[11C]Choline as pharmacodynamic marker for therapy response assessment in a prostate cancer xenograft model.
OBJECTIVE
[(11)C]Choline has been established as a PET tracer for imaging prostate cancer. The aim of this study was to determine whether [(11)C]choline can be used for monitoring the effects of therapy in a prostate cancer mouse xenograft model.


METHODS
The androgen-independent human prostate cancer cell line PC-3 was implanted subcutaneously into the flanks of 13 NMRI (nu/nu) mice. All mice were injected 4-6 weeks after xenograft implantation with 37 MBq [(11)C]choline via a tail vein. Dynamic imaging was performed for 60 min with a small-animal PET/CT scanner (Siemens Medical Solutions). Six mice were subsequently injected intravenously with docetaxel twice (days 1 and 5) at a dose of 3 mg/kg body weight. Seven mice were treated with PBS as a control. [(11)C]Choline imaging was performed prior to and 1, 2 and 3 weeks after treatment. To determine choline uptake the images were analysed in terms of tumour-to-muscle (T/M) ratios. Every week the size of the implanted tumour was determined with a sliding calliper.


RESULTS
The PC-3 tumours could be visualized by [(11)C]choline PET. Before treatment the T/M(mean) ratio was 1.6+/-0.5 in the control group and 1.8+/-0.4 in the docetaxel-treated group (p=0.65). There was a reduction in the mean [(11)C]choline uptake after docetaxel treatment as early as 1 week after initiation of therapy (T/M ratio 1.8+/-0.4 before treatment, 0.9+/-0.3 after 1 week, 1.1+/-0.3 after 2 weeks and 0.8+/-0.2 after 3 weeks). There were no decrease in [(11)C]choline uptake in the control group following treatment (T/M ratio 1.6+/-0.5 before treatment, 1.7+/-0.4 after 1 week, 1.8+/-0.7 after 2 weeks and 1.7+/-0.4 after 3 weeks). For analysis of the dynamic data, a generalized estimation equation model revealed a significant decrease in the T/M(dyn) ratios 1 week after docetaxel treatment, and the ratio remained at that level through week 3 (mean change -0.93+/-0.24, p<0.001, after 1 week; -0.78+/-0.21, p<0.001, after 2 weeks; -1.08+/-0.26, p<0.001, after 3 weeks). In the control group there was no significant decrease in the T/M(dyn) ratios (mean change 0.085+/-0.39, p=0.83, after 1 week; 0.31+/-0.48, p=0.52, after 2 weeks; 0.11+/-0.30, p=0.72, after 3 weeks). Metabolic changes occurred 1 week after therapy and preceded morphological changes of tumour size during therapy.


CONCLUSIONS
Our results demonstrate that [(11)C]choline has the potential for use in the early monitoring of the therapeutic effect of docetaxel in a prostate cancer xenograft animal model. The results also indicate that PET with radioactively labelled choline derivatives might be a useful tool for monitoring responses to taxane-based chemotherapy in patients with advanced prostate cancer.
Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str 22, 81675 München, Munich, Germany. Bernd-Joachim.Krause@tum.de
Bernd J
BJ
Krause
Michael
M
Souvatzoglou
Ken
K
Herrmann
Axel W
AW
Weber
Tibor
T
Schuster
Andreas K
AK
Buck
Roman
R
Nawroth
Gregor
G
Weirich
Uwe
U
Treiber
Hans-Jürgen
HJ
Wester
Sibylle I
SI
Ziegler
Reingard
R
Senekowitsch-Schmidtke
Markus
M
Schwaiger
D000818:Animals; D014408:Biomarkers, Tumor; D002250:Carbon Radioisotopes; D045744:Cell Line, Tumor; D002794:Choline; D000077143:Docetaxel; D006801:Humans; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000628:therapy*; D043823:Taxoids / Q000494:pharmacology / Q000627:therapeutic use; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
D014408:Biomarkers, Tumor; D002250:Carbon Radioisotopes; D043823:Taxoids; D000077143:Docetaxel; D002794:Choline