementary approach that aims at inhibiting membrane insertion of Rheb and related Ras proteins by masking the crucial C-terminal CaaX-box with peptidomimetic receptors identified in combinatorial solid-phase libraries.

Bisphenol A binds to Ras proteins and competes with guanine nucleotide exchange: implications for GTPase-selective antagonists.

We show for the first time that bisphenol A (10) has the capacity to interact directly with K-Ras and that Rheb weakly binds to bisphenol A (10) and 4,4'-biphenol derivatives. We have characterized these interactions at atomic resolution suggesting that these compounds sterically interfere with the Sos-mediated nucleotide exchange in H- and K-Ras. We show that 4,4'-biphenol (5) selectively inhibits Rheb signaling and induces cell death suggesting that this compound might be a novel candidate for treatment of tuberous sclerosis-mediated tumor growth. Our results propose a new mode of action for bisphenol A (10) that advocates a reduced exposure to this compound in our environment. Our data may lay the foundation for the future design of GTPase-selective antagonists with higher affinity to benefit of the treatment of cancer because K-Ras inhibition is regarded to be a promising strategy with a potential therapeutic window for targeting Sos in Ras-driven tumors.

Synthesis and SERCA activities of structurally simplified cyclopiazonic acid analogues.

The indole alkaloid cyclopiazonic acid (CPA) is one of the few known nanomolar inhibitors of sarco(endo)plasmic reticulum Ca²âº-ATPase (SERCA) besides the anticancer drug thapsigargin and the antiplasmoidal terpenoid artemisinin. Due to its less complex structure CPA represents an attractive lead structure for the development of novel antimalarial drugs or for applications in the field of plant protection. We report here the first syntheses of structurally simplified CPA fragments and discuss their SERCA activities on the basis of published crystal structures of CPA-SERCA complexes.

Structures of micelle-bound selected insect neuropeptides and analogues: implications for receptor selection.

Neuropeptides control essential physiological processes in insects such as water balance and muscle activity. Due to their metabolic instability and adverse physiochemical properties, insect neuropeptides are unsuited for a direct application in plant protection. As a first approximation towards the biologically active conformation, the structures of selected neuropeptides from economically important pest insects were determined by NMR spectroscopy and fluorescence measurements in a membrane-mimicking environment. A receptor binding model is suggested for the helicokinins and discussed in connection with biological activities and membrane-bound conformations of linear and cyclic analogues.