conglobatin and Breast-Neoplasms

Human epidermal growth factor receptor 2 (HER2), a member of the HER family of tyrosine kinases and a binding partner of Heat shock protein 90 (Hsp90), is found amplifies in approximately 25% breast cancers. Treatment of HER2+ breast cancers has been greatly improved in recent years, but the accompanying upregulation of HER3 induced by HER2 blockade has subdued the therapeutic effect. FW-04-806, a novel Hsp90 N-terminal inhibitor that disassociates the Hsp90/Cdc37/client complex and degrades Hsp90 clients, was studied alone or in combination with the EGFR/HER2 tyrosine kinase inhibitor lapatinib in HER2+ breast cancer cells. We found that FW-04-806 alone or with laptinib inhibits cell proliferation, induces cell apoptosis and reduces the total and activated HER3 levels in these cells, while lapatinib has been reported to increase HER3 expression followed HER2 inhibition. The combination of FW-04-806 and lapatinib showed synergistic reduction of HER2 expression and the downstream PI3K/Akt and Ras/MEK/ERK pathways, enhanced suppression of Akt-mediated FOXO3a inactivation and augmented antitumor efficacy on SKBR3 xenografts with a favorable toxicity profile, suggesting its viability as a combination therapy for clinical studies in HER2+ breast cancer patients.

Topics: Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; Breast Neoplasms; Cell Proliferation; Drug Resistance, Neoplasm; Drug Synergism; Female; Gene Expression Regulation, Neoplastic; HSP90 Heat-Shock Proteins; Humans; Immunoenzyme Techniques; Lapatinib; Mice; Mice, Inbred BALB C; Mice, Nude; Oxazoles; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; Quinazolines; Real-Time Polymerase Chain Reaction; Receptor, ErbB-2; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

Heat shock protein 90 (Hsp90) is a promising therapeutic target and inhibition of Hsp90 will presumably result in suppression of multiple signaling pathways. FW-04-806, a bis-oxazolyl macrolide compound extracted from China-native Streptomyces FIM-04-806, was reported to be identical in structure to the polyketide Conglobatin.. We adopted the methods of chemproteomics, computational docking, immunoprecipitation, siRNA gene knock down, Quantitative Real-time PCR and xenograft models on the research of FW-04-806 antitumor mechanism, through the HER2-overexpressing breast cancer SKBR3 and HER2-underexpressing breast cancer MCF-7 cell line.. We have verified the direct binding of FW-04-806 to the N-terminal domain of Hsp90 and found that FW-04-806 inhibits Hsp90/cell division cycle protein 37 (Cdc37) chaperone/co-chaperone interactions, but does not affect ATP-binding capability of Hsp90, thereby leading to the degradation of multiple Hsp90 client proteins via the proteasome pathway. In breast cancer cell lines, FW-04-806 inhibits cell proliferation, caused G2/M cell cycle arrest, induced apoptosis, and downregulated Hsp90 client proteins HER2, Akt, Raf-1 and their phosphorylated forms (p-HER2, p-Akt) in a dose and time-dependent manner. Importantly, FW-04-806 displays a better anti-tumor effect in HER2-overexpressed SKBR3 tumor xenograft model than in HER2-underexpressed MCF-7 model. The result is consistent with cell proliferation assay and in vitro apoptosis assay applied for SKBR-3 and MCF-7. Furthermore, FW-04-806 has a favorable toxicity profile.. As a novel Hsp90 inhibitor, FW-04-806 binds to the N-terminal of Hsp90 and inhibits Hsp90/Cdc37 interaction, resulting in the disassociation of Hsp90/Cdc37/client complexes and the degradation of Hsp90 client proteins. FW-04-806 displays promising antitumor activity against breast cancer cells both in vitro and in vivo, especially for HER2-overexpressed breast cancer cells.

Topics: Apoptosis; Breast Neoplasms; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Chaperonins; Female; HSP90 Heat-Shock Proteins; Humans; Macrolides; MCF-7 Cells; Multiprotein Complexes; Oxazoles; Protein Binding; Receptor, ErbB-2