Ramu A, Mehta M M, Liu J, Turyan I, Aleksic A
Texas Children's Cancer Center, Texas Children's Hospital, Baylor College of Medicine, 6621 Fannin Street, MC 3-3320, Houston, Texas 77030-2399, USA.
Cancer Chemother Pharmacol. 2000;46(6):449-58. doi: 10.1007/s002800000174.
Previously, it was shown that exposing doxorubicin (ADR) to 365 nm light resulted in the loss of its cytotoxic activity as well as its absorbance at 480 nm. These processes were much enhanced when mediated by riboflavin. In the present study we investigated the quantitative and qualitative aspects of riboflavin-mediated photodegradation of ADR.
ADR solutions containing variable concentrations of riboflavin and other agents were exposed to 365 nm light for variable time periods and then the absorbance spectrum of ADR was measured by a double beam spectrophotometer. These measurements were used to calculate the half-time of the ADR degradation process. The degraded ADR solutions were analyzed by chromatography and mass spectrometry.
Analysis of the riboflavin effect indicated that a maximal rate of photolytic degradation of ADR was obtained only after most of the ADR molecules had formed bimolecular complexes with riboflavin. The retardation of lumichrome formation by ADR and the inhibition of ADR bleaching by excess of ascorbic acid suggested that ADR was degraded by a photooxidation process. Similar spectral changes occurred when ADR was exposed to strong oxidizers such as sodium hypochlorite and dipotassium hexachloroiridate. Cyclic voltammetry revealed that the oxidation-reduction process of ADR was not electrochemically reversible and therefore the oxidation potential could not be determined accurately; however its value should be between 0.23 and 0.78 V. Analysis of the photooxidative process revealed that it was not mediated by the formation of singlet oxygen, superoxide anion radicals, hydrogen peroxide or hydroxyl radicals, and it is suggested that ADR was oxidized directly by the excited triplet riboflavin. The mass spectrograms and the HPLC chromatograms of photooxidized ADR indicate that the central ring of ADR was opened and that 3-methoxysalicylic acid was produced by this cleavage.
The riboflavin-mediated photodegradation of ADR is an oxidative process resulting in the cleavage of the anthraquinone moiety. 3-Methoxysalicylic acid was identified as one of the resulting fragments. It is possible that some of the large fractions of the ADR metabolites that are non-fluorescent are the result of an in vivo oxidation of ADR and that 3-methoxysalicylic acid may play a role in the different biological activities of ADR.
此前研究表明，将阿霉素（ADR）暴露于365nm光下会导致其细胞毒性活性丧失以及在480nm处的吸光度降低。当由核黄素介导时，这些过程会大大增强。在本研究中，我们调查了核黄素介导的阿霉素光降解的定量和定性方面。
将含有不同浓度核黄素和其他试剂的阿霉素溶液暴露于365nm光下不同时间段，然后用双光束分光光度计测量阿霉素的吸收光谱。这些测量用于计算阿霉素降解过程的半衰期。对降解后的阿霉素溶液进行色谱分析和质谱分析。
对核黄素作用的分析表明，只有在大多数阿霉素分子与核黄素形成双分子复合物后，才能获得阿霉素光解降解的最大速率。阿霉素对发光色素形成的延迟以及过量抗坏血酸对阿霉素漂白的抑制表明，阿霉素是通过光氧化过程降解的。当阿霉素暴露于强氧化剂如次氯酸钠和六氯铱酸钾二钾时，会发生类似的光谱变化。循环伏安法表明，阿霉素的氧化还原过程在电化学上是不可逆的，因此无法准确测定其氧化电位；然而其值应在0.23至0.78V之间。对光氧化过程的分析表明，它不是由单线态氧、超氧阴离子自由基、过氧化氢或羟基自由基的形成介导的，并且表明阿霉素是被激发的三线态核黄素直接氧化的。光氧化阿霉素的质谱图和高效液相色谱图表明，阿霉素的中心环被打开，并且通过这种裂解产生了3-甲氧基水杨酸。
核黄素介导的阿霉素光降解是一个氧化过程，导致蒽醌部分的裂解。3-甲氧基水杨酸被鉴定为产生的片段之一。有可能阿霉素代谢物中一些大量的非荧光部分是阿霉素体内氧化的结果，并且3-甲氧基水杨酸可能在阿霉素的不同生物活性中起作用。
