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Biodistribution and Pharmacokinetic Analysis of a Targeted Alpha Particle Therapy

Christopher J. Tichacek1,2,3*, Mikalai M. Budzevich4 , Narges K. Tafreshi3 , Thaddeus J. Wadas5 , Mark L. McLaughlin6,7 , David L. Morse2,4,8 , Eduardo G. Moros1,2,3 , (1) Dept. of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, (2) Dept. of Physics, University of South Florida, Tampa, FL, (3) Dept. of Cancer Physiology, Moffitt Cancer Center, Tampa, FL, (4) Small Animal Imaging Laboratory, Moffitt Cancer Center, Tampa, FL, (5) Dept. of Cancer Biology, Wake Forest University Health Sciences, Winston-Salem, NC, (6) Dept. of Pharmaceutical Sciences, West Virginia University, Health Sciences Center, Morgantown, WV, (7) Modulation Therapeutics Inc., Morgantown, WV, (8) Dept. of Oncologic Sciences, University of South Florida, Tampa, FL.


(Wednesday, 8/1/2018) 7:30 AM - 9:30 AM

Room: Davidson Ballroom A

Purpose: Targeted alpha particle therapy (TAT) is ideal for treating disease while minimizing damage to surrounding non-targeted tissues due to short path-length and high LET. A TAT has been developed for metastatic uveal melanoma, targeting the Melanocortin 1 Receptor (MC1R) which is expressed in 94% of uveal melanomas. Two versions of our therapy are being investigated: ²²�Ac-DOTA-Ahx-MC1RL (Ahx) and ²²�Ac-DOTA-di-D-Glu-MC1RL (di-D-Glu). The biodistribution (BD) from each was studied and a multi-compartment pharmacokinetic (PK) model was developed to describe drug distribution rates.

Methods: Two groups of 16 SCID mice bearing high MC1R expressing tumors were intravenously injected with Ahx or di-D-Glu. After injection, 4 groups (n=4) were euthanized at 24, 96, 144 and 288 hour time points for each cohort. Tumors and 13 other organs were harvested at each time point. Isomeric gamma spectra were measured in tissue samples using a scintillation gamma detector and converted to alpha activity using factors for gamma ray abundance per alpha decay. Time activity curves were calculated for each organ. A 5-compartment PK model was built with the following: blood, tumor, normal tissue, kidney liver. This model is characterized by a system of 5 ordinary differential equations using mass action kinetics which describe uptake, inter-compartmental transitions and clearance rates. The ODE’s were simultaneously solved and fit to experimental data using a genetic algorithm for optimization.

Results: BD data shows that both compounds have minimal distribution to organs at risk other than kidney and liver. The PK parameter estimates had less than 5% error. From these data, the Ahx showed larger and faster uptake in the liver. Both compounds had comparable uptake and clearance rates for other compartments.

Conclusion: BD and PK behavior for two targeted radiopharmaceuticals were investigated. The PK model fit the experimental data and provided insight into the kinetics of the compounds systematically.

Funding Support, Disclosures, and Conflict of Interest: Funding: Melanoma Research Alliance Team Science Award, NIH/NCI SBIR Phase I, NIH/NCI P50, Moffitt Skin SPORE Career enhancement Program, Moffitt Imaging and Technology COE funds. Disclosures and Conflict of Interest: This work has been performed in part, in collaboration with Modulation Therapeutics Inc


Targeted Radiotherapy, Alpha-particles, Pharmacokinetic Modeling


IM/TH- Radiopharmaceutical therapy: Pharmacokinetics

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