Effect of cobalt-60 gamma rays and DTIC (5-(3,3 dimethyl-1-triazeno)-imidazole-r-carboxamide) on human malignant melanomas grown in athymic nude mice

[Treatment of metastatic malignant melanoma localized to an extremity]

BACKGROUND

At the Norwegian Radium Hospital, most patients who were treated for metastases (localized to an extremity) from malignant melanoma in the period 1977-99 underwent intra-arterial chemotherapy combined with radiotherapy. We have evaluated the effects of this treatment, which has now been replaced by isolated limb perfusion (with melphalan and tumor necrosis factor).

MATERIAL AND METHODS

Medical records were reviewed for patients with metastatic malignant melanoma (localized to an extremity) who had been treated at the Norwegian Radium Hospital with intra-arterial chemotherapy (5-[3,3 dimethyl-1-triazeno]-imidazole-4-carboxamide [DTIC]) in the period 1977-99.

RESULTS

36 patients had received such treatment; in 30 of these the induction treatment was combined with radiation of the tumour area.. 24 patients were in complete remission after treatment (12 of these had all the metastases surgically removed before treatment). Nine patients had a partial remission while three patients had progressive disease. Median observation time was 49 months. 15 of 31 patients had an observation time of more than five years, and seven of these patients were alive after ten years. Three patients with metastasis localized to the lower extremity died of other causes. In one case the intra-arterial catheterisation caused serious aortic damage.

INTERPRETATION

It is possible to achieve long-term remission in patients with metastatic malignant melanoma localized to an extremity after intra-arterial chemotherapy combined with radiotherapy.

Tumour necrotisation in nude mice xenografts by the reversible protein synthesis inhibitor zilascorb(2H)

The deuterated benzaldehyde derivative zilascorb(2H), 5,6-O-benzylidene-d-L-ascorbic acid, was administered once daily by i.v. injection in nude mice with grafted tumours of a human malignant melanoma (E.E.) and ovarian carcinoma (OVCAR-3) origins. Like benzaldehyde, zilascorb(2H) has been shown to induce protein synthesis inhibition at otherwise non-toxic doses in cells grown in vitro, and acts reversibly in the sense that protein synthesis returns to normal shortly after removal of the drug. The present data indicate that daily injections with zilascorb(2H) induce a tumour volume growth inhibitory effect in both tumour xenografts studied. Furthermore, from histological examinations of each single tumour it was found that tumours of drug-treated animals, although smaller than those of placebo-treated (i.e. control) animals, had, on average, a higher necrotic fraction than control tumours. Thus, it is concluded that zilascorb(2H) induces tumour necrotisation and not just inhibition of the rate of tumour cell production. Continued measurement of tumour volume after ended treatment with zilascorb(2H) indicated that surviving tumour cells resumed their normal growth rate immediately. The reversibility of the effect induced by this compound, earlier observed in vitro only, is therefore here confirmed to be valid also in two different tumour xenografts in vivo. The present data accords well with the assumption that protein synthesis inhibition is the primary cellular effect of zilascorb(2H) in vivo. We therefore conclude that zilascorb(2H)-induced cancer cell lethality in tumour xenografts probably comes as a secondary consequence of prolonged protein synthesis inhibition.

The search for therapeutic gain in the combination of radiotherapy and chemotherapy

The literature on combined treatment with radiation and cytotoxic drugs in experimental tumours and normal tissues of laboratory animals is reviewed in the context of the four previously proposed mechanisms whereby a therapeutic advantage might be gained. There is evidence for strong time-dependent processes occurring in some normal tissues. In tumours, the evidence for this is much weaker and there is considerable disparity among experimental tumours in optimum timing. This review leads to the conclusion that the clinical use of drug-radiation combinations should not be based on an anticipated beneficial interaction; gain will most probably come from the best radiotherapy and the best chemotherapy given as far as possible independently. Deleterious interactions can be reduced by allowing a gap of some weeks between chemotherapy and radiotherapy and by avoiding drugs that are known to enhance radiation damage to the normal tissues that are irradiated.

Radiation biology of malignant melanoma

The survival curves for melanoma cells exposed to single radiation doses in vitro and the specific growth delays for melanoma xenografts irradiated with single doses in vivo were found to differ considerably among individual cell lines and tumours. In fact, the differences could be almost as large as the largest differences observed among cell lines and xenografts from tumours of different histology with very different clinical radiocurability. Moreover, radiobiologic parameters that may have significant influence on tumour response to fractionated irradiation, e.g. growth rate, hypoxic fraction, reoxygenation ability, PLD-repair capacity and contact repair capacity, were found to differ greatly in magnitude among individual melanomas. This review therefore concludes that malignant melanoma is a tumour type that is very heterogeneous in radioresponsiveness, i.e. malignant melanomas should no longer be considered to be radiation resistant in general. The values of the alpha/beta ratio derived from cell survival curves for melanoma cells irradiated in vitro and melanoma xenografts irradiated in vivo were found to cover a wide range relative to those for acutely and late responding normal tissues. Although these alpha/beta ratios are no more than estimates of the effective alpha/beta ratios in a clinical situation, they still indicated that hyperfractionation may be beneficial in the treatment of some melanomas, whereas others may be more efficiently treated by use of conventional fractionation regimes, either based on 2 Gy or higher doses per fraction. Consequently, optimum radiation therapy of malignant melanoma will probably require an individualized treatment strategy. In vitro assays for prediction of radiocurability and choice of treatment strategy for individual melanoma patients seem therefore highly warranted.

Non-nitro radiation sensitizers

A review of the literature on radiosensitization reveals that at least some of the non-nitro compounds, such as metabolic inhibitors and membrane-active drugs, could be considered as potentially valuable radiosensitizers for possible use in future cancer radiotherapy.

Human tumour xenografts in radiotherapeutic research

The radiation response of human tumour xenografts has been shown to vary considerably among tumours of different histological types, tumours of the same histological type and cell subpopulations of single tumours. There is encouraging evidence that the radiation response correlates with clinical responsiveness when xenografts are exposed to single radiation doses and single cell survival in vitro or growth delay in vivo is used as endpoint. If subsequent research supports this conclusion, human tumour xenografts may be useful in studies aimed at (a) elucidating the underlying mechanisms for intertumour differences in radiation response and (b) developing short-term in vitro assays for clinical radiosensitivity testing. However, there are at least three main disadvantages with xenografts as models for human cancer. Firstly, the volume-doubling time is usually shorter than for tumours in man. Secondly, the vascular system and the supporting stromal elements originate from the host. Thirdly, host defence mechanisms may be active against xenografts. The radiation response of xenografts may be influenced by these three aspects and hence fail to reflect clinical responsiveness, especially when exposed to fractionated irradiation or when local tumour control is used as endpoint.

Micronucleus formation in human melanoma xenografts following exposure to hyperthermia

The formation of micronuclei in two human melanoma xenografts (E. E. and V. N.) following hyperthermic treatment (42.5 degrees C for 60 min) was studied and compared to that following single dose irradiation. The melanomas were grown in the hind leg of athymic mice and heated by immersing the tumour-bearing leg into a water-bath. Histological sections were prepared from tumours removed from the mice at predetermined times after treatment and the fraction of abnormal mitotic figures and the number of micronuclei per nucleus were scored. During the first 24 h after treatment, the fraction of abnormal mitotic figures increased abruptly to 90%-100% followed by a rapid decrease to 40%-50%. It then decreased slowly towards about twice the level in untreated tumours. The number of micronuclei started to increase at about the same time as the fraction of abnormal mitotic figures was highest, reached a maximum at about 2-3 days after treatment, and then decreased slowly. The number of micronuclei seen after the hyperthermic treatment was lower than that seen after radiation treatments causing similar tumour regrowth delays. The same hyperthermic treatment resulted in more micronuclei and larger regrowth delays for E. E. than for V. N. melanoma. The present results indicate that DNA damage is involved in heat-induced cell death in tumours treated in vivo.

Sensitising effect of misonidazole on NHIK 1922 cells irradiated in vitro or as solid tumour in athymic nude mice

The sensitising effect of the hypoxic cell sensitiser misonidazole (MIS) on NHIK 1922 cells irradiated either as single cells in vitro or as tumours in vivo in air-breathing and in dead mice was investigated with subsequent determination of in vitro colony-forming ability. In absence of MIS no significant difference was found between the dose-response curves after irradiation of tumours in dead mice and of cells in suspension under hypoxic conditions. After irradiation of tumours in air-breathing mice the same enhancement ratio of 1.4 was found whether MIS was administered in doses of 250 or 1000 micrograms/g body weight. In dead mice the enhancement ratio was 1.3 and 2.6 after 250 and 1000 micrograms/g, respectively. The sensitising effect of MIS for cells irradiated in suspension under extremely hypoxic conditions corresponded to that found in dead mice when a comparable concentration of MIS was used.

Broad-shouldered survival curves of a human melanoma xenograft. Implications for radiation therapy in the absence and presence of misonidazole

A human malignant melanoma (E.E.) was irradiated in vivo in athymic nude mice, with subsequent assay of single cell survival in vitro. By assuming the survival curves for the hypoxic as well as for the aerobic cells in the tumour to be of the form S = exp(-D/D1) X (1-[1-exp (-D/D2]n), theoretic survival curves were fitted to the experimental data for tumours irradiated in air-breathing mice. Assumptions were made about hypoxic fraction, oxygen enhancement ratio, sensitization by misonidazole, repair of potentially lethal damage, and reoxygenation, all based upon own experimental data on E.E. melanoma. Theoretic surviving fractions were calculated for several clinically relevant fractionation regimes, both for irradiation in the absence and in the presence of misonidazole. The results indicate that tumours with biologic parameters like those of E.E. melanoma are best treated with fractionation regimes with few fractions and high doses per fraction, whether misonidazole is present or not.

Effect of single dose irradiation on the proliferation kinetics in a human malignant melanoma in athymic nude mice

The effect of single dose irradiation on the proliferation kinetics in a human malignant melanoma grown in the athymic mutant nude mouse was analysed. DNA-histograms were obtained with flow cytofluorometry. Percentage labelled mitoses curves were established by the use of conventional autoradiographic techniques. Changes in the fraction of clonogenic cells with time after irradiation were measured in vitro in soft agar. In non-irradiated tumours the fraction of cells in G1/G0, S and G2 + M was 66.21 and 13 per cent, respectively. The median duration of G1, S, G2, M and Te was 19.0 h, 13.3 h, 5.0 h, 1.0 h and 41.4 h, respectively. The growth fraction was calculated as 0.66 and the cell loss factor as 0.67. The growth fraction was increased after irradiation and the cell cycle time reduced, due to a shortening of G1. These effects were dose dependent and decreased with time after exposure, but were still present after the tumours had resumed a continuous volume growth. The rate of volume growth was slower for irradiated tumours than for non-irradiated tumours of the same size, due to a larger cell loss factor for the former.

Growth kinetics of a rat mammary tumour transplanted into immune-suppressed mice

The growth kinetics of a transplanted rat mammary tumour and its xenografts in immune-suppressed mice were studied using the technique of labelled mitoses. Growth of the tumour in rats was regular and uniform but when transplanted into mice the growth of the implants was irregular and generally slower. The second passage tumours in mice showed rapid and regular growth with a volume doubling time approximately half that for the tumours in the rat. Values for the G1 phase duration, intermitotic time and growth fraction were greater for the tumours in the mouse although the data for the first passage in mice were difficult to interpret. The kinetic changes between the rat and mouse hosts primarily reflect a large and variable amount of cell loss from the first passage xenografts in the mouse, with adaptation by the second passage towards reduced cell loss.

Radiosensitizing effect of misonidazole in fractionated gamma-ray treatment of a human malignant melanoma grown in athymic nude mice

The effect of the hypoxic cell radiosensitizer misonidazole (Ro-07-0582) has been tested on a human malignant melanoma grown subcutaneously in the athymic mutant nude mouse. A 60Co therapy unit was used for local irradiation of the animals. The tumours were exposed daily to 3.75 Gy (375 rad) over four consecutive days, to a total dose of 15.0 Gy. Misonidazole in doses of 500 mg/kg bodyweight was administered intraperitoneally in the mice 45 minutes before each irradiation. The time necessary for the tumours to regrow to their original sizes was compared with that of tumours treated with four daily fractions of 3.75, 4.50 and 5.25 Gy without sensitizer. The enhancement ratio of misonidazole was found to be 1.05.

Evaluation of single-agent therapy in human colorectal tumour xenografts

The response of 6 human colorectal tumour xenografts to 7 cytotoxic agents have been established. Tumour responses have been quantified by growth inhibition, and the time taken for 3H-thymidine fractional incorporation (TFI) to recover to the control value after treatment. The chemosensitivity of each tumour line to a spectrum of agents was individual, and no pattern of response which would allow prediction of individual agent efficacy was apparent. Cyclophosphamide, methyl-CCNU and 5-fluorouracil produced marked growth inhibition in individual tumour lines, whereas actinomycin-D, cis-dichlorodiammine platinum, doxorubicin and pentamethylmelamine showed little activity. Data presented agree with clinical evaluation for single-agent therapy. The uptake and incorporation of radiolabelled 5-fluorouracil into 4 tumour lines is reported. No marked differences between 3 FU-insensitive lines and 1 sensitive line have been observed.

The radiosensitizing effect of metronidazole and misonidazole (Ro-07-0582) on a human malignant melanoma grown in the athymic mutant nude mouse

The radiosensitizing effect of two electron-affinic nitroimidazoles, metronidazole and misonidazole (Ro-07-0582), has been tested on a human malignant melanoma grown subcutaneously in the athymic mutant nude mouse. A 60Co therapy unit was used for local irradiation of the mice. Metronidazole in doses of 750 mg/kg and misonidazole in doses of 500 mg/kg were administered intraperitoneally to the animals 45 min before exposure to 1250 rad. The time necessary for the tumours to regrow to their original sizes was compared with that of tumours treated with 1250, 1875 and 2500 rad without drug. The enhancement ratios were found to be 1.2-1.3 and 1.4-1.5 for metronidazole and misonidazole respectively. It is concluded that misonidazole is a more efficient hypoxic cell radiosensitizer for this human malignant melanoma than metronidazole. The former may prove to be of value in human radiotherapy.

Effect of clinically relevant irradiation regimes on human malignant melanomas grown in athymic nude mice

Human tumors grown subcutaneously in the thymus deficient nude mice are used as a model system to compare the effectiveness of clinically relevant irradiation regimes. Procedures for local irradiation of the tumors with 60Co radiation are described in detail. A preliminary test of the regression of two malignant melanomas, following three clinically relevant fractionation schedules, is performed. The overall treatment time and the nominal standard dose (NSD) are kept equal for the irradiation regimes chosen.