Tumor instructed normal tissue : studies of potential extratumoral biomarkers and therapeutic targets in prostate cancer
Abstract: Prostate cancer is the most common cancer in men in Sweden and but luckily the majority of the patients will carry on their life without any consequences from the disease. Unfortunately, some will develop aggressive tumors and eventually die. However, current prognostic and diagnostic techniques used to distinguish lethal prostate cancer from harmless prostate cancer are insufficient. It is therefore necessary to find novel diagnostic and prognostic markers, so aggressive prostate cancer can be detected and treated as early as possible whilst allowing non-aggressive variants to be safely left without extensive treatment. Interestingly, aggressive tumors have been shown to induce certain adaptive changes in the non-malignant parts of the tumor-bearing prostate – changes probably necessary for subsequent tumor growth and spread. Our research group have termed this response “Tumor Instructed (and thus Indicating) Normal Tissue (TINT)” and proposed this tissue as an alternative source of diagnostic/ prognostic markers. The aim of this thesis is to analyze factors related to tumor aggressiveness in prostate TINT. Experimental studies and studies on patient material were executed to investigate potential TINT markers at the mRNA and protein level.In patients we saw that high expression of lysyl oxidase (LOX) in TINT epithelial cells was associated with poor prognosis and served as a prognostic factor. In an animal model, created by injecting tumor cells into rat prostates, expression of LOX was increased in the surrounding non-malignant tissue. If LOX was inhibited while tumors were establishing in the prostate, tumor growth was decreased. In contrast, if LOX was inhibited after tumors were established, tumor growth was increased. Taken together, this suggests that tumors can induce LOX expression in TINT and that the function of LOX is context dependent.Another gene that was significantly increased in TINT was heme oxygenase-1 (HO-1). TINT in rat prostates injected with aggressive tumor cells was infiltrated by HO-1 expressing macrophages. In patients, HO-1 expressing macrophages was mainly seen in the invasive front of high-grade primary tumors, which also correlated with the presence of bone metastases. HO-1 expressing macrophages was more common in bone metastases than in primary tumors, and had an inverse correlation to AR expression in castration resistant prostate cancer.Microseminoprotein-β (MSMB) is normally expressed by prostate epithelial cells but is reduced in prostate tumors. Decreased levels of MSMB in serum are currently used as a biomarker for prostate cancer. Both in experimental studies and in patients, we saw that levels of MSMB were also decreased in TINT and related to tumor aggressiveness. This suggests that decreased levels of MSMB in serum could be caused by decreased levels of MSMB in the non-malignant prostate tissue and that TINT-markers possibly could be measured in blood.In conclusion, findings presented in this thesis show several alterations in TINT associated with tumor aggressiveness which have good potential of being useful as clinical prognostic markers for prostate cancer after further research.
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