Long-term evaluation of a <sup>68</sup>Ga-PSMA-11 kit radiolabeling procedure and performance assessment for imaging GCPII/PSMA expression in patients with breast and prostate cancer — ASN Events
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  3. Long-term evaluation of a 68Ga-PSMA-11 kit radiolabeling procedure and performance assessment for imaging GCPII/PSMA expression in patients with breast and prostate cancer

Long-term evaluation of a 68Ga-PSMA-11 kit radiolabeling procedure and performance assessment for imaging GCPII/PSMA expression in patients with breast and prostate cancer (#97)

Janine Suthiram 1 2 , Mariza Vorster 2 , Judith Wagener 1 , Biljana Marjanovic-Painter 1 , Mike M Sathekge 2 , Jan Rijn Zeevaart 1 3 , Thomas Ebenhan 1 2
  1. Radiochemistry, The South African Nuclear Energy Corporation (Necsa), Brits Magisterial District, Madibeng Municipality, North West Province, South Africa
  2. Nuclear Medicine, University of Pretoria and Steve Biko Academic Hospital, Gezina/Pretoria, Gauteng, South Africa
  3. Preclinical Drug Development Platform, Department of Science and Technology, North West University, Potchefstroom, North West Province, South Africa

Background PET/CT imaging plays a critical role in personalized medicine and molecular oncology. It allows for better cancer management by delineating the presence of malignancy, facilitating tumor staging or monitoring early response after therapeutic interventions. Glutamate carboxypeptidase II (GCPII), often referred to as prostate-specific membrane antigen (PSMA), was recently discovered being associated with high risks for breast and prostate cancer (1). Due to its overexpression in prostate cancer, GCPII/PSMA represents an excellent target for its diagnostics and radio-endotherapy, but also for imaging breast cancer metastases (2, 3). We developed a quantitative kit labeling solution for 68Ga-PSMA-11 (Glu-NH-CO-NH-Lys-(Ahx)-68Ga(HBED-CC)) (4). We herein report this procedure supported by long-term validations determining influences of 68Ga-purification, longitudinal labeling performance, 68Ge-monitoring and imaging performance in cancer patients.

Methods Freeze-dried kits were manufactured over 18 months. Eluate processing was implemented using cation-exchange techniques. 1 mL 68Ga-activity was added to the kit initiating labeling (pH 4.0). 68Ge-breakthrough was identified re-measuring decayed product solutions in an ionization chamber. Prostate cancer patients (n>100) received 77-277 MBq 68Ga-PSMA-11; female breast cancer patients received one of two68Ga-PSMA-11 doses: 109±7 MBq (n=7) or 180±25 MBq (n=16).

Results The small eluate fraction added (855±189 MBq; 69-88% total 68Ga-activity) reduced 68Ge-levels (P<0.026) significantly. The 68Ge-breakthrough (maximum 0.00062%; range 0.00034±0.00009) was well below 0.001%. The radiochemical purity (%RCP) remained uncompromised (>96%, n>100) notwithstanding procedure modifications (±10% eluate acidity, shelf-life, 68Ga-activity concentration). Decreasing %RCP was observed following eluate processing (NaCl/HCl: –66%; Acetone/HCl: –68%); PSMA-11 kits stored >6 months provoked ≤33% labeling losses. The overall 68Ga-PSMA-11-kit labeling repeatability was ≥79% (n=164). One 68Ga-PSMA-11 production yielded 2-3 patient doses (>100 MBq, administered within 90 min). All administered patient doses provided excellent imaging quality and tumor delineation, proving superior kit performance.

Conclusion The 68Ga-PSMA-11-kit development achieved an easy-to-adopt technique that may be operated in a similar straightforward fashion as already existing 99mTc-kit-based procedures.

  1. Divyya S, et al. (2013), Gene 516:76-81.
  2. Sathekge M, et al. (2015), Eur J Nucl Med Mol Imaging 42:1482-3.
  3. Nomura N, et al. (2014), Cancer Cell International 14:26.
  4. Ebenhan T, et al. (2015), Molecules 20:14860-78