Gerardo G. Mackenzie

Epicatechin, catechin, and dimeric procyanidins inhibit PMA-induced NF-κB activation at multiple steps in Jurkat T cells

The capacity of the flavan‐3‐ols [(–)‐epicatechin (EC) and (+)‐catechin (CT)] and a B dimeric procyanidin (DP‐B) to modulate phorbol 12‐myristate 13‐acetate (PMA)‐induced NF‐κB activation in Jurkat T cells was investigated. The classic PMA‐triggered increase in cell oxidants was prevented when cells were preincubated for 24 h with EC, CT, or DP‐B (1.7–17.2 μM). PMA induced the phosphorylation of IKKβ and the subsequent degradation of IκBα: These events were inhibited in cells pretreated with the flavonoids. PMA induced a 4.6‐fold increase in NF‐κB nuclear binding activity in control cells. Pretreatment with EC, CT, or DP‐B decreased PMA‐induced NF‐κB binding activity and the transactivation of the NF‐κB‐driven gene IL‐2. EC, CT, and DP‐B inhibited, in vitro, NF‐κB binding to its DNA consensus sequence, but they had no effect on the binding activity of CREB or OCT‐1. Thus, EC, CT, or DP‐B can influence the immune response by modulating NF‐κB activation. This modulation can occur at early (regulation of oxidant levels, IKK activation) as well as late (binding of NF‐κB to DNA) stages of the NF‐κB activation cascade. A model is presented for possible interactions between DP‐B and NF‐κB proteins, which could lead to the inhibition of NF‐κB binding to κB sites.

Curcumin induces cell‐arrest and apoptosis in association with the inhibition of constitutively active NF‐κB and STAT3 pathways in Hodgkin's lymphoma cells

Although treatment of Hodgkins lymphoma (HL) with a multi‐drug approach has been very successful, its toxicity becomes evident after several years as secondary malignancies and cardiovascular disease. Therefore, the current goal in HL treatment is to find new therapies that specifically target the deregulated signaling cascades, such as NF‐κB and STAT3, which cause Hodgkin and Reed‐Sternberg (H‐RS) cell proliferation and resistance of apoptosis. Based on the above information, we investigated the capacity of curcumin to inhibit NF‐κB and STAT3 in H‐RS cells, characterizing the functional consequences. Curcumin is incorporated into H‐RS cells and acts inhibiting both NF‐κB and STAT3 activation, leading to a decreased expression of proteins involved in cell proliferation and apoptosis, e.g. Bcl‐2, Bcl‐xL, cFLIP, XIAP, c‐IAP1, survivin, c‐myc and cyclin D1. Interestingly, curcumin caused cell cycle arrest in G2‐M and a significant reduction (80–97%) in H‐RS cell viability. Furthermore, curcumin triggered cell death by apoptosis, as evidenced by the activation of caspase‐3 and caspase‐9, changes in nuclear morphology and phosphatidylserine translocation. The above findings provide a mechanistic rationale for the potential use of curcumin as a therapeutic agent for patients with HL.

The Role of Zinc in the Modulation of Neuronal Proliferation and Apoptosis

Although a requirement of zinc (Zn) for normal brain development is well documented, the extent to which Zn can modulate neuronal proliferation and apoptosis is not clear. Thus, we investigated the role of Zn in the regulation of these two critical events. A low Zn availability leads to decreased cell viability in human neuroblastoma IMR-32 cells and primary cultures of rat cortical neurons. This occurs in part as a consequence of decreased cell proliferation and increased apoptotic cell death. In IMR-32 cells, Zn deficiency led to the inhibition of cell proliferation through the arrest of the cell cycle at the G0/G1 phase. Zn deficiency induced apoptosis in both proliferating and quiescent neuronal cells via the intrinsic apoptotic pathway. Reductions in cellular Zn triggered a translocation of the pro-apoptotic protein Bad to the mitochondria, cytochrome c release, and caspase-3 activation. Apoptosis is the resultant of the inhibition of the prosurvival extracellular-signal-regulated kinase, the inhibition of nuclear factor-kappa B, and associated decreased expression of antiapoptotic proteins, and to a direct activation of caspase-3. A deficit of Zn during critical developmental periods can have persistent effects on brain function secondary to a deregulation of neuronal proliferation and apoptosis.

Dimeric procyanidins are inhibitors of NF-κB–DNA binding

Given the central role of the transcription factor NF-kappaB in inflammation, molecules that can inhibit NF-kappaB are being actively investigated. The present work characterize potential interactions between dimeric procyanidins [B-type (B1 and B2) and A-type (A1 and A2)] and NF-kappaB proteins. B1 and B2, inhibited tumor necrosis factor alpha (TNFalpha)- and phorbol 12-myristate 13-acetate (PMA)-induced transactivation of NF-kappaB-driven genes and the increase of NF-kappaB-DNA nuclear binding in Jurkat T cells. B1 and B2, added in vitro to nuclear fractions, inhibited NF-kappaB binding to its DNA consensus sequence. B1 and B2 prevented the binding of RelA and p50 recombinant proteins to its DNA consensus sequence. All these effects were not observed with A1 and A2. Putative molecular models for possible interactions of B1, B2, A1 and A2, with NF-kappaB proteins were constructed, indicating that B-type dimeric procyanidins have higher possibilities of chemical interactions with NF-kappaB than A-type dimeric procyanidins. The results support the concept that B-type dimeric procyanidins can provide anti-inflammatory benefits due to their ability to reduce NF-kappaB binding to the DNA.

Microtubules are required for NF-κB nuclear translocation in neuroblastoma IMR-32 cells: modulation by zinc

The relevance of a functional cytoskeleton for Nuclear Factor‐κB (NF‐κB) nuclear translocation was investigated in neuronal cells, using conditions that led to a disruption of the cytoskeleton [inhibition of tubulin (vinblastine, colchicine), or actin (cytochalasin D) polymerization and zinc deficiency]. We present evidence that an impairment in tubulin polymerization can inhibit the formation of the complex tubulin‐dynein‐karyopherin α‐p50 that is required for neuronal retrograde and nuclear NF‐κB transport. Cells treated with vinblastine, colchicine or cytochalasin D, and zinc deficient cells, all showed a low nuclear NF‐κB binding activity, and low nuclear concentrations of RelA and p50. The altered nuclear translocation was reflected by a decreased transactivation of NF‐κB‐driven genes. The immunocytochemical characterization of cellular RelA showed that cytoskeleton disruption can lead to an altered distribution of RelA resulting in the formation of peripheral accumuli. These results support the concept that cytoskeleton integrity is necessary for the transport and translocation of NF‐κB required for synapse to nuclei communication. We suggest that during development, as well as in the adult brain, conditions such as zinc deficiency, that affect the normal structure and function of the cytoskeleton can affect neuronal proliferation, differentiation, and survival by altering NF‐κB nuclear translocation and subsequent impairment of NF‐κB‐dependent gene regulation.

Phospho-Sulindac (OXT-328), a Novel Sulindac Derivative, Is Safe and Effective in Colon Cancer Prevention in Mice

BACKGROUND & AIMS Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective cancer chemopreventive agents. However, chronic administration of NSAIDs is associated with significant side effects, mainly of the gastrointestinal tract. Given these limitations, we synthesized phospho-sulindac (P-S; OXT-328), a novel sulindac derivative. METHODS Here, we evaluated the safety and efficacy of P-S in preclinical models, including its mechanism of action with human colon cancer cell (HCCC) lines and animal tumor models. RESULTS (1) Compared with sulindac, P-S is much more potent in inhibiting the growth of cultured HCCCs and more efficacious in preventing the growth of HT-29 xenografts in nude mice. P-S also prevents the growth of intestinal tumors in Apc/Min mice. (2) In combination with difluoromethylornithine (DFMO), P-S reduced tumor multiplicity in Apc/Min mice by 90%. (3) P-S is much safer than sulindac as evidenced by its in vitro toxicologic evaluation and animal toxicity studies. Mechanistically, P-S increases the intracellular levels of reactive oxygen and nitrogen species, which are key early mediators of its chemopreventive effect. Moreover, P-S induces spermidine/spermine N(1)-acetyltransferase enzymatic activity, and together with DFMO it reduces polyamine levels in vitro and in vivo. CONCLUSIONS P-S displays considerable safety and efficacy, two pharmacologic properties that are essential for a potential cancer chemopreventive agent, and thus merits further evaluation.

Dimeric procyanidin B2 inhibits constitutively active NF-κB in Hodgkin's lymphoma cells independently of the presence of IκB mutations

Due to long-term toxicity of current Hodgkins lymphoma (HL) treatment, the present challenge is to find new therapies that specifically target deregulated signaling cascades, including NF-kappaB, which are involved in Hodgkin (H) and Reed-Sternberg (RS) cell proliferation and resistance to apoptosis. We previously presented evidence that dimeric procyanidin B2 (B2) can interact with NF-kappaB proteins inhibiting the binding of NF-kappaB to DNA. Herein, we investigated if B2, acting at a late event in NF-kappaB signaling cascade, could be effective in inhibiting NF-kappaB in H-RS cells with different mechanisms of constitutive NF-kappaB activation. B2 caused a concentration-dependent inhibition of NF-kappaB-DNA binding to a similar extent (41-48% inhibition at 25 microM B2) in all the tested H-RS cell lines (L-428, KM-H2, L-540, L-1236 and HDML-2). This was associated with the inhibition of NF-kappaB-driven gene expression, including cytokines (IL-6, TNFalpha and RANTES) and anti-apoptotic proteins (Bcl-xL, Bcl-2, XIAP and cFLIP). The finding of similar amounts of RelA and p50 proteins in the nucleus, but decreased NF-kappaB-DNA binding, even in those H-RS cells characterized by mutations in the inhibitory IkappaB proteins, supports that B2 acts by preventing the binding of NF-kappaB to DNA. B2 did not inhibit AP-1 and STAT3 constitutive activation in H-RS cells, indicating that the moderate effects of B2 on cell viability are due to the complex signaling aberrations in HL. Thus, several signaling pathways should be targeted when designing therapeutics for HL. In this regard, the capacity of B2 to inhibit NF-kappaB could be valuable in a multi-drug approach.

Targeting Mitochondrial STAT3 with the Novel Phospho-Valproic Acid (MDC-1112) Inhibits Pancreatic Cancer Growth in Mice

New agents are needed to treat pancreatic cancer, one of the most lethal human malignancies. We synthesized phospho-valproic acid, a novel valproic acid derivative, (P-V; MDC-1112) and evaluated its efficacy in the control of pancreatic cancer. P-V inhibited the growth of human pancreatic cancer xenografts in mice by 60%–97%, and 100% when combined with cimetidine. The dominant molecular target of P-V was STAT3. P-V inhibited the phosphorylation of JAK2 and Src, and the Hsp90-STAT3 association, suppressing the activating phosphorylation of STAT3, which in turn reduced the expression of STAT3-dependent proteins Bcl-xL, Mcl-1 and survivin. P-V also reduced STAT3 levels in the mitochondria by preventing its translocation from the cytosol, and enhanced the mitochondrial levels of reactive oxygen species, which triggered apoptosis. Inhibition of mitochondrial STAT3 by P-V was required for its anticancer effect; mitochondrial STAT3 overexpression rescued animals from the tumor growth inhibition by P-V. Our results indicate that P-V is a promising candidate drug against pancreatic cancer and establish mitochondrial STAT3 as its key molecular target.

Oxidative Stress Mediates through Apoptosis the Anticancer Effect of Phospho-Nonsteroidal Anti-Inflammatory Drugs: Implications for the Role of Oxidative Stress in the Action of Anticancer Agents

We assessed the relationship between oxidative stress, cytokinetic parameters, and tumor growth in response to novel phospho-nonsteroidal anti-inflammatory drugs (NSAIDs), agents with significant anticancer effects in preclinical models. Compared with controls, in SW480 colon and MCF-7 breast cancer cells, phospho-sulindac, phospho-aspirin, phospho-flurbiprofen, and phospho-ibuprofen (P-I) increased the levels of reactive oxygen and nitrogen species (RONS) and decreased GSH levels and thioredoxin reductase activity, whereas the conventional chemotherapeutic drugs (CCDs), 5-fluorouracil (5-FU), irinotecan, oxaliplatin, chlorambucil, paclitaxel, and vincristine, did not. In both cell lines, phospho-NSAIDs induced apoptosis and inhibited cell proliferation much more potently than CCDs. We then treated nude mice bearing SW480 xenografts with P-I or 5-FU that had an opposite effect on RONS in vitro. Compared with controls, P-I markedly suppressed xenograft growth, induced apoptosis in the xenografts (8.9 ± 2.7 versus 19.5 ± 3.0), inhibited cell proliferation (52.6 ± 5.58 versus 25.8 ± 7.71), and increased urinary F2-isoprostane levels (10.7 ± 3.3 versus 17.9 ± 2.2 ng/mg creatinine, a marker of oxidative stress); all differences were statistically significant. 5-FUs effects on tumor growth, apoptosis, proliferation, and F2-isoprostane were not statistically significant. F2-isoprostane levels correlated with the induction of apoptosis and the inhibition of cell growth. P-I induced oxidative stress only in the tumors, and its apoptotic effect was restricted to xenografts. Our data show that phospho-NSAIDs act against cancer through a mechanism distinct from that of various CCDs, underscore the critical role of oxidative stress in their effect, and indicate that pathways leading to oxidative stress may be useful targets for anticancer strategies.

α-Lipoic acid and N-acetyl cysteine prevent zinc deficiency-induced activation of NF-κB and AP-1 transcription factors in human neuroblastoma IMR-32 cells

This work investigated the capacity of α-lipoic acid (LA) and N-acetyl-l-cysteine (NAC) to reduce zinc deficiency-induced oxidative stress, and prevent the activation of nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), and the cross-talk between both activated cascades through β-Transducin Repeat-containing Protein (β-TrCP). IMR-32 cells were incubated in control media or media containing variable concentrations of zinc, without or with 0.5 mM LA or 1 mM NAC. Relative to control and zinc supplemented (15 μM Zn) groups, Hydrogen peroxide (H2O2) and total oxidant cell concentrations were higher, and total glutathione concentrations were lower in the zinc deficient groups (1.5 and 5 μM Zn). Both, LA and NAC, markedly reduced the increase in cell oxidants and the reduction in glutathione concentrations in the zinc deficient cells. Consistent with this, LA and NAC prevented zinc deficiency-induced activation of the early steps of NF- κB (IκBα phosphorylation) and AP-1 [c-Jun-N-terminal kinase (JNK) and p38 phophorylation] cascades, and the high NF-κB- and AP-1-DNA binding activities in total cell extracts. Thus, LA and NAC can reduce the oxidative stress associated with zinc deficiency and the subsequent triggering of NF-κB- and AP-1-activation in neuronal cells.