Daswani Varsha P, Ayesa Umme, Venegas Berenice, Chong Parkson Lee-Gau
Department of Medical Genetics and Molecular Biochemistry, Temple University School of Medicine , Philadelphia, Pennsylvania 19140, United States.
Mol Pharm. 2015 Oct 5;12(10):3724-34. doi: 10.1021/acs.molpharmaceut.5b00500. Epub 2015 Sep 22.
Combretastatin A4 disodium phosphate (CA4P) is a fluorescent, water-soluble prodrug able to induce vascular shutdown within tumors at doses less than one-tenth of the maximum tolerated dose. As a continued effort to develop efficient liposomal CA4P to treat solid tumor, we herein investigate the physical and spectroscopic properties of CA4P in aqueous solution and the mechanism of CA4P release from archaeal tetraether liposomes (archaeosomes). We found that cis-CA4P can be photoisomerized to trans-CA4P. This photoisomerization results in an increase in fluorescence intensity. Both cis- and trans-CA4P undergo fluorescence intensity self-quenching after they reach a critical concentration Cq (∼0.15-0.25 mM). Moreover, both cis- and trans-CA4P in buffer exhibit a red shift in their excitation spectrum and an increase in excitation spectrum band sharpness with increasing concentration, which can be attributed to the formation of J-aggregates. The onset of the dramatic change in excitation maximum occurs at concentrations close to Cq, suggesting that the self-quenching arises from extensive J-aggregate formation and that, when CA4P concentration exceeds Cq, J-aggregate formation begins to increase sharply. Our data also suggest that the extent of J-aggregate formation plays a critical role in CA4P release from tetraether archaeosomes and in the subsequent cytotoxicity on cultured human breast cancer MCF-7 cells. The drug leakage and cytotoxicity rate constants vary with the initial CA4P concentration entrapped inside archaeosomes in a biphasic manner, reaching a local maximum at 0.25-0.50 mM. A mechanism based on the concept of J-aggregate formation has been proposed to explain the biphasic changes in drug release and cytotoxicity with increasing drug concentration. Tetraether archaeosomes are extraordinarily stable and relatively nontoxic to animals; thus, they are promising nano drug carriers. The results obtained from this study pave the way for future development of archaeosomal CA4P to treat solid tumors.
磷酸二钠康普瑞他汀A4（CA4P）是一种荧光水溶性前药，在剂量低于最大耐受剂量的十分之一时就能诱导肿瘤内血管关闭。作为开发高效脂质体CA4P治疗实体瘤的持续努力，我们在此研究了CA4P在水溶液中的物理和光谱性质以及CA4P从古细菌四醚脂质体（嗜盐菌脂质体）释放的机制。我们发现顺式CA4P可光异构化为反式CA4P。这种光异构化导致荧光强度增加。顺式和反式CA4P在达到临界浓度Cq（约0.15 - 0.25 mM）后都会发生荧光强度自猝灭。此外，缓冲液中的顺式和反式CA4P随着浓度增加，其激发光谱出现红移且激发光谱带锐度增加，这可归因于J - 聚集体的形成。激发最大值急剧变化的起始点出现在接近Cq的浓度处，表明自猝灭源于广泛的J - 聚集体形成，并且当CA4P浓度超过Cq时，J - 聚集体形成开始急剧增加。我们的数据还表明，J - 聚集体形成的程度在CA4P从四醚嗜盐菌脂质体的释放以及随后对培养的人乳腺癌MCF - 7细胞的细胞毒性中起关键作用。药物泄漏和细胞毒性速率常数随包裹在嗜盐菌脂质体内的初始CA4P浓度呈双相变化，在0.25 - 0.50 mM时达到局部最大值。已提出一种基于J - 聚集体形成概念的机制来解释药物释放和细胞毒性随药物浓度增加的双相变化。四醚嗜盐菌脂质体极其稳定且对动物相对无毒；因此，它们是有前途的纳米药物载体。本研究获得的结果为未来开发用于治疗实体瘤的嗜盐菌脂质体CA4P铺平了道路。
