Macrophage infiltration has been associated with an improved prognosis in patients with colorectal cancer (CRC), but a poor prognosis in prostate cancer (PC) patients. In this study, the distribution and prognostic value of proinflammatory M1 macrophages (NOS2⁺) and immunosuppressive M2 macrophages (CD163⁺) was evaluated in a cohort of 234 PC patients. We found that macrophages infiltrating PC were mainly of an M2 type and correlated with a more aggressive tumor and poor patient prognosis. Furthermore, the M1/M2 ratio was significantly decreased in PC compared to CRC. Usingin vitrocell culture experiments, we could show that factors secreted from CRC and PC cells induced macrophages of a proinflammatory or immunosuppressive phenotype, respectively. These macrophages differentially affected autologous T lymphocyte proliferation and activation. Consistent with this, CRC specimens were found to have higher degrees of infiltrating T-helper 1 cells and active cytotoxic T lymphocytes, while PC specimens displayed functionally inactive T cells. In conclusion, our results imply that tumour-secreted factors from cancers of different origin can drive macrophage differentiation in opposite directions and thereby regulate the organization of the anti-tumour immune response. Our findings suggest that reprogramming of macrophages could be an important tool in the development of new immunotherapeutic strategies.

Accumulating data indicates that tumor-derived extracellular vesicles (EVs) are responsible for tumor-promoting effects. However, if tumor EVs also prepare the tumor-bearing organ for subsequent tumor growth, and if this effect is different in low and high malignant tumors is not thoroughly explored. Here we used orthotopic rat Dunning R-3327 prostate tumors to compare the role of EVs from fast growing and metastatic MatLyLu (MLL) tumors with EVs from more indolent and non-metastatic Dunning G (G) tumors. Prostate tissue pre-conditioned with MLL-EVs in vivo facilitated G tumor establishment compared to G-EVs. MLL-EVs increased prostate epithelial proliferation and macrophage infiltration into the prostate compared to G-EVs. Both types of EVs increased macrophage endocytosis and the mRNA expression of genes associated with M2 polarization in vitro, with MLL-EVs giving the most pronounced effects. MLL-EVs also altered the mRNA expression of growth factors and cytokines in primary rat prostate fibroblasts compared to G-EVs, suggesting fibroblast activation. Our findings propose that EVs from metastatic tumors have the ability to prime the prostate tissue and enhance tumor growth to a higher extent than EVs from non-metastatic tumors. Identifying these differences could lead to novel therapeutic targets and potential prognostic markers for prostate cancer.

Increasing evidence indicates calcium-binding S100 protein involvement in inflammation and tumor progression. In this prospective study, we evaluated the mRNA levels of two members of this family, S100A9 and S100A12, in peripheral blood mononuclear cells (PBMCs) in a cohort of 121 prostate cancer patients using RT-PCR. Furthermore, monocyte count was determined by flow cytometry. By stratifying patients into different risk groups, according to TNM stage, Gleason score and PSA concentration at diagnosis, expression of S100A9 and S100A12 was found to be significantly higher in patients with metastases compared to patients without clinically detectable metastases. In line with this, we observed that the protein levels of S100A9 and S100A12 in plasma were higher in patients with advanced disease. Importantly, in patients with metastases at diagnosis, high monocyte count and high levels of S100A9 and S100A12 were significantly associated with short progression free survival (PFS) after androgen deprivation therapy (ADT). High monocyte count and S100A9 levels were also associated with short cancer-specific survival, with monocyte count providing independent prognostic information. These findings indicate that circulating levels of monocytes, as well as S100A9 and S100A12, could be biomarkers for metastatic prostate cancer associated with particularly poor prognosis.

Prostate cancer (PC) bone metastases show weak responses to conventional therapies. Bone matrix is rich in growth factors, with insulin-like growth factor-1 (IGF-1) being one of the most abundant. IGF-1 acts as a survival factor for tumor cells and we speculate that bone-derived IGF-1 counteracts effects of therapies aimed to target bone metastases and, consequently, that therapeutic effects could be enhanced if given in combination with IGF-1 receptor (IGF-1R) inhibitors. Simvastatin inhibits the mevalonate pathway and has been found to induce apoptosis of PC cells. The aims of this study were to confirm stimulating effects of bone-derived IGF-1 on PC cells and to test if IGF-1R inhibition enhances growth inhibitory effects of simvastatin on PC cells in a bone microenvironment. The PC-3 and 22Rv1 tumor cell lines showed significantly induced cell growth when co-cultured with neonatal mouse calvarial bones. The tumor cell IGF-1R was activated by calvariae-conditioned media and neutralization of bone-derived IGF-1 abolished the calvarium-induced PC-3 cell growth. Treatment of PC-3 and 22Rv1 cells with simvastatin, or the IGF-1R inhibitor NVP-AEW541, reduced tumor cell numbers and viability, and induced apoptosis. Combined simvastatin and NVP-AEW541 treatment resulted in enhanced growth inhibitory effects compared to either drug given alone. Effects of simvastatin involved down-regulation of IGF-1R in PC-3 and of constitutively active androgen receptor variants in 22Rv1 cells. In conclusion, we suggest that IGF-1 inhibition may be a way to strengthen effects of apoptosis-inducing therapies on PC bone metastases; a possibility that needs to be further tested in pre-clinical models.

The local anti-tumour immune response has important prognostic value in colorectal cancer (CRC). In the era of immunotherapy, a better understanding of the immune response in molecular subgroups of CRC may lead to significant advances in personalised medicine. On this note, microsatellite instable (MSI) tumours have been characterised by increased immune infiltration, suggesting MSI as a marker for immune inhibitor checkpoint therapy. Here, we used flow cytometry to perform a comprehensive analysis of immune activity profiles in tumour tissues, adjacent non-malignant tissues and blood, from a cohort of 69 CRC patients. We found several signs of immune suppression in tumours compared to adjacent non-malignant tissues, including T cells more often expressing the immune checkpoint molecules programmed cell death protein (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4). We further analysed immune cell infiltration in molecular subgroups of CRC. MSI tumours were indeed found to be associated with increased immune infiltration, including increased fractions of PD-1⁺ T cells. No correlation was, however, found between MSI and the fraction of CTLA-4⁺ T cells. Interestingly, within the group of patients with microsatellite stable (MSS) tumours, some also presented with increased immune infiltration, including comparably high portions of PD-1⁺ T cells, but also CTLA-4⁺ T cells. Furthermore, no correlation was found between PD-1⁺ and CTLA-4⁺ T cells, suggesting that different tumours may, to some extent, be regulated by different immune checkpoints. We further evaluated the distribution of immune activity profiles in the consensus molecular subtypes of CRC. In conclusion, our findings suggest that different immune checkpoint inhibitors may be beneficial for selected CRC patients irrespective of MSI status. Improved predictive tools are required to identify these patients.