Investigating PSMA-targeted radioligand therapy efficacy as a function of cellular PSMA levels and intratumoral PSMA heterogeneity
Clinical Cancer Research, 2020•AACR
Purpose: Prostate-specific membrane antigen (PSMA) targeting radioligands deliver
radiation to PSMA-expressing cells. However, the relationship between PSMA levels and
intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand
therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell,
and the fraction of PSMA+ cells in a tumor. Experimental Design: RM1 cells expressing
different levels of PSMA (PSMA−, PSMA+, PSMA++, PSMA+++; study 1) or a mix of PSMA+ …
radiation to PSMA-expressing cells. However, the relationship between PSMA levels and
intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand
therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell,
and the fraction of PSMA+ cells in a tumor. Experimental Design: RM1 cells expressing
different levels of PSMA (PSMA−, PSMA+, PSMA++, PSMA+++; study 1) or a mix of PSMA+ …
Purpose
Prostate-specific membrane antigen (PSMA) targeting radioligands deliver radiation to PSMA-expressing cells. However, the relationship between PSMA levels and intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell, and the fraction of PSMA+ cells in a tumor.
Experimental Design
RM1 cells expressing different levels of PSMA (PSMA−, PSMA+, PSMA++, PSMA+++; study 1) or a mix of PSMA+ and PSMA− RM1 (study 2, 4) or PC-3/PC-3-PIP (study 3) cells at various ratios were injected into mice. Mice received 177Lu- (studies 1–3) or 225Ac- (study 4) PSMA617. Tumor growth was monitored. Two days post-RLT, tumors were resected in a subset of mice. Radioligand uptake and DNA damage were quantified.
Results
177Lu-PSMA617 efficacy increased with increasing PSMA levels (study 1) and fractions of PSMA positive cells (studies 2, 3) in both, the RM1 and PC-3-PIP models. In tumors resected 2 days post-RLT, PSMA expression correlated with 177Lu-PSMA617 uptake and the degree of DNA damage. Compared with 177Lu-PSMA617, 225Ac-PSMA617 improved overall antitumor effectiveness and tended to enhance the differences in therapeutic efficacy between experimental groups.
Conclusions
In the current models, both the degree of PSMA expression and the fraction of PSMA+ cells correlate with 177Lu-/225Ac-PSMA617 tumor uptake and DNA damage, and thus, RLT efficacy. Low or heterogeneous PSMA expression represents a resistance mechanism to RLT.
See related commentary by Ravi Kumar and Hofman, p. 2774
AACR