thiourea and Head-and-Neck-Neoplasms

We have previously demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to induce tumor-specific apoptosis. The apoptotic effects of lovastatin were regulated in part by the integrated stress response (ISR) that regulates cellular responses to a wide variety of stress inducers. A key regulator of the ISR apoptotic response is activating transcription factor 3 (ATF3) and its target gene CHOP/GADD153. In our study, we demonstrate that in multiple lovastatin-resistant clones of the squamous cell carcinoma (SCC) cell line SCC9, lovastatin treatment (1-25 μM, 24 hr) in contrast to the parental line failed to significantly induce ATF3 expression. Furthermore, the SCC-derived cell lines SCC25 and HeLa that are sensitive to lovastatin-induced apoptosis also preferentially induce ATF3 expression compared to resistant breast (MCF-7) and prostate carcinoma (PC3)-derived cell lines. In HeLa cells shRNA targeting ATF3 expression as well as in ATF3-deficient murine embryonic fibroblasts, lovastatin-induced cytotoxicity and apoptosis were attenuated. In ex vivo HNSCC tumors, lovastatin also induced ATF3 mRNA expression in two of four tumors evaluated. Salubrinal, an agent that can sustain the activity of a key regulator of the ISR eIF2α, further increased the expression of ATF3 and demonstrated synergistic cytotoxicity in combination with lovastatin in SCC cells. Taken together, our results demonstrate preferential induction of ATF3 in lovastatin-sensitive tumor-derived cell lines that regulate lovastatin-induced apoptosis. Importantly, combining lovastatin with salubrinal enhanced ATF3 expression and induced synergistic cytotoxicity in SCC cells.

Topics: Activating Transcription Factor 3; Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; Breast Neoplasms; Carcinoma, Squamous Cell; Cell Membrane Permeability; Cell Proliferation; Cinnamates; Drug Resistance, Neoplasm; Drug Synergism; Embryo, Mammalian; Eukaryotic Initiation Factor-2; Female; Fibroblasts; Flow Cytometry; Head and Neck Neoplasms; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Immunoenzyme Techniques; Lovastatin; Male; Membrane Potential, Mitochondrial; Mice; Phosphorylation; Prostatic Neoplasms; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; RNA, Small Interfering; Thiourea; Tumor Cells, Cultured

Head and neck cancer (HNC), one of the most common cancers worldwide, frequently involves mutation of the TP53 gene and dysregulation of the p53 pathway. Overexpression of MDM2 or MDM4 inactivates the tumor-suppressive function of p53. Restoration of p53 function that counteracts these p53 repressors can lead to in vivo tumor regression. Therefore, the present study assessed the ability of the small molecule p53 activator XI-011 (NSC146109) to induce apoptosis in HNC by restoring p53 function. We tested the effects of XI-011 treatment in HNC cell lines, either individually or in combination with cisplatin and assessed growth suppression, cell cycle arrest, and apoptosis. The drug effects on in vivo growth of HNC cells were examined in mice xenograft model. XI-011 exerted the highest growth suppression in tumor cells that overexpress MDM4, in which p53 is degraded. XI-011 treatment downregulated MDM4 mRNA and protein levels, and upregulated expression of proapoptotic genes and promoted apoptosis, in a dose-dependent manner. The apoptotic response was blocked by inhibition of p53 or expression of MDM4, demonstrating that the effects of XI-011 depend on p53 and MDM4. In combination treatments, XI-011 acted synergistically with cisplatin to inhibit growth of HNC cells in vitro and in vivo. MDM4 inhibition and functional restoration of p53 by XI-011 effectively enhanced cisplatin-induced cytotoxicity in HNC cells, an activity that suggests a promising strategy for treating HNC.

Topics: Animals; Anthracenes; Antineoplastic Agents; Apoptosis; Cell Cycle Checkpoints; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cisplatin; Drug Synergism; Head and Neck Neoplasms; Male; Mice, Nude; Nuclear Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-mdm2; RNA, Messenger; Thiourea; Tumor Suppressor Protein p53