The prostatic environment suppresses growth of androgen-independent prostate cancer xenografts: an effect influenced by testosterone.

BACKGROUND: Interactions between prostate cancer cells and their surrounding stroma play an important role in the growth and maintenance of prostate tumors. To elucidate this further, we investigated how growth of androgen-dependent (AD) LNCaP and androgen-independent (AI) LNCaP-19 prostate tumors was affected by different microenvironments and androgen levels. METHODS: Tumor cells were implanted subcutaneously and orthotopically in intact and castrated immunodeficient mice. Orthotopic tumor growth was followed by magnetic resonance imaging (MRI). Gene expression in the tumors was evaluated by means of microarray analysis and microvessel density (MVD) was analyzed using immunohistochemistry. RESULTS: The results showed that LNCaP-19 tumors grew more rapidly at the subcutaneous site than in the prostate, where tumors were obviously inhibited. Castration of the mice did not affect ectopic tumors but did result in increased tumor growth in the prostatic environment. This effect was reversed by testosterone treatment. In contrast to LNCaP-19, the LNCaP cells grew rapidly in the prostate and castration reduced tumor development. Gene expression analysis of LNCaP-19 tumors revealed an upregulation of genes, inhibiting tumor growth (including ADAMTS1, RGS2 and protocadherin 20) and a downregulation of genes, promoting cell adhesion and metastasis (including N-cadherin and NRCAM) in the slow-growing orthotopic tumors from intact mice. CONCLUSIONS: The results show that the prostatic environment has a varying impact on AD and AI tumor xenografts. Data indicate that the androgen-stimulated prostatic environment limits growth of orthotopic AI tumors through induction of genes that inhibit tumor growth and suppression of genes that promote cell adhesion and metastasis.

Prostate cancer progression into androgen independency is associated with alterations in cell adhesion and invasivity.

BACKGROUND: Mortality in prostate cancer is primarily due to failure to cure hormone refractory patients with metastatic disease. The present study focused on elucidating alterations in invasive properties, which are connected with progression into androgen independency. METHODS: Ability to grow without anchor, migration, cell adhesion properties and expression of invasive factors were investigated in LNCaP and its androgen-independent subline LNCaP-19. Also, invasive capacity into blood vessels was examined in subcutaneous tumors. RESULTS: Transition into an androgen-independent state was associated with ability to grow without anchor, increased migration, and alterations in cell adhesion properties. The tumor suppressor E-cadherin was downregulated and the proinvasive factors N-cadherin, MMP-9, and membrane type 1 (MT1)-MMP were upregulated in LNCaP-19. In addition, LNCaP-19 displayed a markedly increased invasivity into blood vessels. CONCLUSIONS: The results show that LNCaP-19 mimics hormone refractory prostate cancer and therefore is an excellent tool for studies on androgen-independent cancer and invasion. This study shows that transition into an androgen-independent state correlates with several proinvasive alterations.

The anti-tumour effect of low-dose continuous chemotherapy may partly be mediated by thrombospondin.

BACKGROUND: Tumour growth is dependent on angiogenesis. Antiangiogenic chemotherapy, i.e. continuous or metronomic low-dose chemotherapy, is a method for administrating cytostatics at a low and well-tolerated concentration without prolonged breaks. The target is the genetically stable endothelial cells playing a pivotal role in angiogenesis within the tumour. Different mediators could mediate the antiangiogenic effect of metronomic chemotherapy. One of these mediators could be thrombospondin (TSP). TSP is a potent inhibitor of angiogenesis and might therefore be important in controlling tumour growth. This study was designed to evaluate the effects of low-dose continuous or moderate-dose bolus chemotherapy on tumour growth and on tumour expression of TSP. MATERIALS AND METHODS: Rats bearing a malignant prostate tumour (Dunning AT-1) not expressing TSP were treated systemically with cyclophosphamide, doxorubicin or paclitaxel and the combination of cyclophosphamide and doxorubicin. Tumour growth and body weight were measured during the treatment. CD36, one of TSP's main receptors, was also analysed. The expression pattern of TSP-1, TSP-2 and CD36 was investigated using immunohistochemistry and Western blot analyses. Q-PCR was used to analyse TSP-1 mRNA expression. RESULTS: Low-dose cyclophosphamide and paclitaxel re-induced the expression of TSP in the tumours. However, following a bolus dose of doxorubicin, tumours showed no expression of TSP. Both cyclophosphamide and doxorubicin treatments decreased the tumour weight by more than 60% compared with vehicle controls. When cyclophosphamide and doxorubicin were combined the tumour weight was reduced by 47%, while paclitaxel reduced the tumour weight by 18% compared to the vehicle controls. CONCLUSIONS: Systemic low-dose continuous treatment of a rat prostate cancer model with cyclophosphamide and paclitaxel induced the expression of TSP in tumour tissue and inhibited tumour growth. These findings support the hypothesis that the anti-tumour effect of low-dose metronomic chemotherapy, at least with certain chemotherapeutics, is partly mediated by induction of endogenous antiangiogenic factors.

Thrombospondins, metallo proteases and thrombospondin receptors messenger RNA and protein expression in different tumour sublines of the Dunning prostate cancer model.

Thrombospondin is a potent inhibitor of angiogenesis and might therefore be important in controlling tumour growth. TSP interacts with a number of proteases and receptors and in this way inhibits stimulation of angiogenesis. An earlier study showed that thrombospondin is expressed in benign prostatic hyperplasia (BPH) and high-grade prostatic intraepithelial neoplasia (PIN) but is absent in prostate cancer. The present study was therefore designed to evaluate the expression of thrombospondin 1 and 2 (TSP-1, TSP-2), TSP receptors CD36 and CD47, and matrix-metalloproteases 2 and 9 (MMP-, MMP-9) in a rat prostate cancer model. By using immunohistochemistry, Western blot, and real-time PCR the expression patterns of TSP-1, TSP-2, CD36, CD47, MMP-2, and MMP-9 were investigated in normal rat prostate tissue and five malignant Dunning sublines tissue. TSP-1 mRNA levels were decreased in all tumours compared with normal prostate. However, there was no difference in expression of TSP-2 and CD36 mRNA in these samples. MMP-2 was increased with malignancy, but no expression of MMP-9 was seen. The CD47 receptor did slightly increase with malignancy except for H3327. The results showed that thrombospondin is expressed in normal prostate but not in prostate tumours in a rat model. Simultaneously, MMP-2 expression increases with malignancy.

Expression of vascular endothelial growth factor C (VEGF-C) and VEGF receptor-3 in human prostate cancer is associated with regional lymph node metastasis.

BACKGROUND: Vascular endothelial growth factor C (VEGF-C) and its receptor, VEGFR-3, have been implicated as important factors in the formation of lymphatic vessels and recent evidence suggests that tumor lymphangiogenesis promotes lymphatic metastasis. METHODS: The expression of VEGF-C and VEGFR-3 was examined in 22 human prostate cancer specimens with immunohistochemistry. A semi-quantitative scoring system was used for evaluation of staining. RESULTS: Expression of VEGF-C was stronger in prostate cancer areas in comparison to adjacent benign glands. In addition, patients with lymph node metastases had a significantly higher expression of VEGF-C than patients without lymph node metastases. Interestingly, VEGFR-3 was expressed in malignant prostate epithelial cells and its expression was significantly higher in the lymph node positive group compared to the lymph node negative group. CONCLUSIONS: The results of the present study indicate that increased expression of VEGF-C and VEGFR-3 play a role in prostate cancer progression and in metastasis to regional lymph nodes.

The antimicrotubule drug estramustine but not irradiation induces apoptosis in malignant glioma involving AKT and caspase pathways.

Irradiation is one of the cornerstones used in the treatment of malignant glioma. However, the effect is modest and glioma cells generally display a pronounced radio-resistance. In this study, the effect of irradiation, alone and in combination with the antimicrotubule drug estramustine (EaM), was investigated in vitro using the BT4C rat glioma cell line, and in vivo the BT4C rat intracerebral glioma model was used. Apoptosis was detected by analysing DNA laddering, in situ end labelling (ISEL) and Annexin V reactivity. In addition, phosphorylation status of MAPK, JNK, p38, and AKT, proteins involved in pro- and anti-apoptotic signalling pathways was analysed by Western blotting. Irradiation did not induce apoptosis, neither in vitro nor in vivo. EaM, however, induced apoptosis in vivo and in vitro, regardless of whether EaM was given alone, before or after irradiation. When BT4C cells were treated with the caspase-3 inhibitor Ac-DEVD-CHO prior to EaM, the number of apoptotic cells was decreased, indicating an involvement of caspase-3. The signalling pathways regulating apoptosis are complex and involve kinases such as MAPK, JNK, p38 and AKT. Irradiation did not induce any changes in the expression levels or phosphorylation status of these proteins. On the other hand, the phosphorylation level of AKT was reduced after EaM treatment, which might, in part, propose how EaM induces apoptosis in glioma cells.