14C]Fluciclovine (alias anti-[14C]FACBC) uptake and ASCT2 expression in castration-resistant prostate cancer cells

Abstract

Introductiontrans-1-Amino-3-[18F]fluorocyclobutanecarboxylic acid ([18F]fluciclovine, also known as anti-[18F]FACBC), is a tracer for positron emission tomography (PET) imaging for detection of tumors such as prostate cancer (PCa). Our previous study showed that ASCT2 (Na+-dependent amino acid transporter (AAT)) mediates fluciclovine uptake in androgen-dependent PCa cells; its expression is influenced by androgen, a key hormone in the progression of primary PCa and castration-resistant prostate cancer (CRPC). In this study, we investigated the uptake mechanisms and feasibility of [18F]fluciclovine for CRPC in the androgen-dependent PCa cell line LNCaP and LNCaP-derivatives LNCaP-SF and LN-REC4. MethodsLNCaP-SF was established after long-term cultivation of LNCaP in steroid-free conditions, and LN-Pre and LN-REC4 were established from LNCaP inoculated in intact and castrated severe combined immunodeficient mice, respectively. Uptake and competitive inhibition experiments were performed with trans-1-amino-3-fluoro[1-14C]cyclobutanecarboxylic acid ([14C]fluciclovine) to characterize the involvement of AATs in androgen-dependent PCa (LNCaP and LN-Pre) and CRPC-like (LNCaP-SF and LN-REC4) cell lines. AAT expression was analyzed by Western blotting, and [14C]fluciclovine uptake in androgen-dependent PCa and CRPC-like cell lines were investigated in the presence or absence of dihydrotestosterone (DHT). ResultsThe contribution of Na+-dependent AATs to [14C]fluciclovine uptake in all cell lines was 88−98%, and [14C]fluciclovine uptake was strongly inhibited by l-glutamine and l-serine, the substrates for Na+-dependent alanine-serine-cysteine (system ASC) AATs, in the presence of Na+. DHT enhanced ASCT2 expression in LNCaP, LN-Pre, and LN-REC4, but not in LNCaP-SF, and the responses of ASCT2 expression to DHT correlated with [14C]fluciclovine uptake. ConclusionsSystem ASC, especially ASCT2, could play a major role in [14C]fluciclovine uptake into CRPC-like and androgen-dependent PCa cells, suggesting [18F]fluciclovine-PET is applicable to the detection of CRPC as well as androgen-dependent PCa. Advance in knowledge[18F]fluciclovine-PET may be applied for the detection of CRPC. Implication for patient care[18F]fluciclovine-PET may permit early intervention for CRPC treatment.