Modeling a lethal prostate cancer variant with small-cell carcinoma features

Abstract

Purpose: Small-cell prostate carcinoma (SCPC) morphology predicts for a distinct clinical behavior, resistance to androgen ablation, and frequent but short responses to chemotherapy. We sought to develop model systems that reflect human SCPC and can improve our understanding of its biology.

Experimental design: We developed a set of castration-resistant prostate carcinomas xenografts and examined their fidelity to their human tumors of origin. We compared the expression and genomic profiles of SCPC and large-cell neuroendocrine carcinoma (LCNEC) xenografts to those of typical prostate adenocarcinoma xenografts. Results were validated immunohistochemically in a panel of 60 human tumors.

Results: The reported SCPC and LCNEC xenografts retain high fidelity to their human tumors of origin and are characterized by a marked upregulation of UBE2C and other mitotic genes in the absence of androgen receptor (AR), retinoblastoma (RB1), and cyclin D1 (CCND1) expression. We confirmed these findings in a panel of samples of CRPC patients. In addition, array comparative genomic hybridization of the xenografts showed that the SCPC/LCNEC tumors display more copy number variations than the adenocarcinoma counterparts. Amplification of the UBE2C locus and microdeletions of RB1 were present in a subset, but none displayed AR nor CCND1 deletions. The AR, RB1, and CCND1 promoters showed no CpG methylation in the SCPC xenografts.

Conclusion: Modeling human prostate carcinoma with xenografts allows in-depth and detailed studies of its underlying biology. The detailed clinical annotation of the donor tumors enables associations of anticipated relevance to be made. Future studies in the xenografts will address the functional significance of the findings.

Figure 1

A, Representative images of the xenografts and their donor tumors, with hematoxylin and eosin staining; the insets show IHC staining for AR. Note that the MDA PCa 146-10 donor tumor was mixed, containing adenocarcinoma (AdCa) and SCPC components. The inset shows that the AdCa component was AR⁺, whereas the SCPC component was AR^–. (Chr: chromogranin; Syn: synaptophysin. Original magnification of all images except 155-2, ×200, original magnification of 155-2 images, X100). B, mRNA levels of AR (exons 1 and 2), UBE2C, cyclin D1, and RB1 exons 2/3 in SCPC/LCNEC (gray bars, MDA PCa 144-4, 144-13, 146-10, and 155-2) and AdCa xenografts (black bars, MDA PCa 79, 117-9, 130, 170-4, and 180-30). C, Representative images of AR, UBE2C, cyclin D1, and RB immunostaining in SCPC/LCNEC and AdCa xenografts. Original magnification, ×200.

Figure 2

Results of aCGH analyses. A, Principal component analysis (PCA). B, Copy number variations (CNVs) in SCPC/LCNEC (blue) and adenocarcinoma (red) xenografts. C, aCGH of the UBE2C, CCND1, AR, and RB1 genetic loci (SCPC/LCNEC xenografts are shown in blue and adenocarcinoma xenografts in red)

Figure 3

A, Schematic representation of the RB mRNA and the primers used for the qRT-PCR and RT-PCR experiments. B, qRT-PCR results for RB1 exons (ex) 2/3, 18/19, 21/22, and 26/27. C, Upper panel, RT-PCR results for exons 17 through 27; lower panel, Western blotting results for AR and RB expression, in which the bands correspond to the molecular weight of the full-length proteins (SCPC, small cell prostate carcinoma; LCNEC, large cell neuroendocrine carcinoma; AdCa, adenocarcinoma)

Figure 4

UBE2C, cyclin D1, RB, and AR protein expression in clinical CRPC tissues with SCPC/LCNEC prostate carcinoma or adenocarcinoma (AdCa) morphology. A, Scatter plots of UBE2C, cyclin D1, RB, and AR expression in the clinical CRPC samples. B, Representative images of hematoxylin and eosin (H&E)–stained and UBE2C-, cyclin D1-, Rb-, and AR–stained sections from a mixed SCPC–AdCa tumor and a pure AdCa tumor. (CRPC: castrate-resistant prostate carcinoma; SCPC, small cell prostate carcinoma; LCNEC, large cell neuroendocrine carcinoma; Original magnification, ×200).