Aggressive rat prostate tumors reprogram the benign parts of the prostate and regional lymph nodes prior to metastasis

Abstract

In order to grow and spread tumors need to interact with adjacent tissues. We therefore hypothesized that small but aggressive prostate cancers influence the rest of the prostate and regional lymph nodes differently than tumors that are more indolent. Poorly metastatic (Dunning AT1) or highly metastatic (Dunning MLL) rat prostate tumor cells were injected into the ventral prostate lobe of immunocompetent rats. After 10 days—when the tumors occupied about 30% of the prostate lobe and lymph node metastases were undetectable—the global gene expression in tumors, benign parts of the prostate, and regional iliac lymph nodes were examined to define tumor-induced changes related to preparation for future metastasis. The tumors induced profound effects on the gene expression profiles in the benign parts of the prostate and these were strikingly different in the two tumor models. Gene ontology enrichment analysis suggested that tumors with high metastatic capacity were more successful than less metastatic tumors in inducing tumor-promoting changes and suppressing anti-tumor immune responses in the entire prostate. Some of these differences such as altered angiogenesis, nerve density, accumulation of T-cells and macrophages were verified by immunohistochemistry. Gene expression alterations in the regional lymph nodes suggested decreased quantity and activation of immune cells in MLL-lymph nodes that were also verified by immunostaining. In summary, even when small highly metastatic prostate tumors can affect the entire tumor-bearing organ and pre-metastatic lymph nodes differently than less metastatic tumors. When the kinetics of these extratumoral influences (by us named TINT = tumor instructed normal tissue) are more precisely defined they could potentially be used as markers of disease aggressiveness and become therapeutic targets.

Reduced number of CD169+ macrophages in pre‐metastatic regional lymph nodes is associated with subsequent metastatic disease in an animal model and with poor outcome in prostate cancer patients

“…In line with this, the global gene expression in regional LNs from rats carrying highly metastatic MLL‐prostate tumors indicated increased immunosuppression and reduced antigen presentation prior to metastasis . Cd169 ( Siglec1 ) mRNA expression was shown to be decreased in highly metastatic MLL‐ versus poorly metastatic AT1‐LNs . Consistent with the previous study, we now demonstrate that this is accompanied by a reduced number of CD169 + macrophages in MLL‐LNs.…”

“…Metastatic cancers suppress anti‐tumor immune responses in regional LNs prior to metastasis . In line with this, the global gene expression in regional LNs from rats carrying highly metastatic MLL‐prostate tumors indicated increased immunosuppression and reduced antigen presentation prior to metastasis . Cd169 ( Siglec1 ) mRNA expression was shown to be decreased in highly metastatic MLL‐ versus poorly metastatic AT1‐LNs .…”

“…Immunocompetent and syngeneic adult Copenhagen rats (Charles River, Sulzfeld, Germany) were used in all experiments. Animals were anesthetized and 2 × 10 4 AT1 cells, or 1 × 10 3 MLL cells (suspended in 10 μL RPMI 1640) were carefully injected into one of the ventral prostate lobes as earlier described . Rats were sacrificed 3 ( n = 8/treatment), and 10 days ( n = 8/treatment) after tumor cell injection.…”

“…We recently compared the global gene expression in tumor‐draining LNs from rats implanted with two different orthotopic tumors − the poorly metastatic AT1‐tumors and the highly metastatic MatLyLu (MLL)‐tumors . The gene expression profile in pre‐metastatic MLL‐LNs was associated with decreased antigen presentation, increased immunosuppression, and a reduced density of T lymphocytes . One gene with lower expression in pre‐metastatic MLL‐LNs was Cd169 ( Siglec1) (fold change −1.7, P = 0.01 vs LNs from treatment naive animals, and fold change −1.5, P = 0.08 vs AT1‐LNs) .…”

“…The gene expression profile in pre‐metastatic MLL‐LNs was associated with decreased antigen presentation, increased immunosuppression, and a reduced density of T lymphocytes . One gene with lower expression in pre‐metastatic MLL‐LNs was Cd169 ( Siglec1) (fold change −1.7, P = 0.01 vs LNs from treatment naive animals, and fold change −1.5, P = 0.08 vs AT1‐LNs) . CD169 is normally expressed by subsets of macrophages in secondary lymphoid organs, for example, by subcapsular‐ and medullary sinus macrophages in LNs .…”