Effect of a hypoxic cell sensitizer doranidazole on the radiation-induced apoptosis of mouse L5178Y lymphoma cells

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

The prospective application of a hypoxic radiosensitizer, doranidazole to rat intracranial glioblastoma with blood brain barrier disruption

Background

Glioblastoma is one of the intractable cancers and is highly resistant to ionizing radiation. This radioresistance is partly due to the presence of a hypoxic region which is widely found in advanced malignant gliomas. In the present study, we evaluated the effectiveness of the hypoxic cell sensitizer doranidazole (PR-350) using the C6 rat glioblastoma model, focusing on the status of blood brain barrier (BBB).

Methods

Reproductive cell death in the rat C6 glioma cell line was determined by means of clonogenic assay. An intracranial C6 glioma model was established for the in vivo experiments. To investigate the status of the BBB in C6 glioma bearing brain, we performed the Evans blue extravasation test. Autoradiography with [¹⁴C]-doranidazole was performed to examine the distribution of doranidazole in the glioma tumor. T2-weighted MRI was employed to examine the effects of X-irradiation and/or doranidazole on tumor growth.

Results

Doranidazole significantly enhanced radiation-induced reproductive cell death in vitro under hypoxia, but not under normoxia. The BBB in C6-bearing brain was completely disrupted and [¹⁴C]-doranidazole specifically penetrated the tumor regions. Combined treatment with X-irradiation and doranidazole significantly inhibited the growth of C6 gliomas.

Conclusions

Our results revealed that BBB disruption in glioma enables BBB-impermeable radiosensitizers to penetrate and distribute in the target region. This study is the first to propose that in malignant glioma the administration of hydrophilic hypoxic radiosensitizers could be a potent strategy for improving the clinical outcome of radiotherapy without side effects.

Flow cytometry in radiation research: past, present and future

Flow cytometry is an invaluable technique in research and clinical laboratories. The technique has been applied extensively to many areas of radiation research at both the experimental and clinical level. In the past few years, there has been a significant increase in the capabilities of modern flow cytometers to undertake multicolor analysis in a user-friendly manner. The developments in cytometric technology are being matched by the rapid development of new reagents, new fluorochromes and new platforms such as bead arrays. These developments are facilitating many new applications in both basic and clinical research that have relevance for many fields of biology, including radiation research. This review provides a historical overview of the application of flow cytometry to radiobiology and an update on how technology and reagents have changed and cites examples of new applications relevant to radiation researchers. In addition, some entirely new flow instrumentation is currently under development that has significant potential for applications in radiation research.

Hypoxic regulation of glucose transport, anaerobic metabolism and angiogenesis in cancer: novel pathways and targets for anticancer therapeutics

Cancer cells require a steady source of metabolic energy in order to continue their uncontrolled growth and proliferation. Accelerated glycolysis is one of the biochemical characteristics of cancer cells. Recent work indicates that glucose transport and metabolism are essential for the posttreatment survival of tumor cells, leading to poor prognosis. Glycolytic breakdown of glucose is preceded by the transport of glucose across the cell membrane, a rate-limiting process mediated by facilitative glucose transporter proteins belonging to the facilitative glucose transporter/solute carrier GLUT/SLC2A family. Tumors frequently show overexpression of GLUTs, especially the hypoxia-responsive GLUT1 and GLUT3 proteins. There are also studies that have reported associations between GLUT expression and proliferative indices, whilst others suggest that GLUT expression may be of prognostic significance. In this article we revisit Warburg's original hypothesis and review the recent clinical and basic research on the expression of GLUT family members in human cancers and in cell lines derived from human tumors. We also explore the links between hypoxia-induced genes, glucose transporters and angiogenic factors. Hypoxic tumors are significantly more malignant, metastatic, radio- and chemoresistant and have a poor prognosis. With the discovery the oxygen-sensitive transcription factor hypoxia-inducible factor (HIF-1) has come a new understanding of the molecular link between hypoxia and deregulated glucose metabolism. HIF-1 induces a number of genes integral to angiogenesis, e.g. vascular endothelial growth factor (VEGF), a process intimately involved with metastatic spread. This knowledge may enhance existing chemotherapeutic strategies so that treatment can be more rationally applied and personalized for cancer patients.

Post-irradiation hypoxic incubation of X-irradiated MOLT-4 cells reduces apoptotic cell death by changing the intracellular redox state and modulating SAPK/JNK pathways

To elucidate radiobiological effects of hypoxia on X-ray-induced apoptosis, MOLT-4 cells were treated under four set of conditions: (1) both X irradiation and incubation under normoxia, (2) X irradiation under hypoxia and subsequent incubation under normoxia, (3) X irradiation under normoxia and subsequent incubation under hypoxia, and (4) both X irradiation and incubation under hypoxia, and the induction of apoptosis was examined by fluorescence microscopy. About 28-33% apoptosis was observed in cells treated under conditions 1 and 2, but this value was significantly reduced to around 18-20% in cells treated under conditions 3 and 4, suggesting that post-irradiation hypoxic incubation rather than hypoxic irradiation mainly caused the reduction of apoptosis. The activation and expression of apoptosis signal-related molecules SAPK/JNK, Fas and caspase-3 were also suppressed by hypoxic incubation. Effects of hypoxic incubation were canceled when cells were treated under conditions 3 and 4 with an oxygen-mimicking hypoxic cell radiosensitizer, whereas the addition of N-acetyl-L-cysteine again reduced the induction of apoptosis. From these results it was concluded that hypoxia reduced the induction of apoptosis by changing the intracellular redox state, followed by the regulation of apoptotic signals in X-irradiated MOLT-4 cells.

Effects of Hypoxia on Radiation-Responsive Stress-Activated Protein Kinase, p53, and Caspase 3 Signals in TK6 Human Lymphoblastoid Cells

Despite significant evidence of a role of hypoxia in cellular resistance to ionizing radiation–induced toxicity, the underlying molecular mechanisms remain unclear. This study focused on the influence of hypoxia on radiation-induced signals in TK6 human lymphoblastoid cells. Hypoxic (<10 ppm oxygen) and aerobic cells were exposed to equilethal doses of ionizing radiation, radiation dose ratio, 3:1 (hypoxia:air). Hypoxia alone or radiation treatment under aerobic or hypoxic conditions led to increased levels of phospho-p44/42 mitogen-activated protein kinase. Levels of phospho-p38 mitogen-activated protein kinase did not change as a result of either hypoxia or irradiation. Hypoxia alone had no effect on expression of phospho-stress-activated protein kinase (SAPK), wild-type p53, or cleaved caspase 3. Irradiation under aerobic conditions resulted in an increase in the phospho-SAPK signal, whereas hypoxia suppressed the irradiation-induced increase in the level of phospho-SAPK. Both hypoxic and aerobic cells showed increases in p53 levels in response to radiation. Hypoxia blocked radiation-induced cleavage of caspase 3 and poly-ADP-ribose polymerase. Irradiation of aerobic and hypoxic TK6 cells using 6 and 18 Gy, respectively, resulted in a similar and significant increase in fraction of apoptotic cells within 24 hours postirradiation. In contrast, basal levels of apoptosis were observed at 24 hours postirradiation in aerobic and hypoxic NH32 cells, a p53 null derivative of TK6 cells. These results suggest that radiation-induced apoptosis under hypoxia occurs independent of phospho-SAPK and caspase 3, and the p53 response is an obligatory apoptotic signal in TK6 cells.

Analysis of gene expression profile in gastric cancer cells stimulated with Helicobacter pylori isogenic strains

To understand the biological processes within host cells induced by VacA, isogenic strains of Helicobacter pylori (NCTC 11638 or 11638-DeltavacA) were used to stimulate gastric cancer cells SGC7901, and differentially expressed genes in host cells were identified using cDNA microarray technology. More than 300 genes were found to alter their mRNA expression at different time points, among which 68 were related to the cytoskeleton, 87 were associated with cell cycle, cell death and proliferation, IL8 expression was also found to be up-regulated. Cells co-cultured with broth-culture supernatant (BCS) of NCTC 11638 showed more alteration in microtubule cytoskeleton morphology, as observed by laser scanning confocal microscopy, and a lower apoptosis rate, detected by flow cytometry, compared with those co-cultured with BCS of 11638-DeltavacA. The supernatants of cells co-cultured with NCTC 11638 showed significantly higher IL8 expression than those co-cultured with 11638-DeltavacA. It is concluded that VacA disrupts cytoskeletal architecture by influencing the expression of cytoskeleton-associated genes. VacA breaks the balance between cell proliferation and cell death by inducing the maladjustment of genes related to cell cycle. VacA is also able to induce the inflammatory response.

Bystander effect in lymphoma cells vicinal to irradiated neoplastic epithelial cells: nitric oxide is involved

Evidence has been accumulated for attached cells demonstrating that nonirradiated cells can have a response to the ionization events delivered to their neighbors. In the present study, we first investigated the bystander responses between suspension and neoplastic cells by coculturing L5178Y (LY) cells with human salivary gland (HSG) cells that had been irradiated with either 290 MeV/u carbon ions or X-rays. After this coculture, the survival of nonirradiated recipient LY cells showed dichotomous responses to the irradiation dose delivered to HSG cells. Apoptosis and necrosis were also produced in a 48 h subculture of the recipient LY cells, and their yield increased, but then had a tendency to decrease when the irradiation dose increased. Treatment of cells with PTIO, a nitric oxide specific scavenger, diminished apoptosis and necrosis of the recipient LY cells to the control level. As an oxidization product of NO, nitrite was detected in the coculture medium and its time course corresponded well to the decrease of the viability of irradiated HSG cells. Moreover, the relationship of the survival and the apoptotic and necrotic production of the recipient LY cells to the nitrite concentration followed a linear-quadratic model. The present findings of NO being involved in the radiation-induced bystander effect may have significance in terms of radiotherapy.

Radiosensitizer sanazole (AK-2123) enhances gamma-radiation-induced apoptosis in murine fibrosarcoma

Sanazole (AK-2123) (N-2'-methoxy ethyl)-2-(3"-nitro-1"-triazolyl)acetamide, which has completed phase III clinical trials as a radiosensitizer, enhanced gamma-radiation induced apoptosis in murine fibrosarcoma upon i.p. administration at 40 mg/kg body weight one hour prior to irradiation. A microscopic examination of Giemsa-May-Grunwald stained cells has shown a higher frequency of condensed nuclei and fragmented nuclei in the tumor cells. The administration of sanazole to tumor-bearing animals enhanced the radiation-induced internucleosomal fragmentation in the nuclear genome of tumor cells. Higher levels of caspase-3 activity were also observed in the cell extracts of tumours from AK-2123 administered mice. Exposure to gamma-radiation of AK-2123-treated mouse further enhanced the caspase-3 activity, indicating the induction of apoptosis. The radiation sensitization property of sanazole was discernible by comparing the relative tumor diameter following irradiation after i.p. administration of AK-2123 and irradiation alone; it was higher during the first few days followed by the treatment.