Calcium antagonist radioprotectors do not reduce radiotherapeutic efficacy in three human tumor xenografts.

AIM: Calcium antagonists, which protect normal tissue as exemplified by bone marrow cells from radiation injury, were evaluated for radioprotection of tumor cells. MATERIALS AND METHODS: One Ewing's sarcoma and 2 colon carcinomas were grown as xenografts in immunosuppressed mice. The mice were treated with diltiazem, nifedipine, nimodipine and nitrendipine. The effect of whole body gamma-radiation on the growth of the subcutaneously implanted tumors was assessed. RESULTS: Growth delay or regression of the tumors in mice treated with the calcium antagonists prior to irradiation was not reduced as compared to only irradiated controls. CONCLUSION: The tested calcium antagonists, which are well tolerated and protect mice from death after lethal radiation, did not prevent the radiotherapeutic effect on 3 human tumors. This points to the possibility of differential radioprotection and thus to improve the therapeutic ratio in cancer radiotherapy.

Radiosensitization by dimethylbenzanthracene, diphenylcyclopropenone and aminoanthraquinones.

Radiosensitization of mice by dimethylbenzanthracene, diphenylcyclopropenone and aminoanthraquinones was investigated in a model where survival time after lethal radiation was scored. Survival time was shortened by nontoxic doses of the chemicals. The used in vivo system confirmed the radiosensitizing potential of dimethylbenzanthracene reported previously with in vitro studies. Moreover, radiosensitizing properties of diphenylcyclopropenone and aminoanthraquinones could be demonstrated. The sensitizing interaction of these chemicals with radiation adds a new facet to their toxicological spectrum and could, by enhancing radiation effects, influence estimates of risk. On the other hand, diphenylcyclopropenone or aminoanthraquinones deserve consideration as topical sensitizers in conditions where radiation is indicated to treat cutaneous malignancies.

Modification of radiation sensitivity by salts of the metals beryllium and indium and the rare earths cerium, lanthanum and scandium.

The LD50 of 46 salts of metals and rare earths (lanthanoids) was determined in mice. Half the LD50 of the compounds was then combined with lethal radiation (10.5 Gy) and the modification of survival time was scored. Only the metals beryllium and indium and the rare earths cerium, lanthanum and scandium displayed activity in our assay. They were then tested at a wider range of lower doses and reduced survival time in a dose-dependent fashion. This appears to be compatible with enhancement of radiation sensitivity. The interaction of these metals and rare earths with radiation adds a new facet to their toxicological spectrum and, by enhancing radiation effects, may influence estimates of risk. On the other hand, the radiosensitizing properties of the metals may be useful for further development of compounds to be used as adjuncts in specific situations of cancer radiotherapy.

Allopurinol, indomethacin and riboflavin enhance radiation lethality in mice.

Two widely used drugs, allopurinol and indomethacin, and the vitamin riboflavin increased the response of mice to ionizing radiation. In mice a dose of 10.5 Gy of gamma rays from a 60Co source resulted in a dose-dependent shortening of survival times after pretreatment with the three agents, applied at doses which were well tolerated alone. When the dose dependency of these drugs on the influence on survival was tested, two response patterns emerged. Indomethacin (25 mg/kg) shifted the survival curve to the left and reduced the LD50 from approximately 6.5 Gy to approximately 4.5 Gy. Allopurinol (100 mg/kg) diminished the survival rate to approximately 50% irrespective of the radiation dose (ranging from 0.75 to 6.0 Gy). A similar though less striking trend was seen with riboflavin (120 mg/kg), which reduced the survival rate to approximately 65% in the dose range from 3 to 6 Gy. Mortality in mice treated with allopurinol or riboflavin and irradiated with nonlethal exposures (from radiation alone) occurred within the first few days after irradiation, suggesting a different type of injury than is usually associated with radiation death. Although doses of the three drugs used clinically are clearly lower than those providing enhanced radioresponse in our experiments, subtle and nonovert injury caused by combined exposure to the drugs and radiation cannot be completely excluded.

Radioprotective effects of calcium antagonists used alone or with other types of radioprotectors.

Diltiazem, a benzothiazepine calcium channel blocker used widely in cardiovascular therapy, protected mice against death by ionizing radiation. Diltiazem was active in male and female C3H mice and could be administered subcutaneously or intraperitoneally. Protection was also seen in BALB/c, C57Bl/6, and NMRI mice. Moderate activity was afforded by oral administration of effective levels of diltiazem. Injection at 10 or 30 min before irradiation was similarly effective, but injection 2 h prior to the irradiation provided only marginal protection. The dihydropyridine calcium channel blockers nifedipine and nimodipine were also effective, but since these compounds were in an ethanol-containing solvent their radioprotective activity had to be distinguished from that of the ethanol. Synergistic effects occurred by combining diltiazem with zinc aspartate, dimethyl sulfoxide, and nifedipine. Protection by calcium antagonists may be due to interference with the damaging cellular influx of calcium after membrane injury by radiation-induced free radicals or by their direct inactivation. Calcium antagonists could play a role as less toxic radioprotectors, providing modest dose reduction factors but without the prohibitive side effects of aminothiols such as WR-2721.

Calcium antagonists protect mice against lethal doses of ionizing radiation.

Currently available radioprotectors are poorly tolerated in man and the general use of aminothiol radioprotectors is compromised by their side-effects. In a search for less toxic radioprotective agents, diltiazem, a calcium antagonist with a benzothiazepine structure, was found to protect mice against a lethal (LD100) gamma radiation dose allowing survival of up to 93%. Dihydropyridine calcium antagonists such as nifedipine, nimodipine, isradipine and nitrendipine also provided radioprotection. Calcium antagonists might attenuate radiation-induced injury by inhibiting cellular calcium overload, subsequent to cell membrane damage caused by radiation-generated free radicals. In view of their good tolerance, calcium antagonists may be applied safely in situations of radiation exposure, including radiotherapy and internal radionuclide contamination. These calcium antagonists may also be viewed in other contexts where free radicals are implicated in pathological processes.

Radiation-induced lymphoid tumors and radiation lethality are inhibited by combined treatment with small doses of zinc aspartate and WR 2721.

Combined small doses of zinc aspartate and WR 2721 provided additive protection against radiation lethality in mice. Survival obtained with a small dose of WR 2721 which was ineffective alone could be enhanced to 83% by combining the drug with zinc aspartate, which on its own also displayed no effect. The survival of 25% provided by a higher dose of WR 2721 was increased significantly by adding zinc aspartate. Additivity was also tested in a model of radiation carcinogenesis. For this purpose, lethality and occurrence of lymphoid tumors induced by fractionated total-body irradiation were studied in C57B1/6 mice treated with zinc aspartate and WR 2721. In order to reveal additive effects, both agents were used at sub-optimal dosages. In mice subjected to 5 daily exposures of 1.9 Gy, the combination of zinc aspartate and WR 2721 was effective and enhanced the survival to 83% as compared with 25% afforded by WR 2721 alone (p < 0.005). Similarly, histological assessment of organ involvement with lymphoma revealed that zinc aspartate and WR 2721 alone did not bring about a significant reduction of lymphoma incidence. On the other hand, the combined agents diminished organ involvement with lymphoma to 9.1% as against 90% in the controls (p < 0.0005) and 62.5% with WR 2721 alone (p < 0.025). Thus, combined treatment with zinc aspartate and WR 2721 also inhibited radiation-induced lymphoid tumors.

Treatment of brittle fingernails and onychoschizia with biotin: scanning electron microscopy.

Pathologic hoof changes in horses and swine can be normalized by administration of biotin. This vitamin has been given orally to women with brittle fingernails or onychoschizia. The aim of the study was to test whether the favorable clinical results could be corroborated by scanning electron microscopy. We investigated the distal ends of the fingernails from 32 persons. They were placed into three groups: group A consisted of 10 control subjects with normal nails, group B comprised eight patients with brittle nails studied before and after biotin treatment, and group C was 14 patients with brittle nails in whom the administration of biotin did not coincide exactly with the initial and terminal clipping of the nails. The thickness of the nails in group B increased significantly by 25%. In group C, the increase was 7%. Splitting of the nails were reduced in groups B and C and the irregular cellular arrangement of the dorsal surface of brittle nails became more regular in all nails of group B and in 8 of 11 nails of group C.

Further studies on selective radioprotection by organic zinc salts and synergism of zinc aspartate with WR 2721.

The organic zinc salts zinc aspartate, zinc histidine, zinc orotate and zinc acetate reduced the fall of the haematocrit, thrombocytes, erythrocytes and leucocytes in irradiated mice. In general, zinc aspartate was more effective than the other organic zinc salts. Protection of the haematocrit and thrombocytes by small doses of the aminothiol radioprotector WR 2721 was markedly improved by the concomitant administration of small doses of zinc aspartate. Zinc aspartate was the only one of the four tested organic zinc salts that did not inhibit in any instance the regression induced by radiotherapy of human tumours grown as xenografts in immunosuppressed mice. This also applied to the combination of zinc aspartate with WR 2721. In an experiment performed to determine the toxicity of the combined regimen, a dose of zinc aspartate which afforded synergistic haematological protection did not enhance the toxicity of WR 2721. The synergism of zinc aspartate with WR 2721 and the differential radioprotection of the combined protocol may make it possible in clinical cancer radiotherapy to obtain selective radioprotection at a lower toxicity giving an improved therapeutic ratio compared with WR 2721 alone.

Protection against Amanita phalloides by the iridoid glycoside mixture of Picrorhiza kurroa (kutkin).

Survival of mice after lethal doses of lyophilizate from Amanita phalloides ('death cap') was markedly increased by pretreatment with single doses of kutkin, a mixture of iridoid glycosides picroside I and kutkoside isolated from the roots of Picrorhiza kurroa. The protective effect of kutkin was comparable to that of silibinin. The curative efficacy of kutkin appeared to be slightly superior.

[Treatment of brittle fingernails with biotin]. / Behandlung brüchiger Fingernägel mit Biotin.

Frailty and brittleness of the finger nails is frequently seen, particularly in women. In veterinary medicine, it has been documented that defect hooves of horses or claws of swines respond well to oral application of biotin. Accordingly, we studied the effect of biotin on human dystrophic finger nails, a keratin structure as well. 71 patients were treated with a daily oral dose of biotin of 2.5 mg. Out of the 45 cases which finally could be evaluated, 41 (91%) showed definite improvement with firmer and harder finger nails after an average treatment of 5.5 +/- 2.3 months. In 4 of the 45 patients (9%), the improvement was questionable. None of the patients considered the treatment altogether ineffective. We conclude that biotin in most of the cases provides an effective therapy also for human patients with brittle nails.

Differential radioprotection of bone marrow and tumour cells by zinc aspartate.

The radioprotector zinc aspartate did not inhibit the radiotherapeutic effect of gamma rays on human tumours grown as xenografts in immunosuppressed mice, while aminothiol radioprotectors afforded a slight inhibition. On the other hand, zinc aspartate significantly reduced the fall in the haematocrit and numbers of thrombocytes, erythrocytes and leucocytes caused by irradiation, indicating a sparing effect on bone marrow precursors of peripheral blood cells. This differential protection of neoplastic and normal cells may be of considerable benefit in clinical cancer radiotherapy, provided that zinc aspartate is better tolerated and has a more favourable therapeutic index in humans than aminothiol radioprotectors.

Synergism of organic zinc salts and sulfhydryl compounds (thiols) in the protection of mice against acute ethanol toxicity, and protective effects of various metal salts.

Organic zinc salts such as zinc aspartate, zinc orotate, zinc histidine and zinc acetate protected mice against the lethality of an acute intraperitoneal challenge with ethanol. A similar activity was also provided by salts of cobalt, zirconium, lithium and magnesium. Organic zinc salts acted synergistically with sulfhydryl compounds in protecting the mice and potentiation between the two categories of agents was seen. The results are in analogy to radioprotective effects by zinc and thiols and imply that organic zinc salts may, alone or in conjunction with thiols, reduce in a wider context tissue injury caused by free radical-mediated mechanisms.

Protection against ionising radiation and synergism with thiols by zinc aspartate.

Pre-treatment with zinc aspartate protected mice against the lethal effects of radiation and raised the LD50 from 8 Gy to 12.2 Gy. Zinc chloride and zinc sulphate were clearly less active. The radioprotective effect of zinc aspartate was equivalent to cysteamine and slightly inferior to S,2-aminoethylisothiourea (AET). Zinc aspartate displayed a similar therapeutic index to the thiols but could be applied at an earlier time before irradiation. Synergistic effects occurred with the combined administration of zinc aspartate and thiols. By giving zinc aspartate with cysteamine, the LD50 was increased to 13.25 Gy and, by combining it in the optimal protocol with AET, to 17.3 Gy. The radioprotection by zinc and its synergism with thiols is explained by the stabilisation of thiols through the formation of zinc complexes.

Xenografts in pharmacologically immunosuppressed mice as a model to test the chemotherapeutic sensitivity of human tumors.

A human tumor xenograft model using pharmacologically immunosuppressed mice was assessed for its suitability to test preclinically the sensitivity of colorectal carcinomas, bone sarcomas and melanomas against anticancer agents. Besides ionizing radiation, 14 cytotoxic drugs including 5-fluorouracil (5-FU), dimethylmyleran (DMM), cytosine arabinoside, cyclophosphamide, melphalan, BCNU, mitomycin C, adriamycin, bleomycin, etoposide, vinblastine, cisplatin, procarbazine and DTIC were assayed. Ionizing radiation, 5-FU and DMM were also applied at lethal doses followed by bone-marrow rescue heavy therapy. Four colon carcinomas responded poorly to most of the agents but one tumor displayed marked sensitivity to BCNU. Lethal doses of radiation, 5-FU and DMM could also show considerable activity. High sensitivity was shown by a Ewing sarcoma to DMM and cyclophosphamide and by an osteosarcoma to the latter drug. No strong effects were seen against melanomas. Lethal doses of DMM induced the best regression of one colon carcinoma. In general, the superiority of heavy therapy for solid human tumors compared to maximally tolerated doses was demonstrated. Individual carcinomas of the same type displayed different drug sensitivity.

Protection against acute ethanol toxicity in mice by zinc aspartate, glycols, levulose and pyritinol.

The lethality in mice after an acute intraperitoneal challenge with ethanol could be largely prevented by treatment with single doses of zinc aspartate. Other zinc salts or aspartates were not or clearly less effective than zinc aspartate. Marked protection was also provided by polyethylene glycol and propylene glycol. The antagonistic effects of levulose and pyritinol against acute ethanol intoxication were confirmed.

Protection by bone marrow grafts against lethal doses of 5-fluorouracil.

C3H (H-2k) mice were treated with lethal doses of the antimetabolite 5-fluorouracil (5-FU). After 16 hr the mice received an intravenous injection of 25 X 10(6) syngeneic or allogeneic bone marrow cells. With syngeneic cells, survival after a single dose of 350 mg/kg 5-FU was increased from 27 to 83% and after 450 mg/kg 5-FU from 14 to 84%. Allogeneic CBA (H-2k) donor cells allowed 81% of the mice to survive after 350 mg/kg 5-FU and 42% after 450 mg/kg 5-FU. Allogeneic marrow from A (H-2a) donors was ineffective after both doses of 5-FU. The results show that the lethality of 5-FU is largely prevented by a hemopoietic graft. Experimentally, 5-FU belongs to the agents which may be applied in cancer chemotherapy at lethal and thus potentially tumor-eradicative doses in combination with autologous or syngeneic bone marrow. In humans it remains to be seen whether the use of this protocol is precluded by prevailing gut toxicity.

Ethanol diminishes the toxicity of the mushroom Amanita phalloides.

Survival of mice after lethal doses of a lyophilizate from Amanita phalloides ('death cap') was markedly increased by single doses of ethanol applied 30 min before or 5 min after the mushroom. Hepatic histopathological damage (confluent necrosis) was largely prevented. Acute, but not chronic, consumption of ethanol may thus influence favorably the outcome of death cap poisoning and should be taken into consideration in the evaluation of therapeutic measures.