Maraviroc decreases CCL8-mediated migration of CCR5(+) regulatory T cells and reduces metastatic tumor growth in the lungs.

Regulatory T cells (Tregs) play a crucial physiological role in the regulation of immune homeostasis, although recent data suggest Tregs can contribute to primary tumor growth by suppressing antitumor immune responses. Tregs may also influence the development of tumor metastases, although there is a paucity of information regarding the phenotype and function of Tregs in metastatic target organs. Herein, we demonstrate that orthotopically implanted metastatic mammary tumors induce significant Treg accumulation in the lungs, which is a site of mammary tumor metastasis. Tregs in the primary tumor and metastatic lungs express high levels of C-C chemokine receptor type 5 (CCR5) relative to Tregs in the mammary fat pad and lungs of tumor-free mice, and Tregs in the metastatic lungs are enriched for CCR5 expression in comparison to other immune cell populations. We also identify that C-C chemokine ligand 8 (CCL8), an endogenous ligand of CCR5, is produced by F4/80(+) macrophages in the lungs of mice with metastatic primary tumors. Migration of Tregs toward CCL8 ex vivo is reduced in the presence of the CCR5 inhibitor Maraviroc. Importantly, treatment of mice with Maraviroc (MVC) reduces the level of CCR5(+) Tregs and metastatic tumor burden in the lungs. This work provides evidence of a CCL8/CCR5 signaling axis driving Treg recruitment to the lungs of mice bearing metastatic primary tumors, representing a potential therapeutic target to decrease Treg accumulation and metastatic tumor growth.

Effects of mitomycin C on the oxygenation and radiosensitivity of murine and human tumours in mice.

BACKGROUND AND PURPOSE: Mitomycin C was one of the first chemotherapeutic agents to be shown to have preferential cytotoxicity toward hypoxic cells in vitro. Consequently, it has been used clinically with radiotherapy, and has stimulated considerable interest for analogue development. More recent studies also suggested a possible role for the drug in enhancing tumour blood flow; we therefore undertook a comprehensive examination of mitomycin C as a potential radiosensitizer in murine and human tumours growing in mice. MATERIALS AND METHODS: Two dissimilar human tumour xenograft systems, SiHa and WiDr cells, were used as was the murine SCCVII line. Effects of mitomycin C treatment on the regional and microregional blood flow in these tumours was evaluated, and cell sorting based on dye perfusion techniques was used to study the cytotoxicity of mitomycin C as a single agent or in combination with radiation in the xenograft systems. RESULTS: Contrary to our expectations, no preferential killing of less-well oxygenated tumour cells in situ was observed, nor were any consistent effects on tumour blood flow found. The inclusion of mitomycin C with radiation did, however, produce a modest increase in cell killing in the hypoxic subpopulations of the xenograft system with the largest hypoxic fraction. CONCLUSIONS: Our results indicate that combined treatment with mitomycin C and radiation cannot be rationalized on the expectation of either complementary cytotoxicity of the modalities, or of drug-induced improvement in tumour oxygenation.

Tumour blood flow influences combined radiation and doxorubicin treatments.

BACKGROUND AND PURPOSE: Doxorubicin is usually an effective radiosensitizer in vitro, but in vivo reports have been more variable. We have examined potential explanations for those observations by comprehensively evaluating doxorubicin and radiation treatments in xenografted human tumors, and in conventional mice with syngeneic tumours. MATERIALS AND METHODS: Nude or SCID mice bearing the SiHa cervical squamous cell carcinoma or WiDr colon adenocarcinoma were studied, as were C3H/HeN animals with SCCVII tumours. Assays included a clonogenic assay in combination with cell sorting, laser Doppler flowmetry, and the dual staining mismatch technique. RESULTS: Doxorubicin decreased tumour blood flow in all tumour systems, in a dose-dependent fashion with each assay. This resulted in increased tumour hypoxia and decreased response to radiation when inappropriate treatment sequences were employed. However, significant variability from animal to animal was noted. CONCLUSIONS: To the extent that these results can be extrapolated to human tumour treatments, we conclude that unless compelling evidence suggests that a tumour will be exceedingly sensitive to the drug, the potential effects of doxorubicin on tumour blood flow contraindicate its administration immediately prior to irradiation.

Contribution of transient blood flow to tumour hypoxia in mice.

Tumours grown in mice typically exhibit regions of hypoxia believed to result from two different processes: chronic oxygen deprivation due to consumption/diffusion limitations, and periodic deprivation resulting from transient reductions in tumour blood flow. The relative contribution of each is, however, not generally known. We have addressed this issue in transplanted SCCVII squamous cell carcinomas in C3H mice, using a quantitative extension of the fluorescence 'mismatch' technique coupled with cell sorting from irradiated tumours. At least half of the vessels in these tumours exhibit transient perfusion changes. Additionally, a majority of the 15-20% of cells that are sufficiently hypoxic to be resistant to radiation in the SCCVII tumours appear to result from cyclic, not continuous (diffusion-limited) hypoxia. Since different strategies may be necessary to counteract cyclic hypoxia in tumours, the possibility of transient blood flow changes should not be ignored when planning cancer therapy for humans.

Modulation of tumor hypoxia by conventional chemotherapeutic agents.

PURPOSE: We have evaluated the capacity of a number of common cancer chemotherapeutic drugs to modulate the oxygenation of human tumor xenografts growing in murine hosts. METHODS AND MATERIALS: Considerable effort has been expended on developing methods to radiosensitize hypoxic cells, or to selectively kill them with appropriate chemicals. Another approach, suggested by our ongoing studies with spheroids in vitro, is to modify tumor oxygenation by physiological means. The feasibility of this approach is illustrated in this article using human tumor xenografts in mice treated with doxorubicin or mitomycin C plus radiation. The therapeutic potential of the combination treatments has been assessed using fluorescence-activated cell sorting techniques to isolate and differentially study hypoxic vs. aerobic cell subpopulations from the xenografts. Additionally, drug-induced changes in blood flow have been quantified at the macroscopic level with laser Doppler flowmetry, and at the microregional level with image analysis techniques. RESULTS: At doses which produced only modest amounts of tumor cell killing, doxorubicin and mitomycin C markedly altered tumor blood flow in all tumor types examined, and with all assays used. CONCLUSION: Common anti-cancer agents may find new use as blood flow modifiers for combined modality treatments, in addition to their conventional use as "pure" cytotoxins.