Natural somatostatin （SMS）

dextran-70 (Dx

70

) and a bifunctional chelator 2- methyl-6-（p-amidobenzyl） -diethylenetriaminepentaacetic acid （1B4M-DTPA） were used to synthesize a novel somatostatin-dextran-DTPA (SMS-Dx

70

-DTPA) conjugate and radiolabeled with

90

Y. An in vitro somatostatin receptor competition binding study was carried out by using

125

I-Tyr

3

-Octreotide as a radioligand to measure the IC

50

value of SMS-Dx

70

-DTPA. Bio- distribution and blood half-life of

90

Y-DTPA-Dx

70

-SMS were investigated in normal rats. The results show that SMS-Dx70-DTPA has a high receptor binding affinity to somatostatin receptor subtype 2

with the IC

50

value being in the same range as somatostatin. The blood half-life of

90

Y-DTPA-Dx

70

-SMS in normal rats was 6.39h post-injection. Digestion and excretion of

90

Y-DTPA-Dx

70

-SMS was mainly through the hepatobiliary and kidney systems. Increased uptake was seen in the adrenals and pancreas

and it kept almost constant during 24h. Therefore

90

Y-DTPA-Dx

70

-SMS has targeting properties towards somatostatin receptor positive organs and it may become a promising therapeutic agent candidate for somatostatin receptor positive tumors.