SZU-101

In recent years, inhibitors of the BET bromodomain proteins, such as BRD4 inhibitors, have demonstrated robust antitumor activity. JQ‐1, a representative small molecular BRD4 inhibitor, is also effective to block PD‐1/PD‐L1 signaling by significantly decreasing the PD‐L1 expression on tumor cells. However, toxicity of BRD4 inhibitors on lymphoid and hematopoietic tissues limits their clinical usage. In this research, we designed and studied an immunogenic BRD4 inhibitor, SZU‐119, by coupling JQ‐1 with a TLR7 agonist, SZU‐101. In vitro, SZU‐119 stimulated the production of cytokines in mouse BMDCs and spleen lymphocytes, and inhibited the expression of PD‐L1 in mouse B16 tumor cells. In vivo, SZU‐119 suppressed the B16 tumor growth at both injected and uninjected sites, and prolonged the survival time of mice. SZU‐119 elevated the number of total CD8+ and IFN‐γ+ CD8+ T cells in spleens, with greater CTL cytotoxicity to B16 tumor cells. It was also observed that the infiltration of CD8+ T cells was increased in tumors at both local and distant sites, and the PD‐L1 expression was decreased in tumor cells at the primary site. In conclusion, we have demonstrated that SZU‐119 activated the innate immune cells, kept efficacy of PD‐L1 blockade and abrogated immune toxicity, showing more potent antitumor effects than the simple mixture of SZU‐101 and JQ‐1 in a mouse melanoma model. Our work provides new insights for the development of anti‐melanoma drugs that concurrently target innate and adaptive immunity.

Porcine reproductive and respiratory syndrome virus (PRRSV), a common viral pathogen, causes huge annual economic losses to the swine industry worldwide. After triggering by specific ligands, the Toll-like receptor 7 (TLR7), a type of pattern-recognition receptor (PRR), induces antiviral cytokines production. Previously, we synthesized an adenine analog, designated SZU101, a TLR7-specific ligand. In this study, we assessed the inhibitory effect of SZU101 on PRRSV infection in vitro. SZU101 significantly suppressed PRRSV infection in primary porcine alveolar macrophages (PAMs) in a dose-dependent manner. Moreover, SZU101-induced inhibition involved NF-κB pathway activation in PAMs to initiate expression of TLR7-mediated cytokines and induce expression of downstream signaling IFN-stimulated genes (ISGs). Chloroquine, a TLR7 inhibitor, and BAY 11-7082, an NF-κB inhibitor, reversed both the SZU101-induced antiviral effect and induction of cytokine genes and ISGs expression. Therefore, SZU101 antiviral effects depend at least in part on TLR7-NF-κB signaling pathway. Additionally, administration of SZU101 enhanced the humoral and cell-mediated immune responses against PRRSV antigens in mice. Given these results, SZU101 holds promise as an antiviral agent and a vaccine adjuvant to prevent PRRSV infection in pigs.