Clin Cancer Res. 2012 Dec 15;18(24):6668-78.

Synergy of topical toll-like receptor 7 agonist with radiation and low-dose cyclophosphamide in a mouse model of cutaneous breast cancer.

Dewan MZ, Vanpouille-Box C, Kawashima N, DiNapoli S, Babb JS, Formenti SC, Adams S, Demaria S.

Department of Pathology, Radiology, Radiation Oncology, and Medicine, New York University School of Medicine, and NYU Langone Medical Center, New York, New York 10016, USA.

 

ABSTRACT

PURPOSE: This study tested the hypothesis that topical Toll-like receptor (TLR) 7 agonist imiquimod promotes antitumor immunity and synergizes with other treatments in a model of skin-involving breast cancer.

EXPERIMENTAL DESIGN: TSA mouse breast carcinoma cells were injected s.c. into syngeneic mice. Imiquimod 5% or placebo cream was applied topically on the shaved skin overlying tumors three times/wk. In some experiments, local ionizing radiation therapy (RT) was delivered to the tumor in three fractions of 8 Gy, given on consecutive days. Cyclophosphamide was given intraperitoneally (i.p.) in one dose of 2 mg/mouse. Mice were followed for tumor growth and survival.

RESULTS: Treatment with imiquimod significantly inhibited tumor growth, an effect that was associated with increased tumor infiltration by CD11c(+), CD4(+), and CD8(+) cells, and abolished by depletion of CD8(+) cells. Administration of imiquimod in combination with RT enhanced significantly tumor response compared with either treatment alone (P < 0.005), and 11% to 66% of irradiated tumors completely regressed. Importantly, the addition of topical imiquimod also resulted in growth inhibition of a secondary tumor outside of the radiation field. Low-dose cyclophosphamide given before start of treatment with imiquimod and RT further improved tumor inhibition and reduced tumor recurrence. Mice that remained tumor-free rejected a tumorigenic inoculum of TSA cells, showing long-term immunologic memory.

CONCLUSIONS: Topical imiquimod inhibits tumor growth and synergizes with RT. Addition of cyclophosphamide further increases the therapeutic effect and induces protective immunologic memory, suggesting that this combination is a promising strategy for cutaneous breast cancer metastases.

PMID: 23048078

 

SupplementSandra Demaria-FIG1

Pathogenic infectious agents cause cell stress and death associated with danger signals that powerfully activate the immune system, leading to development of defense responses specific to the pathogen. Radiotherapy has been used in cancer treatment for its ability to kill cancer cells. Cell death occurring in the absence of infection elicits repair responses without triggering defense. Cancer cell death caused by ionizing radiation generates some endogenous danger signals that are sensed by the immune system. However, these are often insufficient to overcome the tolerogenic and immunosuppressive tumor microenvironment. We reasoned that provision of a compound that mimics a strong danger signal, the TLR 7 agonist imiquimod, would complement the effects of radiotherapy to induce powerful anti-tumor immune responses. This hypothesis was tested in a mouse model of breast cancer metastatic to the skin in which imiquimod was applied topically over the irradiated tumor. The combination proved to be synergistic inducing complete regression of the tumors. Importantly, the locally-induced immune response was able to at least partially control tumors outside of the field of radiation, suggesting that this local treatment could be effective systemically and have an impact on patients survival. These data provided the rationale for an ongoing clinical trial in patients with cutaneous metastases of breast cancer (clinicaltrials.gov NCT01421017).

In the mouse model we also tested a tri-pronged approach by combining (1) killing of cancer cells by radiation, (2) immune activation by imiquimod and (3) elimination of an immunosuppressive cell subset by administration of a chemotherapy agent, cyclophosphamide, that at low doses selectively reduces regulatory T cells. The triple combination led to more sustained responses, indicating that combination treatments based on the rationale targeting of selected immune pathways have the potential to dramatically improve cancer treatment.

 

Contact: Sandra Demaria, Department of Pathology and Radiation Oncology, NYU Langone Medical Center and NYU School of Medicine, Alexandria Center for Life Sciences, 450 East 29th Street, Room 330, New York, NY 10016. Phone: 212-263-7308. Email: Sandra.Demaria@nyumc.org.

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