Poster
# 33
Poster |
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6th Internet World Congress for Biomedical Sciences |
Sergej P. Osinsky, M.D.,(1), I Levitin(2), L Bubnovskaya(3), A Sigan(4), I. Ganusevich(5), V. Michailenko(6), T. Kovelskaya(7)
(1)(2)(3)(4)(5)(6)(7)Inst. exp. Pathol. Oncol. Radiobiol. - Kiev . Ukraine
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[Biophysics] |
[Oncology] |
The interactions of metal complexes with biological systems, which is the field of biocoordination chemistry, is receiving increasing interest. Some authors have presented the first results of their studies concerning the biological activity of organometallic compounds, in particular several alkyne-cobalt carbonyl complexes which inhibited the growth of human melanoma and lung carcinoma cell lines (1).
It is relevant to notice that cobalt compounds have been under the increased interest as potential radiosensitizers during the last 10 years. It was observed that cobalt(III) complexes have shown specific hypoxic radiosensitization and thermosensitization as well as antitumor activity in vivo (2-4). Some current observations have suggested that further investigations with cobalt-containing complexes are warranted (5,6).
It was supposed that cobalt compounds would be of particular interest because of coordination capacity of the metal center and their ability to catalyze redox processes involving (di)oxygen and active oxygen species as well as biogenic substrates. In this connection, we take notice of Dori & Gershon patent (7) claiming antitumor action of cobalt(III) complexes with tetradentate Schiff bases derived from aliphatic beta-diketones and diamines, which was observed in the case of ascite form of Erlich carcinoma. Carrying out a more thorough biomedical examination of the complexes in question, it was found in our experiments that above a moderate conventional antitumor activity, similar to that described in the just mentioned patent, they exhibit a pronounced modifying effect sharply enhancing the action of radiation and local microwave hyperthermia (8,9). Furthemore, the complexes alone are found to display a significant antimetastatic activity exceeding that of platidiam and cyclophosphamid (8,9). It was then succeeded in our experiments the synthesizing complexes superior to the known ones in their modifying and antitumor activities.
This study was aimed to perform the biomedical examination of new synthesized "inorganic" cobalt(III) complexes in experiments in vivo.
Compounds. Some cobalt(III) complexes with basic structure [ Co(acac2en)(NH3)2] Cl that are containing no metal-carbon bond, and their analogs with different ligands were tested in vivo. Here they are exemplified by AC-11, AC-30 and AC-40 complexes (8). They were dissolved in aqua pro injectionibus immediately before use and injected intraperitoneally (mice) or intravenously (rat).
Tumors. Transplanted rat (Guerin carcinoma, Walker-256 carcinoma) and mice [Lewis lung carcinoma (3LL), melanoma B16, adenocarcinoma Ca755] tumors were used in this study. Tumors were transplanted into the right flank (rat) or intramuscularly into the leg (mice). Moreover, 3LL was transplanted into the pad of hind leg in experiments with amputation of the leg with primary tumors. The principles and methods of transplantation were conventional. Animals were kept in Makrolon cages bedded with dust-free wood granulate, and had free access to a standard diet and tap water. Rats treated with hyperthermia and radiation were anaesthetized with sodium pentobarbital (45 mg/kg i.p.). All experiments had been approved by the regional animal ethics committee.
Treatments. Local hyperthermia (LHT) (1 h, 43 or 410C) was performed by microwave unit Luch-2 ("Medradioelectronics", Ukraine) operating at 2450 MHz with a 20 W power output. Each LHT treatment, either single or combined, was three-fold with a two-days break. The details of microwave heating and temperature measurement were described earlier (10). Irradiation (RT) was carried out using a 190 kV (current 10 mA, HVL= 0.5 mm Cu+1 mm Al) X-ray machine (RUM-17, Russia) at a dose of 1.23 Gy/min. Tumors were treated in a single exposure. Cobalt complexes were given 60 min before LHT or RT onset. Doses and schedules of complexes using alone in the experiments without LHT or RT are presented in a definite tables. Tumor´s response to treatment was estimated by standard methods.
Acute toxicity of complexes. The acute toxicity was found to be as follows: rat (strain IEPOR bred) - LD50/14 = 41.6 (AC-11) and 66.7 (AC-30) mg/kg; mice
[F1 (C57Bl/DBA2)] - LD50/14 = 34.2 (AC-11), 68.3 (AC-30) and 69.2 (AC-40) mg/kg.
Antitumor activity of complexes. It was observed that all cobalt complexes of AC-series have produced a substantial anticancer activity. Table 1 shows the response of primary tumor to AC-complexes treatment. It is noticable that the antitumor effect of complexes was not higher than 80%.
Table 1. Antitumor activity of "inorganic" cobalt(III) complexes in animals bearing transplanted tumors (inhibition of primary tumor growth, %)
| Complex | Guerin | Walker-256 | Mammary | Melanoma B-16 |
| AC-11 | 72 (n=13) | 60 (n=11) | 76 (n=15) | 50 (n=12) |
| AC-30 | 74 (n=10) | 62 (n=10) | 79 (n=14) | 65 (n=17) |
| AC-40 | n.d. | n.d | 77 (n=19) | n.d. |
Complexes were given at a dose of 15- 20 mg/kg intravenously (rat) or 12 mg/kg intraperitoneally (mice). The treatment was three-four-fold with a two-days break (rat) or ten-fold with a one-day break (mice). The treatment was initiated in 6-7 days (rat) or one-two days (mice) after tumor transplantation.
n - number of animals. n.s. non determined.
At the same time it was observed significant antimetastatic effect of complexes in experiments with Lewis lung carcinoma and melanoma B-16 (tables 2-4). It is important that antimetastatic activity of complexes, especially of AC-30, was considerably higher than that of cisDDP or cyclophosphamide (data are not presented).
Table 2. Antimetastatic activity of "inorganic" cobalt(III) complexes in mice bearing Lewis lung carcinoma (model without amputation)
| complex | Number of mice without | Inhibition of | metastases growth |
| AC-11 | 15 (n=15) | 67 | 70 |
| AC-30 | 17.5 (n=13) | 74 | 69 |
| AC-40 | 15 (n=12) | 77 | 78 |
Complexes were given at a dose of 12 mg/kg intraperitoneally. The treatment was ten-fold with a one day break. n = number of mice.
Table 3. Antimetastatic activity of "inorganic" cobalt(III) complexes in mice bearing Lewis lung carcinoma (model with amputation)
| complex | Number of mice without | Inhibition of | metastases growth |
| AC-11 | 27.5 (n=20) | 67 | 90 |
| AC-30 | 34 (n=14) | 84 | 99 |
| AC-40 | 35 (n=12) | 84 | 95 |
Complexes were given at a dose of 12 mg/kg. The treatment was ten-fold with a one day break. n = number of mice.
Table 4. Antimetastatic activity of "inorganic" cobalt(III) complexes in mice bearing melanoma B-16
| complex | Number of mice without | Inhibition of | metastases growth |
| AC-11 | 37.5 (n=12) | 75 | 76 |
| AC-30 | 40 (n=17) | 71 | 99 |
Complexes were given at a dose of 12 mg/kg. The treatment was ten-fold with a one-day break. n = number of mice.
Modifying activity of complexes. AC-11 or AC-30 given 60 min before LHT (410C, 60 min) produced a tumor growth delay (TGD) of about 10.5 and 15 days, respectively. It must be noted that efficacy of the combined treatment was higher than that of the local heating alone (430C, 60 min) which produced TGD of about 6.5 days.
Table 5 demonstrates the Guerin carcinoma response to radiation alone and supplemented with complex AC-30. One can see the significant potentiation of the radiation effect on Guerin carcinoma by the AC-30: radiation alone at a dose of 20 Gy and radiation at a dose of 10 Gy supplemented with AC-30, given 60 min before radiation, produced in 75% of tumor complete regression, respectively. Hence, the enhancement ratio was found to be 2.0 in this case.
Table 5. Radiopotentiating activity of complex AC-30 (15 mg/kg) in rats bearing
Guerin carcinoma (n = number of rats)
| Treatment | Tumor growth inhibition | Complete regression of tumor |
| Control (n=9) | ----- | 0 |
| 10 Gy (n=7) | 67 | 50 |
| AC-30+10 Gy (n=8) | 70.5 | 75 |
| 15 Gy (n=6) | 90 | 50 |
| AC-30+15 Gy (n=7) | 99 | 100 |
| 20 Gy (n=7) | 80 | 75 |
| AC-30+20 Gy (n=7) | 89 | 75 |
The interaction of metal complexes with biological systems, which is the field of biocoordination chemistry, draws increasing interest. Some authors have shown the anticancer activity of a number of cobalt-containing compounds in vitro and in vivo (1,3-7). These data suggest that further investigations with cobalt complexes are warranted. The novel cobalt(III) complexes have been designed in our laboratories.
These complexes contain, besides a tetradentate Schiff ligand, certain biogenic and hence physiologically active Lewis bases (8). Such "inorganic" cobalt(III) complexes (that are containing no metal-carbon bond) can be reduced in tumor, due to the reductive nature of many tumors which contain significant regions at low oxygen tensions. Thus they initiate a catalytic autooxidation process involving generation of reactive oxygen species. The coordinated biogenic ligands may reduce toxic side effects caused by xenobiotic core of these complexes, contribute to their antitumor action and facilitate their transport through cell membranes. Above mentioned results have shown that "inorganic" cobalt(III)- Schiff base complexes display significant antitumor, in particular antimetastatic, and thermoradiomodifying activities in vivo with rodent tumors.
The working hypothesis to explain the above mentioned effects of cobalt complexes is based on the suggestion that the partial reduction products of dioxygen, in the presence of transition metal complexes yield very reactive species, which could start catalytic oxidation of substrates and show antitumor action. The study of detailed mechanisms of biological activity of our cobalt(III) complexes are under way. Some preliminary results are presented below.
Our investigations have shown that malonyldialdehyde concentration was increased by a factor of 3,5 in tumor to the 60th min after AC-30 injection, in liver and kidney - 1,5 and 2, respectively. Glutathione (GSH) content was decreased by a factor of 2 in tumor, at the same time, in liver and kidney - by 10% and by a factor of 3, respectively. Glutathione-S-transferase activity was decreased by a factor of 2 in tumor, in liver and kidney - by 10 and 20%, respectively. Decreased both GSH content and GST activity in tumor were kept unchanged within 24 h. All indices in normal tissues were reached the pretreatment values to the 24 h. These data confirm the suggestion that our complexes are selectively reduced in tumor with the following initiation of catalytic autooxidation process involving generation of reactive oxygen species. This oxidative stress activated the peroxidation of lipid and other biomolecules with the formation of MDA and definite response of gluthatione´s system. It was observed by 31P-NMR spectroscopy that the ratio of nucleotide/inorganic phosphate and phosphocreatine/inorganic phosphate in tumor tissue fell by 76 and 90% respectively within 2 h of AC-30 complex administration and remained constant for a further 4 h. The ratio of these metabolites in muscle fell by 25 and 32% within 2 h of treatment. These results indicated that cobalt complex selectively and significantly decreased the bioenergetic status of the tumor.
Above mentioned results have indicated that "inorganic" cobalt(III) complexes can be regarded as prospective selective anticancer agents with significant modifying activity. The future results may be used to indicate the strategic pathway of the design and directional selection of redox active metal complexes for anticancer and/or modifying activity.
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[Biophysics] |
[Oncology] |
