Xiuquan Luo

Superparamagnetic Iron Oxide Nanoparticles: Amplifying ROS Stress to Improve Anticancer Drug Efficacy

Superparamagnetic iron oxide nanoparticles (SPION) are an important and versatile nano- platform with broad biological applications. Despite extensive studies, the biological and pharmacological activities of SPION have not been exploited in therapeutic applications. Recently, β-lapachone (β-lap), a novel anticancer drug, has shown considerable cancer specificity by selectively increasing reactive oxygen species (ROS) stress in cancer cells. In this study, we report that pH-responsive SPION-micelles can synergize with β-lap for improved cancer therapy. These SPION-micelles selectively release iron ions inside cancer cells, which interact with hydrogen peroxide (H2O2) generated from β-lap in a tumor-specific, NQO1-dependent manner. Through Fenton reactions, these iron ions escalate the ROS stress in β-lap-exposed cancer cells, thereby greatly enhancing the therapeutic index of β-lap. More specifically, a 10-fold increase in ROS stress was detected in β-lap-exposed cells pretreated with SPION-micelles over those treated with β-lap alone, which also correlates with significantly increased cell death. Catalase treatment of cells or administration of an iron chelator can block the therapeutic synergy. Our data suggest that incorporation of SPION-micelles with ROS-generating drugs can potentially improve drug efficacy during cancer treatment, thereby provides a synergistic strategy to integrate imaging and therapeutic functions in the development of theranostic nanomedicine.

Targeting glutamine metabolism sensitizes pancreatic cancer to PARP-driven metabolic catastrophe induced by ß-lapachone

BackgroundPancreatic ductal adenocarcinomas (PDA) activate a glutamine-dependent pathway of cytosolic nicotinamide adenine dinucleotide phosphate (NADPH) production to maintain redox homeostasis and support proliferation. Enzymes involved in this pathway (GLS1 (mitochondrial glutaminase 1), GOT1 (cytoplasmic glutamate oxaloacetate transaminase 1), and GOT2 (mitochondrial glutamate oxaloacetate transaminase 2)) are highly upregulated in PDA, and among these, inhibitors of GLS1 were recently deployed in clinical trials to target anabolic glutamine metabolism. However, single-agent inhibition of this pathway is cytostatic and unlikely to provide durable benefit in controlling advanced disease.ResultsHere, we report that reducing NADPH pools by genetically or pharmacologically (bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES) or CB-839) inhibiting glutamine metabolism in mutant Kirsten rat sarcoma viral oncogene homolog (KRAS) PDA sensitizes cell lines and tumors to ß-lapachone (ß-lap, clinical form ARQ761). ß-Lap is an NADPH:quinone oxidoreductase (NQO1)-bioactivatable drug that leads to NADPH depletion through high levels of reactive oxygen species (ROS) from the futile redox cycling of the drug and subsequently nicotinamide adenine dinucleotide (NAD)+ depletion through poly(ADP ribose) polymerase (PARP) hyperactivation. NQO1 expression is highly activated by mutant KRAS signaling. As such, ß-lap treatment concurrent with inhibition of glutamine metabolism in mutant KRAS, NQO1 overexpressing PDA leads to massive redox imbalance, extensive DNA damage, rapid PARP-mediated NAD+ consumption, and PDA cell death—features not observed in NQO1-low, wild-type KRAS expressing cells.ConclusionsThis treatment strategy illustrates proof of principle that simultaneously decreasing glutamine metabolism-dependent tumor anti-oxidant defenses and inducing supra-physiological ROS formation are tumoricidal and that this rationally designed combination strategy lowers the required doses of both agents in vitro and in vivo. The non-overlapping specificities of GLS1 inhibitors and ß-lap for PDA tumors afford high tumor selectivity, while sparing normal tissue.

ATM Regulates Insulin-Like Growth Factor 1-Secretory Clusterin (IGF-1-sCLU) Expression that Protects Cells against Senescence

Downstream factors that regulate the decision between senescence and cell death have not been elucidated. Cells undergo senescence through three pathways, replicative senescence (RS), stress-induced premature senescence (SIPS) and oncogene-induced senescence. Recent studies suggest that the ataxia telangiectasia mutant (ATM) kinase is not only a key protein mediating cellular responses to DNA damage, but also regulates cellular senescence induced by telomere end exposure (in RS) or persistent DNA damage (in SIPS). Here, we show that expression of secretory clusterin (sCLU), a known pro-survival extracellular chaperone, is transcriptionally up-regulated during both RS and SIPS, but not in oncogene-induced senescence, consistent with a DNA damage-inducible mechanism. We demonstrate that ATM plays an important role in insulin-like growth factor 1 (IGF-1) expression, that in turn, regulates downstream sCLU induction during senescence. Loss of ATM activity, either by genomic mutation (ATM-deficient fibroblasts from an ataxia telangiectasia patient) or by administration of a chemical inhibitor (AAI, an inhibitor of ATM and ATR), blocks IGF-1-sCLU expression in senescent cells. Downstream, sCLU induction during senescence is mediated by IGF-1R/MAPK/Egr-1 signaling, identical to its induction after DNA damage. In contrast, administration of an IGF-1 inhibitor caused apoptosis of senescent cells. Thus, IGF-1 signaling is required for survival, whereas sCLU appears to protect cells from premature senescence, as IMR-90 cells with sCLU knockdown undergo senescence faster than control cells. Thus, the ATM-IGF-1-sCLU pathway protects cells from lethality and suspends senescence.

ATM-dependent IGF-1 induction regulates secretory clusterin expression after DNA damage and in genetic instability

Secretory clusterin (sCLU) is a stress-induced, pro-survival glycoprotein elevated in early-stage cancers, in particular in APC/Min-defective colon cancers. sCLU is upregulated after exposure to various cytotoxic agents, including ionizing radiation (IR), leading to a survival advantage. We found that stimulation of insulin-like growth factor-1 (IGF-1) and IGF-1R protein kinase signaling was required for sCLU induction after IR exposure. Here, we show that activation of Ataxia telangiectasia-mutated kinase (ATM) by endogenous or exogenous forms of DNA damage was required to relieve basal repression of IGF-1 transcription by the p53/NF-YA complex, leading to sCLU expression. Although p53 levels were stabilized and elevated after DNA damage, dissociation of NF-YA, and thereby p53, from the IGF-1 promoter resulted in IGF-1 induction, indicating that NF-YA was rate limiting. Cells with elevated endogenous DNA damage (deficient in H2AX, MDC1, NBS1, mTR or hMLH1) or cells exposed to DNA-damaging agents had elevated IGF-1 expression, resulting in activation of IGF-1R signaling and sCLU induction. In contrast, ATM-deficient cells were unable to induce sCLU after DNA damage. Our results integrate DNA damage resulting from genetic instability, IR, or chemotherapeutic agents, to ATM activation and abrogation of p53/NF-YA-mediated IGF-1 transcriptional repression, that induces IGF-1–sCLU expression. Elucidation of this pathway should uncover new mechanisms for cancer progression and reveal new targets for drug development to overcome resistance to therapy.

Tumor-selective use of DNA base excision repair inhibition in pancreatic cancer using the NQO1 bioactivatable drug, β-lapachone.

Base excision repair (BER) is an essential pathway for pancreatic ductal adenocarcinoma (PDA) survival. Attempts to target this repair pathway have failed due to lack of tumor-selectivity and very limited efficacy. The NAD(P)H:Quinone Oxidoreductase 1 (NQO1) bioactivatable drug, ß-lapachone (ARQ761 in clinical form), can provide tumor-selective and enhanced synergy with BER inhibition. ß-Lapachone undergoes NQO1-dependent futile redox cycling, generating massive intracellular hydrogen peroxide levels and oxidative DNA lesions that stimulate poly(ADP-ribose) polymerase 1 (PARP1) hyperactivation. Rapid NAD+/ATP depletion and programmed necrosis results. To identify BER modulators essential for repair of ß-lapachone-induced DNA base damage, a focused synthetic lethal RNAi screen demonstrated that silencing the BER scaffolding protein, XRCC1, sensitized PDA cells. In contrast, depleting OGG1 N-glycosylase spared cells from ß-lap-induced lethality and blunted PARP1 hyperactivation. Combining ß-lapachone with XRCC1 knockdown or methoxyamine (MeOX), an apyrimidinic/apurinic (AP)-modifying agent, led to NQO1-dependent synergistic killing in PDA, NSCLC, breast and head and neck cancers. OGG1 knockdown, dicoumarol-treatment or NQO1- cancer cells were spared. MeOX + ß-lapachone exposure resulted in elevated DNA double-strand breaks, PARP1 hyperactivation and TUNEL+ programmed necrosis. Combination treatment caused dramatic antitumor activity, enhanced PARP1-hyperactivation in tumor tissue, and improved survival of mice bearing MiaPaca2-derived xenografts, with 33% apparent cures. Significance: Targeting base excision repair (BER) alone has limited therapeutic potential for pancreatic or other cancers due to a general lack of tumor-selectivity. Here, we present a treatment strategy that makes BER inhibition tumor-selective and NQO1-dependent for therapy of most solid neoplasms, particularly for pancreatic cancer.

Low dose IR-induced IGF-1-sCLU expression: a p53-repressed expression cascade that interferes with TGFβ1 signaling to confer a pro-survival bystander effect

Inadvertent mammalian tissue exposures to low doses of ionizing radiation (IR) after radiation accidents, remediation of radioactive-contaminated areas, space travel or a dirty bomb represent an interesting trauma to an organism. Possible low-dose IR-induced bystander effects could impact our evaluation of human health effects, as cells within tissue are not equally damaged after doses of IR ⩽10 cGy. To understand tissue responses after low IR doses, we generated a reporter system using the human clusterin promoter fused to firefly luciferase (hCLUp-Luc). Secretory clusterin (sCLU), an extracellular molecular chaperone, induced by low doses of cytotoxic agents, clears cell debris. Low-dose IR (⩾2 cGy) exposure induced hCLUp-Luc activity with peak levels at 96 h, consistent with endogenous sCLU levels. As doses increased (⩾1 Gy), sCLU induction amplitudes increased and time-to-peak response decreased. sCLU expression was stimulated by insulin-like growth factor-1, but suppressed by p53. Responses in transgenic hCLUp-Luc reporter mice after low IR doses showed that specific tissues (that is, colon, spleen, mammary, thymus and bone marrow) of female mice induced hCLUp-Luc activity more than male mice after whole body (⩾10 cGy) irradiation. Tissue-specific, non-linear dose- and time-responses of hCLUp-Luc and endogenous sCLU levels were noted. Colon maintained homeostatic balance after 10 cGy. Bone marrow responded with delayed, but prolonged and elevated expression. Intraperitoneal administration of α-transforming growth factor (TGF)β1 (1D11), but not control (13C4) antibodies, immediately following IR exposure abrogated CLU induction responses. Induction in vivo also correlated with Smad signaling by activated TGFβ1 after IR. Mechanistically, media with elevated sCLU levels suppressed signaling, blocked apoptosis and increased survival of TGFβ1-exposed tumor or normal cells. Thus, sCLU is a pro-survival bystander factor that abrogates TGFβ1 signaling and most likely promotes wound healing.

Prodrug strategy to achieve lyophilizable, high drug loading micelle formulations through diester derivatives of β-Lapachone.

β-Lap prodrug micelle strategy improves the formulation properties of β-lap therapeutics. The resulting micelles yield apparent high β-lap solubility (>7 mg mL(-1) ), physical stability, and ability to reconstitute after lyophilization. In the presence of esterase, β-lap prodrugs are efficiently converted into parent drug (i.e., β-lap), resulting in NQO1-dependent lethality of NSCLC cells.

The NQO1 bioactivatable drug, β-lapachone, alters the redox state of NQO1+ pancreatic cancer cells, causing perturbation in central carbon metabolism

Many cancer treatments, such as those for managing recalcitrant tumors like pancreatic ductal adenocarcinoma, cause off-target toxicities in normal, healthy tissue, highlighting the need for more tumor-selective chemotherapies. β-Lapachone is bioactivated by NAD(P)H:quinone oxidoreductase 1 (NQO1). This enzyme exhibits elevated expression in most solid cancers and therefore is a potential cancer-specific target. β-Lapachones therapeutic efficacy partially stems from the drugs induction of a futile NQO1-mediated redox cycle that causes high levels of superoxide and then peroxide formation, which damages DNA and causes hyperactivation of poly(ADP-ribose) polymerase, resulting in extensive NAD+/ATP depletion. However, the effects of this drug on energy metabolism due to NAD+ depletion were never described. The futile redox cycle rapidly consumes O2, rendering standard assays of Krebs cycle turnover unusable. In this study, a multimodal analysis, including metabolic imaging using hyperpolarized pyruvate, points to reduced oxidative flux due to NAD+ depletion after β-lapachone treatment of NQO1+ human pancreatic cancer cells. NAD+-sensitive pathways, such as glycolysis, flux through lactate dehydrogenase, and the citric acid cycle (as inferred by flux through pyruvate dehydrogenase), were down-regulated by β-lapachone treatment. Changes in flux through these pathways should generate biomarkers useful for in vivo dose responses of β-lapachone treatment in humans, avoiding toxic side effects. Targeting the enzymes in these pathways for therapeutic treatment may have the potential to synergize with β-lapachone treatment, creating unique NQO1-selective combinatorial therapies for specific cancers. These findings warrant future studies of intermediary metabolism in patients treated with β-lapachone.

Abstract 4614: β-lapachone suppresses glucose metabolism in a NQO1-dependent, tumor-selective manner.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC β-Lapachone (β-lap) is a very unique quinone that can be reduced by two-electron oxidoreductase, NQO1, but unlike most other quinones, its hydroquinone form is unstable and spontaneously oxidizes back to β-lap in two steps. This redox cycle occurs in a futile manner in which one mole of β-lap generates ∼120 moles of superoxide in two minutes, causing predominately DNA base and single strand break damage. This results in PARP1 hyperactivation and programmed necrosis in an NQO1-dependent manner. Most solid cancers, such as nearly 90% of pancreatic and non-small cell lung cancers have 10- to 40- fold of elevated levels of NQO1. Since β-lap causes DNA damage that is dependent on NQO1 expression, and therefore tumor-selective for most solid cancers, use of this ‘NQO1 bioactivatable’ drug is perfect for improving efficacy of cancer therapy. Our recent work also showed that β-lap efficaciously kills pancreatic cancer cells in an NQO1-dependent manner (Li et al., Clin. Cancer Res., 2011). In mechanism of action studies of β-lap, we found that PARP1 hyperactivation led to dramatic depletion of NAD+ and ATP pools in NQO1+ cancer cells (Bentle et al., JBC, 2006). Since NAD+ is a key cofactor for many enzymes in cellular metabolism, we theorized that NAD+ loss may significantly affect cellular metabolism and energy generation. To elucidate how β-lap affects metabolism, we examined metabolites using 13C-labeled glucose. After two hours exposure of β-lap, glucose utilization in MiaPaca-2 cells was completely repressed, lasting 12 h after removal of β-lap. β-Lap treatment also inhibited lactate generation, indicating a suppression of glycolysis after β-lap treatment. In examining metabolic recovery, however, we found that the TCA cycle was not, or only moderately affected by β-lap, indicating that this metabolic process was essential for recovery from this agent. A proportion of 13C-labeled metabolites (i.e., citrate, fumarate) generated by TCA cycle increased vs untreated control cells. Consistently, ATP levels in β-lap-treated NQO1+ pancreatic cancer cells gradually recovered from <10% of untreated cells to ∼50% in 12 h. These data indicate that β-lap predominately represses glycolysis, while the TCA cycle remains functional and possibly the only source of ATP production in the cell. Our results indicated that β-lap a very unique DNA damage-inducing NQO1-dependent agent that simultaneously suppresses glucose metabolism and energy generation. This may explain why β-lap is so potent in cell death induction in comparison with other DNA damage-inducing agents. Further studies will be performed to elucidate the exact mechanism how β-lap represses glycolysis while apparently stimulating the TCA cycle. Understanding how cells recover from β-lap exposures should shed light on improved therapies for NQO1 bioactivatable drugs. This work was supported by an AACR Innovator Award from the George and June Block Foundation to DAB. Citation Format: Xiuquan Luo, Malina Patel, Longshan Li, Ralph Deberardinis, David A. Boothman. β-lapachone suppresses glucose metabolism in a NQO1-dependent, tumor-selective manner. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4614. doi:10.1158/1538-7445.AM2013-4614

Abstract 3344: Inhibiting base excision repair synergistically enhances beta-lapachone-mediated ‘kiss of death’ for tumor-selective therapy of pancreatic cancer.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Pancreatic cancer will be the second leading cause of cancer-related deaths in the US by 2020, where 5-year survival is <6%. Current standard of care therapies offer little selectivity and high toxicity. Novel, tumor-selective approaches are desperately needed. Nearly 90% of pancreatic cancers have elevated levels (10- to 40-fold) NQO1 and we recently showed that beta-lapachone (beta-lap) was efficacious against pancreatic cancers in an NQO1-dependent manner (Li et al., Clin. Cancer Res., 2011). Beta-Lap is reduced by NQO1 like most quinones, but unlike most, its hydroquinone form is unstable and spontaneously redox cycles in a futile manner where one mole of beta-lap generates ∼120 moles of superoxide in two mins., inducing predominately DNA base and single strand break (SSB) damage. This results in PARP1 hyperactivation and programmed necrosis, killing NQO1+ cancer cells independent of: i, p53; ii, cell cycle; iii, all known oncogenic drivers; and iv, apoptotic/antiapoptotic gene expression (e.g., Bax, Bak, Bcl2). This ‘NQO1 bioactivatable drug’ is tumor-selective and a perfect candidate for improving efficacy of pancreatic cancer therapy. To improve its efficacy, we examined the synergistic effects of adding the AP site-modifying drug and base excision repair (BER) inhibitor, methoxyamine (MeOX), with beta-lap against NQO1 over-expressing pancreatic cancer cells. MeOX + beta-lap synergy resulted in: a, enhanced lethality of sublethal doses of beta-lap, reducing the shoulder (Dq), increasing the lethality rate (Do), and inducing apoptosis (TUNEL+) in NQO1+, but not in NQO1-, MIA PaCa-2 cells; b, increased DNA lesion formation; c, dramatic losses in ATP levels, with little recovery; and d, dramatic suppression of glycolysis. These data strongly suggests that MeOX enhances PARP1 hyperactivation and synergistic cell killing of beta-lap. Similar results were noted in shRNA-XRCC1 knockdown cells. Mechanistically, our data suggests that PARP1 detects MeOX-AP modified sites or SSBs, allowing PARP1 hyperactivation and synergistic cell death. Since MeOX is a nontoxic agent, and both agents are currently in clinical trials (i.e., beta-lap as Arq761, Arqule, Boston, MA), combination therapies for the treatment of pancreatic, as well as other NQO1 over-expressing solid cancers could be rapidly developed. An AACR Innovator Award from the George and June Block Foundation to DAB supported this work. Citation Format: Xiuquan Luo, Longshan Li, Xiumei Huang, Lifen Cao, Zachary Moore, Ralph Deberardinis, Rolf Brekken, Stanton Gerson, Lili Liu, David A. Boothman. Inhibiting base excision repair synergistically enhances beta-lapachone-mediated ‘kiss of death’ for tumor-selective therapy of pancreatic cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3344. doi:10.1158/1538-7445.AM2013-3344