SPECT/CT imaging of prostate cancer xenografts using a new bombesin

receptor antagonist

Molecular Radiopharmacy

L.M. van der Graaf1, T. Maina2, P.J. Marsouvanidis2, M. Melis1, S.C. Berndsen1, E.P. Krenning1, J. Martinez3, L. Brunel3, J. Fehrentz3,

B.A. Nock2, M. de Jong1

1Erasmus MC, Rotterdam, Netherlands, 2NCSR “Demokritos”, Athens, Greece, 3Faculté

de Pharmacie, CNRS-Universités de Montpellier 1 et 2, Montpellier, France

Introduction

Bombesin analogues bind GRP-receptors

overexpressed on prostate cancer and breast

cancer

Proof of concept obtained clinically: AMBA, MP2248Different structures/linkers/radionuclides: All targeting GRPR

Agonists, disadvantages: High bioactivity (side effects) High pancreatic uptake (problems during PRRT)Mitogenic effects

Introduction Antagonists: affinity, no bioactivity, less internalization

We have always believed, antagonists would not work for

imaging and radionuclide therapy

However:

- [99mTc]Demobesin 1: Maina et al, Eur J Nucl Med Mol Imaging,

2003; Reubi et al, J Nucl Med,2008

- RM2: Maecke et al, Eur J Nucl Med Mol Imaging, 2011

J Martinez et al. compounds (JMV): J. Med. Chem. 2000, 43, 2356-2361, Peptides, 1998, 19, 57-63

- DOTA coupled to JMV594: JMV4168 (JMV)

Aim

Evaluate JMV versus AMBA in the PC3-model• In vitro: receptor affinity, antagonistic properties, internalization• In vivo biodistribution in SCID and Nu/Nu mice, 111In vs. 177Lu,

PC-3: commonly used

PC-295: more physiological• In vivo stability• In vivo nanoSPECT/CT

JMV4168

Results:GRP receptor affinity

IC50 JMV: 1.3 nM versus 0.7 nM for AMBA

IC50 JMV & AMBA

-14 -12 -10 -8 -6 -40

50

100

150

111In-JMV+JMV111In-AMBA+AMBA

Log block (M)

% b

ind

ing

Competitive antagonistBinds the same binding site on the receptor

Results:Internalization, 60 min, 37°C in PC3

Results: in vivo biodistribution- 111In in male Nu/Nu mice

4h p.i. PC3 vs PC295

1 MBq/mouse; 10 pmol

Results:in vivo biodistribution- 111In in SCID mice with PC3 xenograft

111In-JMV4168

1 MBq/mouse; 10 pmol

Results:in vivo biodistribution- 177Lu in SCID mice with PC3 xenograft

1 MBq/mouse; 10 pmol

ResultsScintigraphy, NanoSPECT/CT

4h p.i.

24h p.i.

1h p.i.

17-20 MBq 111In-JMV, 250 pmol,Scanning time 26 min Pinhole: 1.4 mm

ResultsDynamic nanoSPECT/CT

Time activity curve

Antagonists: very interesting approach, less side effects

JMV: High tumor uptake

JMV: retention in tumor not as good as agonist, excellent

for short-lived radionuclides

Pancreas low: tumor/pancreas ratio much better than for

agonist!

Future outlook:

Stabilized compounds

Dimers: better retention in tumor?

Radionuclide therapy to erradicate tumors

Conclusions

Uptake in PC3 cells Athens vs Rotterdam

Culture media: - DMEM+ pyruvate+FBS+p/s - RPMI+FBS +p/s

Incubation: 2 hours at 4°C

JMV

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MP2248

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MP2248

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Results:metabolites [177Lu]JMV4168

mouse urine, 30 min pi

Parent, 0%

Metabolite A, 49%

Metabolite B, 51%