Synthesis and Renal Excretion of Technetium 99m-Labeled Organic Cations

Kevin M. Herzog, Edward Deutsch, Karen Deutsch, Edward B. Silberstein, Rangaprasad Sarangarajan and William Cacini

CollegeofPharmacyand BiomedicalChemistryResearchCenter,DepartmentofChemistry, Universityof Cincinnati, Cincinnati, Ohio

ERPF determination. The unfavorable radiation proper Organic cations are excreted more efficiently than organic ties of ‘@‘I(fi, 364 keY “@‘)are a distinct disadvantage anions in uremia suggesting superiority as renal imaging clinically, particularly in patients with obstructed agents. In this study, three @TC-1abeIedcationic cydam flow. Although a hippurate labeled with 1231(no beta complexesweresynthesizedandtheirrenalclearancequan emission, 159 keV, gamma emission) offers improved tified in rats. The complexes are deared at a rate of about characteristics, its cost is much higher. An agent labeled 2.5—3times that of and about 60% that of p-aminohip with @Tc(no beta emission, 140 keY, gamma emission) purate. Inhibitionof @“Tc-cydamexcretion by quinine mdi would be more desirable and the anionic @mT@@MAG3 cates transport by the organic cation process. Comparative in vivoimagingexperiments demonstrated that in normal rats agent has been developed to this end (1-3). However, a @Fc-cyciamreached peak renal activity I .8 ±0.6 mm after second problem often little appreciated, is the general injection, a value intermediate between that for [131l]OlH decline in renal secretory efficiency of organic anions as (1.0 ±0) and @“Tc-MAG3(2.8 ±0.6). In rats injected with uremia develops (4,5). This arises from the progressive the acute nephrotoxin cisplatin, the times to peak were length buildup in plasma of organic anions formed as a conse ened with the relative order being @Tc-cydam> @Tc quence ofthe uremic state (6,7). The accumulated anions MAG3 > [131110IH.The results demonstrate that cationic can competitively inhibit renal tubular transport (reducing complexes may be useful for renal imaging diagnostic appli rate) of anionic substrates like the hippurates @ cations. leading to artifactually low estimates of ERPF and tubular J NucI Med 1992; 33:2190-2195 function in uremic patients. Because uremic plasma fac tors do not interfere with tubular excretion of positively charged organic molecules, an attractive alternative is to use efficiently cleared organic cations as ERPF agents (5). ccurate assessment of renal functional status is a The purpose of this study was to determine the feasibility necessary part of the development of an appropriate ther ofestimating renal function through the assessment of the apy for the kidney patient. Among the oldest and most renal clearances of novel @“Tc-labeledorganic cations. widely employed techniques for renal function evaluation Some of these results have been previously presented in are the renal clearance methods, the most fundamental of abstract form (8). which is directed toward determination of glomerular fil tration rate (GFR) as indicated by inulin or MATERIALS AND METhODS clearance. In addition, the clearance of compounds that undergo extensive tubular secretion in addition to filtra Radlolabeling tion allow evaluation of functional tubular mass and esti All organicligandswere purchasedfrom Strem chemicaland mation of effective renal plasma flow (ERPF). The stand used without further purification. @TcO@was obtained from a ard for ERPF determination is p-aminohippurate (PAH) commercial @Mofl@mTcgenerator upon elution with normal which is about 90% extracted from renal arterial plasma saline.Radiolabelingwas carried out as follows: @mTc@l,4,8,ll@ in a single pass through the renal parenchyma. An ‘@‘Itetraazacyclotetradecane(cyclam)and 99mTcl,4,8,ll-tetraazaun labeled structural analog, ortho-iodohippurate ([‘31I]OIH;decane (@“Tc-TAU):0.060 mmol cyclamor 1,4,8,1l-TAU was added to 2.0 ml of [99m]TcO@solution. This solution was then Hippuran), had been the clinical standard for the past 25 degassed with argon for 5 mm, after which 0.150 ml of6 x l0@ yr. Although it is rapidly and efficiently cleared by the M stannoustartratein 0.01M HC1wasadded.The solutionwas kidney, [13s1]OIHis not an ideal radiopharmaceutical for then quickly capped and allowed to stand at room temperature for 45 mm. Technetium-99m-l,4,8,ll-tetramethyl-l,4,8,l 1-te traazacyclotetradecane (@‘Tc-tetramethylcyclam, TMC): TMC ReCeiVedNov. 29, 1991 ; revision accepted Jul. 10, 1992. Forreprintscontact:WilliamCacini,PhD.,CollegeofPharmacy.Lkilversity (0.06 mmol)wasadded to 2.0 ml [@mTcJO;solutionwhichwas of Cincinnati,Ck@clnnati,OH45267-0004. degassed with argon for 5 mm, afterwhich 0.150 mlof6 x l0@

2190 The Journal of Nuclear Medicine •Vol. 33 •No. 12 •December 1992 @ @II@N@H

M stannous tartrate in 0.01 M HC1was added. The solution was versity of Cincinnati Institutional Animal Care and Use Com then cappedas quicklyas possibleand heatedfor 2 hr at 120°C. mittee. Radiochemical purity was routinely assessed by the paper To furthercharacterizethe renal handlingof@mTc@cyclam,its chromatographymethod of Colombettiet al. (9). The accuracy renal handlingwas comparedto that of @“Tc-MAG3and [‘@‘I] ofthis method was confirmed by high pressure liquid chromato OIHin bothnormaland renallyimpairedSprague-Dawleyrats graphicanalysisof samplesas describedby Volkert et al. (10). of 250—400g BW. Renal impairment was induced by a single 5 Technetium-99m-pertechnetatewas the only detectable impurity. mg/kg i.p. injection of the nephrotoxin cisplatin. Normal rats were injected with saline vehicle. Degree of impairment was Electrophoresis indicated by blood urea nitrogen (BUN) level four days after A 15mm X 1.0m strip of Whatman chromatographypaper cisplatin injection (14). BUN was determined colorimetrically wassoakedin a Tris-barbital-sodiumelectrophoresisbuffer(Gel with a commercially available kit (Sigma procedure 640). On the man Sciences,Inc., product No. 51104)composedof 32.1%w/ fourth day after injection of cisplatin or saline, the rats were w Tris [2-amino-2-(hydroxymethyl)-1,3-propanediol, l37% w/w anesthetized with pentobarbital (40 mg/kg i.p.). Technetium barbital,and 54.2%w/w sodiumbarbital.The ends ofthe paper 99m-cyclam(200 @iCi),@mTc@MAG3(200 sCi)or [‘311]OIH(50 werethen connectedto the electrodesof the chamber(Gelman). @zCi)was injectedinto a lateraltail vein and the animal imaged Thecenterofthe stripwasspottedwitha smallamount ofsample for 30—45mm with a 37-photomultipliertube gamma camera solution, current was applied and the strip was allowed to develop with computer interface. Areas of interest were drawn around for 2 hr. The strip was serially cut into eight equal sections, each kidney, liver and heart from a posterior viewand time-activity of whichwas assayedin an LKB Wallac 1282gamma counter. curvesproduced. These procedures have been reviewed and approved by the Uni versityof CincinnatiRadiationSafetyCommittee. Statistics Statistical significance (p < 0.05) was assessed using Student's RenalClearanceExperiments t-test Male Sprague-Dawleyrats (250—400g BW) were used. All animals were housed in temperature and light cycle-controlled RESULTS quarters and were given free access to food and water. Anesthesia was induced with chloral hydrate (350 mg/kg i.p.), and the rat Synthesis and Protein Binding of Radiolabeled then placed on a heating pad. The urinary bladder, ajugular vein Organic Cations (for drug infusions) and a carotid artery (for blood sampling) Radiolabeling of the polyamine ligands in very high were cannulated with polyethylene tubing and a slow (50 @d/min) yields (>98%) without further purification was readily infusion ofchloral hydrate (25 mg/kg BW/min.) in 5% mannitol achieved (15—17). The cyclam and TMC complexation in normal saline was initiated to induce adequate urine flow and reactions were conducted at room temperature while that maintainanesthesia. for TAU required elevated temperature. TLC and HPLC Aftercollectionofblank urine and blood samples,the chloral results consistently indicated the lack of measurable hydrate/mannitol solution was stopped and a priming injection TcO@ and Tc02 impurities in 99mTc4abeled cyclam deriv ofinulin (20 mg in I ml) was administered. A sustaining infusion (50 @il/min)containing the labeled cation (50—100sCi total), atives. Electrophoresis results for these same compounds inulin (20mg/mI),PAH(5 mg/mI),and chioralhydrate(25 mg/ showed a single strong cationic peak and no anionic peaks. kg BW/ml) in 5% mannitol/saline was begun. Preliminarycx The chemical structures of the complexes are assigned on periments showed that 60 mm of such an infusion was adequate the basis of literature characterizations (12—14)and are to allow attainment of steady state plasma concentrations of inulin, PAH and all labeledcations. Three consecutive 12-mm urinecollectionswereobtained;a midpointarterialbloodsample wasdrawnforeachcollection.The volumeofeach bloodsample wasreplacedwithan equalvolumeofsaline.The renalclearances r#— \II/ for inulin, PAH and the labeledcation during each of the three @Tc periods were calculated using the conventional formula U x Nil j v/P whereU = urineconcentration,V = urinevolume(ml/min) H /j,@JN H and P = plasmaconcentration.Plasmaconcentrationswerecor rected for protein binding which was determined by usingthe AmiconCentrifreesystem. +1 Concentrations of inulin (11) and PAH (12) in plasma and H urine samples were determined colorimetrically. Radioactivity in plasmaand urinewasquantifiedwitha LKBWallac1282gamma r@\II@ counter. I Tc Insomeexperiments,theeffectofthe cationtransportinhibitor Toi quinine on renalclearanceof the labeledcyclamderivativeswas H H determined.In these,the otherjugular vein wascannulatedand a loadingdose of quinine sulfate(30 mg/kg BWin 1 ml saline) 2 3 was administered. An infusion of quinine was begun via the secondjugular cannula at a rate of 0.75 mg/kg BW/min (13). FIGURE1. Structureof synthesized @“Tccomplexes.1 = These procedures have been reviewed and approved by the Uni @Tc-cydam,2 = @‘Tc-TAUand 3 = @‘Tc-TMC.

@“Tc-LabeledCation Excretion •Herzog et al 2191 TABLE I fusion rates employed in these experiments. The relative Plasma Protein Binding of Synthesized @‘TcComplexes in clearance values for the cations demonstrate that @“Tc the Rat cyclam, 99mTCTMC and @Tc-TAUare cleared at a rate Labaledcation % Bound 2 to 3 timesfasterthancouldbeaccountedforbyglomer 99mTc-cydam 36.8 ±4.2 ular ifitration as estimated by inulin clearance, indicating @Tc-TMC 38.9 ±2.6 net tubular secretion. The renal clearance rates relative to @Tc-TAU 32.6±3.8 that of simultaneously infused PAH, for @mTc@cyclam, @mTC@TMCand @Tc-TAUare 61% ±18%, 58% ±10% Extent of protein binding was determined by ultrafiftratlon of and 59% ±8%, respectively, values that are not signifi plasmathrougha30,000molwtcutoffmembrane.Eachvalueisthe cantly different from each other. mean ±s.d. of 3-4 indivIdualdeterminations. Effect of Quinine on @‘Tc-CyclamClearance To determine whether the secretory component of the the basis of literature characterizations (12-14) and are clearance of the labeled cations involves the cation trans shown in Figure 1. port system of the proximal renal tubule, the effect of Plasma protein binding data for the three labeled poly quinine on 99mTc@c1am clearance was examined. Qui amine derivatives are shown in Table 1. The extent of nine is considered to be the definitive inhibitor ofthe renal binding was similar for the three complexes, the range organic cation secretory transport process (18). In view of being 33%—39%.The slight differences within the group the virtually identical protein binding and renal clearance cannot be considered physiologically significant. rates ofthe radiolabeled complexes, we used @mTc@cyclam RenalClearanceRates as representative of the group. Results from a representative clearance experiment are In these experiments (n = 4), the renal clearances of presented in Table 2. The renal clearance rates of simul inulin and 99mTc@c1amwere determined before initiation taneously infused @“Tc-cyclam,PAH and inulin are given. ofquinine infusion (control period) and compared to their In these experiments, inulin clearance was used to estimate clearances during quinine infusion. The results are sum GFR while that ofPAH was used to estimate renal plasma marized in Figure 2. The significant inhibitory effect of flow. PAH, as an organic anion, is secreted by a renal quinine on renal excretion of the labeled cation is clear. tubular transport process separate from that by which During the control period, @mTc-cyclamis excreted at organic cations are secreted, so that any decline in PM! about 2.5 times the rate of glomerular ifitration. During clearance relative to that of inulin would indicate altered quinine infusion, inulin clearance is not significantly renal blood flow rather than a competitive inhibition by changed, but that of the labeled complex is markedly co-infusion of a cationic labeled complex. Steady-state reduced to a value that is not significantly different from plasma concentrations of the three co-infused substrates that of inulin. are clearly evident. Table 3 summarizes the mean renal clearances for the three @“Tc-labeledcations synthesized RenalUptakeof ‘@“Tc-Cyclam and the reference compounds inulin and PAH. The mean The results of in vivo imaging experiments designed to absolute clearances for inulin (5.2 ±1.8 mI/mm/kg BW) compare the uptake of @Tc-cyclam, @mTc@MAG3and and for PAH (24.9 ±3. 1 mi/mm/kg BW) as well as the [‘311J01Hare summarized in Table 4. Data from normal clearance ofPAH relative to that ofinulin (i.e., 1/ and renally impaired rats are presented. The overall mean fraction) are values expected for normal rats. BUN concentration calculated from all of the saline-in This is consistently seen during simultaneous cation jected rats is 21.4% ±4.2% mg, a value within the normal infusion and is notable because it indicates that the cations range. Mean BUN values for the cisplatin-injected animals did not appreciably alter renal hemodynamics at the in are 91.8% ±9.6%, 87.7% ±21.5% and 73.0% ±5.7% mg

TABLE2 RenalClearanceof SimultaneouslyInfused @“‘Tc-Cydam,InulinandPAHin Rats

(mi/mm/kg)Inulin concentrationsRenal clearance vol Time@Tc-CycIam(mm)mm)(,@g/mi)PeriodUrine ume(ml/Plasma PAH (cpm/ml)InulinPAH@“Tc-CycIam0—120.568673.9(,@g/mi) 12,7135.2825.7114.0312—240.584595.9 62.2 12,8366.6422.8714.1924—360.554605.3 65.7 13,8076.4522.3513.11Mean 70.8

0.48(Values±s.d.6.12 ±0.6023.64 ±1.48 13.78 ± from indMdual clearanceperiods in one male Sprague-Dawleyrat are presented)

2192 The Journal of Nuclear Medicine •Vol. 33 •No. 12 •December 1992 3Renal TABLE for development as renal imaging/diagnostic agents. The andReferenceClearance Values for @rc-LabaledComplexes use of cationic substrates for renal functional assessment Standards±s.d. in the Rat (Each value is the mean has been little exploited, partly because of the historical from “n―experiments)Renalindividual precedent of diagnostic anions, the fact that the cation ratioSubstrate clearance Clearance process is less well studied than is the anion process, and (substrate/inulin)Inulinn mi/mm/kgBW the demonstrated pharmacologic effects of the most rap —PAH 23 5.2 ±1.8 idly transported cations on renal hemodynamics. 4.8@“Tc-Cyclam23 24.9±3.1 The theoretical advantage of cationic diagnostic agents 3.2@“Tc-TAU10 16.5±4.7 rests upon observations that the renal tubular transport of 2.3@“‘Tc-TMC3 12.0±2.2 4 15.4 ±2.5 3.0 anions is selectively depressed by the presence of compet ing anions which progressively accumulate in uremic plasma. In vitro studies have demonstrated that the addi tion of human uremic serum or serum from nephrecto for rats injected with the labeled cyclam, MAG3 and OIH, mized rats inhibits uptake of PAH by incubated renal respectively, demonstrating significant renal impairment. cortex (4,21). Hook et al. (22), demonstrated that the In the normal rats, the time to peak activity for @Tc inhibitory effect of uremic serum was selective for the cyclam (1.8 ±0.6 mm) was significantly (p < 0.01) shorter anionic transport process by showing that accumulation than that for 99mTcMAG3 (2.8 ±0.6 mm). By compari of PM! by rat renal cortical slices was depressed in the son, [‘311]OIHactivity in the kidney peaked within the first presence of uremic serum but that of the model organic mm after injection. The time required for @mTc@cyclamcation N-methylnicotinamide was unaffected. Subse activity to decline to half-maximum (9.4 ±3.9 mm) was quently, McNay et al. (5) performed clearance experi significantly shorter than that for @mTc@MAG3(13.9 ± ments in uremic dogs with intact kidneys and observed an 2.8 mm) but longerthan that for [‘311]OIH(5.4 ±1.6 inverse relationship between PAH clearance and blood mm). As expected, both time to peak activity and time to urea nitrogen levels while no such relationship was seen half-maximum activity were lengthened for all three agents for tetraethylammomum. Taken together, these results in the renally impaired rats. The labeled cyclam complex indicate that anionic renal diagnostic and imaging drugs exhibited the longest time to peak activity with [‘311]OIH are cleared with less efficiency and accumulate to a lesser the shortest and 99mTcMAG3 intermediate. As indicated extent in the kidney as uremia progresses than are cationic in Table 4, neither 99mTclabeled agent exhibited a decline agents. Thus, clearance of efficiently secreted organic cat to half-maximum renal activity within the time frame of ions can be expected to provide a more accurate assess the experiment. In the renally impaired rats, the liver was ment of renal blood flow and function in uremic patients. visualized longer after injection of@mTc@cyclamthan after We have synthesized three @mTc@labeledcyclam deriv injection of 99mTcMAG3 atives and evaluated their potential for use as renal diag nostic agents (Fig. 1).The choice ofligand was based upon DISCUSSION the observations ofTroutner et al. (15), which documented Optimal application of radionucides to evaluation of rapid appearance of 99mTc..@yclamin the urine following renal function requires careful consideration ofthe clinical condition itself, and the effect of the condition on the mechanisms by which the drug is handled by the kidney. In some cases, GFR estimates may be adequate while in others, supplementation with ERPF data is clearly advan tageous, allowing, for example, determination of ifitration C fraction. Additionally, ERPF measurements are invaluable E for monitoring kidney transplant status and determination E a of residual function after unilateral nephrectomy (19). U C In order to be useful for measurement of ERPF and a a tubular functional capacity, a radiopharmaceutical must U undergo extensive renal tubular secretion in addition to a C ifitration. All currently available diagnostic agents includ a ing PAH, [‘3111O1Hand 99mTc@G3 are negatively Before Quinine During Quinine charged and as a consequence are secreted by the organic anion transport process of the proximal renal tubule. However, a wide variety of endogenous and exogenous FIGURE 2. Effectof quinineon renalclearanceof simultane ously infused @“Tc-cydamand inulin.Eachvalueis the mean± positively charged substrates are efficiently secreted by the s.d. of threeclearanceperiodsfrom eachof four rats. An asterisk analogous, but distinct, organic cation transport process represents a value statisticallysignificantfromthe value before (18,20);thismakesavailableanotherclassof compounds quinineinfusion.Clearbar= @“Tc-cydam;shadedbar= inulin.

@Tc-LabeIedCation Excretion •Herzog et al 2193 TABLE 4 Comparative Renal Uptake of @‘Tc-Cyclam,@“‘Tc-MAG3and [‘311]OlHin Normaland RenallyImpairedRats Normalrats ratsn impaired

Radiopharmaceuticai n BUN t@ t@—*t@Aerially BUN L, 9am@[email protected]>30@“Tc-MAG3825.6±3.51.8 ±0.69.4 ±3.9891.8 ±9.630.6 ± 23.1>30[131l]OlH420.9 ±2.82.8 ±0.613.9 ±2.8687.7 ±21.511.7 ± ±2.91.0 ±05.4 ±1.6473.0 ±5.72.5 ±0.729.8 ±2.31

Each value is the mean ±s.d. from n kidneys. The t@ and t,@values are time (mm) after radiopharmaceutical injection to maximal accumulationinthe kidneyandto declineto one-halfmaximum,respectively.BUNconcentrations(mean±s.d. mg%)weredeterminedfour daysafteri.p.injectionofsaline(normal)or 5 mg/kgb.w.cisplatin(impaired).

its intravenous injection into unanesthetized mice. Zuck infusion of the labeled complexes. This is important in erman et al. (1 7) confirmed that the technetium cation view of the fact that many secreted organic cations (e.g., consists ofthe trans[TcO2]@core complexed by the neutral acetylcholine, catecholamines, histamine, cocaine) can cyclam ligand. This determination, combined with electro themselves alter hemodynamics even at low infusion rates phoresis studies of Simon et al. (16), establishes that the making them unsuitable for ERPF determinations. overall + 1 charge on Tc-cyclam complex is centered on The renal uptake/excretion pattern for one of the cati the Tc(V) core. In addition to the cyclam complex, we onic complexes, 99mTcyclam, was examined by gamma synthesized and evaluated two structural analogs. 1,4,8,11- camera imaging in anesthetized rats, and compared to Tetraazaundecane (TAU) is a linear analog of cyclam, those obtained from two anionic imaging drugs. In addi which permits more flexibility in the final [@mTcO2@TAU] tion to using normal rats, the results also included data

+ cation. Tetramethylcyclam (TMC) contains only tertiary obtained from rats injected with the acutely nephrotoxic nitrogen atoms and thus the final [@mTcO2@TMC]+ cation antineoplastic drug cisplatin. While clearly not a model is more restricted and lipophilic than the parental @TcO2@for chronic human uremia, during which organic anions cyclam cation. accumulate in plasma, the data from the cisplatin-injected No meaningful differences were noted in the extent of animals do allow an initial comparison of renal handling plasma protein binding or the renal handling of the three in an acute model of renal impairment (Table 4). In 99mTclabeled cyclam derivatives. All are 33% to 39% normal rats, the renal uptake/excretion pattern for @mTc@ protein bound in plasma, a value very close to the 33% cyclam compared favorably with [1311]OIHand, in fact, its for [‘311JO1Hand about half of the 77% binding reported excretion was more rapid than that of @mTc-MAG3.In for 99mTcMAG3 (1). Because plasma protein binding does the renally impaired rats, however, 99mTc@cyclamdid not not necessarily relate directly to the extent ofrenal tubular perform as well as either ofthe other two agents at least as uptake/secretion, these differences are probably of no par indicated by its significantly prolonged peak activity time. ticular clinical relevance other than for correcting renal The reasons for this are unclear as yet as is the influence clearance values. Rather, the degree of secretion is of of this particular model of acute nephrotoxin-induced central importance. All three radiolabeled derivatives are renal damage on the renal handling of the radiopharma extensively secreted (Table 3). There are no significant ceuticals. Imaging experiments using a chronic rat uremia differences among the efficiencies of renal clearance of the model may prove more informative and relevant to poten three 99mTccations, all being cleared at a rate of about tial clinical application. 60% ofthat ofsimultaneously infused PAH. Since labeled In summary, we have synthesized three related @mTc@ OIHis clearedata rateof 85%ofthat of PM! (23), it can labeled complexes which exhibit high and essentially com be estimated that the labeled cations would be cleared at parable rates of renal clearance. Because the secretory a rate of approximately 70% that of OIH. This compares component of their renal clearance occurs by the cationic favorably with the 71% clearance ratio for anionic @mTc@tubular transport process which is largely unaffected by MAG3 under constant infusion conditions in Sprague uremic serum, such agents represent a new class of renal Dawley rats reported by Müller-Suurand Müller-Suur imaging drugs that may provide a more accurate assess (24), but it is less than the 90%—l10% value found by ment of renal status in chronically uremic patients. After Fritzberg et al. (1) under similar experimental conditions. completion of this work, two abstracts appeared (25,26) The observation that quinine reduces the clearance of which described the initial evaluation of cationic 99mTc 99mTcyclam relative to that of simultaneously infused polyamine complexes for renal imaging. It thus appears inulin strongly suggests that the secretory component of likely that the data we have obtained in rats will be relevant the labeled complex is via the organic cation transport to clinical observations in humans. The present investiga process. Also of note is the fact that PAH clearance, an tion demonstrates the feasibility of estimating ERPF with estimate ofthe ERPF, remains within normal limits during cationic 99mTccomplexes. Efforts are underway to further

2194 The Journal of Nuclear Medicine•Vol.33 •No. 12 •December 1992 characterize the renal handling of labeled cyclam com 33:891—896. 11. HeyrovskyA. A new method for the determination of inulin in plasma plexes and to develop more efficiently excreted cationic and urine. C!in Chim Ada 1956;1:470-474. analogues. 12. SmithHW, FmnkeisteinN, AliminosaL,CrawfordB,Graber M. The renal clearancesofsubstitutedhippuricacidderivativesand other aromaticacids in dog and man. J C!in Invest 194524:388—404. ACKNOWLEDGMENTS 13. TOTCttiJ,WerneriM, MudgeGH. Renaltubularsecretion and reabsorption Supported by a grant from the Kidney Foundation of Greater oforganic bases in the dog. I C/in Invest 1962;41:793—804. Cincinnati and a gift from Mallinkrodt Medical Inc. The authors 14. CaciniW, SinghY. Renal metallothioneinand platinum levelsin diabetic and non-diabetic rats injected with cisplatin. Proc Soc Exp BiolMed 1991; thank Dr. Francesco Tisato for assistance with the 99mTclabeling 197:285—289. reactions. 15. Troutner DE, Simon J, Ketring AR, Volkert W, Holmes RA. Complexing of Tc-99m with cyclam: concise communication. I Nud Med 1980;2l: REFERENCES 443—448. 16. Simon J, Troutner DE, Volkert WA, Holmes RA. Radiochemical charac 1. FrItZbCTgAR, Kasina 5, Eshima D, Johnson DL Synthesis and biological terization of technetium-cyclam. Radiochem Radioanal Let: 1981;47: evaluation of tcchnetium-99m-MAG3 as a hippuran replacement J Nuci 111—123. Med 18627:111—116. 17. Zuckerman SA. Freeman GM, Troutner DE, et al. Preparation and x-ray 2. Taylor A, Eshima D, christian PE, Milton, W. Evaluation of @Tc structure of trans-dioxo(l,4,8,11-tetraazacyclatetradecane) technetium mercaptoacetyltiiglycine in patients with impaired renal function. Radio! (V)perchlorate hydrate. Jnorg Chem 198120:2386—2389. ogy 1987;162:365—370. 18. Rennick BR. Renal tubule transport oforganic cation. Am JPhysio! 1981; 3. TaylorA, ZifferJA,StevesA, Eshima,D, DelaneyVB,WelchelJD. 240:F83—F89. ainical comparison of 1-131 orthoiodohippuratc and the kit formulation 19. Tauxe WN. Prediction ofresidual renal function after unilateral nephrec oP'°Tc-mercaptoacetylglycine. Radiology l989;170:721—725. tomy. In: Tauxe WN and DUbrOVSICYEV, eds. Nuclearmedicine in dinical 4. Pieu&@HG, Massry SO, Maher if, Gilliece M, Schreiner GS. Effects of urologyand nephrology.Norwalk, Cr: Appleton-Century-Crofts;1985: ureinic mi@on renal tubular p-aminohippurate transport. 1966; 279—286. 3:265—273. 20. PetersL Renal tubular excretionof organicbases.Pharmaco!Rev 1960; 5. McNayJL, RoselloS, DaytonPG. Effectsofazotemia on renalextraction 12:1—35. and clearance ofPAH and TEA. Am JPhysiol 1976230:901-906. 21. White AG. Uremic serum inhibition of renal paraaminohippurate trans 6. Boumendil-PodevinEF, Podevin PA, Richet 0. Uricosuiic agents in port. ProcSocExpBio!Med l966;l23:309-3l0. uremic sera. Identification of indoxyl sulfate and hippuric acid. J Clin 22. Hook JB, Munro JR. Specificity ofthe inhibitory effect of―uremic―serum Invest1975;55:l142—1152. on p.aminohippuratetransport.Proc Soc Exp Bio! Med 1968;127: 7. Monti J-P, Gallice P, Braguer D, Durand C, MurisascoA, Crevat A. 289—292. Identification of two uremic toxins by nuclear magnetic resonance and 23. Chervu LR, Freeman LM, Blaufox MD. Radiopharmaceuticals for renal spectrometry. In: Ringoir S. Vanholder R, Massry 0, eds@Uremk toxins. studies. Semin NuciMed 1974;4:3—22. New Yo& Plenum Press l986223-226. 24. Muller-SuurR, MOller-SuurC. Renal and extrarenal handling of a new 8. HerzogKA,CaciniW, DeutschE, LibsonK. Renalclearancestudieswith imagingcompound (‘@“Tc-MAG-3)in the rat. Eur J Nud Med 1986:12: w@Tc@1abelledorganic cations. Pharmacologist 1989;31:133. 438-442. 9. ColombettiLO,[email protected] 25. Solanki KK, Theobald AE, Britton KE. Potential new renal imaging agents state of unbound @Tcand labeling yield in @Tc-labdedradiopharma using the active tubular cationic mechanism. J Nuc!Med 199l;32:1102. ceuticals. JNucIMed 1976;17:805-809. 26. Solanki K.K,Bomanji J, Nimmon CC, Carroll M, Theobald AE. Tc-99m- 10. VolkertWA, Troutner DE, Holmes PA. Labelingof amine ligandswith labeled cationic compkxes—a new class of renal imaging agents—results @Tcin aqueoussolutionsbyligandexchange.IntJApp!Radiatlsot 1982; ofpreliminary human studies.JNucIMed 199132:1105.

@Tc-LabeledCation Excretion •Herzog et al 2195