Aberrant IDH3α expression promotes malignant tumor growth by inducing HIF-1-mediated metabolic reprogramming and angiogenesis.

Cancer cells gain a growth advantage through the so-called Warburg effect by shifting glucose metabolism from oxidative phosphorylation to aerobic glycolysis. Hypoxia-inducible factor 1 (HIF-1) has been suggested to function in metabolic reprogramming; however, the underlying mechanism has not been fully elucidated. We found that the aberrant expression of wild-type isocitrate dehydrogenase 3α (IDH3α), a subunit of the IDH3 heterotetramer, decreased α-ketoglutarate levels and increased the stability and transactivation activity of HIF-1α in cancer cells. The silencing of IDH3α significantly delayed tumor growth by suppressing the HIF-1-mediated Warburg effect and angiogenesis. IDH3α expression was associated with the poor postoperative overall survival of lung and breast cancer patients. These results justify the exploitation of IDH3 as a novel target for the diagnosis and treatment of cancers.

Involvement of decreased hypoxia-inducible factor 1 activity and resultant G1-S cell cycle transition in radioresistance of perinecrotic tumor cells.

Cancer patients often suffer from local tumor recurrence after radiation therapy. Some intracellular and extracellular factors, such as activity of hypoxia-inducible factor 1 (HIF-1), cell cycle status and oxygen availability, have been suggested to affect DNA damage responses and eventual radioresistant characteristics of cancer cells. But when, where, and how these factors affect one another and induce cellular radioresistance is largely unknown. Here, we analyzed mechanistic and spatio-temporal relationships among them in highly heterogeneous tumor microenvironments. Experiments in vitro demonstrated that a decrease in the glucose concentration reduced the transcriptional activity of HIF-1 and expression of a downstream gene for the cell cycle regulator p27(Kip1) even under hypoxic conditions. Then, the proportion of cells in the radioresistant S phase increased, whereas that in the radiosensitive G1 phase decreased, significantly. Immunohistochemical analyses showed that cancer cells in perinecrotic hypoxic regions, which should be under low-glucose conditions, expressed little HIF-1α, and therefore, were mainly in S phase and less damaged by radiation treatment. Continuous administration of glucagon, which increases the blood glucose concentration and so improves glucose availability in perinecrotic hypoxic regions, induced HIF-1α expression and increased radiation-induced DNA damage. Taken all together, these results indicate that cancer cells in perinecrotic regions, which would be under low-glucose and hypoxic conditions, obtain radioresistance by decreasing the level of both HIF-1 activity and p27(Kip1) expression, and adjusting their cell cycle to the radioresistant S phase.

Treatment regimen determines whether an HIF-1 inhibitor enhances or inhibits the effect of radiation therapy.

Hypoxia-inducible factor-1 (HIF-1) has been reported to promote tumour radioresistance; therefore, it is recognised as an excellent target during radiation therapy. However, the inhibition of HIF-1 in unsuitable timing can suppress rather than enhance the effect of radiation therapy because its anti-angiogenic effect increases the radioresistant hypoxic fraction. In this study, we imaged changes of HIF-1 activity after treatment with radiation and/or an HIF-1 inhibitor, YC-1, and optimised their combination. Hypoxic tumour cells were reoxygenated 6 h postirradiation, leading to von Hippel-Lindau (VHL)-dependent proteolysis of HIF-1alpha and a resultant decrease in HIF-1 activity. The activity then increased as HIF-1alpha accumulated in the reoxygenated regions 24 h postirradiation. Meanwhile, YC-1 temporarily but significantly suppressed HIF-1 activity, leading to a decrease in microvessel density and an increase in tumour hypoxia. On treatment with YC-1 and then radiation, the YC-1-mediated increase in tumour hypoxia suppressed the effect of radiation therapy, whereas on treatment in the reverse order, YC-1 suppressed the postirradiation upregulation of HIF-1 activity and consequently delayed tumour growth. These results indicate that treatment regimen determines whether an HIF-1 inhibitor enhances or inhibits the therapeutic effect of radiation, and the suppression of the postirradiation upregulation of HIF-1 activity is important for the best therapeutic benefit.

Significance of HIF-1-active cells in angiogenesis and radioresistance.

Human solid tumors contain hypoxic regions that have considerably lower oxygen tension than the normal tissues. Hypoxia offers resistance to radiotherapy and anticancer chemotherapy, as well as predispose to increased tumor metastases. Furthermore, hypoxia induces hypoxia-inducible factor-1 (HIF-1), which in turn increases tumor angiogenesis. Thus, eradication of HIF-1-active/hypoxic tumor cells is very important for cancer therapy. We have previously reported that procaspase-3 fused with a von Hippel-Lindau (VHL)-mediated protein destruction motif of alpha subunit of HIF-1 (HIF-1alpha) containing Pro564, named TAT-ODD-procaspase-3 (TOP3), specifically induced cell death to hypoxic cells in vivo as well as in vitro. We now report that TOP3 also eradicates the radiation-induced HIF-1-active tumor cells. HIF-1 activity in the xenografts of human tumor cells, which express luciferase under the transcriptional control of HIF-1, were monitored and quantified daily with an in vivo bioluminescence photon-counting device. HIF-1 activity in tumors was more rapidly increased by ionizing radiation (IR) compared to untreated tumors. TOP3 efficiently decreased the HIF-1-activity in irradiated tumors as well as unirradiated ones, indicating TOP3 eradicated tumor cells with HIF-1-activity induced by IR as well as hypoxia. Eradication of HIF-1-active/hypoxic cells in the xenografts during irradiation exhibited significant suppression in angiogenesis and strong enhancement in a long-term growth suppression of tumor xenografts. These results further strengthen the argument that HIF-1-active/hypoxic cells play crucial roles in angiogenesis and radioresistance.

Evaluation of glass microspheres for intra-arterial radiotherapy in animal kidneys.

PURPOSE: To evaluate the histologic distribution of nonradioactive microspheres when intra-arterially infused into normal kidneys, and to evaluate the histologic changes after the infusion. MATERIALS AND METHODS: The glass microspheres were SiO2 microspheres with a smooth spherical shape measuring 20-30 micrometers in diameter with a specific gravity of 2.2 g/cm3. After the microspheres were mixed with contrast medium, they were infused into the renal artery. Twelve rabbits were sacrificed at 1 day, 3 days, 1 week, and 8 weeks after the treatment, respectively. The specimen was fixed with 10% buffered formalin, specially embedded in methyl methacrylate (MMA) resin and was stained by hematoxylin-eosin. The distribution of the microspheres in the kidney was analyzed microscopically, and histologic changes were also evaluated. RESULTS: The microspheres were found in arterioles whose diameters were about 20-30 micrometers, within normal kidneys. All vessels containing microspheres were confined to arterioles or arteries. No migration of microspheres was detected in the normal lung or the contralateral kidney. Severe ischemic changes were observed in kidneys, developing within 8 weeks of the infusion. CONCLUSION: Glass microspheres seemed to be a useful embolic material for intra-arterial radiation therapy.

Small angiomyolipoma of the liver diagnosed by fine-needle aspiration biopsy under ultrasound guidance.

The first reported case of small hepatic angiomyolipoma to be diagnosed by fine-needle aspiration biopsy (FNAB) is described. A 53 year old man presented with a tumour in segment VI of the liver measuring 0.9 x 0.8 cm. The tumour was hyperechoic on ultrasound examination, showed relatively low density (+ 33 Hounsfield units) on computed tomography (CT), and was hypervascular on angiography. Computed tomography during arterial portography demonstrated a perfusion defect. Magnetic resonance imaging (MRI) revealed high intensity by both T1- and T2-weighted imaging. Diagnosis could not be obtained by these imaging modalities, but it was established successfully by FNAB under ultrasound guidance. Histologically, the tumour was an angiomyolipoma made up of three components: blood vessels, smooth muscle and fatty tissue. Surgery is unnecessary for this benign condition, and the patient has been followed up. Ten months later, the patient is currently doing well without growth of the hepatic angiomyolipoma.

Intermittent bursts of motor activity in the human rectum and absence of propagation.

Manometric recordings from multiple sites were performed to determine the propagating properties of intermittent bursts of motor activity in the human rectum. Pressure changes were recorded simultaneously at 12.5 cm, 10 cm and 7.5 cm from the anal verge in nine healthy subjects for a total recording time of 32 hours, each study lasting 2.7-4.8 hours. The burst motor activity was identified on 19 occasions in 7 of 9 subjects at 12.5 cm; 26 occasions in all subjects at 10 cm; and 11 occasions in 3 of 9 subjects at 7.5 cm. In most cases, the burst motor activity was observed at a single recording site while other recording sites were quiescent. It did not appear to migrate in either an oral or aboral direction. The burst motor activity contained in part runs of pressure waves with a regular frequency: at 12.5 and 10 cm of the recording site, runs of regular pressure waves were dominated by a frequency of 2.5-5 cycle per minute, whereas those at 7.5 cm occurred with a higher frequency and a lower amplitude as compared with the more proximal recording sites. No evidence of propagation of each pressure wave was seen even when the burst occurred simultaneously at more than two recording sites. These results suggest that the intermittent bursts of rectal motor activity occur locally and do not propagate in either on oral or aboral direction. They appear dissimilar to the interdigestive migrating motor complex observed in the more proximal part of the gut.

Stimulation of intramural secretory reflex by luminal distension pressure in rat distal colon.

The effects of distension on epithelial transport were examined by increasing intraluminal pressure in the rat distal colon in vitro. Two kinds of preparation, one with the musculature intact (intact preparation) and the other with the musculature and the myenteric neurons detached (mucosa-submucosa preparation), were used and the transmural potential difference (PD) changes were measured. In the intact preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused a transient increase in PD (the lumen being more negative) of 3.7 +/- 0.6 mV. The distension-induced increase in PD was largely sustained when the pressure was applied for 10 min. Distension caused by intraluminal pressure, if it is of a similar degree to that caused by fecal pellets, is enough to elicit a PD increase. The distension-induced PD increase was largely abolished by the removal of Cl- from the bathing solution, or by the addition of furosemide or bumetanide. In the mucosa-submucosa preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused an increase in PD of 5.8 +/- 0.6 mV. The distension-induced increase in PD was partially inhibited by atropine and was further decreased in the presence of tetrodotoxin both in the intact and mucosa-submucosa preparation. Indomethacin reduced the distension-induced PD increase in both preparations. These results suggest that distension by increased intraluminal pressure elicits the activation of Cl- secretion, which is mediated by submucosal plexus neurons. In addition, this distension-induced reflex is likely to be activated by normal fecal pellets.