Transforming growth factor (TGF)-β1 and prostaglandin E2 (PGE2) are humoral factors critically involved in the induction of immunosuppression in the microenvironment of various types of tumors, including melanoma. In this study, we identified a natural compound that attenuated TGF-β1- and PGE2-induced immunosuppression and examined its effect on B16 melanoma growth in mice. By screening 502 natural compounds for attenuating activity against TGF-β1- or PGE2-induced suppression of cytolysis in poly(I:C)-stimulated murine splenocytes, we found that betulin was the most potent compound. Betulin also reduced TGF-β1- and PGE2-induced downregulation of perforin and granzyme B mRNA expression and cell surface expression of NKG2D and CD69 in natural killer (NK) cells. Cell depletion and coculture experiments showed that NK cells, dendritic cells, B cells, and T cells were necessary for the attenuating effects of betulin. Structure–activity relationship analysis revealed that two hydroxyl groups at positions C3 and C28 of betulin, their cis-configuration, and methyl group at C30 played crucial roles in its attenuating activity. In a subcutaneous implantation model of B16 melanoma in mice, intratumor administration of betulin and LY2157299, a TGF-β1 type I receptor kinase inhibitor, significantly retarded the growth of B16 melanoma. Notably, betulin increased significantly the number of CD69 positive NK cells in tumor sites at early stages of post-tumor cell injection. Our data suggest that betulin inhibits the growth of B16 melanoma by enhancing NK cell activity through attenuating the immunosuppressive tumor microenvironment.
转化生长因子(TGF)-β1和
前列腺素E2(
PGE2)是体液因子,在包括
黑色素瘤在内的各种肿瘤微环境中,它们对免疫抑制的诱导起着关键作用。在这项研究中,我们确定了一种天然化合物,它可以减弱TGF-β1和
PGE2诱导的免疫抑制,并研究了它对小鼠B16
黑色素瘤生长的影响。通过筛选502种天然化合物,以减弱它们对TGF-β1或
PGE2诱导的多聚(I:C)刺激小鼠脾细胞细胞溶解的抑制作用,我们发现白桦脂素是最有效的化合物。白桦脂素还可以减少TGF-β1和
PGE2诱导的穿孔素和颗粒酶B mRNA表达下调,以及自然杀伤(NK)细胞中NKG2D和CD69的细胞表面表达。细胞耗竭和共培养实验表明,NK细胞、树突状细胞、B细胞和T细胞对于白桦脂素的减弱作用是必需的。结构-活性关系分析表明,白桦脂素C3和C28位上的两个羟基、它们的顺式构象以及C30上的甲基在它的减弱活性中起着关键作用。在小鼠B16
黑色素瘤皮下植入模型中,在肿瘤内施用白桦脂素和TGF-β1 I型受体激酶
抑制剂LY215