Application Note 6

Study of radio-labeled model drug
compound (123I-NaI)
release from GrowDex® in vivo
Patrick Laurén
University of Helsinki, Finland

INTRODUCTION

Injectable hydrogels can be used as controlled drug release matrices, but their use is often
hampered by the gel activation properties. GrowDex® is an injectable hydrogel that does notneed a separate activation step. In this protocol, performing of an in vivo drug release study
using GrowDex hydrogel in mice is described. Radio-labeled model drug compound NaI
was embedded in radio-labeled GrowDex, the hydrogel was injected subcutaneously into
mice, and the release of model drug compound was observed non-invasively over 5 h using
single photon emission computed tomography (SPECT/CT).

MATERIALS

99m

METHODS

1.
2.

RESULTS

Tc-labeled GrowDex hydrogel (See instructions for the preparation of radio-labeled
GrowDex described in Application Note #5: 99mTc-GrowDex labelling for SPECT/CT
molecular imaging studies)Radio-labeled study compound 123I-NaII-NaI was mixed to 1% 99mTc-GrowDex at the ratio of 1:5 (compound:GrowDex)
123
I-NaI -containing 99mTc-GrowDex was injected subcutaneously into the pelvic regionof micea. Hydrogel volume was 200 µl/mouseb. Radioactivity dose was 50-60 MBq/200 µl
3. The release of 123I-NaI from 99mTc-GrowDex was studied using SPECT/CT imaging(NanoSPECT/CT, Bioscan, USA)a. Mice were sedated with e.g. 4% isofluran for the time of imaging
b. SPECT images were acquired immediately after the injection and once an hour
during a total of 5 h.
123

Both radio-labeled GrowDex and NaI were visualized with SPECT/CT imaging after
subcutaneous injection to mice (Fig 1A). GrowDex remained intact without showing
migration or disintegration during the experiment, when comparing 0 h and 5 h timepoints (Fig1 A-B). The distribution of 123I-NaI was seen mostly to thyroid glands, stomachand excretion to urine (Fig 1B). The 123I-NaI release from GrowDex and distribution to
thyroid glands were quantitatively analyzed by recording the counts and calculating theactivity at the injection site and target organ (thyroid glands) at different time points(Fig 1C).

Fig 1. The release of 123I-NaI from radiolabeled GrowDex injection over 5 h. A) Split
image is shown to visualize both radio-tracers separately at the beginning of the experiment.
B) Dual tracing images show GrowDex placement and stability, and 123I-NaI release anddistribution to thyroid glands, stomach and urinary bladder. C) The release of 123I-NaI from
GrowDex and distribution to thyroid glands were analyzed by image processing techniques.

CONCLUSIONSREFERENCESThe SPECT/CT study with radio-labeled GrowDex and model drug compound showed
the possibility to trace both materials simultaneosly in vivo. GrowDex can be injected
sub-cutaneously into the mice due to the shear thinning property of the material, and it
remained intact at the injection site despite the activity of the animals during the experiment.
The release of radio-labeled model drug compound, 123I-NaI, from GrowDex suggests thepossibility to use GrowDex as a drug releasing implant.

1.

Laurén P et al. 2014 “Technetium-99m-labeled nanofibrillar hydrogel for in vivo drug
release” Eur J Pharm Sci, vol 65, 79-88.

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