One Atom Makes All the Difference: Getting a Foot in the Door between SOS1 and KRAS.

KRAS, the most common oncogenic driver in human cancers, is controlled and signals primarily through protein-protein interactions (PPIs). The interaction between KRAS and SOS1, crucial for the activation of KRAS, is a typical, challenging PPI with a large contact surface area and high affinity. Here, we report that the addition of only one atom placed between Y884SOS1 and A73KRAS is sufficient to convert SOS1 activators into SOS1 inhibitors. We also disclose the discovery of BI-3406. Combination with the upstream EGFR inhibitor afatinib shows in vivo efficacy against KRASG13D mutant colorectal tumor cells, demonstrating the utility of BI-3406 to probe SOS1 biology. These findings challenge the dogma that large molecules are required to disrupt challenging PPIs. Instead, a "foot in the door" approach, whereby single atoms or small functional groups placed between key PPI interactions, can lead to potent inhibitors even for challenging PPIs such as SOS1-KRAS.

Enantiopure Trans-4,5-Disubstituted 2-Imidazolidinones via Copper(I)-Catalyzed Ring Opening of 1,1'-DiBoc-2,2'-Biaziridine with Grignard Reagents.

The copper-catalyzed ring opening of chiral-pool-derived 1,1'-diBoc-2,2'-biaziridine with Grignard reagents affords enantiopure 2-imidazolidinones in a desymmetrizing, cascade process involving the Boc protecting group. This divergent strategy provides reaction-ready, N-differentiated products and allows two C-C bond constructions concurrent to imidazolidinone formation. A variety of alkyl, cyclic, and aryl Grignard reagents are tolerated in reasonable to good yields.

Chronic phencyclidine (PCP)-induced modulation of muscarinic receptor mRNAs in rat brain: impact of antipsychotic drug treatment.

Many antipsychotics (APDs) have a high affinity for muscarinic receptors, which is thought to contribute to their therapeutic efficacy, or side effect profile. In order to define how muscarinic receptor gene expression is affected by atypical or typical APDs, rats were treated with chronic (2.58 mg/kg) PCP (a psychotomimetic) or vehicle, plus clozapine (20 mg/kg/day) or haloperidol (1 mg/kg/day), and M1, M2 and M3 receptor mRNA levels were determined in brain sections. Negligible changes in M2 or M3 muscarinic mRNA were detected in any region after clozapine or haloperidol. Chronic PCP administration increased M1 mRNA expression in the prefrontal cortex, which was not reversed by either chronic clozapine or haloperidol treatment. Chronic clozapine treatment in combination with PCP treatment decreased M1 receptor mRNA levels in the nucleus accumbens core, whereas chronic haloperidol in combination with PCP treatment increased M1 receptor mRNA levels in the ventromedial hypothalamus and medial amygdala. Thus M1 receptor gene expression is targeted by APDs, although the regions affected differ according to the APD treatment and whether PCP has been administered. The different brain circuitry modulated, may reflect the differing modes of action of typical and atypical APDs. These data provide support for the dysregulation of M1 receptors in schizophrenia, and furthermore, modulation by antipsychotic agents in the treatment of schizophrenia.

Importance of the C-terminus of the human 5-HT3A receptor subunit.

Amongst the family members of Cys-loop LGICs, the atypical ability of the 5-HT3A subunit to form functional homomeric receptors allowed a direct investigation of the role of the C-terminus. Deletion of the three C-terminal amino acids (DeltaGln453-DeltaTyr454-DeltaAla455) from the h5-HT3A subunit prevented formation of a specific radioligand binding site as well as expression within the cell membrane. Removal of merely the C-terminal residue (DeltaAla455) reduced specific radioligand binding (to 4+/-1% relative to the wild-type; cells grown at 37 degrees C) and also cell membrane expression; these reductions were less evident when the DeltaAla455 expressing cells were grown at 27 degrees C (specific radioligand binding levels 27+/-5% relative to wild-type also grown at 27 degrees C). Mutation of the h5-HT3A C-terminal amino acid, alanine, for either glycine (Ala455Gly), valine (Ala455Val) or leucine (Ala455Leu) reduced specific radioligand binding levels by 24+/-23%, 32+/-12% and 88+/-1%, respectively; the latter mutant also displaying reduced membrane expression. In contrast, mutation to alanine of the two amino acids preceding the C-terminal alanine (Gln453Ala and Tyr454Ala) had no detrimental effects on specific radioligand binding or cell membrane expression levels. The present study demonstrates an important role for the C-terminus in the formation of the functional h5-HT3A receptor. The partial restoration of 5-HT3 receptor binding and cell membrane expression when cells expressing C-terminal mutant 5-HT3A subunits were grown at a lower temperature (27 degrees C) suggests that the C-terminus stabilises the 5-HT3 receptor allowing subunit folding and subsequent maturation.

The atypical antipsychotic drug clozapine enhances chronic PCP-induced regulation of prefrontal cortex 5-HT2A receptors.

The ability of antipsychotic drugs to affect 5-HT(2A) receptor function has been widely suggested to contribute to their therapeutic properties. We have compared the ability of the antipsychotic drugs clozapine and haloperidol, alone and in combination with chronic phencyclidine (PCP), to modulate 5-HT(2A) receptor binding and mRNA. Acute (i.p. 45 min) and chronic (21-day) clozapine (osmotic minipump (OMP); 20 mg/kg/day) produced widespread decreases in 5-HT(2A) receptor binding (-60%-80%), measured using [(3)H]ketanserin autoradiography. Conversely, 5-HT(2A) mRNA levels, determined using in-situ hybridisation, were modestly increased by chronic clozapine treatment (+10%-30%). Chronic PCP treatment, at a dose (2.58 mg/kg i.p. intermittently for 28 days) that reproduces many of the neurochemical deficits of schizophrenia, decreased 5-HT(2A) receptor binding in the prefrontal cortex (PFC; -16%), consistent with the changes in post-mortem brain tissue from schizophrenic patients. Combined chronic PCP (i.p.) and clozapine (OMP) treatment down-regulated 5-HT(2A) receptor binding in many areas, similar to the effects of clozapine treatment alone and clozapine further enhanced the effects of PCP in the prefrontal cortex. In contrast 5-HT(2A) mRNA was not altered. Haloperidol treatment alone (1 mg/kg/day; OMP) and in combination with PCP (i.p.), generally produced no changes in 5-HT(2A) receptor protein or mRNA. Hence chronic PCP treatment, as employed here, mimics the decreased 5-HT(2A) receptor binding observed in the PFC of schizophrenic patients. Clozapine's enhancement of the natural response of PCP to down-regulate PFC 5-HT(2A) receptors may contribute to it's improved therapeutic profile against negative symptoms and cognitive deficits.