Discovery of Potent, Selective, and Brain-Penetrant 1 H-Pyrazol-5-yl-1 H-pyrrolo[2,3- b]pyridines as Anaplastic Lymphoma Kinase (ALK) Inhibitors.

Anaplastic lymphoma kinase (ALK), a member of the receptor tyrosine kinase family, is predominantly expressed in the brain and implicated in neuronal development and cognition. However, the detailed function of ALK in the central nervous system (CNS) is still unclear. To elucidate the role of ALK in the CNS, it was necessary to discover a potent, selective, and brain-penetrant ALK inhibitor. Scaffold hopping and lead optimization of N-(2,4-difluorobenzyl)-3-(1 H-pyrazol-5-yl)imidazo[1,2- b]pyridazin-6-amine 1 guided by a cocrystal structure of compound 1 bound to ALK resulted in the identification of (6-(1-(5-fluoropyridin-2-yl)ethoxy)-1-(5-methyl-1 H-pyrazol-3-yl)-1 H-pyrrolo[2,3- b]pyridin-3-yl)((2 S)-2-methylmorpholin-4-yl)methanone 13 as a highly potent, selective, and brain-penetrable compound. Intraperitoneal administration of compound 13 significantly decreased the phosphorylated-ALK (p-ALK) levels in the hippocampus and prefrontal cortex in the mouse brain. These results suggest that compound 13 could serve as a useful chemical probe to elucidate the mechanism of ALK-mediated brain functions and the therapeutic potential of ALK inhibition.

Discovery of Novel and Potent Stearoyl Coenzyme A Desaturase 1 (SCD1) Inhibitors as Anticancer Agents.

A lead compound A was identified previously as an stearoyl coenzyme A desaturase (SCD) inhibitor during research on potential treatments for obesity. This compound showed high SCD1 binding affinity, but a poor pharmacokinetic (PK) profile and limited chemical accessibility, making it suboptimal for use in anticancer research. To identify potent SCD1 inhibitors with more promising PK profiles, we newly designed a series of 'non-spiro' 4, 4-disubstituted piperidine derivatives based on molecular modeling studies. As a result, we discovered compound 1a, which retained moderate SCD1 binding affinity. Optimization around 1a was accelerated by analyzing Hansch-Fujita and Hammett constants to obtain 4-phenyl-4-(trifluoromethyl)piperidine derivative 1n. Fine-tuning of the azole moiety of 1n led to compound 1o (T-3764518), which retained nanomolar affinity and exhibited an excellent PK profile. Reflecting the good potency and PK profile, orally administrated compound 1o showed significant pharmacodynamic (PD) marker reduction (at 0.3mg/kg, bid) in HCT116 mouse xenograft model and tumor growth suppression (at 1mg/kg, bid) in 786-O mouse xenograft model. In conclusion, we identified a new series of SCD1 inhibitors, represented by compound 1o, which represents a promising new chemical tool suitable for the study of SCD1 biology as well as the potential development of novel anticancer therapies.

Antitumor Activity of TAK-285, an Investigational, Non-Pgp Substrate HER2/EGFR Kinase Inhibitor, in Cultured Tumor Cells, Mouse and Rat Xenograft Tumors, and in an HER2-Positive Brain Metastasis Model.

Breast cancer therapy has improved following the development of drugs with specific molecular targets, exemplified by inhibitors of human epidermal growth factor receptor-2 (HER2) or epidermal growth factor receptor (EGFR) such as trastuzumab and lapatinib. However, these drugs have little effect on brain metastasis due to the combined effects of poor penetration of the blood-brain barrier and their removal from the central nervous system (CNS) by the p-glycoprotein (Pgp) drug efflux pump. We investigated the effects of TAK-285, a novel, investigational, dual EGFR/HER2 inhibitor that has been shown to penetrate the CNS and has comparable inhibitory efficacy to lapatinib which is a known Pgp substrate. Tested against a panel of 96 kinases, TAK-285 showed specificity for inhibition of HER family kinases. Unlike lapatinib, TAK-285 is not a substrate for Pgp efflux. In mouse and rat xenograft tumor models, TAK-285 showed antitumor activity against cancers that expressed HER2 or EGFR. TAK-285 was as effective as lapatinib in antitumor activity in a mouse subcutaneous BT-474 breast cancer xenograft model. TAK-285 was examined in a model of breast cancer brain metastasis using direct intracranial injection of BT-474-derived luciferase-expressing cells and showed greater inhibition of brain tumor growth compared to animals treated with lapatinib. Our studies suggest that investigational drugs such as TAK-285 that have strong antitumor activity and are not Pgp substrates may be useful in the development of agents with the potential to treat brain metastases.

Design and synthesis of novel pyrimido[4,5-b]azepine derivatives as HER2/EGFR dual inhibitors.

A novel 7,6 fused bicyclic scaffold, pyrimido[4,5-b]azepine was designed to fit into the ATP binding site of the HER2/EGFR proteins. The synthesis of this scaffold was accomplished by an intramolecular Claisen-type condensation. As the results of optimization lead us to 4-anilino and 6-functional groups, we discovered 6-substituted amide derivative 19b, which has a 1-benzothiophen-4-yloxy group attached to the 4-anilino group. An X-ray co-crystal structure of 19b with EGFR demonstrated that the N-1 and N-3 nitrogens of the pyrimido[4,5-b]azepine scaffold make hydrogen-bonding interactions with the main chain NH of Met793 and the side chain of Thr854 via a water-mediated hydrogen bond network, respectively. In addition, the NH proton at the 9-position makes an additional hydrogen bond with the carbonyl group of Met793, as we expected. Compound 19b revealed potent HER2/EGFR kinase (IC50: 24/36 nM) and BT474 cell growth (GI50: 18 nM) inhibitory activities based on its pseudo-irreversible (PI) profile.

Structure-Based Approach for the Discovery of Pyrrolo[3,2-d]pyrimidine-Based EGFR T790M/L858R Mutant Inhibitors.

The epidermal growth factor receptor (EGFR) family plays a critical role in vital cellular processes and in various cancers. Known EGFR inhibitors exhibit distinct antitumor responses against the various EGFR mutants associated with nonsmall-cell lung cancer. The L858R mutation enhances clinical sensitivity to gefitinib and erlotinib as compared with wild type and reduces the relative sensitivity to lapatinib. In contrast, the T790M mutation confers drug resistance to gefitinib and erlotinib. We determined crystal structures of the wild-type and T790M/L858R double mutant EGFR kinases with reversible and irreversible pyrrolo[3,2-d]pyrimidine inhibitors based on analogues of TAK-285 and neratinib. In these structures, M790 adopts distinct conformations to accommodate different inhibitors, whereas R858 allows conformational variations of the activation loop. These results provide structural insights for understanding the structure-activity relationships that should contribute to the development of potent inhibitors against drug-sensitive or -resistant EGFR mutations.

Design and synthesis of pyrrolo[3,2-d]pyrimidine HER2/EGFR dual inhibitors: improvement of the physicochemical and pharmacokinetic profiles for potent in vivo anti-tumor efficacy.

During the course of our studies on a novel HER2/EGFR dual inhibitor (TAK-285), we found an alternative potent pyrrolo[3,2-d]pyrimidine compound (1a). To enhance the pharmacokinetic (PK) profile of this compound, we conducted chemical modifications into its N-5 side chain and conversion of the chemically modified compounds into their salts. Among them, 2cb, the tosylate salt of compound 2c, showed potent HER2/EGFR kinase inhibitory activity (IC(50): 11/11 nM) and cellular growth inhibitory activity (BT-474 cell GI(50): 56 nM) with a good drug metabolism and PK (DMPK) profile. Furthermore, 2cb exhibited significant in vivo antitumor efficacy in both mouse and rat xenograft models with transplanted 4-1ST gastric cancer cell lines (mouse, T/C=0%, 2cb po bid at 100 mg/kg; rat, T/C: -1%, 2cb po bid at 25 mg/kg).

Design and synthesis of pyrrolo[3,2-d]pyrimidine human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) dual inhibitors: exploration of novel back-pocket binders.

To develop novel human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) kinase inhibitors, we explored pyrrolo[3,2-d]pyrimidine derivatives bearing bicyclic fused rings designed to fit the back pocket of the HER2/EGFR proteins. Among them, the 1,2-benzisothiazole (42m) ring was selected as a suitable back pocket binder because of its potent HER2/EGFR binding and cell growth inhibitory (GI) activities and pseudoirreversibility (PI) profile as well as good bioavailability (BA). Ultimately, we arrived at our preclinical candidate 51m by optimization of the N-5 side chain to improve CYP inhibition and metabolic stability profiles without a loss of potency (HER2/EGFR inhibitory activity, IC(50), 0.98/2.5 nM; and GI activity BT-474 cells, GI(50), 2.0 nM). Reflecting the strong in vitro activities, 51m exhibited potent tumor regressive efficacy against both HER2- and EGFR-overexpressing tumor (4-1ST and CAL27) xenograft models in mice at oral doses of 50 mg/kg and 100 mg/kg.

Design and synthesis of novel human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) dual inhibitors bearing a pyrrolo[3,2-d]pyrimidine scaffold.

Dual inhibitors of human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor (EGFR) have been investigated for breast, lung, gastric, prostate, and other cancers; one, lapatinib, is currently approved for breast cancer. To develop novel HER2/EGFR dual kinase inhibitors, we designed and synthesized pyrrolo[3,2-d]pyrimidine derivatives capable of fitting into the receptors' ATP binding site. Among the prepared compounds, 34e showed potent HER2 and EGFR (HER1) inhibitory activities as well as tumor growth inhibitory activity. The X-ray cocrystal structures of 34e with both HER2 and EGFR demonstrated that 34e interacts with the expected residues in their respective ATP pockets. Furthermore, reflecting its good oral bioavailability, 34e exhibited potent in vivo efficacy in HER2-overexpressing tumor xenograft models. On the basis of these findings, we report 34e (TAK-285) as a promising candidate for clinical development as a novel HER2/EGFR dual kinase inhibitor.