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Re: Non-Specialized cell



Last month there was a discussion about stem and

differentiated cells.  The following appeared in

Monday's Washington Post.  It highlights new findings

about cancers and why they are so hard to kill with

radiation or chemotherapy.



--- jjacobus@mail.nih.gov wrote:

How to Kill Cancer So It Doesn't Grow Back

 

 By Rob Stein

 

  In Greek mythology, a terrifying swamp monster known

as Hydra would regrow two heads for every one lost

when one of the serpent's many necks was severed,

making the beast nearly impossible to slay. Modern

scientists think they may have discovered why cancer

often behaves like Hydra, refusing to die despite

every seemingly mortal blow that medicine inflicts

upon it. 

 

 Current cancer therapies may attack only the

equivalent of Hydra's head -- the majority of cancer

cells removed by surgery or destroyed by radiation and

chemotherapy. Spared is  a crucial pool of mutant

cells that acts as the source of the malignancy,

leaving the cancer able to rise again and again.

 

 According to this theory, which has steadily been

gaining credence, the only effective strategy for

defeating cancer will be found in treatments that

stanch cancer's ability to regrow, such as what

Hercules did when he finally slew the beast of ancient

Greece by cauterizing each of the monster's necks.

 

 In the case of cancer, the solution would lie in

stamping out the highly specialized cells, known as

cancer stem cells, that appear to give rise to the

cancer in the first place. Such cells are largely

impervious to current treatments, enabling them to

lurk silently until they repeatedly spawn new tumors,

either in the same part or in other parts of the body.

 

 "What we've been doing is simply making the tumor

shrink -- leaving the equivalent of the source of the

head behind. So it just regrows," said Michael Clarke,

a professor of medicine at the University of Michigan

in Ann Arbor, who has found evidence for the existence

of breast cancer stem cells. "We need to figure out

how to sever the head so it doesn't grow back." 

 

 In addition to breast cancer, scientists have

produced evidence for the existence of cancer stem

cells in two leukemias and a variety of brain cancers.



 

 In the most recent evidence, published in the Aug. 12

issue of the New England Journal of Medicine,

researchers at Stanford University showed that among

the millions of cancerous cells found in patients

suffering from chronic myelogenous leukemia, only a

small, discrete population had the ability to

replenish the cancer. 

 

 "We showed that only certain cells have the ability

to self-renew," said Irving Weissman, who directs

Stanford's Institute for Cancer/Stem Cell Biology and

Medicine. 

 

 These cells appear to have specific characteristics

-- they are mutant versions of normal stem cells,

which are the immature versions of all cells that have

been the focus of attention in recent years because of

their potential for treating a host of ailments. 

 

 It remains unclear how cancer stem cells originate.

But they probably arise as a result of genetic defects

or exposure to toxins, researchers said. 

 

 "Normal stem cells are regulated by the body to make

just the amount you need," Weissman said. "But a

cancer stem cell has broken out of that control. It

self-renews in an unregulated fashion. Its

self-renewal gets way too big."

 

 Regardless of the cause, scientists are urgently

trying to identify cancer stem cells for every type of

malignancy.

 

 "We're going to keep going through each and every

human cancer to isolate each of the cancer stem cells

and show what their properties are so one can look for

new kinds of therapies," Weissman said.

 

 Identifying the properties of the cancer stem cells

could provide  crucial information, according to Peter

Dirks, a neurosurgeon at the University of Toronto who

has found evidence for cancer stem cells in every form

of brain cancer he has examined. 



 Brain cancer tumors that tend to be more aggressive

appear to have higher concentrations of cancer stem

cells, he said. "We're trying to apply this to patient

prognosis," Dirks said. "This may identify which

tumors are most likely to respond to treatment but

then relapse."

 

 Scientists trying to understand cancer better at a

fundamental level should focus their efforts on cancer

stem cells, he said.

 

 "A lot of research on cancer involves the whole tumor

mass," Dirks said. "If you study the expression of

genes in all those cells you may not be studying the

genes that are the most important."

 

 But perhaps the most important implication is that

identifying and understanding cancer stem cells could

lead to more potent treatments.

 

 "If you think about the basis for leukemia treatment,

generally it is predicated on the idea that leukemia

cells grow faster than the normal cells. So that's

what it goes after," said John E. Dick, a professor of

molecular genetics at the University of Toronto, who

discovered cancer stem cells for acute myelogenous

leukemia.

 

 "But these cells aren't. These leukemia stem cells

are resting. They behave just like a normal stem cell.

They sit there and eventually will regrow the

leukemia," Dick said. "It's critically important to

understand these leukemia stem cells so we can target

them.

 

 "What we need to be able to do is identify these

cancer stem cells to understand their properties so we

can begin to be more strategic and kill the cancer at

its source, which are these cancer stem cells."

 

 That is exactly what Craig T. Jordan, a professor of

medicine at the University of Rochester, has started

to try to do. Jordan has identified a molecular switch

involved in cell survival that appears to be unique to

leukemia stem cells and absent from normal blood stem

cells. "We don't think normal treatments would hit

this target, which is why patients relapse," he said.

 

 Jordan  has begun testing drugs that, at least in the

laboratory, appear highly effective at killing 

leukemia stem cells while sparing healthy stem cells,

he said. 

 

 "It looks fantastic in the lab. In the laboratory we

can very effectively kill the tumor without killing

the normal stem cells," he said. 

 

 A preliminary trial involving leukemia patients has

begun at the University of Kentucky, Jordan said. 

 

 "It's finally getting to the exciting point," he

said.

 

------------------   



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© 2004 The Washington Post Company





=====

+++++++++++++++++++

"Everyone is ignorant, only on different subjects."

Will Rogers



-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com





		

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