Intratumoral Injection of TLR4 Agonist (G100) Leads to Tumor Regression of A20 Lymphoma and Induces Abscopal Responses

Background: Toll-like receptors (TLRs) are components of the innate immune system that recognize pathogen-associated molecular patterns present on bacterial, fungal, or viral pathogens. Glucopyranosyl lipid A (GLA) is a synthetic TLR4 agonist that activates dendritic cells (DC) and enhances antigen-specific Th1 cell responses.

Scientific question: Can an oil-in-water emulsion of GLA (G100) induce an anti-tumor effect due to modulation of the tumor microenvironment?

Results: In our A20 murine lymphoma tumor model, intratumoral (i.t) administration of G100 resulted in tumor regression in approximately 50% of the mice in a dose dependent manner with an optimal dose of 10-20 μg/mouse. Surviving mice remained tumor-free at three months post G100 treatment and were resistant to a secondary tumor challenge with A20 cells, but not with CT26 colon cancer cells or 4T1 breast cancer cells. The effect was CD8+ T cell mediated as CD8+ depletion resulted in a significant loss of the effect. To examine the potential systemic effect of G100 i.t. treatment, Balb/c mice were implanted bilaterally with A20 tumors. Injection of G100 into the ipsilateral tumor three times a week resulted in an abscopal effect on the contralaterally implanted, untreated tumor, as evidenced by reduced tumor growth. Furthermore, the potential synergy between G100 and immunomodulatory antibodies was investigated: mice with bilateral A20 tumors received intratumoral G100 alone, systemic anti-PD-1 mAb alone, or a combination of both agents. Mice receiving combination therapy showed best overall survival, as measured by regression or reduced growth of both treated and untreated tumors. In addition, injection of low doses of anti-CTLA4 and anti-OX40 mAbs together with G100, directly into the tumor, was able to cure mice with established disease.

Significance: Immunomodulatory antibodies are currently under clinical development for cancer treatment. We show here that combining these antibodies with a TLR4 agonist is sufficient to trigger a systemic anti-tumor response able to eradicate tumor at a distant site. This anti-tumor immune response was long lasting, specific and required CD8+ T cells as the effect was lost in CD8+ T cell depleted mice.

Impact: We recently published positive results of intra-tumoral CpG (TLR9 agonist) in combination with immunomodulatory antibodies (Marabelle, Levy, et al. JCI, 2013). Both anti-CTLA4 and anti-PD1 antibodies have been FDA approved, and anti-PD-L1 and anti-OX40 antibodies are currently in advanced clinical trials. Our results suggest that G100 alone or in combination with immunomodulatory mAbs may be a promising new treatment for patients with injectable sites of lymphoma. Clinical studies investigating intratumoral G100 are underway.