Apoptosis/drug effects; Cell Proliferation/drug effects; Protein Tyrosine Phosphatase, Non-Receptor Type 6/metabolism; STAT3 Transcription Factor/metabolism; Xanthones/pharmacology; Blotting, Western; Breast Neoplasms/drug therapy; Breast Neoplasms/metabolism; Breast Neoplasms/pathology; Carcinoma, Squamous Cell/drug therapy; Carcinoma, Squamous Cell/metabolism; Carcinoma, Squamous Cell/pathology; DNA, Neoplasm/metabolism; Electrophoretic Mobility Shift Assay; Female; Head and Neck Neoplasms/drug therapy; Head and Neck Neoplasms/metabolism; Head and Neck Neoplasms/pathology; Humans; Immunoenzyme Techniques; Janus Kinase 1/metabolism; Janus Kinase 2/metabolism; Male; Multiple Myeloma/drug therapy; Multiple Myeloma/metabolism; Multiple Myeloma/pathology; Phosphorylation/drug effects; Prostatic Neoplasms/drug therapy; Prostatic Neoplasms/metabolism; Prostatic Neoplasms/pathology; Protein Transport; Protein Tyrosine Phosphatase, Non-Receptor Type 6/antagonists & inhibitors; Protein Tyrosine Phosphatase, Non-Receptor Type 6/genetics; RNA, Small Interfering/genetics; Tumor Cells, Cultured