Targeting the p97-Npl4 Interaction Inhibits Tumor-infiltrated Regulatory T but Promotes Th17 Cell Development to Selectively Trigger Antitumor Immunity

Therapeutic targeting of tumor-infiltrated regulatory T (TI-Treg) cells is attracting for cancer treatment; yet current ways remain lacking of selectivity and efficiency. Due to its crucial role in protein homeostasis and cancer cell proliferation, the ATPase p97 in complex with its cofactors such as Npl4 has been intensively investigated as a drug target. However, whether p97 plays a role in immune cells is unclear. Instead of directly inhibiting p97 enzymatic activity as usual, here we first performed an AlphaScreen using purified recombinant proteins of p97 and Npl4, which identified thonzonium bromide (TB), an FDA-approved drug, as an inhibitor for p97-Npl4 interaction; then by serendipity we discovered an essential role for the p97-Npl4 complex in TI-Treg; and finally, we demonstrated a highly selective effect of TB on boosting antitumor immunity alone or in combination with anti-PD-1 immunotherapy. Mechanistically, the p97-Npl4 complex was found to bridge Stat3 with E3 ligases PDLIM2/5, thereby promoting Stat3 degradation. TB inhibition of the p97-Npl4 interaction caused Stat3 accumulation to block TI-Treg but promote Th17 development. Notably, TB selectively reshaped tumor microenvironment without affecting immune homeostasis outside of tumor. Collectively, this work revealed a key role for the p97-Npl4 complex in controlling the TI-Treg-Th17 balance, offering a new type of antitumor immunotherapy with oral administration of TB.