Synthesis, characterization and biological evaluation of N-substituted asymmetric squaraines for photodynamic therapy

Abstract

광역학 치료(PDT)는 임상적으로 확립되어 있고 고도로 발전한 암 치료법입니다. PDT는 광 조사시 종양세포를 선택적으로 파괴하는 감광제(photoensitizer)라는 광 반응성 약물을 사용합니다. Squaraine 화합물은 근적외선 내에서 강하고 좁은 흡수 띠를 가지는 유기 염료의 일종입니다. 캡슐화, 생체 분자 결합, 새로운 합성 수정 등 최근 Squaraine 화합물이 생체 의학 imaging 및 기타 응용 분야에서 중심으로 부상하고 있습니다. 또한, Squaraine은 감광제의 모든 유리한 특성을 갖는 염료 계열이며 차세대 PDT의 유력한 후보로 여겨져 왔습니다. 이 연구에서 종양 특이성에 대해서는 보고되었지만, 세포 및 분자 기능에 관해 가장 연구가 적은 Squaraine N-치환된 비대칭 유도체를 선택하였습니다. 연구에서 Squaraine N-치환된 asymmetric 유도체가 인간 대장암 세포 HCT116에서 최대 광역학적 활성을 가지며 정상적인 대장 세포인 Ccd-18co에서는 세포독성이 거의 없다는 것을 알 수 있었습니다. N-alkylated asymmetric Squaraine은 주로 mitochondria에 축적되고 mitochondria의 사멸을 유도하는 것을 알 수 있습니다.|Photodynamic therapy (PDT) is a clinically established and highly evolving treatment modality for cancer. PDT utilizes a light responsive drug called photosensitizer that selectively destroys tumor cells upon light irradiation. Squaraine dyes are a class of organic dyes with strong and narrow absorption bands in the near-infrared. Despite high molar absorptivities and fluorescence quantum yields, these dyes have been less explored than other dye scaffolds due to their susceptibility to nucleophilic attack. Recent strategies in probe design including encapsulation, conjugation to biomolecules, and new synthetic modifications have seen squaraine dyes emerging into the forefront of biomedical imaging and other applications. In addition, squaraines are a class of dyes possessing all favorable characteristics of a photosensitizer and have been considered to be a potent candidate for next generation PDT. In this study we chose an N-alkylated asymmetric derivatives of squaraine which has been reported for its tumor specificity but least studied for its cellular and molecular functions. Our studies revealed that the N-alkylated asymmetric derivatives of squaraine possess maximum photodynamic activity in human colon cancer cells HCT116 and had very little cytotoxicity in normal colon cells Ccd-18co. We analyzed its pro and anti-apoptotic events initiated by oxidative stress exploring a proteomic approach and delineated other critical molecular pathways and key proteins involved in regulating the complex network of cellular response upon PDT. Our study showed that, N-alkylated asymmetric squaraines predominantly accumulate in mitochondria and induce mitochondriamediated apoptosis. Our study also reveals the novel mechanistic role of N-alkylated asymmetric squaraines to induce oxidative stress there by activating both protective and death inducing pathways post PDT.