Synthesis, Characterization and Antitumour Activity of Metal Complexes of 5-Carboxy-2-Thiouracil

Metal complexes of 5-carboxy-2-thiouracil with Mn(ll), Co(ll), Ni(ll), Cu(ll), Zn(ll) and Cd(ll) ions were synthesized, characterized, and subjected to a screening system for evaluation of antitumour activity against Sarcoma-180 (S-180) tumour cells. The complexes were characterized by elemental analysis, infrared, electronic spectra, room temperature magnetic measurements and powder X-ray diffraction. The antitumour activity results indicate that some complexes have antitumour activity both in vivo and in vitro against S-180 tumour cells.

. The bacteriostatic or bacteriocidal activities of 5CTU and scanty information on its metal complexes [2] as antitumour agent encouraged to undertake a systematic study of its metal complexes and to test the antitumour activity of synthesized compounds. The present paper describes the structural as well as the antitumour activity studies of Mn(II),Co(II), Ni(II), Cu(ll), Zn(ll) and Cd(ll) complexes with 5CTU.

Results and Discussion
The satisfactory elemental analyses have been obtained for all compounds. They display 1:1 stoichiometry. All the complexes are coloured except Zn(ll) and Cd(ll). They are insoluble in almost all common organic solvents except Mn(II) complex which is sparingly soluble in dimethylsulfoxide on heating.
Infrared spectra Table 1 shows some important infrared absorption bands of 5CTU and its complexes. Complexation can be expected to lead the shifts in the carboxylate, thioamide and amide band positions in the spectra of the complexes. The characteristic bands of the coordinated water molecule are present in the lower region of the spectra. The position of v(fOO)asym (1660 cm1) and v(fOO)sy m (| 450 cm"1) bands are shifted after complexation. The shift of v(COO)asy m band towards higher wave numbers and v(COO)sym band towards lower wave numbers suggest the unsymmetrical bonding of the carboxylate group and it acts as monodentate ligand towards one metal ion. The thioamide bands also show shifting in the spectra of complexes whereas SNI-H, SN3-H bands do not exhibit any shift suggesting that N-H and N3-H groups do not interact with metal ions.
Thus the binding of 5CTU with metal ions is suggested through CO0 and C=S groups which have been confirmed on the basis of the presence of vM-0 and vM-S bands in the lower region of spectra [3].

Metal-Based Drugs
Antitumour activity against  The ligand 5CTU has the antitumour activity with T/C value 115 at the dose of 25.0 mg/kg body weight. Among the transition metal complexes only Co(H), Ni(II) and Cu(II) complexes have significant antitumour activity ( Table  2). With Co(II)-SCTU and Cu(II)-SCTU treatment at the dose of 12.5 and 25.0 mg/kg body weight respectively all mice survived beyond six months.
Further it was found that none of the test compounds were toxic up to the dose of 50.0 mg/kg body weight except the complex containing Cd(II) ion (as observed by body weight change upt to six days of drug treatment). The compound Cd(II)-5CTU was found to be toxic even at the dose of 2.5 mg/kg body weight.  In each set of experiment six mice were used. T/C 6/6, T= tumoured, C control. (a) in calculating average survival time mice surviving >6 months were not included. (b) number of parenthesis indicates percentage of mice surviving six months or more. (c) single injection of the reported dose was given.
The ligand 5CTU and its complexes were also tested for their inhibitory effect on 3H-thymidine,3H-uridine and 3H-leucine incorporation in S-1 80 tumour cells in vitro. Most of the compounds that caused inhibition of 3Hthymidine, 3H-uridine and 3H-leucine incorporation in S-180 tumour cells, also showed antitumour activity i___o_n v_ix.o_ (Table 3a, 3b, 3c). Thus it is concluded from the resluts obtained in the present study that all the complexes have octahedral structure. Regarding the antitumour activity study, the ligand 5CTU and its complexes with Co(II), Ni(II) and Vol. 5, No. 1, 1998 Synthesis, Characterization and Antitumour Activity of Metal Complexes of 5-Carboxy-2-Thiouracil Cu(II) ions have antitumour activity. The mechanism of antitumour action of these compounds is not well known. It is propable from the results obtained in the present study that these compounds may be effective antitumour agents due to their inhibitory action on the replication of DNA, synthesis of RNA and protein in tumour cells.

Experimental
Method of Synthesis lm mole of hydrated metal nitrates were dissolved in a mixture of 35ml ethylalcohol and 15 ml triethylorthoformate by refluxing for about 10hrs. Then, lm mole of 5CTU was added and the resultant mixture was refluxed for 20-25 days after which the volume of the reaction mixture was reduced to about one third of its original volume and the precipitation was initiated by adding ether. The solid complexes were separated by filtration, washed several times with ethanol, finally with ether and dried at 50o55c.
The metal ions were determined volumetrically after dissolving the complexes in dilute nitric acid 10]. Carbon, hydrogen, and nitrogen were analyzed with a Perkin-Elmer model 240C elemental analyzer. The infrared spectra were obtained in Nujol on a Perkin-Elmer model 783 spectrophotometer in the 4000-200 cm -1 region. The electronic spectra of the complexes were recorded in Nujol with a UV/VIS-168A Shimadzu spectrophotometer at room temperature. The room temperature (298K) magnetic susceptibility measurements were made on Cahn Faraday magnetic susceptibility balance. X-ray powder diffraction data of the complexes were obtained on a Philips X-ray diffractometer PW1710 using CuKct radiation. Indexing of X-ray powder lines was done by Ito's method [9].
Antitumour activity of the ligand 5CTU and its synthesized metal complexes were tested against Sarcoma-180 (S-180) tumour system both in vivo and in vitro according to the method described earlier [11]. Therapeutic effectiveness of each compound against tumour bearing mice was assessed from the T/C percentage which was calculated as follows: Mean life span of treated mice* T/C% Mean life span of untreated mice * excluding tumour free survivors.

X 100
A T/C value of 115 indicates significant activity whereas > 125 indicates that complex is worthy of testing in other tumour systems [12].