kobe2602

Kobe2602 is a small-molecule inhibitor of Ras with Ki value of 149 μM [1].

Kobe2602 is a compound screened out by a computer-assisted search of about 160,000 compounds. It dose-dependently inhibited the binding of H-RasG12V to c-Raf-1 in NIH 3T3 cells with a rough IC50 value of 10 μM. 20 μM of Kobe2602 effectively suppressed the phosphorylation of down-stream kinases of Raf, including MEK and ERK. Besides that, in NIH 3T3 cells transfected with H-rasG12V, Kobe2602 inhibited the colony formation with IC50 value of 1.4 μM. Kobe2602 also showed effect on other cancer cells carrying activated ras oncogenes, such as PANC-1(K-rasG12V), HT1080 (N-rasQ61L) and HCT116 (H-rasG13D). Moreover, in mice bearing SW480 xenografts, administration of Kobe2602 resulted in 40-50% inhibition of the tumor growth at dose of 80 mg/kg [1].

References:
[1] Shima F, Yoshikawa Y, Ye M, et al. In silico discovery of small-molecule Ras inhibitors that display antitumor activity by blocking the Ras–effector interaction. Proceedings of the National Academy of Sciences, 2013, 110(20): 8182-8187.

In silico discovery of small-molecule Ras inhibitors that display antitumor activity by blocking the Ras-effector interaction.[Pubmed:23630290]

Proc Natl Acad Sci U S A. 2013 May 14;110(20):8182-7.

Mutational activation of the Ras oncogene products (H-Ras, K-Ras, and N-Ras) is frequently observed in human cancers, making them promising anticancer drug targets. Nonetheless, no effective strategy has been available for the development of Ras inhibitors, partly owing to the absence of well-defined surface pockets suitable for drug binding. Only recently, such pockets have been found in the crystal structures of a unique conformation of RasGTP. Here we report the successful development of small-molecule Ras inhibitors by an in silico screen targeting a pocket found in the crystal structure of M-RasGTP carrying an H-Ras-type substitution P40D. The selected compound Kobe0065 and its analog kobe2602 exhibit inhibitory activity toward H-RasGTP-c-Raf-1 binding both in vivo and in vitro. They effectively inhibit both anchorage-dependent and -independent growth and induce apoptosis of H-ras(G12V)-transformed NIH 3T3 cells, which is accompanied by down-regulation of downstream molecules such as MEK/ERK, Akt, and RalA as well as an upstream molecule, Son of sevenless. Moreover, they exhibit antitumor activity on a xenograft of human colon carcinoma SW480 cells carrying the K-ras(G12V) gene by oral administration. The NMR structure of a complex of the compound with H-RasGTP(T35S), exclusively adopting the unique conformation, confirms its insertion into one of the surface pockets and provides a molecular basis for binding inhibition toward multiple RasGTP-interacting molecules. This study proves the effectiveness of our strategy for structure-based drug design to target RasGTP, and the resulting Kobe0065-family compounds may serve as a scaffold for the development of Ras inhibitors with higher potency and specificity.

Discovery of small-molecule Ras inhibitors that display antitumor activity by interfering with Ras.GTP-effector interaction.[Pubmed:25034098]

Enzymes. 2013;34 Pt. B:1-23.

Ras proteins, particularly their active GTP-bound forms (Ras.GTP), were thought "undruggable" owing to the absence of apparent drug-accepting pockets in their crystal structures. Only recently, such pockets have been found in the crystal structures representing a novel Ras.GTP conformation. We have conducted an in silico docking screen targeting a pocket in the crystal structure of M-Ras(P40D).GTP and obtained Kobe0065, which, along with its analogue kobe2602, inhibits binding of H-Ras.GTP to c-Raf-1. They inhibit the growth of H-rasG12V-transformed NIH3T3 cells, which are accompanied by downregulation of not only MEK/ERK but also Akt, RalA, and Sos, indicating the blockade of interaction with multiple effectors. Moreover, they exhibit antitumor activity on a xenograft of human colon carcinoma carrying K-rasG12V. The nuclear magnetic resonance structure of a complex of the compound with H-Ras(T35S).GTP confirms its insertion into the surface pocket. Thus, these compounds may serve as a novel scaffold for the development of Ras inhibitors with higher potency and specificity.

kobe2602 is a novel and effective small-molecule compound inhibiting Ras–Raf interaction by SBDD; exhibits potent activity to competitively inhibit the binding of H-Ras·GTP to c-Raf-1 RBD with a Ki value of 149 ± 55 μM.

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