A Short Post-Reattachment Ultrasensitive Window of Time in Human Cancer Cells as Therapeutic Target of Prolonged Low-Dose Administration of Specific Compounds.

Prolonged low-dose administration (PLDA) of several FDA-approved drugs for noncancer conditions or dietary compounds is associated with a lower incidence of specific types of cancers and with the lower formation of metastasis. However, the underlying mechanism is unknown; there is a discrepancy between the concentration of drugs needed to kill cancer cells in vitro and the actual serum levels (10 and >1000 times lower) found in patients. In this study, we evaluated the hypothesis that clonogenicity may be the target of PLDA. We compared the effect of nigericin (NIG) and menadione (MEN) on the human A549 and H460 lung and MCF-7 and MDA-MB-231 breast cancer cell lines using routine MTT and colony forming assays (CFA). The ability of both NIG and MEN to eliminate 100% of cancer cells was at least 2-10 times more potent in CFA compared to MTT assays. Our results revealed the existence of a short post-reattachment window of time when cancer cells growing at low density are more sensitive to PLDA of specific drugs likely by targeting clonogenic rather than proliferation pathways. This short ultrasensitive window of time (SUSWoT) was cell- and drug-type specific: the SUSWoT for NIG was present in H460, A549, and MDA-MB-231 cells but not evident in MCF-7 cells. Conversely, a similar SUSWoT for MEN was present in MCF-7, MDA-MD-231, and A549 cells but not evident in H460 cells. Our findings partially explain the decreased incidence of specific types of cancer by PLDA of FDA-approved drugs (or dietary compounds) for noncancer conditions.

Alternative models of cancer stem cells: The stemness phenotype model, 10 years later.

The classical cancer stem cell (CSCs) theory proposed the existence of a rare but constant subpopulation of CSCs. In this model cancer cells are organized hierarchically and are responsible for tumor resistance and tumor relapse. Thus, eliminating CSCs will eventually lead to cure of cancer. This simplistic model has been challenged by experimental data. In 2010 we proposed a novel and controversial alternative model of CSC biology (the Stemness Phenotype Model, SPM). The SPM proposed a non-hierarchical model of cancer biology in which there is no specific subpopulation of CSCs in tumors. Instead, cancer cells are highly plastic in term of stemness and CSCs and non-CSCs can interconvert into each other depending on the microenvironment. This model predicts the existence of cancer cells ranging from a pure CSC phenotype to pure non-CSC phenotype and that survival of a single cell can originate a new tumor. During the past 10 years, a plethora of experimental evidence in a variety of cancer types has shown that cancer cells are indeed extremely plastic and able to interconvert into cells with different stemness phenotype. In this review we will (1) briefly describe the cumulative evidence from our laboratory and others supporting the SPM; (2) the implications of the SPM in translational oncology; and (3) discuss potential strategies to develop more effective therapeutic regimens for cancer treatment.

The Biguanides Metformin and Buformin in Combination with 2-Deoxy-glucose or WZB-117 Inhibit the Viability of Highly Resistant Human Lung Cancer Cells.

The biguanides metformin (MET) and to a lesser extent buformin (BUF) have recently been shown to exert anticancer effects. In particular, MET targets cancer stem cells (CSCs) in a variety of cancer types but these compounds have not been extensively tested for combination therapy. In this study, we investigated in vitro the anticancer activity of MET and BUF alone or in combination with 2-deoxy-D-glucose (2-DG) and WZB-117 (WZB), which are a glycolysis and a GLUT-1 inhibitor, respectively, in H460 human lung cancer cells growing under three different culture conditions with varying degrees of stemness: (1) routine culture conditions (RCCs), (2) floating lung tumorspheres (LTSs) that are enriched for stem-like cancer cells, and (3) adherent cells under prolonged periods (8-12 days) of serum starvation (PPSS). These cells are highly resistant to conventional anticancer drugs such as paclitaxel, hydroxyurea, and colchicine and display an increased level of stemness markers. As single agents, MET, BUF, 2-DG, and WZB-117 potently inhibited the viability of cells growing under RCCs. Both MET and BUF showed a strong synergistic effect when used in combination with 2-DG. A weak potentiation was observed when used with WZB-117. Under RCCs, H460 cells were more sensitive to MET and BUF and WZB-117 compared to nontumorigenic Beas-2B cells. While LTSs were less sensitive to each single drug, both MET and BUF in combination with 2-DG showed a strong synergistic effect and reduced cell viability to similar levels compared to the parental H460 cells. Adherent cells growing under PPSS were also less sensitive to each single drug, and MET and BUF showed a strong synergistic effect on cell viability in combination with 2-DG. Overall, our data demonstrates that the combination of BGs with either 2-DG or WZB-117 has "broad-spectrum" anticancer activities targeting cells growing under a variety of cell culture conditions with varying degrees of stemness. These properties may be useful to overcome the chemoresistance due to intratumoral heterogeneity found in lung cancer.

Chemoresistance of cancer floating cells is independent of their ability to form 3D structures: Implications for anticancer drug screening.

Three-dimensional (3D) culture systems such as floating spheroids (FSs) and floating tumorspheres (FTs) are widely used as tumor models of chemoresistance. FTs are considered to be enriched in cancer stem-like cells (CS-LCs). In this study, we used cancer cell lines (lung H460, prostate LnCAP, and breast MCF-7) able to form FSs under anchorage-independent conditions and compared with cell lines (prostate PC3 and breast MDA-MB-231) that cannot form FSs under similar conditions. Independent of their ability to form FTs all cell lines growing under anchorage-independent conditions become highly resistant to obatoclax, colchicine, and hydroxyurea. We used anti-E-cadherin antibody (that blocked the formation of FSs) and demonstrated that floating LnCAP cells showed similar chemoresistance regardless of the formation of spheroids. Our results demonstrate that the development of chemoresistance is not because of the formation of a complex 3D structure and/or enrichment of CS-LCs but is likely the result of cell detachment per se and their ability to survive under anchorage-independent conditions. We propose that FSs and FTs could be useful models to study chemoresistance of cancer cells associated with cell detachment (e.g., circulating tumor cells) but they may not be representative of other types of chemoresistance that arise in vivo in attached cells.

Ionophores: Potential Use as Anticancer Drugs and Chemosensitizers.

Ion homeostasis is extremely important for the survival of both normal as well as neoplastic cells. The altered ion homeostasis found in cancer cells prompted the investigation of several ionophores as potential anticancer agents. Few ionophores, such as Salinomycin, Nigericin and Obatoclax, have demonstrated potent anticancer activities against cancer stem-like cells that are considered highly resistant to chemotherapy and responsible for tumor relapse. The preclinical success of these compounds in in vitro and in vivo models have not been translated into clinical trials. At present, phase I/II clinical trials demonstrated limited benefit of Obatoclax alone or in combination with other anticancer drugs. However, future development in targeted drug delivery may be useful to improve the efficacy of these compounds. Alternatively, these compounds may be used as leading molecules for the development of less toxic derivatives.

Translational gap in ongoing clinical trials for glioma.

Despite the vast amounts of information gathered about gliomas, the overall survival of glioma patients has not improved in the last four decades. This could partially be due to an apparent failure to include basic concepts of glioma biology into clinical trials. Specifically, attempts to overcome the limitations of the blood brain barrier (BBB) and the chemoresistance of glioma stem cells (GSCs) were seldom included (a phenomenon known as the translational gap, TG) in a study involving 29 Phase I/II clinical trials (P2CT) published in 2011. The aim of this study was to re-evaluate this finding with a new series of 100 ongoing, but still unpublished, P2CT in order to determine if there is a TG reduction. As indicators, we evaluated in each P2CT the number of drugs tested, concomitant radiotherapy, and the ability of drugs to pass the BBB and to target GSCs. Compared to clinical trials published in 2011, we found that while in OCT there is an increase in the number of P2CT using two drugs (from 24.1% to 44.9%), and an increase in the number of drugs able to pass the BBB (7.14% versus 64.29%) and target GSCs (0% versus 16.3%), there was a decrease in the number of P2CT using concomitant radiotherapy (34.5% versus 18.37%). Overall our results suggest that there is only a modest improvement regarding reducing the TG because the vast majority of ongoing P2CT are still not including well known concepts of glioma biology important for a successful treatment.

A Lipidomics Approach to Identifying Key Lipid Species Involved in VEGF-Inhibitor Mediated Attenuation of Bleomycin-Induced Pulmonary Fibrosis.

PURPOSE: Poor molecular characterization of idiopathic pulmonary fibrosis (IPF) has led to insufficient understanding of the pathogenesis of the disease, resulting in lack of effective therapies and poor prognosis. Particularly, the role of lipid imbalance due to impaired lipid metabolism in the pathogenesis of IPF has been poorly studied. EXPERIMENTAL DESIGN: The authors have used shotgun lipidomics in a bleomycin (BLM) mouse model of pulmonary fibrosis with vascular endothelial growth factor (VEGF)-inhibitor CBO-P11 as a therapeutic measure, to identify a comprehensive set of lipids that contribute to the pathogenesis of pulmonary fibrosis. RESULTS: The authors report that attenuation of BLM-induced fibrotic response with CBO-P11 cotreatment is accompanied by a decrease in total lipid content and specific downregulation of lipids, which are upregulated in response to BLM treatment. CONCLUSION AND CLINICAL RELEVANCE: Dysregulated lipids identified in this study hold the potential of being future biomarkers for IPF.

Selective and Irreversible Induction of Necroptotic Cell Death in Lung Tumorspheres by Short-Term Exposure to Verapamil in Combination with Sorafenib.

The presence of highly resistant cancer cells and the toxicity to normal cells are key factors that limit chemotherapy. Here, we used two models of highly resistant lung cancer cells: (1) adherent cells growing under prolonged periods of serum starvation (PPSS) and (2) cells growing as floating tumorspheres (FTs) to evaluate the effect of Verapamil (VP) in combination with Sorafenib (SF). Compared to cells growing under routine culture conditions (RCCs), PPPS cells or FTs were highly sensitive to short-term exposure (24 h) to VP 100 µM + SF 5 µM (VP100 + SF5). Recovery experiments exposing cells to VP100 + SF5 for 24 h followed by incubation in drug-free media for 48 h demonstrated that while PPSS as well as FT cells were unable to recover, cancer cells and the noncancerous cell line Beas-2B growing under RCCs were less sensitive and were also able to recover significantly. VP100 + SF5 induced significant changes in the expression of protein associated with apoptosis, autophagy, and to a lesser extent necroptosis. Coincubation experiments with z-VAD-FMK, necrostatin 1, or chloroquine showed evidence that necroptosis played a central role. Our data demonstrates that highly resistant cancer cells can be selectively eliminated by VP + SF and that necroptosis plays a central role.

Leadership and Management Are One and the Same.

Defining the attributes of change catalysts within high functioning organizations, including the academic enterprise, is desirable. An understanding of these attributes within our academy may foster faculty interest and engagement in seeking administrative roles and serve to bolster succession planning within our schools. On one hand, there have been numerous publications teasing out the purported differences between leadership and management. On the other hand, does segregating these important characteristics based upon arbitrary distinctions do more harm than good? This commentary represents the work of a group of academic leaders participating in the 2015-2016 AACP Academic Leadership Fellowship Program. This work was presented as a debate at the 2016 AACP Interim Meeting in Tampa, Florida, in February 2016.

A novel resveratrol-salinomycin combination sensitizes ER-positive breast cancer cells to apoptosis.

BACKGROUND: Resveratrol is a dietary compound that has been widely reported for its anticancer activities. However, successful extrapolation of its effects to pre-clinical studies is met with limited success due to inadequate bioavailability. We investigated the potential of combination therapy to improve the efficacy of resveratrol in a more physiologically relevant dose range. METHODS: The effect of resveratrol on canonical Wnt signaling was evaluated by Western blotting. Wnt modulators HLY78 (activator) and salinomycin (inhibitor) were evaluated in combination with resveratrol for their effect on breast cancer cell viability (MTT assay), cell cycle progression and apoptosis (Western blotting). Bliss independency model was used to evaluate combinatorial effects of resveratrol-salinomycin combination. RESULTS: Resveratrol downregulated canonical Wnt signaling proteins in treated breast cancer cells (MCF-7, MDA-MB-231 and MDA-MB-468) in the dose range of 50-200µM, which also affected cellular viability. However, at very low doses (0-50µM), resveratrol exhibited no cellular toxicity. Co-treatment with salinomycin significantly potentiated the anti-cancer effects of resveratrol, whereas HLY78 co-treatment had minimal effect. Bliss independency model revealed that Wnt inhibition synergistically potentiates the effects of resveratrol in MCF-7 and BT474 cells. Significantly downregulated canonical Wnt signaling proteins and marker of epithelial-mesenchymal transition (EMT), vimentin were observed in cells treated with resveratrol-salinomycin combination. Cell cycle arrest, caspase activation and apoptosis induction in cells treated with resveratrol-salinomycin combination further confirmed the efficacy of the combination. CONCLUSION: We report a novel resveratrol-salinomycin combination for targeting ER-positive breast cancer cells and present evidence for successful pre-clinical implementation of resveratrol.

Anti-tumorigenic effects of a novel digitoxin derivative on both estrogen receptor-positive and triple-negative breast cancer cells.

While there are targeted treatments for triple positive breast cancers, lack of specific biomarkers for triple-negative breast cancers (TNBC) has hindered the development of therapies for this subset of cancers. In this study, we evaluated the anticancer properties of cardiac glycoside Digitoxin (Dtx) and its synthetic analog MonoD on breast cancer cell lines MCF-7 (estrogen receptor-positive breast cancer) and MDA-MB-468 (triple-negative breast cancer). Both cardiac glycosides, at concentrations within the therapeutic range, increased the fraction of cells in the G0/G1 phase of the cell cycle, decreased viability, and inhibited the migration of MCF-7 and MDA-MB-468 cells. Both cardiac glycosides increased production of superoxide and induced apoptosis in both cell types. Reduced protein levels of nuclear factor kappa B and IkappaB kinase-beta were found in cardiac glycoside-treated cells, indicating that the cellular effects of these compounds are mediated via nuclear factor kappa B pathway. This study demonstrates the cytotoxic potential of digitoxin, and more importantly its synthetic analog MonoD, in the treatment of triple-positive breast cancer and more importantly the aggressive triple-negative breast cancer. Collectively, this study provides a basis for the reevaluation of cardiac glycosides in the treatment of breast cancer and more importantly reveals their potential in the treatment of triple-negative breast cancers.

Anti-Tumorigenic Potential of a Novel Orlistat-AICAR Combination in Prostate Cancer Cells.

Prostate cancer (PCa) is one of the leading causes of cancer-related deaths in men worldwide. Fatty acid synthase (FASN) is reported to be overexpressed in several cancers including PCa, and this has led to clinical cancer treatments that utilize various FASN inhibitors such as the anti-obesity drug, Orlistat. However, pharmacological limitations have impeded the progress in cancer treatments expected thus far with FASN inhibition. In this study, we investigated a novel therapeutic combination to enhance the toxic potential of Orlistat in three different PCa cell-lines (DU145, PC3, and LNCaP). We show that Orlistat and 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) (AMP-activated protein kinase [AMPK] activator) co-treatment induces significant downregulation of two key fatty acid synthesis regulatory proteins (FASN, Sterol regulatory element-binding protein 1 [SREBP-1c]) as compared to control and Orlistat alone. Orlistat and AICAR co-treatment induced a significant decrease in cell viability and proliferation, and a significant increase in apoptosis in all three PCa cell-lines. Apoptosis induction was preceded by a marked increase in reactive oxygen species (ROS) production followed by G0/G1 cell cycle arrest and activation of pro-apoptotic caspases. We also observed a significant decrease in migration potential and VEGF expression in Orlistat and AICAR co-treated samples in all three PCa cell-lines. Compound C (AMPK inhibitor) negatively affected some of the enhanced anti-cancer effects observed with Orlistat treatment. We conclude that AICAR co-treatment potentiates the anti-proliferative effects of Orlistat at a low dose (100 µM), and this combination has the potential to be a viable and effective therapeutic option in PCa treatment. J. Cell. Biochem. 118: 3834-3845, 2017. © 2017 Wiley Periodicals, Inc.

Antitumor effects of naturally occurring cardiac glycosides convallatoxin and peruvoside on human ER+ and triple-negative breast cancers.

Breast cancer is second most prevalent cancer in women, and the second only to lung cancer in cancer-related deaths. It is a heterogeneous disease and has several subtypes based on the presence or absence of hormone receptors and/or human epidermal growth factor receptor 2 (HER2). Hormone receptor-positive and HER2-enriched cancers can be targeted using hormone and HER2-targeting therapies such as trastuzumab or lapatinib. However, triple-negative breast cancers (TNBCs) do not express any of the receptors and therefore are resistant to most targeted therapies, and cytotoxic chemotherapies are the only viable option available for the treatment of TNBCs. Recently, cardiac glycosides (CGs) have emerged as potential anticancer agents that impart their antiproliferative effect by targeting multiple pathways. In this study our aim was to evaluate anticancer effects of two naturally occurring CGs, Convallatoxin (CT) and Peruvoside (PS), on ER+ and TNBCs cells. CT and PS demonstrated dose- and time-dependent cytotoxic effect on MCF-7 cells, which was further supported by loss of colony formation on drug treatment. CT and PS arrested MCF-7 cells in the G0/G1 phase and reduced the viability of MCF-7-derived mammospheres (MMs). Interestingly, while CT and PS imparted cell death in TNBCs cells from both Caucasians (MDA-MB-231 cells) and African Americans (MDA-MB-468 cells) in a dose- and time-dependent manner, the drugs were much more potent in MDA-MB-468 as compared with TNBC MDA-MB-231 cells. Both drugs significantly inhibited migration and invasion of both MCF-7 and MDA-MB-468 cells. An assessment of intracellular pathways indicated that both drugs were able to modulate several key cellular pathways such as EMT, cell cycle, proliferation and cell death in both cell types. Our data suggest a promising role for CGs in breast cancer treatment specifically in targeting TNBCs derived from African Americans, and provides impetus for further investigation of the anticancer potential of this class of drugs.

Anti-Tumorigenic Effects of Resveratrol in Lung Cancer Cells Through Modulation of c-FLIP.

BACKGROUND: Resveratrol has been shown to have antioxidant and anti-proliferative properties in multiple cancer types. Here we demonstrate that H460 lung cancer cells are more susceptible to resveratrol treatment in comparison to human bronchial epithelial Beas-2B cells. Resveratrol decreases cell viability and proliferation, and induces significant apoptosis in H460 cells. The apoptosis observed was accompanied by an increase in hydrogen peroxide (H2O2) production, Bid, PARP and caspase 8 activation, and downregulation of pEGFR, pAkt, c-FLIP and NFkB protein expression. Furthermore, treatment with HH2O2 scavenger catalase significantly inhibited resveratrol-induced c-FLIP downregulation, caspase-8 activation and apoptosis. Overexpression of c-FLIP in H460 cells (FLIP cells) resulted in the inhibition of resveratrol-induced HH2O2 production, and a significant increase in resveratrolinduced apoptosis in comparison to H460 cells. In FLIP cells, catalase treatment did not rescue cells from a decrease in cell viability and apoptosis induction by resveratrol as compared to H460 cells. Resveratrol treatment also led to VEGF downregulation in FLIP cells. Furthermore, inhibition of pEGFR or pAkt using erlotinib and LY294002 respectively, enhanced the negative effect of resveratrol on FLIP cell viability and apoptosis. The reverse was observed when FLIP cells were supplemented with EGF, or transfected with WT-AKT plasmid; resulting in a 20% decrease in resveratrol-induced apoptosis. In addition, transfection with WT-AKT plasmid resulted in the inhibition of pro-apoptotic protein activation, and c-FLIP and pAkt downregulation. CONCLUSION: Overall, resveratrol induced apoptosis in H460 lung cancer cells by specifically targeting pAkt and c-FLIP dowregulation by proteasomal degradation in a EGFR-dependent manner.

Nigericin decreases the viability of multidrug-resistant cancer cells and lung tumorspheres and potentiates the effects of cardiac glycosides.

Multiple factors including tumor heterogeneity and intrinsic or acquired resistance have been associated with drug resistance in lung cancer. Increased stemness and the plasticity of cancer cells have been identified as important mechanisms of resistance; therefore, treatments targeting cancer cells independent of stemness phenotype would be much more effective in treating lung cancer. In this article, we have characterized the anticancer effects of the antibiotic Nigericin in cells displaying varying degrees of stemness and resistance to anticancer drugs, arising from (1) routine culture conditions, (2) prolonged periods of serum starvation. These cells are highly resistant to conventional anticancer drugs such as Paclitaxel, Hydroxyurea, Colchicine, Obatoclax, Wortmannin, and LY294002, and the multidrug-resistant phenotype of cells growing under prolonged periods of serum starvation is likely the result of extensive rewiring of signaling pathways, and (3) lung tumorspheres that are enriched for cancer stem-like cells. We found that Nigericin potently inhibited the viability of cells growing under routine culture conditions, prolonged periods of serum starvation, and lung tumorspheres. In addition, we found that Nigericin downregulated the expression of key proteins in the Wnt canonical signaling pathway such as LRP6, Wnt5a/b, and ß-catenin, but promotes ß-catenin translocation into the nucleus. The antitumor effects of Nigericin were potentiated by the Wnt activator HLY78 and by therapeutic levels of the US Food and Drug Administration-approved drug Digitoxin and its novel synthetic analog MonoD. We believe that Nigericin may be used in a co-therapy model in combination with other novel chemotherapeutic agents in order to achieve potent inhibition of cancers that display varying degrees of stemness, potentially leading to sustained anticancer effects.

Effects of titanium dioxide nanoparticles on human keratinocytes.

Titanium dioxide (TiO2) is a ubiquitous whitening compound widely used in topical products such as sunscreens, lotions and facial creams. The damaging health effects of TiO2 inhalation has been widely studied in rats, mice and humans showing oxidative stress increase, DNA damage, cell death and inflammatory gene upregulation in lung and throat cells; however, the effects on skin cells from long-term topical use of various products remain largely unknown. In this study, we assessed the effect of specific TiO2 nanoparticles (H2TiO7) on a human keratinocyte cell line (HaCaT). We performed a comparative analysis using three TiO2 particles varying in size (Fine, Ultrafine and H2TiO7) and analyzed their effects on HaCaTs. There is a clear dose-dependent increase in superoxide production, caspase 8 and 9 activity, and apoptosis in HaCaTs after treatment with all three forms of TiO2; however, there is no consistent effect on cell viability and proliferation with either of these TiO2 particles. While there is data suggesting UV exposure can enhance the carcinogenic effects of TiO2, we did not observe any significant effect of UV-C exposure combined with TiO2 treatment on HaCaTs. Furthermore, TiO2-treated cells showed minimal effects on VEGF upregulation and Wnt signaling pathway thereby showing no potential effect on angiogenesis and malignant transformation. Overall, we report here an increase in apoptosis, which may be caspase 8/Fas-dependent, and that the H2TiO7 nanoparticles, despite their smaller particle size, had no significant enhanced effect on HaCaT cells as compared to Fine and Ultrafine forms of TiO2.

MnTBAP Inhibits Bleomycin-Induced Pulmonary Fibrosis by Regulating VEGF and Wnt Signaling.

Cellular oxidative stress is implicated not only in lung injury but also in contributing to the development of pulmonary fibrosis. We demonstrate that a cell-permeable superoxide dismutase (SOD) mimetic and peroxynitrite scavenger, manganese (III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) significantly inhibited bleomycin-induced fibrogenic effects both in vitro and in vivo. Further investigation into the underlying mechanisms revealed that MnTBAP targets canonical Wnt and non-canonical Wnt/Ca2+ signaling pathways, both of which were upregulated by bleomycin treatment. The effect of MnTBAP on canonical Wnt signaling was significant in vivo but inconclusive in vitro and the non-canonical Wnt/Ca2+ signaling pathway was observed to be the predominant pathway regulated by MnTBAP in bleomycin-induced pulmonary fibrosis. Furthermore, we show that the inhibitory effects of MnTBAP involve regulation of VEGF which is upstream of the Wnt signaling pathway. Overall, the data show that the superoxide scavenger MnTBAP attenuates bleomycin-induced pulmonary fibrosis by targeting VEGF and Wnt signaling pathways. J. Cell. Physiol. 232: 506-516, 2017. © 2016 Wiley Periodicals, Inc.

Anti-Tumor Effects of Cardiac Glycosides on Human Lung Cancer Cells and Lung Tumorspheres.

Lung cancer is a leading cause of cancer-related death in the United States. Although several drugs have been developed that target individual biomarkers, their success has been limited due to intrinsic or acquired resistance for the specific targets of such drugs. A more effective approach is to target multiple pathways that dictate cancer progression. Cardiac glycosides demonstrate such multimodal effects on cancer cell survival, and our aim was to evaluate the effect of two naturally occurring monosaccaridic cardiac glycosides-Convallatoxin and Peruvoside on lung cancer cells. Although both drugs had significant anti-proliferative effects on H460 and Calu-3 lung cancer cells, Convallatoxin demonstrated twofold higher activity as compared to Peruvoside using both viability and colony forming assays, suggesting a role for the aglycone region in dictating drug potency. The tumor suppressor p53 was found to be important for action of both drugs-p53-underexpressing cells were less sensitive as compared to p53-positive H460 cells. Further, assessment of p53-underexpressing H460 cells showed that drugs were able to arrest cells in the G0/G1 phase of the cell cycle in a dose-dependent manner. Both drugs significantly inhibited migration and invasion of cancer cells and decreased the viability of floating tumorspheres. An assessment of intracellular pathways indicated that both drugs were able to modulate proteins that are involved in apoptosis, autophagy, cell cycle, proliferation, and EMT. Our data suggest, a promising role for cardiac glycosides in lung cancer treatment, and provides impetus for further investigation of the anti-cancer potential of this class of drugs. J. Cell. Physiol. 232: 2497-2507, 2017. © 2016 Wiley Periodicals, Inc.

Chemoresistance of Lung and Breast Cancer Cells Growing Under Prolonged Periods of Serum Starvation.

The efficacy of chemotherapy is hindered by both tumor heterogeneity and acquired or intrinsic multi-drug resistance caused by the contribution of multidrug resistance proteins and stemness-associated prosurvival markers. Therefore, targeting multi-drug resistant cells would be much more effective against cancer. In this study, we characterized the chemoresistance properties of adherent (anchorage-dependent) lung H460 and breast MCF-7 cancer cells growing under prolonged periods of serum starvation (PPSS). We found that under PPSS, both cell lines were highly resistant to Paclitaxel, Colchicine, Hydroxyurea, Obatoclax, Wortmannin, and LY294002. Levels of several proteins associated with increased stemness such as Sox2, MDR1, ABCG2, and Bcl-2 were found to be elevated in H460 cells but not in MCF-7 cells. While pharmacological inhibition of either MDR1, ABCG2, Bcl-2 with Verapamil, Sorafenib, or Obatoclax, respectively decreased the levels of their target proteins under routine culture conditions as expected, such inhibition did not reverse PX resistance in PPSS conditions. Paradoxically, treatment with inhibitors in serum-starved conditions produced an elevation of their respective target proteins. In addition, we found that Digitoxin, an FDA approved drug that decrease the viability of cancer cells growing under PPSS, downregulates the expression of Sox2, MDR1, phospho- AKT, Wnt5a/b, and ß-catenin. Our data suggest that PPSS-induced chemoresistance is the result of extensive rewiring of intracellular signaling networks and that multi-resistance can be effectively overcome by simultaneously targeting multiple targets of the rewired network. Furthermore, our PPSS model provides a simple and useful tool to screen drugs for their ability to target multiple pathways of cancer resistance. J. Cell. Physiol. 232: 2033-2043, 2017. © 2016 Wiley Periodicals, Inc.

Cancer Cell Plasticity: Rapid Reversal of Chemosensitivity and Expression of Stemness Markers in Lung and Breast Cancer Tumorspheres.

In cancer cells, the reversible nature of the stemness status in terms of chemoresistance has been poorly characterized. In this study, we have simulated one cycle of environmental conditions to study such reversibility by first generating floating tumorspheres (FTs) from lung and breast cancer cells by culturing them in serum-free media without the addition of any external mitogenic stimulation, and subsequently (after 2 weeks) re-incubating them back in serum-containing media to simulate routine culture conditions (RCCs). We found that cancer cells are extremely plastic: cells grown under RCCs become multidrug-resistant when grown as FTs, but upon re-incubation under RCCs quickly re-attach and lose the acquired resistance. These phenotypic changes are accompanied by concomitant changes in the expression of key proteins associated with multiple pathways important for chemoresistance, survival, and stemness maintenance. Therefore, our strategy provides an excellent experimental model to study environmental factors that modulate the plasticity of cancer cells. J. Cell. Physiol. 232: 2280-2286, 2017. © 2016 Wiley Periodicals, Inc.