The prostate-specific membrane antigen holds potential as a vascular target for endogenous radiotherapy with [177Lu]Lu-PSMA-I&T for triple-negative breast cancer

Abstract

Introduction: Overexpression of prostate-specific membrane antigen (PSMA) on the vasculature of triple-negative breast cancer (TNBC) presents a promising avenue for targeted endogenous radiotherapy with [¹⁷⁷Lu]Lu-PSMA-I&T. This study aimed to assess and compare the therapeutic efficacy of a single dose with a fractionated dose of [¹⁷⁷Lu]Lu-PSMA-I&T in an orthotopic model of TNBC.

Methods: Rj:NMRI-Foxn1^nu/nu mice were used as recipients of MDA-MB-231 xenografts. The single dose group was treated with 1 × 60 ± 5 MBq dose of [¹⁷⁷Lu]Lu-PSMA-I&T, while the fractionated dose group received 4 × a 15 ± 2 MBq dose of [¹⁷⁷Lu]Lu-PSMA-I&T at 7 day intervals. The control group received 0.9% NaCl. Tumor progression was monitored using [¹⁸F]FDG-PET/CT. Ex vivo analysis encompassed immunostaining, TUNEL staining, H&E staining, microautoradiography, and autoradiography.

Results: Tumor volumes were significantly smaller in the single dose (p < 0.001) and fractionated dose (p < 0.001) groups. Tumor growth inhibition rates were 38% (single dose) and 30% (fractionated dose). Median survival was notably prolonged in the treated groups compared to the control groups (31d, 28d and 19d for single dose, fractionated dose and control, respectively). [¹⁷⁷Lu]Lu-PSMA-I&T decreased the size of viable tumor areas. We further demonstrated, that [¹⁷⁷Lu]Lu-PSMA-I&T binds specifically to the tumor-associated vasculature.

Conclusion: This study highlights the potential of [¹⁷⁷Lu]Lu-PSMA-I&T for endogenous radiotherapy of TNBC.

Keywords: Anti-angiogenic therapy; Endogenous radiotherapy; Orthotopic xenograft; Prostate-specific membrane antigen; Triple-negative breast cancer.

Fig. 1

A Schematic therapy regime of single dose (pink) and fractionated dose (violet) of [¹⁷⁷Lu]Lu-PSMA-I&T. Tumor growth was monitored weekly via [¹⁸F]FDG-PET/CT (blue arrows). Day 0 marks the start of the treatment. B Tumor growth curve in control (gray), single dose (pink) and fractionated dose therapy (violet) animals (n ≥ 5); ** p = 0.002, *** p < 0.001). C Waterfall plot analysis of tumor volumes on the day of finalization. Volumetric differences were significant for the single dose (** p = 0.003) and fractionated dose (** p = 0.001) treated animals when compared to the control group

Fig. 2

A Tumor growth analysis comparing the time period (in days) until reaching 200% of the initial tumor volume (TV) in control and therapy receiving groups (n ≥ 5); ** p = 0.008). B Kaplan–Meier survival of single dose and fractionated dose group compared to the control

Fig. 3

Representative PET/CT images of [¹⁸F]FDG distribution 30 min post injection in control (A–D), single dose (E–H), and fractionated dose (I–L) group before (− 1d) and 6 or 27 d after therapy. Colored images represent PET/CT images with a SUV_max of 2.6 and HU range from − 1000 to 1000. Black and white images represent PET with a SUV_max of 2.6

Fig. 4

TUNEL staining (green) of tumor and organs of control (A, D, G, J, M, P), single dose (B, E, H, K, N, R, Q) and fractionated dose group (C, F, I, L, O, R). Nuclei were counterstained with DAPI (blue). The staining solution without enzyme served as negative control (S–U). Scale bar: 100 µm

Fig. 5

Microscopic evaluation of HIF1α (red) expression in tumor tissue from control (A, D), single dose therapy (B, E), and fractionated dose therapy (C, F) animals. Nuclei were counterstained with DAPI (blue). The black box inside the schematic tumor tissue illustrates the location of interest. Scale bar: 50 µm

Fig. 6

Evaluation of PSMA expression in TNBC tumors using [¹⁷⁷Lu]Lu-PSMA-I&T AURA (A–C; zoom-in: D–F) with corresponding H&E staining (G–I); and [¹⁷⁷Lu]Lu-PSMA-I&T mAURA (J–L) with corresponding PSMA/CD31 immunofluorescence staining analysis (M–R). Scale bars: A–C & G–I: 4 mm, J–L: 20 µm; M–O: 50 µm; P–R: 100 µm