Kinetics of Neuroendocrine Differentiation in an Androgen-Dependent Human Prostate Xenograft Model

Abstract

It was previously shown in the PC-295 xenograft that the number of chromogranin A (CgA)-positive neuroendocrine (NE) cells increased after androgen withdrawal. NE cells did not proliferate and differentiated from G 0 -phase-arrested cells.Here we further characterized NE differentiation , androgen receptor status, and apoptosis-associated Bcl-2 expression in the PC-295 model after androgen withdrawal to assess the origin of NE cells. PC-295 tumor volumes decreased by 50% in 4 days. Intraperitoneal bromodeoxyuridine (BrdU) incorporation and MIB-1 labeling decreased to 0% , and the apoptosis was maximal at day 4. Androgen receptor expression and prostate-specific antigen (PSA) serum levels decreased rapidly within 2 days. The number of NE cells increased 6-fold at day 4 and 30-fold at day 7. Five and ten percent of the CgApositive cells were BrdU positive after continuous BrdU labeling for 2 and 4 days , respectively. However , no MIB-1 expression was observed in CgA-positive cells. NE cells expressed the regulated secretory pathway marker secretogranin III but were negative for androgen receptor and Bcl-2. Bcl-2 expression did increase in the non-NE tumor cells. In conclusion, androgen withdrawal leads to a rapid PC-295 tumor regression and a proliferation-independent induction of NE differentiation. The strictly androgen-independent NE cells that were still present after 21 days differentiated mainly from G 0 -phase-arrested cells. 2-8 These cells produce various growth-modulating neuropeptides in a paracrine or autocrine way. -15Possible roles for NE cells in the prostate may be regulation of homeostasis and secretion of prostatic fluid, either actively or passively. NE cells can be identified by routine electron microscopy (dense core granules) or by immunohistochemistry with specific antibodies against secreted products, for example, serotonin, 16 or secretion-associated proteins, such as chromogranin A (CgA), [17][18][19] which is a marker for neuroendocrine differentiation. NE cells are considered to be nonproliferating cells and do not express the androgen receptor 20 and are therefore probably unaffected by androgen deprivation. Consequently, they will not undergo apoptosis under such circumstances. Therefore, it is relevant to assess whether or not CgA-positive cells co-express the antiapoptotic oncogene Bcl-2. 21 Moreover, NE cells show a heterogeneous cytokeratin expression pattern as there are basal, luminal, and intermediate NE cell types 16,22,23 and are often found near Bcl-2-positive prostate cancer cells. 24,25The single expression of CgA is not the only requisite for the determination of NE differentiated cells as there exists a regulated secretory pathway (RSP) in NE cells 26 next to the lysosomal and an exocrine constitutive pathway. Along the RSP pathway, secretion and processing of bioactive neuropeptides and growth hormones, such as insulin and glucagon in the pancreas, 27,28 are regulated. The RSP consists of a sequence of processes linked from transcription/translation of various factors ...

Peptidylglycine ?-amidating monooxygenase- and proadrenomedullin-derived peptide-associated neuroendocrine differentiation are induced by androgen deprivation in the neoplastic prostate

“…This can be related to the variability found in the clinical specimens as well as each of the models originated from a different patient. During androgen-deprivation experiments, the PC-295 and PC-310 models exhibited tumor regression 21,22 but PC-310 tumors survived as dormant residues for at least 5 months. PC-295 tumor epithelium regressed completely in a short period after androgen ablation.…”

“…27 These androgen-dependent models exhibit significantly increased NE differentiation after androgen ablation. 21,22 Small pieces of tumor were heterotransplanted in NMRI athymic nude mice by s.c. implantation. Mice (Harlan, Indianapolis, IN) were androgen-supplemented through silicone (Silastic) implants containing testosterone (Sigma, St. Louis, MO).…”

“…19,20 PAM mRNA has been detected in rat prostate and human prostatic xenografts. 21,22 Although PAM is expressed by many NE cells, this enzyme cannot be considered a general NE marker as it is not present in every cell from the diffuse NE system. 23 PC is androgen-dependent in early stages but usually relapses to an androgen-insensitive state after androgen-withdrawal therapy, 24 which implies more aggressive tumors and a poor prognosis for the patient.…”

A Prominent Couple

“…INSM1-mediated cell cycle arrest was suggested to facilitate entry into a NE differentiation route [83,84]. NE cancer cells have been considered as non-proliferative, postmitotic cells located adjacent to proliferative Bcl-2-positive cells [13,85]. NED areas exhibited the highest proliferation index across tumor tissue and the extent of NED correlated with a higher proliferation index of the whole tumor [86,87].…”

“…NEPC can arise de novo, however, it is more prevalent in previously treated adenocarcinomas. There is a growing body of evidence that the extent of neuroendocrine differentiation (NED) correlates with exposure to ADT and represents an adaptive clinical phenotype, which is of special significance regarding the advent of novel highly potent AR-targeted therapies [75,[77][78][79][80][81][82][83][84][85][86]. Androgen-deprived culture conditions were shown to induce a neuronal morphology and expression of NSE and CHGA in LNCaP cells [87].…”