Castration-induced changes in morphology, androgen levels, and proliferative activity of human prostate cancer tissue grown in athymic nude mice

A Prospective Comparison of 18F-Sodium Fluoride PET/CT and PSMA-Targeted 18F-DCFBC PET/CT in Metastatic Prostate Cancer

The purpose of this study was to compare the diagnostic performance of 18F-DCFBC PET/CT, a first-generation 18F-labeled prostate-specific membrane antigen (PSMA)-targeted agent, and 18F-NaF PET/CT, a sensitive marker of osteoblastic activity, in a prospective cohort of patients with metastatic prostate cancer. Methods: Twenty-eight prostate cancer patients with metastatic disease on conventional imaging prospectively received up to 4 PET/CT scans. All patients completed baseline 18F-DCFBC PET/CT and 18F-NaF PET/CT scans, and 23 patients completed follow-up imaging, with a median follow-up interval of 5.7 mo (range, 4.2-12.6 mo). Lesion detection was compared across the 2 PET/CT agents at each time point. Detection and SUV characteristics of each PET/CT agent were compared with serum prostate-specific antigen (PSA) levels and treatment status at the time of baseline imaging using nonparametric statistical testing (Spearman correlation, Wilcoxon rank). Results: Twenty-six patients had metastatic disease detected on 18F-NaF or 18F-DCFBC at baseline, and 2 patients were negative on both scans. Three patients demonstrated soft tissue-only disease. Of 241 lesions detected at baseline, 56 were soft-tissue lesions identified by 18F-DCFBC only and 185 bone lesions detected on 18F-NaF or 18F-DCFBC. 18F-NaF detected significantly more bone lesions than 18F-DCFBC (P < 0.001). Correlation of PSA with patient-level SUV metrics was strong in 18F-DCFBC (ρ > 0.5, P < 0.01) and poor in 18F-NaF (ρ < 0.3, P > 0.1). When PSA levels were combined with treatment status, patients with below-median levels of PSA (<2 ng/mL) on androgen deprivation therapy (n = 11) demonstrated more lesions on 18F-NaF than 18F-DCFBC (P = 0.02). In PSA greater than 2 ng/mL, patients on androgen deprivation therapy (n = 8) showed equal to or more lesions on 18F-DCFBC than on 18F-NaF. Conclusion: The utility of PSMA-targeting imaging in metastatic prostate cancer appears to depend on patient disease course and treatment status. Compared with 18F-NaF PET/CT, 18F-DCFBC PET/CT detected significantly fewer bone lesions in the setting of early or metastatic castrate-sensitive disease on treatment. However, in advanced metastatic castrate-resistant prostate cancer, 18F-DCFBC PET/CT shows good concordance with NaF PET/CT.

Current mouse and cell models in prostate cancer research

Mouse models of prostate cancer (PCa) are critical for understanding the biology of PCa initiation, progression, and treatment modalities. Here, we summarize recent advances in PCa mouse models that led to new insights into specific gene functions in PCa. For example, the study of transgenic mice with TMPRSS2/ERG, an androgen-regulated fusion protein, revealed its role in developing PCa precursor lesions, prostate intraepithelial neoplasia; however, it is not sufficient for PCa development. Double deficiency of Pten and Smad4 leads to a high incidence of metastatic PCa. Targeted deletion of Pten in castration-resistant Nkx3-1-expressing cells results in rapid carcinoma formation after androgen-mediated regeneration, indicating that progenitor cells with luminal characteristics can play a role in initiation of PCa. Transgenic mice with activated oncogenes, growth factors, and steroid hormone receptors or inactivated tumor suppressors continue to provide insights into disease progression from initiation to metastasis. Further development of new PCa models with spatial and temporal regulation of candidate gene expression will probably enhance our understanding of the complex events that lead to PCa initiation and progression, thereby invoking novel strategies to combat this common disease in men.

Targeting ErbB3: the New RTK(id) on the Prostate Cancer Block

Most prostate cancers (PCa) are critically reliant on functional androgen receptor (AR) signaling. At its onset, PCa is androgen-dependent and although temporarily halted by surgically or pharmacologically blocking the AR (androgen ablation), the disease ultimately recurs as an aggressive, fatal castration resistant prostate cancer (CRPC). FDA-approved treatments like docetaxel, a chemotherapeutic agent, and Provenge, a cancer vaccine, extend survival by a scant 3 and 4 months, respectively. It is clear that more effective drugs targeting CRPC are urgently needed. The ErbB family (EGFR/ErbB1, ErbB2/HER2/neu, ErbB3/HER3 and ErbB4/HER4) of receptor tyrosine kinases (RTKs) have long been implicated in PCa initiation and progression, but inhibitors of ErbB1 and ErbB2 (prototypic family members) fared poorly in PCa clinical trials. Recent research suggests that another family member ErbB3 abets emergence of the castration-resistant phenotype. Considerable efforts are being directed towards understanding ErbB3-mediated molecular mechanisms of castration resistance and searching for novel ways of inhibiting ErbB3 activity via rational drug design. Antibody-based therapy that prevents ligand binding to ErbB3 appears promising and fully-humanized antibodies that inhibit ligand-induced phosphorylation of ErbB3 are currently in early development. Small molecule tyrosine kinase inhibitors are also being vigorously pursued, as are siRNA-based approaches and combination treatment strategies- the simultaneous suppression of ErbB3 and its signaling partners or downstream effectors - with the primary purpose of undermining the resiliency of ErbB3-mediated signal transduction. This review summarizes the existing literature and reinforces the importance of ErbB3 as a therapeutic target in the clinical management of prostate cancer.

Serially heterotransplanted human prostate tumours as an experimental model

* Introduction * Serially heterotransplanted human tumours in immunosuppressed mice: similarity to the tumour of origin - Cytological and histological analysis - Karyotype - Marker expression - Other PC markers - Tumour cell proliferation and frequency of mitosis - Vasculature - Stromal compartment - Heterotransplant hormone dependency - Androgen dependent - Partially androgen dependent - Androgen independent - Metastases * Conclusions Preclinical research on prostate cancer (PC) therapies uses several models to represent the human disease accurately. A common model uses patient prostate tumour biopsies to develop a cell line by serially passaging and subsequent implantation, in immunodeficient mice. An alternative model is direct implantation of patient prostate tumour biopsies into immunodeficient mice, followed by serial passage in vivo. The purpose of this review is to compile data from the more than 30 years of human PC serial heterotransplantation research. Serially heterotransplanted tumours are characterized by evaluating the histopathology of the resulting heterotransplants, including cellular differentiation, karyotype, marker expression, hormone sensitivity, cellular proliferation, metastatic potential and stromal and vascular components. These data are compared with the initial patient tumour specimen and, depending on available information, the patient's clinical outcome was compared with the heterotransplanted tumour. The heterotansplant model is a more accurate preclinical model than older generation serially passaged or genetic models to investigate current and newly developed androgen-deprivation agents, antitumour compounds, anti-angiogenic drugs and positron emission tomography radiotracers, as well as new therapeutic regimens for the treatment of PC.

Human prostate cancer heterotransplants: a review on this experimental model

A common model used for preclinical research was in vitro human tumor cell culture. An alternative model was the direct implantation of a unique patient's tumor biopsy specimens into immunodeficient host mice. Published data from PubMed (http://www.ncbi.nlm.nih.gov) and Current Contents Connect databases (http://thomsonreuters.com/products_services/science/science_products/a-z/current_contents_connect) were reviewed. Prostate cancer (PCa) heterotransplantation was evaluated using histopathology, morphology, cell differentiation, DNA content, tumor marker expression, metastases, tumor kinetics, tumor take rate and tumor vasculature in the first tumor heterotransplant. The heterotransplanted tumor retained the biological properties of the original tumor, such as morphology, degree of differentiation, pathology, secretory activity, expression of tumor markers and human vasculature. Human PCa heterotransplants have considerable experimental advantages over cell culture following xenotransplantation.

Dietary n-3 polyunsaturated fatty acids enhance hormone ablation therapy in androgen-dependent prostate cancer

Hormone ablation therapy typically causes regression of prostate cancer and represents an important means of treating this disease, particularly after metastasis. However, hormone therapy inevitably loses its effectiveness as tumors become androgen-independent, and this conversion often leads to death because of subsequent poor responses to other forms of treatment. Because environmental factors, such as diet, have been strongly linked to prostate cancer, we examined the affects of dietary polyunsaturated fatty acids (PUFAs; at 1.5 wt%) on growth of androgen-dependent (CWR22) and androgen-independent (CWR22R) human prostatic cancer xenografts, the acute response of CWR22 tumors to ablation therapy, and their progression to androgen independence. Significant diet-induced changes in tumor n-3 or n-6 PUFA content had no affect on CWR22 or CWR22R tumors growing with or without androgen support, respectively. However, dietary changes that increased tumor eicosapentaenoic acid and linoleic acid content enhanced responses to ablation therapy, measured by cancer cell apoptosis and mitosis. In addition, relapse to androgen-independent growth (measured by renewed increases in tumor volume and serum prostate-specific antigen after ablation) positively correlated with tumor arachidonic acid content. There was no correlation between expression of 15-lipoxygenase isozymes or their products and tumor growth or responses to ablation. In conclusion, dietary n-3 PUFA may enhance the response of prostate cancer to ablation therapy and retard progression to androgen-independent growth by altering tumor PUFA content.

The Human PC346 Xenograft and Cell Line Panel: A Model System for Prostate Cancer Progression

OBJECTIVE

Prostate cancer (PC) model systems that reflect the different disease stages are essential for studying the development and progression of PC and for testing new treatment modalities. This review summarizes the establishment and characterization of the PC346 progression model and compares it to other available human PC cell lines and xenografts.

METHODS

The PC346 model was derived from the transurethral resection of a primary prostate tumor. Tumor samples were subcutaneously implanted into athymic mice, which resulted in the development of a series of xenografts from which in vitro cell cultures were established.

RESULTS

The PC346 panel includes sublines with hormone-response characteristics that range from androgen-sensitive to androgen-independent (AI) growth. In vivo and in vitro selection of androgen-sensitive lines under androgen-depleted conditions replicated the clinically relevant relapse phenomenon, and resulted in a series of modifications in the androgen-receptor (AR) pathway: AR mutation, overexpression, and downregulation.

CONCLUSIONS

The PC346 panel reproduces many biological characteristics of the different phases of clinical PC and the most common AR modifications observed in hormone-refractory tumors, being a valuable addition to the limited collection of available model systems.

BM18: A novel androgen-dependent human prostate cancer xenograft model derived from a bone metastasis

BACKGROUND

Androgen-dependent prostate cancer (PrCa) xenograft models are required to study PrCa biology in the clinically relevant in vivo environment.

METHODS

Human PrCa tissue from a femoral bone metastasis biopsy (BM18) was grown and passaged subcutaneously through male severe combined immune-deficient (SCID) mice. Human mitochondria (hMt), prostate specific antigen (PSA), androgen receptor (AR), cytokeratin-18 (CK-18), pan-cytokeratin, and high molecular weight-cytokeratin (HMW-CK) were assessed using immunohistochemistry (IHC). Surgical castration was performed to examine androgen dependence. Serum was collected pre- and post-castration for monitoring of PSA levels.

RESULTS

BM18 stained positively for hMt, PSA, AR, CK-18, pan keratin, and negatively for HMW-CK, consistent with the staining observed in the original patient material. Androgen-deprivation induced tumor regression in 10/10 castrated male SCID mice. Serum PSA levels positively correlated with BM18 tumor size.

CONCLUSIONS

BM18 expresses PSA and AR, and rapidly regresses in response to androgen withdrawal. This provides a new clinically significant PrCa model for the study of androgen-dependent growth.

Cell proliferation and apoptosis in prostate tumors and adjacent non-malignant prostate tissue in patients at different time-points after castration treatment

BACKGROUND

Androgen ablation is the standard treatment for advanced prostate cancer but the short-term cellular effects are largely unknown.

METHODS

Sextant prostate biopsies were taken from 77 prostate cancer patients before and 1-10 days after castration treatment. Apoptosis, cell proliferation, and morphology were studied in malignant and non-malignant tissue, using stereological and immunohistochemical methods.

RESULTS

Epithelial cell proliferation was significantly decreased both in non-malignant and malignant epithelium already 1 day after therapy. It remained low until day 7, but increased thereafter in the remaining non-malignant epithelial cells and in some tumors. Epithelial cell apoptosis was significantly increased during the first week and then returned to basal levels. The maximal apoptotic indexes, seven- and two-times the intact levels in the non-malignant and malignant glands, respectively, were found at days 3-4 or even earlier in the tumors. Signs of tumor shrinkage such as glandular collapse and decreased tumor cell size were observed from day 3 in most tumors.

DISCUSSION

The present study shows that the magnitude and kinetics of the response to castration in the normal human prostate is very similar to the response previously described in rodents. We also demonstrate that most human prostate tumors rapidly respond to castration indicating the need for further evaluation of when and how to best monitor the effects of hormone ablation therapy in prostate cancer patients.

Characterization of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) as a model to study effects of castration therapy

BACKGROUND

In order to learn more about short- and long-term effects of castration therapy, relevant model systems for prostate cancer are required. In this study, we examined whether the transgenic adenocarcinoma of the mouse prostate (TRAMP) tumor response to castration in C57BL/6 mice mimics that seen in patients.

METHODS

Transgenic animals were examined before and 3 days after castration, at the ages of 17, 24, and 36 weeks. Moreover, 24-weeks old animals were castrated and followed for 6 months. Immunohistochemistry (IHC) and stereology were used to evaluate epithelial cell proliferation and death, blood vessel volume, androgen receptor (AR) expression, and transgenic expression of SV40 large T.

RESULTS

Cancer developed preferentially in the dorso-lateral prostate lobe. Tumor burden and incidence of metastases increased with age. The majority of tumors were well differentiated, while poorly differentiated, large tumors and macroscopic metastases developed in 8% of the animals. Well and moderately differentiated tumors responded to castration with cessation of proliferation and induction of apoptosis. Poorly differentiated tumors and metastases did not respond. Castration prevented local tumor growth for at least 6 months in 82% of the cases. Although, 45% of the treated animals developed wide-spread metastatic disease suggesting that castration may enhance growth of distant metastases.

CONCLUSIONS

The C57Bl/6 TRAMP tumor in several ways mimics how prostate cancer in patients responds to castration both in the short and long term, but some differences may also exist. This model can preferably be used to elucidate how this treatment works, and to test how it can be improved by additional therapies.

Apoptosis levels increase after castration in the CWR22 human prostate cancer xenograft

BACKGROUND

The role of apoptosis in the regression of human prostate cancer after androgen deprivation therapy remains controversial. Detection of caspase-3, an ubiquitous effector of apoptosis, is a highly specific technique for in vivo evaluation of apoptosis.

METHODS

Apoptotic rates were evaluated in the androgen-dependent CWR22 human prostate cancer xenograft in tumors that represented time points throughout the progression from androgen-stimulated to recurrent prostate cancer. Caspase-3 levels in formalin-fixed, paraffin-embedded specimens were quantified using immunohistochemical detection and video image analysis. Western blot analysis was used to confirm the results of immunodetection.

RESULTS

Expression of caspase-3 reached a maximum on day 2 after castration, decreased on day 6, and remained low until tumor recurrence. The percentage of tumor area expressing caspase-3 increased from 2.51 +/- 0.44% in tumors from intact mice to 20.84 +/- 1.75% on day 2 after castration. Among immunopositive cells, the intensity of caspase-3 expression measured using the mean optical density (MOD) increased 45% (0.3762 +/- 0.003 to 0.5461 +/- 0.001) on day 2 after castration compared to levels detected in tumors from intact mice.

CONCLUSIONS

Apoptosis contributes to tumor regression after castration in the CWR22 human prostate cancer xenograft model.

13-cis retinoic acid and complete androgen blockade in advanced hormone-naive prostate cancer patients: report of a phase II randomized study

PURPOSE

13 cis Retinoic acid (isotretinoin) is a retinoid with preclinical evidence of anti-prostate cancer activity. This phase II, cross-over, randomized study of advanced, predominantly androgen-dependent prostate cancer patients was designed to assess primarily the effect on prostate-specific antigen (PSA) decline and toxicity of adding isotretinoin to hormonal therapy and, secondarily, the potential antitumor activity of the combination.

PATIENTS AND METHODS

Thirty-seven D0 to D2 patients were randomized soon after initiating luteinizing hormone-releasing hormone agonist with antiandrogen treatment to add (arm 1) or not (arm 2) isotretinoin from weeks 1 to 12. After cross-over on week 13, patients in arm 1 discontinued while patients in arm 2 added isotretinoin from weeks 14 to 25. Observation on hormonal therapy alone continued until week 49.

RESULTS

Baseline and randomization median PSA for 30 assessable patients were, respectively, 34 and 18.2 ng/mL for arm 1 and 31 and 13.4 ng/mL for arm 2. Median PSA at week 13 was 0.5 ng/mL (range, < 0.05 to 136 ng/mL) for arm 1 and 0.7 ng/mL (range, < 0.05 to 4.4 ng/mL) for arm 2; at week 25, 0.1 ng/mL (range, < 0.05 to 121 ng/mL) and 0.4 ng/mL (range, < 0.05 to 3.1 ng/mL), respectively. At week 49, arm 1 had median PSA of 0.1 ng/mL (range, < 0.05 to 345 ng/mL) and arm 2, 0.3 ng/mL (range, < 0.05 to 8.8 ng/mL); seven of 15 and three of 15 patients, respectively, had undetectable PSA levels (P =.12). Frequent isotretinoin-related toxicity included grade 1 cheilitis (76%), skin dryness (43%), and elevated triglycerides (50%).

CONCLUSION

Isotretinoin does not impair PSA decline or add significant toxicity to hormonal therapy. An adequately powered, randomized study would be required to determine whether the combination is superior to standard hormonal treatment.

Prostate Cancer - Old Problems and New Approaches. (Part II. Diagnostic and Prognostic Markers, Pathology and Biological Aspects)

Diagnostic and prognostic markers for prostatic cancer (PCa) include conventional protein markers (e.g., PAP, PSA, PSMA, PIP, OA-519, Ki-67, PCNA, TF, collagenase, and TIMP 1), angiogenesis indicator (e.g., factor VIII), neuroendocrine differentiation status, adhesion molecules (E-cadherin, integrin), bone matrix degrading products (e.g., ICPT), as well as molecular markers (e.g., PSA, PSMA, p53, 12-LOX, and MSI). Currently, only PSA is used clinically for early diagnosis and monitoring of PCa. The histological differential diagnosis of prostatic adenocarcinoma includes normal tissues such as Cowper's gland, paraganglion tissue and seminal vesicle or ejaculatory duct as well as pathological conditions such as atypical adenomatous hyperplasia, atrophy, basal cell hyperplasia and sclerosing adenosis. A common PCa is characterized by a remarkable heterogeneity in terms of its differentiation, microscopic growth patterns and biological aggressiveness. Most PCa are multifocal with signi ficant variations in tumor grade between anatomically separated tumor foci. The Gleason grading system which recognizes five major grades defined by patterns of neoplastic growth has gained almost uniform acceptance. In predicting the biologic behavior of PCa clinical and pathological stages are used as the major prognostic indicators. Among the cell proliferation and death regulators androgens are critical survival factors for normal prostate epithelial cells as well as for the androgen-dependent human prostatic cancer cells. The androgen ablation has been shown to increase the apoptotic index in prostatic cancer patients and castration also promotes apoptotic death of human prostate carcinoma grown in mice. The progression of PCa, similarly to other malignancies, is a multistep process, accompanied by genetic and epigenetic changes, involving phenomenons as adhesion, invasion and angiogenesis (without prostate specific features).

Use of nude mouse xenograft models in prostate cancer research

BACKGROUND

Our understanding of the mechanisms of (progressive) growth of prostatic cancer has been largely obtained through the study of experimental animal models. To be able to validate new concepts, representative model systems of human origin that mimic the clinical process of the disease in patients are essential. Unfortunately, the limited number of human prostate tumor models has considerably hampered research.

METHODS

Various research groups have put much effort in the development of human prostate tumor xenograft models, and large numbers of clinical prostate tumors were heterotransplanted in immune-deficient host animals. This huge effort has resulted in a number of tumor lines which are reviewed here.

RESULTS

Up to now, approximately 25 xenograft models of human prostate cancer have been established and reported in the literature. The available xenografts seem to represent the various stages of clinical prostate cancer, such as early progression and transition from androgen-dependent to androgen-independent growth. In addition, recent efforts are concentrating on the establishment of in vitro cell lines from these xenografts as well as on the development of (bone) metastatic variants.

CONCLUSIONS

Xenograft models are important for elucidating regulatory pathways of tumor growth and progression and are indispensible for testing of new treatment modalities.

Tyrosine kinase inhibitors reduce bcl-2 expression and induce apoptosis in androgen-dependent cells

The signal transduction pathway showing how androgen withdrawal induces apoptosis in androgen-dependent cells has not been clearly understood. In these studies, we focused on the behavior of tyrosine kinases in androgen-dependent cells and investigated its correlation with apoptosis and bcl-2 expression. We used SC2G, an androgen-dependent mouse mammary carcinoma cell line, which had been cloned from Shionogi Carcinoma 115 (SC115). When SC2G cells were cultured with herbimycin A (HMA), a potent tyrosine kinase inhibitor, the number of viable cells decreased significantly after 24 h. Terminal deoxyribonucleotidyltransferase-mediated dUTP-biotin nick end labeling and flow cytometric analysis of annexin V staining showed that HMA induced apoptosis of SC2G cells. The level of bcl-2 mRNA in SC2G cells was suppressed by HMA in a dose-dependent manner on RT-PCR. Preincubation with caspase inhibitors protected HMA-induced apoptosis of SC2G cells. When a human bcl-2 gene was transfected in SC2G cells and overexpressed, SC2G cells seemed to acquire tolerance for HMA. These data indicate that HMA-sensitive tyrosine kinase(s) can regulate apoptosis and inhibit bcl-2 expression in SC2G mouse androgen-dependent cells. Tyrosine kinase(s) seemed to be a member of signal transduction between androgen receptor activation and bcl-2 expression.

Expression of prostasome-like granules by the prostate cancer cell lines PC3, Du145 and LnCaP grown in monolayer

Prostasomes are a granular type of secretory product in the human prostate gland cells. It is not known, whether in vitro grown cells derived from human prostate cancers also express prostate secretory components containing granules with properties similar to the prostasomes. Therefore, we carried out the present investigation and found that cytospins of in vitro grown PC3, DU145 and LNCaP cells generally expressed a granular secretion. DU145 demonstrated the highest ratio of cells with granules (about 90%), while cytospins of PC3 and LNCaP contained less stained cells (50-70%). Purified granules from PC3 cells were immunoreactive with a monoclonal antibody (mAb78) originally raised against human seminal prostasomes. The PC3 granules also shared the property with human seminal prostasomes having an elevated UV260/UV280 absorbance ratio. On the other hand we found a low aminopeptidase activity in PC3 granules contrary to that of human prostasomes. Prostasomes may form a heterogeneous group with different properties due to the source from which they are isolated and perhaps it is justified to recognize them as different members of a prostasome family.

Growth factor involvement in progression of prostate cancer

Understanding how the regulation of growth factor pathways alters during prostate cancer (PC) progression may enable researchers to develop targeted therapeutic strategies for advanced disease. PC progression involves the shifting of cells from androgen-dependent growth to an androgen-independent state, sometimes with the loss or mutation of the androgen receptors in PC cells. Both autocrine and paracrine pathways are up-regulated in androgen-independent tumors and may replace androgens as primary growth stimulatory factors in cancer progression. Our discussion focuses on growth factor families that maintain homeostasis between epithelial and stromal cells in the normal prostate and that undergo changes as PC progresses, often making stromal cells redundant. These growth factors include fibroblast growth factor, insulin-like growth factors, epidermal growth factor, transforming growth factor α, retinoic acid, vitamin D3, and the transforming growth factor β families. We review their role in normal prostate development and in cancer progression, using evidence from clinical specimens and models of PC cell growth.

Short-term cellular effects induced by castration therapy in relation to clinical outcome in prostate cancer

To explore the relationship between short-term effects of castration therapy and clinical response, biopsies obtained before and a week after castration therapy from 15 responding and 13 non-responding patients with prostate cancer were investigated. The biopsies were assessed for regressive morphology, apoptotic index by morphological criteria, nuclear area, and immunoreactivity (IR) for Ki-67, p53, bcl-2, bax and Fas. The index was defined as the percentage of immunoreactive cells in a tumour. Regressive morphology was observed in 14 out of 15 responding tumours after therapy, compared with 4 out of 13 non-responders (P < 0.001). Median tumour epithelial cell nuclear area and Ki-67 index decreased equally in both groups. The median apoptotic index increased from 2.6 to 3.5 after castration among responders (P < 0.05), whereas it remained at 2.8 among non-responders. p53 IR was present in three tumours before castration; after therapy p53 reactivity was seen in three additional tumours belonging to the responding group. Median bcl-2 index increased in responders from 1.5 to 10.0 (P < 0.05), and in non-responders from 0.08 to 2.7 (P < 0.05). Bax IR and Fas IR were present in all tumours before therapy and unchanged after therapy. Thus, regressive morphology and an increase in apoptotic index were related to a favourable clinical response. These data suggest that it might be possible to predict the effect of castration therapy by examining tumour biopsies shortly after treatment.

Target to apoptosis: a hopeful weapon for prostate cancer

BACKGROUND

Prostate cancer is the most commonly diagnosed neoplasm and the second leading cause of male death in this country. Multiple genetic and epigenetic factors have been implicated in the oncogenesis and progression of prostate cancer. However, the molecular mechanisms underlying the disease remain largely unknown. The major difficulty in the clinical management of prostate cancer stems from the reality that reliable and accurate diagnostic/prognostic biomarkers are not available and that effective treatment regimens for hormone-resistant prostate cancers are yet to be developed.

METHODS

The present review, through extensive literature research, summarizes the most recently accumulated experimental and clinical data on the relationship between apoptosis and prostate cancer. We analyze the possibility of inducing prostate cancer cell apoptosis by: 1) androgen ablation by castration or biochemical antagonists: 2) chemotherapeutic drugs or natural/synthetic chemicals; 3) manipulation of apoptosis-related oncoproteins; and 4) modulation of intracellular signal transducers.

RESULTS

1) Prostate cancer, like most other solid tumors, represents a very heterogeneous entity. Most prostate cancers, at the time of clinical diagnosis, present themselves as mixtures of androgen-dependent and androgen-independent cells. 2) Most prostate cancers respond initially to androgen ablation since the population of androgen-dependent cells undergoes rapid apoptosis upon androgen withdrawal. However, androgen ablation rarely cures patients, most of whom will experience recurrence due to takeover of the tumor mass by androgen-independent tumor cells as well as the emergence of apoptosis-resistant clones as a result of further genetic alterations such as bcl-2 amplification. 3) On the other hand, although androgen-independent prostate cancer cells do not undergo apoptosis upon androgen blocking, they do maintain the appropriate molecular machinery of apoptosis. Therefore, certain conventional chemotherapy drugs can eliminate androgen-independent cancer cells by inducing apoptosis. 4) However, most drugs used in chemotherapy induce apoptosis or mediate cytotoxicity only in proliferating cancer cells. Human prostate cancer cells demonstrate very slow growth kinetics. Thus, novel chemical/natural products need be identified to eradicate those nonproliferating cancer cells. In this regard, the angiogenesis inhibitor, linomide, and a plant extract, beta-lapachone, demonstrate very promising apoptosis-inducing effects on prostate cancer cells in a proliferation-independent manner. 5) An alternative way to modulate the apoptotic response is by interfering with the expression levels of essential regulatory molecule of apoptosis. Bcl-2 and p53 represent two prime targets for such manipulations. 6) Finally, modulation of signal transduction pathways (e.g., intracellular Ca2+ levels, PKC activity) involved in apoptosis may also induce and/or enhance the apoptotic response of prostate cancer cells.

CONCLUSIONS

Modulation of apoptotic response represents a novel mechanism-based approach which may help identify novel drugs and/or develop new therapeutic regimens for the treatment of prostate cancers.

Increased cell proliferation activity and decreased cell death are associated with the emergence of hormone-refractory recurrent prostate cancer

The tumour growth kinetics (cell proliferation and apoptosis) of ten hormone-refractory locally recurrent prostate cancers were compared with their matched untreated primary tumour specimens. All recurrent tumours had a higher cell proliferation activity, as defined by Ki-67 immunohistochemistry, than corresponding primary tumours from the same patients. The mean cell proliferation activity in recurrences (13.5 +/- 3.8 per cent) was over two times higher (P < 0.0001) than that in primary tumours (5.5 +/- 2.4 per cent), suggesting that cell clones which progress during androgen withdrawal are actively stimulated to proliferate. The mean percentage of apoptotic cells, as estimated by the in situ end-labelling technique, was 5.4 +/- 4.7 per cent in untreated primary tumours, whereas it was 2.3 +/- 1.5 per cent in locally recurrent tumours (P = 0.05). In all but two cases, the apoptotic index was lower in recurrent than in corresponding primary tumours, suggesting that recurrent prostate carcinomas are able to avoid apoptosis in the androgen-deprived environment. In conclusion, the clinical progression of prostate cancer during androgen withdrawal is associated with increased cell proliferation and decreased apoptosis.

Supraadditive apoptotic response of R3327-G rat prostate tumors to androgen ablation and radiation

PURPOSE

Androgen ablation is often combined with radiation in the treatment of patients with prostate cancer, yet, the optimal sequencing and the mechanisms governing the interaction are not understood. The objectives were to determine if cell killing via apoptosis is enhanced when the combined treatment is administered and to define the relationship of changes in this form of cell killing to tumor volume growth delay.

MATERIALS AND METHODS

Dunning R3327-G rat prostate tumors, grown in the flanks of Copenhagen rats, were used at a volume of approximately 1 cc. Androgen ablation was initiated by castration, and androgen restoration was achieved with 0.5 cm silastic tube implants containing testosterone. 60Co was used for irradiation. The terminal deoxynucleotidyl transferase (TUNEL) histochemical assay was used to quantify apoptosis.

RESULTS

Tumors from intact and castrate unirradiated control rats had average apoptotic indices (percent of apoptotic cells) of 0.4 and 1.0%, respectively. The apoptotic index varied only slightly over time (3 h to 28 days) after castration (range 0.75-1.43%). Irradiation of intact rats to 7 Gy resulted in a peak apoptotic response at 6 h of 2.3%. A supraadditive apoptotic response was seen when castration was initiated 3 days prior to 7 Gy radiation, with peak levels of about 10.1%. When the radiation was administered at increasing times beyond 3 days after castration, the apoptotic response gradually diminished and was back to levels seen in intact rats by 28 days after castration. Tumor volume growth delay studies were consistent with, but not conclusive proof of, a supraadditive effect when the combination was used.

DISCUSSION

A supraadditive apoptotic response was seen when androgen ablation and radiation were used to treat androgen sensitive R3327-G rat prostate tumors. This supraadditive effect was dependent on the timing of the two treatments. Further studies are required to more fully define the optimal timing and administration of androgen ablation and radiation.

Castration plus oestrogen treatment induces but castration alone suppresses epithelial cell apoptosis in an androgen-sensitive rat prostatic adenocarcinoma

The positive effect of castration in prostatic cancer patients is considered to be related to the induction of apoptosis in androgen-dependent tumour cells. However, castration apparently does not induce apoptosis in the highly differentiated, androgen-sensitive Dunning R3327PAP rat prostatic adenocarcinoma. To elucidate potential mechanisms of apoptotic induction in this tumour model, rats with subcutaneously implanted tumours were treated with vehicle (I), castration+vehicle (C) or castration + 50 micrograms of oestradiol benzoate per day s.c. (C + E2). The effects on tumours were examined by morphometry, in situ end labelling (ISEL) of apoptotic cells and immunohistochemically with monoclonal antibodies to proliferating cell nuclear antigen (PCNA) at different time points up to 168 h after castration. Castration inhibited tumour growth and decreased the epithelial cell apoptotic rate (from 12 h) and epithelial cell proliferation rate (from 72 h) compared with that in the I group. Tumour volume, volume densities of epithelium and stroma and stroma cell proliferation rate remained constant in the C group during the study period. C + E2 treatment resulted in increases in cell proliferation in the stroma (from 12 h) and in the volume density of stroma (from 24 h) compared with that in the C and I groups. The number of apoptotic epithelial cells was increased (from 24 h), and this was followed by decreases in the volume density of epithelium (from 24 h), the epithelial cell proliferation rate (from 72 h) and the total tumour volume (from 72 h). We conclude that in the Dunning R3327PAP tumour model C + E2 treatment is more effective than castration alone. C+E2 treatment, in contrast to C, is able to induce tumour cell death and to decrease total tumour volume. The mechanism behind this effect is unknown, but it could be related to stimulatory effects of E2 in the tumour stroma.

Radiotherapy and androgen ablation for clinically localized high-risk prostate cancer

PURPOSE

The response of patients with clinical stages T1-4 prostate cancer to radiotherapy is variable. A particularly poor prognostic group has been found to be comprised of those with pretreatment prostate specific antigen (PSA) levels above 30 ng/ml with any tumor grade, or PSA levels > 10 and < or = 30 with tumors grade 3 or 4. These patients have over an 80% actuarial risk of biochemical failure 3 years after definitive external beam radiotherapy. Thus, patients with these high-risk features require more aggressive therapy. During the last 3-4 years, the policy to treat such patients with radiotherapy and androgen ablation (XRT/HORM) was instituted. A retrospective comparison was made between high-risk patients treated with radiotherapy alone (XRT) vs. XRT/HORM.

METHODS AND MATERIALS

Between 1987 and 1991, there were 81 high-risk patients treated with XRT. There were 38 high-risk patients treated with XRT/HORM between 1990 and 1992. The median follow-up was 37 months for the XRT group and 22 months for the XRT/HORM group. No patient had clinical, radiographic, or pathologic evidence of lymph node involvement. The median dose to the prostate was 66 Gy for the XRT group and 68 Gy for the XRT/HORM group.

RESULTS

The distributions of several potential prognostic factors were analyzed. Significant differences between the groups were observed for tumor grade, pretreatment prostatic acid phosphatase, and age. The XRT/HORM group was composed of patients with worse features, including a greater proportion of patients with grade 4 tumors, more with abnormal acid phosphatase levels, and more under 60 years of age. The actuarial incidence of a rising PSA at 3 years for the XRT group was 81% vs. 15% for the XRT/HORM group (p < 0.0001). In addition, local relapse at 3 years was 34% for the XRT group and 15% for the XRT/HORM group (p < 0.02). There was no difference between the groups in terms of survival. Cox proportional hazards analyses were performed using several disease end points, including a rising PSA, a rising PSA or disease relapse, any disease relapse, and local relapse, and the only prognostic factor of independent predictive value was treatment group, i.e., XRT vs. XRT/HORM.

CONCLUSIONS

Based on biochemical and disease relapse end points, definitive radiotherapy is insufficient treatment for high-risk prostate cancer patients. The addition of androgen ablation significantly reduces the recurrence rates, although longer follow-up is needed to determine if the combined treatment impacts significantly on survival.

Cell proliferation, DNA repair, and p53 function are not required for programmed death of prostatic glandular cells induced by androgen ablation

Androgen ablation induces programmed death of androgen-dependent prostatic glandular cells, resulting in fragmentation of their genomic DNA and the cells themselves into apoptotic bodies. Twenty percent of prostatic glandular cells undergo programmed death per day between day 2 and 5 after castration. During this same period, < 1% of prostatic glandular cells enter the S phase of the cell cycle, documenting that > 95% of these die in G0. During the programmed death of these G0 glandular cells, a futile DNA repair process is induced secondary to the DNA fragmentation. This futile DNA repair is not required, however, since inhibition of this process by > 90% with an appropriately timed hydroxy-urea dosing regimen had no effect upon the extent of the programmed death of these cells after castration. Likewise, p53 gene expression is not required since the same degree of cell death occurred in prostates and seminal vesicles after castration of wild-type and p53-deficient mice.