The Value of In Vitro Binding as Predictor of In Vivo Results: A Case for [18F]FDDNP PET



Caution is warranted when in vitro results of biomarkers labeled with tritium were perfunctorily used to criticize in vivo data and conclusions derived with the same tracers labeled with positron emitters and positron emission tomography (PET). This concept is illustrated herein with the PET utilization of [18F]FDDNP, a biomarker used for in vivo visualization of β-amyloid and tau protein neuroaggregates in humans, later contradicted by in vitro data reported with [3H]FDDNP. In this investigation, we analyze the multiple factors involved in the experimental design of the [3H]FDDNP in vitro study that led to the erroneous interpretation of results.


The present work describes full details on the synthesis, characterization, purity, and kinetics of radiolytic stability of [3H]FDDNP. The optimal in vitro conditions for detecting tau and β-amyloid protein aggregates using macroscopic and microscopic autoradiography with both [18F]FDDNP and [3H]FDDNP are also presented. Macroscopic autoradiography determinations were performed with [3H]FDDNP of verified purity using established methods described previously in the literature.


The autoradiographic results using phosphate buffered saline (PBS) with less than 1 % EtOH and pure, freshly prepared [3H]FDDNP compared with the earlier reported data using [3H]FDDNP of undetermined purity and PBS in 10 % EtOH demonstrate the critical importance of rigorous experimental design for meaningful in vitro determinations. [18F]FDDNP binding to both amyloid plaques and neurofibrillary tangles was confirmed by amyloid and tau immunohistochemical stains of adjacent tissues.


This work illustrates the sensitivity of in vitro techniques to various experimental conditions and underscores that conclusions obtained from translational in vitro to in vivo determinations must always be performed with extreme care to avoid wrong interpretations that can be perpetuated and assumed without further analysis.

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Special thanks to the excellent reviewers and the editor (RG) for constructive comments and valuable advice, which have been incorporated into the manuscript. This work was supported by grants from the Slovenian Research Agency (Research Core Funding Grant P1-0230 and project J1-8147) and by grants P01-AG025831, AG13308, P50 AG 16570, MH/AG58156, MH52453, and AG10123 from the National Institutes of Health; contract DE-FC03-87-ER60615 from the Department of Energy. J.R.B. gratefully acknowledges the Elizabeth and Thomas Plott Endowment in Gerontology. This work was also partially supported within the infrastructures of the EN-FIST Centre of Excellence, Trg Osvobodilne fronte 13, 1000 Ljubljana, Slovenia, and the Centre for Research Infrastructure at the Faculty of Chemistry and Chemical Technology of the University of Ljubljana. The NMR analysis at UCLA Department of Chemistry was supported by the National Science Foundation equipment grant no. CHE-1048804.

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Corresponding authors

Correspondence to Jorge R. Barrio or Andrej Petrič.

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Conflict of Interest

The University of California, Los Angeles, owns a U.S. patent (6,274,119) entitled “Methods for Labeling β-Amyloid Plaques and Neurofibrillary Tangles,” which has been licensed to TauMark, LLC. N.S., G.W.S., S.-C.H., A.P., and J.R.B. are among the inventors. N.S., S.-C.H., G.W.S., and J.R.B. have equity interest in TauMark, LLC. All other authors report no financial conflicts of interest.

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Cole, G.B., Satyamurthy, N., Liu, J. et al. The Value of In Vitro Binding as Predictor of In Vivo Results: A Case for [18F]FDDNP PET. Mol Imaging Biol 21, 25–34 (2019).

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Key words

  • [3H]FDDNP
  • [18F]FDDNP
  • [3H]FENE
  • Kinetics
  • Autoradiolysis
  • Autoradiography