Triple negative breast cancer (TNBC) as a metastatic disease is currently incurable. Unfortunately reliable and reproducible methods for testing drugs against metastasis are not available. We have previously developed a robust metastatic model in which mice are pretreated with tumor cell-conditioned media (TCM) from human TNBC cells (MDA-MB-231 and SUM149) for 2 weeks prior to tumor cell inoculation. In this model we found reproducible metastases in lymph nodes (LN) and lungs within 4-5 weeks after orthotopic tumor inoculation [1]. We have discovered that the TNBC cells secrete large amounts of interleukin-6 (IL-6) that “educates” lymphatic endothelial cells (LEC) in the LN and lungs. Stat3, a transcription factor, gets activated and induces the synthesis of CCL5 and VEGF among other factors. CCL5 recruits the tumor cells to the LN and lungs; VEGF helps build blood vessels in the LN to facilitate tumor cell survival; VEGF produced in the lung helps the tumor cells extravasate into the lung. We have confirmed the importance of these factors by showing that inhibitors of these factors significantly inhibit metastasis.

In this report, using Maraviroc (CCR5 inhibitor) and cMR16-1 Ab (murine surrogate of the anti-IL-6R antibody), we investigated the effect of the combination treatment on the tumor growth and metastasis of orthotopic tumor xenografts generated from MDA-MB-231-Luc-D3H2LN cells. 2x106 TNBC cells tagged with luciferase were suspended in 100 μl PBS/Matrigel (1:1) and injected s.c. into female 3- to 4-week-old BALB/c nu/nu athymic mice pretreated with tumor cell-conditioned media (TCM) from TNBC cells for 2 weeks. We administered the Maraviroc (8 mg/kg Maraviroc, orally daily) and cMR16-1 Ab (i.p. 3-days per week) for 5 weeks. Our data show that tumor growth was dramatically inhibited by cMR16-1 Ab. Further, the drug combination of Maraviroc with cMR16-1 Ab caused significant reduction of TNBC tumor growth in mice compared to single agents. In addition, we measured thoracic metastases by adding luciferin to mice and measuring luminescence ex-vivo in the IVIS imager. Significantly, both single treatment of Maraviroc and the combination of Maraviroc with cMR16-1 abrogated the thoracic metastasis compared to control and single treatment of cMR16-1.

These findings implicate IL-6 and CCL5 signaling as a critical event in TNBC tumor growth and metastasis via crosstalk between cancer cells and stromal components. Further, these studies suggest that IL-6 and CCL5 act as key regulators orchestrating TNBC metastatic breast cancer. Therefore, we have provided evidence that supports the hypothesis that functional inhibition of the IL-6 and CCL-5 signaling pathway has the potential to circumvent TNBC growth and metastasis.

[1] E Lee et al. Breast cancer cells condition lymphatic endothelial cells within pre-metastatic niches to promote metastasis. Nat Commun. 2014 5:4715.

Citation Format: Jin K, Popel AS. Synergistic effect of combinatorial treatment with maraviroc and tocilizumab on TNBC tumor growth and metastasis in mouse xenograft model [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-07-09.