CCR9 Homes Metastatic Melanoma Cells to the Small Bowel 55 Commentary on Amersi Et Al., P

The Biology Behind

CCR9 Homes Metastatic Melanoma Cells to the Small Bowel 55 Commentary on Amersi et al., p. 638

Ann Richmond

The question of why certain types of tumors often metastasize Chemokine/chemokine receptor engagement results in acti- to the same organs has intrigued scientists for over a century. In vation of downstream signals, including phosphatidylino- 1889, Paget put forth the ‘‘seed and soil’’ concept that cancer sitol 3-kinase; ras/raf/mitogen-activated protein kinase; small cells (seed) spread in a nonrandom fashion to distant target GTPases such as Rac, Rho,Cdc42, and others; pAKT; src kinases; organs where they are drawn based on a conducive micro- DOCK/ELMO; p130Cas; FAK; machinery involved in the orga- environmental milieu (soil; ref. 1). A second concept that has nization of the actin cytoskeleton; and PKC-mediated signals been around for sometime is that tumor cells express ‘‘homing that lead to mobilization of intracellular free calcium (3). These signals’’ to direct their movement to appropriate microenviron- events occur in a cyclic fashion that involves local excitation ments for growth of metastatic lesions. A homing signal acts followed by global inhibition, allowing for modulation of the like a lighthouse to allow the ship to move toward the land. We actin cytoskeleton to facilitate extension of pseudopods and have recently come to understand that chemokine receptors retraction of uropods in a continuously cycling manner such displayed on tumor cells allow the tumor cell (seed) to follow a that the end result is directed migration up the chemokine gradient of chemokine to its target organ milieu (soil) that gradient. Activation of integrins is an important component expresses the ligand for this chemokine receptor. The chemo- of the events required for directed migration. This directed kine receptors are seven-transmembrane, G protein–coupled migration is highly important during development, in the receptors that respond to ligand binding to activate a series of immune response, in the inflammatory response, in angiogen- downstream signals that result in a polarized distribution of the esis, and in tumor cell extravasation and intravasation as is actin cytoskeleton to form a leading pseudopod, followed by essential for metastasis. organization of the uropod cytoskeleton to allow a myosin- In addition, a number of transcriptional enhancers are mediated contraction. This process repeats as the cell senses activated by chemokine receptors that allow transcription of higher and higher concentrations of the ligand gradient and, as factors that modulate apoptosis and cell growth (4). Some of a result, the cell moves up the chemokine gradient and stops the CXC chemokines stimulate angiogenesis (CXCR1, CXCR2, when the concentration of the ligand saturates receptors. and several CC chemokine receptors), whereas CXCR3 regu- Chemokine receptors are divided into four classes, based on lates angiostasis. CXCR4 has been described as angiogenic in whether they bind CXC, C, CC, or CX3C chemokines. The CXC some studies (5, for review), but not in others (6). CXCR7 is chemokine binding receptors (CXCR1-7) bind largely CXC involved in tumor cell proliferation (7, 8). CXCL12 binds both chemokines (CXCL1-16); the C chemokine binding receptor CXCR4 and CXCR7 (7, 8). (CR) binds CL1; the CC chemokine receptors (CCR1-10) bind Our knowledge of the role of chemokine/chemokine CC chemokines CCL1-27; and the CX3C chemokine receptor receptor interactions has been developing for >27 years. binds CX3CL1 (2). Most of these chemokine/chemokine recep- However, only in the last 6 to 7 years have we come to tor interactions are quite promiscuous such that receptors understand that chemokine receptor display on tumor cells can bind multiple chemokine ligands and, likewise, the ligands bind have a major effect on directed metastasis of tumor cells to a number of receptors. These receptors are abundantly expressed organs that strongly express the chemokine ligand for the by leukocytes, which, in turn, usually display a number of specific chemokine receptor the tumor cell expresses. Initial chemokine receptors, establishing the necessary redundancy to documentation of chemokine receptors serving as ‘‘homing ensure appropriate recruitment of leukocytes to sites of signals’’ came from the landmark paper of Muller et al. (9), wounding, repair, infection, or inflammation. The expression where CXCR4 chemokine receptor expression in breast cancer of chemokines and their receptors is not limited to leukocytes. tumor cell lines and human ductal breast carcinoma biopsy In fact, most cell and tissue types express chemokines or tissue samples was enhanced, compared with cell lines estab- chemokine receptors at specific stages of differentiation. lished from normal mammary gland or the normal mammary gland tissue itself. Muller et al. also correlated expression of CXCR4 with metastasis to distant organs expressing CXCL12, the chemokine ligand for CXCR4 (bone, liver, lung, and lymph Author’s Affiliation: VA Medical Center, and Departments of Cancer Biology and node). These early studies have been verified by a host of other Medicine,Vanderbilt University School of Medicine, Nashville,Tennessee studies showing CXCR4 expression in melanoma and a number Received 11/5/07; accepted 11/7/07. Grant support: Senior Career Scientist Award from the Department of Veterans of other metastatic tumor types (5, 10). Several antagonist Affairs (A. Richmond) and NIH grant CA3490. for CXCR4/CXCL12 interactions (CXCR4 blocking antibody, Requests for reprints: Ann Richmond, Department of Cancer Biology, 432 PRB, CXCR4 small-molecule antagonists, peptide antagonist for Vanderbilt University School of Medicine, 23rd Avenue South at Pierce, Nashville, CXCR4, small interfering RNA for CXCR4) have been tested in @ TN 37232. Phone: 615-343-7777; Fax: 615-926-4589; E-mail: ann.richmond animal models and were shown to inhibit the number or size of vanderbilt.edu. F 2008 American Association for Cancer Research. tumor metastasis in breast cancer, non–small cell lung cancer, doi:10.1158/1078-0432.CCR-07-2235 melanoma, renal cancer, osteosarcoma, colorectal cancer,

www.aacrjournals.org 621 Clin Cancer Res 2008;14(3) February 1, 2008 Downloaded from clincancerres.aacrjournals.org on September 28, 2021. © 2008 American Association for Cancer Research. The Biology Behind esophageal cancer, gastric cancer, and ovarian cancer (11–17). In this issue of Clinical Cancer Research, Amersi et al. (27) These studies indicate that antagonism of appropriate chemo- have done an in-depth analysis of CCR9 expression in 198 kine receptors displayed on homing tumor cells may offer new melanoma lesions. Using reverse transcription-PCR, fluores- tools for therapy. cence-activated cell sorting analysis, and immunohistochemis- CCR7 is expressed in metastatic breast cancer cell lines, try, they show that 102 of 198 metastatic melanomas metastatic melanoma cell lines, as well as metastatic breast and metastasize to the small bowel. Of the 102 that metastasize melanoma tumor tissues. Lymph nodes, a common site of to the small bowel, 88 express CCR9. The remaining 96 melanoma and breast cancer metastasis, strongly express CCL metastases were CCR9 negative and metastasized to the liver 21, a ligand for CCR7 (18, 19). In contrast, lymph nodes also (n = 19), kidney (n = 5), lung (n = 14), gallbladder (n = 9), express CXCL 9 to 11, all of which activate CXCR3 expressed on pancreas (n = 8), adrenal (n = 7), stomach (n = 18), and colon some melanoma cells as well as T cells and endothelial cells (n = 16). Of the 14 CCR9-negative patients with small-bowel (20, 21). metastases, these tumors also metastasized to colon, spleen, CCR10 expression on melanoma tumor cell lines was shown kidney, or adrenal glands. Moreover, examination of 23 to be associated with enhanced tumor growth for these cell paraffin-embedded archival primary melanomas revealed that lines and xenografts expressing CCR10 migrate to CCL27- 11 of 23 were CCR9 positive and of those 11 positives, 7 (64%) expressing skin. However, CCR10 expression was not observed later developed small-bowel metastases. CCL25 expression in by Siedl et al. in primary or metastatic melanoma lesions the small bowel was higher in those melanoma lesions that (18, 19). Other studies have shown that CCR1 expression is up- were metastatic to the small bowel than for those patients regulated in melanoma and that CCR5 is expressed in primary where CCR9-positive melanoma did not metastasize to the melanoma lesions and some cutaneous metastases (19). Low small bowel. Melanoma lesions that undergo metastasis to the h levels of expression of CXCR1 have been detected in congenital small bowel also showed expression of a4 integrin and 1 nevi and in some, but not all, primary melanoma lesions, integrin, both of which have been associated with lymphoid whereas CXCR2 mRNA expression was detected in congenital tissue in the gut and T cells in the small bowel. It is of interest nevi, f40% of primary melanoma lesions, and 30% of that T cells expressing CCR9 or CCR10 also home to the organs cutaneous metastases (19). that express the ligands for these chemokines, enabling the CCR9 is expressed on human melanoma cells and partic- potential for immune surveillance, which would in turn impair ipates in the enhanced motility of melanoma cells and is establishment of metastatic lesions (24–26, 28–33). likely a ‘‘homing receptor’’ for melanoma to the small bowel For those CCR9-positive metastatic melanoma lesions that (19, 22–24). The ligand for CCR9, CCL25, is strongly metastasized to the lymph nodes, there was no evidence of expressed in the small bowel and the thymus (24–26). The expression of CCL25 in the nodes. Because lymph nodes work of Lentz et al. showed that 8 of 20 melanoma cell lines express CCL21 and CXCL12, these chemokines likely mediate expressed functional CCR9 and CXCR4 receptors and of those the homing of melanoma lesions also expressing CCR7 and/or eight lines positive for CCR9 and CXCR4, three were CXCR4 to lymph node (34, 35). Altogether, the data of Amersi et al. confirm that CCR9 expression on primary tumors suggest established from small-bowel metastases. Another of the eight a >60% likelihood that there will be metastasis to the small CCR9-positive lines was taken from a patient that later bowel. Based on this information, physicians can carefully developed metastasis to the small bowel. This group went on follow their patients after surgical excision with a clear to study melanoma metastases to the small bowel and verify indication that there is a strong chance that if metastases occur, that at the time the tissue was taken, CCR9 was expressed in they will be to the small bowel. Both blocking antibodies to small-bowel metastasis, suggesting a possible link between CCR9 as well as small interfering RNA for CCR9 blocked CCR9 expression and the migration of these cells to organs melanoma cell migration and invasion in response to CCL25 expressing CCL25. For 11 of melanoma cells that did not in vitro. These data offer promise that targeting CCR9 might express CCR9, none metastasized to the small bowel. There was offer rational postsurgical treatment for CCR9-positive mela- one CCR9-negative cell line that developed small-bowel noma patients. metastases 2 years after resection of the skin metastases, but by then there were multiple sites of visceral metastasis (23). Acknowledgments For the three melanoma tumor lines expressing CCR9 and metastasizing to the small bowel, treatment with CCL25 down- We thank Albert Zlotnik and Fran Balkwill for their critical reading of the regulated CCR9 and induced actin polymerization (23). manuscript.

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Ann Richmond

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