Downregulation of apurinic/apyrimidinic endonuclease 1/redox factor-1 enhances the sensitivity of human pancreatic cancer cells to radiotherapy in vitro

Abstract Background: Radiotherapy is an important treatment for the patients with advanced pancreatic cancer. Emerging studies determined apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) might associate with the resistance of human pancreatic cancer cells to radiotherapy.

AIMS

To investigate whether downregulation of APE1/Ref-1 expression by ribonucleic acid interference would increase the sensitivity of chromic-P32 phosphate to pancreatic cancer cells.

METHODS

The plasmids containing APE-specific and unspecific short hairpin were transfected into Patu-8898 cells. Stable cell clones were selected by G418. The mRNA expression of APE1/Ref-1 was detected by semiquantitative reverse transcription-polymerase chain reaction and the protein expression of APE1/Ref-1 was detected by Western blot analysis; cell proliferation was studied by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and colony formation assay; apoptosis was detected by flow cytometry.

RESULTS

After 24 hours irradiation, APE1/Ref-1 mRNA and protein expression were upregulated, in a concentration-dependent manner. Suppression of APE1/Ref-1 by siRNA increased the pancreatic cancer cells hypersensitive to (32)P-CP. In the combination of (32)P-CP and siRNA group, MTT assay showed that the cell inhibition increased to (74.33%±9.02%), the surviving fraction in the colony formation assay was only 25.00%, and the apoptosis rate was up to (16.77%±0.98%).

CONCLUSIONS

Knockdown APE1/Ref-1 gene expression may significantly sensitize the Patu-8988 cells to radiotherapy, which may be a useful target for modifying radiation resistance of pancreatic cancer cells to irradiation.

Diffuse pigmented villonodular synovitis: preliminary results with intralesional resection and p32 synoviorthesis

Because of the high local recurrence rate associated with surgical resection alone, patients with diffuse intraarticular pigmented villonodular synovitis were treated with surgical resection followed by colloidal chromic P32 synoviorthesis. The medical records of nine consecutive patients treated in this manner were reviewed retrospectively to determine the recurrence rate of pigmented villonodular synovitis. All patients had either one or two surgical resections (arthroscopy in one patient, open resection in seven, arthroscopy and open resection in one). The involved joints included six knees and one each, ankle, elbow, and hip. Eight of the nine patients remained recurrence free at a mean followup of 38 months (range, 19-60 months) after surgery. One patient had a suspected asymptomatic recurrence documented by magnetic resonance imaging 29 months after surgery. Seven patients reported their normal activities as unrestricted. Five reported improved activity levels, one reported the activity level remained the same, and one reported activity as the same or better. None reported reduced activity levels. In these patients synoviorthesis with colloidal chromic P32 following gross resection of all obvious pigmented villonodular synovitis provided local disease control in all but one.

Dose model for stent-based delivery of a radioactive compound for the treatment of restenosis in coronary arteries

Radiolabeled drug-eluting stents have been proposed recently as a novel method to potentially reduce restenosis in coronary arteries. A P-32 labeled oligonucleotide (ODN) loaded on a polymer coated stent is slowly released in the arterial wall to deliver a therapeutic dose to the target tissue. However, the relatively low proportion of drugs transferred to the arterial wall (<2%-5% typically) raises questions about the degree to which radiolabeled drugs eluted from the stent can contribute to the total radiation dose delivered to tissues. A three-dimensional diffusion-convection transport model is used to model the transport of a hydrophilic drug released from the surface of a stent to the arterial media. Large drug concentration gradients are observed near the stent struts giving rise to a nonuniform radiation activity distribution for the drug in the tissues as a function of time. A voxel-based kernel convolution method is used to calculate the radiation dose rate resulting from this activity build-up in the arterial wall based on the medical internal radiation dose formalism. Measured residence time for the P-32 ODN in the arterial wall and at the stent surface obtained from animal studies are used to normalize the results in terms of absolute dose to tissue. The results indicate that radiation due to drug eluted from the stent contributes only a small fraction of the total radiation delivered to the arterial wall, the main contribution coming from the activity that remains embedded in the stent coating. For hydrophilic compounds with rapid transit times in arterial tissue and minimal binding interactions, the activity build-up in the arterial wall contributes only a small fraction to the total dose delivered by the P-32 ODN stent. For these compounds, it is concluded that radiolabeled drug-eluting stent will not likely improve the performance of radioactive stents for the treatment of restenosis. Also, variability in the delivery efficacy of drug delivery devices makes accurate dosimetry difficult and the drug washout in the systemic circulatory system may yield an unnecessary activity build-up and dose to healthy organs.

Effect of phosphorus-32 glass microspheres on human hepatocellular carcinoma in nude mice

AIM: To study the effects of phosphorus-32 glass microspheres (³²P-GMS) on human hepatocellular carcinoma in nude mice.

METHODS: Human liver cancer cell line was implanted into the dorsal subcutaneous tissue of 40 BALB/c nude mice. Then the 40 tumor-bearing BALB/c nude mice were allocated into treatment group (n = 32) and control group (n = 8). In the former group different doses of ³²P-GMS were injected into the tumor mass, while in the latter nonradioactive ³¹P-GMS was injected into the tumor mass. The experimental animals were sacrificed on the 14th day. The ultrastructural changes of tumor in both treatment group and control group were studied with transmission electron microscopy (TEM) and stereology.

RESULTS: In treatment group, a lot of tumor cells were killed and the death rate of tumor cells was much higher (35%-70%). Ultrastructurally, severe nuclear damage was observed in the death cells. The characteristics of appoptosis such as margination of heterochromatin was also found in some tumor cells. Besides, well differentiated tumor cells, degenerative tumor cells and some lymphocytes were seen. The skin and muscle adjacent to the tumor were normal. In control group, the tumor consisted of poorly differentiated tumor cells, in which there were only a few of dead cells (5%). Stereologicl analysis of ultrastructral morphology showed that Vv of nuclei (53.31 ± 3.46) and Vv of nucleoli (20.40 ± 1.84) in the control group were larger than those (30.21 ± 3.52 and 10.96 ± 2.52) in the treatment group respectively (P < 0.01), and Vv of RER (3.21 ± 0.54) and Vv of mitochondria (4.53 ± 0.89) in the control group were smaller than those (8.67 ± 1.25 and 7.12 ± 0.95) in the treatment group respectively (P < 0.01, 0.05). Sv of the membrane of microvilli and canaliculi (27.12 um²/100 um³± 11.84 um²/100 um³) in the control group was smaller than that (78.81 um²/100 um³± 19.69 um²/100 um³) in the treatment group (P < 0.01). But Vv of lipid particles (3.71 ± 1.97) and Vv of vacuoles (5.72 ± 1.58) were much larger than those (0.30 ± 0.16 and 0.35 ± 0.15) in the treatment group respectively (P < 0.05, P < 0.01).

CONCLUSION: The experimental results indicate that local administration of ³²P-GMS can produce obvious effect on liver cancer cells and the anticancer effect of ³²P-GMS is directly proportional to the dose administrated. Ultrastructural stereology can also show the effect of ³²P-GMS on the normalization of tumor cells, which is beneficial to the prognosis and treatment of patients. Moreover, local administrtion of ³²P-GMS is also safe.

The "shielding" effect of the guide wire during coronary brachytherapy with P-32 source

Intracoronary beta irradiation (use of beta radiation for intracoronary irradiation) is an effective method in reducing neointimal proliferation after successful angioplasty and stent implantation. However, long-term results may be influenced by absolute dose and by the homogeneity in dose distribution. In our study, we investigated dose perturbation due to the presence of a conventional guide wire during irradiation. The Galileo III centering catheter and P-32 beta source were used. The 55 MD GAF Chromic foil was positioned within a phantom made of PMMA. The dose distribution at cylindrical surfaces has been assessed using GAF Chromic dosimetric foil MD55 (Nuclear Associates, USA). Our study demonstrated the significant dose reduction of 46% in the most "shaded" area. The dose reduction to 80% or less occupy the 60 degrees sector. This phenomenon can cause progression of late restenosis. In conclusion, the results suggest that technical improvements in centering catheter construction should be made to eliminate the "shielding" effect of the guide wire.

A novel 32P deployable balloon system inhibits formation of neointima in porcine coronary arteries after balloon-overstretching injury

BACKGROUND

Intracoronary radiation has shown the potential to reduce formation of neointima in porcine models of restenosis.

OBJECTIVE

To investigate the feasibility, safety, and efficacy of a new 'deployable-balloon' device with radioisotope 32P integrated into the balloon material.

METHODS

Ten swine were subjected to balloon-overstretching injury in 20 coronary arteries and were randomly allocated to receive a radiation dose of 0, 15, or 20Gy prescribed to 1 mm from the surface of the radioactive balloon material. The animals were killed 4 weeks after the procedure. Their coronaries were perfusion fixed and stained. Vessel parameters (area of intima and length of fracture) and area of thrombus area were analyzed by computer-aided histomorphometry.

RESULTS

Radiation treatment with the new 32P balloon device was performed without complications. The lengts of fracture for the three groups were similar (NS). Formation of neointima after balloon injury was less in members of the radiated groups than it was in controls (area of intima/length of fracture was 0.70 +/-0.12 mm for controls, 0.08+/-0.13mm with 15 Gy, and 0.07+/-0.17 mm with 20 Gy; P < 0.001). Vessels treated with 20 Gy had a greater total area of thrombus (0.00+/-0.00 versus 0.51+/-0.98 mm2, P< 0.01).

CONCLUSIONS

Intracoronary radiation therapy using a new 32P deployable-balloon system is feasible and safe. A radiation dose of 15 Gy was sufficient to inhibit neointimal response in the porcine coronary-balloon-injury model.

Late arterial responses (6 and 12 months) after (32)P beta-emitting stent placement: sustained intimal suppression with incomplete healing

BACKGROUND

Three-month studies of stent-delivered brachytherapy in the rabbit model show reduced neointimal growth. However, intimal healing is delayed, raising the possibility that intimal inhibition is merely delayed rather than prevented. The purpose of this study was to explore the long-term histological changes after placement of beta-emitting radioactive stents in normal rabbit iliac arteries.

METHODS AND RESULTS

Three-millimeter beta-emitting (32)P stents (6, 24, and 48 microCi) were placed in normal rabbit iliac arteries with nonradioactive stents as controls. Animals were euthanatized at 6 and 12 months, and histological assessment, morphometry, and analysis of endothelialization were performed. Morphometric measurements demonstrated a >50% reduction in intimal growth and percent lumen stenosis within 24- and 48-microCi stents versus control nonradioactive stents at both 6 and 12 months. However, the 24- and 48-microCi stents also showed delayed healing of the intimal surface, characterized by persistent fibrin thrombus with nonconfluent areas of matrix, incomplete endothelialization, and increased intimal cellular proliferation. Stent edge stenosis was present at 12 months in the 24- and 48-microCi stent groups, characterized by both intimal thickening and negative arterial remodeling.

CONCLUSIONS

Inhibition of intimal growth is maintained 6 and 12 months after (32)P beta-emitting stent placement. However, delayed arterial healing, incomplete endothelialization, and edge effects are present.

Marrow toxicity of 33P-versus 32P-orthophosphate: implications for therapy of bone pain and bone metastases

Several bone-seeking radiopharmaceuticals, such as 32P-orthophosphate, 89Sr-chloride, 186Re-1,1 hydroxyethylidene diphosphonate (HEDP), and 153Sm-ethylene diamine tetramethylene phosphonic acid (EDTMP), have been used to treat bone pain. The major limiting factor with this modality is bone marrow toxicity, which arises from the penetrating nature of the high-energy beta particles emitted by the radionuclides. It has been hypothesized that marrow toxicity can be reduced while maintaining therapeutic efficacy by using radionuclides that emit short-range beta particles or conversion electrons. In view of the significant clinical experience with 32P-orthophosphate, and the similarity in pain relief afforded by 32P-orthophosphate and 89Sr-chloride, this hypothesis is examined in this study using 32P- and 33P-orthophosphate in a mouse femur model.

METHODS

Survival of granulocyte macrophage colony-forming cells (GM-CFCs) in femoral marrow was used as a biologic dosimeter for bone marrow. 32P- and 33P-orthophosphate were administered intravenously, and GM-CFC survival was determined as a function of time after injection and, at the nadir, as a function of injected activity. The kinetics of radioactivity in the marrow, muscle, and femoral bone were also determined. The biologic dosimeter was calibrated by assessing GM-CFC survival at its nadir after chronic irradiation of Swiss Webster mice with exponentially decreasing dose rates of gamma rays (relative biologic effectiveness equivalent to that of beta particles) from a low-dose rate 137Cs irradiator. Dose-rate decrease half-times (Td) (time required for 137Cs gamma ray dose rate to decrease by one half) of 62, 255, and 425 h and infinity were used to simulate the dose rate patterns delivered by the radiopharmaceuticals as dictated by their effective clearance half-times from the mouse femurs. These data were used to experimentally determine the mean absorbed dose to the femoral marrow per unit injected activity. Finally, a theoretical dosimetry model of the mouse femur was developed, and the absorbed doses to the femoral marrow, bone, and endosteum were calculated using the EGS4 Monte Carlo code.

RESULTS

When the animals were irradiated with exponentially decreasing dose rates of 137Cs gamma rays, initial dose rates required to achieve 37% survival were 1.9, 0.98, 0.88, and 0.79 cGy/h for dose rate decrease half-times of 62, 255, and 425 h and infinity, respectively. The D37 values were 144 +/- 15, 132 +/- 12, 129 +/- 3, and 133 +/- 10 cGy, respectively, compared with a value of 103 cGy for acute irradiation. When 32P and 33P were administered, the injected activities required to achieve 37% survival were 313 and 2,820 kBq, respectively. Theoretical dosimetry calculations show that 33P offers a 3- to 6-fold therapeutic advantage over 32P, depending on the source and target regions assumed.

CONCLUSION

The low-energy beta-particle emitter 33P appears to offer a substantial dosimetric advantage over energetic beta-particle emitters (e.g., 32p, 89Sr, 186Re) for irradiating bone and minimizing marrow toxicity. This suggests that low-energy beta or conversion electron emitters may offer a substantial advantage for alleviation of bone pain as well as for specifically irradiating metastatic disease in bone.

Leukemic transformation of essential thrombocythemia without previous cytoreductive treatment

Blastic transformation of essential thrombocythemia (ET) preceded by chemotherapy is occasionally described in the literature. In ET as well as in other myeloproliferative disorders the leukemogenic effect of alkylating agents and (32)P is well established, and recent reports also indicate a certain leukemogenic effect of hydroxyurea in these disorders. However, leukemic transformation in untreated ET seems to be a rare event. This is probably due to the fact that, at some time during their clinical course, most ET patients receive chemotherapy and are thereby exposed to leukemogenic challenge. We report on a woman with ET who had not received cytoreductive treatment prior to the development of acute myeloid leukemia, indicating that this transformation was a natural progression of her disorder.

Long-term coronary vascular response to (32)P beta-particle-emitting stents in a canine model

BACKGROUND

The arterial placement of (32)P beta-particle-emitting stents in various experimental animal models results in discordant effects on neointimal formation. We studied the vascular effects of beta-particle-emitting stents in normal canine coronary arteries because compared with pigs and rabbits, the canine model may more closely mimic the vascular response of humans.

METHODS AND RESULTS

Thirty stents (control nonradioactive, n=10; low-activity (32)P, 3.5 to 6.0 microCi, n=11; high-activity (32)P, 6.5 to 14.4 microCi, n=8) were implanted in normal canine coronary arteries through the use of a single balloon inflation at nominal pressure. Histological analysis after 15 weeks included the measurement of neointimal and adventitial area and thickness. Neointimal fibrin area was measured with the use of computer-assisted color segmentation on Movat pentachrome sections. Luminal stenosis was significantly increased in (32)P stents compared with control stents (44.6+/-16.8% versus 32.7+/-10.8%; P=0.05) and was highest in the high-activity group (45.5+/-24.3%). No evidence of an "edge effect" was seen in adjacent, nonstented coronary segments. All (32)P stents showed incomplete vascular healing as indicated by a dose-dependent increase in fibrin area with increasing stent activity. Arterial radiation resulted in a decrease in adventitial size, which was maximal for high-activity (32)P stents, indicating an inhibitory effect on the adventitial response to injury.

CONCLUSIONS

(32)P beta-particle-emitting stents have adverse vascular effects at 15 weeks in the canine normal coronary artery model. Vascular brachytherapy with this device causes increased neointimal formation and prominent, dose-dependent lack of healing.

p53-Dependent growth arrest and altered p53-immunoreactivity following metabolic labelling with 32P ortho-phosphate in human fibroblasts

The tumour suppressor gene p53 plays a major role in the cellular response to DNA damage, mediating growth arrest and/or apoptosis. Phosphorylation of the protein occurs at numerous sites in vivo and is likely to be a major mechanism for modulation of its activity as a transcriptional transactivator. Not surprisingly, therefore, p53 has been intensively studied by 32P metabolic labelling. Here we show however, using normal human fibroblasts, that typical labelling conditions induce (i) a p53-dependent inhibition of DNA synthesis and (ii) an increase in the cellular content of p53 protein detectable by the phosphorylation-sensitive antibody DO-1 but not by antibody DO-12. These data demonstrate for the first time that 32P labelling is sufficient to induce a biologically-significant, p53-mediated cellular response and strongly suggest that it perturbs the phosphorylation state of p53 which it is being used to measure. This highlights the need to re-evaluate earlier data by non-radioactive approaches using phospho-specific antibodies.

Cellular effects of beta-particle delivery on vascular smooth muscle cells and endothelial cells: a dose-response study

BACKGROUND

Although endovascular radiotherapy inhibits neointimal hyperplasia, the exact cellular alterations induced by beta irradiation remain to be elucidated.

METHODS AND RESULTS

We investigated in vitro the ability of 32P-labeled oligonucleotides to alter (1) proliferation of human and porcine vascular smooth muscle cells (VSMCs) and human coronary artery endothelial cells (ECs), (2) cell cycle progression, (3) cell viability and apoptosis, (4) cell migration, and (5) cell phenotype and morphological features. beta radiation significantly reduced proliferation of VSMCs (ED50 1.10 Gy) and ECs (ED50 2.15 Gy) in a dose-dependent manner. Exposure to beta emission interfered with cell cycle progression, with induction of G0/G1 arrest in VSMCs, without evidence of cell viability alteration, apoptosis, or ultrastructural changes. This strategy also proved to efficiently inhibit VSMC migration by 80% and induce contractile phenotype appearance, as shown by the predominance of alpha-actin immunostaining in beta-irradiated cells compared with control cells.

CONCLUSIONS

32P-labeled oligonucleotide was highly effective in inhibiting proliferation of both VSMCs and ECs in a dose-dependent fashion, with ECs showing a higher resistance to these effects. beta irradiation-induced G1 arrest was not associated with cytotoxicity and apoptosis, thus demonstrating a potent cytostatic effect of beta-based therapy. This effect, coupled to that on VSMC migration inhibition and the appearance of a contractile phenotype, reinforced the potential of ionizing radiation to prevent neointima formation after angioplasty.

[The effect of internal irradiotherapy with 32P glass microspheres on tumor vasculature in mouse sarcoma 180]

In order to investigate the effect of internal irradiotherapy on tumor microvasculature, the vascular changes of tumor S180 following internal irradiotherapy with 32P glass microspheres were observed microscopically with vessel casts of resin perfusion and ink perfusion. The results showed that the microvessels expanded with the endothelial cells swelling and the amount of microvessels and new vessels decreased, which led to peritumoral vascular density descended. It suggests that internal irradiotherapy destroying the tumor microvasculature as external irradiation is an important influence on the efficiency of internal irradiotherapy.

Elevated levels of wild-type p53 induced by radiolabeling of cells leads to apoptosis or sustained growth arrest

BACKGROUND

The tumor suppressor protein p53 regulates progression through the checkpoint between the G1 and S phases of the cell cycle in response to radiation- or drug-induced DNA damage. We have examined potential p53-mediated effects of metabolically labeling cultured mammalian cells with [35S]methionine and [3H]thymidine, methods that are commonly used to study the biochemical properties, synthesis, processing and degradation of proteins and the replication of DNA in proliferating cells.

RESULTS

Wild-type p53 protein concentrations rapidly increased to high levels following metabolic radiolabeling of cells, as determined by four distinct assays. The increased concentration of wild-type p53 resulted in apoptosis of normal human peripheral blood lymphocytes and of murine T-cell acute lymphoblastic leukemia cells. In leukemia cells containing no p53, or only mutant p53 alleles, p53 protein levels were not increased and the cells did not undergo apoptosis in response to radioactive labeling. Radiolabeling of human diploid fibroblasts resulted in a prolonged growth arrest that was maintained for nearly three weeks.

CONCLUSIONS

The results of experiments employing radiolabeling techniques to characterize various aspects of cellular physiology may be seriously influenced by the induction of aberrant cell-cycle arrest and/or apoptosis mediated by wild-type p53. Furthermore, our observations suggest that stabilization of wild-type p53 in response to irradiation may not act primarily to facilitate the repair of DNA damage by inducing a transient G1-phase arrest, but rather to ensure genetic stability through sustained cell-cycle arrest or apoptotic death of the damaged cells.

A histochemical study of irradiated bone

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