68Ga- and 177Lu-Labeled PSMA I&T: Optimization of a PSMA-Targeted Theranostic Concept and First Proof-of-Concept Human Studies

J Nucl Med. 2015 Aug;56(8):1169-76. doi: 10.2967/jnumed.115.158550. Epub 2015 Jun 18.


On the basis of the high and consistent expression of prostate-specific membrane antigen (PSMA) in metastatic prostate cancer (PC), the goal of this study was the development, preclinical evaluation, and first proof-of-concept investigation of a PSMA inhibitor for imaging and therapy (PSMA I&T) for (68)Ga-based PET and (177)Lu-based endoradiotherapeutic treatment in patients with metastatic and castration-resistant disease.

Methods: PSMA I&T was synthesized in a combined solid phase and solution chemistry strategy. The PSMA affinity of (nat)Ga-/(nat)Lu-PSMA I&T was determined in a competitive binding assay using LNCaP cells. Internalization kinetics of (68)Ga- and (177)Lu-PSMA I&T were investigated using the same cell line, and biodistribution studies were performed in LNCaP tumor-bearing CD-1 nu/nu mice. Initial human PET imaging studies using (68)Ga-PSMA I&T, as well as endoradiotherapeutic treatment of 2 patients with metastatic PC using (177)Lu-PSMA I&T, were performed.

Results: PSMA I&T and its cold gallium and lutetium analog revealed nanomolar affinity toward PSMA. The DOTAGA (1,4,7,10-tetraazacyclododecane-1-(glutamic acid)-4,7,10-triacetic acid) conjugate PSMA I&T allowed fast and high-yield labeling with (68)Ga(III) and (177)Lu(III). Uptake of (68)Ga-/(177)Lu-PSMA I&T in LNCaP tumor cells is highly efficient and PSMA-specific, as demonstrated by competition studies both in vitro and in vivo. Tumor targeting and tracer kinetics in vivo were fast, with the highest uptake in tumor xenografts and kidneys (both PSMA-specific). First-in-human (68)Ga-PSMA I&T PET imaging allowed high-contrast detection of bone lesions, lymph node, and liver metastases. Endoradiotherapy with (177)Lu-PSMA I&T in 2 patients was found to be effective and safe with no detectable side effects.

Conclusion: (68)Ga-PSMA I&T shows potential for high-contrast PET imaging of metastatic PC, whereas its (177)Lu-labeled counterpart exhibits suitable targeting and retention characteristics for successful endoradiotherapeutic treatment. Prospective studies on larger cohorts of patients are warranted and planned.

Keywords: 177Lu; 68Ga; PSMA I&T; prostate cancer; prostate-specific membrane antigen.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Anhydrides / chemistry
  • Animals
  • Antigens, Surface
  • Cell Line, Tumor
  • Contrast Media / chemistry
  • Coordination Complexes / chemistry*
  • Female
  • Gallium Radioisotopes*
  • Glutamate Carboxypeptidase II / antagonists & inhibitors*
  • Heterocyclic Compounds, 1-Ring / chemistry
  • Humans
  • Inhibitory Concentration 50
  • Kinetics
  • Lutetium*
  • Male
  • Mice
  • Middle Aged
  • Neoplasm Metastasis
  • Neoplasm Transplantation
  • Oligopeptides / chemistry*
  • Positron-Emission Tomography
  • Prostatic Neoplasms / diagnostic imaging*
  • Prostatic Neoplasms / metabolism*
  • Radiometry
  • Radiotherapy


  • 68Ga-DOTAGA-(3-iodo-y)fk(Sub-KuE)
  • Anhydrides
  • Antigens, Surface
  • Contrast Media
  • Coordination Complexes
  • DOTAGA-anhydride
  • Gallium Radioisotopes
  • Heterocyclic Compounds, 1-Ring
  • Oligopeptides
  • Lutetium
  • FOLH1 protein, human
  • Glutamate Carboxypeptidase II