Novel TGFb inhibitors ameliorate oral squamous cell carcinoma progression and improve the antitumor immune response of anti-PD-L1 immunotherapy

TGFb is a key regulator of oral squamous cell carcinoma (OSCC) progression, and its potential role as a therapeutic target has been investigated with a limited success. This study evaluates two novel TGFb inhibitors as mono or combinatorial therapy with anti-PD-L1 antibodies (a-PD-L1 Ab) in a murine OSCC model. Immunocompetent C57BL/6 mice bearing malignant oral lesions induced by 4-nitroquinoline 1-oxide (4-NQO) were treated for 4 weeks with TGFb inhibitors mRER (i.p., 50 mg/d) or mmTGFb2-7m (10 mg/d delivered by osmotic pumps) alone or in combination with a-PD-L1 Abs (7 x i.p. of 100 mg/72 h). Tumor progression and body weight were monitored. Levels of bioactive TGFb in serum were quantified using a TGFb bioassay. Tissues were analyzed by immunohistology and flow cytometry. Therapy with mRER or mmTGFb2-7m reduced tumor burden (P < 0.05) and decreased body weight loss compared with controls. In inhibitor-treated mice, levels of TGFb in tumor tissue and serum were reduced (P < 0.05), whereas they increased with tumor progression in controls. Both inhibitors enhanced CD8^þ T-cell infiltration into tumors and mRER reduced levels of myeloid-derived suppressor cells (P < 0.001). In combination with a-PD-L1 Abs, tumor burden was not further reduced; however, mmTGFb2-7m further reduced weight loss (P < 0.05). The collagen-rich stroma was reduced by using combinatorial TGFb/PD-L1 therapies (P < 0.05), enabling an accelerated lymphocyte infiltration into tumor tissues. The blockade of TGFb signaling by mRER or mmTGFb2-7m ameliorated in vivo progression of established murine OSCC. The inhibitors promoted antitumor immune responses, alone and in combination with a-PD-L1 Abs.