HIF1A INHIBITION BOOSTS THE ACTIVITY OF ANTI-PD-1 ANTIBODY TREATMENT IN IMMUNE-COLD HNSCC

Introduction

Anti-PD-1 therapies, pembrolizumab and nivolumab, are approved for the treatment of head and neck squamous cell carcinoma; however, their response rates are limited to a subset, ∼15-20%, of these patients. There is considerable interest in developing strategies to boost the activity of anti-PD-1 therapies. The binding partner of PD-1, known as PD-L1, is expressed at increased levels on HNSCC cells and is reported to be regulated by HIF1α. Given the regulatory overlap between HIF1α and PD-1/PD-L1 signaling pathways and their distinct influences on HNSCC outcomes, we hypothesized that suppression of HIF1α would enhance the response to immunotherapy targeting PD-1.

Materials & Methods

To test this hypothesis, we generated an “immune cold” syngeneic mouse model of HNSCC with doxycycline-inducible HIF1α knockdown. Successful knockdown was confirmed by immunoblot analysis, and in vitro proliferation studies showed a 20% reduction in HIF1α-depleted cells compared to controls. C57BL/6 mice inoculated with doxycycline-inducible HIF1α knockdown cells were randomized into four groups once tumors were established and received control- or doxycycline-feed with either IgG control or anti-PD-1 antibody, administered three times weekly by intraperitoneal injection.

Results

Anti-PD-1 immunotherapy did not affect tumor growth, while mice receiving doxycycline-feed showed a 29.8% reduction (p=0.05, n=8). Impressively, suppression of HIF1α combined with anti-PD1 antibody resulted in greater than 50% reduction in tumor growth compared to control mice (p<0.01, n=8). Notably, the effect of PD-1 immunotherapy in the setting of HIF1α knockdown was significantly different from that observed in either single-modality condition (combined treatment vs. HIF1α knockdown: p<0.05; combined treatment vs PD-1 inhibitor: p<0.01). Immunohistochemical examination of tumors revealed a modest increase in tumor infiltration by CD8+ T-cells in each single-modality treatment arm, whereas extensive CD8+ T-cell infiltration was observed for the combination regimen.

Conclusion

Suppression of HIF1α boosts the efficacy of PD-1 blockade through enhancement of CD8+ T-cell infiltration.