Radiation quality-dependent bystander effects elicited by targeted radionuclides.

The efficacy of radiotherapy may be partly dependent on indirect effects, which can sterilise malignant cells that are not directly irradiated. However, little is known of the influence of these effects in targeted radionuclide treatment of cancer. We determined bystander responses generated by the uptake of radioiodinated iododeoxyuridine ([*I]IUdR) and radiohaloanalogues of meta-iodobenzylguanidine ([*I]MIBG) by noradrenaline transporter (NAT) gene-transfected tumour cells. NAT specifically accumulates MIBG. Multicellular spheroids that consisted of 5% of NAT-expressing cells, capable of the active uptake of radiopharmaceutical, were sterilised by treatment with 20 kBqmL(-1) of the alpha-emitter meta-[211At]astatobenzylguanidine ([211At]MABG). Similarly, in nude mice, retardation of the growth of tumour xenografts containing 5% NAT-positivity was observed after treatment with [131I]MIBG. To determine the effect of subcellular localisation of radiolabelled drugs, we compared the bystander effects resulting from the intracellular concentration of [131I]MIBG and [131I]IUdR (low linear energy transfer (LET) beta-emitters) as well as [123I]MIBG and [123I]IUdR (high LET Auger electron emitters). [*I]IUdR is incorporated in DNA whereas [*I]MIBG accumulates in extranuclear sites. Cells exposed to media from [131I]MIBG- or [131I]IUdR-treated cells demonstrated a dose-response relationship with respect to clonogenic cell death. In contrast, cells receiving media from cultures treated with [123I]MIBG or [123I]IUdR exhibited dose-dependent toxicity at low dose but elimination of cytotoxicity with increasing radiation dose (i.e. U-shaped survival curves). Therefore radionuclides emitting high LET radiation may elicit toxic or protective effects on neighbouring untargeted cells at low and high dose respectively. It is concluded that radiopharmaceutical-induced bystander effects may depend on LET of the decay particles but are independent of site of intracellular concentration of radionuclide.

Preclinical study of the systemic toxicity and pharmacokinetics of 5-iodo-2-deoxypyrimidinone-2'-deoxyribose as a radiosensitizing prodrug in two, non-rodent animal species: implications for phase I study design.

We have demonstrated previously an improved therapeutic index for oral 5-iodo-2-deoxypyrimidinone-2'-deoxyribose (IPdR) compared with oral and continuous infusion of 5-iodo-2'-deoxyuridine (IUdR) as a radiosensitizing agent using three different human tumor xenografts in athymic mice. IPdR is a prodrug that is efficiently converted to IUdR by a hepatic aldehyde oxidase, resulting in high IPdR and IUdR plasma levels in mice for > or =1 h after p.o. IPdR. Athymic mice tolerated oral IPdR at up to 1500 mg/kg/day given four times per day for 6-14 days without significant systemic toxicities. In anticipation of an investigational new drug application for the first clinical Phase I and pharmacology study of oral IPdR in humans, we studied the drug pharmacokinetics and host toxicities in two non-rodent, animal species. For the IPdR systemic toxicity and toxicology study, twenty-four male or female ferrets were randomly assigned to four IPdR dosage groups receiving 0, 15, 150, and 1500 mg/kg/day by oral gavage x 14 days prior to sacrifice on study day 15. All ferrets survived the 14-day treatment. Ferrets receiving 1500 mg/kg/day showed observable systemic toxicities with diarrhea, emesis, weight loss, and decreased motor activity beginning at days 5-8 of the 14-day schedule. Overall, both male and female ferrets receiving IPdR at 1500 mg/kg/day experienced significant weight loss (9 and 19%, respectively) compared with controls after the 14-day treatment. No weight loss or other systemic toxicities were observed in other IPdR dosage groups. Grossly, no anatomical lesions were noted at complete necropsy, although liver weights were increased in both male and female ferrets in the two higher IPdR dosage groups. Histologically, IPdR-treated animals showed dose-dependent microscopic changes in liver consisting of minimal to moderate cytoplasmic vacuolation of hepatocytes, which either occurred in the periportal area (high dosage group) or diffusely throughout the liver (lower dosage groups). Female ferrets in the highest IPdR dose group also showed decreased kidney and uterus weights at autopsy without any associated histological changes. No histological changes were found in central nervous system tissues. No significant abnormalities in blood cell counts, liver function tests, kidney function tests, or urinalysis were noted. Hepatic aldehyde oxidase activity was decreased to approximately 50 and 30% of control ferrets in the two higher IPdR dosage groups, respectively, after the 14-day treatment period. The % IUdR-DNA incorporation in ferret bone marrow at the completion of IPdR treatment was < or =0.05% in the two lower dosage groups and approximately 2% in the 1500 mg/kg/day dosage group. The % IUdR-DNA in normal liver was < or =0.05% in all IPdR dosage groups. In a pharmacokinetic study in four Rhesus monkeys, we determined the plasma concentrations of IPdR after a single i.v. bolus of 50 mg/kg over 20 min. Using a two-compartment model to fit the plasma pharmacokinetic data, we found that IPdR was cleared in these non-human primates in a biexponential manner with an initial rapid distributive phase (mean T1/2alpha = 6.5 min), followed by an elimination phase with a mean T1/2 of 63 min. The mean maximum plasma concentration of IPdR was 124+/-43 microM with a mean total body clearance of 1.75+/-0.95 l/h/kg. IPdR was below detection (<0.5 microM) in the cerebrospinal fluid. We conclude that there are dose-limiting systemic toxicities to a 14-day schedule of p.o. IPdR at 1500 mg/kg/day in ferrets that were not found previously in athymic mice. However, no significant hematological, biochemical, or histopathological changes were found. Hepatic aldehyde oxidase activity was reduced in a dose-dependent in ferret liver, suggesting partial enzyme saturation by this IPdR schedule. The plasma pharmacokinetic profile in Rhesus monkeys showing biexponential clearance is similar to our published data in athymic mice. These data are being applied

Simultaneous analysis of DNA replication and apoptosis during treatment of HL-60 cells with camptothecin and hyperthermia and mitogen stimulation of human lymphocytes.

A new method is described which combines the identification of DNA replicating and apoptotic cells in a single measurement by flow cytometry. The detection of DNA replicating cells is based on incorporation of 5-bromo-2'-deoxyuridine or 5-iodo-2'-deoxyuridine, followed by selective photolysis at the site of incorporation of the halogenated DNA precursors. Single-strand breaks in DNA resulting from the photolysis are subsequently labeled with digoxygenin or biotin-conjugated dUTP in a reaction catalyzed by exogenous terminal deoxynucleotidyl transferase. The double-stranded DNA breaks in apoptotic cells resulting from activation of the endonuclease can be labeled in this reaction as well. However, in contrast to the photolysed DNA, the low molecular weight fraction of DNA of apoptotic cells is extractable from the cells, and the degree of DNA elution can be modulated by cross-linking with formaldehyde. Thus, apoptotic cells can be distinguished and quantified by virtue of their fractional DNA content. Replication of less than 1% of a genome of a cell in the presence of 5-bromo-2'-deoxyuridine (equivalent of a 5-min 10 microM 5-bromo-2'-deoxyuridine pulse) can be detected by the selective photolysis method. The method was applied to study apoptosis and proliferation of human leukemic HL-60 cells and normal, mitogen-stimulated lymphocytes. Whereas apoptosis of HL-60 cells induced by the DNA topoisomerase I inhibitor camptothecin was selective to DNA replicating cells, apoptosis induced by hyperthermia showed no such selectivity. Lymphocytes that preferentially underwent apoptosis in cultures stimulated by phytohemagglutinin did not initiate DNA replication. By offering the possibility for identification of both DNA replicating and apoptotic cells in a single measurement, the method may find an application in studies of the prognostic value of both cell proliferation and death in human tumors and the apoptotic response of DNA replicating vs. nonreplicating cells to different treatments.

5-Fluorouracil, hydroxyurea and escalating doses of iododeoxyuridine with concomitant radiotherapy for malignant gliomas: a clinical and pharmacologic analysis.

BACKGROUND: Iododeoxyuridine (IUdR) is a known radiation enhancer, and interacts biochemically with 5-fluorouracil (5-FU) and hydroxyurea (HU). PATIENTS AND METHODS: IUdR was added to the previously studied regimen of continuous infusion 5-FU at 300 mg/m2/day for 5 days, HU 500 mg every 12 hours for 11 doses and radiotherapy 200 cGy/day for 5 days, all administered for 7 consecutive weeks to patients with malignant glioma. IUdR was administered as 5-day continuous intravenous infusion during weeks 1 and 4. The IUdR dose was changed in cohorts of patients. IUdR plasma concentrations were determined during weeks 1 and 4, and IUdR incorporation into the DNA of granulocytes was measured on weeks 2 and 5. RESULTS: Two patients treated at the initial IUdR dose of 500 mg/m2/day developed grade 3 or 4 myelosuppression and mucositis. Additional dose levels of IUdR tested were 250 mg/m2/day and 125 mg/m2/day; at the latter dose, severe or life-threatening toxicity was seen in only 3 of 8 patients treated. IUdR incorporation into DNA of granulocytes was 10.5(+/- 2.3)% at an IUdR dose of 500 mg/m2/day but decreased to 0.76(+/- 0.3)% at 125 mg/m2/day. Similarly, IUdR plasma concentrations decreased from 436 (+/- 114) ng/ml to 99 (+/- 29) ng/ml. CONCLUSIONS: The addition of IUdR to 5-FU and HU results in significant systemic toxicity necessitating limitation of the IUdR dose to 125 mg/m2/day. There is a significant biochemical interaction between IUdR, 5-FU and HU leading to increased IUdR incorporation into DNA and to substantial clinical toxicity. Further clinical studies to exploit this interaction at more feasible schedules may be useful.

Reentry of T cells to the adult thymus is restricted to activated T cells.

To seek information on the capacity of mature T cells to migrate to the thymus, mice were injected with Thy-1-marked populations enriched for resting T cells or T blast cells; localization of the donor cells in the host thymus was assessed by staining cryostat sections of thymus and by FACS analysis of cell suspensions. With injection of purified resting T cells, thymic homing was extremely limited, even with injection of large doses of cells. By contrast, in vivo generated T blast cells migrated to the thymus in substantial numbers. Thymic homing by T blasts was greater than 50-fold more efficient than with resting T cells. Blast cells localized largely in the medulla and remained in the thymus for at least 1 mo post-transfer. Interestingly, localization of T blasts in the thymus was 10-fold higher in irradiated hosts than normal hosts. Thymic homing was especially prominent in mice injected with T blasts incubated in vitro with the DNA precursor, 125I-5-iodo-2'deoxyuridine (125IDUR); with transfer of 125IDUR-labeled blasts to irradiated hosts, up to 5% of the injected counts localized in the host thymus. These data suggest that thymic homing by T blasts might be largely restricted to cells in S phase. The physiological significance of blast cell entry to the thymus is unclear. The possibility that these cells participate in intrathymic tolerance induction is discussed.

Radiotoxicity of 125I in mammalian cells.

The radiotoxicity of 125I in Chinese hamster V79 lung fibroblasts has been studied following extracellular (Na125I), cytoplasmic [125I]iododihydrorhodamine (125I-DR), and nuclear (125IUdR) localization of the radionuclide. Exposure of the cells for 18 h to Na125I (less than or equal to 7.4 MBq/ml) had no effect on survival. A similar exposure to 125I-DR produced a survival curve with a distinct shoulder and with a mean lethal dose (D37) of 4.62 Gy to the nucleus. While this value compares well with the 5.80 Gy X-ray D37 dose, it is in contrast to the survival curve obtained with DNA-bound 125IUdR which is of the high LET type and has a D37 of 0.80 Gy to the nucleus. Furthermore, when the uptake of 125I into DNA is reduced by the addition of nonradioactive IUdR or TdR to the medium and the survival fraction is determined as a function of 125I contained in the DNA, a corresponding increase in survival is observed. This work demonstrates the relative inefficiency of the Auger electron emitter 125I when located in the cytoplasm or outside the cell. It indicates that a high dose deposited within the cytoplasm contributes minimally to radiation-induced cell death and that radiotoxicity depends not upon the specific activity of IUdR but upon the absolute amount of 125I that is associated with nuclear DNA.

An experimental model for predicting the synergism of hyperthermia with cytostatics.

A simple prediction test for a combination of hyperthermia and chemotherapy checked on three experimental tumors and cells of the normal murine thymus is described. The testing procedure is based on checking the incorporation of labeled 125I 5-iodo-2-deoxyuridine into the DNA of tested cells affected solely by the enhanced temperature or by the cytostatic itself, or by a combination of both agents. The statistical analysis of repeated results demonstrated the reproducibility of the test. Testing of the potentiation effect of different non-cytostatic substances with enhanced temperatures also gave results corresponding to findings of other authors, performed in vivo or by the use of other techniques. Thus, this simple method is recommended for a screening, before considering the individual use of the combination of hyperthermia and chemotherapy in patients.

Afferent lymph and lymph borne cells: their influence on lymph node function.

In AO rats the afferent lymphatics to the right cervical lymph nodes (LN) were interrupted and the LN were encased in silicone rubber tubes to prevent reunion of the lymphatics. At regular intervals over the next 12 weeks the following were measured in comparison with the intact contralateral LN - LN weight, influx of lymphocytes from the blood, blood flow, the incorporation of 125IUdR and the incorporation of 35S-sulphate into high endothelial venules (HEV). Systematic histological observations are also reported. One day after deafferentization lymphocyte influx was significantly reduced although blood flow was unchanged and a temporary increase in LN weight was associated with crowding of the lymphatic sinuses with small lymphocytes. The subsequent decline in lymphocyte influx was biphasic and quicker than the decline of other parameters--being undetectable by 6 weeks. Flattening of HEV and diminished secretion of 35S-sulphate was noted at 1 week and progressive degeneration and eventual disappearance of the HEV network was seen by 6-12 weeks. Doubtlessly because of lack of antigenic stimulation 125IUdR incorporation, and numbers of lymphoblasts, plasma cells and finally germinal centres were progressively reduced. The numbers of macrophages and interdigitating cells (IDC) were greatly reduced by 3 weeks and very few were present at 6 weeks probably because most or all arrive in afferent lymph and have a limited life span in the LN. At 12 weeks the LN was difficult to recognize as such since only stromal cells and occasional small lymphocytes remained. In supplementary experiments u.v. irradiation of the LN at the time of deafferentization reduced lymphocyte influx without affecting blood flow suggesting that a u.v. sensitive cell like the IDC may influence lymphocyte influx. In conclusion the involution of the deafferentized LN is partly due to the lack of antigen but progression to the complete loss of specialized structure and function is probably due to lack of other factors including non-lymphoid cells that normally arrive in afferent lymph.

Electrostimulation of rat callus cells and human lymphocytes in vitro.

Asymmetrical pulsing low voltage current was supplied via electrodes to cultured rat fracture callus cells and human peripheral blood lymphocytes. The [3H]thymidine incorporation of the callus cells and 5-[125I]iodo-2'-deoxyuridine incorporation of the lymphocytes were determined. The growth pattern of callus cells (estimated by cellular density) did not respond to electrical stimulation. However, the uptake of [3H]thymidine was increased at the early phase of cell proliferation and inhibited at later phases of proliferation. The [3H]thymidine uptake of confluent callus cell cultures did not respond to electrical stimulation. Lymphocytes reacted in a similar way; stimulated cells took up more DNA precursor than control cells at the early phase of stimulation. During cell division, induced by the mitogens phytohemagglutinin and Concanavalin-A, the uptake of DNA precursor by stimulated cells was constantly inhibited. The results suggest that electrical stimuli affect the uptake mechanisms of cell membranes. The duality of the effect seems to be dependent on the cell cycle.

In vitro assay of erythropoietin in fetal mouse liver cultures. I. Comparison of radioactive tracers and evidence of assay specificity.

In a 13 d fetal mouse liver tissue culture system for assay of erythropoietin, stimulation of incorporation of 3H-thymidine and of 125I-iodo-2'-deoxy uridine into DNA and of 59Fe iron into haem were compared as metameters of erythropoietin effect. With both DNA and haem tracers, log-dose response curves given by two preparations of human urinary erythopoietin purified to different extents (respectively 2 and 1300 IU, by bioassay in vivo, per mg of protein) were essentially identical at low dose levels although at high dose levels the less pure preparation decreased stimulation of both DNA and haem synthesis. Pre-incubation of erythropoietin with an antiserum to human erythropoietin abolished the effects of the hormones on both DNA and haem synthesis.

Treatment of trigeminal and thoracic zoster with idoxuridine.

A double-blind random selection comparison was made of the therapeutic effects in acute herpes zoster of 40% idoxuridine (IDU) dissolved in dimethyl sulphoxide (DMSO) compared with DMSO and saline flavoured with garlic. Thoracic (80 patients) and trigeminal (42 patients) zoster were investigated separately. The patients were evaluated daily until skin healing and then at 1, 3 and 6 months by registering pain, paraesthesia and sensitivity disturbances as well as by clinical and photographic evaluation of the skin lesions. Duration of pain was positively correlated to age, to delayed healing and to elevated temperature in the acute phase of zoster. The period of pain before skin eruption was considerably longer in thoracic than in trigeminal zoster, while the latter was associated with a more severe inflammatory reaction, more neurologic sequelae, but also by a faster healing of the skin lesions. IDU was highly effective in shortening the period of pain and improving skin healing in trigeminal zoster, while no effect of IDU was observed in thoracic zoster. The reason for this difference is presently not understood.

Studies on the microcytotoxicity test. III. Comparison of [75Se]selenomethionine with [3H]proline, Na2, 51CrO4 and [125I]iododeoxyuridine for pre-labelling target cells in long-term cytotoxicity tests.

Four intracellular radioisotope labels, [3H]proline, Na2 51CrO4, [75Se]selenomethionine and [125I]iododeoxyuridine, were evaluated for use in a pre-labelling long-term microcytotoxicity assay for cell-mediated immunity. Adherent rat tumour cells established in tissue culture were used as targets and the basic variables studied were labelling efficiency, toxicity and spontaneous release rates. [125I]Iododeoxyuridine was found unsuitable on account of its high toxicity and correspondingly high spontaneous release rate, and Na2 51CrO4 for its toxicity and low labelling efficiency. Of the two other radiolabels, [75Se]selenomethionine had the advantage over [3H]proline of higher labelling efficiency (especially in Ham's F10 medium), lower toxicity, and being a gamma-emitter. Furthermore, released 75Se was shown to be non-reutilisable and its retention by target cells provided an accurate measure of cell survival in an alloimmune system. Methods of calculating the results of pre-labelling cytotoxicity tests based on the total radioactivity in target cells at the beginning of the assay were found to be invalid.

Studies on the microcytotoxicity test. II. The uptake of amino acids ([3H]leucine or [75Se]methionine) but not nucleosides ([3H]thymidine or [125I]IUdR) or 51CrO24-provides a direct and quantitative measure of target cell survival in the presence of lymphoid cells.

We have studied the suitability of various commonly used radioactive materials for the direct post-labeling of adherent rat target cells in long-term cytotoxicity tests. The use of nucleosides at high concentration avoids the necessity of adding fluorodeoxyuridine to enhance nucleoside uptake by target cells, and reduces the degree of non-specific inhibition of nucleoside uptake caused by products released from effector lymphoid cells. However, when [125I]iododeoxyuridine was used for labelling, such inhibition was not completely avoided even at very high nucleoside concentration, necessitating the washing of target cells prior to labelling. Similarly, without prewashing, the uptake of 51CrO24-ions frequently failed to correlate well with the numbers of surviving target cells as assessed by cell counting. On the other hand, radiolabelled amino acids, when present at semi-saturating concentrations, were taken up quantitatively by target cells under all conditions tested. Furthermore, in comparison to [125I]iododeoxyuridine, radioactive amino acids showed little if any toxicity to target cells. The use of the gamma-emitting amino acid analogue, [75Se]selenomethionine, is particularly recommended.

Assessment of drug sensitivity of human leukaemic myeloblasts. I. Labelling human myeloblasts with 125IUdR for survival studies in mice.

The compound (125)IUdR can be incorporated in a stable form into the DNA of cells. The isotope is released if labelled cells or their progeny die. Consequently the rate of (125)I excretion from mice can be used to follow the fate of labelled cells in vivo. Using these principles we show:(1) Sufficient label can be incorporated in vitro into both fresh and cryopreserved human leukaemic myeloblasts, in non-toxic concentrations, to allow their survival in mice to be estimated by whole-body counting;(2) The release of isotope from labelled cells is sufficiently slow to offer reasonable expectation that this technique can be used for assessing the sensitivity of myeloblasts to cytotoxic agents in vivo (an application described in the second paper in this series, Sonis, Falcão and MacLennon, 1977);(3) The rate of (125)Iexcretion from mice injected with myeloblasts from different donors varies. This probably reflects different rates of spontaneous death of injected myeloblasts;(4) Active rejection of myeloblasts starts within 48 h of their injection into mice;(5) Indirect evidence that phagocytic cells may be active agents in myeloblast destruction in mice;(6) Various methods of immunologically depriving mice were assessed to see if they would result in a useful increase in survival of injected human myeloblasts. We conclude that there is little advantage and some limitations in using mice thus deprived;(7) One of the agents used for immunological deprivation-silica powder-markedly decreased the rate of (125)I loss from mice injected with labelled killed myeloblasts. This experience emphasizes the importance of including the killed-cell control in this assay.

Adjuvant and mitogenic properties of a supernatant fraction of sonically treated Myobacterium bovis (BCG).

A water-soluble, oil-free supernatant fraction of sonically treated BCG (BCG-SS) was shown to be an immunological adjuvant and a mitogen. When BCG-SS and sheep erythrocytes (SRBC) were injected intravenously into mice, the plaque-forming cell (PFC) response was 10 times greater than that induced by injection of SRBC alone. Circulating antibody responses to SRBC and to bovine serum albumin were also enhanced by BCG-SS. The in vitro enhancement of PFC and circulating antibody responses did not require mineral oil or exogenous lipids. In vitro PFC responses by normal mouse spleen cells were also greatly increased in the presence of BCG-SS. Anti-theta serum-treated spleen cells from mice that had been lethally irradiated and reconstituted with normal bone marrow cells also gave a higher PFC response to SRBC in the presence of BCG-SS. This suggests that BCG-SS can stimulate B lymphocytes to develop an immune response when T lymphocytes are severely depleted or absent. BCG-SS also stimulated the uptake of 125IUdR by normal spleen cell cultures, indicating that it is a mitogen.

Effect of hyperthermia on the radiosensitivity of normal and malignant cells in mice.

The effect of systemic hyperthermia on the in vivo radiation response of normal and malignant mouse cells was evaluated. X-irradiation of L1210 cells and Ehrlich ascites cells at body temperatures above 41 degrees C resulted in strongly enhanced tumor cell death. The magnitude of this thermal effect increased with increasing temperatures. Hypoxic tumor cells were particularly sensitive to combined heat-radiation treatment. L1210 leukemia cells did not become resistant to the sensitizing effects of hyperthermia even after repeated heat exposures over several transplant generations. The sensitizing action of hyperthermia varied with different heating strategies. Heating before or during irradiation did not materially alter the radiation response of tumor cells. Maximal potentiation of radiation damage was achieved only when the tumorous mice were subjected to at least 20 minutes heat incubation after irradiation. LD studies on ICR mice revealed that moderate hyperthermia (41.5 degrees C) does not alter the radiation response of normal body tissues. These findings indicate that it is possible to devise hyperthermic treatment regimens that drastically enhance radiation-induced tumor cell death in vivo without reducing the radioresistance of normal tissues.