1370 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 7
Pearson et al.
(compounds 45 and 57). [99mTc]Glucoheptonate was prepared
by reconstituting a glucoscan vial (E.I. DuPont de Nemours,
Inc.; this kit contains stannous chloride as a reducing agent
and glucoheptonate as a transfer ligand) with 1.0 mL of sodium
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[
99mTc]pertechnetate (from a 99Mo/99mTc generator) containing
up to 200 mCi. The vial was allowed to stand at room
temperature for 15 min. A 25-µL aliquot of [99mTc]gluceptate
from this vial was then added to the peptide solution above
and the reaction allowed to proceed at room temperature for
15-30 min (for compounds 40-43) or at 100 °C for 5 min (for
compounds 45 and 57). After filtration through a 0.2-µm filter,
the purity of the 99mTc-labeled peptide was assessed by
analytical reversed-phase HPLC. Compounds 40-43 were
analyzed at 0-100% B/A over 20 min using a Waters Delta-
Pak C18 column, 5 µm, 39 × 150 mm. Compounds 45 and 57
were analyzed at 0-100% B/A over 10 min using a Waters
Nova-Pak Radial Compression C18 column, 4 µm, 8 × 100 mm
(A ) 0.1% TFA in water, B ) 0.1% TFA in 90% acetonitrile/
water). Radioactive components were detected using an in-
line radiometric detector linked to an integrating recorder.
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[
99mTc]Gluceptate and sodium [99mTc]pertechnetate elute be-
tween 1 and 4 min under these conditions, whereas the
99mTc-labeled peptides eluted later as one species (g80%) as
illustrated in Table 4. To compare technetium and rhenium
complexes, a separate experiment was performed in which
compound 42 was labeled with 99mTc and analyzed at 20-50%
B/A over 20 min using the same Delta-Pak column and eluents
used above. A tR of 14.95 min was observed by radiometric
detection. UV detection at 220 nM was also employed with
no peak seen for 99mTc-labeled 42 due to the very low
concentrations of peptide used in the radiolabeling experiment.
The sample was then spiked with the rhenium complex of 42
(compound 64). After spiking, a radiometric tR of 14.85 min
was observed for the 99mTc complex of 42 with a nearly
identical tR of 14.90 min observed at 220 nM for the rhenium
complex. The chromatograms are presented as Supporting
Information.
Biod istr ibu tion Stu d ies of Com p ou n d s 40-43, 45, 57,
a n d 111In -La beled 4 in Som a tosta tin Recep tor -P ositive
Tu m or -Bear in g Rats. The rat pancreatic tumor line CA20948
was obtained from frozen stock, prepared as a brie, and serially
passaged in Lewis rats at Biomeasure. The line was passaged
through the fourth generation after which the subsequent five
passages had desirable SSTR expression levels averaging 80-
100 fmol/mg of tumor. The tumor brie was placed in the
lateral aspect of the right leg subcutaneously and allowed to
grow to an average desired mass of 1-2 g (2-3 weeks).
The 99mTc peptide preparations of compounds 40-43, 45,
and 57 used in the animal studies resulted in solutions of 800
µg of peptide/mL with an activity of 20-30 mCi/mL. Dosing
solutions were prepared by dilution of the parent stock at a
ratio of 1:30 to obtain a dosing solution of 0.6-0.8 mCi/mL.
The rats (mass range ) 248-320 g) were administered 99mTc-
labeled peptides intravenously via the lateral tail vein at a
dose volume of 1 mL/kg. The 111In complex of compound 4
was prepared as follows: 111In chloride was prepared in
citrated acid (1 mL of 0.2 M HCl containing 25 mg of trisodium
citrate) to a final activity of 2 mCi/mL. Compound 4 was
dissolved in 0.9% saline at a concentration of 1 mg/mL, and
10 µL of this solution was added to the 111In in citrated acid
and incubated at room temperature for 15 min. Doses of the
111In-labeled peptide were made by dilution of the stock
solution to 1:20 (final concentration ) 100 µCi/mL) and
delivering 1.0 mL/kg.
(6) Wangberg, B.; Nilsson, O.; Theodørsson, E.; Dahlstrøm, A.;
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DTPA-D-Phe]- Octreotide, A Potential Radiopharmaceutical for
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Radiolabeling and in vitro Validation. Life Sci. 1991, 49, 1593-
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Phe1]- and [123I-Tyr3]-Octreotide: The Rotterdam Experience
with More Than 1000 Patients. Eur. J . Nucl. Med. 1993, 20,
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(11) Dean, R. T.; McBride, W.; Buttram, S. Technetium-99m labeled
peptides for imaging. Patent WO 93/10747, 1993.
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The animals were imaged 90 min after injection and then
sacrificed. Blood, tumor, and other tissues were subsequently
harvested at necropsy. Tissues were counted in a γ-well
counter against dilutions of stock dosing solutions. Percent
injected dose and percent injected dose per gram were calcu-
lated using appropriate decay corrections.
Su p p or tin g In for m a tion Ava ila ble: Electrospray mass
spectral data for compounds 36-79 and chromatograms from
the coinjection of compound 64 with the 99mTc complex of
compound 42 (2 pages). Ordering information is given on any
current masthead page.
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Springer-Verlag: Berlin, 1993; pp 1-329.