PLK1 inhibition selectively induces apoptosis in ARID1A deficient cells through uncoupling of oxygen consumption from ATP production.

Inhibitors of the mitotic kinase PLK1 yield objective responses in a subset of refractory cancers. However, PLK1 overexpression in cancer does not correlate with drug sensitivity, and the clinical development of PLK1 inhibitors has been hampered by the lack of patient selection marker. Using a high-throughput chemical screen, we discovered that cells deficient for the tumor suppressor ARID1A are highly sensitive to PLK1 inhibition. Interestingly this sensitivity was unrelated to canonical functions of PLK1 in mediating G2/M cell cycle transition. Instead, a whole-genome CRISPR screen revealed PLK1 inhibitor sensitivity in ARID1A deficient cells to be dependent on the mitochondrial translation machinery. We find that ARID1A knock-out (KO) cells have an unusual mitochondrial phenotype with aberrant biogenesis, increased oxygen consumption/expression of oxidative phosphorylation genes, but without increased ATP production. Using expansion microscopy and biochemical fractionation, we see that a subset of PLK1 localizes to the mitochondria in interphase cells. Inhibition of PLK1 in ARID1A KO cells further uncouples oxygen consumption from ATP production, with subsequent membrane depolarization and apoptosis. Knockdown of specific subunits of the mitochondrial ribosome reverses PLK1-inhibitor induced apoptosis in ARID1A deficient cells, confirming specificity of the phenotype. Together, these findings highlight a novel interphase role for PLK1 in maintaining mitochondrial fitness under metabolic stress, and a strategy for therapeutic use of PLK1 inhibitors. To translate these findings, we describe a quantitative microscopy assay for assessment of ARID1A protein loss, which could offer a novel patient selection strategy for the clinical development of PLK1 inhibitors in cancer.

FBXW5 Promotes Tumorigenesis and Metastasis in Gastric Cancer via Activation of the FAK-Src Signaling Pathway.

: F-box/WD repeat-containing protein 5 (FBXW5) is a member of the FBXW subclass of F-box proteins. Despite its known function as a component of the Skp1-Cullin-F-box (SCF) ubiquitin ligase complex, the role of FBXW5 in gastric cancer tumorigenesis and metastasis has not been investigated. The present study investigates the role of FBXW5 in tumorigenesis and metastasis, as well as the regulation of key signaling pathways in gastric cancer; using in-vitro FBXW5 knockdown/overexpression cell line and in-vivo models. In-vitro knockdown of FBXW5 results in a decrease in cell proliferation and cell cycle progression, with a concomitant increase in cell apoptosis and caspase-3 activity. Furthermore, knockdown of FBXW5 also leads to a down regulation in cell migration and adhesion, characterized by a reduction in actin polymerization, focal adhesion turnover and traction forces. This study also delineates the mechanistic role of FBXW5 in oncogenic signaling as its inhibition down regulates RhoA-ROCK 1 (Rho-associated protein kinase 1) and focal adhesion kinase (FAK) signaling cascades. Overexpression of FBXW5 promotes in-vivo tumor growth, whereas its inhibition down regulates in-vivo tumor metastasis. When considered together, our study identifies the novel oncogenic role of FBXW5 in gastric cancer and draws further interest regarding its clinical utility as a potential therapeutic target.

Anti-tumor efficacy of Selinexor (KPT-330) in gastric cancer is dependent on nuclear accumulation of p53 tumor suppressor.

Exportin-1 (XPO1) controls the nucleo-cytoplasmic trafficking of several key growth regulatory and tumor suppressor proteins. Nuclear export blockade through XPO1 inhibition is a target for therapeutic inhibition in many cancers. Studies have suggested XPO1 upregulation as an indicator of poor prognosis in gastric cancer. In the current study, we investigated the anti-tumor efficacy of selective inhibitors of nuclear export (SINE) compounds KPT-185, KTP-276 and clinical stage selinexor (KPT-330) in gastric cancer. XPO1 was found to be overexpressed in gastric cancer as compared to adjacent normal tissues and was correlated with poor survival outcomes. Among the 3 SINE compounds, in vitro targeting of XPO1 with selinexor resulted in greatest potency with significant anti-proliferative effects at nano molar concentrations. XPO1 inhibition by selinexor resulted in nuclear accumulation of p53, causing cell cycle arrest and apoptosis. Also, inhibition of XPO1 lead to the cytoplasmic retention of p21 and suppression of survivin. Orally administered selienxor caused significant inhibition of tumor growth in xenograft models of gastric cancer. Furthermore, combination of selinexor with irinotecan exhibited greater anti-tumor effect compared to individual treatment. Taken together, our study underscores the therapeutic utility of XPO1 targeting in gastric cancer and suggests the potential benefits of XPO1 inhibition in-combination with chemotherapy.

Pan-HDAC inhibition by panobinostat mediates chemosensitization to carboplatin in non-small cell lung cancer via attenuation of EGFR signaling.

Accumulating evidence has implicated the aberrant regulation of histone deacetylases (HDACs) as a nexus for multiple cancer hallmarks and in mediating tumor adaptation and resistance to genotoxic chemotherapy, suggesting a rational pairing of HDAC inhibitors with DNA damaging chemotherapeutic agents in the treatment of human malignancies. Here we report that panobinostat (LBH589), a potent pan-HDAC inhibitor, effectively curbed the proliferation of non-small cell lung cancer (NSCLC) cell lines A549, Calu-1, H226, H460, H838 and SKMES-1 at IC50 concentrations between 4 and 31 nmol/L via pleiotropic mechanisms, including crosstalk with EGFR signal transduction cascades. Combination therapy with carboplatin elicited rapid tumor cell kill and effectively restrained anchorage-independent clonogenic survival to a considerably greater extent over either monotherapy. The administration of carboplatin and panobinostat at clinically relevant doses to NOD-SCID xenograft mice drastically stalled disease progression by 92% as compared with negative control (P = .0026), which was greater than the 28% and 54% achieved with either carboplatin (P = .220) or panobinostat (P = .017) alone. These data demonstrate that panobinostat has strong anti-NSCLC activity and chemosensitizes tumors to carboplatin, thus justifying further evaluation of this combination approach in clinical trials.

ATM Expression Predicts Veliparib and Irinotecan Sensitivity in Gastric Cancer by Mediating P53-Independent Regulation of Cell Cycle and Apoptosis.

Identification of synthetically lethal cellular targets and synergistic drug combinations is important in cancer chemotherapy as they help to overcome treatment resistance and increase efficacy. The Ataxia Telangiectasia Mutated (ATM) kinase is a nuclear protein that plays a major role in the initiation of DNA repair signaling and cell-cycle check points during DNA damage. Although ATM was shown to be associated with poor prognosis in gastric cancer, its implications as a predictive biomarker for cancer chemotherapy remain unexplored. The present study evaluated ATM-induced synthetic lethality and its role in sensitization of gastric cancer cells to PARP and TOP1 inhibitors, veliparib (ABT-888) and irinotecan (CPT-11), respectively. ATM expression was detected in a panel of gastric cell lines, and the IC50 against each inhibitors was determined. The combinatorial effect of ABT-888 and CPT-11 in gastric cancer cells was also determined both in vitro and in vivo ATM deficiency was found to be associated with enhanced sensitivity to ABT-888 and CPT-11 monotherapy, hence suggesting a mechanism of synthetic lethality. Cells with high ATM expression showed reduced sensitivity to monotherapy; however, they showed a higher therapeutic effect with ABT-888 and CPT-11 combinatorial therapy. Furthermore, ATM expression was shown to play a major role in cellular homeostasis by regulating cell-cycle progression and apoptosis in a P53-independent manner. The present study highlights the clinical utility of ATM expression as a predictive marker for sensitivity of gastric cancer cells to PARP and TOP1 inhibition and provides a deeper mechanistic insight into ATM-dependent regulation of cellular processes. Mol Cancer Ther; 15(12); 3087-96. ©2016 AACR.