On the Road to Rational Cancer Therapy

The p53 protein is an important human defense against cancer, protecting against cancer at least three ways:

1. It can activate DNA repair proteins when DNA has sustained damage.
2. It can also hold the cell cycle at the G₁/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle.)
3. It can initiate apoptosis, the programmed cell death, if the DNA damage proves to be irreparable.

Source

Researchers at the UPenn Schools of Medicine and Veterinary Medicine plan to pre-screen patients' tumours for p53, to verify if treatment with proteasome inhibitors would be effective for that tumour.

They propose to test for p53, a well-known tumor-suppressor protein that is broken down by cellular machinery called proteasomes. This study appears online in the journal Blood, in advance of print publication in June 2007.

In cancer patients whose tumors do not produce p53, proteasome inhibitors might be ineffective. This patient group could be spared unnecessary treatment with possible harmful side effects. On the other hand, proteasome inhibitors are highly effective against lymphomas that do have the ability to produce p53.

“Proteasomes resemble paper shredders – they break down proteins such as p53 into smaller pieces,” says senior author Andrei Thomas-Tikhonenko, PhD, Associate Professor of Pathology. “A proteosome inhibitor effectively jams the shredder so that p53 is not immediately broken down.”

In this study, the research team used a mutant strain of mice in which p53 activity can be switched on and off. “In principle, tumors in these mice could be obliterated by turning p53 back on,” says Thomas-Tikhonenko. “The problem was that a protein called MDM2 sent p53 into the teeth of the proteasome shredder.” The proteasome inhibitor bortezomib (Velcade®) causes this jamming process and restores p53 function. However, if p53 was inactivated in the mice, bortezomib treatment failed to kill tumors. Similar effects were seen with cell lines derived from human Burkitt’s lymphomas. When implanted into mice, these lymphoma cells were highly sensitive to the proteasome inhibitor, but as soon as p53 was removed, the inhibitor had no effect.

“These findings have important implications for clinical practice,” Thomas-Tikhonenko adds.

Source

Proteasomes degrade short-lived proteins as a normal housekeeping function. Eventually, more selective ways of increasing the action of p53 in tumour cells will be developed, but as a stop-gap measure on the road to rational cancer therapy, proteasome inhibitors will be a useful tool.

Cancer, Hair, Germs, and Steel

First, steel. This story reports on a recently finished bridge that used a new, better form of steel. The copper alloy steel was developed at Northwestern University. The steel has a strength of 70,000 pounds per square inch (psi) compared with 50,000 psi in commonly used structural steel. It is also easy to weld, and tests have shown it has high-impact toughness at low temperatures. In addition, the high copper content gives the alloy much better resistance to atmospheric corrosion than other high-performance steels. Source. I cannot help but wonder why it took 9 years before this better steel was used in large structures when it seems to have so many advantages.

Next, hair. Scientists in the UK have discovered how to command skin cells to become hair follicles. "Which cells are transformed into hair follicles is determined by three proteins that are produced by our genes.

"Our research has identified how one of these proteins working outside of the cell interacts at a molecular level to determine an individual's hair pattern as the embryonic skin spatially organises itself." Source.
The only treatments likely to earn more money for their developers than the cure for baldness, might be the cures for obesity, a true aphrodisiac, and a true life extension drug.

Third, cancer. Researchers at UCR have added to the knowledge of normal prevention of cancer transformation in cells. Liu published her research findings in a featured article titled Mechanistic insights into maintenance of high p53 acetylation by PTEN, in the Aug. 18 issue of Molecular Cell. Co-authors include UCR colleagues Andrew G. Li, Landon G. Piluso Xin Cai and Gang Wei; with William R. Sellers in the Department of Medical Oncology, Dana Ferber Cancer Institute of Harvard University in Boston.

They found that when a cell’s DNA becomes damaged, PTEN forms a complex with another protein, p300, which in effect, switches on p53, a very important tumor suppressor.

“I would like to continue to expand our understanding of how p53 is activated in conjunction with PTEN and under what circumstances it functions to protect the cell,” Liu said. Source.

Finally, germs. Bacterial resistance occurs due to routine mutations in microbes, and is a major cause of morbidity and mortality. Scientists at St. Jude Children's Research Hospital have made a finding that may give drug developers a new advantage in the fight against the gram positive pathogens such as strep and staph. Rock's team showed that gram-positive pathogens first use PlsX to synthesize a compound called fatty acyl-phosphate, then use PlsY to transfer the fatty acid to G3P. These steps initiate membrane phospholipid formation required for cell growth.

"Our discovery of PlsX and PlsY not only solved a troublesome mystery," Rock said. "It's also important because identifying the essential components required for disease-causing bacteria to grow and multiply is a key part of developing new strategies for controlling infections." Source.

Many microbiologists believe that the mutating ability of microbes is so great as to make it unlikely that science will ever develop antibiotics that microbes are unable to resist, eventually. Personally, I believe that evolution only has a limited set of tools for each class of organism. It is up to science to learn what these tools are, then to devise treatments that are not susceptible to those tools. Doing that will require persistence, heightened perception, and invention on the part of scientists.

Update: For an example of a novel attempt to bypass bacterial resistance, read this newsrelease.

Fireflies Help Fight Cancer: Restoring p53 Tumour Suppressor Function

Researchers at the University of Pennsylvania School of Medicine have used the luminescence from fireflies to help screen small molecules that might help restore p53 tumour suppressor gene function to cancer cells that had lost that protection through mutation.

In an attempt to defend the body, a normal p53 protein will bind to DNA during periods of cellular stress or damage. The binding of p53 to DNA initiates downstream reactions that keep the stressed cells from multiplying. Under normal conditions, p53 will activate the p21 gene, causing the cell cycle to freeze, halting cell proliferation; p53 will activate KILLER/DR5, which signals for cell death, or apoptosis. Chemotherapy and radiotherapy set out to deliberately stress tumor cells in hopes of promoting their self-destruction. Unfortunately, mutations to the p53 gene disrupt the intracellular defense system.

"Mutants of p53 that occur in human cancer fail to bind to DNA or to activate target genes, such as p21 and KILLER/DR5," explains El-Deiry, who is also the Co-Program Leader of the Radiation Biology Program at the Abramson Cancer Center at Penn. "Therefore, when cells are stressed or damaged, p53-mutant cells fail to shutdown and continue to divide uncontrollably." The development of a drug screen by El-Deiry's lab allowed the researchers to trace the activity of small molecules in p53-mutant cancer cells.

The small molecule drug screen, developed by El-Deiry's lab, was created by inserting firefly luciferase, a reporter gene capable of emitting light, into human tumor cells carrying the p53 mutation, and observing the subsequent response.

"Just as fireflies emit light that we can see with our eyes, the cancer cells were engineered to emit light if a p53-like response was triggered by any of the small molecules that we examined," explains El-Deiry.

The small molecules screened by El-Deiry's research group were obtained from the Developmental Therapeutics Program at the National Cancer Institute. The molecules represent many classes of compounds and include both natural and man-made chemicals.

"One by one, we introduced the small molecules to the p53 mutant cancer cells, which possessed the luciferase reporter gene and screened for light emissions," describes El-Deiry. The light emissions displayed by the live cell imaging instrumentation revealed which molecules were able to achieve p53 responses in the abnormal cancer cells. Further testing exposed the ability of high doses of several groups of the small molecules to kill human cancer cells in cell culture and in mouse models implanted with human tumors.

"Our work provides a blueprint for how molecularly targeted therapy can be discovered using new optical imaging technology," states El-Deiry. "This is very important going forward in the era of molecular medicine and individualized therapy for cancer patients."

Source.

This is a clever approach to cancer drug discovery. This type of drug, if effective, could become a useful second line defense against cancer, after prevention. As cancer screens become more sensitive--able to pick up malignancies very early--the need for safe broad spectrum anti-tumour drugs such as this type of tumour suppressor gene restorer becomes greater. The key is to find such tumour suppressor gene augmentors/restorers that are both safe and effective. Good luck to the UPenn. lab.

Resveratrol, Quercitin, Calorie Restriction, Longevity

Scientific American's new issue contains an article about "longevity genes" and the search to unlock them. Many articles have been written about the Sir and Sirt genes known to influence longevity in yeast and lower animals. The recent SciAm article brings us fairly up to date on the research of the authors and their associates (David Sinclair and Lenny Guarente).

Calorie restriction (CR) was cited as one of the few maneuvers known to increase lifespan of laboratory animals. Not surprisingly, CR works through the Sirt genes. What was surprising was that resveratrol, found in red grapes and wine, also affects the Sirt genes in much the same way as CR.

First of all, the researchers had to dispense with an old theory that turned out to be false:
The phenomenon (life extension through CR) was long attributed to a simple slowing down of metabolism--cells' production of energy from fuel molecules--and therefore reduction of its toxic by-products in response to less food.

But this view now appears to be incorrect. Calorie restriction does not slow metabolism in mammals, and in yeast and worms, metabolism is both sped up and altered by the diet. We believe, therefore, that calorie restriction is a biological stressor like natural food scarcity that induces a defensive response to boost the organism's chances of survival. In mammals, its effects include changes in cellular defenses, repair, energy production and activation of programmed cell death known as apoptosis.

....Yet if humans are ever to reap the health benefits of calorie restriction, radical dieting is not a reasonable option. Drugs that can modulate the activity of Sir2 and its siblings (collectively referred to as Sirtuins) in a similar manner will be needed. Just such a Sirtuin-activating compound, or STAC, called resveratrol has proven particularly interesting. Resveratrol is a small molecule present in red wine and manufactured by a variety of plants when they are stressed. At least 18 other compounds produced by plants in response to stress have also been found to modulate Sirtuins, suggest?-ing that the plants may use such mole?-cules to control their own Sir2 enzymes.

....Feeding resveratrol to yeast, worms or flies or placing them on a calorie-restricted diet extends their life spans about 30 percent, but only if they possess the SIR2 gene. Moreover, a fly that overproduces Sir2 has an increased life span that cannot be further extended by resveratrol or calorie restriction. The simplest interpretation is that calorie restriction and resveratrol each prolong the lives of fruit flies by activating Sir2.

Resveratrol-fed flies not only live longer, despite eating as much as they want, but they do not suffer from the reduced fertility often caused by calorie restriction. This is welcome news for those of us hoping to treat human diseases with molecules that target Sir2 enzymes. But first we want a better understanding of the role of Sir2 in mammals.

....Increased Sirt1 (the mammalian version of Sir2) in mice and rats, for example, allows some of the animals' cells to survive in the face of stress that would normally trigger their programmed suicide. Sirt1 does this by regulating the activity of several other key cellular proteins, such as p53, FoxO and Ku70, that are involved either in setting a threshold for apoptosis or in prompting cell repair. Sirt1 thus enhances cellular repair mechanisms while buying time for them to work.

....Both our labs are running carefully controlled mouse experiments that should soon tell us whether the SIRT1 gene controls health and life span in a mammal. We will not know definitively how Sirtuin genes affect human longevity for decades. Those who are hoping to pop a pill and live to 130 may have therefore been born a bit too early. Nevertheless, those of us already alive could live to see medications that modulate the activity of Sirtuin enzymes employed to treat specific conditions such as Alzheimer's, cancer, diabetes and heart disease. In fact, several such drugs have begun clinical trials for treatment of diabetes, herpes and neurodegenerative diseases.

The authors were careful not to hype resveratrol, since the research is still ongoing. Other people working with CR are a bit more enthusiastic about resveratrol. Both resveratrol and quercetin have been known for a number of years now to influence Sirt genes. Vitamin and supplement makers are growing quite sophisticated in keeping up with research, and waste no time making natural phytochemicals available to the public, where legal.

It is unlikely that these phytochemicals represent a hazard to the public. Certainly I have been imbibing resveratrol in liquid form for several years now, with no untoward effects noted. Nevertheless, it is hazardous to the purse to buy every supplement that some vitamin salesman promotes. Follow the research and make up your own mind.

I recommend reading the Scientific American article in its entirety.