Induction of hypoxia in experimental murine tumors by the nitric oxide synthase inhibitor, NG-nitro-L-arginine.

The nitric oxide synthase inhibitor NG-nitro-L-arginine (NOARG) was examined for its ability to alter energy metabolism in three murine tumors using 31P magnetic resonance spectroscopy. NOARG (10 mg/kg, i.v.) increased the inorganic phosphate:total phosphate ratio (Pi:total) 2-3-fold in the KHT, RIF-1, and SCCVII/Ha intradermal back tumors from 30 min to 6 h after injection, but the 31P magnetic resonance spectrum from normal tissue on the mouse back was unchanged after this treatment. NOARG (10 mg/kg, i.v.) injected 30 min before X-rays increased tumor cell survival 3-5-fold in SCCVII/Ha and 50-200-fold in RIF-1, measured using an in vivo/in vitro clonogenic assay. These effects were equivalent to those obtained from clamped tumors, indicating full radiobiological hypoxia. In KHT, only a 2-fold increase in radioresistance was observed after NOARG, which was less than the response of clamped tumors. In RIF-1 tumors, NOARG induced full radiobiological hypoxia when given from 30 min to 6 h prior to X-rays, consistent with the time course for the increase in Pi:total, measured by 31P magnetic resonance spectroscopy. Pi:total after NOARG doses of 0.1-10 mg/kg, i.v., increased in a dose-dependent manner in this tumor. Increased RIF-1 tumor radioresistance was similarly dependent on NOARG dose. The combination of the bioreductive agent RB6145 (300 mg/kg, i.p.) 15 min prior to NOARG (10 mg/kg, i.v.) produced greater than 5 decades of KHT tumor cell killing at 24 h after treatment. This combination also increased Pi:total 4.5-fold over the control value at 24 h in the KHT tumor. Histological examination of tumors at this time indicated extensive necrosis.

The response of spontaneous and transplantable murine tumors to vasoactive agents measured by 31P magnetic resonance spectroscopy.

31P magnetic resonance spectroscopy has been used to compare the effects of the vasoactive agents hydralazine and flunarizine on the oxygenation of the transplantable tumors, SCCVII/Ha and 16C, and a range of spontaneous mammary tumors arising in the breeding stock in the Genetics Division at the Radiobiology Unit. The vasodilator hydralazine, previously shown to increase the radiobiological hypoxic fraction of transplantable murine tumors, increased inorganic phosphate to total phosphate (Pi/total) in SCCVII/Ha and 16C tumors. However, only two spontaneous tumors responded to this agent (2/12). The calcium antagonist flunarizine, which sensitizes the SCCVII tumor to X rays, consistent with a reduction in hypoxic fraction, reduced Pi/total in this and the 16C tumor. Further, most spontaneous tumors tested (8/10) responded to this agent, as measured by a reduction in Pi/total. These results point to fundamental differences between transplantable and spontaneously arising tumors in mice in their response to vasoactive agents.

Comparing the anti-tumor effect of several bioreductive drugs when used in combination with photodynamic therapy (PDT).

PURPOSE: To compare the effect on the RIF-1 murine sarcoma of nine bioreductive agents from five different classes when used in combination with either photodynamic therapy or clamping. METHODS AND MATERIALS: RIF-1 tumors implanted intradermally in C3H mice were treated with either 50J photodynamic therapy or with 120 min clamping in combination with either misonidazole, pimonidazole, metronidazole, nimorazole, RB6145, RSU1069, SR4233, mitomycin-C, or RB90740. The tumors were measured 3 times-per-week until reaching 4 x their initial treatment volume. RESULTS: RSU1069 produced the greatest anti-tumor activity in combination with both photodynamic therapy and clamping. RB6145 also substantially enhanced the effect of photodynamic therapy and clamping whereas misonidazole induced a smaller, but significant increase. Mitomycin-C had no effect under clamped conditions, but greatly increased the tumorcidal effect of photodynamic therapy. Mitomycin-C also induced an effect when given with light alone. None of the other agents showed any augmentation of the tumor cell killing induced by photodynamic therapy. CONCLUSION: Of the bioreductive agents studied RSU1069, RB6145 and mitomycin-C showed the greatest anti-tumor response in combination with photodynamic therapy.

Combination of photodynamic therapy (PDT) and melphalan in experimental tumors.

PURPOSE: To investigate whether application of "early" photodynamic therapy (PDT) using a disulphonated aluminium phthallocyanine photosensitizer can potentiate the action of melphalan in experimental RIF-1 tumors in vivo. METHODS AND MATERIALS: Tumors were irradiated with laser light of wavelength 675 nm 60 min after treatment with the photosensitizer and 15 min after melphalan. Melphalan pharmacokinetics were measured using high performance liquid chromatography with optical detection. RESULTS: Melphalan and PDT when given alone, caused a significant delay in tumor growth. This was increased for the combined treatment. Pharmacokinetic analyses showed that levels of free, unreacted melphalan in freely circulating blood are unaffected by combined treatment. However, significant differences in tumor levels were observed between treatment with melphalan alone or in combination. Whereas in the former, melphalan is still present in tumors after 2 h, it was not detectable even at the earliest time of 15-23 min for the combined treatment. CONCLUSION: The antitumor effects were additive with no evidence of significant potentiation.

Modification of the radiation response of pig skin by manipulation of tissue oxygen tension using anesthetics and administration of BW12C.

The importance of tissue oxygen tension on radiosensitivity was studied by examining modifications in the incidence of moist desquamation in pig skin after irradiation with strontium-90 plaques. The effects were analyzed using quantal dose-response data and comparisons were made using ED50 values for moist desquamation. Under standard anesthetic conditions of 2% halothane, approximately 70% oxygen, and approximately 30% nitrous oxide, the ED50 value (+/- SE) for moist desquamation was 27.32 +/- 0.52 Gy with no significant variation in radiosensitivity between dorsal, lateral, and ventral skin sites on the flank. Irradiation with 2% halothane and air increased the ED50 to 31.25 +/- 0.94 Gy, primarily due to an increased radioresistance of the dorsal sites. When combined with BW12C, a drug which binds oxygen selectively to hemoglobin and hence reduced the oxygen availability to tissues, a further increase in the ED50 values was observed. This was approximately 39 Gy with BW12C concentrations of 30 mg/kg and 50 mg/kg b.w. of BW12C, indicating a dose modification factor (DMF) of approximately 1.26. However, when animals were breathing the standard gas mixture, this DMF was reduced to 1.15 for 30 mg/kg of BW12C, indicating that a higher level of oxygen partly counteracted the effects of the drug in these studies with BW12C. The greatest variability in radiosensitivity was seen in the dorsal fields. This suggested complex physiological adaptation, a phenomenon that might also explain the absence of any modification of the radiation response when 100 mg/kg of BW12C was used.

Modification of metabolism of transplantable and spontaneous murine tumors by the nitric oxide synthase inhibitor, nitro-L-arginine.

PURPOSE: To determine the effects of the nitric oxide synthase inhibitor, nitro-L-arginine on energy metabolism in transplantable and spontaneous murine tumors. METHODS AND MATERIALS: The responses of the transplantable murine tumor SCCVII/Ha and a range of spontaneously arising murine mammary adenocarcinomas to 10 mg/kg IV nitro-L-arginine were examined using in vivo 31P magnetic resonance spectroscopy (MRS). The influence of Hypnorm/Hypnovel anesthesia on the response to nitro-L-arginine was also determined in the SCCVII/Ha tumors. Data were expressed as changes in the inorganic phosphate peak area relative to the sum of all peak areas from the 31P MR spectrum, or Pi/total. RESULTS: Nitro-L-arginine at 10 mg/kg IV increased Pi/total 2-3-fold in the SCCVII/Ha tumors for at least 2 h after administration, in both anesthetized and nonanesthetized mice, consistent with increased tumor hypoxia. Similar increases in Pi/total were observed after 10 mg/kg IV nitro-L-arginine in 13 spontaneous murine tumors from three different mouse strains, where anesthetic was used. CONCLUSION: The results indicate that tumor metabolism may be modified by an inhibitor of nitric oxide synthesis, that this modification occurs in both transplantable and spontaneous murine tumors and is not affected by anesthetic.

Protection of pig epidermis against radiation-induced damage by the infusion of BW12C.

BW12C, which was developed as an agent for the treatment of sickle cell anaemia, increases the binding of oxygen to haemoglobin and hence reduces the availability of oxygen to tissues. Due to these changes in oxygen availability BW12C could act as a protector against radiation-induced injury to normal tissues. In this study the potential value of BW12C, as a radioprotector, was studied in the irradiated epidermis of the pig. The infusion of BW12C caused an instant left shift of the oxygen dissociation curve, an effect that lasted for approximately 1.5 h. This left shift in the oxygen dissociation curves increased with increasing dose of the drug. There appeared to be no long-term systemic effects produced by doses of 20-100 mg/kg of BW12C. In the first 90 min after the infusion of BW12C skin fields were irradiated with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint for assessing the severity of the radiation response. With animals breathing approximately 70% oxygen in the anaesthetic gas mixture, the ED50 values for moist desquamation were 30-31 Gy after a dose of 30 and 50 mg/kg, and 37-38 Gy for 75 and 100 mg/kg doses of BW12C. These ED50 values were significantly higher than the value of 27.3 Gy for radiation alone. This indicated dose modification factors (DMF) with mean values of approximately 1.13 and approximately 1.40 for irradiation following the infusion of low (30-50 mg/kg) and high (75-100 mg/kg) doses of the drug, respectively. With the animals breathing air (approximately 21% of oxygen) in the 2% halothane anaesthesia gas mixture, irradiation in the presence of 30 and 50 mg/kg of BW12C resulted in ED50 values of approximately 39 Gy for moist desquamation, which was significantly higher than the value of 31.2 Gy for radiation alone. Surprisingly, a higher dose of 75 mg/kg of BW12C resulted in a lower ED50 value for moist desquamation of 34.38 Gy. Irradiation in the presence of a dose of 100 mg/kg of BW12C produced an ED50 value which was not significantly different from that for radiation alone. In the situation where animals were breathing air (approximately 21% oxygen) during irradiation a DMF of 1.14 was obtained for irradiation alone, when the results were compared with those for irradiation alone with approximately 70% oxygen in the anaesthetic gas mixture.(ABSTRACT TRUNCATED AT 400 WORDS)

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues in the pig. I. Effects on the epidermis and dermal vascular/connective tissues.

The effects of fractionated doses of fast neutrons (42 MeVd----Be) on the early epithelial and later dermal response of pig skin have been assessed and compared with those after X irradiation. For the early epithelial reaction, i.e. moist desquamation, the relative biological effectiveness (RBE) of the neutron beam increased with the decreasing size of the X-ray dose/fraction. There was an experimentally observed upper RBE value of approximately 2.75 for X-ray doses/fraction of between 2 and 5 Gy. For the late reaction of ischaemic dermal necrosis the RBE was greater than 3.0 for X-ray doses/fraction of less than 3 Gy and, based on the assumptions made in the linearquadratic model of cell survival, an upper limiting RBE of 4.32 +/- 0.39 was calculated for infinitely small doses/fraction. These findings were compared with other radiobiological data and the conclusions drawn from the results of clinical trials. It was concluded that for the sparing of late effects in skin and subcutaneous tissues, relative to acute reactions, a relatively small number of fractions in a short overall treatment time may be optimal for fast neutron therapy.

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues. III. Effects on lung function.

The effect of single and fractionated doses of fast neutrons (42 MeVd----Be) on the early and late radiation responses of the pig lung have been assessed by the measurement of changes in lung function using a 133Xe washout technique. The results obtained for irradiation schedules with fast neutrons have been compared with those after photon irradiation. There was no statistically significant difference between the values for the relative biological effectiveness (RBE) for the early and late radiation response of the lung. The RBE of the neutron beam increased with decreasing size of dose/fraction with an upper limit value of 4.39 +/- 0.94 for infinitely small X-ray doses per fraction.

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues in the pig. II. Late effects on cutaneous and subcutaneous tissues.

The late effects of irradiation with single and fractionated doses of X rays (250 kV) and fast neutrons (42 MeVd----Bc), on the cutaneous and subcutaneous tissues of the pig, have been evaluated from measurements of changes in relative field length. These were determined at intervals of 26-104 weeks after irradiation. For fractionated irradiation with X rays the average fractions exponent, N, obtained from a log-log plot of iso-effect dose (ED50) against fraction number was 0.41. This was independent of the period of assessment, with no significant indication of a time factor. However, the exponent N did vary with the level of effect and was in the range 0.33-0.51. It was greatest for a greater than or equal to 10% reduction in relative field length. Assuming the validity of the linear quadratic model of cell survival, the alpha/beta ratio was 1.95 Gy. However, this model fitted the data less well for the least severe levels of damage, and for these the alpha/beta ratios were not significantly different from zero. Irradiation with fast neutrons showed a small effect of fractionation for doses given in greater than or equal to 6 fractions compared with a single dose. There was no significant increase in iso-effect dose when the dose was given in 30 fractions compared with 6 fractions. The relative biological effectiveness for late cutaneous and subcutaneous damage for the energy of fast neutrons used did not vary with the period of assessment, i.e. 26-52 weeks compared with 65-104 weeks, and was not significantly different from that previously obtained for ischaemic dermal necrosis, seen after higher doses, at 12-20 weeks after irradiation.

The relative biological effectiveness of fractionated doses of fast neutrons (42 MeVd----Be) for normal tissues in the pig. IV. Effects on renal function.

The effects of fractionated doses of fast neutrons (42 MeVd----Be) on the radiation response of the pig kidney have been assessed and compared with those observed after X irradiation. Following X irradiation there was a marked increase in the total dose at which renal function was preserved with decreasing fraction size. The rate of this increase was dependent on the overall treatment time; for fractionated irradiation given over 18 or 39 days the exponents related to fraction number, N, were 0.36 +/- 0.03 and 0.48 +/- 0.003, respectively. In contrast, there was no significant change in the iso-effect dose for renal injury following fractionated irradiation with fast neutrons where there was also little effect of varying the overall treatment time. Analysing these data by means of the linear-quadratic (LQ) model, using both an Fe-plot and the Tucker test, gave alpha/beta ratios of 2.42 +/- 0.06 Gy and 2.99 +/- 0.16 Gy, respectively, for X-ray doses given in 18 days. For fractionated doses of X rays given in 39 days the alpha/beta ratios were 0.40 +/- 0.01 Gy and 0.47 +/- 0.02 Gy, respectively. The alpha/beta ratios for renal tissue following fast neutron irradiation obtained by the two methods were also similar, i.e. 15.00 +/- 0.60 Gy and 15.72 +/- 3.76 Gy, respectively. The pronounced fractionation effect seen with X irradiation, particularly for doses administered over 39 days as opposed to 18 days, coupled with the absence of any such effect with fast neutrons, resulted in a marked increase in relative biological effectiveness (RBE) with decreasing X-ray dose/fraction. The slopes of the resulting regression lines were -0.73 +/- 0.05 and -0.33 +/- 0.02, respectively. The lack of dose sparing associated with fractionation, or variation of the overall treatment time for fast neutron irradiation, suggests that doses administered to tumours adjacent to the kidney can be given as a few relatively large dose/fractions in a short overall treatment time without an increased risk of complications related to renal tissue. This may be of therapeutic advantage in the treatment of rapidly proliferating tumours where dose may be wasted using more conventional protracted fractionated irradiation schedules.

Functional changes in the pig kidney following irradiation with fractionated doses of fast neutrons (42 MeVd-->Be).

The right kidney of female Large White pigs, approximately 14 weeks old, was irradiated with fractionated doses of fast neutrons (42 MeVd-->Be). The total doses used were 6.6-9.2 Gy. Changes in kidney function, assessed as the functional index (FI, where FI = irradiated kidney function/unirradiated kidney function) or as individual kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), were serially determined up to 104 weeks after irradiation using 99Tcm-DTPA and 131I-hippuran renography. The animals were then euthanized, the kidneys removed and weighed. A dose-dependent reduction in FI was seen within 13 weeks of irradiation. Measuring individual kidney function revealed a hyperaemic response in both irradiated and unirradiated kidney 4 weeks after irradiation. This was followed by a dose-dependent reduction in irradiated kidney GFR and particularly ERPF. The ED50 value for the impairment in ERPF, assessed as the percentage of irradiated kidneys exhibiting a > or = 50% reduction in ERPF, was significantly lower than that for GFR, i.e. 7.20 +/- 0.10 Gy compared with 8.44 +/- 0.07 Gy (p < 0.001). A dose-related reduction in irradiated kidney weight was also observed. These fast neutron-induced changes in renal function and weight are qualitatively similar to those observed following photon irradiation of the pig kidney.

31P MRS of tumour metabolism in anaesthetized vs conscious mice.

The injectable anaesthetics Hypnorm/Hypnovel, chloral hydrate and etomidate, were examined for their effects on C3H/He mouse core temperature and on the in vivo 31P MR spectra of KHT and SCCVII/Ha transplantable tumours, compared with conscious mice gently restrained in jigs. Hypnorm/Hypnovel at 0.1 mL/mouse i.p. reduced core temperature by 6 degrees C at 30 min after injection, returning to control levels by 100 min, but did not significantly alter the 31P MR spectra of either KHT or SCCVII/Ha tumours. Chloral hydrate at 300 mg/kg i.p. produced a 5 degrees C fall in mouse core temperature, at 25 min after injection, again returning to control levels by 100 min. This agent increased the Pi/total ratio to 155% of control at 15 min after injection in the KHT tumour, and to 170% of control at 45 min in SCCVII/Ha. Etomidate at 25 mg/kg i.p. reduced mouse core temperature by 7.5 degrees C by 20 min after injection, returning to only 84% of control by 100 min. This agent increased the Pi/total ratio by 260% in the KHT tumour 15 min after injection, without recovery to control values by 100 min. In SCCVII/Ha, a maximum increase in Pi/total of 360% was observed at 15 min after injection, with a return to control levels by 60 min. In addition, etomidate caused convulsions in the mice during the induction phase, and myoclonic jerking within 15 min of anaesthesia.

Osteopetrosis of microphthalmic mice -- a defect of the hematopoietic stem cell.?

The recessive genes mi and gl in the homozygous state determine, among other phenotypic effects, osteopetrosis in the house mouse. From a stock carrying mi derived from Grüneberg (1963) the mi gene was bred into the standard CBA/H inbred strain. Microphthalmic mice of these two stocks and their hybrids were treated as newborn by intraperitoneal injection and at weaning or maturity by intravenous injection of cell suspensions containing hematopoietic stem cells from phenotypically normal mice. Resolution of much of the osteopetrosis but not the other phenotypic effects occurred within a few months in the majority of cases, provided syngeneic or H-2 compatible allogeneic cells were given: it did not occur spontaneously or on giving H-2 incompatible cells or on giving compatible material by an inappropriate route. The results accord with hypotheses that (1) osteoclasis of scaffoldtype woven bone is impaired in mi mi, (2) that osteoclastic cells are derived through circulating monocytes from hematopoietic stem cells, and (3) in mi mi this defect can be overcome by a transplant of normal hemopoietic stem cells.

Histochemical phosphatases and metachromasia in murine tumours induced by bone seeking radionuclides.

Tumours induced in mice, either CBA normal and chimaerical, or C3H, by (90)Sr or (226)Ra or plutonium have been examined histochemically with (1) diazotate fast red violet LB salt in naphthol AS-MX phosphate buffer at pH 8·6 and 5·2, (2) 1: 9 dimethyl methylene blue (Taylor).It is concluded:(a) The diagnosis of osteosarcoma is facilitated with Taylor's Blue which stains osteoid metachromatically. Cells of osteosarcoma, like normal osteoblasts, contain alkaline phosphatase but this may be lost by mutation either in the original tumour or subsequently on passage of the tumour serially to compatible hosts.(b) Osteosarcomata may contain giant-cells of two forms, bizarre tumour cells and osteoclasts; the latter contain acid phosphatase. Osteosarcomata which retain their osteoid on serial passage have few cells containing acid phosphatases.(c) Primitive mesenchymal cell tumours of angiomatous form may occur, if the bone marrow is irradiated, e.g. by (90)Sr-(90)Y and Pu. These tumours lack osteoid and cells interpretable as osteoblasts or osteoclasts (though they destroy bone).(d) Tumours classifiable as fibrosarcomata occur rarely, and may be truly of fibroblastic origin or be mutated osteosarcomata.(e) Lymphomata also occur when the marrow is irradiated ((90)Sr-(90)Y and Pu). They may be generalized, when their cells may contain alkaline phosphatase or lack it. They may be localized to abdominal viscera, the reticulo-sarcomatous form, in which case the cells lack alkaline phosphatase.

Reduction of tumour intracellular pH and enhancement of melphalan cytotoxicity by the ionophore Nigericin.

Nigericin is an ionophore which permits the influx of H+ ions into cells down a concentration gradient, thus reducing intracellular pH (pHi) when extracellular pH is low. The effects of nigericin on the pHi of solid murine tumours in vivo were examined using 31P magnetic resonance spectroscopy. Nigericin at 2.5 mg/kg i.p. reduced pHi by 0.2-0.3 pH unit in the KHT and RIF-I tumours but had no effect on pHi in the SCCVII/Ha tumour. In vitro studies have shown that reduced pH can increase the toxicity of melphalan. Therefore, the anti-tumour effect of combining nigericin with melphalan was also examined. Nigericin at 2.5 mg/kg i.p. given before various doses of melphalan resulted in substantial delay in growth of the RIF-I tumour over that induced by melphalan alone. This observation was confirmed by an in vivo/in vitro excision assay, where nigericin given before melphalan produced a 30-fold increase in cell killing. By contrast, no enhancement of melphalan-induced cell killing by nigericin was observed in the KHT and SCCVII/Ha tumours, using growth delay and in vivo/in vitro excision assays, respectively.

The accuracy and reproducibility of measuring blood flow in murine tumours by the D2O uptake and clearance techniques.

The use of D2O as an NMR visible tracer to monitor murine tumour blood flow (TBF) by both the wash-in and wash-out methods has been investigated. The factors that influence the models used to fit the data and the error on the measurement of the clearance and uptake rates have been assessed. The study concentrates on the uptake method which allows TBF to be measured without the need to use anaesthetic. Also, administering the D2O remotely to the mouse means it can remain undisturbed, in the magnet bore, between control and post-treatment readings. The uptake method in KHT and RIF-1 transplanted murine tumours has been investigated in a series of control experiments and after modifying TBF by hydralazine (5 mg/kg) and photodynamic therapy. These studies showed that four uptake measurements could be made on the same mouse at 20 min intervals without affecting TBF, control values were the same for anaesthetized and unanaesthetized mice and the values obtained for RIF-1 tumours were marginally higher than those obtained for the KHT tumours. The decrease in TBF seen after modification was in good agreement with published data where TBF results were obtained by using D2O clearance, radioactive tracers or laser Doppler flowmetry.

Changes in energy metabolism and X-ray sensitivity in murine tumours by the nitric oxide donor SIN-1.

The effect of the nitric oxide (NO) donor SIN-1 on energy metabolism was examined in three murine transplantable tumours in vivo using 31P MRS. SIN-1 at 2 mg kg-1 i.v. reduced Pi/total by 40-50% in SCCVII/Ha and KHT tumours within 5 min of injection, returning to control levels by 20 min. However, this dose of SIN-1 did not consistently alter Pi/total in RIF-1 tumours. Reduction in Pi/total in SCCVII/Ha tumours 10 min after 5 mg kg-1 i.v. SIN-1 was similar to that for 2 mg kg-1. SIN-1 at 10 mg kg-1 had no effect on Pi/total at 10 min after injection, but increased this ratio 2-fold over control at 60 min, at which time no effect of the lower doses of SIN-1 were observed. SIN-1 effects on SCCVII/Ha tumour response to X-rays were also examined, using an in vivo/in vitro clonogenic assay 24 h after treatment. SIN-1 at 0.5-2 mg kg-1 i.v. given immediately before irradiation increased tumour cell killing 2-4-fold over that for 15 Gy X-rays alone, while higher SIN-1 doses were ineffective. The results indicate that NO donors can alter tumour energy metabolism and X-ray response in a manner consistent with increased oxygenation. However, these responses are dependent upon dose, timing and tumour type.

Increasing the effect of photodynamic therapy on the RIF-1 murine sarcoma, using the bioreductive drugs RSU1069 and RB6145.

The effect of combining photodynamic therapy (PDT) and bioreductive drugs has been investigated using the RIF-1 experimental murine tumour. Light was delivered interstially to the tumour at 675 nm using a single optical fibre attached to an argon-ion dye laser. The photosensitizer was disulphonated aluminium phthalocyanine (AlS2Pc) and the bioreductive drugs were the dual function nitroimidazole RSU1069 and its pro-drug RB6145. Varying the time between administration of the photosensitizer and light delivery (TL) from 30 min to 24 h had little influence on the extent of the anti-tumour effect of PDT alone, as measured by the regrowth delay endpoint. When the bioreductive drug was included in the treatment, administered 20 min before light irradiation, regrowth delay was greatly increased. The effectiveness of the combined treatment was optimum for short values of TL (about 1 h). Fluorescence microscopy was used to investigate the distribution of the photosensitizer within the tumours. This showed that the compound was mainly confined to the tumour vasculature over the first few hours post-treatment. The high efficacy of the combined treatment of PDT and bioreductive drugs for short values of TL suggest that photodynamic action, during the period when the photosensitizer AlS2Pc is confined to the vasculature, enhances the severity of tumour hypoxia which is sufficient to induce activation of the bioreductive drugs.

The in vivo release of 90Y from cyclic and acyclic ligand-antibody conjugates.

Yttrium binding ligands DOTA, caDTPA and CT-DTPA were each conjugated to monoclonal antibody B72.3, labelled with 90Y and injected into mice in order to assess the in vivo inertness of the antibody-linked 90Y-ligand complexes. Levels of 90Y in femur shafts of the DOTA-B72.3 mice were low, being approximately 7 and 44%, respectively, of levels in the femur shafts of the caDTPA-B72.3 and CT-DTPA-B72.3 treated mice. This finding demonstrates the greater inertness and by implication the greater suitability for immunotherapy of the DOTA-90Y complex.