Response of mouse skin and the C3HBA mammary carcinoma of the C3H mouse to x-rays and cyclotron neutrons: effect of mixed neutron-photon fractionation schemes

Small-molecule multidrug resistance-associated protein 1 inhibitor reversan increases the therapeutic index of chemotherapy in mouse models of neuroblastoma

The multidrug resistance-associated protein 1 (MRP1) has been closely linked to poor treatment response in several cancers, most notably neuroblastoma. Homozygous deletion of the MRP1 gene in primary murine neuroblastoma tumors resulted in increased sensitivity to MRP1 substrate drugs (vincristine, etoposide, and doxorubicin) compared with tumors containing both copies of wild-type MRP1, indicating that MRP1 plays a significant role in the drug resistance in this tumor type and defining this multidrug transporter as a target for pharmacologic suppression. A cell-based readout system was created to functionally determine intracellular accumulation of MRP1 substrates using a p53-responsive reporter as an indicator of drug-induced DNA damage. Screening of small-molecule libraries in this readout system revealed pyrazolopyrimidines as a prominent structural class of potent MRP1 inhibitors. Reversan, the lead compound of this class, increased the efficacy of both vincristine and etoposide in murine models of neuroblastoma (syngeneic and human xenografts). As opposed to the majority of inhibitors of multidrug transporters, Reversan was not toxic by itself nor did it increase the toxicity of chemotherapeutic drug exposure in mice. Therefore, Reversan represents a new class of nontoxic MRP1 inhibitor, which may be clinically useful for the treatment of neuroblastoma and other MRP1-overexpressing drug-refractory tumors by increasing their sensitivity to conventional chemotherapy.

Neutron radiobiology revisited

The present paper reviews the experimental results of normal tissue and tumour studies in animals. The dose per fraction dependence of the RBE in normal tissues has been long recognised, together with the steeper increase of RBE at low doses for late responding tissues compared with acute reactions. The dose dependence for tumours is more complex, because of hypoxia and reoxygenation, as well as differences in repair capability after high LET damage. A comparison of tumour and normal tissue RBE values shows that there is little experimental evidence for a therapeutic advantage at clinically relevant doses. In particular, the RBE for slow growing tumours is even lower than that for the faster growing mouse tumours. The reasons for the loss of expected neutron benefits in clinically relevant experiments are discussed. The disappointing prospects for neutrons are contrasted with the current multifactorial approaches to overcoming resistance to more conventional low LET radiations, including acceleration, hyperfractionation and several types of hypoxic cell radiosensitizers.

Radiolabelled fluoromisonidazole as an imaging agent for tumor hypoxia

Fluoromisonidazole labeled with H-3 or F-18 has been tested as a quantitative probe for hypoxic cells in vitro and in rodent and spontaneous dog tumors in vivo. In V-79, EMT-6(UW), RIF-1, and canine osteosarcoma cells in vitro, the binding of 50 microM [H-3]Fluoromisonidazole was 50% inhibited by 1000-2000 ppm O2, relative to binding under anoxic conditions. After a 3 hr incubation with labeled drug, the anoxic/oxic binding ratios ranged from 12 to 27 for the four cell types. Retention of [H-3]fluoromisonidazole 4 hr after injection was greater in large KHT tumors (400-600 mm3) with an estimated hypoxic fraction greater than 30%, than in smaller tumors (50-200 mm3) with an estimated hypoxic fraction of 7-12%. RIF-1 tumors, with an estimated hypoxic fraction of 1.5%, retained the least label, with tumor: blood ratios ranging from 1.7 to 1.9. Spontaneous dog osteosarcomas were imaged with a time of flight positron emission tomograph for up to 5 hr following injection of [F-18] fluoromisonidazole. Analysis of regions of interest in images allowed creation of dynamic tissue time activity curves and calculation of tissue uptake in cpm/gram. These values were compared to radioactivity in plasma. In all cases, retention in some tumor regions exceeded that in plasma and in normal tissue, such as muscle or brain, by 3 to 5 hr post injection. Uptake of fluoromisonidazole in tumors was heterogeneous, with ratios of maximum to minimum uptake as high as 4 in different regions of interest in the same tumor. Tumor:plasma values ranged from 0.28 to 2.02. The oxygen dependency of fluoromisonidazole retention was similar in a variety of cell types and was 50% inhibited by O2 levels in the transition between full radiobiological hypoxia and partial sensitization. The quantitative regional imaging of [F-18] fluoromisonidazole in spontaneous canine tumors at varying times post-injection lays the basis for imaging and modeling of oxygen-dependent drug retention in different regions of human neoplasms.

Response of rat rhabdomyosarcoma tumors to split doses of mixed high- and low-let radiation

Radiation-induced growth delay was measured in rat rhabdomyosarcoma tumors exposed to split doses of high-LET (linear energy transfer) neon ions in the extended-peak ionization region and low-LET X rays. Top-off doses of 7.5, 15, and 25 Gy of 225-kVp X rays were administered to the tumors at 0.5, 4.0, and 24.0 hr following priming doses of either peak neon ions or X rays. The priming doses used were 7 Gy of peak neon ions and 20 Gy of X rays, both of which produced a 10 day delay in tumor regrowth to a volume twice that measured on the day of irradiation. The tumor response to split doses of X rays indicated rapid repair of sublethal damage, with significant recovery occurring at 0.5 hr and complete recovery by 4 hr after the initial 20-Gy X ray dose. The top-off doses of X rays required to produce an additional 10 or 20 days of tumor growth delay were 18 and 7% larger, respectively, when the priming dose was 20 Gy of X rays as compared to 7 Gy of peak neon ions. This result indicates that relatively little interaction of the neon-ion and X ray radiations occurred, even when the time interval between split-dose irradiations was as short as 0.5 hr. Our data indicate that the interaction of high- and low-LET radiation modalities is small, and approaches a simple additivity of effects when the tumors repair a major portion of the sublethal radiation injury imparted by a priming dose before the second dose is administered.

Biological effectiveness of fast neutrons on a murine osteosarcoma

The effect of fast neutrons and gamma rays on a murine osteosarcoma was studied. The NROS tumor, a radiation-induced osteosarcoma in a C3H mouse, was transplanted into the right hind legs of syngeneic female mice and locally irradiated with single or four daily doses of either fast neutrons or gamma rays. The NROS contained 13-30% hypoxic cells. It took approximately 7 days for the NROS tumor to show apparent reoxygenation following gamma ray irradiations. Two assays were used to determine the neutrons' relative biological effectiveness (RBE) to gamma rays: tumor growth delay time and tumor control dose. The largest RBE of 4.5 was obtained at the smallest dose of neutrons examined, followed by a gradual decrease down to 2.3. The tumor growth delay assay indicated that the RBE values of 2.6-3.1 after single doses of fast neutrons increased to 3.1-4.5 after four daily fractions. The 50% tumor control doses were 78.5 Gy and 33.0 Gy after single doses of gamma rays and fast neutrons, resulting in an RBE of 2.3. Fractionated doses increased the RBE to 2.6. Mitotic cells disappeared shortly after irradiation but reappeared 7 days after irradiation.

The effect of mixed fractionation with X rays and neutrons on tumour growth delay and skin reactions in mice

We have compared the effects of mixed fractionation schedules with X rays and neutrons on growth delay of a murine tumour and skin reactions in mice. The schedules were five daily fractions of X rays, neutrons or mixtures (NNXXX, XXXNN or NXXXN). For clamped tumours or skin all three mixed schedules had the same effect. In contrast, for unclamped tumours giving the neutrons first (NNXXX) was more effective than the other two mixed schedules. This represented a true therapeutic gain and implies that if neutrons are used clinically as only part of a course of fractionated radiotherapy, they should be given at the beginning rather than at the end of treatment.

The interaction between X-rays and 3 MeV neutrons in the skin of the mouse foot

Mouse feet were irradiated with mixtures of 3 MeV neutrons and 140 kVp X-rays given simultaneously or within 24 hours of each other. The effects of different treatments were contrasted by comparing the doses required to give equal skin reactions. Irradiation was given as 1, 2, 4 or 8 equal fractions, in order to assess r.b.e. and the shapes of the underlying dose-response curves for mixed beams over a wide range of dose per fraction. All dose-effect curves were well fitted by a linear-quadratic (alpha, beta) model. For X-rays and neutrons given simultaneously, the linear coefficient (alpha) decreased by a factor of 4.80 while the quadratic coefficient (beta) increased by a factor of only 1.44 when the proton contamination in the beam increased from 11 to 100 per cent, with alpha/beta changing from 95.0 to 13.8. The data from simultaneous X-ray and neutron irradiation were consistent with full interaction of those effects from the two radiations which give rise to the total quadratic component of effect. When the two radiations are separated by up to 24 h, this interaction decreases but does not entirely disappear.

Phase I pilot study on fast neutron teletherapy for advanced carcinomas of the head and neck region. Final report on local control rate and survival

A final report is presented on the local control rate and length of survival for 100 patients with advanced squamous cell carcinomas of the head and neck region who received fast neutron teletherapy at the University of Washington during the period 1973 through 1977. Sixty-two patients were treated with neutrons alone and 38 were treated with a combination of neutrons and photons as part of a mixed beam fractionation scheme. The overall initial complete remission rate was 68% for the mixed beam group and 44% for the group treated with neutrons alone. Initial complete remission rates for the two groups of patients are given as a function of T-stage and N-stage and acturarial curves are presented which show the time course of local control and survival for the two treatment groups. For T3 and T4 lesions the initial complete remission rate appears to be greater using the mixed beam form of treatment than using neutrons alone. Treatment to high-dose levels using neutrons alone gave rise to significantly greater morbidity--both acute and late effects--than resulted from the mixed beam form of treatment. Local control rates and survival rates are compared with similar groups of patients treated with neutrons at other institutions.

Fast neutron teletherapy for advanced carcinomas of the oral cavity and soft palate

A retrospective study was performed to determine the efficacy of using fast neutron radiation for treating advanced squamous cell carcinomas of the oral cavity and soft palate. The majority of patients were judged to have less than a 10% 5-year survival with conventional medical treatment. Fifteen patients with oral cavity tumors were treated for cure with neutrons alone and six were treated with a combination of neutrons and photons as part of a mixed beam fractionation scheme. In the neutron-only group, the complete regression rate was 33% in the mixed beam group, the rate was 50%. Five patients who had squamous cell carcinomas of the soft palate were treated for cure, one with neutrons alone and four with a mixed beam regimen. The complete regression rate was 100%. The two-year NED results are comparable with literature results for more selected groups of patients with oral cavity and soft palate tumors treated by conventional photon therapy. The acute treatment morbidity was perhaps somewhat greater in the subgroup of patients treated with neutrons alone, and this subgroup later developed a more pronounced subcutaneous fibrosis. Morbidity associated with the mixed beam treatment regimen was comparable to that associated with conventional radiotherapy.

Effect of tumor dissaggregation on results of in vitro cell survival assay after in vivo treatment of the EMT-6 tumor: x-rays, cyclophosphamide, and bleomycin

EMT-6 tumors were treated in vivo with 300 kVp X-rays, cyclophosphamide, or bleomycin. Tumor cell suspensions were prepared by digesting tumors with trypsin or a collagenase-deoxyribonuclease-pronase cocktail, and cells were plated in vitro for determination of fractional cell survival. Cell survival after X-rays was identical for the two disaggregation methods. Trypsin-derived cells were far more sensitive to bleomycin but less sensitive to cyclophosphamide than those prepared with the mixed enzyme cocktail. Interaction of drug produced and enzyme caused damage was the probable cause for these discrepancies. The nature of the interaction may be drug specific and therefore unpredictable. The results were unlikely to be due to different nonrepresentative tumor cell samples being produced by the two digestion methods, because the X-ray cell survival curves were so similar for the two products.

Fast neutron teletherapy for advanced carcinoma of hypopharynx and supraglottic larynx

The results of a Phase I clinical trial using fast neutron teletherapy for advanced squamous cell carcinoma of the hypopharynx and supraglottic larynx are reported. Ten patients with hypopharyngeal tumors were treated for cure using neutrons alone and 6 patients with hypopharyngeal tumors were treated for cure using a combination of neutrons and photons as part of a mixed beam fraction scheme. In the neutron-only group, the initial complete remission rate was 4/10 (40%). The mean survival of this group of patients with initial complete remission was only 5.75 months (range 2--10) but all patients died without evidence of recurrent tumor at the primary site. In the mixed beam group, the initial complete remission rate was 5/6 (83%) but the local control rate dropped rapidly to 41 per cent when displayed on an actuarial plot. Six patients with advanced tumors of the supraglottic larynx were treated for cure, 5 with neutrons alone and one with a mixed beam regime. The initial complete remission rate was 3/6 (50%) but 2 of these patients rapidly recurred, which reduced the local control rate on an actuarial plot to 16 per cent. The relative adverse effects of the neutron-only treatment regime appear to be substantially greater than those of the mixed beam treatment regime.

Effect of roentgen, cyclotron neutron, or mixed neutron-photon fractionated irradiation of mice. LD50/4 day values

Mice were whole-body-irradiated with 5 fractions of roentgen rays in 5 days, 5 fractions of cyclotron neutrons in 5 days, or with mixed neutron-photon fractionated radiation, in the sequence n-n-x-x-x or n-x-x-x-n. The LD50/4 day values were determined. Roentgen rays and neutrons interact in the additive manner in the mixed fractionation schemes: effective dose per fraction is as predicted from the roentgen ray-only and neutron-only experiments. This essentially agrees with HENDRY et coll. (1976). However, no trend was found towards a less-than -additive effect which was observed by those authors and has also been suggested in skin response to mixed schemes (NELSON et coll. 1975).

Preliminary results of fast neutron teletherapy of metastatic cervical adenopathy

Between September 21, 1973 and May 9, 1975, 36 patients with metastatic cervical adenopathy from cancers primarily arising in the pharynx or oral cavity, including six with bilateral cervical involvement, received fast neutron teletherapy at the University of Washington. At the conclusion of treatment, the masses were no longer palpable in nine of 42 (21%) heminecks and were reduced more than 50% in 23 (55%). In 12 patients with partial regression, the masses eventually disappeared, so that in all, 21 heminecks (50%) or 20 patients (56%) were controlled for periods up to 66 weeks. Fixed cervical masses were controlled in 11 of 23 (48%) patients. These results, which must be sustained for longer observation periods, are comparable to results reported in the literature. Treatment was well tolerated; therefore, doses can be raised to study the influence on tumor control.