Theranostic 64Cu-DOTHA2-PSMA allows low toxicity radioligand therapy in mice prostate cancer model

Abstract

Introduction: We have previously shown that copper-64 (⁶⁴Cu)-DOTHA₂-PSMA can be used for positron emission tomography (PET) imaging of prostate cancer. Owing to the long-lasting, high tumoral uptake of ⁶⁴Cu-DOTHA₂-PSMA, the objective of the current study was to evaluate the therapeutic potential of ⁶⁴Cu-DOTHA₂-PSMA in vivo.

Methods: LNCaP tumor-bearing NOD-Rag1^nullIL2rg^null (NRG) mice were treated with an intraveinous single-dose of ⁶⁴Cu-DOTHA₂-PSMA at maximal tolerated injected activity, ^natCu-DOTHA₂-PSMA at equimolar amount (control) or lutetium-177 (¹⁷⁷Lu)-PSMA-617 at 120 MBq to assess their impact on survival. Weight, well-being and tumor size were followed until mice reached 62 days post-injection or ethical limits. Toxicity was assessed through weight, red blood cells (RBCs) counts, pathology and dosimetry calculations.

Results: Survival was longer with ⁶⁴Cu-DOTHA₂-PSMA than with ^natCu-DOTHA₂-PSMA (p < 0.001). Likewise, survival was also longer when compared to ¹⁷⁷Lu-PSMA-617, although it did not reach statistical significance (p = 0.09). RBCs counts remained within normal range for the ⁶⁴Cu-DOTHA₂-PSMA group. ⁶⁴Cu-DOTHA₂-PSMA treated mice showed non-pathological fibrosis and no other signs of radiation injury. Human extrapolation of dosimetry yielded an effective dose of 3.14 × 10^-2 mSv/MBq, with highest organs doses to gastrointestinal tract and liver.

Discussion: Collectively, our data showed that ⁶⁴Cu-DOTHA₂-PSMA-directed radioligand therapy was effective for the treatment of LNCaP tumor-bearing NRG mice with acceptable toxicity and dosimetry. The main potential challenge is the hepatic and gastrointestinal irradiation.

Keywords: DOTHA2-PSMA; copper-64; prostate cancer; radioligand therapy; theranostic.

Figure 1

Structure of ⁶⁴Cu-DOTHA₂-PSMA.

Figure 2

⁶⁴Cu-DOTHA₂-PSMA maximal tolerated IA experiment mice follow-up, weight (w) follow-up. (w_i: initial weight).

Figure 3

Survival assays results (A) Kaplan-Meier survival curves with significantly longer survival with ⁶⁴Cu-DOTHA₂-PSMA than with ^natCu-DOTHA₂-PSMA (p < 0.001, hazard ratio: 0.208 (95%CI: 0.0646 – 0.670) and no significant difference between ⁶⁴Cu-DOTHA₂-PSMA and ¹⁷⁷Lu-PSMA-617 (p = 0.09, hazard ratio: 0.490 (95%CI: 0.165 – 1.45)), (B) Average weight evolution per group, (C) Average tumor size per group, (D-F) Individual tumor size for ⁶⁴Cu-DOTHA₂-PSMA, ¹⁷⁷Lu-PSMA-617 and ^natCu-DOTHA₂-PSMA treated mice, respectively, (G) Time-to-regrowth (TTR) per group, (H) Time to initial volume (TTIV) per group. (V: tumoral volume, V_i: initial tumoral volume. **p < 0.01, ***p < 0.001. Errors bars are standard errors for (A) and standard deviations for B, C and G).

Figure 4

Pathology analysis results from controls, non-treated mice (left colum) in comparison to ⁶⁴Cu-DOTHA₂-PSMA treated mice (middle and right columns): Normal kidney histology was mainly found in controls (A) and treated mice (B), with frequent non-pathological perivascular fibrosis (C) and rare, locally limited interstitial fibrosis (D). Liver analysis also showed normal, non-injured tissue in controls (E) and treated mice (F) with some periportal fibrosis (G). All salivary glands displayed non-pathological, expected fibrosis surrounding vessels and excretory duct and in septa in controls (H) and treated mice (I, J). For LNCaP tumors, controls mainly showed alive tumor bulk, with fibrosis and infrequent necrosis (K). In opposite, the irradiated tumors showed a lower proportion of alive cells and more necrosis (L, M). Fibrosis scores by organs are presented in N and the proportion of alive tumor cells over total tumor tissue is presented in O. Stained by Masson’s trichome. Fibrosis: blue staining, arrow when needed. Necrosis in the tumor: lighter pink, asterix. In graphs, only significatively different relations are shown. *p < 0.05. **p< 0.01. ***p < 0.001.