Development of a Translation-Ready Combination Cancer Immunotherapy Regimen Based on Clinically Available Drugs

Abstract

Objectives:

Immunosuppressive immunocytes induced by cancer-associated inflammation, such as myeloid derived suppressor cells (MDSC) and T-regulatory cells (Treg), mediate immune-escape critical to development of solid tumors, including melanoma and oral squamous cell carcinoma (OSCC). Novel therapeutic approaches, which block tumor-mediated immunosuppression, unmasking endogenous anti-tumor immune responses, are thus a rational treatment approach. The aims of the study were: (1) Demonstrate that inhibition of inducible nitric oxide synthase (iNOS, critical for MDSC development) and Treg depletion in preclinical cancer models leads to potent anti-tumor activity; (2) Design a regimen suitable for testing in clinical trials.

Methods:

Mouse bone marrow cells were co-cultured with MT-RET melanoma supernatants ex vivo to generate MDSC in the presence of doxycycline, an iNOS inhibitor. C57/BL6 wild-type mice were injected with syngeneic MT-RET-1 melanoma. Tumor-bearing mice were treated with injection(s) of cyclophosphamide and/or doxycycline. Tumor growth and survival times were measured, and tumors and spleens harvested for CD8+ T-cell and other immunocyte levels.

Results:

In co-cultures, induction of MDSC was significantly reduced in the presence of doxycycline. Treatment of MT-RET melanoma-bearing C57/B16 mice with doxycycline resulted in tumor-infiltrating CD8+ T cells enhancement and tumor growth suppression. Treatment with cyclophosphamide suppressed intratumoral Treg accumulation. Dual treatment with cyclophosphamide and doxycycline suppressed tumor growth more efficiently than either alone.

Conclusions:

Treatment with the immunomodulators doxycycline and cyclophosphamide is a promising approach to reversing tumor-mediated immunosuppression and suppressing cancer growth in solid tumors, like melanoma and OSCC. Thus, we have designed a window of opportunity clinical trial of doxycycline and cyclophosphamide before surgical resection of OSCC.