- 學位論文
新穎腫瘤治療法：發展以光動力治療法促進低氧性生物還原型前驅藥物之毒殺策略
New tumor therapy: development of photodynamic therapy promoted bioreductive prodrug toxicity for cancer treatment
摘要
光動力療法為常用之癌症治療方法之一，乃透過給予特定波段光源以活化光敏劑，並產生自由基及活性氧化物(如單氧分子)，而引發細胞毒殺作用。然而光動力療法之效果常取決於病灶組織內氧氣濃度，在深層腫瘤區域普遍缺氧或因光動力治療而造成腫瘤處局部缺氧情形而使療效受限，導致癌細胞無法有效地被毒殺。目前針對治療深層腫瘤組織的缺氧區域，已有低氧性生物還原型前驅藥物(TPZ, Tirapazamine)被研發出來並進行臨床試驗中，癌細胞在吞噬該藥物後經由特定還原酵素活化即可產生毒殺的效果。因此本論文研究旨結合光動力治療及低氧性生物還原型前驅藥物，針對腫瘤內組織氧氣分布不均的環境進行治療，期待改善單一藥物在癌症治療上的效果。將光動力治療所造成的腫瘤環境氧氣濃度下降的缺點轉變為有利於低氧性生物還原型前驅藥物作用的微環境，希望藉此複合型治療策略提升癌細胞毒殺效率。本論文結果證實在正常氧壓(21% O2)的環境下，光動力治療所使用之光敏劑PpIX經由波長630 nm激發光活化後會消耗環境中的氧氣並產生單氧分子；且也發現氧氣濃度的降低至5%以下會提高該細胞內CYPOR還原酵素的活性。藉由在模擬實際腫瘤組織內氧氣濃度為5%、2%及1%的細胞實驗中，結果發現隨著氧氣濃度降低會造成光動力治療對細胞的毒殺能力下降，反之TPZ藥物對細胞的毒殺能力有上升趨勢。將兩種療法結合，則可在5%氧濃度環境下發揮協同毒殺作用，推測即為TPZ受到酵素催化形成的中間產物，在有氧的環境下會回復成原前驅形式藥物，伴隨接收電子後生成的超氧化物在細胞中造成毒性傷害。總結來說，本論文所觀察到的研究結果發現，根據腫瘤微環境氧氣濃度的分布而發展出的複合型治療法結合光動力治療和低氧性生物還原型前驅藥物TPZ應可為腫瘤治療策略上提供新的方向。
並列摘要
Photodynamic therapy is one of the common medical treatments that uses a photosensitizer and a specific wavelength of light. When photosensitizers are exposed to a particular type of light, free radicals and singlet oxygen can be produced to subsequently kill nearby cells. However, photodynamic therapy fails to remove tumor cells completely in hypoxic tumor region or photodynamic therapy-induced hypoxia area. To target hypoxia in cancer therapy, a hypoxia-specific drug Tirapazamine (TPZ) has been developed and currently in a number of phase III clinical trials, which is designed to be activated to a toxic free radical under hypoxia condition via the function of NADPH-cytochrome P450 reductase (CYPOR). Therefore, in current study we aimed to combine photodynamic therapy and bioreductive prodrug TPZ to treat cancer cells under biomimetic low oxygen environment to improve the limitation of therapeutic efficacy of a single drug. We expected that the combined therapy was able to turn the downside of photodynamic therapy-induced hypoxia into advantage, as bioreductive prodrug TPZ can be activated at low oxygen environment. The results showed that the tumor oxygenation was reduced and singlet oxygen was generated after photodynamic therapy. It was also observed that the low oxygenation levels in tumor microenvironment have significant difference on cellular CYPOR activity by comparing to normoxia condition (21% O2). In this study, 5%, 2%, 1% oxygenation levels were selected and used in cell culture experiments as biomimetric models of tumor microenvironmental oxygenation level. It was found that PDT remained cytotoxicity effect at 5% oxygen level, but reduced at 2% and 1% oxygen level. In contrast, the cytotoxicity effect of TPZ was activated on 1% oxygen level, but reduced at 2% and 5%oxygen level. Furthermore, the combination of PDT and TPZ prodrug demonstrated a synergistic killing of tumor cells under 5% oxygen level, which might be due to the back-oxidized of TPZ radical coupling with superoxide radical (O2-) production under oxygen present. In summary, our study showed that the newly-developed combined therapy based on the oxygenation feature of tumor microenvironment may provide a promising therapeutic strategy for cancer treatment.
參考文獻
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