Discovery of XL888: a novel tropane-derived small molecule inhibitor of HSP90.

With structural guidance, tropane-derived HTS hits were modified to optimize for HSP90 inhibition and a desirable in vivo profile. Through an iterative SAR development process 12i (XL888) was discovered and shown to reduce HSP90 client protein content in PD studies. Furthermore, efficacy experiments performed in a NCI-N87 mouse xenograft model demonstrated tumor regression in some dosing regimens.

EXEL-7647 inhibits mutant forms of ErbB2 associated with lapatinib resistance and neoplastic transformation.

PURPOSE: Mutations associated with resistance to kinase inhibition are an important mechanism of intrinsic or acquired loss of clinical efficacy for kinase-targeted therapeutics. We report the prospective discovery of ErbB2 mutations that confer resistance to the small-molecule inhibitor lapatinib. EXPERIMENTAL DESIGN: We did in vitro screening using a randomly mutagenized ErbB2 expression library in Ba/F3 cells, which were dependent on ErbB2 activity for survival and growth. RESULTS: Lapatinib resistance screens identified mutations at 16 different ErbB2 amino acid residues, with 12 mutated amino acids mapping to the kinase domain. Mutations conferring the greatest lapatinib resistance cluster in the NH2-terminal kinase lobe and hinge region. Structural computer modeling studies suggest that lapatinib resistance is caused by multiple mechanisms; including direct steric interference and restriction of conformational flexibility (the inactive state required for lapatinib binding is energetically unfavorable). ErbB2 T798I imparts the strongest lapatinib resistance effect and is analogous to the epidermal growth factor receptor T790M, ABL T315I, and cKIT T670I gatekeeper mutations that are associated with clinical drug resistance. ErbB2 mutants associated with lapatinib resistance transformed NIH-3T3 cells, including L755S and T733I mutations known to occur in human breast and gastric carcinomas, supporting a direct mechanism for lapatinib resistance in ErbB2-driven human cancers. The epidermal growth factor receptor/ErbB2/vascular endothelial growth factor receptor inhibitor EXEL-7647 was found to inhibit almost all lapatinib resistance-associated mutations. Furthermore, no ErbB2 mutations were found to be associated with EXEL-7647 resistance and lapatinib sensitivity. CONCLUSIONS: Taken together, these data suggest potential target-based mechanisms of resistance to lapatinib and suggest that EXEL-7647 may be able to circumvent these effects.

Preclinical evaluation of novel fatty acid synthase inhibitors in primary colorectal cancer cells and a patient-derived xenograft model of colorectal cancer.

Fatty Acid Synthase (FASN), a key enzyme of de novo lipogenesis, is upregulated in many cancers including colorectal cancer (CRC); increased FASN expression is associated with poor prognosis. Potent FASN inhibitors (TVBs) developed by 3-V Biosciences demonstrate anti-tumor activity in vitro and in vivo and a favorable tolerability profile in a Phase I clinical trial. However, CRC characteristics associated with responsiveness to FASN inhibition are not fully understood. We evaluated the effect of TVB-3664 on tumor growth in nine CRC patient-derived xenografts (PDXs) and investigated molecular and metabolic changes associated with CRC responsiveness to FASN inhibition. CRC cells and PDXs showed a wide range of sensitivity to FASN inhibition. TVB-3664 treatment showed significant response (reduced tumor volume) in 30% of cases. Anti-tumor effect of TVB-3664 was associated with a significant decrease in a pool of adenine nucleotides and alterations in lipid composition including a significant reduction in fatty acids and phospholipids and an increase in lactosylceramide and sphingomyelin in PDXs sensitive to FASN inhibition. Moreover, Akt, Erk1/2 and AMPK were major oncogenic pathways altered by TVBs. In summary, we demonstrated that novel TVB inhibitors show anti-tumor activity in CRC and this activity is associated with a decrease in activation of Akt and Erk1/2 oncogenic pathways and significant alteration of lipid composition of tumors. Further understanding of genetic and metabolic characteristics of tumors susceptible to FASN inhibition may enable patient selection and personalized medicine approaches in CRC.

Fatty acid synthase - Modern tumor cell biology insights into a classical oncology target.

Decades of preclinical and natural history studies have highlighted the potential of fatty acid synthase (FASN) as a bona fide drug target for oncology. This review will highlight the foundational concepts upon which this perspective is built. Published studies have shown that high levels of FASN in patient tumor tissues are present at later stages of disease and this overexpression predicts poor prognosis. Preclinical studies have shown that experimental overexpression of FASN in previously normal cells leads to changes that are critical for establishing a tumor phenotype. Once the tumor phenotype is established, FASN elicits several changes to the tumor cell and becomes intertwined with its survival. The product of FASN, palmitate, changes the biophysical nature of the tumor cell membrane; membrane microdomains enable the efficient assembly of signaling complexes required for continued tumor cell proliferation and survival. Membranes densely packed with phospholipids containing saturated fatty acids become resistant to the action of other chemotherapeutic agents. Inhibiting FASN leads to tumor cell death while sparing normal cells, which do not have the dependence of this enzyme for normal functions, and restores membrane architecture to more normal properties thereby resensitizing tumors to killing by chemotherapies. One compound has recently reached clinical studies in solid tumor patients and highlights the need for continued evaluation of the role of FASN in tumor cell biology. Significant advances have been made and much remains to be done to optimally apply this class of pharmacological agents for the treatment of specific cancers.

FASN Inhibition and Taxane Treatment Combine to Enhance Anti-tumor Efficacy in Diverse Xenograft Tumor Models through Disruption of Tubulin Palmitoylation and Microtubule Organization and FASN Inhibition-Mediated Effects on Oncogenic Signaling and Gene Expression.

Palmitate, the enzymatic product of FASN, and palmitate-derived lipids support cell metabolism, membrane architecture, protein localization, and intracellular signaling. Tubulins are among many proteins that are modified post-translationally by acylation with palmitate. We show that FASN inhibition with TVB-3166 or TVB-3664 significantly reduces tubulin palmitoylation and mRNA expression. Disrupted microtubule organization in tumor cells is an additional consequence of FASN inhibition. FASN inhibition combined with taxane treatment enhances inhibition of in vitro tumor cell growth compared to treatment with either agent alone. In lung, ovarian, prostate, and pancreatic tumor xenograft studies, FASN inhibition and paclitaxel or docetaxel combine to inhibit xenograft tumor growth with significantly enhanced anti-tumor activity. Tumor regression was observed in 3 of 6 tumor xenograft models. FASN inhibition does not affect cellular taxane concentration in vitro. Our data suggest a mechanism of enhanced anti-tumor activity of the FASN and taxane drug combination that includes inhibition of tubulin palmitoylation and disruption of microtubule organization in tumor cells, as well as a sensitization of tumor cells to FASN inhibition-mediated effects that include gene expression changes and inhibition of ß-catenin. Together, the results strongly support investigation of combined FASN inhibition and taxane treatment as a therapy for a variety of human cancers.

Inhibition of de novo Palmitate Synthesis by Fatty Acid Synthase Induces Apoptosis in Tumor Cells by Remodeling Cell Membranes, Inhibiting Signaling Pathways, and Reprogramming Gene Expression.

Inhibition of de novo palmitate synthesis via fatty acid synthase (FASN) inhibition provides an unproven approach to cancer therapy with a strong biological rationale. FASN expression increases with tumor progression and associates with chemoresistance, tumor metastasis, and diminished patient survival in numerous tumor types. TVB-3166, an orally-available, reversible, potent, and selective FASN inhibitor induces apoptosis, inhibits anchorage-independent cell growth under lipid-rich conditions, and inhibits in-vivo xenograft tumor growth. Dose-dependent effects are observed between 20-200 nM TVB-3166, which agrees with the IC50 in biochemical FASN and cellular palmitate synthesis assays. Mechanistic studies show that FASN inhibition disrupts lipid raft architecture, inhibits biological pathways such as lipid biosynthesis, PI3K-AKT-mTOR and ß-catenin signal transduction, and inhibits expression of oncogenic effectors such as c-Myc; effects that are tumor-cell specific. Our results demonstrate that FASN inhibition has anti-tumor activities in biologically diverse preclinical tumor models and provide mechanistic and pharmacologic evidence that FASN inhibition presents a promising therapeutic strategy for treating a variety of cancers, including those expressing mutant K-Ras, ErbB2, c-Met, and PTEN. The reported findings inform ongoing studies to link mechanisms of action with defined tumor types and advance the discovery of biomarkers supporting development of FASN inhibitors as cancer therapeutics. RESEARCH IN CONTEXT: Fatty acid synthase (FASN) is a vital enzyme in tumor cell biology; the over-expression of FASN is associated with diminished patient prognosis and resistance to many cancer therapies. Our data demonstrate that selective and potent FASN inhibition with TVB-3166 leads to selective death of tumor cells, without significant effect on normal cells, and inhibits in vivo xenograft tumor growth at well-tolerated doses. Candidate biomarkers for selecting tumors highly sensitive to FASN inhibition are identified. These preclinical data provide mechanistic and pharmacologic evidence that FASN inhibition presents a promising therapeutic strategy for treating a variety of cancers.