Apoptosis in Non-Tumorous Adult Human Testis Tissue

18F-ICMT-11, a caspase-3-specific PET tracer for apoptosis: biodistribution and radiation dosimetry

Effective anticancer therapy induces tumor cell death through apoptosis. Noninvasive monitoring of apoptosis during therapy may provide predictive outcome information and help tailor treatment. A caspase-3-specific imaging radiotracer, (18)F-(S)-1-((1-(2-fluoroethyl)-1H-[1,2,3]-triazol-4-yl)methyl)-5-(2(2,4-difluorophenoxymethyl)-pyrrolidine-1-sulfonyl)isatin ((18)F-ICMT-11), has been developed for use in PET studies. We report the safety, biodistribution, and internal radiation dosimetry profiles of (18)F-ICMT-11 in 8 healthy human volunteers.

METHODS

(18)F-ICMT-11 was intravenously administered as a bolus injection (mean ± SD, 159 ± 2.75 MBq; range, 154-161 MBq) to 8 healthy volunteers (4 men, 4 women). Whole-body (vertex to mid thigh) PET/CT scans were acquired at 6 time points, up to 4 h after tracer injection. Serial whole blood, plasma, and urine samples were collected for radioactivity measurement and radiotracer stability. In vivo (18)F activities were determined from quantitative analysis of the images, and time-activity curves were generated. The total numbers of disintegrations in each organ normalized to injected activity (residence times) were calculated as the area under the curve of the time-activity curve, normalized to injected activities and standard values of organ volumes. Dosimetry calculations were then performed using OLINDA/EXM 1.1.

RESULTS

Injection of (18)F-ICMT-11 was well tolerated in all subjects, with no serious tracer-related adverse events reported. The mean effective dose averaged over both men and women was estimated to be 0.025 ± 0.004 mSv/MBq (men, 0.022 ± 0.004 mSv/MBq; women, 0.027 ± 0.004 mSv/MBq). The 5 organs receiving the highest absorbed dose (mGy/MBq), averaged over both men and women, were the gallbladder wall (0.59 ± 0.44), small intestine (0.12 ± 0.05), upper large intestinal wall (0.08 ± 0.07), urinary bladder wall (0.08 ± 0.02), and liver (0.07 ± 0.01). Elimination was both renal and via the hepatobiliary system.

CONCLUSION

(18)F-ICMT-11 is a safe PET tracer with a dosimetry profile comparable to other common (18)F PET tracers. These data support the further development of (18)F-ICMT-11 for clinical imaging of apoptosis.

Testicular germ cell tumours: the paradigm of chemo-sensitive solid tumours

Testicular germ cell tumours (TGCTs) are the most frequent solid malignant tumour in men 20-40 years of age and the most frequent cause of death from solid tumours in this age group. Up to 50% of the patients suffer from metastatic disease at diagnosis. The majority of metastatic testicular cancer patients, in contrast to most other metastatic solid tumours, can be cured with highly effective cisplatin-based chemotherapy. From a genetic point of view, almost all TGCTs in contrast to solid tumours are characterised by the presence of wild type p53. High p53 expression levels are associated with elevated Mdm2 levels and a loss of p21(Waf1/Cip1) expression suggesting a changed functionality of p53. Expression levels of other proteins involved in the regulation of cell cycle progression indicate a deregulated G1-S phase checkpoint in TGCTs. After cisplatin-induced DNA damage, the increasing levels of p53 lead to the trans-activation of a number of genes but not of p21(Waf1/Cip1), preferentially directing TGCT cells into apoptosis or programmed cell death, both via the mitochondrial and the death receptor apoptosis pathways. The sensitivity of TGCTs to chemotherapeutic drugs may lay in the susceptibility of germ cells to apoptosis. Taken together, this provides TGCT as a tumour type model to investigate and understand the molecular determinants of chemotherapy sensitivity of solid tumours. This review aims to summarise the current knowledge on the biological basis of cisplatin-induced apoptosis and response to chemotherapy in TGCTs.