Researchers at The University of Queensland have helped identify genes that could hold the key to treating a common and deadly type of breast cancer.

The discovery suggests a vaccine could be developed for ER negative breast cancer, which accounts for a third of all breast cancer cases, has a generally poor prognosis and few therapy options.

Work carried out by Professor Sunil Lakhani and his team at UQ’s Centre for Clinical Research, played a key role in the project which was lead by the international Ludwig Institute for Cancer Research (LICR).

The study results were published yesterday in the Proceedings of the National Academy of Sciences (PNAS).

The UQCCR team provided analysis of nearly 1,600 tumor samples to confirm the presence of two families of CT-X genes in nearly half of ER negative breast cancers. CT-X genes are thought to be responsible for a natural form of cancer control and might be the cause of spontaneous cancer remission.

“ER negative breast cancer includes a particularly severe type of cancer - triple negative breast cancer, which tends to metastasize early and often to the brain. Many of these cancers are not responsive to current therapies,” Prof Lakhani said.

“These findings suggest that a therapeutic vaccine, combining members of the two CT-X families, could be a new therapy for filling a critical unmet need,” he said.

TNBC is more common in young and African American women.

CT-X gene products are the targets of therapeutic cancer vaccines already in phase III clinical trials for lung cancer and melanoma.

Dr Andrew Simpson, LICR scientific director and an author of the study, said clinical trials based on the findings of the PNAS study could theoretically be initiated in the near future.

Source
University of Queensland

TORONTO, July 29 — Human papillomavirus (HPV), which causes some cases of oropharyngeal cancer, also leads to a more treatable form of the disease and better outcomes for patients, researchers said.

Having an HPV-positive tumor was associated with significantly longer overall survival in both a retrospective analysis and a prospective clinical trial, according to Kevin Cullen, M.D., director of the Greenebaum Cancer Center of the University of Maryland in Baltimore, and colleagues.

The finding also helps to explain why black Americans with oropharyngeal cancer do worse than whites, the researchers said in the September issue of Cancer Prevention Research.

At a press conference, Dr. Cullen and other experts told reporters that the finding should change practice. “We are now testing for HPV, which we weren’t doing even a few months ago,” Dr. Cullen said.

• Explain to interested patients that it has long been known that black patients do worse than whites with squamous cell carcinoma of the head and neck.
• Note that this study shows the difference is driven by differences in oropharyngeal cancer outcomes, and those differences, in turn, are driven by infection with human papillomavirus.

HPV testing for oropharyngeal cancer patients has implications for both prognosis and treatment, he said.

Overall, Dr. Cullen said, blacks are known to have worse outcomes for squamous cell carcinoma of the head and neck although the reasons for the differences have not been entirely clear.

“This is the first clue that it may be biologic rather than related to issues of access, insurance or provider attitudes.”

Indeed, he and his colleagues found, the survival disadvantage is entirely driven by differing outcomes in oropharyngeal cancer and that difference, in turn, is driven by HPV infection.

The “paradox,” Dr. Cullen told reporters, is that “HPV may cause some of these cancers, but HPV-positive cancers behave biologically very well — they are very responsive to chemotherapy and radiation.”

He said the virus is not protective, but instead gives rise to cancers that are more amenable to chemotherapy and radiation than are those caused by tobacco and alcohol use.

The black-white difference is caused by significantly lower rates of oral HPV among blacks, which may be a function of differing sexual practices, Dr. Cullen said during the press conference.

Acquiring an HPV infection through genital sex would tend to protect a person against a subsequent oral infection and vice versa, according to Otis Brawley, MD, chief medical officer of the American Cancer Society.

Dr. Brawley told reporters that there is some evidence of racial differences in sexual behavior risks, especially among teenagers.

The CDC, he said, has found “distinct preferences” among young whites for oral sex as their initial sexual activity and among black youths for genital sex.

Such a difference in behavior “makes a lot of sense in terms of causation,” he said.

In the current study, the researchers first analyzed a retrospective cohort of 106 white and 95 black patients with squamous cell carcinoma of the head and neck and found that median overall survival was 52.1 months for whites and 23.7 months for blacks.

The difference — significant at P=0.009 — was due entirely to overall survival in the subgroup with oropharyngeal cancer, where whites had a median overall survival of 69.4 months and blacks just 23.7 months.

The difference in the oropharyngeal cancer subgroup was significant at P=0.0006, but “if you looked at patients with (cancer in) other sites, there was no difference at all,” Dr. Cullen said.

To understand the effect of HPV, the researchers looked at prospectively collected tissue samples from patients taking part in the phase III multicenter TAX 324 trial of induction chemotherapy followed by concurrent chemoradiation.

All told, the cancers of 196 white patients and 28 black patients could be assessed for HPV status and 68 of them (28%) had HPV-positive tumors — 59 of which (87%) were oropharyngeal.

For all tumor sites, median overall survival was 26.6 months for patients with HPV-negative tumors, but has yet to be reached for patients with HPV-positive oropharyngeal cancers — a difference that yielded a hazard ratio for 5.1, which was significant at P<0.0001.

That was, Dr. Cullen said, “an astounding biologic effect.”

As in the retrospective cohort, most of the effect was caused by differences among oropharyngeal patients, the researchers said.

Half of all of the analyzed oropharyngeal patients — 59 of 119 — were HPV positive and all but one of these patients were white. Median overall survival has yet to be reached for the HPV-positive patients but was only 20.9 months for HPV-negative patients, a difference that was again significant at P<0.0001.

In white patients, the proportion of HPV-positive tumors was nearly nine times higher than in blacks — 66 of 196 tumors or 34% compared with one of 28 or 4%. The difference was significant at P=0.0004.

The study makes an “extremely important finding that has tremendously important public health implications,” according to Scott Lippman, MD, of M.D. Anderson Cancer Center in Houston, editor of the journal.

“It’s the most important development in head and neck cancer that I’ve seen in the past 30 years,” he said.

For clinicians, Dr. Brawley said, the study “will change how we practice. Everybody will now want to look at their head and neck cancers and analyze them for HPV.”

He noted that the study implies that the apparent black-white difference in outcomes is really a difference in who is infected with HPV.

“It’s a landmark paper for two reasons,” said Martin Blaser, MD, of New York University Langhorne Medical Center, an expert in the links between infectious agents and cancer.

First, he said, it clarifies the links between the disease and racial differences in outcomes. But the research also has implications for understanding the biology of cancer and the links with infectious agents, he added.

“This study is important because it helps explain both cancer causation,” he said, ” and also differences in incidence and outcome.”

The study was supported by sanofi-aventis US, the State of Maryland Cigarette Restitution Fund, and the Orokawa Foundation. The researchers did not report any conflicts.

Primary source: Cancer Prevention Research

Source reference:

Settle K, et al “Racial survival disparity in head and neck cancer results from low prevalence of human papillomavirus infection in black oropharyngeal cancer patients” Cancer Prev Res 2009; DOI: 10.1158/1940-6207.CAPR-09-0149.

HOUSTON, July 30 — Children with acute lymphoblastic leukemia (ALL) had a significantly greater likelihood of exposure to household pesticides compared with a control group, investigators found in a small case-control study.

• Explain to parents that exposure to household pesticides has been associated with an increased risk of ALL in children.
• Note that the association does not prove that pesticide exposure causes ALL.

More than twice as many mothers of children with ALL reported using pesticides in the home than did mothers of the control children, according to a report in the August issue of Therapeutic Drug Monitoring.

The findings reinforce a hypothesized association between organophosphate pesticides and ALL.

“The relationship between child health and environmental exposure to organophosphates is limited and has not been shown to be a causal relationship,” said Offie P. Soldin, PhD, of Georgetown University in Washington, and colleagues.

“There is therefore a need for more research, especially research based on biomarkers, of a larger sample size that includes exposures during specific time windows, exposure intensity, exposure-exposure or exposure-gene interactions, and relatively rare health outcomes such as childhood cancer.”

ALL is the most common childhood cancer and tends to affect children ages 3 to 7. Aside from Down syndrome, which increases leukemia risk by 10- to 20-fold, risk factors for ALL have remained largely hypothetical.

Studies have shown higher levels of organophosphates in children than in adolescents and adults, the authors said. And detection of pesticides in cord blood and blood of newborns indicates that pregnant women and their fetuses are exposed to pesticides.

Several recent investigations have suggested that maternal exposure to pesticides increases the risk of ALL in offspring. Exposure to pesticide strips and household pesticides has been associated with a twofold increase in the risk of ALL in children, the authors said. On the other hand, associations with professional extermination have been inconsistent.

The authors continued the examination of associations between pesticides and childhood ALL in a group of 41 children with ALL and their mothers, all from the Washington area. The case group was matched for age and area of residence with 41 children without ALL.

Investigators assessed environmental exposures by means of questionnaires and by analysis of pesticide metabolites in urine samples.

The analysis focused on six organophosphate metabolites commonly found in household and garden insecticides. The metabolites consisted of three dimethyl phosphates and three diethyl phosphates.

The authors said that 33% of case mothers reported use of insecticides in the home compared with 14% of control mothers (P<0.02).

Other environmental exposures were not significantly associated with ALL.

Children with ALL had significantly higher levels of diethyldithiophosphate (P<0.05) and diethylthiophosphate (P<0.03).

Overall, pesticide levels were higher in the cases than in the controls (P<0.05).

Reported pesticide use on the questionnaire did not correlate with the urine pesticide concentrations, the authors said.

They also noted that their study had limitations inherent to case-control studies, including the fact that they will not detect rare events or very small relative risks, do not directly measure risk, and cannot determine causality.

The study was supported by a grant from the National Cancer Institute. The authors reported no competing financial interests.

Primary source: Therapeutic Drug Monitoring

Source reference:

Soldin OP, et al “Pediatric acute lymphoblastic leukemia and exposure to pesticides” Ther Drug Monit 2009; 31(4): 495-501.

The masterpieces that spring from the talents of Rembrandt, Van Gogh and other artists often begin with the creation of a gradient of colors on a palette. In a similar manner, researchers at the National Institute of Standards and Technology (NIST) have created an innovative device called the “microfluidic palette” to produce multiple, steady-state chemical gradients - gradual changes in concentration across an area - in a miniature chamber about the diameter of a pinhead. The tool can be used to study the complex biological mechanisms in cells responsible for cancer metastasis, wound healing, biofilm formation and other fluid-related processes.

The advantage of the NIST system, as described in a new paper,* is that the gradients are generated by diffusion - the gentle movement of matter from one point to another by random molecular motion. Microfluidic systems usually mix fluids more actively, by pumps and the circulation of currents. Diffusion gradients allow cells being studied to remain in the microchamber without the chance of their being swept away. Diffusion also permits chemical molecules to move in and out of the cells naturally and eliminates the risk of shear stresses, commonly produced by currents, which could cause the cells to rupture or behave abnormally.

The NIST microfluidic palette manages this with a clever plumbing trick. The key element of the palette is the microchamber, a small disk-shaped area only 1.5 millimeters (0.06 inch) across etched into the center of a glass wafer. Tiny holes at its circumference - three in the prototype, but it could be more - allow various mixtures to flow into the chamber. Beneath the chamber, each access port connects to the long tail of a Y-shaped channel etched into a second layer. These channels deliver test chemicals to the chamber. Fluid flow in and out of the short arms of each Y at constant pressure assures a constant stream of fresh chemicals. Because the pressure in the chamber is balanced by filling it previously with a buffer solution, the test chemicals that migrate from the channels into the chamber do so almost entirely by diffusion. Therefore, as long as a constant flow of fluid is maintained through the Y’s, the gradients in the chamber can be maintained virtually indefinitely.

To demonstrate how the microfluidic palette works, the NIST researchers inject dyes of the three primary colors - red, yellow and blue - separately into the three inlets of the system. For each dye, an independent gradient forms that remains constant as long as flow rate into the system does not change. Overlapping the three gradients results in a blend of dye concentrations in which the combination of colors at one location is distinctly different from any other location.

Similarly, if three separate drugs were injected into the palette where the microchamber contained a culture of cells, individual cells at different locations in the chamber would be exposed to different combinations of the drugs. In a single experiment, one could easily study the effects of a wide range of mixed drug concentrations on the same cell type.

Another potential application of the microfluidic palette is the study of chemotaxis, the movement of cells along a chemical gradient, a biological phenomenon that plays a role in the spread of cancer (metastasis), wound healing, infection and carbon cycling in the ocean.

The microfluidic palette technology is available for licensing. For more information, see the Federal Register, Vol. 74, No. 73, page 17819 (April 17, 2009).

* J. Atencia, J. Morrow and L.E. Locascio. The microfluidic palette: A diffusive gradient generator with spatio-temporal control. Lab on a Chip. Posted online June 22, 2009.

Source:
Michael E. Newman

National Institute of Standards and Technology (NIST)

Older people with a history of cancer are more likely to have disabilities and be frail and vulnerable than older adults who have not had cancer, according to a study in the Journal of the National Cancer Institute, published online July 29.

The prevalence of frailty and vulnerability among older cancer patients will pose an increasing challenge for physicians as the population ages. By the year 2030, persons who are older than 65 years are projected to make up 70% of cancer patients and have 65% of cancer deaths.

Supriya Gupta Mohile, M.D., from the James P. Wilmot Cancer Center at the University of Rochester in N.Y., and colleagues used data in the 2003 Medicare Current Beneficiary Survey to evaluate whether non-skin cancer was independently associated with vulnerability and frailty. They found that survey respondents with a history of non-skin cancer had statistically significantly more limitations in the activities of daily living and other measures of frailty and vulnerability than those who had not had cancer.

The authors conclude that their study “establishes the increased baseline prevalence of factors among cancer patients that have been associated with adverse health outcomes…” They also note that the study is “a first step in highlighting the importance of “staging the aging” (i.e., assessing factors that characterize physiological and functional capacity) among cancer patients by the use of geriatric assessment.”

Source:
Steve Graff

Journal of the National Cancer Institute

Three studies published on bmj.com examine the merits of conservative versus aggressive treatment policies of women with low-grade abnormal results detected by cervical screening.

Together they form the Trial of Management of Borderline and Other Low-grade Abnormal Smears (TOMBOLA).

The first finds no benefit in referring these women for colposcopy (a detailed inspection of the cervix to detect pre-cancerous cells) compared to regular surveillance.

A second paper also questions the benefit of immediate treatment to remove abnormal tissue from the cervix (a procedure known as large loop excision) over the more conservative strategy of taking small tissue samples (biopsies) and recalling women for treatment only if pre-cancerous lesions are confirmed.

Finally, a cost effectiveness study shows that immediate colposcopy is no more, or no less, cost effective than regular surveillance.

The findings are based on data from about 4,500 women aged 20-59 from two regions of Scotland (Grampian and Tayside) and one of England (Nottingham) with borderline or low-grade abnormal smears detected after NHS cervical screening examinations.

In the first study, women were randomised to either repeat smears or to immediate referral for colposcopy. All women were tracked for three years and underwent a colposcopic examination at the end of the study.

The results showed that, although colposcopy detects more high-grade pre-cancerous lesions (known as cervical intraepithelial neoplasia or CIN) than surveillance, it causes more side effects and can lead to over-treatment, complications and later problems in pregnancy. The authors conclude that “a policy of referral for colposcopy after low-grade cervical abnormalities confers no clear benefit compared to cytological surveillance, and causes more side effects.”

In the second study, women were randomised to either immediate large loop excision or up to four biopsies with recall for treatment if necessary. Again, women were tracked for three years and underwent a colposcopic examination at the end of the study.

There was no difference between the policies with regard to detection of high-grade cervical intraepithelial neoplasia over three years. However, immediate large loop excision resulted in substantial over-treatment and more after effects than biopsy and recall. The authors conclude that a policy of immediate large loop excision confers no clear advantage over a policy of punch biopsies with recall for treatment, and the latter provides the best balance between benefits and harms.”

A cost effectiveness study shows that, taking into account costs, outcomes, and quality of life, follow-up by immediate colposcopy is no more and no less cost effective than follow-up by regular surveillance. The authors conclude that “there is no compelling economic reason to favour any one follow-up method over either of the others.”

The dilemma of choosing between conservative and aggressive policies remains, adds Professor Eduardo Franco of McGill University in an accompanying editorial. Further analyses and secondary economic evaluations of the TOMBOLA data may help policy makers fully appreciate the evidence from this landmark study, he says.

Links

Research: “Cytological surveillance compared with immediate referral for colposcopy in management of women with low grade cervical abnormalities: multicentre randomised controlled trial”

Research: “Biopsy and selective recall compared with immediate large loop excision in management of women with low grade abnormal cervical cytology referred for colposcopy: multicentre randomised controlled trial”

Cost effectiveness study: “Options for managing low grade cervical abnormalities detected at screening”

Editorial: “Managing low grade and borderline cervical abnormalities”

Source
British Medical Journal

Cervical screening in women aged 20-24 has little or no impact on rates of invasive cervical cancer up to age 30, concludes a study published on bmj.com.

A second study shows that the risk of developing pre-cancerous lesions on the surface of the cervix (known as cervical intraepithelial neoplasia or CIN) is much higher in women with persistent human papillomavirus (HPV) infection, especially the high-risk HPV types 16 and 18.

Together, these findings highlight the challenges faced by policy makers in balancing the benefits and harms of screening women at different ages and at different levels of risk.

In 2003, cervical screening in England was moved to start at age 25 as it was felt it did more harm than good in younger women. But recent public controversy has led the government to review whether women aged 20-24 should be offered smear tests, as they are in Scotland, Wales and Northern Ireland.

So researchers at Queen Mary, University of London set out to study the impact of screening on risk of cervical cancer at different ages. They identified 4,012 women aged 20-69 diagnosed with cervical cancer between 1990 and 2008 and a matched group of 7,889 healthy controls of the same age and living in the same area.

They found no evidence that screening women aged 22-24 reduced the incidence of cervical cancer over the next five years (at ages 25-29).

Screening was associated with a 60% reduction of cancers in women aged 40, increasing to 80% at age 64. Screening was particularly effective in preventing advanced stage cancers. However, in younger women, the effect of screening was substantially and significantly less.

For example, screening between the ages of 30 and 37 was associated with a reduction in the risk of cervical cancer over the next five years of between 43 and 60%, while screening at ages 20-24 had no detectable impact on cervical cancer rates under the age of 30.

In fact, a careful review of the screening histories of women aged 20-24 with a diagnosis of cancer suggests that few, if any, of the cancers occurred through a lack of screening, say the authors. Indeed, only five of 73 women had not been screened in the previous six years.

Finally, they point out that the risk of cancer under age 25 in women vaccinated against HPV will be low enough to make screening at such an age unjustifiable.
Policy decisions should be based on balancing the benefits and harms of screening and the need to take into account the underlying risk of cervical cancer at different ages, write the authors. “We have provided more accurate estimates of the benefits of cervical screening in different age groups, which should aid policy makers in making their decisions,” they conclude.

In an accompanying editorial, three cancer specialists suggest that in many developed countries the low incidence of invasive cervical cancer and the lack of effectiveness of screening in young women indicate that screening should not start before the age of 25. At younger ages, the main challenge is to find the progressive lesions and to avoid treating the remaining lesions, given that treatment may be harmful to future reproductive health, they conclude.

Links

Research: “Effectiveness of cervical screening with age: population based case-control study of prospectively recorded data”

Research: “Short term persistence of human papillomavirus and risk of cervical precancer and cancer: population based cohort study”

Editorial: “Cervical screening according to age and HPV status”

Source
British Medical Journal

The International Agency for Research on Cancer (IARC) has moved sunbeds (UV tanning beds) up to the highest cancer risk category-group 1-’carcinogenic to humans’. The use of sunlamps and sunbeds was until now classified as “probably carcinogenic to humans” (group 2A). IARC also moved ultraviolet radiation into group 1. These and other findings are revealed in a Special Report in the August edition of The Lancet Oncology, produced by Dr Fatiha El Ghissassi and her colleagues, IARC, Lyon, France, on behalf of the WHO International Agency for Research on Cancer Monograph Working Group.

The authors say: “The use of UV-emitting tanning devices is widespread in many developed countries, especially among young women. A comprehensive meta-analysis concluded that the risk of skin melanoma is increased by 75% when use of tanning devices starts before 30 years of age. Additionally, several case - control studies provide consistent evidence of a positive association between the use of UV-emitting tanning devices and ocular melanoma. Therefore, the Working Group raised the classification of the use of UV-emitting tanning devices to Group 1, ‘carcinogenic to humans’.”

The characteristic genetic mutation that is caused by solar (ultraviolet/UV) radiation has long been attributed to UVB radiation. However, the same mutation was detected in the skin of UVA-treated mice, and in UVA-induced mouse skin tumours. Thus IARC reclassified UV radiation as a whole (UVA, UVB and UVC) as carcinogenic to humans, or group 1. UVA, UBC, and UVC radiation were each previously in group 2A, “probably carcinogenic to humans”.

The working group also concluded that there was sufficient evidence for ocular melanoma in welders; however, because welders are exposed to other harmful agents, the risk could not be specifically attributed to UV radiation. The authors say: “A full review of the carcinogenic hazards of welding will be undertaken with high priority.”

All types of ionising radiation were also classified as Group 1. This was the first time all these types of radiation were reviewed by one working group during one meeting. Examples of ionising radiation are:

- Radon gas (seeping from soil, rocks, and building materials), which enters the lungs and causes damage (affecting the whole population). The Special Report says that radon is the second leading cause of lung cancer (8-15% of cases) after tobacco smoke

- Plutonium and its decay products, affecting the bones, liver and lungs of plutonium workers.

- Radium and its decay products, affecting the bones of medical patients

- Phosphorous-32 and its decay products, causing acute leukaemia in medical patients

- Radioiodines, affecting the thyroids in children and adolescent survivors of nuclear reactor accidents

Link to Special Report

Source
The Lancet Oncology

A new study investigated the effectiveness of S-adenosylmethionine (SAMe) in the prevention and treatment of hepatocellular carcinoma (HCC) or primary liver cancer. SAMe, a widely available nutritional supplement, with little known side effects, was found to be effective in preventing the formation of HCC in rats. However, high enough levels of SAMe were not attainable to successfully treat established HCC. The findings are available in the August issue of Hepatology, a journal published by John Wiley & Sons on behalf of the American Association for the Study of Liver Diseases.

HCC is the fifth most common cancer and the third most frequent cause of cancer death worldwide. Risk factors for HCC include chronic infection with hepatitis B virus, hepatitis C virus (HCV), dietary aflatoxin, excessive alcohol use, cigarette smoking, obesity. The overall 5-year survival for HCC patients is less than 10% and the disease rate is expected to rise due to the high prevalence of HCV in many areas of the world.

Shelly Lu, M.D., of the Keck School of Medicine at the University of Southern California, and colleagues studied the effects of SAMe on chemoprevention and treatment of HCC. In the U.S. the incidence of HCC doubled from 1979 to 1995 and the number of HCC cases for the following 20 to 30 years is projected to increase. “Given these projections, there is a tremendous interest in developing effective chemoprevention strategies,” said Dr. Lu. “And an important property of SAMe that makes it an attractive agent for chemoprevention and treatment of HCC is its ability to selectively kill liver cancer cells,” she added.

During the study researchers injected H4IIE cells into rats and found a 1cm tumor developed in the liver two weeks after injection. A regimen of IV SAMe was started one day after injecting the cells and continued for ten days. The researchers monitored the animals using MRI, ultrasound, and visual inspection to assess the liver tumors. “Treatment with IV SAMe by continuous infusion significantly reduced the tumor size and significantly prevented tumor development after 11 days,” researchers discovered.

Researchers found that if SAMe infusion was started after sizable tumors had already formed it failed to reduce the rate of tumor growth after 24 days of treatment. This is because of a compensatory response of the liver to metabolize SAMe and prevent its accumulation. “The observation that SAMe failed to exert any therapeutic effect in already established HCC is disappointing,” said Dr. Lu. “But whether SAMe can be effective in treating HCC in man remains unclear because this compensatory mechanism may not work properly in human HCC. Nevertheless, effectiveness of SAMe in chemoprevention of human HCC deserves study now.”

Citation:
“S-Adenosylmethionine in the Chemoprevention and Treatment of Hepatocellular Carcinoma in a Rat Model,”
Shelly Lu, Komal Ramani, Xiaopeng Ou, Mark Lin, Victor Yu, Kwangsuk Ko, Ryan Park, Teodoro Bottiglieri, Hidekazu Tsukamoto, Gary Kanel, Samuel French, Jose Mato, Rex Moats, Edward Grant
Hepatology August 2009

Source
Hepatology

UCSF researchers have identified a new potential drug target for the herpes virus that causes Kaposi’s sarcoma, re-opening the possibility of using the class of drugs called protease inhibitors against the full herpes family of viruses, which for 20 years has been deemed too difficult to attain.

The new drug target, which is known as a protease dimer, could serve as a model for developing new therapeutics for diseases ranging from cancer to Alzheimer’s, the researchers say. Findings are reported in the Advance Online Publication section of the Nature Chemical Biology web site and can be found at http://www.nature.com/nchembio/index.html.

Most current antiviral drugs target the active sites of viral proteins, where enzymes and receptors work in a lock-and-key approach to either activate or deactivate that particular protein, the researchers explained. Traditionally, drug development has focused on inhibiting that lock-and-key action to prevent the enzyme, or receptor from being effective.

Some viral enzymes known as proteases, however, including those for HIV and the herpes virus family, take the form of a dimer, or two identical halves - much like a fully opened clamshell - in their most stable state. Those proteases play an essential role in making the virus infectious, but require the two clamshell halves to bind together to be activated, according to the paper.

The HIV protease was successfully targeted for drug development in the 1980s, by blocking the active site on the surface of the dimer, but the herpes virus protease dimer has consistently eluded efforts to disrupt it at its active site, the researchers said.

The UCSF team set out to find ways to instead prevent the two halves of the dimer from connecting at that clamshell joint, to prevent it from activating. What they found was a new target on the unstable, monomer form of the protease, which responded well to a chemical inhibitor.

“If you disrupt the protein-protein interactions, you don’t need the key to a specific lock,” said Charles S. Craik, PhD, senior author on the paper and a professor of pharmaceutical chemistry in the UCSF School of Pharmacy. “Instead, we’re essentially preventing the lock from being made in the first place.”

Craik, who also led a team that identified HIV protease inhibitors in the late 1980s, said the Nature Chemical Biology paper validates this new site as a viable option for small-molecule drugs to treat Kaposi’s, as well as other members of this viral family.

“All known herpes virus proteases are structurally similar,” Craik explained. “The inhibitor we found knocks out not only KS, but also the cytomegalovirus protease, so the site we’ve identified here could be a target for a broad-acting inhibitor against the entire viral family.”

To their knowledge, the researchers said, this is the first small-molecule inhibitor of a herpes virus protease to not only act outside the active site, but also to select for the partially unfolded protein to keep it from forming the dimer interface.

Herpes viruses make up one of the most prevalent viral families, including eight human viruses that cause a variety of devastating illnesses, the researchers said. Those include mononucleosis (Epstein-Barr virus), shingles (Varicella zoster virus), genital herpes (herpes simplex), retinitis (cytomegalovirus) and cancer (Kaposi’s sarcoma). While therapies exist for these viruses, they often have negative side effects and are facing rising viral resistance.

In addition to validating herpes virus proteases as suitable targets, Craik said this research was also among the first to use computational design to identify and create a potential drug to target that protease interface.

Using high-throughput screening, the team screened a library of 182 compounds that it had specifically and rationally designed to mimic the protease interface. The work identified six molecules that inhibited the Kaposi’s sarcoma virus protease activity by at least 50 percent, including one that was highly potent.

That discovery potentially opens myriad opportunities for drug discovery, Craik said, by making target receptors that were biologically validated, but then deemed undruggable, more attractive. Protein-protein interactions have been researched as drug targets against a range of diseases, from certain cancers to neurodegenerative diseases. This advance could enable researchers to reconsider those targets, he said.

The lead investigator on the paper was Tina Shahian, with the Graduate Group in Biochemistry and Molecular Biology at UCSF. Co-authors were Gregory M. Lee and Ana Lazic, both in the UCSF Department of Pharmaceutical Chemistry; and Leggy A. Arnold, Priya Velusamy, Christina M. Roels and R. Kiplin Guy, all with the Department of Chemical Biology and Therapeutics at St. Jude Children’s Research Hospital, Memphis, TN.

The CMV protease expression plasmid for this work was provided by Wade Gibson, a professor in the Department of Pharmacology and Molecular Sciences at Johns Hopkins School of Medicine. The work was funded by grants from the National Institutes of Health, the American Lebanese and Syrian Associated Charities and St. Jude Children’s Research Hospital.

The authors declare no conflict of interest in this paper.

Source:
Kristen Bole

University of California - San Francisco

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