Extended characterization of MCP110, an inhibitor of Ras-dependent signaling: Mode of action and preclinical analysis
Authors: Natalia Skobeleva, Yen-Fang Keng, Katya Latypova, Disha Dadke, Juran Kato-Stankiewicz, Steven R. Per, Janiel Shields-Miller, Channing J. Der, Fuyuhiko Tamanoi, Erica A. Golemis, Vladimir Khazak
Journal: Cancer Research (2004)

3992   The Ras signaling pathway is activated either by direct mutation of Ras or its effector B-Raf, or by constitutive signaling from upstream Ras-regulatory factors, in a broad variety of human cancers. Numerous studies have documented that the growth and survival of these cancer cells requires uninterrupted Ras signaling, nominating the Ras pathway as an extremely important target for development new anticancer therapies. We have recently identified a new class of small molecular weight inhibitors of the interaction between the Ras and Raf proteins, and confirmed that these agents are effective in reversing numerous hallmarks of Ras-dependent transformation (Khazak et al., AACR 2002, Kato-Stankiewicz et al., PNAS, 2002). We have further explored the target specificity using one family member, MCP110, as prototype. MCP110 effectively reduces epidermal growth factor (EGF)-induced transcriptional activation of the Ras-MEK-ERK-dependent Elk1 promoter. In contrast, MCP110 only minimally affects the transcriptional activation of a large set of nonspecific controls. Furthermore, MCP110 reverses transformed morphology and inhibits both anchorage-dependent and –independent growth of NIH3T3 fibroblasts stably transformed with mutationally activated Ras (K- (12V), N- (12D), or H- (12V)), but not with B-Raf (V599E), or Raf-1 (Raf22W or c-Raf-CAAX). Also, MCP110 has notable potency in NIH3T3 cells transformed with a G-protein-coupled receptor derived from Kaposi’s sarcoma herpesvirus, an upstream regulator of the Ras signaling cascade. Taken together, these results support the idea that MCP110 acts specifically to inhibit transformation at a point between Ras and Raf. In preclinical analysis, we have collaborated with the NCI DTP group to determine GI50 values for MCP110 in inhibiting proliferation at the 60 human tumor cell panel representing 9 different types of cancer. MCP110 effectively inhibits proliferation in a significant fraction of these cells, including lines derived from leukemias, non-small cell lung, breast, and colon carcinomas with known activation of Ras-pathway signaling. We have further explored the ability of MCP110 to potentiate the anti-tumor activity of other established signaling pathway inhibitors and chemotherapeutic agents. In test of MCP110 activity in combination with the MEK inhibitor U0126, the PLC 2  inhibitor AACOCF 3 , the PKC inhibitor Staurosporine, and the microtubule-targeting agent taxol, the most potent and striking potentiation of cell killing is seen in the combination of MCP110 and taxol. We will discuss the mechanistic basis of these combination effects. Finally, we have begun to evaluate the MCP inhibitor class in vivo. Data will be presented demonstrating that MCP110 and related compounds are well tolerated in vivo in mice, as will be preliminary experiments indicating MCP110 anti-tumor efficacy in a mouse xenograft model.