MicroRNAs (miRs) are short non-coding RNAs that bind complementary sequences in mRNA resulting in translation repression and/or mRNA degradation. We investigated expression of the reported metastasis-associated miRs-335, 206, 135a, 146a, 146b, 10b, 21, let7a and let7b in normal mucosa, non-metastatic and metastatic colorectal cancer (CRC). Expression of target miRs in micro-dissected paraffin embedded tissues was evaluated in 15 primary tumours with adjacent normal tissue from patients that were disease-free at 4 years (cohort A) and 19 paired primary tumours with corresponding liver metastases (cohort B) by quantitative real-time PCR. Increased expression of miR-21, mir-135a and miR-335 was associated with clinical progression of CRC, while miR-206 demonstrated an opposite trend. The levels of mir-21 did not associate with the expression of PTEN, an important tumour suppressor in CRC and one of many putative targets of miR-21, but interestingly was associated with stage of disease in the PTEN expressing tumours. Surprisingly, let7a, a KRAS-targeting miR, showed elevated expression in metastatic disease compared to normal mucosa or non-metastatic disease, and only in KRAS mutation positive tumors. Finally, a prognostic signature of miR 21,135a, 335, 206 and let-7a for detecting the presence of metastases had a specificity of 87% and sensitivity of 76% for the presence of metastases. In summary, we have shown stage-associated differential expression of five out of nine tested metastasis-associated miRs. We have further found that an analysis of these five miRs expression levels in primary tumors significantly correlates with the presence of metastatic disease, making this a potential clinically useful prognostic tool.

BackgroundCellular stress responses trigger signaling cascades that inhibit proliferation and protein translation to help alleviate the stress or if the stress cannot be overcome induce apoptosis. In recent studies, we demonstrated the ability of lovastatin, an inhibitor of mevalonate synthesis, to induce the Integrated Stress Response as well as inhibiting epidermal growth factor receptor (EGFR) activation.Methodology/Principal FindingsIn this study, we evaluated the effects of lovastatin on the activity of the LKB1/AMPK pathway that is activated upon cellular energy shortage and can interact with the above pathways. In the squamous cell carcinoma (SCC) cell lines SCC9 and SCC25, lovastatin treatment (1–25 µM, 24 hrs) induced LKB1 and AMPK activation similar to metformin (1–10 mM, 24 hrs), a known inducer of this pathway. Lovastatin treatment impaired mitochondrial function and also decreased cellular ADP/ATP ratios, common triggers of LKB1/AMPK activation. The cytotoxic effects of lovastatin were attenuated in LKB1 null MEFs indicating a role for this pathway in regulating lovastatin-induced cytotoxicity. Of clinical relevance, lovastatin induces synergistic cytotoxicity in combination with the EGFR inhibitor gefitinib. In LKB1 deficient (A549, HeLa) and expressing (SCC9, SCC25) cell lines, metformin enhanced gefitinib cytotoxicity only in LKB1 expressing cell lines while both groups showed synergistic cytotoxic effects with lovastatin treatments. Furthermore, the combination of lovastatin with gefitinib induced a potent apoptotic response without significant induction of autophagy that is often induced during metabolic stress inhibiting cell death.Conclusion/SignificanceThus, targeting multiple metabolic stress pathways including the LKB1/AMPK pathway enhances lovastatin’s ability to synergize with gefitinib in SCC cells.

We have previously demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to induce tumorspecific 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 lovastatinresistant clones of the squamous cell carcinoma (SCC) cell line SCC9, lovastatin treatment (1-25 lM, 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 eIF2a, 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.Deregulated or elevated activity of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase, the initial and rate-limiting enzyme of the mevalonate pathway, has been shown in a range of different tumors.

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Background: NSCLC is the most common cause of cancer-related death. Platinum-based chemotherapy is the mainstay of treatment, but a variety of mechanisms lead to platinum-resistance. ATF3 is a transcription factor, activated in response to a wide variety of stress signals including DNA damage and hypoxia. We recently demonstrated a role for ATF3 as an important regulator of platinum-induced cytotoxicity. In this study, we hypothesize that ATF3 expression correlates with platinum-sensitivity/resistance in NSCLC. Methods: ATF3 induction was examined by Western blots and real-time RT-PCR in isogenic sets of platinum- sensitive (S) or induced resistant (R) NSCLC cell lines. A 1200 compound library was screened to identify platinum-sensitizers in both sets of cell lines. Complete RNA sequencing (RNA-seq) was performed in parental (S) and resistant (R) derived cell lines comparing expression patterns of either untreated or platinum treated cells. Similarly, platinum R and S tumors were identified by screening NSCLC patients’ clinical records and expression patterns compared with RNA-seq analysis. Results: Both mRNA and potein levels of ATF3 were induced 35-120 fold (mRNA) by cisplatin treatment in S cell lines, but only 1-12 fold (mRNA) in the corresponding R lines. The 1200 compound library screen of FDA approved compounds identified several commonly used chemotherapeutic agents as sensitizers of platinum cytotoxicity, as well as vorinostat, a histone deacetylase inhibitor that sensitized only S but not R cell lines. An analogue of this agent, M344, enhanced ATF3 induction and cisplatin cytotoxicity in the S lines but not in the R lines. Comparing RNA-seq results of the S and R lines revealed up-regulation of GADD45A, ATF3 and DDIT3/CHOP in the S but not R cell lines. Comparing samples of S and R NSCLC tumors by RNA-seq demonstrated ATF3 to be among the five genes significantly up-regulated in the S tumors compared to the R tumors. Conclusions: Stress-induced ATF3 is correlated with platinum-sensitivity in NSCLC cells. Tumor ATF3 levels represent a potential predictive marker of response to platinum-based treatment in NSCLC. Revealing the mechanism of ATF3 induction by platinum may lead to the identification of novel platinum-sensitizing therapeutic targets. Citation Format: Jair Bar, Ivan Gorn-Hondermann, Reid Stephanie, Patricia Moretto, Iris Shiran, Shlomit Jessel, Marina Perelman, Eyal Heller, Iris Kamer, Inbal Daniel-Meshulam, Glenwood D. Goss, Jim Dimitroulakos. Activating transcription factor 3 (ATF3) down-regulation correlates with platinum resistance in non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 895. doi:10.1158/1538-7445.AM2013-895

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