We have shown earlier that the iron containing, ferric-sorbitol-citrate complex (FSC) inhibited proliferation of cultured mouse melanoma B16, GHC, KB, HeLa and CaCo2 cells and caused mouse melanoma regression in vivo. This drug did not affect the proliferation of the nonmalignant fibroblast L929 line, human bone marrow-HBS, VERO and HEF cell line. It is also known, that some metallocene derivatives posses antitumour properties resulting principally from their action on the metabolism of DNA, and subsequently, RNA and proteins. We synthesized in our laboratory some ferrocene analogs (F168 and F169) and tested their antiproliferative ability for malignant human carcinoma Hep2 and mouse melanoma F10 cell lines. As control cell lines, human HEF and mice L929 fibroblasts were used. The tested iron substances were very potent in inhibiting the growth of malignant cell lines, whereas they had no significant inhibitory effect on the viability of nonmalignant fibroblasts. The most pronounced growth inhibitory and cytotoxic effect was found in the malignant F10 cells and the most potent was ferrocene F169. Because of their selective effect on malignant cells, the ferric-sorbitol-citrate complex as well as tested ferrocenes will be further investigated and submitted as new antitumour substances.

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A series of experiments has been undertaken in order to test the biological properties of neutrons produced in the cyclotron of the Institute "Ruder Bosković" (IRB) in Zagreb. Protective effect of AET (2-amino ethylisothiuronium bromide hydrobromide) on survival of L cells irradiated by fast neutrons generated in the IRB cyclotron were studied by employing the single cell clonal growth method. For comparison the protective effect of AET after gamma irradiation has also been studied. The most important findings that have emerged from these experiments can be summarized as follows: (1) Protective effect of AET was present after gamma irradiation only. (2) The degree of protection was dependent on AET concentration in the growth medium. (3) No protective effect was found after neutron irradiation. These findings are in agreement with the generally less efficient protection of this compounds after high-LET irradiation.

L929 cells were irradiated by cyclotron-produced neutrons and by 14.8 MeV monoenergetic neutrons. For comparison cells were also irradiated by 60Co gamma rays. Following irradiation cells were treated by an equimolar solution of deoxyribonucleosides, and the effect on cell survival measured. Results show that nucleoside treatment was efficient after low-LET irradiation: gamma ray survival curves were altered by deoxyribonucleosides in terms of significantly increased extrapolation numbers only, but without Do change. Cells irradiated by neutrons from either of the two sources did not respond to nucleoside treatment, and consequently their survival curves remained unaltered. These results show that the nucleoside effect does occur after low-LET irradiation, but apparently not following high-LET irradiation. Since deoxyribonucleosides as well as other cell breakdown products are released in irradiated and necrotic tumours due to massive cell destruction, such a nucleoside effect could possibly enhance the cell survival and thus effect the result of radiotherapy. Absence of the nucleoside effect in case of high-LET irradiation may therefore be an additional potential gain from neutrons in radiotherapy.