——一种由热量引导到达肿瘤的化疗药物载体
据1月4日每日健康新闻报道，1月份第2期《美国国家癌症研究院杂志》上发表的一篇文章称，一项新的动物实验研究表明，充满抗癌药物的显微脂质泡可很快的定位并杀死肿瘤细胞，而几乎无副作用。同时采用实时核磁共振成像（MRI）追踪这些肿瘤破坏“脂质体”也可引导肿瘤治疗。
本研究的高级作者Mark Dewhirst博士解释说，利用MRI，“你可以四处移动你的发热源，因此可以使药物到达想要它们作用的部位。” 他本人是北卡罗来纳州杜兰市杜克大学医学中心的放射肿瘤学教授、超热研究项目的主管。
脂质泡是一种被制造并用于封装运输药物的显微脂肪球，其内充满化疗药物的，可直接注射入人体。脂质体天然就能被产热源吸引，因此热源作用于肿瘤部位时，这种空泡自然就移向这些部位，而远离健康组织。这种高选择性方法给患者带来了更好的肿瘤杀伤效果和更低的药物毒性。
研究人员事先让患肿瘤的大鼠受热，与此同时或之后给它们静脉注射该脂质泡。然后他们用MRI跟踪药物的走向。注射脂质泡并同时受热的大鼠治疗效果最佳，七只大鼠中的两只肿瘤完全萎缩。另外五只肿瘤生长明显推迟。研究还发现，通过脂质体给药可向肿瘤部位给比以前多30倍的化疗药物。
这项新研究仅仅是在动物中进行的。然而，脂质体正在接受进一步的临床试验，其中一项杜克研究项目，研究人员利用该空泡为女性乳腺癌胸壁复发的患者给药。结果只有10%女性患乳腺癌患者复发。
利用MRI追踪脂肪泡并与运送药物是一项非常有价值技术。你可通过MRI测量有多少药物被运送到肿瘤组织，有助于进一步研究患者对治疗的反应。
另外，通过调整作用于肿瘤部位用于吸引脂质泡的热量，他们可以有效地控制药物的进入量，甚至可以让所有的药物到肿瘤体之外、之内或者两者之间。
“据我们所知，脂质体可破坏血管，” Dewhirst说：“我们发现这种药物在肿瘤的外周最有效。”这很合理，他说，因为正是肿瘤的边缘富于这类供应肿瘤生长的血管。
Dewhirst还说，虽然利用热敏脂质体运送药物并不是新观念，但杜克大学另一位科学家David Needham发明的这种用于目前研究的脂质体，可以在更低温度下溶化，导致药物更快的释放。早期的脂质体需要半小时左右，而目前这种脂质体可在20秒内释放出药物。
费城Thomas Jefferson大学Kimmel癌症中心放射肿瘤学教授Dennis Leeper补充说：“该研究真正独一无二的方面就是这种温度敏感性脂质体。” 而同样独到的是研究人员采用实时MRI和对比剂来告诉科学家们脂肪泡具体在何处释放它们的抗癌载荷。
http://www.nlm.nih.gov/medlineplus/news/fullstory_43451.html
Microscopic Fat Bubbles Fight Cancer
Heat pulls the drug-packed bubbles to tumors, researchers explain
HealthDay
Thursday, January 4, 2007
THURSDAY, Jan. 4 (HealthDay News) -- Microscopic fat bubbles packed with anticancer drugs can target and kill tumor cells quickly with few side effects, a new study in rats suggests.
Tracking these tumor-zapping "liposomes" with magnetic resonance imaging (MRI) in real time may also help guide cancer treatment, the researchers added.
Using MRI, "you can move around your heat source, so you can put the drug where you want it to go," explained study senior author Dr. Mark Dewhirst, a professor of radiation oncology and director of the hyperthermia program at Duke University Medical Center, in Durham, N.C.
His team, collaborating with scientists elsewhere, reported the findings in the Jan. 2 issue of the Journal of the National Cancer Institute.
The fat bubbles -- microscopic globules of fat manufactured to enclose and transport medications -- were packed with a chemotherapy drug and infused into the body.
Liposomes are naturally attracted to heat sources, so when heat is applied to the tumor area, the bubbles naturally migrate to these areas, leaving healthy tissue alone. This type of highly targeted approach bring patients better cancer-killing effects with less drug toxicity.
In the study, researchers administered heat to rats with tumors before, during or after they gave them intravenous infusions of the fat bubbles. They then tracked the drug's progress with MRI.
Rodents that got both the fat bubbles and the heat together had the best treatment outcomes, with two of the seven animals displaying a complete shrinkage of the tumors. The five other rats showed significant delays in tumor growth.
Delivering the drugs in liposomes helps scientists deliver 30 times more chemotherapy to the site than they could before, according to Dewhirst.
The new study was conducted only in animals. However, the liposomes are already being tested in clinical trials, including one Duke study in which researchers used the bubbles to deliver drugs to women whose breast cancers had recurred in the chest wall. "Only about 10 percent of women with breast cancer get this [recurrence]," Dewhirst said.
In the current study, using MRI to track the fat bubbles and the drug delivery helped immensely, Dewhirst added.
"If you can measure how much drug is being delivered with the MRI, you could see how much drug is going to that patient's tumor and then say, 'OK, is this patient going to respond to the treatment?'" he explained.
By adjusting the heat at the tumor site -- which attracts the fat bubbles -- they could effectively control where the drug went. "We could make all the drug go to the outside [of the tumor], the inside, or even [between both]," Dewhirst said.
"What we know about this liposome is, this one destroys blood vessels," Dewhirst said. "We found that this drug was most effective on the periphery of the tumor." That makes sense, he said, because it's the tumor's outer edges that are richest in those blood vessels that help the tumor grow.
Using heat-sensitive liposomes to deliver drugs is not a new idea, Dewhirst said. But the liposome used in the current study -- developed by another Duke scientist, David Needham -- is capable of melting at a lower temperature, resulting in a faster release of the drug.
"They release the drug in less than 20 seconds," Dewhirst said, compared to the half-hour or so required of some older liposomes.
"The truly unique aspect [of this research] is the temperature-sensitive liposomes," added Dennis Leeper, a professor of radiation oncology at the Kimmel Cancer Center at Thomas Jefferson University, in Philadelphia.
Also unique, he said, is the researchers' use of the MRI in real time and a contrast material that tells the scientists exactly where the fat bubbles are releasing their anticancer payload.
编辑：蓝色幻想
