This year's Nobel Prize in medicine went to a trio of scientists who discovered the enzyme telomerase, which allows cells to divide without any limits, making them effectively immortal.

    It may be nature's greatest double-edged sword. Coax cells into producing telomerase, and they will survive indefinitely, but they will also become cancerous.

    To safeguard against cancer, adult cells keep track of how many times that they have multiplied, and once they have reached a pre-set limit - often around 80 divisions - they die. Telomerase interferes with this record keeping.

    If you can find a drug or gene therapy that interferes with telomerase, it could fight the unchecked growth of cancer cells, said Mark Muller, a cancer researcher who studies telomeres at the University of Central Florida.

    "Ninety percent of all cancer cells are telomerase rich," Muller said.

    Several companies, including Geron, have started testing drugs that gum up the telomerase enzyme, so that it can't extend the lives of cancer cells.

    Telomerase lengthens telomeres, repetitive DNA sequences that sit at the ends of chromosomes. Each segment of a telomere is like a ticket that gives it permission to divide. When cells run out of those credits, they cease dividing.

    Geron is developing a modified DNA molecule that gets stuck inside of telomerase, so that it can't build up the ends of telomeres in cancer cells. The company is also working with a vaccine that trains cancer patients' immune systems to attack cells that produce telomerase. In adults, almost all of the cells that produce telomerase are cancerous.

    Those cancer treatments took shape almost 20 years after academics made a breakthrough discovery.

    In the early 1980's Elizabeth Blackburn, Carol Greider and Jack Szostak identified telomerase and learned how it works. Some scientists speculated people could live longer by using the enzyme to buy extra time for their aging cells, but that idea remains risky and unproven.

    "By itself, lengthening telomeres would probably just increase the rate of tumor formation," said Chris Patil, a researcher at the Buck Institute for Age Research in Novato, California. "Experiments with mice have shown that lengthening telomeres extends lifespan, but only if you introduce multiple other mutations to block cancer."

    Considering the risks of telomere-extension therapy, he thinks that scientists have bigger fish to fry.

    "In the absence of a comprehensive understanding, it's very dangerous," Muller said. "We have to figure out how to do maintenance on our telomeres."

    Muller thinks humans could live for 90 to 210 years once scientists know more about the molecular basis of aging.

    "If we could figure out how to do maintenance, we could extend our lives," he said. "But it has to be done very carefully, and we'd have to have a comprehensive understanding of the mechanism. "

    本年度諾貝爾醫學獎被發現端粒酶酵素的三位科學家共同奪得，端粒酶酵素使細胞無限分裂，也就是使細胞長生不老。

    對細胞進行誘導
，使之產生端粒酶，這些細胞會無限期的生存下去，但也會癌變。這也許是大自然最大的雙刃劍。

    為預防癌症

，成人細胞記錄細胞分裂的次數，一但達到八十次左右的預定極限

，細胞就會死亡。端粒酶幹擾這一記錄過程。

    在佛羅裏達大學進行端粒酶研究的癌症研究者
，馬克*穆勒說，如果你能找到一種藥物或基因療法，那麼就能抵製癌細胞的過度增長。

    "百分之九十的癌細胞都富含端粒酶，"穆勒說。

    包括傑龍公司在內的幾家公司已開始進行抑製端粒酶酵素的藥物試驗
，使之不能延長癌細胞的生命。

    端粒是位於染色體末端的DNA重複序列，而端粒酶使端粒變長。一個端粒的每一個片段就象一張細胞分裂的通行證。細胞分裂到預定的次數時，就停止分裂。

    傑龍公司正在研發一種經修飾的DNA分(fen)子(zi)
，它(ta)可(ke)附(fu)著(zhe)在(zai)端(duan)粒(li)酶(mei)內(nei)部(bu)
，使(shi)之(zhi)不(bu)能(neng)在(zai)癌(ai)細(xi)胞(bao)內(nei)延(yan)長(chang)端(duan)粒(li)末(mo)端(duan)。該(gai)公(gong)司(si)還(hai)在(zai)研(yan)發(fa)一(yi)種(zhong)疫(yi)苗(miao)，這(zhe)種(zhong)疫(yi)苗(miao)訓(xun)練(lian)患(huan)者(zhe)的(de)免(mian)疫(yi)係(xi)統(tong)去(qu)攻(gong)擊(ji)產(chan)生(sheng)端(duan)粒(li)酶(mei)的(de)細(xi)胞(bao)。在(zai)成(cheng)年(nian)人(ren)中(zhong)，幾(ji)乎(hu)所(suo)有(you)產(chan)生(sheng)端(duan)粒(li)酶(mei)的(de)細(xi)胞(bao)都(dou)是(shi)癌(ai)細(xi)胞(bao)。

    在學術上突破性發現二十年之後，才形成這些癌症療法。

    上世紀八十年代初
，伊利莎白*布拉克本、卡洛*格雷德及傑克*紹shao斯si塔ta克ke三san人ren識shi別bie出chu端duan粒li酶mei
，並bing了le解jie其qi作zuo用yong原yuan理li。有you些xie科ke學xue家jia推tui測ce，用yong這zhe種zhong酶mei為wei正zheng在zai老lao化hua的de細xi胞bao贏ying得de多duo餘yu的de時shi間jian，這zhe樣yang可ke以yi延yan長chang人ren的de壽shou命ming。但dan這zhe種zhong想xiang法fa是shi危wei險xian的de，也ye未wei被bei證zheng實shi。

    "僅僅延長端粒可能隻會增加腫瘤形成率
，"在位於美國加利福尼亞州的巴克老年研究所工作的研究員，克麗絲* 帕蒂爾說
，"白鼠試驗已表明，隻有在導入成倍的其它突變阻止癌症的情況下，延長端粒才會延長壽命。"

    因為延長端粒療法具有危險，他認為還有更大的問題需要科學家去解決。

    "在缺乏全麵了解的情況下，用延長染色體端粒的方法來延長壽命是極其危險的，"穆勒說，"我們必須知道如何保養我們的端粒。"

    穆勒認為，科學家進一步了解了衰老的分子基礎之後，人類就能活到九十到二百一十歲。

    "如果明白如何保養
，我們就能延長壽命。但這樣做必須慎之又慎，還必須對其機理有全麵的了解。"穆勒說。