Prostate-specific membrane antigen (PSMA) is overexpressed in most prostate adenocarcinoma (AdPC) cells and acts as a target for molecular imaging. However, some case reports indicate that PSMA-targeted imaging could be ineffectual for delineation of neuroendocrine (NE) prostate cancer (NEPC) lesions due to the suppression of the PSMA gene (FOLH1). These same reports suggest that targeting somatostatin receptor type 2 (SSTR2) could be an alternative diagnostic target for NEPC patients. This study evaluates the correlation between expression of FOLH1, NEPC marker genes and SSTR2. We evaluated the transcript abundance for FOLH1 and SSTR2 genes as well as NE markers across 909 tumors. A significant suppression of FOLH1 in NEPC patient samples and AdPC samples with high expression of NE marker genes was observed. We also investigated protein alterations of PSMA and SSTR2 in an NE-induced cell line derived by hormone depletion and lineage plasticity by loss of p53. PSMA is suppressed following NE induction and cellular plasticity in p53-deficient NEPC model. The PSMA-suppressed cells have more colony formation ability and resistance to enzalutamide treatment. Conversely, SSTR2 was only elevated following hormone depletion. In 18 NEPC patient-derived xenograft (PDX) models we find a significant suppression of FOLH1 and amplification of SSTR2 expression. Due to the observed FOLH1-supressed signature of NEPC, this study cautions on the reliability of using PMSA as a target for molecular imaging of NEPC. The observed elevation of SSTR2 in NEPC supports the possible ability of SSTR2-targeted imaging for follow-up imaging of low PSMA patients and monitoring for NEPC development.
Table S1. Sequence of primers used for RT-PCR studies.
Table S2. The numbers of patients with amplification of genes of interests based on level of FOLH1 gene expression.
Table S3. An overview of Pearson correlations between FOLH1 and other studied genes and calculated confidence interval parameters.
Fig. (S1). The evaluation of PSMA levels in different human organs. The level of PSMA in a variety of human organs in (a) mRNA and (b) protein level from version 18, Human Protein Atlas (HPA) (https://www.proteinatlas.org/ENSG00000086205-FOLH1/tissue).
Fig. (S2). (a) Alteration of FOLH1 in a variety of cancers from cBioPortal dataset (Gao et al. 2013) (b, c) Survival rate of patients with low vs high PSMA gene expression among patients of (b) Cambridge (Ross-Adams et al. 2015) and (c) MSKCC (Taylor et al. 2010) datasets.
Fig. (S3). Correlative analysis of FOLH1 with AR and AR-targeted genes. The heatmap plot of the mean expression levels of FOLH1, NE genes AR and AR-target genes expression among patients of Cambridge (Ross-Adams et al. 2015) and MSKCC (Taylor et al. 2010) datasets.
Fig. (S4). The probability of freedom from biochemical recurrence of prostate cancer patients grouped according to the gene expression levels. Kaplan Meier survival curves for high and low expression levels of (a) KLK3 (b) ENO2 (c) CHGA (d) NCAM1 (e) SYP (f) SRRM4 (g) REST (h) SSTR2 genes generated by Cambridge dataset (Ross-Adams et al. 2015).
Fig. (S5). The evaluation of PSMA levels. IHC images of PSMA protein expression staining in different stages of AdPC. Image available from version 18, Human Protein Atlas (HPA) (https://www.proteinatlas.org/ENSG00000086205-FOLH1/pathology).
Fig. (S6). A schematic of two possible scenarios for a patient with a suppressed PSMA radio-ligand uptake after ARPI. (a) Delineation tumor and metastatic lesions by PSMA radio-ligand before ARPI. (b) Ideal response to therapy and disappearance of the malignancy (High uptake of PSMA-radioligand and no/low DOTATATE-radioligand uptake). (c) Development of NECP with a suppressed PSMA expression level (No/low PSMA-radioligand uptake and high uptake for DOTATATE-radioligand). Some elements of this figure were produced using Servier Medical Art image bank (www.servier.com).