rational design of peptide radiopharmaceuticals : in vitro studies demonstrate a synergistic effect of carbohydration and c - terminal oxidation of octreotide on ligand induced sst - 2 internalization besides by its pharmacokinetics , the suitability of a receptor based tracer for imaging and therapeutic purposes is mainly determined by its pharmacodynamic profile . aim of this study was to investigate the effect of carbohydration of octreotide and octreotate on sstr endo - and exocytosis ( internalization and externalization ) and reendocytosis ( recirculation ). internalization , externalization and recycling of [ 125 i ] tyr 3 - octreotide ( toc ), [ 125 i ] tyr 3 - octreotate ( toca ) and their glucose ( gluc ) and maltotriose ( mtr ) derivatives were studied using confluent monolayers of ar42j - cells ( sstr 2 ). the cells were incubated with the radioligand for up to 120 min ( n = 3 ). at each time point the activity in the supernatant , the surface - bound and the internalized activity were determined and normalized to the values of toc . externalization and recycling was studied after an incubation time of 120 min over 2 h . specificity of ligand binding was studied in a competition experiment with 10 m sandostatin . after 2 h of incubation the amount of internalized ligand [% internalized toc ] was as follows : mtr - toc ( 35 ± 4 %)& lt ; gluc - toc ( 121 %)& lt ; toca ( 154 %)& lt ; mtr - toca ( 549 %)& lt ; gluc - toca ( 637 %). in the competition experiment internalization of all compounds dropped to & lt ; 0 . 1 ± 0 . 02 % ( 30 min ) of the applied radioactivity . in the externalization experiment that allowed recycling of the ligands , toca and glycated toca &# 39 ; s showed about ⅔ of extracellularly located radioactivity compared to the experiment without recycling , while about 80 % were found for toc , gluc - toc and mtr - toc . carbohydration of toc had no significant effect on the availability of the ligands on the cell surface , whereas surface concentration of toca and mtr - toca is increased by a factor of 2 . 1 and 2 . 3 respectively compared to toc . gluc - toca shows a fivefold increase of the availability of the tracer on the cell surface compared to toc . the internalization rate ( internalized / surface bound act .) of toc is not significantly affected by glycosylation , whereas toca shows a 1 . 4 fold increase . for gluc - toca and mtr - toca we observed internalization rates of 186 and 171 % compared to toc . using ar42j - cells , carbohydration of toca led to a significant increase in cell surface concentration and internalization rate of the radioligands . carbohydrated tc - 99m - octreotide derivatives for spect synthesis , radiolabelling and in vivo data over the past decade different approaches to 99m tc - and 18 f - labelled octreotide derivatives for sstr - scintigraphy using spect and pet have been investigated . decristoforo et al . showed that 99m tc - labelled hynic - tyr 3 - octreotide with edda as a coligand has favourable biokinetics and high tumor uptake in mice . 2 -[ 18 f ] fluoropropionyl - d - phe 1 - octreotide , the only 18 f - labelled octreotide analog known so far , shows predominant hepatobiliary excretion , which is one drawback with respect to its application for in vivo sstr - imaging . the inventors found that n - terminal glycosylation of radioiodinated tyr 3 - octreotide ( toc ) and its thr 8 - derivative tyr 3 - octreotate ( toca ) leads to a significant improvement of the biodistribution , i . e . to an increased tumor accumulation . to investigate the general applicability of this principle , we synthesized and evaluated glycosylated octreotide - and octreotate - derivatives for 99m tc - labelling , n α - glycosylated derivatives of lys 0 ( n ε - his )- toc ( k 0 ( h ) toc ) were used as precursors for 99m tc - labelling using the organometallic aquaion [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + - approach ( egli a . et al . j . nucl . med . 40 : 1913 - 1917 ( 1999 )). the peptide was synthesized according to a standard fmoc - spps protocol . conjugation with glucose ( gluc ) and maltotriose ( mtr ) was performed via amadori reaction . 99m tc - labelling of the lys 5 - deprotected peptides yielded [ 99m tc ] gluc - k 0 ( h ) toc and [ 99m tc ] mtr - k 0 ( h ) toc with radiochemical yields & gt ; 97 % based on the aquaion . biodistribution studies of the 99m tc - labelled derivatives ( 30 and 120 min p . i .) were performed in ar42j - tumor bearing nude mice ( n = 3 - 4 ). internalisation and externalisation experiments were carried out using the same cell line . an increase of internalisation was found for [ 99m tc ] gluc - k 0 ( h ) toc by a factor of 2 . 3 ± 0 . 8 and for [ 99m tc ] mtr - k 0 ( h ) toc by a factor of 3 . 6 ± 0 . 4 compared to the reference [ 125 i ] toc . while [ 125 i ] toc is rapidly externalised from the cell upon incubation , [ 99m tc ] gluc - k 0 ( h ) toc remains trapped within the cell up to 120 min . the biodistribution of [ 99m tc ] gluc - k 0 ( h ) toc and [ 99m tc ] mtr - k 0 ( h ) toc 2 h p . i . are shown in table 1 . both glycosylated compounds show high accumulation in sst 2 positive tissue 120 min p . i . we suppose that the comparatively high non - specific uptake in excretion organs as well as a delayed blood clearance are due to the insufficient complexation of the 99m tc - core by the bidentate histidine ligand . the remaining metal coordination site may be saturated by thiol - containing native proteins in vivo , which can result in rapid trapping of these complexes in the blood , the liver and other excretion organs . the formation of saturated complexes of the [ 99m tc ( h 2 o )) 3 ( co ) 3 ] + - aquaion with tridentate ligands such as n — ac - his result in a significant decrease of activity accumulation in non - tumor tissue . it can be concluded that the introduced tracer design based on the combination of carbohydrate conjugation of octreotide (- tate ) and of tridentate complexation of the [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + - aquaion is the basis of a new series of very promising sstr - tracers . carbohydration is now found to be a powerful tool to improve the pharmacokinetics of radiolabelled octreotide and tyr 3 analogs . glycation of octreotide and octreotate significantly reduces hepatobiliary excretion and kidney uptake and enhances tumor uptake and tumor / tissue ratios . tumor accumulation of a radiolabelled sst 2 - agonist relies upon the dynamic processes of receptor mediated internalisation , degradation and subsequent intracellular accumulation or recycling of both ligand and / or metabolite . quantitative analysis of each step is of critical importance to understand how to control tracer accumulation in sst 2 expressing tumor cells . thus , the objective of this study was to examine the effect of glycation on the internalization and recycling kinetics of radiolabelled octreotide and octreotate analogues . tyr 3 - octreotide ( toc ), tyr 3 - octreotate ( toca ) and their respective glucose ( gluc ), maltose ( malt ) and maltotriose ( mtr ) derivatives were synthesized via fmoc - spps and subsequent carbohydrate conjugation . radioiodination was performed using the iodogen method . radiochemical yields ranged from 50 to 84 % after rp - hplc - purification . precursors for 99m tc - labelling ( gluc - lys 0 ( n ε - his ) toc ( gluc - k ( h )- toc ) and mtr - lys 0 ( n ε - his ) toc ( mtr - k ( h )- toc )) were prepared analogously to the peptides mentioned above . labelling with 99m tc was carried out according to the [[ 99m tc ] ( co ) 3 ( h 2 o ) 3 ] + aquaion protocol previously described ( egli a . et al . j . nucl . med . 40 : 1913 - 1917 ( 1999 )). for comparison , we also included [ 111 in ] octreoscan and [ 111 in ] dotatoc into our study . internalisation and externalisation experiments were performed using the sst 2 expressing rat pancreatic tumor cell line ar42j . free , surface bound and internalised radioactivity were determined after 10 , 30 , 60 , 90 and 120 min . of incubation with the radioligands at 37 ° c . in the externalisation experiments allowing ligand recycling , the fraction of radioactivity released into the supernatant during 10 , 30 , 60 , 90 and 120 min as well as the radioactivity remaining in the cells were determined . we also measured the activity released during 5 subsequent incubations ( 10 , 20 and 3 × 30 min ) with intermediate changes of the medium ( limited recycling ). the influence of carbohydration of toc on the internalization parallels the size of the sugar used . compared to [ 125 i ] toc only the glucose conjugate showed enhanced uptake in the cells . in contrast , intracellular accumulation of both [ 125 i ] gluc - toca and [ 125 i ] mtr - toca ( table 2 ) was significantly increased ( 7 . 36 ± 0 . 50 and 5 . 68 ± 0 . 38 fold compared to [ 125 i ] toc ). comparing the internalisation characteristics of toc and toca and of the respective glucosylated derivatives , we observed a synergistic effect of both structural modifications ( substitution of thr ( ol ) 8 by thr 8 and carbohydration ) on surface availability and on internalisation rate . compared to [ 111 in ] octreoscan and [ 111 in ] dotatoc , the internalization of both 99m tc - labelled carbohydrated derivatives was unexpectedly high . pretreatment experiments with 10 μm sandostatin reduced the ligand uptake to a max . of 5 % of control , indicating i ) sst 2 specific uptake and ii ) that no carbohydrate related uptake mechanism is involved ( table 2 ). for all tracers investigated , the internalized activity strongly correlates with the surface availability of the ligands . with respect to externalisation glycosylation seems to have no influence . the degree of externalisation of radioligand from the cells is primarily determined by the nature of the peptide ( toc or toca ) and also by the intracellular fate of the label . in the externalisation experiment that allowed ligand recycling , toca and its glycated derivatives showed about of extracellularly located radioactivity compared to the experiment without recycling , while about 80 % were found for toc , gluc - toc and mtr - toc . [ 99m tc ] gluc - k 0 ( h )- toc as well as both 111 in - labelled compounds showed nearly quantitative retention in the cell within 120 min under recycling conditions . in contrast , intracellular activity of [ 111 in ] octreoscan and [ 111 in ] dotatoc was depleted by 33 % and 49 % during 120 min , when recycling was limited . [ tc - 99 m ]( co ) 3 - labeled carbohydrated sstr - ligands : synthesis , internalization kinetics and biodistribution on a rat pancreatic tumor model this study is to demonstrate the design of tracers for specific and high - level targeting of sstr expressing tumors . for this purpose we introduced carbohydrated octreotide derivatives to optimize pharmacokinetics and to improve sstr specific internalization and tumor retention . here we describe compounds of a series of new carbohydrated 99m tc - sstr ligands . coupling of glucose ( gluc ) and maltotriose ( mtr ) to n α - lys of n ε -( boc - his ( boc )) lys 0 - tyr 3 - lys 5 ( dde )- octreotide ( protected k ( h ) toc ) and final deprotection yielded gluc - and mtr - k ( h ) toc . 99m tc - labeling was carried out using [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + . internalization and externalization studies (& lt ; 2 h ) were performed using the sstr 2 expressing rat pancreatic cell line ar42j and [ 125 ] tyr 3 - octreotide ([ 125 i ] toc ) as a reference . biodistribution was evaluated in nude mice bearing ar42j tumors at 0 . 5 and 2 h p . i ( n = 4 ). radiolabeling produced efficiently ( 0 . 5 h , rcy & gt ; 97 %) uniform products . compared to [ 125 i ] toc , both carbohydrated peptides showed significantly higher intercellular activity levels ; e . g . at 2 h 2 . 3 ± 0 . 2 times higher levels for [ 99m tc ] gluc - k ( h ) toc and 3 . 6 ± 0 . 4 times higher levels for [ 99m tc ] mtr - k ( h ) toc . externalization studies revealed a decrease of about 50 % of intracellular activity for [ 125 i ] toc within 2 h , while the intercellular level of [ 99m tc ] gluc - k ( h ) toc was almost stable up to 2 h , demonstrating retention of this tracer . in vivo , tumor accumulation reached 12 . 2 ± 1 . 0 and 14 . 0 ± 6 . 3 % id / g at 2 h p . i . with blood levels of 1 . 5 ± 0 . 2 % id / g and 4 . 4 ± 1 . 0 % id / g for [ 99m tc ] gluc - k ( h ) toc ( t / liver 0 . 77 , t / kidney 0 . 63 ) and [ 99m tc ] mtr - k ( h ) toc ( t / liver 0 . 97 , t / kidney 0 . 84 ), respectively . these results demonstrate the usefulness of carbohydration as a tool to improve sstr targeting . [ tc - 99 m ]( co ) 3 - labeled carbohydrated sstr - ligands : synthesis , internalization kinetics and biodistribution on a rat pancreatic tumor model this study is part of our endeavor to design tracers for specific and high - level targeting of sstr expressing tumors . for this purpose we use suitable carbohydrate moieties to optimize the pharmacokinetics and to improve sstr specific internalization and tumor retention . here we describe for the first time carbohydrated sstr binding peptides labeled via the [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + aquaion approach . n ε ( boc - his ( boc )) lys 0 - tyr 3 - lys 5 ( dde )- octreotide ( protected k ( h ) toc ) was synthesized using standard fmoc - chemistry . coupling of glucose ( gluc ) and maltotriose ( mtr ) to n α - lys 0 and final deprotection yielded the gluc - and mtr - derivatives of k ( h ) toc . tc - 99m - labeling was carried out using the organometallic aquaion [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + ( 1 ). internalization and externalization studies (& lt ; 120 min ) were performed for both compounds using the sstr 2 expressing cell line ar42j . for the in vitro studies [ 125 i ] tyr 3 - octreotide ([ 125 i ] toc ) was used as a reference . biodistribution of intravenously administered [ 99m tc ] gluc - k ( h ) toc and [ 99m tc ] mtr - k ( h ) toc was evaluated in nude mice bearing ar42j rat pancreatic tumors at 30 and 120 min p . i ( n = 4 ). the labeling procedure produced efficiently ( 30 min , rcy & gt ; 97 %) uniform products ( lhplc ). compared to the reference [ 125 i ] toc , both carbohydrated peptides were significantly higher internalized at all time points investigated ; e . g . at 120 min 2 . 3 ± 0 . 2 times higher levels for [ 99m tc ] gluc - k ( h ) toc and 3 . 6 ± 0 . 4 times higher levels for [ 99m tc ] gluc - k ( h ) toc and 3 . 6 ± 0 . 4 times higher levels for [ 99m tc ] mtr - k ( h ) toc . furthermore , externalization studies revealed a decrease of about 50 % of intracellular activity for the reference compound within 120 min , while the high level of intracellular [ 99m tc ] gluc - k ( h ) toc was almost stable up to 2h , demonstrating retention of this tracer in the cell line investigated . in vivo , tumor accumulation reached 12 . 2 ± 1 . 0 and 14 . 0 ± 6 . 3 % id / g at 120 min p . i . with corresponding blood activity levels of 1 . 5 ± 0 . 2 % id / g and 4 . 4 ± 11 . 0 % id / g for [ 99m tc ] gluc - k ( h ) toc ( t / liver 0 . 77 , t / kidney 0 . 63 ) and [ 99m tc ] mtr - k ( h ) toc ( t / liver 0 . 97 , t / kidney 0 . 84 ), respectively . these results demonstrate the usefulness of carbohydration as a tool to improve sstr targeting . 1 . fmoc - lys 0 - tyr 3 - lys ( dde ) 5 - octreotide ( fmoc - lys 0 - toc ( dde )) fmoc - thr ( tbu )- ol a solution of fmoc - thr ( tbu )- oh ( 1 . 391 g , 3 . 5 mmol ) in 30 ml of tetrahydrofurane ( thf ) was cooled to − 10 ° c . n - methylmorpholine ( 386 ul , 3 . 5 mmol ) and ethylchloroformate ( 333 ul , 3 . 5 mmol ) were added successively . the reaction mixture was stirred at − 10 ° c . for 30 min . then sodium borohydride ( 396 mg , 10 . 5 mmol ) was added . over a period of 30 min 60 ml of methanol were slowly added to the reaction mixture , which was then stirred at 0 ° c . for 3 hours . after the addition of 50 - 70 ml of 1 n hcl ( the cloudy reaction mixture has to become transparent ) the organic solvents were evaporated and the remaining aqueous phase was extracted twice with dichloromethane ( dcm ). extraction efficiency was monitored by thin layer chromatography ( product r f = 0 . 83 in ethyl acetate ( acoet )) of both phases . the combined organic layers were dried over magnesium sulfate , filtered and concentrated in vacuo to yield a yellowish oil . the crude product was purified by flash chromatography using acoet . the product was obtained as an oil ( 1 . 19 g , 89 %). calculated monoisotopic mass for c 23 h 29 no 4 = 383 . 21 ; found : m / z = 406 . 1 [ m = na ] + . spps of fmoc - lys 0 - dphe 1 - cys 2 - tyr 3 - dtrp 4 - lys ( dde ) 5 - thr 6 - cys 7 - thr - ol 8 dhp - hm ( 3 , 4 - dihydro - 2h - pyran - 2 - ylmethoxymethylpolystyrol )- resin ( 1 . 000 g , 0 . 94 mmol / g ) was allowed to preswell in 10 ml of dry dce ( 1 , 2 - dichloroethane ) for 1 hour . then a solution of fmoc - thr ( tbu )- ol ( 1 . 266 g , 3 . 3 mmol ) and of pyridinium - p - toluenesulfonate ( 414 mg , 1 . 75 mmol ) in 7 ml of dry dce was added and the reaction mixture was stirred overnight at 80 ° c . under argon . to cap free functional groups on the resin 5 ml of pyridine were added and the suspension was stirred for another 15 min at room temperature . the loaded resin was then filtered off , washed twice with dmf ( n , n - dimethylformamide ) and with dcm and dried in an exsiccator . final load of the resin was 0 . 834 mmol / g . the peptide sequence was assembled on the resin bound amino alcohol using standard fmoc - protocol . briefly , the n - terminal fmoc was removed with 20 % piperidine in dmf , and the resin of resin - supported peptide was washed with nmp ( n - methylpyrrolidone ). coupling was carried out in nmp by reacting 1 . 5 eq of amino acid derivative with 1 . 5 eq of hobt ( 1 - hydroxybenzotriazol ), 1 . 5 eq of tbtu ( o -( 1h - benzoltriazol - 1 - yl )- n , n , n ′, n ′- tetramethyluronium - tetrafluoroborate ) and 3 . 5 eq of dipea ( n - ethyl - diisopropylamine ). after adding the activated amino acid to the reaction vessel , the resin was agitated for an appropriate amount of time ( usually 40 - 60 min ). the resin was then washed with additional nmp . the sequence of addition for the synthesis of toc was fmoc - cys ( trt ), fmoc - thr ( tbu ), fmoc - lys ( dde ), fmoc - dtrp , fmoc - tyr , fmoc - cys ( trt ), fmoc - dphe and fmoc - lys ( boc ). after the coupling of the last amino acid to the sequence , the resin was washed several times with nmp and dcm . cleavage from the resin and deprotection of the thr -, cys - and lys 0 - sidechains was performed using a mixture of tfa ( trifluoroacetic acid )/ tibs ( triisobutylsilane )/ water ( 95 : 2 . 5 : 2 . 5 ) and dcm ( 1 : 1 ). after 90 min the resin was filtered and washed twice with dcm . the combined filtrates were concentrated using a rotary evaporator and the crude product was precipitated with ether . we obtained 828 mg of crude produce . yield : 83 % the crude peptide was resuspended in 50 ml of thf ( per 300 mg of peptide ), and 5 mm ammonium acetate was added , until a clear solution was obtained . the ph was adjusted to 7 by dropwise addition of a saturated solution of nahco 3 . then 100 ul ( per 300 mg of peptide ) of hydrogen peroxide ( 30 %) were added . after 30 min of stirring at room temperature cyclisation was complete ( gradient hplc - control : 30 - 80 % b in 15 min ). the solvents were evaporated , and the cyclised product was lyophilized . yields were quantitative . calculated monoisotopic mass for c 80 h 100 n 12 o 16 s 2 = 1548 . 68 ; found : m / z = 1549 . 5 [ m + h ] + , m / z = 1571 . 5 [ m + na ] + . 2 . fmoc - lys 0 - tyr 3 - lys ( dde ) 5 - octreotide ( fmoc - lys 0 - tate ( dde )) fmoc - lys 0 - dphe 1 - cys 2 - tyr 3 - dtrp 4 - lys ( dde ) 5 - thr 6 - cys 7 - thr 8 to 1 . 502 g of dry tcp - resin a solution of 894 mg ( 2 . 25 mmol ) of fmoc - thr ( tbu ) and 321 ul ( 1 . 87 mmol ) of dipea in 15 ml of dry dcm was added . after stirring for 5 min , another 642 up ( 3 . 76 mmol ) of dipea were added . after vigorous stirring for 90 min at room temperature , 1 . 5 ml of methanol were added to cap unreacted tritylchloride groups . after 15 min the resin was filtered , washed twice with dcm , dmf and methanol respectively and dried in vacuo . final load of the resin was 0 . 77 mmol / g . synthesis of the peptide sequence cys ( trt )- thr ( tbu )- lys ( dde )- dtrp - tyr - cys ( trt )- dphe - lys ( boc )- fmoc on the resin - bound amino acid , deprotection and cleavage from the resin as well as cyclisation were performed as described for fmoc - lys 0 - toc ( dde ). calculated monoisotopic mass for c 80 h 98 n 12 o 17 s 2 = 1562 . 66 ; found : m / z =([ m + h ] + ) a solution of 500 mg ( 0 . 32 mmol ) of fmoc - lys 0 - toc ( dde ), 170 mg ( 0 . 48 mmol ) of boc - his ( boc ), 65 mg ( 0 . 048 mmol ) of hobt , 154 mg ( 0 . 48 mmol ) of tbtu and 300 ul ( 1 . 75 mmol ) of dipea in 3 ml of dmf was stirred at room temperature . rp - hplc analysis ( gradient : 30 - 80 % b in 15 main ) revealed that the reaction was complete within 30 min . the product was precipitated using water and dried in vacuo . to remove the n - terminal fmoc - protecting group , the peptide was dissolved in 1 ml piperidine / dmf ( 1 : 4 ) and stirred for 15 min . precipitation with ether afforded the deprotected product with a yield of 86 %. calculated monoisotopic mass for c 81 h 113 n 15 o 19 s 2 = 1663 . 78 ; found : m / z = 1873 . 6 [ m + h ] + , m / z = 1895 . 7 [ m + na ] + . based on a method reported previously 1 , 1 equiv . of lys 0 -( boc - his ( boc ))- toc ( dde ) and 10 equiv . of the respective aldose ( glucose = s1 , maltose = s2 , maltotriose = s3 ) were dissolved in methanol / acetic acid ( 95 : 5 ), and the reaction mixture was stirred at 60 ° c . for 24 - 48 h . the solvents were then evaporated , and the crude product was precipitated by the addition of ether . to remove the dde - protection group , the glycosylated peptide was redissolved in a small volume of dmf , 2 vol % of hydrazine hydrate were added and the solution was stirred at room temperature for 15 min . the deprotected peptide was precipitated by the addition of ether , washed with ether and dried in vacuo . boc - protecting groups on the his - residue were then removed redissolving the crude products in a small volume of tfa / tibs / water ( 95 : 2 . 5 : 2 . 5 ) and stirring for 15 min at room temperature . the products were precipitated using either and purified via preparative rp - hplc ( gradient : 10 - 60 % b in 30 min ). yields ranged from 17 - 32 %. calculated monoisotopic mass for c 67 h 95 n 15 o 18 s 2 = 1461 . 60 ; found : m / s ˜ 1873 . 6 [ m + h ] + , m / z = 1895 . 7 [ m + na ] + . calculated monoisotopic mass for c 73 h 105 n 15 o 23 s 2 = 1623 . 70 ; found : m / z = 1873 . 6 [ m + h ] + , m / z = 1895 . 7 [ m + na ] + . calculated monoisotopic - mass for c 79 h 115 n 15 o 28 s 2 = 1785 . 75 ; found : m / z = 1873 . 6 [ m + h ] + , m / z − 1895 . 7 [ m + na ] + . imino diacetic acid ( 3 . 25 g , 24 . 4 mmol ) was dissolved in a mixture of 30 ml of absolute ethanol and a solution of 1 . 95 g of naoh ( 49 mmol ) in 10 ml of water . after the addition of 4 . 00 g of picolylchloride ( 24 . 4 mmol ) in 9 ml of water and of 1 . 95 g of naoh ( 49 mmol ) in 4 ml of water , the solution was stirred at 70 ° c . for 2 h . then another 1 . 95 g ( 49 mmol ) of naoh were added and the solution was stirred for another 1 . 5 h at 70 ° c . tlc reaction control ( acoet ) revealed complete disappearance of the reactants at that time . the solvents were evaporated in vacuo , and the residue was redissolved in 25 ml of water . after adjusting the ph of the solution to 1 . 5 with concentrated hydrochloric acid , the solution was again evaporated to dryness . by several successive steps of resuspension of the residue with methanol under reflex , hot filtration of the suspension and concentration of the filtrate in vacuo , excess nacl was successfully removed . the picolylamino diacetic acid crystallized from the remaining methanolic solution overnight at − 20 ° c . calculated monoisotopic mass for c 10 h 12 n 2 o 4 = 224 . 08 ; found : m / z =[ m = h ]+( disodium salt ). a solution of 52 mg ( 0 . 19 mmol ) of 2 - picolylamine n , n - diacetic acid , 26 mg ( 0 . 19 mmol ) of hobt , 62 mg ( 0 . 19 mmol ) of tbtu and 176 μl ( 1 . 75 mmol ) of dipea in 2 ml of dmf was stirred at room temperature for 10 min . this solution was added dropwise to a solution of 200 mg ( 0 . 13 mmol ) of fmoc - lys 0 - tate ( dde ) in 1 ml of dmf under vigorous stirring . after 30 min the product was precipitated using diethyl either and dried in vacuo . to remove the n - terminal fmoc - protecting group , the peptide was dissolved in 2 ml piperidine / dmf ( 1 : 4 ) and stirred for 10 min . precipitation with ether afforded the deprotected product with a yield of 84 %. calculated monoisotopic mass for c 75 h 98 n 14 o 18 s 2 = 1546 . 66 ; found : m / z =[ m = h ] + , m / z =[ m + na ] + . conjugation of lys 0 ( pic ) tate ( dde ) with glucose and subsequent dde - deprotection were carried out as described for the lys 0 - n a - amadori derivatives of lys 0 ( boc - his ( boc ))- toc ( dde ) calculated monoisotopic mass for c 71 h 96 n 14 o 21 s 2 = 1544 . 63 ; found : m / z =[ m = h ] + , m / z =[ m + na ] + . based on the organometallic aquaion [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + - method reported recently 3 , 10 mg of nabh 4 , 8 mg of na 2 co 3 and 41 . 5 mg of na / k tartrate were dissolved in 600 μl of [ 99m tc ] pertechnetate eluate in a glass flask . the flask was then connected to a co - filled balloon and sealed tightly . after stirring at 75 ° c . for 45 min , the solution was cooled on an ice bath and 150 μl of phosphate buffered saline ( pbs , ph - 7 . 4 ) were added . to destroy the reducing agent , 600 μl of 1 n hcl were added . then the solution was neutralized with 500 μl of a saturated solution of nahco 3 . the presence of the [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + - aquaion was confirmed via tlc ( 5 % conc . hcl in methanol ). after adding 1 ml of the [ 99m tc ( h 2 o ) 3 ( co ) 3 ] + - solution ( 51 mbq ) to 700 μg of s1 - lys 0 ( his ) toc , the mixture was heated to 75 ° c . for 30 min . gradient hplc purification afforded the radiochemically pure peptide n a -( 1 - deoxy - d - fructosyl )- lys 0 ( n ε - his [ 99m tc ( h 2 o )( co ) 3 ]+)- tyr 3 - octreotide with a radiochemical yield of 34 %. to a solution of app . 300000 cpm of radiolabeled peptide in 500 ml of pbs ( ph 7 . 4 ), 500 ml of octanol were added ( n = 6 ). vials were vortexed for 3 min and then centrifuged at 15000 rpm for 6 min . aliquots of 100 ml of pbs and octanol were measured in a γ - counter . ar42j cells were maintained in rpmi 1640 , supplemented with 10 % fcs and 2 mm l - glutamine . six - well plates with a cell population of 8 × 10 5 - 5 × 10 6 ar42j - cells per well were incubated at 37 ° c . with fresh culture medium ( rpmi 1640 , 1 % bsa , 2 mm l - glutamine ) for 1 h prior to the experiment . then app . 300000 cpm of radiometallated peptide in 10 μl of culture medium were added to each well ( triplicate experiments for the reference compound ( internal standard ) [ 125 i ] toc and for the radiometallated compound of interest each ). after incubating for 10 , 30 , 60 , 90 or 120 min . at 37 ° c . the supernatant was collected and the cells were washed once with 1 ml of cold medium . the supernatant was pooled with the supernatant of the previous step . to remove receptor bound ( acid releasable ) radioactivity the cells were incubated at 37 ° c . with 1 ml of 0 . 02 m naoac ( acid wash ). after 10 min . the supernatant was collected , the cells were washed once with 1 ml of 0 . 02 m naoac and the supernatant was again pooled with the supernatant of the previous step . then the cells were extracted with 1 ml of 1 n naoh and the wells were rinsed once with pbs . this pooled fraction represents internalized radioligand . the activity in the naoh - fraction as well as in the supernatant - and in the acid wash - fractions was counted in a γ - counter . as described for the internalization studies , the six - well plates were incubated at 37 ° c . with fresh culture medium ( rpmi 1640 , 1 % bsa , 2 mm l - glutamine ) for 1h prior to the experiment . then app . 300000 cpm of radiometallated peptide in 10 μl of culture medium were added to each well ( triplicate experiments for the reference compound ( internal standard ) [ 125i ] toc and for the radiometallated compound of interest each ). after incubating for 120 min . at 37 ° c ., the supernatant was collected and the cells were washed once with 1 ml of cold medium . the supernatant was pooled with the supernatant of the previous step . to collect externalized radioactivity the cells were then incubated at 37 ° c . with 1 ml of culture medium . after 10 , 30 , 60 , 90 and 120 minutes respectively , the supernatant was collected , the cells were washed once with 1 ml of culture medium and the supernatant was again pooled with the supernatant of the previous step . then the cells were extracted with 1 ml of 1 n naoh and the wells were rinsed once with pbs . this pooled fraction represents radioligand still located in the cell . the activity in the naoh - fraction as well as in the supernatant - and in the externalisation - fractions was counted in a γ - counter . as described for the previous experiment , a six - well plate was incubated for 120 min . at 37 ° c . with radioligand . the supernatant was collected and the cells were washed once with 1 ml of cold medium . the supernatant was pooled with the supernatant of the previous step . to collect externalized radioactivity the cells were then incubated at 37 ° c . with 1 ml of culture medium . after 10 min . the supernatant was collected and the cells were again incubated with 1 ml of culture medium for another 20 min . at 37 ° c . the supernatant was collected and the cells were three more times incubated with 1 ml of culture medium for 30 min . at 37 ° c . then the cells were extracted with 1 ml of 1 n naoh and the wells were rinsed once with pbs . this pooled fraction represents radioligand still located in the cell . the activity in the naoh - fraction as well as in the externalisation - fractions at all time points was counted in a 7 - counter . to establish tumor growth , subconfluent monolayer cells were treated with 1 mm edta , suspended , centrifuged and resuspended in rpmi 1640 . nude mice ( male and female , 6 - 8 weeks ) were inoculated s . c . in the flank with 2 . 5 - 3 × 10 7 cells suspended in 100 μl of pbs ( ph 7 . 4 ), were injected i . v . into the tail vein of nude mice bearing an ar42j tumor . the animals ( n = 3 - 4 ) were sacrificed 30 and 120 min p . i , and the organs of interest were dissected . the radioactivity was measured in weighted tissue samples using a gamma counter . data are expressed in % id / g tissue ( mean ± ds , n = 3 - 4 ).
improved sst - receptor binding peptidic ligands for diagnostic and therapeutic applications in nuclear medicine are provided . the improved ligands contain either natural or unnatural amino acids or peptidomimetic structures that are modified at either the n - terminal or the c - terminal end or at both termini , a carbohydrate unit and a chelator or prosthetic group to provide a complexation of a radioisotope binding or holding the radioisotope . the sst - or sstr - receptor binding peptidic ligands may also contain one or more multifunctional linker units optionally coupling the peptide , and / or the sugar moiety and / or the chelator and / or the prosthetic group . upon administering the ligand to a mammal through the blood system the ligand provides improved availability , clearance kinetics , sst - receptor targeting and internalization over the non - carbohydrated ligands .