cx-5461 and Breast-Neoplasms

Upregulation of RNA Polymerase (Pol I)-mediated transcription of rRNA and increased ribogenesis are hallmarks of breast cancer. According to several datasets, including The Cancer Genome Atlas (TCGA), amplification/upregulation of genes encoding for basal components of the Pol I transcriptional machinery is frequent at different breast cancer stages. Here we show that knock down of the RNA polymerase I-specific transcription initiation factor RRN3 (TIF-IA) in breast cancer cells is sufficient to reduce rRNA synthesis and inhibit cell proliferation, and second that stable ectopic expression of RRN3 in human mammary epithelial (HME1) cells, by increasing rRNA transcription, confers increased sensitivity to the anti-proliferative effects of a selective Pol I inhibitor. Further, RRN3-overexpressing HME1 cells, when grown in in vitro 3-dimensional (3D) culture, develop into morphologically aberrant acinar structures lacking a lumen and filled with proliferative cells, thus acquiring a morphology resembling in situ ductal breast cancer lesions (DCIS). Consequently, interference with RRN3 control of Pol I transcription seems capable of both compromising mammary epithelial morphogenetic processes at early breast cancer stages, and driving breast cancer progression by fostering proliferation.

Topics: Benzothiazoles; Breast Neoplasms; Cell Proliferation; Epithelial Cells; Female; Gene Knockdown Techniques; Genome, Human; Humans; Mammary Glands, Human; MCF-7 Cells; Morphogenesis; Naphthyridines; Neoplasm Invasiveness; Pol1 Transcription Initiation Complex Proteins; Protein Stability; RNA Polymerase I; RNA, Ribosomal; Transcription, Genetic; Up-Regulation

PICT-1 was originally identified as a tumor suppressor. Here, we found that PICT-1 overexpression triggered pro-death autophagy without nucleolar disruption or p53 accumulation in U251 and MCF7 cells. Truncated PICT-1 fragments 181-346 and 1-346, which partly or totally lack nucleolar localization, showed weaker autophagy-inducing effects than full-length PICT-1 and a well-defined nucleolar mutant (181-479). Furthermore, PICT-1 partly localizes to the nucleolar fibrillar center (FC) and directly binds to ribosomal DNA (rDNA) gene loci, where it interacts with upstream binding factor (UBF). Overexpression of PICT-1 or the 181-479 mutant, but not the 1-346 or 181-346 mutants, markedly inhibited the phosphorylation of UBF and the recruitment of rRNA polymerase I (Pol I) to the rDNA promoter in response to serum stimulation, thereby suppressing rRNA transcription, suggesting that rRNA transcription inhibition might be an important contributor to PICT-1-induced autophagy. This is supported by the finding that CX-5461, a specific Pol I inhibitor, also induced autophagy. In addition, both CX-5461 and PICT-1, but not the 1-346 or 181-346 mutants, significantly suppressed the activation of the Akt/mTOR/p70S6K signaling pathway. Our data show that PICT-1 triggers pro-death autophagy through inhibition of rRNA transcription and the inactivation of AKT/mTOR/p70S6K pathway, independent of nucleolar disruption and p53 activation.

Topics: Antineoplastic Agents; Autophagy; Benzothiazoles; Binding Sites; Brain Neoplasms; Breast Neoplasms; Cell Nucleolus; Cell Proliferation; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Gene Expression Regulation, Neoplastic; Glioblastoma; Humans; MCF-7 Cells; Mutation; Naphthyridines; Phosphorylation; Pol1 Transcription Initiation Complex Proteins; Promoter Regions, Genetic; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases, 70-kDa; RNA Polymerase I; RNA, Ribosomal; Signal Transduction; Time Factors; TOR Serine-Threonine Kinases; Transcription, Genetic; Transfection; Tumor Suppressor Proteins

A number of previous studies has provided evidence that the well-known anti-bacterial quinolones may have potential as anti-cancer drugs. The aim of this study was to evaluate potential anti-tumour activity and selectivity of a set of 6-aminoquinolones showing some chemical similarity to naphthyridone derivative CX-5461, recently described as innovative anti-cancer agent.. In-house quinolones 1-8 and ad hoc synthesized derivatives 9-13 were tested on Michigan Cancer Foundation-7 (MCF-7) breast cancer cells and mesenchymal progenitor (MePR2B) cell lines, analysing their effects on the cell cycle and cell death using FACS methodology. Activation of p53 was evaluated by western blotting.. Benzyl esters 4, 5 and their amide counterparts 12, 13 drastically modulated MCF-7 cell cycles inducing DNA fragmentation and cell death, thus proving to be potential anti-tumour compounds. When assayed in non-tumour MePR2B cells, compounds 4 and 5 were cytotoxic while 12 and 13 had a certain degree of selectivity, with compound 12 emerging as the most promising. Western blot analysis revealed that severe p53-K382ac activation was promoted by benzylester 5. In contrast, amide 12 exerted only a moderate effect which was, however, comparable to that of suberoylanilide hydoxamic acid (SAHA).. Taken together, these results further reinforce evidence that quinolones have potential as anti-cancer agents. Future work will be focused on understanding compound 12 mechanisms of action, and to obtain more potent and selective compounds.

Topics: Aminoquinolines; Antineoplastic Agents; Apoptosis; Benzothiazoles; Breast Neoplasms; Cell Cycle; Cell Division; Cell Line, Tumor; Cell Proliferation; DNA Fragmentation; Female; Humans; MCF-7 Cells; Naphthyridines