Role of hydroxyl radicals in radiation-induced activation of lyn tyrosine kinase in human B-cell precursors

Weak Magnetic Fields Enhance the Efficacy of Radiation Therapy

Purpose

The clinical efficacy of radiation therapy is mechanistically linked to ionization-induced free radicals that cause cell and tissue injury through direct and indirect mechanisms. Free radical reaction dynamics are influenced by many factors and can be manipulated by static weak magnetic fields (WMF) that perturb singlet-triplet state interconversion. Our study exploits this phenomenon to directly increase ionizing radiation (IR) dose absorption in tumors by combining WMF with radiation therapy as a new and effective method to improve treatment.

Methods and Materials

Coils were custom made to produce both homogeneous and gradient magnetic fields. The gradient coil enabled simultaneous in vitro assessment of free radical/reactive oxygen species reactivity across multiple field strengths from 6 to 66 G. First, increases in IR-induced free radical concentrations using oxidant-sensitive fluorescent dyes in a cell-free system were measured and verified. Next, human and murine cancer cell lines were evaluated in in vitro and in vivo models after exposure to clinically relevant doses of IR in combination with WMF.

Results

Cellular responses to IR and WMF were field strength and cell line dependent. WMF was able to enhance IR effects on reactive oxygen species formation, DNA double-strand break formation, cell death, and tumor growth.

Conclusions

We demonstrate that the external presence of a magnetic field enhances radiation-induced cancer cell injury and death in vitro and in vivo. The effect extends beyond the timeframe when free radicals are induced in the presence of radiation into the window when endogenous free radicals are produced and therefore extends the applicability of this novel adjunct to cancer therapy in the context of radiation treatment.

Enhancement of apoptotic damage of squamous cell carcinoma cells by inhibition of the mitochondrial DNA repairing system

Mitochondrial DNA (mtDNA) repair systems are thought to be associated with the susceptibility of cancer cells to anticancer agents. The present study investigated the relationship between the susceptibility to gamma-rays and the mtDNA repair ability of oral squamous cell carcinoma (OSC) cell lines. The levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and mtDNA common deletion in both nuclear and mitochondrial DNA of OSC-2, OSC-3 and OSC-6 cells (radio-sensitive cell lines) after gamma-ray-irradiation were higher than those of OSC-1, OSC-4 and OSC-5 cells (radio-resistant cell lines). Compared with OSC-2, OSC-3 and OSC-6 cells, OSC-1, OSC-4 and OSC-5 cells had higher levels of activity of phosphoinositide-3 kinase (PI-3K)/Akt and more strongly expressed 8-hydroxyguanine DNA glycosylase (OGG1), DNA polymerase gamma (POLG) and mitochondrial transcription factor A (Tfam). Down-regulation of these mtDNA-repair-associated molecules by the RNA interference technique enhanced the susceptibility of OSC-2 and OSC-5 cells to gamma-rays, and the expression of Tfam and POLG was down-regulated by inhibitors of PI-3K/Akt signaling. These results indicate that the inhibition of mtDNA repair capacity by PI-3K/Akt signal inhibitors and OGG1 down-regulator in cancer cells may be a useful strategy for cancer treatment when combined with ionizing irradiation and chemotherapeutic drugs.

Glucose deprivation-induced oxidative stress in human tumor cells. A fundamental defect in metabolism?

Recently, glucose deprivation-induced oxidative stress has been shown to cause cytotoxicity, activation of signal transduction (i.e., ERK1, ERK2, JNK, and Lyn kinase), and increased expression of genes associated with malignancy (i.e., bFGF and c-Myc) in MCF-7/ADR human breast cancer cells. These results have led to the proposal that intracellular oxidation/reduction reactions involving hydroperoxides and thiols may provide a mechanistic link between metabolism, signal transduction, and gene expression in these human tumor cells. The current study shows that several other transformed human cell types appear to be more susceptible to glucose deprivation-induced cytotoxicity and oxidative stress than untransformed human cell types. In a matched pair of normal and SV40-transformed human fibroblasts the cytotoxic process is shown to be dependent upon ambient O2 concentration. A theoretical model to explain the results is presented and implications to unifying modern theories of cancer are discussed.

Metabolic oxidative stress activates signal transduction and gene expression during glucose deprivation in human tumor cells

The mechanism of glucose deprivation-induced activation of Lyn kinase (Lyn), c-Jun N-terminal kinase 1 (JNK1) and increased expression of basic fibroblast growth factor (bFGF) and c-Myc was investigated in MCF-7/ADR adriamycin-resistant human breast carcinoma cells. Glucose deprivation significantly increased steady state levels of oxidized glutathione content (GSSG) and intracellular prooxidants (presumably hydroperoxides) as well as caused the activation of Lyn, JNK1, and the accumulation of bFGF and c-Myc mRNA. The suppression of GSSG accumulation and prooxidant production by treatment with the thiol antioxidant, N-acetylcysteine, also suppressed all the increases in kinase activation and gene expression observed during glucose deprivation. In addition, glucose deprivation was shown to induce oxidative stress in IMR90 SV40 transformed human fibroblasts, indicating that this phenomena is not limited to the MCF-7/ADR cell line. These and previous observations from our laboratory show that glucose deprivation-induced oxidative stress in MCF-7/ADR cells activates signal transduction involving Lyn, JNK1, and mitogen activated protein kinases (ERK1/ERK2) which results in increased bFGF and c-Myc mRNA accumulation. These results provide support for the hypothesis that alterations in intracellular oxidation/reduction reactions link changes in glycolytic metabolism to signal transduction and gene expression in these human tumor cells.

Bruton's tyrosine kinase (BTK) as a dual-function regulator of apoptosis

Multiple counterregulatory mechanisms have been identified in B-cell precursors that operate to regulate cell survival and growth, thereby ensuring the orderly development and differentiation of B-cells. Inappropriate apoptosis may underlie the pathogenesis of immunodeficiencies, as well as pathogenesis and drug/radiation resistance of human leukemias and lymphomas, which makes control of apoptosis an important potential target for therapeutic interventions. Therefore, identification of the molecular regulators of apoptosis is an area of intense investigation. Bruton's tyrosine kinase (BTK) is the first tyrosine kinase to be identified as a dual-function regulator of apoptosis, which promotes radiation-induced apoptosis but inhibits Fas-activated apoptosis in B-cells. BTK functions in a pro-apoptotic manner when B-cells are exposed to reactive oxygen intermediates, at least in part, by down-regulating the anti-apoptotic activity of STAT-3 transcription factor. In contrast, BTK associates with the death receptor Fas and impairs its interaction with Fas-associated protein with death domain (FADD), which is essential for the recruitment and activation of FLICE by Fas during the apoptotic signal, thereby preventing the assembly of a pro-apoptotic death inducing signaling complex (DISC) after Fas-ligation. The identification of BTK as a dual-function regulator of apoptosis will significantly increase our understanding of both the biological processes involved in programmed cell death and the diseases associated with dysregulation of apoptosis. New agents with BTK-modulatory activity may have clinical potential in the treatment of B-cell malignancies (in particular acute lymphoblastic leukemia, the most common form of childhood cancer), as well as B-cell immunodeficiencies.

Local inhibition of tyrosine kinase activity markedly attenuates the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Intimal hyperplasia is due to the migration and proliferation of vascular smooth muscle cells after bypass surgery. Tyrosine kinases are involved in many signal transduction pathways including cell proliferation. This study examines the effects of local treatment with the tyrosine kinase inhibitor, tyrphostin AG-51, on the formation of intimal hyperplasia in vein grafts.

MATERIALS AND METHODS

Thirty-nine New Zealand White rabbits underwent interposition bypass grafting of the carotid artery using the jugular vein. In the first group (TKI), tyrphostin AG-51 (5 mg), dissolved in 600 microliter of dimethyl sulfoxide and Ringer's lactate (2:1, v:v), was used to incubate the veins ex vivo prior to grafting and delivered locally in 2.5 ml of 30% pluronic gel after grafting. The second group (DMSO) received the same treatment but without tyrphostin. In the third group (control), tyrphostin and DMSO were omitted from the incubation and gel delivery solutions. Postoperatively, vein grafts were harvested on Day 3 for Western analysis using an antiphosphotyrosine antibody (PY-20) to assess for tyrosine kinase activity, and on Day 28 for either morphologic or contractile function studies.

RESULTS

Local application of the TKI to vein grafts resulted in a 49% reduction in intimal hyperplasia compared to DMSO-treated vein grafts (31 +/- 4 micrometer vs. 61 +/- 5 micrometer, P < 0.01). Treatment with DMSO alone reduced intimal hyperplasia by 28% compared to control (85 +/- 4 micrometer, P < 0.05). The contractile responses in the DMSO and TKI-treated vein grafts were equivalent. Western analysis showed a 39-fold decrease in tyrosine phosphorylation with TKI treatment compared to control.

CONCLUSION

This study demonstrates that local short-term treatment with TKI produces a 49% reduction in intimal hyperplasia and suggests that phosphorylation of tyrosine residues is involved in the signaling pathways leading to the development of intimal hyperplasia in vein grafts.