SOMATOSTATIN ANALOGUES AND ESTROGENS IN THE TREATMENT OF ANDROGEN ABLATION REFRACTORY PROSTATE ADENOCARCINOMA

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Clinical Efficacy of a Novel Therapeutic Principle, Anakoinosis

Classic tumor therapy, consisting of cytotoxic agents and/or targeted therapy, has not overcome therapeutic limitations like poor risk genetic parameters, genetic heterogeneity at different metastatic sites or the problem of undruggable targets. Here we summarize data and trials principally following a completely different treatment concept tackling systems biologic processes: the principle of communicative reprogramming of tumor tissues, i.e., anakoinosis (ancient greek for communication), aims at establishing novel communicative behavior of tumor tissue, the hosting organ and organism via re-modeling gene expression, thus recovering differentiation, and apoptosis competence leading to cancer control - in contrast to an immediate, "poisoning" with maximal tolerable doses of targeted or cytotoxic therapies. Therefore, we introduce the term "Master modulators" for drugs or drug combinations promoting evolutionary processes or regulating homeostatic pathways. These "master modulators" comprise a broad diversity of drugs, characterized by the capacity for reprogramming tumor tissues, i.e., transcriptional modulators, metronomic low-dose chemotherapy, epigenetically modifying agents, protein binding pro-anakoinotic drugs, such as COX-2 inhibitors, IMiDs etc., or for example differentiation inducing therapies. Data on 97 anakoinosis inducing schedules indicate a favorable toxicity profile: The combined administration of master modulators, frequently (with poor or no monoactivity) may even induce continuous complete remission in refractory metastatic neoplasia, irrespectively of the tumor type. That means recessive components of the tumor, successively developing during tumor ontogenesis, are accessible by regulatory active drug combinations in a therapeutically meaningful way. Drug selection is now dependent on situative systems characteristics, to less extent histology dependent. To sum up, anakoinosis represents a new substantive therapy principle besides novel targeted therapies.

Zoledronic acid but not somatostatin analogs exerts anti-tumor effects in a model of murine prostatic neuroendocrine carcinoma of the development of castration-resistant prostate cancer

BACKGROUND

Since neuroendocrine (NE) cells play an important role in the development of castration-resistant prostate cancer (CRPC), target therapy to NE cells should be considered for treating CRPC. We investigated the effects zoledronic acid (ZOL) and two somatostatin analogs (octreotide: SMS, and pasireotide: SOM) on an NE allograft (NE-10) and its cell line (NE-CS), which were established from the prostate of the LPB-Tag 12T-10 transgenic mouse.

METHODS

We examined the in vivo effects of ZOL, SMS and SOM as single agents and their combinations on subcutaneously inoculated NE-10 allografts and the in vitro effects on NE-CS cells. Apoptosis and cell cycle activity were assessed by immunohistochemistry using TdT-mediated dUTP-biotin nick-end labeling (TUNEL) and a Ki-67 antibody, respectively.

RESULTS

In vivo growth of NE-10 tumors treated with ZOL, ZOL plus SMS, or ZOL plus SOM was significantly inhibited compared to the control as a consequence of induction of apoptosis and cell cycle arrest. ZOL induced time- and dose-dependent inhibition of in vitro proliferation of NE-CS cells, but the somatostatin analogs (SMS and SOM) did not. ZOL also inhibited migration of NE-CS cells. These effects were caused by inhibition of Erk1/2 phosphorylation via impairment of prenylation of Ras.

CONCLUSIONS

ZOL, but not SMS or SOM, induced apoptosis and inhibition of proliferation and migration through impaired prenylation of Ras in NE carcinoma models. Our findings support the possibility that ZOL could be used in the early phase for controlling NE cells, which may trigger progression to CRPC.

Neuroendocrine differentiation in castration-resistant prostate cancer: a systematic diagnostic attempt

BACKGROUND

Assessing the neuroendocrine (NE) pattern in castration-resistant prostate cancer (CRPC) may prove useful in selecting potential responders to target therapies such as somatostatin analogues. The aim of this study was to define a panel of markers or examinations appropriate to characterize NE differentiation (NED).

METHODS

Forty-seven patients with CRPC underwent a systematic diagnostic attempt to characterize the NE phenotype using a plasma blood test for chromogranin A (CgA) and immunohistochemical staining of needle biopsy-obtained specimens (CgA, somatostatin receptor 2 [SSTR2], Ki-67, and androgen receptors). In a subgroup of 26 patients, somatostatin receptor scintigraphy using (111)In-DTPA-d-Phe octreotide (octreotide scintigraphy; Octreoscan, Covidien, Hazelwood, MO) was also performed.

RESULTS

NED was found in 85.1% of patients (if serum CgA, tissular CgA, and tissular SSTR2 were considered separately: 54%, 67%, and 58%, respectively). Only 15% of the 26-patient subgroup had an abnormal octreotide scintigraphy result. Although p-CgA and t-CgA were associated with more aggressive disease with a worse prognosis, patients with positive tissular SSTR2 staining had longer overall survival (OS).

CONCLUSION

This systematic approach to explore the NED in a quite homogeneous group of patients with CRPC seems reproducible and appropriate. Further investigations are required to validate this panel and better characterize potential responders to targeted therapy.

Somatostatin analog lanreotide in the treatment of castration-resistant prostate cancer (CRPC)

Prostate cancer is a common disease affecting males. Despite initial sensitivity to hormone treatment, prostate cancer eventually progresses to a castration-resistant stage (CRPC), which carries an ominous prognosis. Lanreotide is a long-acting somatostatin analog with the same properties with the native peptide. It has been shown to be highly efficacious in treating various hypersecretoty disorders and tumors. Lanreotide has been administered to patients with CRPC within a novel treatment concept, with the aim of targeting not only cancer cells but also various factors secreted in the tumor cell milieu that confer protection from apoptosis. Within this concept, lanreotide has been administered as part of the "antisurvival factor therapy" in combination with dexamethasone and a gonadotropin releasing hormone (GnRH) analog. It has also been given combined with oestrogens in patients with CRPC. The so far published series have documented a clinical response in many patients treated along with significant improvement in parameters related to quality of life. In view of these promising results, large-scale, randomized, controlled trials are warranted to clearly define the exact role of lanreotide and other somatostatin analogs in the treatment of patients with CRPC.

Visualization of somatostatin receptors in prostate cancer and its bone metastases with Ga-68-DOTATOC PET/CT

PURPOSE

To assess DOTATOC-affine somatostatin receptor expression in advanced prostate cancer and its bone metastases with regard to DOTATOC-mediated receptor therapies, using a Ga-68-DOTATOC PET/CT.

PROCEDURES

Twenty consecutive patients with advanced prostate cancer underwent bone scintigraphy, followed by Ga-68-DOTATOC PET/CT within 3 weeks. Through side-by-side comparison with bone scintigraphy, the number of visible bone metastases on PET was determined. In addition, in cases of visible metastases, the maximum standard uptake value (SUV(max)) of Ga-68-DOTATOC was measured in the metastases and in normal bone. In patients who did not undergo a prostatectomy (n = 12), the SUV(max) was additionally measured in the prostate and in adjacent tissue. For focal lesions, the difference in SUV(max) (Delta SUV(max)) between the metastases and normal bone was calculated. For patients still having their prostate, a Delta SUV(max) between the prostate and its adjacent tissue was calculated.

RESULTS

Sixty four of 216 metastases (30%) were visible in 13 patients with focal metastases. Of six patients with diffuse metastases (superscan), one showed diffuse metastases, three showed a total of ten focal metastases, and two showed no correlate on PET. One patient with a neuroendocrine prostate cancer showed no correlate on PET. The maximum Delta SUV(max) between metastases and normal bone was 4.9 (mean = 1.6 +/- 0.9) and between the prostate and adjacent tissue 5.9 (mean = 2.8 +/- 1.6).

CONCLUSIONS

In prostate cancer and its bone metastases, DOTATOC-affine somatostatin receptors (subtype 2 and 5) can be visualized with Ga-68-DOTATOC PET/CT. But their expression is so weak that other conjugates should be tested for receptor-mediated therapies which are better at addressing the prostate cancer-specific somatostatin receptor subtypes 1 and 4-or even other receptors.

Neuroendocrine differentiation in the progression of prostate cancer

Neuroendocrine (NE) cells originally exist in the normal prostate acini and duct, regulating prostatic growth, differentiation and secretion. Clusters of malignant NE cells are found in most prostate cancer (PCa) cases. NE differentiation (NED) is the basic character of the prostate, either benign or malignant. NE cells hold certain peptide hormones or pro-hormones, which affect the target cells by endocrine, paracrine, autocrine and neuroendocrine transmission in an androgen-independent fashion due to the lack of androgen receptor. NED is accessed by immunohistochemical staining or measurement of serum levels of NE markers. The extent of NED is associated with progression and prognosis of PCa. Chromogranin A (CGA) is the most important NE marker. In metastatic PCa, pretreatment serum CGA levels can be a predictor for progression and survival after endocrine therapy. It is recommended to measure longitudinal change in serum CGA. The NE pathway can also be a therapeutic target.

Relapsed prostate cancer with neuroendocrine differentiation and high serum levels of carcinoembryonic antigen without elevation of prostrate-specific antigen: A case report

A 62-year-old man had been treated with combined androgen blockade due to cT2bN1M0 prostate cancer, and his serum prostate-specific antigen (PSA) levels decreased and remained under the level of 0.5 ng/mL during therapy. Approximately 40 months after the initial therapy, difficulty on urination and constipation developed gradually, and serum carcinoembryonic antigen (CEA) and pro-gastrin-releasing peptide (ProGRP) levels were high at this point. He underwent transrectal and transurethral biopsy of the prostate, which revealed adenocarcinoma positive for CEA and chromogranin A. He received palliative pelvic irradiation, and oral estramustine phosphate and etoposide combined therapy. Tumor markers decreased and clinical symptoms improved for several months. The patient died of encephalopathy of unknown etiology approximately 11 months after the relapse.

Small-cell neuroendocrine carcinoma as a variant form of prostate cancer recurrence: a case report and short literature review

BACKGROUND

Small-cell neuroendocrine carcinoma has been recognized as a rare histologic variant occurring in only 0.5% to 2% of prostatic primary tumors. However, recent autopsy studies suggest development to this phenotype in up to 10% to 20% of the cases with hormone-refractory disease.

CASE PRESENTATION

A case of conventional adenocarcinoma before androgen-ablation therapy but showing progression to small-cell neuroendocrine carcinoma at the recurrence. The immunohistochemistry of the tumor showed strong positive staining for progastrin-releasing peptide (ProGRP), a carboxy terminal region common to 3 precursors for gastrin-releasing peptide, but almost negative staining for chromogranin-A and prostate-specific antigen. Combination chemotherapy based on cisplatin and etoposide was effective for controlling the tumor progression for 7 months, and the serum ProGRP level correlated well to the clinical course. Neither objective nor subjective responses were observed to somatostatin analogue therapy performed in the late stage of disease.

CONCLUSIONS

The present case reminds the urologist that small-cell neuroendocrine carcinoma may be a variant form of disease recurrence during androgen ablation in advanced prostate cancer. A strategic approach for this phenotype evaluating serum neuroendocrine markers, such as ProGRP, should be taken when serum prostate-specific antigen does not reflect the disease state. This approach would allow one to choose alternative therapies targeting neuroendocrine cells other than androgen ablation.

Clinical implications of neuroendocrine differentiation in prostate cancer

The cellular signaling pathways of the prostate play a central role in the induction, maintenance, and progression of prostate cancer (CaP). Neuroendocrine (NE) cells demonstrate attributes that suggest they are an integral part of these signaling cascades. We summarize what is known regarding NE cells in CaP focusing on NE cellular transdifferentiation. This significant event in CaP progression appears to be accelerated by androgen deprivation (AD) treatment. We examine biochemical pathways that may impact NE differentiation in a chronological manner focusing on AD therapy (ADT) as a central event in inducing androgen-independent CaP. Our analysis is limited to the common adenocarcinoma pattern of CaP and excludes small-cell and carcinoid prostatic variants. In conclusion, we speculate on the future of treatment and research in this area.