Neuroendocrine prostate cancer xenografts with large-cell and small-cell features derived from a single patient's tumor: morphological, immunohistochemical, and gene expression profiles

Abstract

Background: Small-cell carcinoma (SCC) of the prostate is an AR-negative variant of prostate cancer found at progression in 10-20% of castrate-resistant disease. Its finding predicts a distinct clinical course and a poor prognosis. Large-cell neuroendocrine carcinoma (LCNEC) is a much rarer variant that behaves similarly to SCC. The biological mechanisms that drive these disease variants are poorly understood.

Methods: Eight tumor fragments from the salvage pelvic exenteration specimen of a patient with castrate-resistant prostate carcinoma were subcutaneously implanted into 6- to 8-week-old male CB17 SCID mice. Serial tissue sections and tissue microarrays of the resulting MDA PCa 144 xenograft lines were used for histopathologic and immunohistochemical characterization of the xenografts and their tissue of origin. RNA from two representative xenograft sublines was used for gene-expression profiling.

Results: All eight fragments formed tumors: four of the MDA PCa 144 xenograft sublines had morphologic characteristics of SCC and four, of LCNEC. All retained high fidelity to their parent tumor tissue, which remained stable through serial passages. Morphological transitions in the specimen of origin suggested LCNEC represents an intermediate step between adenocarcinoma and SCC. Over 2,500 genes were differentially expressed between the SCC (MDA PCa 144-13) and the LCNEC (MDA PCa 144-4) sublines and enriched in "Nervous System Development" Gene Ontology subtree.

Conclusion: The eight xenograft models described represent the spectrum of neuroendocrine carcinomas in prostate cancer and will be valuable preclinical tools to study the pathogenesis of and therapy targets for this increasingly recognized subset of lethal prostate cancer.

Fig. 1

Representative images of the human specimen of origin of the MDA PCa 144 xenografts. A and B photomicrographs show a gradual transition from small-cell carcinoma (SCC) to large-cell neuroendocrine carcinoma (LCNEC). C is a high magnification photomicrograph of the small cell component. Synaptophysin (syn) is expressed diffusely in SCC and LCNEC cells (D) whereas androgen receptor (AR) is expressed only rarely (E). Ki67 is highly expressed in the cells of the neuroendocrine components of the tumor (F). Gradual transition of adenocarcinoma to LCNEC is shown in G, H and I. In I a higher magnification of the adenocarcinoma (arrow) and the LCNEC (star) cells is shown. LCNEC cells express synaptophysin (J), are negative for AR (K), and have a high Ki67 index (L), whereas the opposite is true for the adenocarcinoma cells shown in the same photomicrographs. Original magnification of A, G, × 100; B, D–F, H, J-L, × 200, C, I × 400.

Fig. 2

Representative images of the MDA PCa 144 xenograft. (A–E) MDA PCa 144-4 xenograft. The tumor is composed of large cells with a nested arrangement (A,B). The tumor cells express cytokeratin (CK) (C), synaptophysin (syn) (D), and Ki67 diffusely (E). (F–J) MDA PCa 144-13 xenograft. The tumor is composed of small hyperchromatic cells (F, G) and expresses cytokeratin in a dot-like pattern (H). High expression of synaptophysin (I) and Ki67 (J) is noted (original magnification, A, C-F, H-J, × 200, B, G, × 400.

Fig. 3

Reverse-transcriptase polymerase chain reaction analysis validation of gene-expression array results for MDA PCa 144-13 and MDA PCa 144-4 sublines. Data for the listed transcription factors and protein tyrosine phosphatase receptor type Z (PTPRZ1), a potential target for therapy, are expressed as mean relative mRNA level to GAPDH (× 10⁻⁴) ± standard deviation. Similar results were obtained using β-actin gene as a reference (data not shown). (*Standard deviation of PTPRZ1 in 144-4 is greater than mean value.)

Fig. 4

Photomicrographs illustrate immunohistochemical validation of gene-expression array results for the transcription factor SOX-9 (A-D) and the protein tyrosine phosphatase receptor type Z (PTPRZ1) (E-H), a potential target for therapy. High expression of SOX-9 is noted in the large-cell neuroendocrine carcinoma (LCNEC) (A, inset in A) and the adenocarcinoma (arrow in A) components of the donor tumor and the MDA PCa 144-4 xenograft (B), whereas low expression is noted in the small-cell carcinoma (SCC) component of both the donor tumor (C) and the MDA PCa 144-13 xenograft (D). PTPRZ expression is low in the adenocarcinoma component (arrow in E) and moderate in the LCNEC component of the donor tumor (E, inset in E) and the 144-4 xenograft (F) but is high in the SCC component of the donor tumor (G) and the 144-13 xenograft (H). (Original magnification of A, E, × 100; inset boxes in A and E, BD, F-H × 200).