Scaffold repurposing of fendiline: Identification of potent KRAS plasma membrane localization inhibitors.

KRAS plays an essential role in regulating cell proliferation, differentiation, migration and survival. Mutated KRAS is a major driver of malignant transformation in multiple human cancers. We showed previously that fendiline (6) is an effective inhibitor of KRAS plasma membrane (PM) localization and function. In this study, we designed, synthesized and evaluated a series of new fendiline analogs to optimize its drug properties. Systemic structure-activity relationship studies by scaffold repurposing led to the discovery of several more active KRAS PM localization inhibitors such as compounds 12f (NY0244), 12h (NY0331) and 22 (NY0335) which exhibit nanomolar potencies. These compounds inhibited oncogenic KRAS-driven cancer cell proliferation at single-digit micromolar concentrations in vitro. In vivo studies in a xenograft model of pancreatic cancer revealed that 12h and 22 suppressed oncogenic KRAS-expressing MiaPaCa-2 tumor growth at a low dose range of 1-5 mg/kg with no vasodilatory effects, indicating their potential as chemical probes and anticancer therapeutics.

Interaction of antagonists with calmodulin: insights from molecular dynamics simulations.

We report results of 12 ns, all-atom molecular dynamics simulation (MDS) and Poisson-Boltzmann free energy calculations (PBFE) on calmodulin (CaM) bound to two molecules of trifluoperazine (TFP) and of N-(3,3, diphenylpropyl)- N'-[1- R-(3,4-bis-butoxyphenyl)-ethyl]-propylenediamine (DPD). X-ray data show very similar structures for the two complexes, yet the antagonists significantly differ with respect to their CaM binding affinities, the neutral DPD is much more potent. The goal of the study was to unravel the reason why TFP is less potent although its positive charge should facilitate binding. The electrostatic energy terms in CHARMM and binding free energy terms of the PBFE approach showed TFP a better antagonist, while inspection of hydrophobic contacts supports DPD binding. Detailed inspection of the amino acid contributions of PBFE calculations unravel that steric reasons oppose the favorable binding of TFP. Structural conditions are given for a successful drug design strategy, which may benefit also from charge-charge interactions.

3-Chloro,4-methoxyfendiline is a potent GABA(B) receptor potentiator in rat neocortical slices.

Using grease-gap recording from rat neocortical slices, the GABA(B) receptor agonist baclofen elicited reversible and concentration-dependent hyperpolarizing responses (EC50=18+/-2.3 microM). The hyperpolarizations were antagonised by the GABA(B) receptor antagonist Sch 50911 [(+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid). (+)-N-1-(3-chloro-4-methoxyphenyl)ethyl-3,3-diphenylpropylamine (3-chloro,4-methoxyfendiline; 3-Cl,4-MeO-fendiline) reversibly potentiated baclofen-induced hyperpolarizing responses, which were reduced by Sch 50911, producing leftward shifts of the baclofen concentration-response curves, with a marked increase in the maximal hyperpolarization (EC50=2+/-0.5 microM). In slices preincubated with either [3H]GABA or [3H]glutamic acid, 3-Cl,4-MeO-fendiline (1 microM) potentiated the inhibitory effect of baclofen (2 microM) on the electrically evoked release of [3H]GABA and had a similar effect on the release of [3H]glutamic acid at a concentration of 0.5 microM, without affecting the basal release. These effects were blocked by Sch 50911 (10 microM). Our findings suggest that 3-Cl,4-MeO-fendiline is a potent potentiator of pre- and postsynaptic GABA(B) receptor-mediated functions.

Calcium sensing receptors as integrators of multiple metabolic signals.

Calcium sensing receptors are critical to maintenance of organismal Ca2+ homeostasis, translating small changes in serum Ca2+ into changes in PTH secretion by the parathyroid glands and Ca2+ excretion by the kidneys. Calcium sensing receptors are also expressed in many cells and tissues not directly involved in Ca2+ homeostasis where their role(s) are less defined. Recent studies have demonstrated that calcium sensing receptors integrate a variety of metabolic signals, including polyvalent cations, pH, ionic strength, amino acids, and polypeptides, making CaR uniquely capable of generating cell- and tissue-specific responses, sensing not only Ca2+, but the local metabolic environment. The challenge for future studies is to define CaR responsiveness in each varied physiological context.

Calcimimetic and calcilytic drugs: just for parathyroid cells?

The cell surface calcium receptor (Ca2+ receptor) is a particularly difficult receptor to study because its primary physiological ligand, Ca2+, affects numerous biological processes both within and outside of cells. Because of this, distinguishing effects of extracellular Ca2+ mediated by the Ca2+ receptor from those mediated by other mechanisms is challenging. Certain pharmacological approaches, however, when combined with appropriate experimental designs, can be used to more confidently identify cellular responses regulated by the Ca2+ receptor and select those that might be targeted therapeutically. The Ca2+ receptor on parathyroid cells, because it is the primary mechanism regulating secretion of parathyroid hormone (PTH), is one such target. Calcimimetic compounds, which active this Ca2+ receptor and lower circulating levels of PTH, have been developed for treating hyperparathyroidism. The converse pharmaceutical approach, involving calcilytic compounds that block parathyroid cell Ca2+ receptors and stimulate PTH secretion thereby providing an anabolic therapy for osteoporosis, still awaits clinical validation. Although Ca2+ receptors are expressed throughout the body and in many tissues that are not intimately involved in systemic Ca2+ homeostasis, their physiological and/or pathological significance remains speculative and their value as therapeutic targets is unknown.

A new potent calmodulin antagonist with arylalkylamine structure: crystallographic, spectroscopic and functional studies.

An arylalkylamine-type calmodulin antagonist, N-(3, 3-diphenylpropyl)-N'-[1-R-(3, 4-bis-butoxyphenyl)ethyl]-propylene-diamine (AAA) is presented and its complexes with calmodulin are characterized in solution and in the crystal. Near-UV circular dichroism spectra show that AAA binds to calmodulin with 2:1 stoichiometry in a Ca(2+)-dependent manner. The crystal structure with 2:1 stoichiometry is determined to 2.64 A resolution. The binding of AAA causes domain closure of calmodulin similar to that obtained with trifluoperazine. Solution and crystal data indicate that each of the two AAA molecules anchors in the hydrophobic pockets of calmodulin, overlapping with two trifluoperazine sites, i.e. at a hydrophobic pocket and an interdomain site. The two AAA molecules also interact with each other by hydrophobic forces. A competition enzymatic assay has revealed that AAA inhibits calmodulin-activated phosphodiesterase activity at two orders of magnitude lower concentration than trifluoperazine. The apparent dissociation constant of AAA to calmodulin is 18 nM, which is commensurable with that of target peptides. On the basis of the crystal structure, we propose that the high-affinity binding is mainly due to a favorable entropy term, as the AAA molecule makes multiple contacts in its complex with calmodulin.