SummaryThe exposure of foodstuffs containing bone or other calcified tissue to a dose of ionizing radiation results in the formation of long lived free radicals which give rise to characteristic ESR signals. The presence of this signal provides clear evidence that the sample has been irradiated. In order to determine the radiation dose by post‐irradiation calibration, it is necessary to consider factors that might influence the radical yield and to allow for the stability of the radicals under likely conditions of storage. Using chicken bone we have shown that the yield is influenced by the nature of the bone, temperature of irradiation, and gaseous atmosphere, although not by dose rate, water content, or type of radiation. Cooking before irradiation greatly enhances the subsequent yield of radicals, while cooking after irradiation causes little or no destruction of the radiation‐induced radicals, which also appear to be unaffected by length and conditions of storage.

The free radical (II) produced by one-electron reduction of adriamycin (I) exists in aqueous solution at pH 7.0 in equilibrium with the parent and the two-electron reduced form (III). Over some hundreds of milliseconds deglycosylation takes place yielding an aglycone (IV) which subsequently rearranges to form a more stable aglycone, 7-deoxyadriamycinone (V). The changes in the optical absorption spectrum accompanying these processes are reported. The rate constant for III----IV is 1.1 s-1 and for IV----V is 1.5 x 10(-2) s-1. At pH 4.0 the two electron reduced form of adriamycin exists predominantly in a different tautomeric form (VII). It is suggested that this deglycosylates via a free radical mechanism involving the acidic form of the semiquinone free radical (VI).

Eight analogues of 2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone have been synthesized and tested for cytotoxicity against four different leukemic and lymphomic cell lines. For K562 and BSM cells, the toxicity could be correlated with the ease of reduction of the compounds as determined by the one-electron reduction potentials and the electron spin resonance detection of the reduced compounds produced by the cells. The cell toxicity could also be correlated with the efficiency of the compounds to form cross-links in DNA. However, no such correlations could be observed for the L1210 and Raji cells, although the activity of the NADPH dependent reducing enzymes in these cells was similar to that in the others. It is believed that for the L1210 and Raji cells, the influx/efflux of the different compounds may be more important to the cytotoxicity than their reduction or alkylation.

The mechanisms of cytotoxicity of the antitumour diaziridinylbenzoquinones, AZQ and BZQ, have been investigated. HPLC analysis has been used to study the products as well as the rate of decomposition of acid-assisted ring-opening in aqueous medium as a function of pH. Microconcentrators with a molecular weight cutoff of 30 kDa were utilised to study the covalent binding of both compounds to calf thymus DNA. Radical production of both compounds in K562 cell incubations was followed using ESR and their uptake into K562 cells was monitored using radiolabelled compounds. The results show that these two diaziridinylbenzoquinones, although very similar in structure, have diverse mechanisms of cytotoxicity. The implications of these findings are discussed in the light of antitumor action.

Summary A multinational co‐trial was organized to determine if electron spin resonance (ESR) spectroscopy could be used to monitor foods exposed to ionizing radiation. The bones of chicken legs, frog legs and pork rib bones were prepared and distributed as unknowns to the participating laboratories. In every instance, non‐irradiated bones were correctly identified as such. Moreover, irradiated bones were not only correctly identified, but relatively good estimates of the absorbed dose were obtained. An intercomparison of the different approaches used by each laboratory is discussed, and recommendations for future trials are presented.

Numerous improvements have been made to the Paterson Institute linear accelerator since its installation in 1967. New light sources, improved light guidance, smaller cells and a wider range of photo-detecting devices are now in routine use. Data are collected and processed by a computer-based method which has replaced the original oscilloscope-based system. Processes taking place over more than a few seconds can be studied with an arrangement combining pulse radiolysis with an ordinary spectrophotometer and arrangements for “single-shot” studies of faster processes are now being designed. Detection methods are also available which do not rely on transmission of light, and transient changes in conductivity can be measured.

Previous work has shown that the calcified tissues in several foods give rise to characteristic ESR spectra on irradiation. Further foods have now been examined. Mussel and crab shelss give large signals, compared with bones of poultry, beef or frog, while prawn cuticle gives a smaller signal. The limits of detection of irradiation vary between species but are blow the doses likely to be used commercially. Quantitative estimation of dose can be achieved by re-irradiation and extrapolation to zero signal.

Summary A method for the detection of irradiated poultry is described. For chicken, free radicals produced by ionizing radiation within the hard crystalline matrix of bone can be detected by the technique of electron spin resonance (ESR) spectroscopy. The ESR signal increases linearly with dose over the likely commercial range and is stable over the probable shelf‐life under likely storage conditions. The lower limit of detection is equivalent to a radiation dose of 50 Gy. The test appears equally applicable to turkey, duck and goose.

L1210 and K562 leukaemic cells have been used to study the relationship between cytotoxicity and free radical production by two aziridinyl benzoquinones, 2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone (AZQ) and 2,5-bis(2-hydroxyethylamino)-3,6-diaziridinyl-1,4-benzoquinone (BZQ). BZQ showed a high level of toxicity in both cell lines, but no ESR signal was detectable, while AZQ readily produced an ESR signal but much lower cytotoxicity was observed, particularly in L1210 cells. The rate of Superoxide formation was measured for each drug. The results demonstrate that cell killing and free radical production do not necessarily concur.

NADPH consumption and esr spectroscopy have been used to study the rate of formation and signal intensity of free radicals produced by various anthracycline anti-tumour drugs in rat liver microsomal extract. The drugs investigated were Adriamycin, 4'Deoxyadriamycin, Daunorubicin, 4 Demethoxydaunorubicin and Carminomycin. Pulse radiolysis was also used to determine the case of reduction of each of the analogues to its semiquinone radical and some kinetic properties of the radicals produced. It is believed that the occurrence of reactions other than dismutation could be responsible for the shortened lifetimes of the semiquinone radicals observed in biological systems.

The properties of the semiquinone radicals produced for 2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone (AZQ) and 2,5-bis(2-hydroxyethylamino)-3,6-diaziridinyl-1,4-benzoquinone (BZQ), have been investigated. AZQ semiquinone radicals can be produced from the reduction of AZQ by superoxide radicals, whereas BZQ semiquinone radicals are unstable in the presence of oxygen. The one-electron reduction potentials of the couples Q/Q⨪ at pH 7.0 were determined as − 70 ± 10 mV for AZQ and −376 ± 15 mV for BZQ. The difference in these potentials is explained. As a consequence of ESR studies on the enzymatically produced radicals, we have considered the factors which determine the detection of ESR signals for reduced quinones produced in a biological system.