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Bone remodeling in relation to androgen receptor activity in prostate cancer bone metastases
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Prostate cancer often metastasizes to bone and the metastases are generally classified as osteoblastic, although a mixed osteoblastic/osteolytic bone response may exist. The present study aimed to characterize the bone remodeling activity in clinical bone metastasis samples, with the overall hypothesis that diversities exist that may be of importance for clinical response to current therapies. Specifically, we aimed to study bone remodeling activity in relation to tumor cell androgen receptor (AR) activity. Metastasis tissue obtained from treatment-naïve (n=11) and castration-resistant (n=28) patients during surgery for spinal cord compression was characterized using whole-genome expression analysis followed by multivariate modeling and functional enrichment analysis as well as by histological evaluation. By analyzing expression levels of a predefined set of markers representing osteoclasts (ACP5, CTSK, MMP9), osteoblasts (ALPL, BGLAP, RUNX2) and osteocytes (SOST), we found high osteoblast activity to be coupled to a high osteoclast activity. Immunohistochemistry verified a significant correlation between RUNX2 positive osteoblasts and TRAP (ACP5) positive osteoclasts lining metastatic bone surfaces in close contact to tumor cells. No difference in bone remodeling activity was seen between treatment naïve and castration-resistant patients, while the bone remodeling activity was inversely correlated to AR activity within the tissue (measured as expression of the AR, FOXA1, HOXB13, KLK2, KLK3, NKX3-1, STEAP2, and TMPRSS2) and patient serum PSA levels. Ontology analysis suggested enriched BMP signaling in metastases with high bone remodeling activity and, accordingly, BMP4 mRNA expression was significantly higher in bone metastases with than without ongoing bone formation, as determined from histological evaluation of van Gieson-stained sections. In conclusion, we have observed diversities in bone remodeling activity among clinical samples of prostate cancer bone metastases that may be of importance when selecting therapy for patients with bone metastatic cancer, especially when bone-targeting therapies are considered. The importance of the BMP signaling system for the development of sclerotic metastasis lesion deserve further exploration.

National Category
Cancer and Oncology
Research subject
Oncology
Identifiers
URN: urn:nbn:se:umu:diva-131806OAI: oai:DiVA.org:umu-131806DiVA: diva2:1076171
Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2017-02-23
In thesis
1. Prostate cancer and bone cell interactions: implications for metastatic growth and therapy
Open this publication in new window or tab >>Prostate cancer and bone cell interactions: implications for metastatic growth and therapy
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The skeleton is the most common site of prostate cancer bone metastasis, and at present, there are no curable treatments for these patients. To further understand what stimulates tumor cell growth in the bone microenvironment and to find suitable therapies, reliable model systems are needed. For this purpose, we have developed an in vitro co-culture system that can be used to study interactions between tumor cells and murine calvarial bones. To validate the model, we measured the release of collagen fragments and monitored changes in expression levels of genes normally expressed during active bone remodeling.

One of the major reasons why prostate cancer cells colonize bone is the abundance of tumor-stimulating factors, such as insulin-like growth factors (IGFs), present in this milieu. We found that the IGF-1 receptor (IGF-1R) was one of the most highly activated receptor tyrosine kinases in tumor cell lines stimulated with bone conditioned media. Since IGF-1 is known to be a strong survival factor for tumor cells, we hypothesized, that concurrent inhibition of IGF-1R signaling can enhance the effects of apoptosis-inducing therapies, such as castration. We used our co-culture model to target human prostate cancer cell lines, PC-3 and 22Rv1, with simvastatin (an inhibitor of the mevalonate pathway and an inducer of apoptosis), in combination with anti-IGF-1R therapy. Tumor cell viability declined with either one of the therapies used alone, and the effect was even more pronounced with the combined treatment. The hypothesis was also tested in rats that had been inoculated with rat prostate cancer cells, Dunning R3327-G, into the tibial bone, and treated with either anti-IGF-1R therapy, castration, or a combination of both therapies. Immunohistochemistry was used to evaluate therapeutic effects on tumor cell proliferation and apoptosis, as well as tumor cell effects on bone remodeling. The tumor cells were found to induce an osteoblastic response, both in vivo in rats, and in vitro using the co-culture model. Interestingly, the therapeutic response differed depending on whether tumor cells were located within the bone marrow cavity or if they had leaked out into the knee joint cavity, highlighting the role of the microenvironment on metastatic growth and therapeutic response. Therapies targeting the IGF-1R have been tested in clinical trials, unfortunately with disappointing results. By immunohistochemical evaluation of bone metastases from patients with castration-resistant prostate cancer, we found a large variance in IGF-1R staining within this group of patients. Hence, we postulate that the effects of anti-IGF-1R therapies could be more beneficial in patients with high tumoral IGF-1R-activity than in IGF-1R negative cases. We also believe that side effects, such as hyperglycemia, associated with anti-IGF-1R therapy, could be reduced if this treatment is administered only to selected patients and for shorter time periods.

In a separate study, using whole-genome expression data from bone metastases obtained from prostate cancer patients, we present evidence that a high activity of osteoblasts is coupled to a high activity of osteoclast. Moreover, we found that high bone remodeling activity is inversely related to tumor cell androgen receptor (AR) activity. The results from this study may be of importance when selecting therapy for patients with bone metastatic cancer, especially when bone-targeting therapies are considered, and could aid in the search for novel therapeutic targets.

In summary, we present an in vitro model for studies of the bidirectional interplay between prostate cancer cells and the bone microenvironment. We also demonstrate the importance of IGF-1 in prostate cancer bone metastases and suggest that inhibition of IGF-1R signaling can be used to treat prostate cancer as well as to enhance effects of other treatments such as androgen deprivation therapy. Furthermore, we emphasize the possibility of molecular tumor characterization when designing treatment plans for individual patients, thereby maximizing the therapeutic effects.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. 65 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1886
National Category
Cancer and Oncology
Research subject
Oncology
Identifiers
urn:nbn:se:umu:diva-131809 (URN)978-91-7601-678-7 (ISBN)
Public defence
2017-03-17, Hörsal E04, Byggnad 6A, Norrland universitetssjukhus, Umeå, 09:00 (English)
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Supervisors
Available from: 2017-02-24 Created: 2017-02-22 Last updated: 2017-03-16Bibliographically approved

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