Evidence suggests that the CXC–chemokine receptor-4 pathway plays a role in cancer cell homing and metastasis, and thus represents a potential target for cancer therapy. The homeostatic microenvironment chemokine CXCL12 binds the CXCR4 and CXCR7 receptors, activating divergent signals on multiple pathways, such as ERK1/2, p38, SAPK/JNK, AKT, mTOR, and the Bruton tyrosine kinase (BTK). An activating mutation in CXCR4 is responsible for a rare disease, WHIM syndrome (warts, hypogammaglobulinemia, infections, and myelokathexis), and dominant CXCR4 mutations have also been reported in Waldenstrom macroglobulinemia. The CXCR4–CXCL12 axis regulates the hematopoietic stem cell niche—a property that has led to the approval of the CXCR4 antagonist plerixafor (AMD3100) for mobilization of hematopoietic precursors. In preclinical models, plerixafor has shown antimetastatic potential in vivo, offering proof of concept. Other antagonists are in preclinical and clinical development. Recent evidence demonstrates that inhibiting CXCR4 signaling restores sensitivity to CTLA-4 and PD-1 checkpoint inhibitors, creating a new line for investigation. Targeting the CXCR4–CXCL12 axis thus offers the possibility of affecting CXCR4-expressing primary tumor cells, modulating the immune response, or synergizing with other targeted anticancer therapies. Clin Cancer Res; 21(19); 4278–85. ©2015 AACR.

Purpose: CXCR4 receptor and its unique ligand, the CXCL12 chemokine, have been recently implicated in cancer metastasis. Evidence about the role of CXCR4/CXCL12 axis has been reported in several cancers including melanoma. Our goal was to investigate if CXCR4 expression has a prognostic value in malignant melanoma.

Purpose: Individuals with metastatic melanoma have a poor prognosis. Many human melanomas are auxotrophic for arginine, and arginine is not an essential amino acid in humans. We hypothesized that this auxotrophy may be therapeutically exploited. A novel amino acid–degrading enzyme (arginine deiminase) conjugated to polyethylene glycol (ADI-SS PEG 20,000 mw) was used to lower plasma arginine in individuals with metastatic melanoma.Patients and Methods: Two cohort dose-escalation studies were performed. A phase I study in the United States enrolled 15 patients, and a phase I to II study in Italy enrolled 24 patients. The Italian patients also received two subsequent cycles of treatment, each consisting of four once-weekly injections of 160 U/m². The goals of these studies were to determine pharmacokinetics (PK), pharmacodynamics (PD), safety, and the antitumor activity of ADI-SS PEG 20,000 mw.Results: PK and PD studies indicated that a dose of 160 U/m²lowered plasma arginine from a resting level of approximately 130 μmol/L to less than 2 μmol/L for at least 7 days; nitric oxide levels also were lowered. There were no grade 3 or 4 toxicities directly attributable to the drug. Six of 24 phase I to II patients responded to treatment (five partial responses and one complete response; 25% response rate) and also had prolonged survival.Conclusion: Elimination of all detectable plasma arginine in patients with metastatic melanoma was well tolerated and may be effective in the treatment of this cancer. Further testing of ADI-SS PEG 20,000 mw in a larger population of individuals with metastatic melanoma is warranted.

To gather further insight into the interaction between P-glycoprotein (Pgp) and its substrates, 167 compounds were analyzed in multidrug resistant human colon carcinoma cells. These compounds were selected from the National Cancer Institute Drug Screen repository using computer-generated correlations with known Pgp substrates and antagonists. The compounds were prospectively defined as Pgp substrates if cytotoxicity was increased ≥4-fold by the addition of cyclosporin A (CsA) and as Pgp antagonists if inhibition of efflux increased rhodamine accumulation by 4-fold. Among the 84 agents that met either criterion, 35 met only the criterion for substrates, 42 met only the criterion for antagonists, and only seven met both criteria. Thus, compounds interacting with Pgp form two distinct groups: one comprising cytotoxic compounds that are transported and have poor or no antagonistic activity and a second comprising compounds with antagonistic activity and no evidence of significant transport. Vinblastine accumulation and kinetic studies performed on a subset of 18 compounds similarly differentiated substrates and antagonists, but inhibition of ³H-azidopine labeling and induction of ATPase activity did not. These data support an emerging concept of Pgp in which multiple regions instead of specific sites are involved in drug transport.

Purpose: CXC chemokine receptor 4 (CXCR4) and vascular endothelial growth factor (VEGF) are implicated in the metastatic process of malignant tumors. However, no data are currently available on the biological relationship between these molecules in colorectal cancer. We studied whether CXCR4 and VEGF expression could predict relapse and evaluated in vitro the contribution of CXCR4 in promoting clonogenic growth, VEGF secretion, and intercellular adhesion molecule-1 (ICAM-1) expression of colorectal cancer cells. Experimental Design: CXCR4 and VEGF were studied in colorectal cancer tissues and in Lovo, HT29, and SW620 colorectal cancer cell lines by immunohistochemistry. Correlations with baseline characteristics of patients and tumors were analyzed by χ² test. VEGF secretion induced by CXCL12 was measured by ELISA. The effect of CXCL12 on ICAM-1 expression was evaluated by flow cytometry. Clonogenic growth induced by CXCL12 was determined by clonogenic assays. Functional effects induced by CXCL12 were prevented by the administration in vitro of AMD3100, a bicyclam noncompetitive antagonist of CXCR4. Results: Seventy-two patients, seen between January 2003 and January 2004, were studied. CXCR4 was absent in 16 tumors (22.2%); it was expressed in ≤50% of cells in 25 (34.7%) tumors and in >50% of cells in 31 (43.0%) tumors. VEGF was absent in 17 (23.6%) tumors; it was expressed in ≤50% of cells in 16 (22.2%) tumors and in >50% of cells in 39 (54.2%) tumors. There was a significant association between CXCR4 expression and lymph nodal status (P = 0.0393). There were significant associations between VEGF and tumor invasion (P = 0.0386) and lymph nodal involvement (P = 0.0044). American Joint Committee on Cancer stage (P = 0.0016), VEGF expression (P = 0.0450), CXCR4 expression (P = 0.0428), and VEGF/CXCR4 expression (P = 0.0004) had a significant prognostic value for disease-free survival with univariate analysis. The predictive ability of the American Joint Committee on Cancer stage and of the concomitant and high expression of VEGF and CXCR4 was confirmed by multivariate analysis. Prognosis is particularly unfavorable for patients whose primary tumors express CXCR4 and VEGF in >50% of cells (median disease-free survival in relapsed patients, 5.8 months; hazard ratio of relapse, 8.23; 95% confidence interval, 7.24-14.29). In clonogenic assays, CXCL12 (20 ng/mL/d) significantly increased the number of clones in SW620, HT29, and Lovo cells at 7 and 14 days. Again, CXCL12 was able to stimulate VEGF secretion in SW620, HT29, and Lovo cells as well as up-regulated ICAM-1. These effects were prevented by the administration of AMD3100 (1 μmol/L). Conclusions: We have shown that concomitant and high expression of CXCR4 and VEGF is a strong and independent predictor of early distant relapse in colorectal cancer. CXCR4 triggers a plethora of phenomena, including stimulation of clonogenic growth, induction of VEGF release, and ICAM-1 up-regulation. These data support the inhibition of CXCR4 to prevent the development of colorectal cancer metastasis.