Affinity and cooperativity modulate ternary complex formation to drive targeted protein degradation.

Targeted protein degradation via "hijacking" of the ubiquitin-proteasome system using proteolysis targeting chimeras (PROTACs) has evolved into a novel therapeutic modality. The design of PROTACs is challenging; multiple steps involved in PROTAC-induced degradation make it difficult to establish coherent structure-activity relationships. Herein, we characterize PROTAC-mediated ternary complex formation and degradation by employing von Hippel-Lindau protein (VHL) recruiting PROTACs for two different target proteins, SMARCA2 and BRD4. Ternary-complex attributes and degradation activity parameters are evaluated by varying components of the PROTAC's architecture. Ternary complex binding affinity and cooperativity correlates well with degradation potency and initial rates of degradation. Additionally, we develop a ternary-complex structure modeling workflow to calculate the total buried surface area at the interface, which is in agreement with the measured ternary complex binding affinity. Our findings establish a predictive framework to guide the design of potent degraders.

Discovery of a Covalent Inhibitor of KRASG12C (AMG 510) for the Treatment of Solid Tumors.

KRASG12C has emerged as a promising target in the treatment of solid tumors. Covalent inhibitors targeting the mutant cysteine-12 residue have been shown to disrupt signaling by this long-"undruggable" target; however clinically viable inhibitors have yet to be identified. Here, we report efforts to exploit a cryptic pocket (H95/Y96/Q99) we identified in KRASG12C to identify inhibitors suitable for clinical development. Structure-based design efforts leading to the identification of a novel quinazolinone scaffold are described, along with optimization efforts that overcame a configurational stability issue arising from restricted rotation about an axially chiral biaryl bond. Biopharmaceutical optimization of the resulting leads culminated in the identification of AMG 510, a highly potent, selective, and well-tolerated KRASG12C inhibitor currently in phase I clinical trials (NCT03600883).

Discovery of N-(1-Acryloylazetidin-3-yl)-2-(1H-indol-1-yl)acetamides as Covalent Inhibitors of KRASG12C.

KRAS regulates many cellular processes including proliferation, survival, and differentiation. Point mutants of KRAS have long been known to be molecular drivers of cancer. KRAS p.G12C, which occurs in approximately 14% of lung adenocarcinomas, 3-5% of colorectal cancers, and low levels in other solid tumors, represents an attractive therapeutic target for covalent inhibitors. Herein, we disclose the discovery of a class of novel, potent, and selective covalent inhibitors of KRASG12C identified through a custom library synthesis and screening platform called Chemotype Evolution and structure-based design. Identification of a hidden surface groove bordered by H95/Y96/Q99 side chains was key to the optimization of this class of molecules. Best-in-series exemplars exhibit a rapid covalent reaction with cysteine 12 of GDP-KRASG12C with submicromolar inhibition of downstream signaling in a KRASG12C-specific manner.

Discovery of ( R)-8-(6-Methyl-4-oxo-1,4,5,6-tetrahydropyrrolo[3,4- b]pyrrol-2-yl)-3-(1-methylcyclopropyl)-2-((1-methylcyclopropyl)amino)quinazolin-4(3 H)-one, a Potent and Selective Pim-1/2 Kinase Inhibitor for Hematological Malignancies.

Pim kinases are a family of constitutively active serine/threonine kinases that are partially redundant and regulate multiple pathways important for cell growth and survival. In human disease, high expression of the three Pim isoforms has been implicated in the progression of hematopoietic and solid tumor cancers, which suggests that Pim kinase inhibitors could provide patients with therapeutic benefit. Herein, we describe the structure-guided optimization of a series of quinazolinone-pyrrolodihydropyrrolone analogs leading to the identification of potent pan-Pim inhibitor 28 with improved potency, solubility, and drug-like properties. Compound 28 demonstrated on-target Pim activity in an in vivo pharmacodynamic assay with significant inhibition of BAD phosphorylation in KMS-12-BM multiple myeloma tumors for 16 h postdose. In a 2-week mouse xenograft model, daily dosing of compound 28 resulted in 33% tumor regression at 100 mg/kg.

Targeted Degradation of MDM2 as a New Approach to Improve the Efficacy of MDM2-p53 Inhibitors.

MDM2 is a key oncogenic protein that serves as a negative regulator of the tumor suppressor p53. While a number of inhibitors of the MDM2-p53 interaction have progressed to clinical testing as treatments for a variety of hematologic and solid tumor cancers, the results thus far have been mixed, with perhaps the strongest responses observed in relapsed/refractory acute myeloid leukemia (AML). In an effort to improve the efficacy for this class of compounds, researchers have turned to targeted degradation of MDM2. IMiD-based MDM2 PROTAC 8, which potently reduces MDM2 protein levels through targeted degradation, exhibits enhanced efficacy in the RS4;11 xenograft model relative to a nondegrading MDM2-p53 inhibitor MI-1061.

A "Click Chemistry Platform" for the Rapid Synthesis of Bispecific Molecules for Inducing Protein Degradation.

Proteolysis targeting chimeras (PROTACs) are bispecific molecules containing a target protein binder and an ubiquitin ligase binder connected by a linker. By recruiting an ubiquitin ligase to a target protein, PROTACs promote ubiquitination and proteasomal degradation of the target protein. The generation of effective PROTACs depends on the nature of the protein/ligase ligand pair, linkage site, linker length, and linker composition, all of which have been difficult to address in a systematic way. Herein, we describe a "click chemistry" approach for the synthesis of PROTACs. We demonstrate the utility of this approach with the bromodomain and extraterminal domain-4 (BRD4) ligand JQ-1 (3) and ligase binders targeting cereblon (CRBN) and Von Hippel-Lindau (VHL) proteins. An AlphaScreen proximity assay was used to determine the ability of PROTACs to form the ternary ligase-PROTAC-target protein complex and a MSD assay to measure cellular degradation of the target protein promoted by PROTACs.

Photoinduced, Copper-Catalyzed Decarboxylative C-N Coupling to Generate Protected Amines: An Alternative to the Curtius Rearrangement.

The Curtius rearrangement is a classic, powerful method for converting carboxylic acids into protected amines, but its widespread use is impeded by safety issues (the need to handle azides). We have developed an alternative to the Curtius rearrangement that employs a copper catalyst in combination with blue-LED irradiation to achieve the decarboxylative coupling of aliphatic carboxylic acid derivatives (specifically, readily available N-hydroxyphthalimide esters) to afford protected amines under mild conditions. This C-N bond-forming process is compatible with a wide array of functional groups, including an alcohol, aldehyde, epoxide, indole, nitroalkane, and sulfide. Control reactions and mechanistic studies are consistent with the hypothesis that copper species are engaged in both the photochemistry and the key bond-forming step, which occurs through out-of-cage coupling of an alkyl radical.

Discovery of imidazopyridazines as potent Pim-1/2 kinase inhibitors.

High levels of Pim expression have been implicated in several hematopoietic and solid tumor cancers, suggesting that inhibition of Pim signaling could provide patients with therapeutic benefit. Herein, we describe our progress towards this goal using a screening hit (rac-1) as a starting point. Modification of the indazole ring resulted in the discovery of a series of imidazopyridazine-based Pim inhibitors exemplified by compound 22m, which was found to be a subnanomolar inhibitor of the Pim-1 and Pim-2 isoforms (IC50 values of 0.024nM and 0.095nM, respectively) and to potently inhibit the phosphorylation of BAD in a cell line that expresses high levels of all Pim isoforms, KMS-12-BM (IC50=28nM). Profiling of Pim-1 and Pim-2 expression levels in a panel of multiple myeloma cell lines and correlation of these data with the potency of compound 22m in a proliferation assay suggests that Pim-2 inhibition would be advantageous for this indication.

Discovery and Optimization of Quinazolinone-pyrrolopyrrolones as Potent and Orally Bioavailable Pan-Pim Kinase Inhibitors.

The high expression of proviral insertion site of Moloney murine leukemia virus kinases (Pim-1, -2, and -3) in cancers, particularly the hematopoietic malignancies, is believed to play a role in promoting cell survival and proliferation while suppressing apoptosis. The three isoforms of Pim protein appear largely redundant in their oncogenic functions. Thus, a pan-Pim kinase inhibitor is highly desirable. However, cell active pan-Pim inhibitors have proven difficult to develop because Pim-2 has a low Km for ATP and therefore requires a very potent inhibitor to effectively block the kinase activity at cellular ATP concentrations. Herein, we report a series of quinazolinone-pyrrolopyrrolones as potent and selective pan-Pim inhibitors. In particular, compound 17 is orally efficacious in a mouse xenograft model (KMS-12 BM) of multiple myeloma, with 93% tumor growth inhibition at 50 mg/kg QD upon oral dosing.

Discovery and Optimization of Macrocyclic Quinoxaline-pyrrolo-dihydropiperidinones as Potent Pim-1/2 Kinase Inhibitors.

The identification of Pim-1/2 kinase overexpression in B-cell malignancies suggests that Pim kinase inhibitors will have utility in the treatment of lymphoma, leukemia, and multiple myeloma. Starting from a moderately potent quinoxaline-dihydropyrrolopiperidinone lead, we recognized the potential for macrocyclization and developed a series of 13-membered macrocycles. The structure-activity relationships of the macrocyclic linker were systematically explored, leading to the identification of 9c as a potent, subnanomolar inhibitor of Pim-1 and -2. This molecule also potently inhibited Pim kinase activity in KMS-12-BM, a multiple myeloma cell line with relatively high endogenous levels of Pim-1/2, both in vitro (pBAD IC50 = 25 nM) and in vivo (pBAD EC50 = 30 nM, unbound), and a 100 mg/kg daily dose was found to completely arrest the growth of KMS-12-BM xenografts in mice.

Oxopyrido[2,3-d]pyrimidines as Covalent L858R/T790M Mutant Selective Epidermal Growth Factor Receptor (EGFR) Inhibitors.

In nonsmall cell lung cancer (NSCLC), the threonine(790)-methionine(790) (T790M) point mutation of EGFR kinase is one of the leading causes of acquired resistance to the first generation tyrosine kinase inhibitors (TKIs), such as gefitinib and erlotinib. Herein, we describe the optimization of a series of 7-oxopyrido[2,3-d]pyrimidinyl-derived irreversible inhibitors of EGFR kinase. This led to the discovery of compound 24 which potently inhibits gefitinib-resistant EGFR(L858R,T790M) with 100-fold selectivity over wild-type EGFR. Compound 24 displays strong antiproliferative activity against the H1975 nonsmall cell lung cancer cell line, the first line mutant HCC827 cell line, and promising antitumor activity in an EGFR(L858R,T790M) driven H1975 xenograft model sparing the side effects associated with the inhibition of wild-type EGFR.

The discovery and optimization of aminooxadiazoles as potent Pim kinase inhibitors.

High levels of Pim expression have been implicated in several hematopoietic and solid tumor cancers. These findings suggest that inhibition of Pim signaling by a small molecule Pim-1,2 inhibitor could provide patients with therapeutic benefit. Herein, we describe our progress towards this goal starting from the highly Pim-selective indole-thiadiazole compound (1), which was derived from a nonselective hit identified in a high throughput screening campaign. Optimization of this compound's potency and its pharmacokinetic properties resulted in the discovery of compound 29. Cyclopropane 29 was found to exhibit excellent enzymatic potency on the Pim-1 and Pim-2 isoforms (Ki values of 0.55nM and 0.28nM, respectively), and found to inhibit the phosphorylation of BAD in the Pim-overexpressing KMS-12 cell line (IC50=150nM). This compound had moderate clearance and bioavailability in rat (CL=2.42L/kg/h; %F=24) and exhibited a dose-dependent inhibition of p-BAD in KMS-12 tumor pharmacodynamic (PD) model with an EC50 value of 6.74µM (18µg/mL) when dosed at 10, 30, 100 and 200mg/kg po in mice.

Discovery of 5-(1H-indol-5-yl)-1,3,4-thiadiazol-2-amines as potent PIM inhibitors.

PIM kinases are a family of Ser/Thr kinases that are implicated in tumorigenesis. The discovery of a new class of PIM inhibitors, 5-(1H-indol-5-yl)-1,3,4-thiadiazol-2-amines, is discussed with optimized compounds showing excellent potency against all three PIM isoforms.

Phosphoinositide-3-kinase inhibitors: evaluation of substituted alcohols as replacements for the piperazine sulfonamide portion of AMG 511.

Replacement of the piperazine sulfonamide portion of the PI3Kα inhibitor AMG 511 (1) with a range of aliphatic alcohols led to the identification of a truncated gem-dimethylbenzylic alcohol analog, 2-(5-(4-amino-6-methyl-1,3,5-triazin-2-yl)-6-((5-fluoro-6-methoxypyridin-3-yl)amino)pyridin-3-yl)propan-2-ol (7). This compound possessed good in vitro efficacy and pharmacokinetic parameters and demonstrated an EC50 of 239 ng/mL in a mouse liver pharmacodynamic model measuring the inhibition of hepatocyte growth factor (HGF)-induced Akt Ser473 phosphorylation in CD1 nude mice 6 h post-oral dosing.

Pyridin-2-one synthesis using ester enolates and aryl aminoaldehydes and ketones.

An aldol-like cyclocondensation has been used to prepare heterocyclic-fused pyridin-2-ones from aminoaldehydes and ketones upon treatment with a lithium enolate of ethyl acetate or α-substituted acetates. These motifs are present in a large number of biologically active natural products and synthetic compounds and can be accessed using mild reaction conditions using readily available starting materials. This methodology allows access to pyrimidinopyridin-2-ones, pyrazolopyridin-2-ones, and pyridopyridazine diones with varying substitution patterns.

Selective class I phosphoinositide 3-kinase inhibitors: optimization of a series of pyridyltriazines leading to the identification of a clinical candidate, AMG 511.

The phosphoinositide 3-kinase family catalyzes the phosphorylation of phosphatidylinositol-4,5-diphosphate to phosphatidylinositol-3,4,5-triphosphate, a secondary messenger which plays a critical role in important cellular functions such as metabolism, cell growth, and cell survival. Our efforts to identify potent, efficacious, and orally available phosphatidylinositol 3-kinase (PI3K) inhibitors as potential cancer therapeutics have resulted in the discovery of 4-(2-((6-methoxypyridin-3-yl)amino)-5-((4-(methylsulfonyl)piperazin-1-yl)methyl)pyridin-3-yl)-6-methyl-1,3,5-triazin-2-amine (1). In this paper, we describe the optimization of compound 1, which led to the design and synthesis of pyridyltriazine 31, a potent pan inhibitor of class I PI3Ks with a superior pharmacokinetic profile. Compound 31 was shown to potently block the targeted PI3K pathway in a mouse liver pharmacodynamic model and inhibit tumor growth in a U87 malignant glioma glioblastoma xenograft model. On the basis of its excellent in vivo efficacy and pharmacokinetic profile, compound 31 was selected for further evaluation as a clinical candidate and was designated AMG 511.

Synthesis and structure-activity relationships of dual PI3K/mTOR inhibitors based on a 4-amino-6-methyl-1,3,5-triazine sulfonamide scaffold.

Phosphoinositide 3-kinase (PI3K) is an important target in oncology due to the deregulation of the PI3K/Akt signaling pathway in a wide variety of tumors. A series of 4-amino-6-methyl-1,3,5-triazine sulfonamides were synthesized and evaluated as inhibitors of PI3K. The synthesis, in vitro biological activities, pharmacokinetic and in vivo pharmacodynamic profiling of these compounds are described. The most promising compound from this investigation (compound 3j) was found to be a pan class I PI3K inhibitor with a moderate (>10-fold) selectivity over the mammalian target of rapamycin (mTOR) in the enzyme assay. In a U87 MG cellular assay measuring phosphorylation of Akt, compound 3j displayed low double digit nanomolar IC(50) and exhibited good oral bioavailability in rats (F(oral)=63%). Compound 3j also showed a dose dependent reduction in the phosphorylation of Akt in a U87 tumor pharmacodynamic model with a plasma EC(50)=193 nM (91 ng/mL).

Structure-based design of a novel series of potent, selective inhibitors of the class I phosphatidylinositol 3-kinases.

A highly selective series of inhibitors of the class I phosphatidylinositol 3-kinases (PI3Ks) has been designed and synthesized. Starting from the dual PI3K/mTOR inhibitor 5, a structure-based approach was used to improve potency and selectivity, resulting in the identification of 54 as a potent inhibitor of the class I PI3Ks with excellent selectivity over mTOR, related phosphatidylinositol kinases, and a broad panel of protein kinases. Compound 54 demonstrated a robust PD-PK relationship inhibiting the PI3K/Akt pathway in vivo in a mouse model, and it potently inhibited tumor growth in a U-87 MG xenograft model with an activated PI3K/Akt pathway.

Identification of triazolopyridazinones as potent p38α inhibitors.

Structure-activity relationship (SAR) investigations of a novel class of triazolopyridazinone p38α mitogen activated protein kinase (MAPK) inhibitors are disclosed. From these studies, increased in vitro potency was observed for 2,6-disubstituted phenyl moieties and N-ethyl triazolopyridazinone cores due to key contacts with Leu108, Ala157 and Val38. Further investigation led to the identification of three compounds, 3g, 3j and 3m that are highly potent inhibitors of LPS-induced MAPKAP kinase 2 (MK2) phosphorylation in 50% human whole blood (hWB), and possess desirable in vivo pharmacokinetic and kinase selectivity profiles.

Discovery of pyridazinopyridinones as potent and selective p38 mitogen-activated protein kinase inhibitors.

The p38 mitogen-activated protein kinase (MAPK) plays an important role in the production of proinflammatory cytokines, making it an attractive target for the treatment of various inflammatory diseases. A series of pyridazinopyridinone compounds were designed as novel p38 kinase inhibitors. A structure-activity investigation identified several compounds possessing excellent potency in both enzyme and human whole blood assays. Among them, compound 31 exhibited good pharmacokinetic properties and showed excellent selectivity against other related kinases. In addition, 31 demonstrated efficacy in a collagen-induced arthritis disease model in rats.