Techniques for studying Metal-Drug- DNA interactions. Techniques used to Study MetalloDrugs- DNA interactions

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1 Techniques for studying Metal-Drug- DA interactions Techniques used to Study MetalloDrugs- DA interactions Study of the interaction between the metal complexes with DA by different techniques : Covalent Binding o Covalent : Spectrophotometric Titration by UV-vis Maribel avarro mnavarro@ivic.gob.ve IVIC-Venezuela Brasil-Florianópolis Julio 2010 Metal Complexes against Different Diseases DA : important target for metal complexes Leishmania + COVALET This kind of interaction involves covalent bond formation of the metal complex to either the phosphate or the nucleic acid bases Trypanosomiasis Cancer Malaria Mini-Reviews in Medicinal Chemistry, 2004, 4,

2 Covalent inner-sphere binding Covalent binding of the cisplatin to the AD This kind of interaction involves covalent bond formation of the metal complex to either the phosphate or the nucleic acid bases. Where more than one metal - DA bond is formed, crosslink results which can be either intra- or inter-strand. 1,2-Intrastrand 1,2-Interstrand AD 1,2-Intrastrand 1,2-Interstrand Coor. Chem. Rev , 383,( 2001) Covalent binding of the cisplatin to the AD Covalent binding of the metal complexes to the AD In the Laboratory 2

3 Covalent binding Incubation 120 h Precipitation EtOH, acl Then redisolution Metal Complex DA solution Metal Quantification (AA o ICP) nmol Metal/mg AD metal DA Quantification (UV-Vis) Burton Assay Quantification of [Metal] HClO 4 H(C 6 H 5 ) 2 Calibration Metal standards HCl, 70C 600 nm HClO 4 H(C 6 H 5 ) 2 [AD] quantification K. Burton, Biochem. J.,62, 315 (1956) Metal samples Covalent binding Techniques for studying Metal-Drug- DA interactions Study of the interaction between the metal complexes with DA by different techniques : Base Pair /metal Complejo nmol metal/mg ADtt (P.B./A.M.) (1) Pt(CQDF) 2(I) 2, 183,41 8,39 (2) Pt(CQDF) 2(Cl) 2 171,72 8,96 (3) Pt(CQ) 2(Cl) 2 721,49 2,13 (4) Pd(CQDF) 2(I) 2 125,07 12,32 (5) Pd(CQ) 2(Cl) ,21 1,13 (6) Au(CQ)(Cl) 1420,75 1,03 (7) Au(CQ)(TgTa) 531,52 2,89 (8) [Au(CQDF)(PPh 3)]PF 6 10,91 140,98 cis-pt(h 3) 2(Cl) ,52 1,45 trans-pt(h 3) 2(Cl) ,47 1,46 Covalent Interaction Spectrophotometric Titration by UV-vis 3

4 DA : important target for metal complexes on-covalent outer sphere binding + O COVALET Hydrogen bonding Electrostatic interactions Minor or Major Groove Intercalation. egatively charged backbone of DA interacts with positively charged molecules through electrostatic interactions or phosphate - oxygen binding. Exocyclic groups on the purines/pirimidines can be involved trough hydrogen bonding to suitable ligand atoms. Depends primary, on the nature and concentration of the metal. measured by T m and CD. o covalent interaction Mutat Res. 623, 3, (2007) Interacción no covalente Pt S OH Mutat Res. 623, 3, (2007) 4

5 Absorbance Electronic Excitation by UV/Vis Spectroscopy : An Electronic Spectrum Hypsochromic shift Bathochromic shift max with certain extinction UV Visible Make solution of concentration low enough that A 1 (Ensures Linear Beer s law behavior) Even though a dual beam goes through a solvent blank, choose solvents that are UV transparent. Can extract the value if conc. (M) and b (cm) are known UV bands are much broader than the photonic transition event. This is because vibration levels are superimposed on UV Wavelength,, generally in nanometers (nm) UV-vis * and * transitions: high-energy, accessible in vacuum UV ( max <150 nm). ot usually observed in molecular UV-Vis. n * and * transitions: non-bonding electrons (lone pairs), wavelength ( max) in the nm region. n * and * transitions: most common transitions observed in organic molecular UV-Vis, observed in compounds with lone pairs and multiple bonds with max = nm. Metal Ligand Charge Transitions (MLCT) or Metal Ligand Charge Transitions (LMCT) CT * MLCT d * H 2 Ru 2+ H 2 (PF 6 ) 2 CT * MLCT d * (PF 6 ) 2 O Ru 2+ O Buffer Tris-HCl(5mM), acl(50mm) ph 7.2 Buffer Tris-HCl(5mM), acl(50mm) ph 7.2 5

6 Absorbancia [AD] / (ea-ef) Absorbancia Studies of no covalent interaction Spectroscopic Titrations DA Aliquots Gráfica absorbancia Vs. longitud de onda del complejo [Au(CQ)(PPh3)] PF6 en buffer (comportamiento durante 0 ul la titulación con AD) DA 5 ul DA 10 ul DA Longitud de onda 330 (nm) 350 Metal Complex at fixed concentration eighbor exclusion equation. [AD]/( a- f) = [AD]/( a- b) + 1/[Kb( a- b)] %H= (Ai-Af/Ai)100 [DA]/( a- f) = [DA]/( a- b) + 1/[Kb(εa-εb)] The intrinsic binding constant Kb was determined from the plot of [DA]/(ea - ef) vs [DA], where [DA] is the concentration of DA in base pairs the apparent absorption coefficients, εa, εf, εb correspond to Aobs/[M], the extinction coefficient for the free metal complex and the extinction coefficient of the metal complex in the totally bound form. The slope equal to 1/(εb - εf) and the intercept equal to 1/[Kb(εb - εf)] and Kb was obtained adjusting the data to the corresponding curve [AD]/( a- f) = [AD]/( a- b) + 1/[Kb( a- b)] [AD]/( a- f) = [AD]/( a- b) + 1/[Kb( a- b)] 3.5E E-08 Kb = Slope/ Cut off 2.5E E-08 y = 0,0009x + 2E-09 R 2 = 0,999 Slope Cut off point 9.00E E E-08 Kb 4.50E+05 %hip E E E E E-05 [AD] 3.0E E E-05 Spectroscopic titration Scatchard s Equation DA Complex metal Scatchard s Equation 0.5 Gráfica absorbancia Vs. longitud de onda del complejo [Au(CQ)(PPh3)] PF6 en buffer (comportamiento durante la titulación con 0 ul AD) D A Longitud de 330 onda (nm) 350 6

7 v/[l] Data from UV-vis experiment 2.5E E E+06 y = -3.02E+07x E+06 R² = Compounds K b1(x10 7 M -1 ) K b1(x10 5 M -1 ) CQDP 1.38 ± ± 0.15 [Au(CQ)(PPh 3)] PF ± ± 0.89 Complex % Hypochromism Bathochromi sm (Δnm) eighbor exclusion Constant binding Scatchard Kb(x10 5 M -1 ) Kb2(x10 5 M -1 ) Kb1(x10 7 M -1 ) 1.9E E E E+06 Au(CQ)(Cl) [Au(CQ)(PPh3)]PF6 21% 4 2,68 ± 0, ± ± % ± ± ± E E+05 y = -2.01E+05x E+04 R² = E E v [Au(CQDF)(PPh3)]PF6 31% 5 0,79 ± ± ± 0.61 CQDF 24% 2 1,02 ± 0, ± ± 0.55 Thermal denaturation of DA Metal Complex/DA Ri= 0.2 Spectrofotometric Titration of [Au(CQ)(PPh 3)]PF 6 with DA. [Complejo] = 9,98x10-4 M and [DA] = 0 50 µm Fluorimetríc Titration [Au(CQ)(PPh 3)]PF 6 with DA. [Complejo] = 7,32x10-4 M and [DA] = 0 10 µm umber Start Stop Incremen Hold time t o C 55.0 o C 3.0 o C 0.5 min o C 70.0 o C 1.0 o C 0.5 min o C 94.0 o C 3.0 o C 0.5 min Compounds UV-Vis Titration Fluorescence Titration K b1 (x10 7 M -1 ) K b1 (x10 5 M -1 ) K b1 (x10 7 M -1 ) K b2 (x10 5 M -1 ) CQDP 1.38 ± ± 0, ± ± 1.01 [Au(CQ)(PPh 3 )] PF ± ± ± ± 1.69 Tm Tm DA Melting Temperature after interaction with metal complex Complex Tm Δ Tm Au(CQ)(Cl) 69,6 ± 0,6 4,7 [Au(CQ)(PPh 3 )] PF 6 80,6 ± 0,4 15,7 [Au(CQDF)(PPh3)]PF6 85,4 ± 1,5 20,5 DA 64,9 ± 0,1 --- CQDP 87,6 ± ,7 7