Modification of the radiation response of mouse lung by actinomycin D: dependence on interval between radiation and drug treatments

Dactinomycin potentiation of radiation pneumonitis: a forgotten interaction

No mention of dactinomycin potentiation of pulmonary radiation was found in a review of the literature of the past 12 years. Before that, this complication was well described and investigators had calculated that dactinomycin increased the toxic effect of lung radiation by a factor of 1.3 and reduced the radiation tolerance of the lung by at least 20%. An example of such a toxic effect is described in the treatment of a 7-year-old girl with lung metastases from Ewing's sarcoma. The chemotherapy protocol followed contained cyclophosphamide, vincristine, dactinomycin, adriamycin, cisplatinum, VP16, and radiotherapy. The treatment was associated with fatal pulmonary fibrosis following the reintroduction of dactinomycin after radiotherapy. Our experience suggests that there is clinical significance to this complication in sarcoma therapy when dactinomycin-containing protocols are used with radiation in the treatment of pulmonary metastases.

Combined treatment of radiation and cisdiamminedichloroplatinum (II): a review of experimental and clinical data

Cis-diamminedichloroplatinum (II) (c-DDP), a highly effective cytostatic drug, is increasingly used in combination with irradiation both in the laboratory and in patients. This review aims at a critical reassessment of the potential role of this drug as a "radiosensitizer." The opinion about c-DDP being an effective hypoxic cell radiosensitizer in bacteria was substantiated in some studies on mammalian cells in culture but not in others. More powerful mechanisms of radiation enhancement, which are not yet fully explored, may be depletion of endogenous thiols, inhibition of cellular repair processes, and proliferation inhibition. The effects of c-DDP in combination with irradiation in experimental tumors seem to vary between different investigators and between different tumor systems. Occasionally, supra-additive effects have been observed in some animal tumors. This stresses the need for testing this combination treatment in various tumor types, preferentially of human origin. In normal tissues, the effects are, to a large extent, explained by independent cell killing by each agent. A substantial number of clinical pilot studies have shown that the combination treatment is feasible, but the results of ongoing phase III trials will be needed to assess the potential therapeutic benefit of this combined treatment modality.

The effect of actinomycin D on radiation induced reactions of the lip mucosa of mice

The interaction of intraperitoneally injected Actinomycin D and irradiation was investigated in the lip mucosa of NMRI mice. In this rapidly proliferating tissue, a semiquantitative assessment of possible modifications of the radiation response by a drug can be done without using lethality as an endpoint. It was shown that a single dose of 0.5 mg/kg drug given at different times between 24 hr prior to and 24 hr after single radiation doses did not effect the rate of development nor the intensity of mucosal radiation damage. With extended time intervals of 2, 3, or 7 days between both single agents, a slight increase of the lip mucosal reaction was measured. Similar results were obtained when 5 daily drug injections of 0.15 mg/kg were administered starting at day 5 after a single radiation exposure. No differences in response could be demonstrated when fractionated irradiations with intervals ranging from 1 to 24 hr were closely combined with either single or repeated drug treatments (0.5 mg/kg in total) as compared to irradiation alone. However, a slight modification of the iso-effect dose was measured when 0.5 mg/kg Actinomycin D was administered at various periods in between 2 radiation doses separated by 10 days. A maximal effect was measured with 5 daily injections of 0.15 mg/kg drug each and given at a time when proliferative capacity was high. With 0.1 mg/kg Actinomycin D per daily injection, no enhancement of the radiation injury was found. Thus, in these circumstances no influence of Actinomycin D on radiosensitivity nor on repair of sublethal damage could be demonstrated. A clear inhibitory effect on lip mucosal repopulation by the drug is evident, but only at high drug doses close to toxic concentrations.