Copper-64 Chloride Exhibits Therapeutic Potential in Three-Dimensional Cellular Models of Prostate Cancer.

Catarina I G Pinto,Cláudia L Da Silva,Alexandra Fonseca,Sara Bucar,Joana F Guerreiro,Filipa Mendes,Antero J Abrunhosa,Vítor Alves

doi:10.3389/fmolb.2020.609172

Abstract

Prostate cancer (PCa) is the second most common cancer type in men, and in advanced metastatic stages is considerable incurable. This justifies the need for efficient early diagnostic methods and novel therapies, particularly radiopharmaceuticals with the potential for simultaneous diagnosis and therapy (theranostics). We have previously demonstrated, using monolayer-cultured cells, that copper-64 chloride, a promising theranostic agent for PCa, has the potential to induce significant damage in cancer cells while having minimal side effects in healthy tissues. Here, we further explored this compound for its theranostic applications using more advanced PCa cellular models, specifically multicellular spheroids. Namely, we evaluated the cellular uptake of 64CuCl2 in three human PCa spheroids (derived from 22RV1, DU145, and LNCaP cells), and characterized the growth profile and viability of those spheroids as well as the clonogenic capacity of spheroid-derived cells after exposure to 64CuCl2. Furthermore, the populations of cancer stem cells (CSCs), known to be important for cancer resistance and recurrence, present in the spheroid models were also evaluated using two different markers (CD44 and CD117). 64CuCl2 was found to have significant detrimental effects in spheroids and spheroid-derived cells, being able to reduce their growth and impair the viability and reproductive ability of spheroids from both castration-resistant (22RV1 and DU145) and hormone-naïve PCa (LNCaP). Interestingly, resistance to 64CuCl2 treatment seemed to be related with the presence of a CSC population, since the most resistant spheroids, derived from the DU145 cell line, had the highest initial percentage of CSCs among the three cell lines under study. Altogether, these results clearly highlight the theranostic potential of 64CuCl2.

Highlights

Prostate cancer (PCa)’s global incidence has been increasing over time, in Asia, and Northern and Western Europe (Teoh et al, 2019), where it remains the second most common cancer type in men, posing a significant burden to healthcare systems (Bray et al, 2018; Teoh et al, 2019)
While 22RV1 and LNCaP spheroids grew in size throughout time, DU145 spheroids exhibited an initial decrease in size that stabilized at around the 5th day of growth (Figure 1B)
Given that cancer stem cells (CSCs) are known to be involved in treatment failure and cancer relapse (Ishiguro et al, 2017), we tried to understand if the 3D cellular model used harbored an enriched population of CSCs

Summary

Introduction

Prostate cancer (PCa)’s global incidence has been increasing over time, in Asia, and Northern and Western Europe (Teoh et al, 2019), where it remains the second most common cancer type in men, posing a significant burden to healthcare systems (Bray et al, 2018; Teoh et al, 2019). Copper is known to play important roles in cancer development and growth, having been shown to accumulate in several cancer types, including PCa (Gutfilen et al, 2018) This presents an opportunity that can be explored for cancer imaging and diagnosis through the use of medical radioisotopes of copper, of which 64Cu has been under the spotlight in recent years due to its many favorable characteristics (Boschi et al, 2018). Clinical studies in humans have already been performed to investigate 64Cu biodistribution, dosimetry and lesion kinetics in patients with biochemical relapse of PCa, demonstrating 64CuCl2 effectiveness on the detection of local recurrence and bone and lymph nodes metastasis (Piccardo et al, 2018) This simplest form of 64Cu, which doesn’t require complexation with targeting ligands, is neither excreted via the urinary tract nor accumulated in the bladder, having a favorable biodistribution for detection of prostate tumors (Paparo et al, 2020). This could be explained by a deficient DNA-damage repair in PCa cells, which was in contrast with the non-tumor cells that were found to be able to efficiently repair the lesions induced by the radionuclide (Guerreiro et al, 2018)

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