Abstract：
Owing to its biopenetrability and minimal invasiveness, near-infrared (NIR) light in the region between 700-1100 nm has attracted attention in cancer diagnosis and therapy. Our group previously reported that the hydrophobic diradical-platinum(II) complex PtL2 is a promising agent for cancer photothermal therapy (L = 3,5-dibromo-1,2-diiminobenzosemiquinonate radical). Because PtL2 does not fluoresce, its intercellular uptake of PtL2 cannot be observed with a fluorescence microscope. In this study, we clarified the uptake and intracellular behavior of PtL2 solubilized by bovine serum albumin (BSA) using hyperspectral imaging enabling spectrophotometric analysis of the image. The spectral changes in the obtained images indicated that the internalization of PtL2 was followed by crystallization of the complex during the long incubation period (> 4 h). Additionally, the binding constant Kb = 5.91 × 104 M-1 could be estimated upon fluorescence quenching analysis of BSA upon binding of PtL2; Kb is two orders of magnitude smaller than that of albumin-common drugs. Considering the small Kb and low solubility of PtL2 in water, we ultimately proposed the internalization path and fate of PtL2 in the cell: release of PtL2 from BSA near cellular membranes and subsequent cellular uptake via membrane permeation followed by saturation, resulting in crystallization.
摘要：
由于其可双向开放和最小的侵入性，在癌症诊断和治疗中,700-1100nm之间的近红外(NIR)光引起了人们的关注。我们的小组先前报道说，疏水性双自由基-铂（II）络合物PtL2是用于癌症光热治疗的有前途的药物（L=3,5-二溴-1,2-二亚氨基苯并半醌基）。因为PtL2不发荧光，用荧光显微镜无法观察到其对PtL2的细胞间摄取。在这项研究中,我们使用高光谱成像技术对图像进行分光光度分析，阐明了牛血清白蛋白（BSA）溶解的PtL2的摄取和细胞内行为。获得的图像中的光谱变化表明，在长孵育期（>4小时）期间，PtL2的内化伴随着复合物的结晶。此外,通过对PtL2结合后的BSA进行荧光猝灭分析，可以估计结合常数Kb=5.91×104M-1；Kb比白蛋白常见药物小两个数量级。考虑到PtL2在水中的Kb小、溶解度低,我们最终提出了PtL2在细胞中的内化途径和命运：PtL2从细胞膜附近的BSA释放，随后通过膜渗透和饱和进行细胞摄取，导致结晶。
