Triple negative (ER, PR and HER2/neu negative) breast cancers (TNBC) constitute 15-24% of breast cancers, but account for a disproportionate share of mortality. TNBC tumors are more aggressive, lack a targeted therapy, and are prone to relapse and metastasis after cytotoxic drug treatments, the only drug therapy currently available. Serum and glucocorticoid-regulated kinase 1 (SGK1) promotes the growth, invasiveness and chemo-resistance of cancer cells and is overexpressed in 48% of breast cancers, yet is not detected in normal breast tissue. In particular, SGK1 is overexpressed in TNBC cells and knockdown of SGK1 blocks the proliferation and invasiveness of TNBC cells. Thus, SGK1 is an attractive targeted therapy for TNBC. In the SGK1 inhibitors that have been reported previously, poor physicochemical properties have prevented these inhibitors from being active in vivo and advancing to the clinic. To discover drug-like inhibitors of SGK1, we used our technology platform (Leap-To-Lead™) and a fragment-based screening approach to find SGK1 inhibitor scaffolds. Low molecular weight inhibitors like ours are more readily optimized for potency while retaining drug-like properties. From this screen, we identified 11 scaffolds as novel inhibitors of SGK1. Four scaffold series had clear structure activity relationships (SAR). To illustrate the potential of these scaffolds, we carried out a limited synthetic expansion around one scaffold and improved potency more than 600-fold (SGK1 IC50 = 1 μM; LE = 0.4). Several compounds dose-dependently inhibited the proliferation of a TNBC cell line (MDA-MB-231) and inhibited the phosphorylation of the biomarker protein N-Myc downstream regulated 1 (NDRG-1). Unlike previously reported SGK1 inhibitors, our fragment lead compounds show excellent cellular penetration in Caco-2 assays. In summary, a fragment-based screening approach was used to identify four novel scaffolds with clear SAR trends. A single scaffold series was further optimized and shows anti-proliferative activity and biomarker modulation in a TNBC cell line. These SGK1 inhibitor series represent excellent starting points for further SAR studies and development of a novel preclinical candidate. Citation Format: James Zapf, Todd Meyer, Warren Wade, Laura Lingardo, Ayse Batova, Gordon Alton, Peter Pallai. Drug-like inhibitors of SGK1: Discovery and optimization of low molecular weight fragment leads. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2180.

Abstract Triple negative (ER, PR and HER2/neu negative) breast cancer (TNBC) can have an unfavorable prognosis compared to other breast cancers. TNBC is more difficult to treat since most targeted breast cancer therapies are directed at one of the three receptors. Aggressive combinatorial therapies are usually required and the cytotoxic agents used in these regimens frequently loose effectiveness with time. Serum and glucocorticoid-regulated kinase 1 (SGK1) (a serine/threonine protein kinase), promotes the growth and invasiveness of breast cancer cells. SGK1 is a key protein regulated by the glucocorticoid receptor (GR). In TNBC tumors, high expression/activity in the GR/SGK axis correlates with shorter survival times and resistance to chemotherapy. The small numbers of SGK1 inhibitors reported in the literature have resulted from screening against other kinases (such as CHK1/azaindoles) and thus are not selective and lack patentable chemical diversity. We describe the identification of novel SGK1 inhibitors using a fragment-based library screening approach. The BioBlocks Leap-To-Lead platform contains a library of novel fragment-like compounds that span a range of polarities and sizes without compromising on flexibility. For example, this 275 compound library has an average molecule weight of 160 Da; AlogP, 1.1; hydrogen bond donors, 1.1; hydrogen bond acceptors, 2.2, and rotatable bonds, 0.7 yet still contains 114 unique rings. The library was screened against fully activated human SGK1 in an ADP-Glo assay using physiologically relevant peptide substrate and an optimal ATP concentration to also identify non-classical kinase inhibitor mode binders. The fragment library was screened at 2 mM and hits were profiled in IC50 dose response. From these, several novel chemical matter hit compounds were selected that had ligand efficiency values greater than 0.3 and spanned IC50 values from 75 µM to 2000 µM. In summary, a fragment-based screening approach was used to identify several novel scaffolds that represent both classical and non-classical kinase inhibitor binding modes as hit-to-lead starting points for the optimization of novel, potent and selective SGK1 inhibitors. Citation Format: Gordon Alton, Warren Wade, Laura Lingardo, Ayse Batova, Tom Smart, Chris Buhr, James W. Zapf, Peter Pallai. Discovery of novel SGK1 inhibitors by a fragment-based approach: Generating patentable, chemically tractable and ligand efficient leads. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-16. doi:10.1158/1538-7445.AM2014-LB-16

The design synthesis and SAR of a series of chiral ring-constrained norepinephrine reuptake inhibitors with improved physicochemical properties is described. Typical compounds are potent (IC(50)s<10 nM), selective against the other monoamine transporters, weak CYP2D6 inhibitors (IC(50)s>1 microM) and stable to oxidation by human liver microsomes. In addition, the compounds exhibit a favorable polarity profile.

Incorporation of a carboxylic acid into a series of uracil derivatives as hGnRH-R antagonists resulted in a significant reduction of CYP3A4 inhibitory activity. Highly potent hGnRH antagonists with low CYP3A4 inhibitory liability, such as 8a and 8d, were identified. Thus, 8a had a Ki of 2.2 nM at GnRH-R and an IC50 of 36 μM at CYP3A4.

A series of heterocyclic ring-constrained norepinephrine reuptake inhibitors have activities as racemates equivalent to atomoxetine (IC50’s<10nM).

The design, synthesis, and SAR of a series of ring-constrained norepinephrine reuptake inhibitors are described. A substantially rigid inhibitor with potent functional activity at the transporter (IC(50)=8 nM) was used to develop a model for the distance and orientation of key features necessary for interaction with the norepinephrine transporter (NET).

The synthesis and SAR of a series of chiral heterocyclic ring-constrained norepinephrine reuptake inhibitors are described. The best compounds compare favorably with atomoxetine in potency (IC(50)s<10 nM), selectivity against the other monoamine transporters, and inhibition of CYP2D6 (IC(50)s>1 microM). In addition, the compounds are generally more stable than atomoxetine to oxidative metabolism and thus are likely to have lower clearance in humans.

The discovery of novel uracil phenylethylamines bearing a butyric acid as potent human gonadotropin-releasing hormone receptor (hGnRH-R) antagonists is described. A major focus of this optimization was to improve the CYP3A4 inhibition liability of these uracils while maintaining their GnRH-R potency. R-4-{2-[5-(2-Fluoro-3-methoxyphenyl)-3-(2-fluoro-6-[trifluoromethyl]benzyl)-4-methyl-2,6-dioxo-3,6-dihydro-2H-pyrimidin-1-yl]-1-phenylethylamino}butyric acid sodium salt, 10b (elagolix), was identified as a potent and selective hGnRH-R antagonist. Oral administration of 10b suppressed luteinizing hormone in castrated macaques. These efforts led to the identification of 10b as a clinical compound for the treatment of endometriosis.

The design, synthesis, and SAR of a series of retro bis-aminopyrrolidine ureas are described. Compounds from this series exhibited considerable binding affinity (Ki=1nM) and functional activity at MCH-R1, acceptable CYP2D6 inhibition, and good rat brain exposure.

A series of substituted chromones were designed, synthesized, and evaluated for their ability to bind melanin-concentrating hormone receptor 1. Compounds with subnanomolar binding affinity and 66% oral bioavailability in rats were discovered.

The design, synthesis, and SAR of a series of retro bis-aminopyrrolidine ureas are described. Compounds from this series exhibited potent binding affinity and functional activity at MCH-R1, and good oral bioavailability in rat.