Luke H. Stockwin

Sodium dichloroacetate selectively targets cells with defects in the mitochondrial ETC

The “Warburg effect,” also termed aerobic glycolysis, describes the increased reliance of cancer cells on glycolysis for ATP production, even in the presence of oxygen. Consequently, there is continued interest in inhibitors of glycolysis as cancer therapeutics. One example is dichloroacetate (DCA), a pyruvate mimetic that stimulates oxidative phosphorylation through inhibition of pyruvate dehydrogenase kinase. In this study, the mechanistic basis for DCA anti‐cancer activity was re‐evaluated in vitro using biochemical, cellular and proteomic approaches. Results demonstrated that DCA is relatively inactive (IC50 ≥ 17 mM, 48 hr), induces apoptosis only at high concentrations (≥25 mM, 48 hr) and is not cancer cell selective. Subsequent 2D‐PAGE proteomic analysis confirmed DCA‐induced growth suppression without apoptosis induction. Furthermore, DCA depolarizes mitochondria and promotes reactive oxygen species (ROS) generation in all cell types. However, DCA was found to have selective activity against rho(0) cells [mitochondrial DNA (mtDNA) deficient] and to synergize with 2‐deoxyglucose in complex IV deficient HCT116 p53(−/−) cells. DCA also synergized in vitro with cisplatin and topotecan, two antineoplastic agents known to damage mitochondrial DNA. These data suggest that in cells “hardwired” to selectively utilize glycolysis for ATP generation (e.g., through mtDNA mutations), the ability of DCA to force oxidative phosphorylation confers selective toxicity. In conclusion, although we provide a mechanism distinct from that reported previously, the ability of DCA to target cell lines with defects in the electron transport chain and to synergize with existing chemotherapeutics supports further preclinical development.

A copper chelate of thiosemicarbazone NSC 689534 induces oxidative/ER stress and inhibits tumor growth in vitro and in vivo.

In this study, a Cu(2+) chelate of the novel thiosemicarbazone NSC 689534 was evaluated for in vitro and in vivo anti-cancer activity. Results demonstrated that NSC 689534 activity (low micromolar range) was enhanced four- to fivefold by copper chelation and completely attenuated by iron. Importantly, once formed, the NSC 689534/Cu(2+) complex retained activity in the presence of additional iron or iron-containing biomolecules. NSC 689534/Cu(2+) mediated its effects primarily through the induction of ROS, with depletion of cellular glutathione and protein thiols. Pretreatment of cells with the antioxidant N-acetyl-l-cysteine impaired activity, whereas NSC 689534/Cu(2+) effectively synergized with the glutathione biosynthesis inhibitor buthionine sulfoximine. Microarray analysis of NSC 689534/Cu(2+)-treated cells highlighted activation of pathways involved in oxidative and ER stress/UPR, autophagy, and metal metabolism. Further scrutiny of the role of ER stress and autophagy indicated that NSC 689534/Cu(2+)-induced cell death was ER-stress dependent and autophagy independent. Last, NSC 689534/Cu(2+) was shown to have activity in an HL60 xenograft model. These data suggest that NSC 689534/Cu(2+) is a potent oxidative stress inducer worthy of further preclinical investigation.

Artemisinin dimer anticancer activity correlates with heme-catalyzed reactive oxygen species generation and endoplasmic reticulum stress induction.

Analogs of the malaria therapeutic, artemisinin, possess in vitro and in vivo anticancer activity. In this study, two dimeric artemisinins (NSC724910 and 735847) were studied to determine their mechanism of action. Dimers were >1,000 fold more active than monomer and treatment was associated with increased reactive oxygen species (ROS) and apoptosis induction. Dimer activity was inhibited by the antioxidant L‐NAC, the iron chelator desferroxamine and exogenous hemin. Similarly, induction of heme oxygenase (HMOX) with CoPPIX inhibited activity, whereas inhibition of HMOX with SnPPIX enhanced it. These results emphasize the importance of iron, heme and ROS in activity. Microarray analysis of dimer treated cells identified DNA damage, iron/heme and cysteine/methionine metabolism, antioxidant response, and endoplasmic reticulum (ER) stress as affected pathways. Detection of an ER‐stress response was relevant because in malaria, artemisinin inhibits pfATP6, the plasmodium orthologue of mammalian sarcoplasmic/endoplasmic reticulum Ca2+‐ATPases (SERCA). A comparative study of NSC735847 with thapsigargin, a specific SERCA inhibitor and ER‐stress inducer showed similar behavior in terms of transcriptomic changes, induction of endogenous SERCA and ER calcium mobilization. However, thapsigargin had little effect on ROS production, modulated different ER‐stress proteins and had greater potency against purified SERCA1. Furthermore, an inactive derivative of NSC735847 that lacked the endoperoxide had identical inhibitory activity against purified SERCA1, suggesting that direct inhibition of SERCA has little inference on overall cytotoxicity. In summary, these data implicate indirect ER‐stress induction as a central mechanism of artemisinin dimer activity.

Gene expression profiling of alveolar soft-part sarcoma (ASPS).

BackgroundAlveolar soft-part sarcoma (ASPS) is an extremely rare, highly vascular soft tissue sarcoma affecting predominantly adolescents and young adults. In an attempt to gain insight into the pathobiology of this enigmatic tumor, we performed the first genome-wide gene expression profiling study.MethodsFor seven patients with confirmed primary or metastatic ASPS, RNA samples were isolated immediately following surgery, reverse transcribed to cDNA and each sample hybridized to duplicate high-density human U133 plus 2.0 microarrays. Array data was then analyzed relative to arrays hybridized to universal RNA to generate an unbiased transcriptome. Subsequent gene ontology analysis was used to identify transcripts with therapeutic or diagnostic potential. A subset of the most interesting genes was then validated using quantitative RT-PCR and immunohistochemistry.ResultsAnalysis of patient array data versus universal RNA identified elevated expression of transcripts related to angiogenesis (ANGPTL2, HIF-1 alpha, MDK, c-MET, VEGF, TIMP-2), cell proliferation (PRL, IGFBP1, NTSR2, PCSK1), metastasis (ADAM9, ECM1, POSTN) and steroid biosynthesis (CYP17A1 and STS). A number of muscle-restricted transcripts (ITGB1BP3/MIBP, MYF5, MYF6 and TRIM63) were also identified, strengthening the case for a muscle cell progenitor as the origin of disease. Transcript differentials were validated using real-time PCR and subsequent immunohistochemical analysis confirmed protein expression for several of the most interesting changes (MDK, c-MET, VEGF, POSTN, CYP17A1, ITGB1BP3/MIBP and TRIM63).ConclusionResults from this first comprehensive study of ASPS gene expression identifies several targets involved in angiogenesis, metastasis and myogenic differentiation. These efforts represent the first step towards defining the cellular origin, pathogenesis and effective treatment strategies for this atypical malignancy.

The “survivin suppressants” NSC 80467 and YM155 induce a DNA damage response

PurposeTo establish whether NSC80467, a novel fused naphthquinone imidazolium, has a similar spectrum of activity to the well-characterized “survivin suppressant” YM155 and to extend mechanistic studies for this structural class of agent.MethodsNSC80467 and YM155 were analyzed in parallel using assays measuring viability, survivin suppression, inhibition of DNA/RNA/protein synthesis and the cellular response to DNA damage.ResultsGI50 values generated for both compounds in the NCI-60 screen yielded a correlation coefficient of 0.748, suggesting significant concordance. Both agents were also shown to inhibit protein expression of survivin [BIRC5]. COMPARE analysis identified DNA damaging agents chromomycin A3 and bisantrene HCl and one DNA-directed inhibitor of transcription, actinomycin D, as correlating with the activity of NSC80467 and YM155. Furthermore, both agents were shown to preferentially inhibit DNA, over RNA and protein synthesis. Thus, the ability of NSC80467 and YM155 to induce a DNA damage response was examined further. Treatment of PC3 cells with either agent resulted in dose-dependent induction of γH2AX and pKAP1, two markers of DNA damage. The concentrations of agent required to stimulate γH2AX were considerably lower than those required to inhibit survivin, implicating DNA damage as an initiating event. The DNA damage response was then confirmed in a panel of cell lines treated with NSC80467 or YM155, suggesting that γH2AX and pKAP1 have potential as response biomarkers.ConclusionsThese data provide the first evidence that NSC80467 and YM155 are DNA damaging agents where suppression of survivin is a secondary event, likely a consequence of transcriptional repression.

Therapeutic vulnerability of an in vivo model of alveolar soft part sarcoma (ASPS) to antiangiogenic therapy.

In vivo growth of alveolar soft part sarcoma (ASPS) was achieved using subcutaneous xenografts in sex-matched nonobese diabetic severe combined immunodeficiency mice. One tumor, currently at passage 6, has been maintained in vivo for 32 months and has maintained characteristics consistent with those of the original ASPS tumor including (1) tumor histology and staining with periodic acid Schiff/diastase, (2) the presence of the ASPL-TFE3 type 1 fusion transcript, (3) nuclear staining with antibodies to the ASPL-TFE3 type 1 fusion protein, (4) maintenance of the t(X;17)(p11;q25) translocation characteristic of ASPS, (5) stable expression of signature ASPS gene transcripts and finally, the development and maintenance of a functional vascular network, a hallmark of ASPS. The ASPS xenograft tumor vasculature encompassing nests of ASPS cells is highly reactive to antibodies against the endothelial antigen CD34 and is readily accessible to intravenously administered fluorescein isothiocyanate-dextran. The therapeutic vulnerability of this tumor model to antiangiogenic therapy, targeting vascular endothelial growth factor and hypoxia-inducible factor-1 alpha, was examined using bevacizumab and topotecan alone and in combination. Together, the 2 drugs produced a 70% growth delay accompanied by a 0.7 net log cell kill that was superior to the antitumor effect produced by either drug alone. In summary, this study describes a preclinical in vivo model for ASPS which will facilitate investigation into the biology of this slow growing soft tissue sarcoma and demonstrates the feasibility of using an antiangiogenic approach in the treatment of ASPS.

Proteomic Analysis Identifies Oxidative Stress Induction by Adaphostin

Purpose: Activities distinct from inhibition of Bcr/abl have led to adaphostin (NSC 680410) being described as “a drug in search of a mechanism.” In this study, proteomic analysis of adaphostin-treated myeloid leukemia cell lines was used to further elucidate a mechanism of action. Experimental Design: HL60 and K562 cells treated with adaphostin for 6, 12, or 24 h were analyzed using two-dimensional PAGE. Differentially expressed spots were excised, digested with trypsin, and analyzed by liquid chromatography–tandem mass spectrometry. The contribution of the redox-active hydroquinone group in adaphostin was also examined by carrying out proteomic analysis of HL60 cells treated with a simple hydroquinone (1,4-dihydroxybenzene) or H2O2. Results: Analysis of adaphostin-treated cells identified 49 differentially expressed proteins, the majority being implicated in the response to oxidative stress (e.g., CALM, ERP29, GSTP1, PDIA1) or induction of apoptosis (e.g., LAMA, FLNA, TPR, GDIS). Interestingly, modulation of these proteins was almost fully prevented by inclusion of an antioxidant, N-acetylcysteine. Validation of the proteomic data confirmed GSTP1 as an adaphostin resistance gene. Subsequent analysis of HL60 cells treated with 1,4-dihydroxybenzene or H2O2 showed similar increases in intracellular peroxides and an almost identical proteomic profiles to that of adaphostin treatment. Western blotting of a panel of cell lines identified Cu/Zn superoxide dismutase (SOD) as correlating with adaphostin resistance. The role of SOD as a second adaphostin resistance gene was confirmed by demonstrating that inhibition of SOD using diethyldithiocarbamate increased adaphostin sensitivity, whereas transfection of SOD I attenuated toxicity. Importantly, treatment with 1,4-dihydroxybenzene or H2O2 replicated adaphostin-induced Bcr/abl polypeptide degradation, suggesting that kinase inhibition is a ROS-dependent phenomenon. Conclusion: Adaphostin should be classified as a redox-active–substituted dihydroquinone.

ARC (NSC 188491) has identical activity to Sangivamycin (NSC 65346) including inhibition of both P-TEFb and PKC.

BackgroundThe nucleoside analog, ARC (NSC 188491) is a recently characterized transcriptional inhibitor that selectively kills cancer cells and has the ability to perturb angiogenesis in vitro. In this study, the mechanism of action of ARC was further investigated by comparing in vitro and in vivo activity with other anti-neoplastic purines.MethodsStructure-based homology searches were used to identify those compounds with similarity to ARC. Comparator compounds were then evaluated alongside ARC in the context of viability, cell cycle and apoptosis assays to establish any similarities. Following this, biological overlap was explored in detail using gene-expression analysis and kinase inhibition assays.ResultsResults demonstrated that sangivamycin, an extensively characterized pro-apoptotic nucleoside isolated from Streptomyces, had identical activity to ARC in terms of 1) cytotoxicity assays, 2) ability to induce a G2/M block, 3) inhibitory effects on RNA/DNA/protein synthesis, 4) transcriptomic response to treatment, 5) inhibition of protein kinase C, 6) inhibition of positive transcription elongation factor b (P-TEFb), 7) inhibition of VEGF secretion, and 8) activity within hollow fiber assays. Extending ARC activity to PKC inhibition provides a molecular basis for ARC cancer selectivity and anti-angiogenic effects. Furthermore, functional overlap between ARC and sangivamycin suggests that development of ARC may benefit from a retrospective of previous sangivamycin clinical trials. However, ARC was found to be inactive in several xenograft models, likely a consequence of rapid serum clearance.ConclusionOverall, these data expand on the biological properties of ARC but suggest additional studies are required before it can be considered a clinical trials candidate.

Challenges in plasma membrane phosphoproteomics

The response to extracellular stimuli often alters the phosphorylation state of plasma membrane- associated proteins. In this regard, generation of a comprehensive membrane phosphoproteome can significantly enhance signal transduction and drug mechanism studies. However, analysis of this subproteome is regarded as technically challenging, given the low abundance and insolubility of integral membrane proteins, combined with difficulties in isolating, ionizing and fragmenting phosphopeptides. In this article, we highlight recent advances in membrane and phosphoprotein enrichment techniques resulting in improved identification of these elusive peptides. We also describe the use of alternative fragmentation techniques, and assess their current and future value to the field of membrane phosphoproteomics.

ASPS-1, a novel cell line manifesting key features of alveolar soft part sarcoma.

In vitro growth of alveolar soft part sarcoma (ASPS) and establishment of an ASPS cell line, ASPS-1, are described in this study. Using a recently developed xenograft model of ASPS derived from a lymph node metastasis, organoid nests consisting of 15 to 25 ASPS cells were isolated from ASPS xenograft tumors by capture on 70 &mgr;m filters and plated in vitro. After attachment to the substratum, these nests deposited small aggregates of ASPS cells. These cells grew slowly and were expanded over a period of 3 years and have maintained characteristics consistent with those of both the original ASPS tumor from the patient and the xenograft tumor including (1) presence of the alveolar soft part locus-transcription factor E3 type 1 fusion transcript and nuclear expression of the alveolar soft part locus-transcription factor E3 type 1 fusion protein; (2) maintenance of the t(X;17)(p11;q25) translocation characteristic of ASPS; and (3) expression of upregulated ASPS transcripts involved in angiogenesis (ANGPTL2, HIF-1-&agr;, MDK, c-MET, VEGF, and TIMP-2), cell proliferation (PRL, PCSK1), metastasis (ADAM9), as well as the transcription factor BHLHB3 and the muscle-specific transcripts TRIM63 and ITG&bgr;1BP3. This ASPS cell line forms colonies in soft agar and retains the ability to produce highly vascularized ASPS tumors in NOD.SCID/NCr mice. Immunohistochemistry of selected ASPS markers on these tumors indicated similarity to those of the original patient tumor as well as to the xenografted ASPS tumor. We anticipate that this ASPS cell line will accelerate investigations into the biology of ASPS including identification of new therapeutic approaches for treatment of this slow growing soft tissue sarcoma.