The small molecule SI113 hinders epithelial-to-mesenchymal transition and subverts cytoskeletal organization in human cancer cells.

The small molecule SI113 is an inhibitor of the kinase activity of SGK1, a key biological regulator acting on the PI3K/mTOR signal transduction pathway. Several studies demonstrate that this compound is able to strongly restrain cancer growth in vitro and in vivo, alone or in associative antineoplastic treatments, being able to elicit an autophagic response, either cytotoxic or cytoprotective. To elucidate more exhaustively the molecular mechanisms targeted by SI113, we performed activity-based protein profiling (ABPP) proteomic analysis using a kinase enrichment procedure. This technique allowed the identification via mass spectrometry of novel targets of this compound, most of them involved in functions concerning cell motility and cytoskeletal architecture. Using a glioblastoma multiforme, hepatocarcinoma and colorectal carcinoma cell line, we recognized an inhibitory effect of SI113 on cell migration, invading, and epithelial-to-mesenchymal transition. In addition, these cancer cells, when exposed to this compound, showed a remarkable subversion of the cytoskeletal architecture characterized by F-actin destabilization, phospho-FAK delocalization, and tubulin depolimerization. These results were definitely concordant in attributing to SI113 a key role in hindering cancer cell malignancy and, due to its negligible in vivo toxicity, can sustain performing a Phase I clinical trial to employ this drug in associative cancer therapy.

The SGK1 Kinase Inhibitor SI113 Sensitizes Theranostic Effects of the 64CuCl2 in Human Glioblastoma Multiforme Cells.

BACKGROUND/AIMS: The importance of copper in the metabolism of cancer cells has been widely studied in the last 20 years and a clear-cut association between copper levels and cancer deregulation has been established. Copper-64, emitting positrons and ß-radiations, is indicated for the labeling of a large number of molecules suitable for radionuclide imaging as well as radionuclide therapy. Glioblastoma multiforme (GBM) is the CNS tumor with the worse prognosis, characterized by high number of recurrences and strong resistance to chemo-radio therapy, strongly affecting patients survival. We have recently discovered and studied the small molecule SI113, as inhibitor of SGK1, a serine/threonine protein kinase, that affects several neoplastic phenotypes and signaling cascades. The SI113-dependent SGK1 inhibition induces cell death, blocks proliferation, perturbs cell cycle progression and restores chemo-radio sensibility by modulating SGK1-related substrates. In the present paper we aim to characterize the combined effects of 64CuCl2 and SI113 on human GBM cell lines with variable p53 expression. METHODS: Cell viability, cell death and stress/authopagic related pathways were then analyzed by FACS and WB-based assays, after exposure to SI113 and/or 64CuCl2. RESULTS: We demonstrate here, that i) 64CuCl2 is able to induce a time and dose dependent modulation of cell viability (with different IC50 values) in highly malignant gliomas and that the co-treatment with SI113 leads to ii) additive/synergistic effects in terms of cell death; iii) enhancement of the effects of ionizing radiations, probably by a TRC1 modulation; iv) modulation of the autophagic response. CONCLUSIONS: Evidence reported here underlines the therapeutic potential of the combined treatment with SI113 and 64CuCl2 in GBM cells.

The kinase inhibitor SI113 induces autophagy and synergizes with quinacrine in hindering the growth of human glioblastoma multiforme cells.

BACKGROUND: Glioblastoma multiforme (GBM), due to its location, aggressiveness, heterogeneity and infiltrative growth, is characterized by an exceptionally dismal clinical outcome. The small molecule SI113, recently identified as a SGK1 inhibitor, has proven to be effective in restraining GBM growth in vitro and in vivo, showing also encouraging results when employed in combination with other antineoplastic drugs or radiotherapy. Our aim was to explore the pharmacological features of SI113 in GBM cells in order to elucidate the pivotal molecular pathways affected by the drug. Such knowledge would be of invaluable help in conceiving a rational offensive toward GBM. METHODS: We employed GBM cell lines, either established or primary (neurospheres), and used a Reverse-Phase Protein Arrays (RPPA) platform to assess the effect of SI113 upon 114 protein factors whose post-translational modifications are associated with activation or repression of specific signal transduction cascades. RESULTS: SI113 strongly affected the PI3K/mTOR pathway, evoking a pro-survival autophagic response in neurospheres. These results suggested the use of SI113 coupled, for maximum efficiency, with autophagy inhibitors. Indeed, the association of SI113 with an autophagy inhibitor, the antimalarial drug quinacrine, induced a strong synergistic effect in inhibiting GBM growth properties in all the cells tested, including neurospheres. CONCLUSIONS: RPPA clearly identified the molecular pathways influenced by SI113 in GBM cells, highlighting their vulnerability when the drug was administered in association with autophagy inhibitors, providing a strong molecular rationale for testing SI113 in clinical trials in associative GBM therapy.

The small molecule SI113 synergizes with mitotic spindle poisons in arresting the growth of human glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the deadliest brain tumor. State-of-art GBM therapy often fails to ensure control of a disease characterized by high frequency of recurrences and progression. In search for novel therapeutic approaches, we assayed the effect of compounds from a cancer drug library on the ADF GBM cell line, establishing their elevated sensitivity to mitotic spindle poisons. Our previous work showed that the effectiveness of the spindle poison paclitaxel in inhibiting cancer cell growth was dependent on the expression of RANBP1, a regulatory target of the serine/threonine kinase SGK1. Recently, we developed the small molecule SI113 to inhibit SGK1 activity. Therefore, we explored the outcome of the association between SI113 and selected spindle poisons, finding that these drugs generated a synergistic cytotoxic effect in GBM cells, drastically reducing their viability and clonogenic capabilities in vitro, as well as inhibiting tumor growth in vivo. We also defined the molecular bases of such a synergistic effect. Because SI113 displays low systemic toxicity, yet strong activity in potentiating the effect of radiotherapy in GBM cells, we believe that this drug could be a strong candidate for clinical trials, with the aim to add it to the current GBM therapeutic approaches.

SI113, a SGK1 inhibitor, potentiates the effects of radiotherapy, modulates the response to oxidative stress and induces cytotoxic autophagy in human glioblastoma multiforme cells.

Glioblastoma multiforme (GBM) is the most aggressive CNS tumor and is characterized by a very high frequency of clinical relapse after therapy and thus by a dismal prognosis, which strongly compromises patients survival. We have recently identified the small molecule SI113, as a potent and selective inhibitor of SGK1, a serine/threonine protein kinase, that modulates several oncogenic signaling cascades. The SI113-dependent SGK1 inhibition induces cell death, blocks proliferation and perturbs cell cycle progression by modulating SGK1-related substrates. SI113 is also able to strongly and consistently block, in vitro and in vivo, growth and survival of human hepatocellular-carcinomas, either used as a single agent or in combination with ionizing radiations. In the present paper we aim to study the effect of SI113 on human GBM cell lines with variable p53 expression. Cell viability, cell death, caspase activation and cell cycle progression were then analyzed by FACS and WB-based assays, after exposure to SI113, with or without oxidative stress and ionizing radiations. Moreover, autophagy and related reticulum stress response were evaluated. We show here, that i) SGK1 is over-expressed in highly malignant gliomas and that the treatment with SI113 leads to ii) significant increase in caspase-mediated apoptotic cell death in GBM cell lines but not in normal fibroblasts; iii)enhancement of the effects of ionizing radiations; iv) modulation of the response to oxidative reticulum stress; v) induction of cytotoxic autophagy. Evidence reported here underlines the therapeutic potential of SI113 in GBM, suggesting a new therapeutic strategy either alone or in combination with radiotherapy.