探討SC5005與天然物對抗藥性金黃色葡萄球菌、休眠細胞與生物膜的協同抗菌機制

Abstract

金黃色葡萄球菌(Staphylococcus aureus)是身體表面菌相中常見的一員，約出現於30%的人口之中，常造成伺機性感染，症狀可從輕微的皮膚感染到較為嚴重的菌血症。隨著對大多數抗生素有抗藥性的抗甲氧苯青黴素金黃色葡萄球菌methicillin-resistant Staphylococcus aureus (MRSA)的出現與傳播，金黃色葡萄球菌感染症已成為全球性的健康議題，凸顯出新穎抗金黃色葡萄球菌藥物開發的重要性。在我們先前的研究中，從抗癌藥物蕾莎瓦(Nexavar；sorafenib)的衍生物篩選出了一個小分子化合物SC5005，於體外體內試驗中皆展現了良好的抗菌能力，並發現SC5005會造成細菌膜的去極化，甚至造成通透性的增加以達到殺菌的效果。爾後在優化SC5005於動物實驗的劑型時，意外發現其與特定天然物NP7合併使用後可大幅提升抑菌效果達8000倍。在這次的研究中，我們通過殺菌效力評估試驗測試SC5005與NP7合併使用後抗細菌休眠細胞的能力，結果表明合併使用後可在短時間內達到完全殺菌的效果，此外其還可以穿過細菌生物膜殺滅其內部的休眠細胞，並在MRSA皮膚感染模型中表現出顯著的抗菌活性。而此SC5005與NP7的協同作用是屬於細菌特異性的，因為在存在NP7的情況下SC5005的細胞毒性並不會隨之增加，之後的研究中指出SC5005會幫助NP7對細菌造成殺傷效果，並發現細菌內部的氧化反應扮演了相當重要的角色。接著我們進一步修飾SC5005的結構，以尋找並評估更具有潛力的化合物。在利用Time-killing assay測試一系列的SC5005衍生物與NP7的協同殺菌能力後，發現衍生物SC5178以及SC5103在與NP7合併使用下，展現出比SC5005更好的協同殺菌效果。鑑於SC5005的細胞毒性並不會因為加入NP7而有顯著的增加，此一特殊的協同殺菌活性，提供了一個開發治療抗甲氧苯青黴素金黃色葡萄球菌感染症藥物的新方向。

Staphylococcus aureus is colonized on approximately 30% of the human population. It is also an opportunistic pathogen, and infections can cause disease from minor skin infections to severe bacteremia. Moreover, the emergence of methicillin-resistant Staphylococcus aureus (MRSA) with resistance to most antibiotics has become a serious threat worldwide. Thus, the development of a novel antibacterial agent against MRSA has been an urgent need for public health. In our previous study, we identified a novel small-molecule compound named SC5005, which is a derivative of the anti-cancer drug sorafenib (Nexavar). SC5005 exhibited high antibacterial activity at in vitro and in vivo assays. Our results indicated that SC5005 can cause membrane depolarization and increase permeability of S. aureus membrane. While developing SC5005’s formulation for the in vivo test, we unexpectedly found a natural product, NP7, that can significantly enhance SC5005’s antibacterial activity to more than 8,000-fold. The combination of SC5005 and NP7 can completely eradicate MRSA and planktonic persister cells in the time-killing assay. Furthermore, this combination is also capable of penetrating into the biofilm to kill persisters inside, and exhibited a significant antibacterial activity in the MRSA skin infection model. The synergistic effect of SC5005 with NP7 is bacteria-specific as SC5005’s cytotoxicity is not increased in the presence of NP7. Subsequent investigation indicated that SC5005 increased MRSA susceptibility to NP7, and the oxidative stress in the bacteria is essential to this synergistic bactericidal effect of NP7 and SC5005. To further optimize the bacterial killing activity of this combination, a series of SC5005 derivatives were designed and synthesized. The synergistic killing activity of SC5005 derivatives with NP7 was assessed using a time-killing assay. The screening identified SC5103 and SC5178 which showed a better killing activity in combined with NP7 than that of SC5005. Altogether, our findings showed that the synergistic bactericidal activity of SC5005 and NP7 is promising and could be further exploited as a new therapeutic against MRSA.