Chem.-Biol. Interactions, 14 (1976) 179-193 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

PLATINUM COMPLEXES OF SUBSTITUTED ETHYLENEDIAMINES AND THEIR ANTI-TUMOUR ACTIVITY

K.P. BEAUMONT, C.A. McAULIFFE and M.J. CLEARE * Department of Chemistry. University of Manchester, Institute of Science and Technology, Manchester M60 1QD and, l JohnGon, Matthey and Co. Ltd., Manchester (Great Britain)

(Received January 12th, 1976) (Accepted February 2Oth, 1976)

SUMMARY

A large number of substituted ethylenediamine complexes of platinum (II) and platinum(IV) have been prepared and characterised, and their antitumour activity tested against sarcoma 180, leukemia L1210, and ADJ/PCGA plasma cell tumours. In general these complexes are less active than simpler amine analogues, though several complexes show activity against all of the screens. Difference in activig of platinum(I1) and platinum(IV) analogues leads us to cast doubt on the “in vivo reduction” theory hitherto used to describe the action of platinum(IV) complexes. _--___-_-.

-

_______~

___-

INTRODUCTION

Since the original discovery by Rosenberg et al. [l] that certain platinum complexes, in particular cis-diamminedichloroplatinum(II), inhibit the growth of sarcoma 180 and leukemia L1210 tumours in mice, several studies have now been reported with a view to determining structure-activity relationships (see, for example, refs l-5). Most of the work has involved platinum(I1) complexes containing monodentate ligands, although some studies of complexes containing bidentate amines have been reported [ 51. More recently Gale et al. have shown that dichloro( 1,2-diaminocyclohexane)platinum(I1) IS highly effective against leukemia L1210 in BDF mice [6], complementing earlier work on the ADJ/PC6A tumour in BALB/c and sarcoma 180 in Swiss white mice. We now report results for an extended series of alkyl-substituted ethylenediamine complexes of platinum(I1) and platinum(IV) using three different tumour screens. The species are all of the type (Pt(A#&] and Pt(A$%l

ethylenediamine or other bidentate amine) and we report (A2 = substituted tests against mice bearing sarcoma 180, leukemia L1210, and ADJ/PCG (plasma cell) tumours. Several active complexes have been found, with particularly interesting results against leukemia L1210. We thus confirm the wide spectrum of activity of this type of platinum(I1) and platinum(IV) complex. METHODS Sarcoma 180 tests. Control and test groups of 18-22 g male non-inbred Swiss albino mice were implanted subcutaneously with equal small amounts of finely minced 14day tumour (-30 mg) in the flank region. The control and test groups usually contained at least 6 mice. The complex to be screened was dry-milled for 24 h to reduce particle size, mixed with the suspending medium, 0.5% carboxymethylcellulose in 0.9% saline solution (CMC), and further milled for approx. 18 h. The complex suspension was then injected intraperitoneally into the test group of animals on days l-4 and 7. The control group was injected on the same days with 0.2 ml/mouse of (XC. Solid tumours were excised and weighed, usually on the 8th day following implantation. The results are expressed at T/C where T is the arithmetical mean of the tumour weights of treated and untreated animals and C is the arithmetical mean of the tumour weights of the control animals. Leukemiu Ll210 tests. Control and test groups of female BDF mice were implanted subcutaneously in the flank region with approx. 10” spleen cells (obtained from a leukemia donor mouse) suspended in 0.1 ml sterile saline. Control and test groups usually contained 8 mice. The complex to be screened was prepared as for the S180 tests and injected intraperitoneally into the test group of animals on days l--3,6 and 7. The control group was treated with 0.2 ml CMC/mouse on the same days. The percentage weight change for each group was calculated using the mean weight on the last day the majority of the mice were alive in any particular group. The results are expressed as mean survival time of test group divided by mean survival time of control group. Mean survival times were calculated according to the formula adopted by the Camzr Chemotherapy National Service Centre for this tumour [7]. ADJ/PCGA tests. New compounds were assayed against female BALB/c mice bearing the established ADJ/PCGA tumour by the method previously described [ 81. Tumours were transplanted subcutaneously by means of tumour fragments and treatment commenced at 24 days after implantation when the tumours were approx. 2 g in weight. In preliminary tests, 6 control animals were used and several groups of 3 treated animals. Several dose levels were given at 5-fold dose spacings and ranged from lethal to non-tumour inhibitory, allowing the calculation of LDSO and IDg0 (minimum dose to cause 90% tumour regression) in one experiment. The ratio LDSO/IDPOis a therapeutic index and is a measure of the selectivity of the compound as an antitumour agent. Agents found to be active were then further tested using

180

the same protocol, but smaller intervals (2-fold) between doses, enabling tbe calculation of LDSO and II& to be made with narrower fiducial limits. All compounds were administered intraperitoneally as a single dose suspended in arachis oil. The tumour-inhibitory cisdichlorodiammineplatinum (II) served as a positive control. Tumours were dissected out and weighed 10 days after drug treatment. Preparation of pla tinum complexes Dichloro(N-substituted ethylenediamirte)platinum(II). Potassium tetrachloroplatinite(I1) (2.0 mmole) was dissolved in distilled water (20 ml) and filtered. Potassium iodide (8.0 mmole) was added and the solution stirred for approx. 10 min. The N-substituted ethylenediamine (approx. 2.2 mmole) was then added in a small amount of water and the solution stirred for approx. 18 h. The dark yellow or brown precipitate which formed was filtered off, washed with water and ether and dried in vacua. This product, diiodobis(N-substituted ethylenediamine)platinum(II) was suspended m water (approx. 15 ml) and two equivalents of silver nitrate were added, the solution stirred for approx. 13 h and filtered clear of silver iodide. After purging for any remaining Ag* ions (using 0.1 M I-ICl), excess potassium chloride was added and the solution warmed gently on a hot plate. The product usually precipitated after a few minutes. After allowing_$o stand in the refrigerator for approx. 3 h the light yellow crystals were filtered, washed with water and ether and dried in vacua. Tetrachloro(N-substituted ethylenediamine)platinum(IV): The method was similar as that for the platinum (II) complexes except that after filtering off the silver iodide and purging for any remaining Ag’ ions, excess concentrated hydrochloric acid was added, the solution heated and allowed to boil until chlorine gas was evolved. The solution was then refrigerated and the bright yellow precipitate was filtered, washed with water and ether and dried in vacua. Dichloro(adenine)platinum(lI). Adenine (5.0 mmole) was added to a filtered solution of potassium chloroplatinite (II) (3.0 mmole) in water. The yellow solid which formed im&nediately was stirred for 5 h, filtered, washed with water and ether and dried in vacua. Dichloro(4,5-diamino-o-xylene)platinum( II) and dichloro( 2,2’-bipyridyl)platinum( 11) were prepared similarly . Physical measurements. Infrared and electronic spectra were obtained as previously described [ 91. The metal complexes (a) [Pt(A2)ClJ complexes. [(A,) = en, Eten, “Pren, ‘Pren, EtMeen, Et?en, *Prlen, MeJen, Me&ten, E&Meen, &en, ‘Pr3en, Me&en, (EtMekm, EtzMelen, EtJMeen] * When a slight excess of ligand is added with stirring to an aqueous solution * See Glossary for ligand abbreviations.

181

1

1

1

80 73 68 65 70 70 24 66 42 67 68 42 56 26 27 16 70 81 71 52 78 37 57 30 33 45 37 38 48 76 67 34

yellow pale yellow pale yellow pale yellow pale yellow pale yellow yellow yellow yellow pale yellow yellow pale ydlow yellow pale yellow yellow yellow deep yellow brown yellow deep yellow yellow deep yellow yellow yellow c!zp yellow deep yellow deep yellow deep yellow deep yellow deep yellow orange yellow

ILBased on K2[PtC14]. b found (talc.).

[Pt(Et3Meen)C14]

1 P4Me&4~d WO%M-WLI tpt(%e~)cl41 PWhE~n)C14 1 IWEtMeheNhl CWEtzMe~eO& 1

[Pt(Me3en)Ch

[P@Ren)CIG ] [Pt(EtMeen)CL] [ Pt( Et2en)C14 ]

[WnP=nW4

F-a4

1 [WEt.d&l

[Pt(bipy)CIz [Pt(xY ICI2 1

[Pt( Et3Meen;C1;, ]

[Pt(EhMezen(Cl,

tW(EtMehenFhl

[Pt(Me3Etcn)C12]

]

1

[Pt(EtzMeen)Ch

FWt3enKh 1 [ P@Pr,en( Cl2 ]

]1

[Pt(MezEten)Cl,

[ Pt(Meaen)C12 ]

W(Et2en)Ch 1 [ Pt(‘Pr2en)C12 ]

Yield a (%) 7.5( 7.4) 13.7(13.6) 16.1( 16.3) 15.9( 16.3) 16.5( 16.3) 18.7( 18.8) 23.5I23.4) 16.3( 16.3) 18.9( 18.8) 20.6(21.2) 23.3( 23.4) 29.0( 29.2) 21.2(21.2) 23.3( 23.4) 23.3( 23.4) 25.2(25.2) 28.5(28.7) 25.8(24.0) 5.9( 6.1) 11.4( 11.3) 13.9( 13.7) 13.5(13.7) 13.8( 13.7) 15.7(15.9) 13.fq13.7) 16.0f15.9) 18.1(18.0) 20.0( 20.0) 17.9(18.0) 20.0( 20.0) 20.1( 20.0) 21.8(21.8)

% C b 2.5(2.5) 3.6(3.4) 3.9( 3.8) 3.9( 3.8) 3.9(3.8) 4.2(4.4) 4.9(4.9) 3.9( 3.8) 4.2(4.2) 4.4(4.5) 4.9(4.9) 5.5( 5.8) 4.5(4.5) 4.9(4.9) 4.9(4.9) 5.1( 5.2) 1.8( 1.9) 3.4(3.0) 1.8(2.0) 2.8( 2.8) 3.2(3.2) 3.5( 3.2) 3.4( 3.2) 3.5(3.5) 3.3(3.2) 3.6(3.2) 3.9(3.9) 4.1(4.2) 3.8( 3.9) 4.1(4.2) 4.3(4.2) 4.3(4.4)

%Hb

DATA OF THE PLATINUS! CsMPT.EXES

Colour

YIELDS AND ANALYTICAL

[Pt(Eten)C12 ] [PtJnPren)C12] [ Pt( Qren)Cl, ] [Pt( EtMeen)Cl* ]

[Wen)Cl2

Complex

COLOURS,

TABLE I

_

8.5(8.6) 7.7(7.9) 7.6(7.6) 7.2( 7.6) 7.5(7.6) 7.1(7.3) 6.8(6.8) 7.6(7.6) 7.3(7.3) 6.6(7.1) 6.7(6.8) 6.2(6.2) 7.2(7.1) 6.7(6.8) 6.7(6.8) 6.4(6.6) 6.5(6.6) 7.6(7.0) 7.0(7.1) 6.8(6.6) 6.4(6.4) 6.3(6.4) 6.4(6.4) 6.1(6.2) 6.6(6.4) 6.2(6.2) 5.9(6.0) 5.9( 5.8) S.O(S.0) 5.9(5.8) 6.0(5.8) 5.7( 5.7)

%Nb’

’ 21.9(21.8) 20.1(20.1) 19.1( 19.3) 18.7( 19.3) 18.9( 19.3) 18.0( 18.3) 17.7(17.3) 19.2(19.3) 18.4(18.6) 17,1(17.9) 16.9( 17.3) 16.1( 15.7) 18.1(17.5) 17.3(17.3) 17.6( 17.3) 16.9( 16.7) 16.8( 16.8) 16.4(17.6) 35.4(35.8) 33.1(33.4) 32.2(32.3) 33.1( 32.3) 32.5(32.3) 31.4(31.3) 31.9(32.3) 31.7(31.3) 29.fq30.4) 29.1(29.5) 30.2(30.4) 29.6(29.5) 28.4(29.5) 28.7(28.7)

%Jci b

[ P@Pren)Cll J

Complex

ms ah m m

3155 m 3142 ah

3260 3235 3200 3187

3118 sh

3232 8

3150 m 3115 m 3070 sh

3240 ms 3200 sh 3180 ms 3110s

3241 s 3190 m 3129s 3110 sh

1585 mw

1603 w 1566 br

1583 sh 1562 ms

335 320 307 280

337 5 325 vs 305 m 353 m,ah 322 vs 288 mw

662 VW 483 w 464 w 358 w 510 mw 577 rns 618 m

597 mw (588 m)

658 w

594 m

329 m 335 m& 319 s 296,288 w 336 VI 327 vs -..

567 w 517 w

545 wsh 531 mw .

597 mw

626 VW 597 w

B vs s VW

325 s,sh 320 vs 299 m

577 m 500 mw

628 mw

333 323 317 310

m ms m m

274 m 259 m - -------

279 VW

267 w

250 VW

271 m

275 mw

&N-Pt-N) + v( Pt-CI)+ GIN-Pt- -N’N) otter ring modes

(680 ms) 497 mw

1590 w 1455 w

s w w s sh

3243 3200 3182 3126 3100

601 w (580 ms)

1560 br

ms m ms w

3272 3245 3200 3108

Ring u(Pt-N) skeletal mode

1587 w 1563 VW

6(N-H)

v( N-H)

IMPORTANT INFRARED SPECTRAL ASSIGNMENTS FOR THE PLATINUM COMPLEXES a

TABLE II

I>

425 w 403 VW

466 w

444 mw 412 w

454 V-ub 392 VW

403 w

- ~-

Other modes

tiz

I@

[PtWCL

I

3211 3160 3128 3069

w m sh w 1574 w

595

[Pt(EtsMeen)Cfz ]

585 w

VW

620 w

[Pt(EtzMezen)C12]

572 m 551 m

467 w 452 w

559 w 537 w 464 mw

528 mw 474 w 436 w

601 w 5b5 w

[Pt f(EtMe)zen 1 Cl2 I

575 mw 543 w 517 mw 526 mw

626 w 601 w

588 w 568 mw 549 VW

621 VW 608 w

3149 m 3135 sh 3110 sh

[Pt(‘Pr~en)C1, f

606 w (588 w)

wash w mw mw

(585 mw) 501 mw

579 572 535 529

[Pt(Me3Eten)C12]

3148 sh 3127 s

(585 mw)

3160 br 3140 sh 3128 sh

[Pt(Etsen)C&]

655 m

3148 s 3138 sh 3119 mw

Ring u(Pt-N) skeletal mode

[Pt(MezEten)&f

6(N-H)

v( N-H)

Complex

TABLE II (continued)

s,sh s,sh s m

349 337 328 320

sh s sh sh

330 s,sh 327 s 323 s

437 w,sh 324s

262 w

275 VW 242 w

327 vs 305 vz,sh 325 s 305 mw

280 w

266 mw

G(N-Pt-N) + other ring modes

327 vs 288 w

327 vs 324 vs 282 mw

331 326 323 294

335 vs 326 vs 280 w

vu(Pt-cl) * G(N-Pt-N)

408 w

409 VW

435 vw 400 VW 385 VW

451 mn

448 mw 390 yi

399 w

Other modes

-

G cn

337 s 323 s s sh s sh sh s sh sh

335 327 321 317 341 328 321 310

581 w 518 w 598 VW

595 VW 526 mw

3150 br 3128 sh

3165 s 3152 sh 3137 sh

3181 m

1

[ Pt( MeaEten)C14

a s, strong; m, medium;

[Pt(EtzMeen)C14]

1

[Pt(Mesen)C]4

340 s 328 sh 325 sh

592 VW 528 mw

3170 sh 3162 m 3139 sh

[ Pt( Etzen)C14 1

349 sh 334 s 325 sh

545 w 501 w

sh w w sh

3186 3180 3162 3140

[Pt( EtMeen)Cla 3

342 s 330 s

600 br 570 m

1575 sh 1558 m

w sh m sh

3225 3219 3185 3164

[Pt(iPren)C14 ]

sh sh s m

357 348 340 318

582 m

1560 w

w, weak; sh, sharp; br, broad.

w sh sh w

3240 3204 3192 3180

[ Pt( nPren)Cla ]

sh s s sh

1554 w

3211 mw 3162 m 3094 w

[Pt( Eten)C:4 ]

344 339 325 307

Ring skeletal mode 589 .w 571 ms

@N-H)

Y( N-H)

Complex

v(Pt-Cl) + &N-Pt-N)

II (continued) v( Pt-N)

TABLE 6(N-Pt-N) other ring modes

Other modes

of K2[Pt14] (Pt: ligand ratio 1 : 1.1) the complex [Pt(A&] is precipitated. This product and its sometime contaminant [Pt(N-en)C12 ] (present since K2 [Pt14 ] is prepared in situ from Kz [PtCL,] + 4KI), react readily with silver nitrate to produce the species [Pt(At)(HzO)z J (NO& in solution. Addition of excess potassium halide to the filtered solution and warming effects precipitation of the pure complexes [Pt(A,)X2] which were isolated. The

TABLE III ELECTRONIC SPECTRA OF THE PLATINUM COMPLEXES Complex UWWl2

E max, (e,,~)kK,

WW2enW2

I I

[Pt(Mesen)Clz] [ Pt(Mesen)Brz ] [ Pt( Me2Eten)Cl2 ] [ Pt( Et2Meen)Clz ] [ Pt( Etsen)Cl2 1 [Pt(‘Pr3en)C12 ] [Pt(Me3Eten)C12] [Pt((EtMe)2en)C11 ] [ Pt( EtzMezen)Cl:: ] [Pt(EtaMeen)Clz ] W(eW14 1 [ Pt( Eten)C14 1

[Pt(“Pren)Cl4] [ Pt( +ren)C14 ] [Pt( EtMeen)C14 ] [ Pt( Et2en)C14 ] [ Pt( MeJen)Cl4 ] [ Pt( Me2Eten)C14 ] [ Pt( Et&een)Ch ] [Pt( Etjen)C14 ] [Pt(MesEten)Cl,,] [Pt((EtMe)2en)C14] [Pt(Et2Me2en)C14] [ Pt( EtsKeen)Cl4 ]

I:; -42.6 sh, 42.1, 34.0 sh, 32.0, 26.0 41.0 (-), 34.6(347) sh, 33.6(372), 26.0(202), 21.9(151) 45.0, 43.2 sh 42.Osh, 41.6, 34.3 sh, 30.9, 25.4 40.0, 34.0, 31.1, 26.1, 21.6 44.1(2076) sh, 43.1(2147), 38.0(747)sh, 31.0(205) 43.9(555) sh, 43.1(605), 35.5(114), 31.7(123), 27.4( 50) 42.3(523) sh, 41.7(630), 34.5(155) sh, 32.1(199), 26.5(46) 41.8(549), 34.5(210) sh, 31.4(142), 26.5(35) 41.6(1489), 33.9(348), 28.5(286), 26.2(250) 41.6(611), 34.0(122), 31.1(134), 26.1(38) 43.8(790) sh, 43.3(809), 35.1(159) sh, 31.4(134) 43.3(506) sh, 42.6(605), 35.0(92), 31.2(92), 27.4( 50) 44.1(506) sh, 42.7(605), 34.1( 110) sh, 31.6( 114), 26.9(4) 43.7, 42.0 41.5 42.1 sh, 41.5, 36.6, 23.3 42.1 sh, 41.5, 34.4 41.2, 35.7 43.9 sh, 42.7, 35.9 42.8( 2265), 36.1( 1644) sh, 22.1( 33) 42.8, 36.1 sh, 22.1 41.7(20600) sh, 41.2(23020), 35.2(5016) sh, 22.3(79) 41.2(23965), 34.9(4511) sh, 23.3(33) 35.0(3665) sh, 22.5(71) 41.2(25000), 34.5(3848) sh, 22.2(44) 42.2(32040), 34.3(3565) sh, 21.8(151) 41.2(9600), 33.9( 1419) sh, 22.0(6) -

a Solutions in dichloromethane. and no spectrum was obtained.

186

cm-l)a

43.3, 41.2 sh, 32.3 sh, 27.2

I

[ Pt( Eten)ClZ ] [ Pt(“Pren)Clz ] [ Pt(‘Pren)Cb ] [ Pt( EtMeen)Clz ] UV~t2eW12

(1 - mole-’

E maw kKb 24.8 25.0 23.3 24.1 23.7 23.9 23.0 24.1 25.5 24.1 24.0 24.1 23.9 25.3 23.9 25.0 22.6 23.5 23.2 26.5, 23.5 25.7, 23.2 22.8 22.6 23.0 22.7 23.9, 22.7 23.9 25.0, 22.2 23.0 27.6, 22.7

b Solid reflectance. c These complexes were insoluble

complexes vary in colour from pale yellow in the case of most chlorides to brown in some iodide. Yields {Table I) generally reflected the amount of steric hindrance at the nitrogen atoms of the incoming Nen ligand, varying from 16-80%. The [Pt(Nen)& ] complexes so produced (Table I) are non-electrolytes in lo-’ M nitromethane solution and exhibit IR and electronic spectra (Tables II and III) characteristic of square-planar platinum (II) com~unds. On coo~ination N-H stretching vibrations y(N-H) decrease in fluency m all cases as reported previously for ethylenediamine [ 10)) and increase in intensity relative to the VIC-H) bands of the ligand (11). The free ligands exhibit one or two bands in this region whereas the complexes show between two and four, none of which are near the frequencies observed in the uncoordinated ligands sho~ng that both N atoms are coo~~a~d to the metal atom. As alkyl substitution of the N atoms of the AZ ligands increases the v(N-H) frequencies decrease generally and the bands become less well defined. The N-H banding mode &N-H) is shown only by those ligands containing a primary N atom and on complexation the frequency of this band decreases. The bands in the v(Pt-N) region are more difficult to assign since they are generally combination bands and not an isolated vibration of the Pt-N bond. Consequently the assignments are tentative without the use of isotope studies. The assignments have been made in accordance with the results of Berg and Rasmussen (121. The symmetry of the necessarily cis-[Pt(A#& ] is CS and two y(Pt-Cl) bands are expected in this case due ta symme~ic and ~y~e~ic Pt-Cl stretching [ 131. In most of the chloro complexes two strong bands are seen in agreement with the theory, while in others a strong band and a shoulder are present. There is iittle shift in the WV-Cl) absorption in the series of complexes [Pt(A2)C12] , all bands occurring in the range 296-328 cm-“, showing that the N-substituen~ have little effect on u(Pt-Cl). This vib~~ion appears to be sensitive to donors but not to substituents on the donor atoms [ 141. Broadening of some of these bands is observed and it is possible that hydrogen bonding of the type - N-H ... Cl- is responsible for this. The electronic spectra of platinum complexes (Table III) can be divided roughly into two regions; &he first at frequencies above 35 kK due to ch transfer bands (M+L), and the second due to d-d t~nsitions at lower ene 1151. The d-d bands are formally forbidden but gain intensity by v~b~tion~~ perturbations or by borrowing from the intense allowed bands [15]. in electronic ab The spectra of the complexes show an incre energies on ~placement of two of the chloride li also found on replacement by two cis NH3 mol tion of [Pt(EtMeen)CIz], and [~(Me~en~~l~ ‘1which kK and 21.6 kK respectively, the lowest frequency ban complexes observed in dichloromethane solutio This apparent anomaly may be ~~~ciat~ with ~~(EtMeen~Cl~] was taken in 1 e-3 M ~lution at concentrations of 10-j M.

The solid reflectance spectra of the complexes exhibit absorptions at lower energy than in solution, which is characteristic of square-planar d8 compounds and may be explained by the effect of interactions at axial sites on the platinum with molecules in the layers above and below [ 141. (b) [Pt(A2)CZ4] complexes. (A2 = en, Eten, “Pren, %en, EtMeen, Etlen, Me3en, MezEten, &Meen, EtJen, Me3Eten, (EtMe)zen, EtzMelen and Et3Meen). Addition of concentrated hydrochloric acid to an aqueous solution of [Pt(A2)(HzO),] (NO,), and boiling until chlorine gas was detected, or bubbling chlorine gas through the solution followed by refrigeration produced yellow or deep yellow crystals of the complexes [Pt(A,)Cl,]. The eomplexes are non-electrolytes in 10q3 M nitromethane solution. The infrared spectra of these complexes are generally similar to those of the corresponding platinum(I1) compounds. N-H stretching vibrations, v(N-H), occur at lower frequencies and are weaker in these complexes than in the platinum(I1) complexes in most cases, suggesting that the N-H bond is weaker in [ Pt( N-en)Cl.+] . This is expected on electroneutrality grounds, as the platinum(IV) atom will require more charge to be donated from the nitrogen atoms resulting in a weaker N-H bond and a stronger Pt-N bond than in the platinum(I1) complexes. No bands were observed in the v(N-H) region of the free ligand vibrations showing both nitrogen atoms to be coordinated. There are between two and four bands assigned to u(N-H), the number decreasing as the N-substitution increases. The &N-H) bands are somewhat weaker in the platinum(IV) species and occur over roughly the same frequency range as in the platinum(II)‘complexes. Surprisingly, the complex [Pt(Etzen)C14] shows no absorption in this region. Assigments of v(Pt-N) are tentative for the reasons outlined previously, but it is noticeable that in the platinum(IV) complexes the v(Pt-N) absorptions are ar higher frequencies than in the corresponding platinum(I1) complexes. This suggest a stronger Pt-N bond. Between two and four bands are assigned to stretching vibrations of the Pt-Cl bonds and these are observed in the region 350-310 cm-‘, at higher frequencies than in the corresponding platinum(I1) compounds. The range of different N-substituents seems to have little effect on the v(Pt-Cl) frequencies. Group theory predicts 4 infrared active bands due to v(M-X) in complexes of type cis-[MLzXg ] [ 171, and in the instances where four bands are not observed in the complexes [Pt(Nen)C& ] this may be attributable to degeneracy of two or more bands due to coupling with other vibrations in the complex or accidental degeneracy. ‘The platinum(IV) complexes are less soluble in dichloromethane than the corresponding platinum(I1) compounds and so in some cases only the bands due to chkge transfer (M+L) could be observed. These bands occur at 4141 kK and 42-43 kK (usually as a shoulder on the previous bands), and where concentrations of 10m4M could be obtained the extinction coefficients are approx. 2 q 10e4 1 mole” cm” which is, typically, about 30 times greater l

188

than the coxrespondin energy comlates spectrum

which is n

species.

in TABLE IV ANTI-Tt_Q PLBXBS w Complex

20

30-60 30-100 100 l-100 I-100 1=-l l-5 l-100 I-1 l-1 l-1 l-l l-108 30-10 100 100 100

amine group (A) in compounds of the type cis-[Pt(A)&] has a primary ~uence on ~titumo~ activity [2,3,5]. This p~ticul~ly applies to the ~J~PC6A tumour system which has proved to be sensitive to platinum compounds [2,4]. The kinetic data which are available indicate that changes in the A ligand have a relatively small effect on the reactivity of the Cl ligands (i.e. their leaving ability) except when steric hindrance causes a marked reduction of reaction rates [18]. The majority of the antitumour data has involved monoden~~ amines, but our results show that similar effects are to be found with bidentate amine ligands although in general the activity (and selectivity against the ADJ/PCGA system) is somewhat lower than the monodentate compounds. The parent complex [PtQen)Cl,] was originally shown to be effective against Sl86 in Swiss white mice by Rosenberg as a first analogue of cis-fPt(NH&Cll] , the original active compound [l] . Monoalkyl substituted ethylenediamines form complexes which in general maintain the activity against Sl80 albeit at a slightly lower level (Table IV). These complexes are less active against the ADJ/PC6A plasma cell tumour but show less selectivity ~rn~ifes~d by a lower value of the therapeutic index, Table VI) than [ Pt(en)Cl, ] . Toxic levels were found to be similar to those for f Pt(en)Clz ] but the effective dose increased with alkyl substitution. Values of T/C of 146-169 (values >125 are usually considered to be significant) were obtained for some monosubstituted ethylenediamine complexes against leukemia Ll2lO tumours (Table V). Increasing alkyl ~~ubsti~tion (di-, tri-, and te~a-substitution) lowers the toxicity of the complexes against all the tumour systems but also requires increased doses for effective treatment, thus reducing the overall activity. The S180 system does not respond to any of these multisubstituted ethylenediamine complexes (with the exception of A = Mejen), confirming earlier work [5] . The L12l.O is also rather insensitive to these complexes, whilst the TABLE V ANTI-TUMOUR SCREENING SUMMARY PLEXES vs. I,1210LEUKEMIA Complex

[ Pt( Eten)C12 ] fPt(‘Pren)Cl, ] r~tMe3en~~Iz 3 [ Pt( Me$ten)C12 J [ Pt( EtzMeen)Clz ] [P@&en)CI2 1 [Pt(Me3Eten)C12 ]

wtbYm2l

[Pt(nPren~C14] [Pt( EtM~n)CI~ ]

190

OF lPt(L)CI,]

AND [Pt(N-enfCl4J

Dose range (mgbg)

T1C (%I

Dose (mg/kg)

Weight loss @J) (day 4)

l-6 l-4 12.5-35 20 30 30 50 5-100 2-8 10

148 169 134 115 106 100 109 141 140 106

4 4 35 20 30 30 60 100 8 110

9.7 14.4 14.4 6.4 0.8 14.0 17.5 0.9

COM-

TABLE VI ANTI-T~O~R ROLEXES

SCREENING SCARY OF [~(N~n~~~] vs. ADJ/PCGA PLASM-9 CELL T~~UR

Complex

;PttEtW.X 1 :Pt(n~n)C12

I

:Pt(‘Pr2en)Clz ] :Pt(Me~en)@h 3 $‘t(Me&en)C12] Pt(Etaen)C12 ] ;Pt(Et2Me2en)Cfa ] ~~tn~en)Cl~] [Pt(Megm)Cl,] [Pt(Me2Eten)C& ] [Pt(Me3Eten)C14] [Pt((EtMe)2en)C14] [ Pt( EtsMeen)Cla ] -

L&o (mdw)

I&o (mg/W

18 26.5 132 132 132 132 132 27 135 90 450 670 450

2.2 5.0

2.35 3.05 1.8 1.7 2.35 7.8

ADJ/PCGA system (Table VI) again shows itself to be the most sensitive. However, in the latter cases minor variations in the ligand do not have the profound effect noted for some monodentate systems, particularly alicyclic and branchedchain amines [2,4]. Rosenberg es~bli~ed for the original active platinum compounds that platinum(IV) analogues, cis-[Pt(A)&le], with axial chloro Iigands were also active [ 11. Indeed it is believed that in vivo reduction occurs with loss of axial chloro ligands although direct evidence for this is still lacking 1191. In the original compounds cis-[Pt(NH3)2Cl,] and [Pt(en)C& ] the effective and toxic doses were not greatly different from the platinum (11) analogues ill. Tobe et al. have reported [ 43 that for a variety of monodenate amine complexes, cls-[Pt(A)&IQ], against the ADJ/PCGA system the toxicity is increased while the effective dose is little changed, compared to the corresponding cis-[Pt(A)&l2] compounds, leading to a much lowered therapeutic index. For our compounds both the toxic and effective doses are greatly increased in some cases (namely, for those complexes with ligands with a high degree of alkyl substitution). Some platinum(lV) complexes are active when the corresponding platinum(R) species is inactive against the same tumour system, although in each case the platinum(I1) complex shows some activity against a different system. This is the first study where this has been shown to be the case and our results cast doubt on the “in vivo reduction theory” [1 J, and consequently on the mode of action of platinum~IV) antitumour agents as a whole. It is of particular interest that several of the compounds show activity against two or three of the screening systems, confirming the wide spectrum of activity of some platinum ~titumour agents. The activity against Eke L1210 system is particularly encouraging as some compounds with bulky 191

amine ligands have previously been shown to be relatively ineffective against this, the most widely used of primary antitumour screens [ 201. Structurelrctivity relationships All the complexes tested in this study have cis leaving chloro groups, but the effectiveness is rather sensitive to the nature of the bidentate amine. In general the lesser alkyl-substituted ethylenediamine complexes are active in several tumour systems while the more substituted ones are only active against the most sensitive system, the ADJ/PCGA plasma cell tumour. At present there is no obvious explanation for the variation of activity with amine structure and much further work is needed to clarify this. Kinetic effects, such as the rate of loss of the cis-chloro groups, are unlikely to account for the variations here and in other work it has been suggested that hydrogen bonding interactions may be important in stabilising a receptordrug complex. Certainly, increased alkyl substitution of the -NH2 groups of ethylenediamine will tend to decrease the H-bonding potential, but this does not explain many of the variations. We plan to determine lipid solubilities, as membrane interactions are likely to be important. ACKNOWLEDGEMENTS

This work was supported by The Science Research Council and The North Atlantic Treaty Organisation. We also wish to acknowledge with gratitude discussions with, and the antitumour testing done for us by, Professor K. Hellman, Imperial Cancer Research Pund, and Dr. T.A. Connors, Chester Beatty Research Institute. REFERENCES 1 B. Rosenberg, L. Van Camp, J.E. ‘hosko and V.H. Mansour, Nature, 222 (1969) 385. 2 T.A. Connors, M. Jones, W.C.J. Ross, P.D. Braddock, A.R. Khokhar and M.L. Tobe, Chem.-Biol. Interact., 5 (1972) 415. 3 M.J. Cleare, J.D. Hoeschele and C.A. McAuliffe, Proceedings of XVI Conference on Coordination Conference, Dublin, 1973, p. 1.8. 4 M.L. Tobe, T.A. Connors, M.Jones, A.R. Khokar and P.D. Braddock, C&em.-Biol. Interact.. in press. 5 M.J. Clesre and J.D. Hoeschele, Bioinorg. Chem., 2 (1973) 187. 6 G.R. Gals, Proc. Sot. Exptl. Biol., (1973) 142 (4). 7 Cancer Chemotherapy National Service Center, Cancer Chemotherapy Rep. No. 26 (1962) 1. 8 V.M. Rasenoer, B.C.V. Mitchley, F.C.J. Roe and T.A. Connors, Cancer Res., Suppl. 26 (1966) 937. 9 L. Baracco and CA. McAuliffe, J.C.S. Dalton, (1!)72) 942, 10 R.W. Berg and K. Rasmussen, Spectrochim. Acta, 29A (1973) 319. 11 G.F. Svatos, C. Curran and J.V. Quagliano, J. Amer. Chem. Sot., 77 (1955) 6159. 12 R.W. Berg and K, Rasmussen, Spectrochim. Acta, 29A (1973) 37. 13 K. Nakamnto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd ed., Interscience, New York, 1970, p. 214. 14 W. Levasoan, Ph.D. Thesis, Univ. of Manchester, 1975

192

15 A.J. Thompson, R.J. P. Williams and S. Restova, Struct. and Bonding, 11 (1972) 1. 16 H. Ito, J. Fujita and K. Saito, Bull. Chem. Sot. Japan, 42 (1969) 2863. 17 K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd ed., Interscience, New York, 1970, p. 214. 18 F. Basolo and R.G. Pearson, Mechanisms of Inorganic Reactions, 2nd ed., Wiley, New York, 1967. 19 M.J. Cleare, Coord. Chem. Rev., 12 (1974) 349. 20 T.A. Connors, Personal communication of National Cancer Institute results.

GLOSSARY LIGANDS USED IN THIS STUDY AND THEIR ABBREVIATIONS HzNCHzCHINHz EtHNCHICH2NH2 “PrHNCH2CH2NHI i PrHNCHzCH2NH2 EtHNCHzCHlNHMe Et,NCH2CH2 NH2 ‘PrlNCH2CH2NH2 Me?NCH&HaNHMe Me2NCHzCHINHEt Et2NCHlCH2NHMe EtlNCHICHINHEt ‘Pr2NCH2CHzNHiPr Me2NCHxCH1NMeEt EtMeNCH&H*NMeEt Et2NCH2C!H&lMe EtzNCHzCHzNMeEt

ethylenediamine N-ethylethylenediamine N-(n-propyl)ethylenediamine ZV-(i-propyl)ethylenediamine N-ethyl-ZV’-methylethylenediamine N.N-diethylethylenediaaine N,N-di( i-propyl)ethylenediamine N.iV,N’-trimethylethylenediamine N,N-dimethyl-N’-ethylethylenediamins N.N-diethyl-N’-methylethylenediamine N,N,N’-triethylethylenediamine N,N,M-tri(i-propyl)ethylenediamine N&N’-trimethyl-N’-ethylethylenediamine N,N’-diethyl-N.iV’-dimethylethylenediamine N,N-diethyl-N’,N’-dimethylethylenediamine N&N’-triethyl-N(-methylethylenediamine

2,2’-bipyridyl

4,5-diamine-s-xytene

en

Eten nPren iPren Ehen &Zen Meaen

Platinum complexes of substituted ethylenediamines and their anti-tumour activity.

Chem.-Biol. Interactions, 14 (1976) 179-193 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands PLATINUM COMPLEXES OF SU...
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