BASICSCIENCES

RADIOCHEMISTRY AND RADIOPHARMACEU11CALS

[125I]IodobenzoylDerivativesof Acebutololas PotentialMyocardial Imaging Agents

Robert N. Hanson, Michael A. Davis, and B. Leonard Holmat.

HarvardMedical School and Northeastern University, Boston, Massachusetts

Threenew Iodobenzoylderivativesof acebutolol,a cardioselectivebeta antago nist, were synthesized and labeled with iodine-125. The blodistrlbutlons of these labeled compoundswere determinedin normal rats and compared with that of thallium-201. Fifteen minutesfolloWingi.v. administration,the Iodlne-125-Iabeled meta- and para-iodobenzoylacebutololspossessedthe greatest ventricularup take and the highest ventricle-to-bloodand ventricle-to-lungratIos of the new agents.The correspondingvaluesfor thallium-201 were 2.5 to 3.0 tImes as high. The data in this studysuggestthat more lipophillcderivativesof the cardioselec tlve beta antagonists will possess increased uptake and cardloselectivity, and thereby will compare more favorably with thalllum-201 as myocardlal Imaging agents.

J NucI Med 21: 846—851, 1980

The development of gamma-emitting radiopharma (4) andacebutolol(5), respectively,tendstoenhancethe ceuticals that could provide more accurate imaging of cardioselectivity of the drug. regional myocardial perfusion than thallium-20l would Since benzoylated analogs of practolol and acebutolol be useful in the early detection of coronary disease and are cardioselective (4,5), it seemed reasonable to expect assessment of therapy. Our approach to the development that the iodobenzoyl derivatives would also show this of such agents utilizes radiolabeled derivatives of drugs, pharmacologic selectivity. Derivatives of the beta an such as the beta-adrenergic antagonists, that exert a tagonists were synthesized in which the iodine-containing selective pharmacologic effect upon the heart. moiety is distal to the oxyisopropylaminopropanol The beta antagonists have the ability to decrease heart pharmacophore. These compounds should be more re rate, myocardial contractility, and myocardial metabo sistant to deiodination in vivo than the o-iodophenolic lism. As defined by Lands et al. (I ), these are beta-i beta antagonists previously prepared (6—8).To test the responses, and structure-activity relationship studies theory that derivatives of cardioselective antagonists (2,3) have demonstrated that selective inhibition of these would have better myocardial uptake and selectivity than beta- I responses can be achieved by the selective intro derivatives of noncardioselective antagonists, a series of duction of functional groups onto the parent 3-phe three 1-125-labeled beta antagonists was made (9). noxy- I-isopropylaminopropan-2-ol structure. For ex Meta-[' 25I]-iodobenzoyl practolol (m-IBP) and -ace ample, the placement of hydrogen-bonding moieties in butolol (m-IBA) were prepared as the cardioselective the para position of the phenoxy group, such as the derivatives, and 4'-['251]iodopropranolol (IP) was pre acetamido and butyramido groups present in practolol pared as a nonselective beta antagonist. The biodistri bution data indicated that m-IBP and m-IBA had sig nificantly better myocardial uptake and target-to-non Received March 30, 1979; revision accepted March 10, 1980. target ratios (T/NT) than the noncardioselective IP. For reprints contact: Robert N. Hanson, PhD, Dept. of Medicinal These data supported the decision to examine derivatives Chemistry and Pharmacology, Collegeof Pharmacy and Allied Health of the cardioselective beta-adrenergic antagonists as Professions, 360 Huntington Ave., Boston, MA 021 15. possible cardiovascular imaging agents.

846 THE JOURNAL OF NUCLEAR MEDICINE BASIC SCiENCES RADIOCHEMJSTRY AND RADIOPHARMACEUTICALS

Pharmacokinetic studies with radiolabeled f3-adren chloride and rneta-iodobenzoic acid were obtained ergic antagonists have demonstrated that i.v. adminis commercially.* Sodium [125l]iodide in 0.08 N sodium trationofthedrugresultsina rapiddistributionphase hydroxide, and [201T1Jthallous chloride, were carrier followed by a slower elimination process that isconsistent free. The acebutolol hydrochloride was used without with a two-compartment body model. At doses less than puriuication.t 2 mg/kg there is little distribution to a tissue compart Chemical and radiochemical purity analyses. The ment with a slower equilibration constant (10,1!). This chemical and radiochemical purity of the products were is reflected in the biodistributional studies conducted by determined by thin layer chromatography using the other investigators (8,12—15),and by ourselves (9), following analytical systems: (a) Silica gel plates@(250 where the target- (heart) to-nontarget ratios for the ra @Lwith fluorescent indicator) and chloroform : methanol diolabeled /3-adrenergic antagonists remain relatively (85 : I 5); (b) Silica gel plates* (250 @zwith fluorescent constant between 5 mm and 2 hr after administration. indicator) and butanol:acctic acid:water (4: 1:2); and Therefore, for the purpose of comparing the uptake and (c) KC18 plates (200 /2 with fluorescent indicator) and selectivity of radiopharmaceuticals, we chose a single methanol : water :acetic acid (60 : 40 : 1). The unlabeled time interval that falls in the early elimination phase for starting materials were applied adjacent to the radiola the rat. beled products, the chromatograms were developed, and Because the myocardial uptake and heart-to-lung 0.5-cm segments of the adsorbent were removed and ratio for meta-['251]iodobenzoyl acebutolol were corn counted in a Nal(Tl ) well counter. In all three systems, parable to those of the corresponding practolol deriva 95-99% of the radioactivity was associated with a single tive, and because of the side effects reported in the component having an R1 value identical to that of the clinical use ofpractolol (16), the acebutolol derivatives unlabeled material. No other organic products could be were selected for primary consideration. A comparison visualized by ultraviolet light. The nonlabeled corn of the organ distribution with that of Tl-20l and the pounds were characterized by their infrared, nuclear elucidation of the effect of positional isomerism in the magnetic resonance, and mass spectra. Elemental iodobenzoyl prosthetic group upon iodine exchange, analyses (C, H, N, I) were performed commercially and biodistribution in normal rats at I 5 mm, and myocardial agreed to within ±0.4%of the theoretical values. selectivity were thought to be reasonable objectives. Chemicalsynthesisandexchange.Theortho-,meta-, These data would provide a basis for determining the and para-iodobcnzoyl derivatives of accbutolol (IBA) relative merits of the labeled beta antagonists vis-a-vis were prepared using the previously published procedure a currently used myocardial perfusion imaging agent. (Fig. I) (9). The radioisotopic exchange with the ortho-iodo isomer was achieved by autoclaving an am poule containing a buffered solution of the compound MATERIALS AND METHODS and sodium [‘251]iodide(5-9 mCi) at I30°Cfor 90 mm Chemical reagents. Ortho- and para-iodobenzoyl (17). Adjustment of the cooled solution to pH 10, fol

3 CH3 CR5 OH 2NHCI

CH3 1H2

0 O@('@N'@CH3

CR5 ortho, meta,poro pH 5.5 HN@(I@

FIG. 1. Preparation of isomeric iodoben ortho, meto, poro zoyl derivatives of acebutolol. 355O@'/e overall yield

Volume 21, Number 9 847 HANSON, DAVIS,AND HOLMAN

CH3 [email protected] ortho8O90% 1300 meto,pora 1-4%

.@

I

No'251melt mete poro7OBO% l80

@ Na 1251 5 @9mCi ( 2 3 -4.1 nmol) FiG. 2. Radioisotopic labeling of isomeric @ IBA 0.5 - 1.0mg ( I -2jnnol) iodobenzoylderivatives of acebutolol.

lowed by extraction with chloroform, gave the product, or Sprague—Dawleyoutbred rats. Fifteen minutes after which was virtually free of inorganic [‘25ljiodide. In administration the animals were killed by ether as corporation proceeded with an 89% yield, 99% purity, phyxiation and the organs of interest excised. Blood and specific activity of 3.2 Ci/millimole. The same samples were obtained from a vein in the thoracic cavity. procedure with the meta and para isomers gave only a The tissue samples were weighed, counted in a NaI(T1) 1—4%incorporation, and therefore exchange was well scintillation counter, and the percent of the dose per achieved by using the melt method (18) to give a 75—80% gram of tissue (% ID/g) and/or per organ (% ID/organ) incorporation and specific activities of 0.38 and I .9 determined. Ci/millimole, respectively (Fig. 2). RESULTS AND DISCUSSION Biodistribution. A solution of iodine- 125-labeled product or [201T1Jthallous chloride (0.1 ml, 10 zCi per The chemical syntheses for the three iodobenzoyl rat) was injected intravenously into 150-250 g Wistar acebutolol isomers resulted in yields adequate to provide

TABLE1. TISSUECONCENTRATIONSOF RADIOPHARMACEUT1CALS15 MIN AFTERINTRAVENOUS ADMIN1STRATIONTO RATS

TI (n = 6) o@lBAt(n = 3) m-IBA (n 6) p-IBA (n 5)

Liver 0.72t 1.57 1.84 1.70 (0.49—0.93) (1.39—1.88) (1.54—2.04) (1.40—2.11) Spleen 0.86 0.60 0.65 0.91 (0.67—1.12) (0.49—0.70) (0.57—0.82) (0.67—1.16) Lungs 2.03 1.07 1.76 1.34 (1.79—2.70) (0.96—1.16) (1.45—2.63) (1.08—2.16) Kidneys 5.83 0.95 3.42 3.30 (4.23—7.49) (0.92—0.99) (2.57—4.03) (2.63—3.96) Pelt 0.19 0.19 0.15 0.19 (0.16—0.22) (0.06—0.26) (0.11—0.22) (0.16—0.23) Muscle 0.28 0.21 0.15 0.17 (0.24—0.33) (0.18—0.24) (0.12—0.17) (0.15—0.22) Bones 0.49 0.19 0.17 0.19 (0.36—0.71) (0.12—0.24) (0.14—0.21) (0.15—0.29) Blood 0.07 0.24 0.07 0.17 (0.05—0.08) (0.20—0.28) (0.05—0.09) (0.09—0.23) Thyroid 10.91 5.65 4.25 5.88 (7.83—16.32) (5.13—6.20) (2.39—6.29) (5.58—6.44) Atria 2.16 0.42 0.77 0.80 (1.45—3.46) (0.36—0.51) (0.59—1.02) (0.67—0.87) Ventricles (normal) 3.09 0.43 1.06 0.93 (1.90—4.11) (0.36—0.55) (0.74—1.19) (0.75—1.07)

. Dose 0.01 mCi in 0.1 ml saline. t o-IBA = ortho-iodobenzoylacebutolol, m-IBA meta-lodobenzoylacebutolol, p-IBA para-iodobenzoylacebutolol. t Percentinjecteddoseper gramof tissue,meanand(range)for n animals.

848 THE JOURNAL OF NUCLEAR MEDICINE BASIC SCIENCES RADIOCHEMISTRY AND RADIOPHARMACEUTICALS

TABLE2. ORGANCONCENTRATiONSOF RADIOPHARMACEUTICALS15 MIN AFTERINTRAVENOUS ADMINISTRATiONTO RATS TI (n 6) o@IBAt(n = 3) m@IBAt(n = 6) p@lBAt(n = 5)

Liver 7.86* 14.4 19.8 21.4 (6.55—11.0) (13.0—15.8) (18.4—21.4) (15.6—25.3) Spleen 0.57 0.26 0.43 0.58 (0.48—0.83) (0.21—0.34) (0.35—0.51) (0.51—0.70) Lungs 2.26 1.56 1.96 2.63 (2.08—2.75) (1.46—1.70) (1.59—2.69) (2.12—3.25) Stomac.h 1.19 1.57 1.46 2.58 (0.46—1.96) (0.15—2.45) (0.63—2.59) (0.57—3.21) Smallintestine 7.27 2.54 9.63 4.96 (3.80—11.2) (0.55—3.68) (7.59—14.4) (3.53—6.41) Large intestine 3.32 1.76 0.87 (1.60—4.72) (0.54—5.28) (0.60—1.42) Kidneys 11.6 1.76 6.77 7.28 (8.80—15.0) (1.65—1.84) (6.39—7.66) (6.80—7.83) Pelt 8.90 9.80 6.94 10.2 (7.77—10.6) (9.57—10.0) (5.77—9.87) (8.43—12.1) Muscle 26.4 16.4 13.8 21.6 (22.2—29.3) (15.4—18.0) (12.2—15.2) (15.4—24.2) Bones 7.07 3.70 2.25 5.85 (5.73—10.6) (2.20—4.74) (2.12—2.42) (4.13—7.13) Blood 0.99 2.86 1.41 3.33 (0.74—1.18) (2.52—3.12) (0.86—3.10) (2.91—3.51) Thyroid 0.22 0.11 0.09 0.12 (0.15—0.33) (0.10—0.13) (0.05—0.12) (0.11—0.13) Head 2.17 0.22 0.70 0.76 (1.56—2.83) (0.13—0.30) (0.63—0.77) (0.54—0.94) Total 79.8 55.2 67.0 82.2

. Dose 0.01 mCi in 0.1 ml saline. t o-IBA = ortho-iodobenzoylacebutolol. m-IBA = meta-iodobenzoylacebutolol, p-IBA para-iodobenzoylacebutolol. * Percentinjecteddoseper organ,meanand(range)for n animals. well-characterized products. Either method of exchange acebutolol derivatives were generally lower in most produced good incorporation of the label. The specific tissues at i5 mm than for Tl-201 . The most significant activities were sufficient to permit the collection of bio differences in organ distribution for the two classes of distribution data at subpharmacologic (nmol) doses. The agents were in the liver values, where the labeled beta conditions for exchange have not been optimized and antagonists were two to three times as high as TI -201, significant enhancement of the specific activity could be and in the muscle and bone values where Ti-20l was achieved by increasing the quantity of sodium [l25l]@ higher by factors of I .3 to 2. iodide and/or decreasing the amount of iodobenzoyl Greater uptake in the myocardium was also observed precursor. The position of the iodine on the benzoyl for Tl-20I (3.09 and 2.16 % ID/g in the ventricles and moiety has a dramatic but predictable effect upon the atria). Comparison of the TINT ratios for the agents ease of exchange. Whereas the ortho-iodobenzoyl isomer indicates that at 15 mm T1-20i possesses better cardi underwent facile exchange both by autoclaving in a oselectivity than the radioiodinated beta blockers (Table buffer and by melting, autoclaving the meta- and para 3). The ratios of heart-to-lung, -blood, and -liver (i .5, iodobenzoyl acebutolol derivatives in pH 6.0 to 6.5 buffer 44, and 4.3, respectively) were significantly better than in the presence of sodium [‘25ljiodide produced only the corresponding values for the beta antagonists. 1—4%radioisotopic exchange. This experience is analo Positional isomerism has several effects upon the io gous to that encountered in the preparation of the ortho-, dobenzoyl acebutolols. As described earlier, the method meta-, and para-iodobenzoic acids (17). of radionuclide exchange is governed by whether the The biologic distribution data for the four radio iodine is located in the activated ortho position or in the pharmaceuticals are shown in Tables I and 2. The % more resistant meta or para positions. The meta- and ID/g and % ID/organ values for the [‘251]iodobenzoyl para-iodobenzoyl derivatives are significantly more

Volume 21, Number 9 849 HANSON. DAVIS.AND HOLMAN

TABLE3. UPTAKEAND TARGET-TO-NONTARGETVALUESFOR 1-125-LABELED IODOBENZOYLACEBUTOLOLSAND T1-201, AT 15 MIN AFTER ADMINISTRATIONTO RATS Myocardialuptake Myocardium Radiopharmaceutical (% lD/g) Lung Liver Blood TI-201 (n = 6) 3.09 1.58 4.85 40.8 (1.90—4.11) (1.05—2.06) (3.36—6.06) (26.1—78.8) o@lBAt(1-125) (n = 3) 0.43 0.39 0.28 1.84 (0.36—0.55) (0.35—0.45) (0.21—0.36) (1.30—2.60) m@lBAt(1-125)(n = 6) 1.06 0.55 0.53 12.1 (0.74—1.19) (0.45—0.65) (0.48—0.58) (10.4—14.8) p-IBAt (l-125)(n = 5) 0.93 0.58 0.60 11.1 (0.75—1.07) (0.52—0.69) (0.45—0.76) (9.30—13.2)

. Dose 0.01 mCi in 0.1 ml saline.

t o-IBA = ortho-iodobenzoylacebutolol, m.IBA = meta-iodobenzoylacebutolol, p-IBA para-iodobenzoylacebutolol.

lipophilic than the ortho-iodobenzoyl compound (R1 = This work was presented in part at the I78th National Meeting of 0.46-0.47 against0.60 on KC18reversed-phase,thin the American Chemical Society, Washington, D.C., September, 1979. layer chromatographic plates), and this may be a con tributing factor to the greater uptake and selectivity REFERENCES (T/NT) shown by these two radiolabeled agents corn pared with the ortho isomer. I. LANDS AM, ARNOLD A, MCAULIFF JP, et al: Differen tiation of receptor systems activated by sympathomimetic On the basis of biodistribution data I5 mm after i.v. amines. Nature 214:597-598, 1967 administration to rats, none of the iodobenzoyl acebu 2. CLARKSON R: /3-Adrenoceptor antagonists as antihyper tolol derivatives examined was superior to Tl-20l as a tensive agents. In Antihyperiensive Agents. Engelhardt EL, selective myocardial imaging agent. However, the po ed. ACS Symposium Series 27. Oak Ridge, TN, 1976, pp tential advantages of incorporating iodine-I 23 into these I-26 3. BARRETT AM: Design of/3-blocking drugs. In Drug Design. kinds ofcompounds make this an attractive approach to Ariens EJ, ed. Vol 3. New York, Academic Press, 1972, pp radiopharmaceutical design. In order for these deriva 205-299 tives to be more effective as myocardial imaging agents, 4. CROWTHERAF, HOWE R, SMITH LH: fl-Adrenergic it will be necessary to increase the uptake in the myo blocking agents. 10. (3-Amino-2-hydroxypropoxy) anilides. JMedChem 14:511-513,1971 cardium and decrease the concentrations in the lungs and 5. BASILB,CLARKJR. COFFEEECJ,et al:A newseriesof blood. This study suggests that the meta- and para-io cardioselective adrenergic /3-receptor blocking compounds. dobenzoyl isomers provide better uptake and selectivity I-(2-acyl-4-acylaminophenoxy) -3- isopropylaminopropan than the ortho isomer. In addition, these biodistributional 2-ols. J Med Chem 19:399-402, 1976 parameters may be further improved by adding or 6. AURBACH GD, FEDAK SA, WOODARD Ci, et al: f3-A- modifying functional groups on the molecule. Non drenergic receptor: Stereospecific interaction of iodinated /3-blocking agent with high affinity site. Science 186:1223- chemical techniques, such as exercise or positioning, may 1224, 1974 also increase the tissue uptake and T/NT values. Studies 7. HARDENTK, WOLFEBB, MOLINOFFPB: Binding of io to examine these effects are in progress. dinated beta adrenergic antagonists to proteins derived from rat heart. Mo! Pharmaco! I2: 1- I5, 1976 8. JIANGVW, GIBSONRE, RZESZOTARSKIWJ, Ctal: Ra FOOTNOTES dioiodinated derivatives of /3 adrenoceptor blockers for myocardial imaging. J Nuc! Med 19:918-924, 1978 0 Eastman Kodak Company, Eastman Organic Chemicals, Roch 9. HANSONRN, HOLMANBL, DAVISMA: Synthesisand ester, NY. biologicdistributionofradioiodinatedfl-adrenergicantago t This compound was a generous gift from May and Baker, Ltd. (England). nists.JMedChem 21:830—833,1978 10. SCHNELLE K, GARRETT ER: Pharmacokinetics ofthe 13-a- t Fisher Scientilic Company, Pittsburgh, PA. drenergic blocker sotalol in dogs. J Pharmaco! Sci 62:362- 375, 1973 ACKNOWLEDG M ENTS !I. BORG KO, FELLENIUS E, JOHANSSON R, et aI: Phar macokinetic studies of metoprolol-(3H) in the rat and the dog. The authors thank Alice Carmel and Tanya Wisotsky for their Ada Pharmaco!Toxico!36 (SupplV):104-1I5,1975 technical assistance. This investigation was supported in part by a 12. BODIN N-O, BORG KO, JOHANSSON R, ci al: Tissue dis Grant-in-Aid (78-819) from the American Heart Association and the tribution of metoprolol-(3H) in the mouse and the rat. Ada Massachusetts Heart Association,and by NIH Grant No. l-ILl7739, PharmacolToxicol36(SupplV):II6-124,1975 DOEContract EY-76-S-4l15,and HEW Grant RRO7143. 13. BYLUND DB, CHARNESSME, SNYDER SH: Beta adren

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ergicreceptorlabelingin intactanimalswith ‘25I-hydroxy16. NICHOLLS JT: Adverse effects of practolol. Ann Clin Res benzylpindolol.J Pharmacol Exp Ther 201:644-653, 1977 8:229—231,1976 14. REEVES PR, BARNFIELD DJ, LONGSHAW 5, et al: Dispo 17. TUBISM, ENDOWJS,RAWALAY55: Thepreparationand sition and metabolism of atenolol in animals. Xenobiotica properties of I-i 3i-labeled iodobenzoic acids. ml i App! 8:305—311,i978 Radiatlsot15:397—400,i964 15. STREET JA, HEMSWORTH BA, ROACH AG, et al: Tissue 18. ELIAS H, ARNOLD C, KLOSS G: Preparation of I3 1-I-la levelsof severalradiolabelledf3-adrenoceptorantagonistsafter beledm-iodohippuricacid and its behaviorin kidneyfunction intravenous administration in rats. Arch ml Pharmacodyn studies compared to o-iodohippuric acid. ml J App! Radial 237:180—190,1979 1501 24:463—469, 1973

MISSOURI VALLEYCHAPTER SOCIETY OF NUCLEARMEDICINE

. ANNUAL MEETING PracticalAdvancesin NuclearMedicine October 3-5,1980 Sheraton West Port Inn St. Louis, Missouri TM Missouri Valley Chapter ofthe Society of Nuclear Medicine announces its annual meeting to be held October 3-5, l98oatthe Sheraton West Port Inn, 191 West Port Plaza, St. Louis, Missouri.

The programwill includecontinuingeducationcoursescoveringvariouspracticaladvancesin NuclearMedicinesuch astomographicimaging,hepatobiliaryimaging,plateletandleucocytelabelingandimagingandpediatriccardiovas cular nuclear medicine. AMA category 1creditfor physicians and VOICE creditfortechnologists has been applied for.

TheYoungInvestigatorAwardwillbegiventotheauthorofthebestpaperpresentedbyayounginvestigatororatech nologist.Two additionalawardswill begivento the runners-up.Paperswill bejudged onqualityofpresentation, visual aids, and subject matter. Only MVC members are eligible for the award but anyone is welcome to submit abstracts.

For further information contact

JamesW. Fletcher, M.D. Chief,NuclearMedicineII5JC St. LouisVeteransAdministrationHospital John Cochran Division St. Louis, MO 63125

SIXTH ANNUAL SCIENTIFIC MEETING GREATERNEWYORKCHAPTER SOCIETY OF NUCLEARMEDICINE

Nov.mbr 7-9, 1980 Grand Hyaft Hotl NswYork,Nw York ANNOUNCEMENT AND CALL FOR ABSTRACTS The6thAnnualScientificMeetingoftheGreaterNewYorkChapteroftheSocietyofNuclearMedicinewillbeheldFri daythroughSunday,November7-9, 1980attheGrandHyattHotelinNewYork,NewYork.

In addition to Scientific Papers,Scientific Exhibits,and Commercial Exhibits,the meetingwillfeature SurveyPapers, Teaching Sessions, and Workshops conducted by invited faculty. There will be a Chapter Business Meeting on Satur day,November8that8:00am.

For further information concerning commercial exhibit space and registration please contact:

Mitchell H. Stromer, M.B.A. Greater New York Chapter, SNM 360CedarLane EastMeadow, NY 11554 Tel: (212) 671-0540

This program will be submitted for approvalfor credit in Category lfor the Physicians Recognition Award of the A.MA. andforVOICEcreditfortechnologists.

Voluthe 21, Number 9 851