Abstract 5344: Treatment efficacy of 212Pb-RM2 targeted alpha therapy in human prostate cancer cell lines: An in vitro investigation
Authors: Rold Tammy L. , Okoye Nkemakonam C. , Quinn Thomas P. , Hoffman Timothy J. 
Published: September 2020

Introduction: Receptor targeted alpha therapy (TAT) has garnered attention with isotopes such as Pb-212, Bi-213, and Ac-225 due to the receptor specific and potentially lethal damage caused by the in vivo alpha decay of these isotopes when linked to small peptides. We are investigating Pb-212-RM2, a BB2 receptor (BB2r) antagonist as a potential TAT agent for use in BB2r positive prostate cancer. This in vitro study evaluates Pb-212-RM2 at 3 dose levels in a panel of human prostate cancer cell lines assessing cell viability (MTT), DNA damage (53BP1), and clonogenic potential.

Methods: Pb-212-RM2 was evaluated in the PC3, LNCAP, C42, C42B, DU-145, VCAP, and 22Rv1 human prostate cancer cell lines. Cells were plated the day before treatment. Pb-212-RM2 was prepared using an automated radiosynthesizer and QC was performed by HPLC. Cells were exposed to 3, 6, 13, or 25uCi/mL of Pb-212 RM2. Cell viability was evaluated at 24, 48, 72, 96, 120, and 144hrs after treatment. DNA damage was evaluated at 24hrs post treatment using the 53BP1 marker. Media in clonogenic plates was refreshed every 5-7 days until colonies of ≥50 cells were present. All assays were conducted in triplicate on different days.

Results: LNCAP, C42, 22Rv1, and C42B cell lines were ≤50% viable at all dose levels by 72hrs. PC3 and DU-145 did not show a decrease to 50% viability until 96-144hrs post administration. At 144hrs post treatment, only the 25uCi/mL treated VCAP cells showed less than 50% viability (43.9%±4.1%). Observed DNA damage was highest in the PC3 and LNCAP cell lines with a range of 5.4±0.7 to 26.6±1.7 and 2.4±0.5 to 19.7±1.2 avg 53BP1 foci/cell at 3 and 25uCi/mL, respectively. Clonogenic potential was lowest in PC3 and LNCAP lines with &lt;20% surviving fraction (SF) at 3uCi/mL and decreasing to &lt;5% SF at 6uCi/mL. DU-145, C42B, 22Rv1, and C42 showed a SF of 71.4±11.8%, 57.1±8.8%, 55.5±2.8%, and 41.5±6.5% at 3uCi/mL.

Conclusions: Targeted alpha therapy (TAT), in the form of 212Pb-RM2, was evaluated in the PC3, LNCAP, C42, C42B, DU-145, VCAP, and 22Rv1 human prostate cancer cell lines representing the spectrum of human prostate cancer in relation to androgen dependence and sensitivity. At dose levels of 3, 6, 13, or 25uCi/mL, treatment response does not appear to be related to androgen dependence or sensitivity. Cell viability decreased with increasing time and dose level in all cell lines treated with 212Pb-RM2. The VCAP cell line demonstrated the most resistance to Pb-212-TAT. DNA damage, using the 53BP1 marker, was highest in the PC3 and LNCAP cell lines. As expected, this sensitivity was also demonstrated in clonogenic response with the PC3 and LNCAP cell lines exhibiting the lowest surviving fraction. These studies provide the foundation for further exploration of the therapeutic efficacy of 212Pb-RM2 for the treatment of BB2r positive prostate cancer. This work was supported by USVA IK6BX004856, USVA IO1BX001699, and NCI RO1CA222293.

Citation Format: Tammy L. Rold, Nkemakonam C. Okoye, Thomas P. Quinn, Timothy J. Hoffman. Treatment efficacy of 212Pb-RM2 targeted alpha therapy in human prostate cancer cell lines: An in vitro investigation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5344.