Jie Wang

Tumor immune escape is an important strategy of tumor survival. There are many mechanisms of tumor immune escape, including immunosuppression, which has become a research hotspot in recent years. The programmed death ligand-1/programmed death-1 (PD-L1/PD-1) signaling pathway is an important component of tumor immunosuppression, which can inhibit the activation of T lymphocytes and enhance the immune tolerance of tumor cells, thereby achieving tumor immune escape. Therefore, targeting the PD-L1/PD-1 pathway is an attractive strategy for cancer treatment; however, the therapeutic effectiveness of PD-L1/PD-1 remains poor. This situation requires gaining a deeper understanding of the complex and varied molecular mechanisms and factors driving the expression and activation of the PD-L1/PD-1 signaling pathway. In this review, we summarize the regulation mechanisms of the PD-L1/PD-1 signaling pathway in the tumor microenvironment and their roles in mediating tumor escape. Overall, the evidence accumulated to date suggests that induction of PD-L1 by inflammatory factors in the tumor microenvironment may be one of the most important factors affecting the therapeutic efficiency of PD-L1/PD-1 blocking.

Tumor angiogenesis is necessary for the continued survival and development of tumor cells, and plays an important role in their growth, invasion, and metastasis. The tumor microenvironment-composed of tumor cells, surrounding cells, and secreted cytokines-provides a conducive environment for the growth and survival of tumors. Different components of the tumor microenvironment can regulate tumor development. In this review, we have discussed the regulatory role of the microenvironment in tumor angiogenesis. High expression of angiogenic factors and inflammatory cytokines in the tumor microenvironment, as well as hypoxia, are presumed to be the reasons for poor therapeutic efficacy of current anti-angiogenic drugs. A combination of anti-angiogenic drugs and antitumor inflammatory drugs or hypoxia inhibitors might improve the therapeutic outcome.

Immune checkpoint blockade targeting PD-1/PD-L1 has promising therapeutic efficacy in a variety of tumors, but resistance during treatment is a major issue. In this review, we describe the utility of PD-L1 expression levels, mutation burden, immune cell infiltration, and immune cell function for predicting the efficacy of PD-1/PD-L1 blockade therapy. Furthermore, we explore the mechanisms underlying immunotherapy resistance caused by PD-L1 expression on tumor cells, T cell dysfunction, and T cell exhaustion. Based on these mechanisms, we propose combination therapeutic strategies. We emphasize the importance of patient-specific treatment plans to reduce the economic burden and prolong the life of patients. The predictive indicators, resistance mechanisms, and combination therapies described in this review provide a basis for improved precision medicine.

BACKGROUND: High doses of estrogen can promote tumor regression in postmenopausal women with hormone-dependent breast cancer, but the mechanism is unknown. We investigated the molecular basis of this process by using LTED cells, which were derived by growing MCF-7 breast cancer cells under long-term (6-24 months) estrogen-deprived conditions. METHODS: We treated LTED and MCF-7 cells with various concentrations of 17beta-estradiol (estradiol) and assayed their growth by counting the cells and measured apoptosis by annexin V staining and DNA fragmentation. Using western blot analysis, we also examined the expression of the apoptosis-inducing system of the Fas death receptor protein and its ligand, FasL, in these cells. To assess the involvement of Fas and FasL in the induction of apoptosis in LTED cells, we used activating anti-Fas antibodies and the universal caspase inhibitor Z-VAD. Finally, we examined the expression of Fas protein in E8CASS and BSK3 cells, two other cell lines derived by depriving MCF-7 cells of estrogen long term, and the responses of these cells to high-dose estradiol. All statistical tests were two-sided. RESULTS: High concentrations of estradiol (>or=0.1 nM) resulted in a statistically significant, 60% reduction in the growth of LTED cells (P< .001) and in a sevenfold increase in apoptosis (P< .001) as compared with levels in vehicle-treated cells. Both LTED and MCF-7 cells expressed FasL, but only LTED cells expressed Fas. Treatment of LTED cells with 0.1 nM estradiol increased the expression of FasL. Activating anti-Fas antibodies increased apoptosis of LTED cells, which was further stimulated by estradiol. Z-VAD blocked estradiol-induced apoptosis. E8CASS cells, which express Fas protein, but not BSK3 cells, which do not, also responded to 0.1 nM estradiol by increasing apoptosis. CONCLUSION: Tumor regression induced by high-dose estrogen therapy in postmenopausal woman may result from estrogen activation of Fas-mediated apoptosis.

The restoration of tumor suppressor PTEN by synthetic mRNA nanoparticles sensitizes Pten -null or mutated tumors to immune checkpoint blockade therapy.