将干细胞变成跟踪并摧毁癌细胞的导弹(ZT)

marrowstem

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4 e: n. k/ O2 K" ^) \6 G将经过基因改选的干细胞注入癌症患者的大脑内，干细胞会将脑内的不活跃的抗癌药物转变为可以消灭肿瘤的、强有力的、靶向明确的抗癌剂。: p/ r& w9 j/ _1 J* F' d6 B
      由于癌细胞会强力吸引干细胞，因此科学家希望干细胞被引导追踪肿瘤主体的同时，也被肿瘤的二次生长或癌细胞转移所吸引。这样更高剂量的药物会对癌细胞穷追猛打，同时又把副作用（即对身体其它部分的影响）降到最低。" l- ^+ M5 e2 `2 T
       一支由美国希望之城贝克曼研究院加州杜阿尔特分院的Karen Aboody率领的研究小组在实验中应用了神经干细胞（采自人类胎儿， 并经基因工程改造以产生胞嘧啶脱氨酶）。胞嘧啶脱氨酶是一种能够将叫做5-氟胞嘧啶（5-FC）的药物转化为活跃的化疗药物5-氟尿嘧啶的酶，但这种情形只发生于干细胞的紧邻。
: ?8 Y- H2 I/ G0 [% W        然后研究小组将经过改造的干细胞注射进罹患神经胶质瘤（一种恶性大脑肿瘤）的小鼠，接着给小鼠5-FC。与未接受治疗的小鼠相比，接受治疗的小鼠，其肿瘤体积减少了70%。“实际上，我们准备将更高剂量的化疗药物布置于肿瘤所在的部位。”Aboody说。在今年五月份德国特罗弗明德召开的国际脑肿瘤会议上，Aboody提交了研究结果。
: g  M; Z7 a3 t       美国食品及药物管理局已批准Aboody就该疗法进行安全实验，实验对象多达20名，均为罹患多发性神经胶质瘤患者。这些患者预期只能活3到6个月。在肿瘤摘除手术后，干细胞将被注入瘤腔，给出四天时间让干细胞追踪一切剩余的癌细胞。其后一周内，患者将每天接受5-FC治疗。2 W* r/ a" b  }% \  p1 H
        神经胶质瘤的微小集落通常会扩散、深入健康的大脑组织，但是Aboody希望新的疗法将有能力锁定目标、追杀每一个癌细胞，这意味着，即使最微不足道的肿瘤转移也会被扑灭。
+ f: J# _9 t& l" V$ Z         美国桑福德-伯纳姆医学研究所加州拉由拉市分院的Evan Snyder是第一个建议用干细胞抗击肿瘤的人，他提示说，让肿瘤入侵正常组织的同一指令也会让干细胞移向该地址。他说：“我相信，同一的理念对会跑出大脑的转移性肿瘤也起作用，对其它类型的肿瘤也是如此。”
8 d5 t1 Y) _3 |+ ~3 p5 o2 r- }7 |        与运用神经干细胞修复中风引起的损伤的临床试验不同，Aboody所用的干细胞并未被观察到有分化行为，实际上这些干细胞在48小时后就停止分裂。这样，无须过分担心干细胞本身会触发癌症。
8 Q& q* J6 ]  Y2 x& M  （转载，撰文：Linda Geddes  译者：Docofsoul）

marrowstem

Stem cells turn into seek-and-destroy cancer missiles
' i9 P0 ]( u& S% F0 o. W$ g 04 June 2010 by Linda Geddes
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     GENETICALLY modified stem cells are to be injected into the brains of cancer patients, where they will convert an inactive cancer drug into a potent and targeted tumour-killing agent.
8 m. n, o3 B; H5 T/ D. ~' y         Stem cells are strongly attracted towards cancer cells, so it is hoped that as well as homing in on the main tumour, they will also be drawn to secondary growths, or metastases. This will enable higher doses of drug to be delivered to cancer cells while minimising the risk of side effects in the rest of the body.
6 J( O6 S/ S9 A/ l7 Z            A team led by Karen Aboody at the City of Hope Beckman Research Institute in Duarte, California, used neural stem cells originally derived from human fetuses which had been genetically engineered to produce cytosine deaminase. This is an enzyme that converts a drug called 5-fluorocytosine (5-FC) into an active chemotherapy drug, 5-fluorouracil (5-FU), but only in the immediate vicinity of the stem cell.- r6 ^2 ^# o- d; j% G
         The team then injected the modified stem cells into the brains of mice with glioma, an aggressive form of brain cancer. The animals were subsequently given 5-FC. Treated mice saw a 70 per cent reduction in tumour mass compared with untreated animals. "In effect, we're allowing a much higher dose of chemo to be localised to the tumour site," says Aboody, who presented the results in May at an international brain tumour conference in Travemünde, Germany.
3 Q: U- j& \  y/ f3 O* z( L         The US Food and Drug Administration has granted Aboody approval to carry out a safety trial of the therapy in up to 20 patients with recurrent glioma, for whom life expectancy is just three to six months. The stem cells will be injected into the tumour cavity following surgery to reduce its mass, and then given four days to home in on any remaining cancer cells. Patients will then be treated with daily 5-FC for one week.9 V) g6 r! s: [( I: ]
         Tiny colonies of glioma cells often spread deep into healthy brain tissue, but Aboody hopes that the new treatment will be able to zero in on single tumour cells, meaning it could destroy even the smallest metastases." q5 N/ W: u6 r  a5 ?
         Evan Snyder at the Sanford-Burnham Medical Research Institute in La Jolla, California, who first proposed the use of stem cells to fight cancer, suggests the same cues that make a tumour invade normal tissue also make a stem cell migrate to that site. "I believe the same concept will work for metastatic cancers that go outside the brain, and for other kinds of cancers," he says.
. }& _- n% a8 s, l& G6 d         Unlike clinical trials that use neural stem cells to repair damage caused by stroke, the stem cells used by Aboody have not been seen to differentiate, and stop dividing after 48 hours. This should reduce concerns about the potential for stem cells to trigger cancers in their own right.

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