Functional imaging of multidrug resistance in breast cancer

Intrinsic or acquired multidrug resistance is the major cause of treatment failure in many human cancers. Multiple cellular mechanisms may contribute to the development of multidrug resistance including overexpression of P-glycoprotein (Pgp). The use of 99mTc-labeled lipophilic cations, which are transport substrate of Pgp, raised the possibility to predict the tumor response to treatment and to identify patients who will become refractory to subsequent therapy. Among these agents, 99mTc-MIBI is the most widely evaluated tracer and may serve as a paradigm of this class of compounds. In particular, many studies have shown the prognostic value of 99mTc-MIBI scan in different types of malignancy including breast cancer and the correlation with the expression of Pgp. However, additional mechanisms of cell resistance, mainly involving alterations of apoptosis, may also affect 99mTc-MIBI uptake in tumors. In particular, overexpression of the anti-apoptotic protein Bcl-2 prevents tumor cells to enter apoptosis and inhibits tracer accumulation into mitochondria. Therefore, while an absent or reduced early tracer uptake in large breast carcinomas reflects the existence of a defective apoptotic program, an enhanced tracer clearance in 99mTc-MIBI positive lesions reflects the activity of drug transporters such as Pgp. The existence of two different mechanisms underlying the predictive role of 99mTc-MIBI scan may be important to establish whether individual patients may benefit from Pgp inhibitors or Bcl-2 antagonists.     

In vivo exposure of human lymphocytes to technetium-99m in nuclear medicine patients does not induce detectable genetic effects.

Recent reports have demonstrated that exposure of nuclear medicine patients to thallium-201 does not result in a detectable increase in mutation at the hprt locus in human lymphocytes. In an effort to study further the potential genetic effects of medical exposures to low dose radiation, we have examined chromosome aberrations and mutations in peripheral blood lymphocytes from nuclear medicine patients exposed to clinical doses of technetium-99m. Our results show that there is no exposure-related increase in chromosomal damage; furthermore, the data do not confirm earlier reports of exposure-related increases in mutations induced by technetium-99m.     

Physical and radiobiological bases of the use of125I in the management of thyrotoxicosis

Increasing interest is recently shown in the use of¹²⁵I as an alternative isotope to¹³¹I for the management of thyrotoxicosis based on the postulate that there is a relative sparing of the reproductive integrity of the thyroid follicular cell and a consequent possibility of smaller incidence of hypothyroidism after therapy. A review of the dosimetric, radiobiological and clinical aspects of the use of¹²⁵I are presented here.For the same activity though¹²⁵I gives smaller mean glanddose than¹³¹I, the dose computations at microscopic level have revealed that there is a preferential irradiation of the apical membrane compared to the nucleus of the follicular cell. The ratio of the dose to the apical membrane and that to the nucleus increases with the decrease of the percentage colloid mass of the gland. Radiobiological significance of this non-uniform dose distribution across a follicular cell, with¹²⁵I, is brought out using rat thyroid as the biological system. For the same mean gland dose the follicular cell survival is larger with¹²⁵I than with¹³¹I. 24 h radioiodine uptake is reduced in case of¹²⁵I treatment whereas it is not affected with¹²⁵I. Pilot clinical trials using¹²⁵I for the management of thyrotoxicosis are underway in some centres. Preliminary results from centres using doses 3–4 times that of the conventional¹³¹I dose are not very different from those with conventional¹³¹I therapy. Centres that used doses same as or less than the conventional¹³¹I doses, reported smaller incidence of hypothyroidism.Alexander von Humboldt Fellow in Klinikum Steglitz, Berlin     

O6-3-[131I]iodobenzylguanine: improved synthesis and further evaluation of a potential agent for imaging of alkylguanine-DNA alkyltransferase

O(6)-Benzylguanine derivatives with suitable radionuclides attached to the benzyl ring are potentially useful in the noninvasive imaging of the DNA repair protein, alkylguanine-DNA alkyltransferase (AGT). Previously, O(6)-3-[(131)I]iodobenzylguanine ([(131)I]IBG) was prepared using a two-step approach; we now report its synthesis in a single step by the radioiododestannylation of O(6)-3-(trimethylstannyl)benzylguanine in 85-95% radiochemical yield. The in vitro specific uptake of [(131)I]IBG in DAOY human medulloblastoma cells, in TE-671 human rhabdomyosarcoma cells and a CHO cell line transfected to express AGT was linear (r(2) = 0.9-1.0) as a function of cell density. After intravenous injection of [(131)I]IBG in athymic mice bearing TE-671 xenografts, tumor uptake was 1.38 +/- 0.34% ID/g at 0.5 h and declined at 2 and 4 h. Preadministration of O(6)-(3-iodobenzyl)guanine (IBG) at 0.5 h increased uptake not only in tumor but also in several normal tissues. Notable exceptions were thyroid (p < 0.05), lung (p <0.05) and stomach. After intratumoral injection of [(131)I]IBG in the same xenograft model, the uptake in tumors that were depleted of AGT by BG treatment (165.8 +/- 27.5% ID/g) was about 60% of that in control mice (272.4 +/- 48.2% ID/g; p < 0.05).     

131I]metaiodobenzylguanidine in neuroblastoma patients at diagnosis.

Treatment of resistant neuroblastoma with high dosage [131I]metaiodobenzylguanidine (131I-MIBG) appears effective since encouraging results have been obtained so far even in patients with very advanced, intensively pre-treated disease. We have already reported a stage III NB patient treated at diagnosis, who is at present in complete remission with a 4-year follow-up. To further explore the potential role of this new drug in untreated patients, we administered radionuclide to two children with stage III neuroblastoma. Both cases received 131I-MIBG at relatively low doses, and showed a significant reduction of the tumor mass and, interestingly enough, no evidence of 131I-MIBG uptake of a tracer dose in the remaining tumor. Particularly in case 1, the permanence and subsequent progression of the part of the tumor mass without 131I-MIBG uptake, after therapeutic doses of 131I-MIBG which apparently destroyed the 131I-MIBG-positive cell population, clearly suggest heterogeneity at diagnosis, with a dual neuroblastoma cell population, one with 131I-MIBG uptake and the other without. Aside from the biological implications of the heterogeneous MIBG uptake in neuroblastoma at diagnosis, our findings suggest that in stage III neuroblastoma patients even a relatively small dose of 131I-MIBG administered at diagnosis is sufficient to either completely destroy the primary tumor, as reported by our group, or to destroy that part of the tumor which shows 131I-MIBG uptake (as in the present cases), without any significant hematologic toxicity. Furthermore, a single course of 131I-MIBG at the dosage employed here does not appear to jeopardize the subsequent use of chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Post-Surgical Rai Therapy on Parathyroid Function in Patients with Differentiated Thyroid Cancer

Objective: Radiotherapy with radioactive iodine (RAI) has become a common treatment for postsurgical differentiated thyroid carcinoma (DTC). The objective of this study was to determine the effect of RAI therapy following surgery on the function of the parathyroid glands in DTC patients.Methods: A total of 81 DTC patients who received RAI therapy after surgery were enrolled in the study. The size of the residual thyroid was detected by technetium-99m (^99mTc)-pertechnetate thyroid scan (^99mTc thyroid scan) before RAI therapy. The iodine uptake ability of residual thyroid was evaluated by iodine-131 (¹³¹I) whole-body scan (WBS). All patients were treated with an activity of 3.7 GBq (100 mCi) ¹³¹I. Parathyroid hormone (PTH), serum calcium, phosphorus, and magnesium were evaluated at 1 day before treatment, and at 1 month and 3 months after treatment.Results: The results show that there was no statistically significant difference in blood PTH level observed (P>.05) between 3 time points (pre-treatment, 1 month post-treatment and 3 months post-treatment). The serum calcium and phosphorus did not change significantly (P>.05), but serum magnesium level was elevated after treatment (P<.05). There were no significant differences between PTH changes and sex, age, scores of ^99mTc thyroid scan, scores of ¹³¹I WBS, Tumor (T) stage, and Node (N) stage.Conclusion: RAI therapy following surgery did not significantly affect parathyroid function in DTC patients.Abbreviations: ATA = American Thyroid Association; DTC = differentiated thyroid carcinoma; FT3 = free triiodothyronine; FT4 = free thyroxine; 131I = iodine-131; PTH = parathyroid hormone; RAI = radioiodine; 99mTc = Technetium-99m; TG = thyroglobulin; TNM = Tumor Node Metastasis; TSH = thyroid-stimulating hormone; WBS = whole-body scan     

Safety,biodistribution, pharmacokinetics,and immunogenicity of <Superscript>99m</Superscript>Tc-labeled humanized monoclonal antibody BIWA 4 (bivatuzumab) in patients with squamous cell carcinoma of the head and neck

Previous studies have shown the potential of murine and chimeric anti-CD44v6 monoclonal antibodies (MAbs) for radioimmunotherapy (RIT) of head and neck squamous cell carcinoma (HNSCC). A limitation of these MAbs, however, appeared to be their immunogenicity. Therefore, humanized monoclonal antibody BIWA 4 (bivatuzumab), with an intermediate affinity for CD44v6, was recently selected. As a prelude to RIT, we evaluated the safety, tumor-targeting potential, pharmacokinetics, and immunogenicity of technetium-99m-labeled BIWA 4 in patients undergoing operations for primary HNSCC in this study. Ten patients were treated at BIWA 4 dose levels of 25 mg (n=3), 50 mg (n=4), and 100 mg (n=3). Patients received 2 mg of 750 MBq 99mTc-BIWA 4, together with 23-, 48-, and 98-mg unlabeled BIWA 4, respectively. Radioimmunoscintigraphy (RIS) was performed within 1 h and after 21 h, and patients underwent surgery at 48 h after injection. Biodistribution of 99mTc-BIWA 4 was evaluated by radioactivity measurements in blood, bone marrow, and in biopsies of a surgical specimen obtained 48 h after injection. BIWA 4 concentration in blood was assessed by ELISA and high performance liquid chromatography and related to soluble CD44v6 levels in serum samples. The development of human anti-human antibody (HAHA) responses was determined. Administration of 99mTc-BIWA 4 was well tolerated by all patients and no HAHA responses were observed. A mean t1/2 in plasma of 54.8 +/- 11.5 h, 76.1 +/- 21.8 h, and 68.5 +/- 21.2 h was found for the 25-, 50-, and 100-mg dose group, respectively. No complex formation of BIWA 4 with soluble CD44v6 in blood was observed. RIS showed targeting of primary tumors and lymph node metastases in 8 of 10 and 1 of 5 patients, respectively. The highest tumor uptake and tumor to nontumor ratios were observed for the 50-mg dose group. Tumor uptake was 12.9 +/- 5.9, 26.2 +/- 3.1, and 15.4 +/- 1.9% of the injected dose (ID)/kg for the 25-, 50-, and 100-mg dose group, respectively, while the tumor to bone marrow ratios for these groups were 1.7 +/- 0.5, 3.2 +/- 1.1, and 2.0 +/- 0.6, respectively. CONCLUSION: 99mTc-BIWA 4 can safely be administered to patients with HNSCC, with absence of detectable HAHA responses. The 50-mg dose level showed the highest tumor uptake and tumor to nontumor ratios. These findings support the use of BIWA 4 for RIT studies in patients with HNSCC.     

Nuclear medicine patients do not have higher mutant frequencies after exposure to thallium-201

The HPRT-lymphocyte clonal assay has been used to detect mutants induced in vivo in humans. This method has previously detected a rise in mutant frequency among nuclear medicine patients following ex posure to technetium-99m, at a dose corresponding in theory to 5.1 mGy. In the present study, nuclear medicine patients were sampled before and after exposure to thallium-201, corresponding to a whole-body dose of 4.2 mGy. No rise in mutant frequency was found. We suggest that a difference in the effective dose received by the patients' lymphocytes accounts for the apparent contradiction with earlier results.     

99mTc-labeled MIBG derivatives: novel 99mTc complexes as myocardial imaging agents for sympathetic neurons

Radioactive-iodine-labeled meta-iodobenzylguanidine (MIBG) is currently being used as an in vivo imaging agent to evaluate neuroendocrine tumors as well as the myocardial sympathetic nervous system in patients with myocardial infarct and cardiomyopathy. It is generally accepted that MIBG is an analogue of norepinephrine and its uptake in the heart corresponds to the distribution of norepinephrine and the density of sympathetic neurons. A series of MIBG derivatives containing suitable chelating functional groups N2S2 for the formation of [TcvO]3+N2S2 complex was successfully synthesized, and the 99mTc-labeled complexes were prepared and tested in rats. One of the compounds, [99mTc]2, tested showed significant, albeit lower, heart uptakes post iv injection in rats (0.21% dose/g at 4 h) as compared to [125I]MIBG (1.7% dose/g at 4 h). The heart uptake of the 99mTc-labeled complex appears to be specific and can be reduced by co-injection with nonradioactive MIBG or by pretreatment with desipramine, a selective norepinephrine transporter inhibitor. Further evaluation of the in vitro uptake of [99mTc]2 in cultured neuroblastoma cells displayed consistently lower, but measurable uptake (approximately 10% of that for [125I]MIBG). These preliminary results suggested that the mechanisms of heart uptake of [99mTc]2 may be related to those for [125I]MIBG uptake. If suitable 99mTc-labeled MIBG derivatives can be further developed, the prevalent availability of 99mTc in nuclear medicine clinics will allow them to be readily available for widespread application.     

Hoechst 33342 induces radiosensitization in malignant glioma cells via increase in mitochondrial reactive oxygen species

Abstract

Mitochondrial DNA plays an important role in cellular sensitivity to cancer therapeutic agents. Hoechst 33342, a DNA minor groove binding ligand, has shown radiosensitizing effects in different cancer cell lines. In the present study, the possible binding of Hoechst 33342 with mitochondrial DNA, isolated from human cerebral glioma (BMG-1) cells, was investigated and consequences of this binding on excessive reactive oxygen species (ROS) generation in irradiated BMG-1 cells were studied. Alteration in the fluorescence spectroscopic characteristics of Hoechst 33342 suggested binding of Hoechst 33342 with isolated mitochondria and mitochondrial DNA. Persistent increase in level of ROS in the presence of Hoechst 33342 has been observed, which was further enhanced in irradiated cells. Investigations using inhibitors of ETC complex I suggested that mitochondrial bound Hoechst 33342 contributed to increased ROS, which was associated with alteration in ΔΨm and antioxidant machinery. These factors appeared to contribute in potentiating radiation-induced cell death in BMG-1 cells. The finding from these studies will be useful in designing better anti-cancer strategies.     

A radioiodinated MIBG-octreotate conjugate exhibiting enhanced uptake and retention in SSTR2-expressing tumor cells

Several neuroendocrine tumors are known to express both the somatostatin receptor subtype 2 (SSTR2) and the norepinephrine transporter (NET), and radiopharmaceuticals directed toward both these targets such as MIBG and octreotide derivatives are routinely used in the clinic. To investigate the possibility of targeting both NET and SSTR2 conjointly, a conjugate of radioiodinated MIBG and octreotate was synthesized. Attempts to synthesize the radioiodinated target compound (MIBG-octreotate; [ (131)I] 12a) from a tin precursor were futile; however, it could be accomplished from a bromo precursor by exchange radioiodination in 3-36% ( n = 10) radiochemical yields. The total uptake of [ (131)I] 12a in SK-N-SH human neuroblastoma cells transfected to express SSTR2 (SK-N-SHsst2) was similar to that for [ (125)I]MIBG at all time points (34.9 +/- 2.4% vs 43.8 +/- 1.2% at 4 h; p < 0.05), while it was substantially lower (5.4 +/- 0.3% vs 35.9 +/- 1.2%) in the SH-SY5Y cell line, a subclone of SK-N-SH line that is known to express SSTR2. The NET blocker desipramine reduced the uptake of [ (131)I] 12a only to a small extent, further suggesting a limited role of NET in its binding and accumulation. Uptake of [ (131)I] 12a in SK-N-SHsst2 cells was 8-10-fold higher ( p < 0.05) than that of [ (125)I]I-Gluc-TOCA, an octreotide analogue, at all time points over a 4 h period and was reduced to about 20% by 10 muM octreotide demonstrating that the uptake of [ (131)I] 12a in this cell line is predominantly mediated by SSTR2. The intracellularly trapped radioactivity in SK-N-SHsst2 cells was substantially higher for [ (131)I] 12a compared to that for [ (125)I]OIBG-octreotate, an isomeric congener of 12a. Because MIBG has more specific NET-mediated uptake than OIBG, this suggests at least a partial role for NET-mediated uptake of [ (131)I] 12a in this cell line. While further refinement in the structure of the conjugate-probably interposition of a flexible and/or cleavable linker between the MIBG and octreotate moieties-may be necessary to make it a substrate/ligand for both NET and SSTR2, this conjugate is demonstrated to be much superior than I-Gluc-TOCA with respect to the uptake in SSTR2-expressing cells.     

Targeted imaging of hypoxia-induced integrin activation in myocardium early after infarction.

The alphavbeta3-integrin is expressed in angiogenic vessels in response to hypoxia and represents a potential novel target for imaging myocardial angiogenesis. This study evaluated the feasibility of noninvasively tracking hypoxia-induced alphavbeta3-integrin activation within the myocardium as a marker of angiogenesis early after myocardial infarction. Acute myocardial infarction was produced by coronary artery occlusion in rodent and canine studies. A novel (111)In-labeled radiotracer targeted at the alphavbeta3-integrin ((111)In-RP748) was used to localize regions of hypoxia-induced angiogenesis early after infarction. In rodent studies, the specificity of (111)In-RP748 for alphavbeta3-integrin was confirmed with a negative control compound ((111)In-RP790), and regional uptake of these compounds correlated with (201)Tl perfusion and a (99m)Tc-labeled nitroimidazole (BRU59-21), which was used as a quantitative marker of myocardial hypoxia. The ex vivo analysis demonstrated that only (111)In-RP748 was selectively retained in infarcted regions with reduced (201)Tl perfusion and correlated with uptake of BRU59-21. In canine studies, myocardial uptake of (111)In-RP748 was assessed using in vivo single-photon-emission computed tomography (SPECT), ex vivo planar imaging, and gamma well counting of myocardial tissue and correlated with (99m)Tc-labeled 2-methoxy-2-methyl-propyl-isonitrile ((99m)Tc-sestamibi) perfusion. Dual-radiotracer in vivo SPECT imaging of (111)In-RP748 and (99m)Tc-sestamibi provided visualization of (111)In-RP748 uptake within the infarct region, which was confirmed by ex vivo planar imaging of excised myocardial slices. Myocardial (111)In-RP748 retention was associated with histological evidence of alphavbeta3-integrin expression/activation in the infarct region. (111)In-RP748 imaging provides a novel noninvasive approach for evaluation of hypoxia-induced alphavbeta3-integrin activation in myocardium early after infarction and may prove useful for directing and evaluating angiogenic therapies in patients with ischemic heart disease.     

Evaluation of respiratory chain failure in mitochondrial cardiomyopathy by assessments of 99mTc-MIBI washout and 123I-BMIPP/99mTc-MIBI mismatch

Cardiomyopathy is one of the main features that determines prognosis in patients with mitochondrial encephalomyopathy. We investigated respiratory chain failure using 99mTc-MIBI- and 123I-BMIPP-SPECT in vivo in five patients with mitochondrial cardiomyopathty. With the lowering of cardiac function, the 99mTc-MIBI-washout rate (WOR) increased, and the 99mTc-MIBI-uptake decreased, conversely. In patients who showed severe cardiac involvement, 99mTc-MIBI-uptake was markedly reduced, and by contrast, 123I-BMIPP-uptake increased (123I-BMIPP/99mTc-MIBI mismatch). There were significant correlations between the WOR on 99mTc-MIBI-SPECT and interventricular septal thickness (IVST) on echocardiography and between WOR and left ventricular ejection fraction (LVEF) on 99mTc-MIBI-SPECT. The increased WOR and decreased uptake of 99mTc-MIBI were reflected by the lowered mitochondrial membrane potential created by mitochondrial respiratory chain whereas 123I-BMIPP/99mTc-MIBI mismatch may be created by the enhanced triglyceride-pool. These nuclear medicine techniques are the potential tools to evaluate the energy state in mitochondrial cardiomyopathy.     

Low-dose radiation hypersensitivity in human tumor cell lines: effects of cell-cell contact and nutritional deprivation

The hyper-radiosensitivity at low doses recently observed in vitro in a number of cell lines is thought to have important implications for improving tumor radiotherapy. However, cell-cell contact and the cellular environment influence cellular radiosensitivity at higher doses, and they may alter hyper-radiosensitivity in vivo. To confirm this supposition, we investigated the effects of cell density, multiplicity and nutritional deprivation on low-dose hypersensitivity in vitro. Cell survival in the low-dose range (3 cGy to 2 Gy) was studied in cells of two human glioma (BMG-1 and U-87) and two human oral squamous carcinoma (PECA-4451 and PECA-4197) lines using a conventional macrocolony assay. The effects of cell density, multiplicity and nutritional deprivation on hyper-radiosensitivity/induced radioresistance were studied in cells of the BMG-1 cell line, which showed prominent hypersensitivity and induced radioresistance. The induction of growth inhibition, cell cycle delay, micronuclei and apoptosis was also studied at the hyper-radiosensitivity-inducing low doses. Hyper-radiosensitivity/induced radioresistance was evident in the cells of all four cell lines to varying extents, with maximum sensitivity at 10-30 cGy, followed by an increase in survival up to 50 cGy-1 Gy. Both the glioma cell lines had more prominent hyper-radiosensitivity than the two squamous carcinoma cell lines. Low doses inducing maximum hyper-radiosensitivity did not cause significant growth inhibition, micronucleation or apoptosis in BMG-1 cells, but a transient G(1)/S-phase block was evident. Irradiating and incubating BMG-1 cells at high density for 0 or 4 h before plating, as well as irradiating cells as microcolonies, reduced hyper-radiosensitivity significantly, indicating the role of cell-cell contact-mediated processes. Liquid holding of BMG-1 cells in HBSS + 1% serum during and after irradiation for 4 h significantly reduced hyper-radiosensitivity, suggesting that hyper-radiosensitivity may be due partly to active damage fixation processes at low doses. Therefore, our findings suggest that the damage-induced signaling mechanisms influenced by (or mediated through) cell-cell contact or the cellular environment, as well as the lesion fixation processes, play an important role in hyper-radiosensitivity. Further studies are required to determine the exact nature of the damage that triggers these responses as well as for evaluating the potential of low-dose therapy.     

The effect of Mn2+ on thyroid iodine metabolism in rats]

Injection into rats of manganous chloride (2 mg/100 g) showed, after a 24-hr period, a marked depression of thyroidal 131I uptake. There is a decrease in serum T3 and T4 levels and an increase in I- level. These results demonstrate that the action of manganous ions is to block uptake of I- by the thyroid.     

131I]metaiodobenzylguanidine therapy in advanced neuroblastoma.

Forty-two children with advanced neuroblastoma who either failed with first-line therapy or relapsed after achieving a complete remission, were considered for treatment with [131I]metaiodobenzylguanidine (131I-MIBG). We subdivided 42 cases into 5 groups, in accordance with the stage of disease at diagnosis, response to first-line therapy and relapse. A total of 99 courses of 131I-MIBG were administered with doses ranging from 2.8 to 6.0 GBq. One child received six courses, 3 four courses, 18 three courses, 6 two courses and 15 one course of 131I-MIBG. The total delivered dose in single measurable lesions ranged from 286 to 1691 cGy with an uptake factor ranging from 3% to 10%. We obtained a major response in primary tumors, and a long-term response was observed in 5 cases, lasting more than 2 years without further chemotherapy.     

Role of topoisomerases in cytotoxicity induced by DNA ligand Hoechst-33342 and UV-C in a glioma cell line

DNA ligand Hoechst-33342 significantly enhances UV induced cytotoxicity in human glioma cell lines (BMG-1 & U-87) with supra additive increase in cell death, cytogenetic damage, cell cycle delay, apoptosis and inhibition of PLDR. Cytotoxicity of Hoechst-33342 arises due to its interference in the breakage-rejoining reaction of DNA topoisomerases by stabilization of cleavable complexes. Since topoisomerases have also been implicated in the generation of potentially lethal DNA breaks by interaction with various types of DNA damage including UV induced DNA lesions, we investigated in present studies the role of functional topoisomerases in the synergistic cytotoxicity of Hoechst-33342 and UV in a human glioma cell line (BMG-1). Topoisomerase I activity analyzed by the plasmid relaxation assay, was significantly enhanced upon UV irradiation, implying a possible role of this enzyme in the processing of UV induced lesions. However, this increase in the activity was reduced by >50% in cells incubated with Hoechst-33342 for 1 hr prior to irradiation. Imunoflowcytometric analysis of the chromatin bound topoisomerases I and II levels (cleavable complex) using topoisomerases I and II anti-antibodies showed a good correlation between the induction of apoptosis by Hoechst-33342 and UV and enhancement in the level of topoisomerase II mediated cleavable complexes. Induction of apoptosis was associated with a decline in the level of Bcl2. Taken together, these studies show that supra additive cytotoxic effects of UV-C and Hoechst-33342 in BMG-1 cells are consequences of enhanced stabilization of topo II mediated cleavable complexes and alterations in specific signal transduction pathways of apoptosis, besides the inhibition of topoisomerase mediated repair processes.     

Biological evaluation of ring- and side-chain-substituted m-iodobenzylguanidine analogues

A number of ring- and side-chain-substituted m-iodobenzylguanidine analogues were evaluated for their lipophilicity, in vitro stability, uptake by SK-N-SH human neuroblastoma cells in vitro, and biodistribution in normal mice. As expected, the lipophilicity of m-iodobenzylguanidine increased when a halogen was introduced onto the ring and decreased with the addition of polar hydroxyl, amino, and nitro substitutents. Most of the derivatives showed reasonable stability up to 24 h in PBS at 37 degrees C. While N(1)-hydroxy-N(3)-3-[(131)I]iodobenzylguanidine and 3,4-dihydroxy-5-[(131)I]iodobenzylguanidine generated a more nonpolar product in addition to the free iodide, 3-[(131)I]iodo-4-nitrobenzylguanidine decomposed to a product more polar than the parent compound. The specific uptake of 4-chloro-3-[(131)I]iodobenzylguanidine, 3-[(131)I]iodo-4-nitrobenzylguanidine, and N(1)-hydroxy-N(3)-3-[(131)I]iodobenzylguanidine by SK-N-SH human neuroblastoma cells in vitro, relative to that of m-[(125)I]iodobenzylguanidine, was 117 +/- 10%, 50 +/- 4%, and 12 +/- 2%, respectively. The specific uptake of the known m-iodobenzylguanidine analogues 4-hydroxy-3-[(131)I]iodobenzylguanidine and 4-amino-3-[(131)I]iodobenzylguanidine was 80 +/- 4% and 66 +/- 4%, respectively. None of the other m-iodobenzylguanidine derivatives showed any significant specific uptake by SK-N-SH cells. Heart uptake of 4-chloro-3-[(131)I]iodobenzylguanidine in normal mice was higher than that of m-[(125)I]iodobenzylguanidine at later time points (11 +/- 1% ID/g versus 3 +/- 1% ID/g at 24 h; p < 0.05) while uptake of 3-[(131)I]iodo-4-nitrobenzylguanidine and of N(1)-hydroxy-N(3)-3-[(131)I]iodobenzylguanidine in the heart was lower than that of m-iodobenzylguanidine at all time points. In accordance with the in vitro results, none of the other novel m-iodobenzylguanidine derivatives showed any significant myocardial or adrenal uptake in vivo.     

Effect of short-term and long-term lithium treatment on uptake and retention of iodine-131 in rat thyroid

No significant change occurred in the uptake by the thyroid of male Wistar rats of a standard dose of carrier-free 131I administered intraperitoneally and its retention by the thyroid, as measured by biological and effective half-life, after feeding these rats a powdered pelleted diet containing lithium carbonate (1.1 g per kg of diet) for 7 days. However, continuing this diet for 10 days inhibited thyroid uptake and increased the retention of 131I. Uptake remained suppressed for up to 4 months after lithium treatment and continuing this treatment for 6 months did not result in any significant change in 131I uptake by the thyroid. Lithium treatment for 10 days increased the biological and effective half-life of 131I in the thyroid and this increase continued for the 6 months treatment period. The dose of 131I delivered to the thyroid was significantly lower after 10 days and 1 month of lithium treatment but there was no change in this dose after 2 and 4 months of treatment. However, there was a significant increase after 6 months.     

The effects of ionizing radiation on the pulmonary vasculature of intact rats and isolated pulmonary endothelium

We studied the effects of ionizing radiation on the morphology of the pulmonary circulation using an in vivo rat model and an in vitro pulmonary artery endothelial cell model. Gamma radiation was given as either an acute (30 Gy) or fractionated (5 X 6 Gy) dose to one hemithorax of rats. An acute 30-Gy dose delivered resulted in a 70% decrease in pulmonary arterial perfusion, using technetium-99m microaggregated albumin (99mTc-MAA), in the irradiated lung by 2-3 weeks after irradiation. Pulmonary microradiographs, using a barium sulfate perfusion method, obtained 2-3 weeks after irradiation demonstrated widespread loss of capillary filling and segmentation of the vessels. Histologic examination demonstrated intact capillaries, suggesting that the alterations in pulmonary perfusion were at the precapillary level. Similar abnormalities in lung perfusion and morphology were found after delivery of fractionated doses of radiation, but the onset of the changes was delayed, occurring 4-6 weeks postirradiation. Using cultured pulmonary endothelial cell monolayers, cell sloughing and retraction from the surface substrate were observed within 24 h after in vitro delivery of 30 Gy. Similar findings occurred in monolayers given fractionated doses (5 X 6 Gy) of radiation 2-3 days after the final dose. The in vivo animal and in vitro endothelial cell models offer a useful means of examining the morphologic alterations involved in radiation lung vascular damage.