Day: 02/01/2011

How Genetically Engineered Mouse Tumor Models Provide Insights Into Human Cancers

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Genetically engineered mouse models (GEMMs) of human cancer were first created nearly 30 years ago. These early transgenic models demonstrated that mouse cells could be transformed in vivo by expression of an oncogene. A new field emerged, dedicated to generating and using mouse models of human cancer to address a wide variety of questions in cancer biology. The aim of this review is to highlight the contributions of mouse models to the diagnosis and treatment of human cancers. Because of the breadth of the topic, we have selected representative examples of how GEMMs are clinically relevant rather than provided an exhaustive list of experiments. Today, as detailed here, sophisticated mouse models are being created to study many aspects of cancer biology, including but not limited to mechanisms of sensitivity and resistance to drug treatment, oncogene cooperation, early detection, and metastasis. Alternatives to GEMMs, such as chemically induced or spontaneous tumor models, are not discussed in this review.

source: journal of clinical oncology

Bisphosphonate Use May Be Linked to Reduced Risk of Colorectal Cancer

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Bisphosphonates may hold promise for chemoprevention of colorectal cancer, based on a case-control study conducted in Israel, but randomized trials will be needed to confirm the results.

Among the 1,866 postmenopausal women studied, the use of a bisphosphonate for more than 1 year was associated with a 59% reduction in the risk of colorectal cancer, according to data reported at the meeting on gastrointestinal cancers sponsored by the American Society of Clinical Oncology.

“It’s an association study. … One needs to be careful,” lead investigator Dr. Gad Rennert acknowledged in an interview. “It will call for randomized trials now to see that it really is true.”

The vast majority of women were taking alendronate, an oral bisphosphonate sold in the United States under the brand name Fosamax but also available generically. The apparent anticancer benefit became significant after 1 year of use and did not increase by much with longer duration.

“If it is shown to be true, then we are talking about a simple, cheap drug for short use,” commented Dr. Rennert, who is director of the National Israeli Cancer Control Center and a professor at Technion–Israel Institute of Technology in Haifa. “This is perfect … if it is supported by other studies.”

Last year, his research team found that bisphosphonate use was associated with a reduced risk of breast cancer, a finding that has since been verified by three other investigative groups. However, a concern with that association is the potential confounding by low estrogen levels, which would not only cause osteoporosis (and hence bisphosphonate use) but also reduce breast cancer risk.

The new study, therefore, looked at colorectal cancer, in which such confounding is unlikely. “This is a tumor that is not known to have strong hormonal influences, so estrogen deprivation is not necessarily known to be a protective situation for colorectal cancer,” he explained.

The study was conducted within the MECC (Molecular Epidemiology of Colorectal Cancer) study, which ascertained all incident cases of the disease diagnosed in northern Israel in 1998-2004 and matched those patients with unaffected individuals from the general population. Study participants were interviewed to collect information on their social, demographic, and medical characteristics.

The bisphosphonate analysis focused only on postmenopausal women: 933 who had experienced colorectal cancer and 933 who had not. They had mean ages of 71 and 72 years, respectively, according to results reported in a poster session.

Pharmacy records indicated that the women who had experienced colorectal cancer were less likely to have filled at least three bisphosphonate prescriptions (10% vs. 15%; P = .004) and to have used these agents for more than 1 year (6% vs. 11%; P less than .0001).

The analyses showed that compared with no bisphosphonate use, any use was associated with a significantly lower risk of colorectal cancer (odds ratio, 0.67).

When duration was considered, there was no benefit with less than 1 year of use. But there was significant benefit with at least 1 year of use (OR, 0.50) that was roughly the same with more than 2 years of use (OR, 0.51) and with more than 3 years of use (OR, 0.39).

This protection with relatively short use and its fairly stable magnitude thereafter bode well for using bisphosphonates for chemoprevention, according to Dr. Rennert.

“It’s important because if we ever want to use this drug for prevention, it actually means that we will be able to give it for a very short period only,” he explained. “So it’s not a drug that somebody will need to take for years or for a lifetime.”

In a multivariate model that took into account confounders (family history, sports activity, body mass index, vegetable intake, and use of aspirin, statins, postmenopausal hormones, vitamin D, and calcium), the use of bisphosphonates for more than 1 year was associated with a greater-than-one-half reduction in the risk of colorectal cancer (relative risk, 0.41; 95% confidence interval, 0.25-0.67).

Moreover, a similar risk reduction was seen for cancers of the right colon and cancers of the left colon individually. The risk of rectal cancer was also reduced, but not significantly so.

The investigators speculate that the anticancer benefit of bisphosphonates is related to their effects on the mevalonate metabolic pathway and inhibition of isoprenoid biosynthesis, which cancer cells require for growth-related processes.

Fosamax is currently approved by the U.S. Food and Drug Administration for the prevention of osteoporosis in postmenopausal women, for the treatment of osteoporosis in men and postmenopausal women, and for some other conditions compromising skeletal health.

Choice of Surgical Treatment for Mesothelioma Remains Complex

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Surgery for malignant pleural mesothelioma remains a complicated and controversial issue. Thus far, the benefits of surgery vs. nonsurgical treatment have yet to be demonstrated.

Complete resection with surgery alone (R0) appears theoretically unattainable since it is impossible to eradicate residual microscopic disease, regardless of the surgical method used. Hence, most surgical treatment today is coupled to various adjuvant treatments, primarily a trimodality mode with radiotherapy and chemotherapy, according to Dr. Raja M. Flores, professor and chief of thoracic surgery, Mount Sinai School of Medicine, New York.

A “curative” surgical procedure remains an elusive goal, and thus the focus of lung surgery for malignant pleural mesothelioma (MPM) has shifted to R1 surgical resection for cytoreduction in the hope of prolonging life, relieving symptoms, and enhancing the effectiveness of adjuvant therapies. This approach has often meant a shift from the more radical extrapleural pneumonectomy (EPP), when possible, to the more lung-sparing pleurectomy/decortication (PD) procedure, according to Dr. Flores (Sem. Thorac. Cardiovasc. Surg. 2009;21:149-53).

EPP involves a radical en bloc resection of the lung, pleura, diaphragm, and pericardium. PD involves resection of the parietal and visceral pleurae, pericardium, and – when necessary – the diaphragm, but it spares the entire lung. Both operations are technically complex and require extensive surgical expertise.

The operative mortality rate of EPP in the literature ranges from 4% to 15%, vs. and 1% to 5% for PD. In addition, PD has lower morbidity than does EPP. But the two techniques are not interchangeable, according to Dr. Flores. The choice of surgical technique depends on multiple factors, and the decision is often made at the time of surgery because the preoperative imaging may have underestimated the amount of disease present.

Staging is critical in determining the appropriate procedure, and the merits of each surgical approach have been debated in several recent clinical and registry trials examining individual mortality and morbidity of these procedures at different stages, coupled with the use of a variety of adjuvant therapies. However, many decisions are based on surgical conjecture and bias rather than scientific data.

Evidence indicates that PD provides a survival advantage for patients with stage I MPM, which may be accounted for by “lower mortality, lower postoperative adverse events, and greater lung capacity when relapse occurs,” according to Dr. Flores. However, he explained, most patients with mesothelioma will present at a stage that requires EPP to eradicate all gross disease. PD can provide an R1 resection in early-stage disease, but as the tumor enlarges and invades the lung, fissures, and costophrenic sulcus, a PD is suboptimal regardless of resection of the pericardium and diaphragm.

There is, however, a critical balance between optimal cytoreduction and morbidity that varies across stages for these two procedures. For stage II disease, there is a “trend toward improved survival for EPP, despite an inherently higher tumor stage than PD,” Dr. Flores said.

Stage III disease proved more complex, with similar survival data seen for both EPP and PD. Ultimately, “one should focus on obtaining a complete macroscopic resection based on the extent of tumor” for this stage of disease, choosing the best procedure accordingly, he advised.

For more advanced (stage IV) disease characterized by diffuse chest wall invasion and extensions through the diaphragm to the underlying peritoneum, the situation is much different.

“The tumor may be amenable to EPP, but there will be gross residual tumor left behind in the hemithorax. Because one of the most likely sites of recurrence is the contralateral pleura, the patient is better served by preserving lung function,” Dr. Flores explained.

In stage IV disease, PD trended toward better survival, presumably because “when disease spreads to the contralateral lung, PD or debulked patients will be less symptomatic and better functionally able to tolerate systemic therapy because of their greater pulmonary reserve,” he said.

“The goal is to remove all gross tumor while preserving as much of the lung as possible. Every patient and clinical situation is unique; therefore, treatment is difficult to generalize. Find an experienced mesothelioma surgeon you trust and leave it in their hands,” Dr. Flores said in an interview.

Ultimately, the situation remains complex. Dr. Heyman Luckraz of the New Cross Hospital, Wolverhampton, United Kingdom, and his colleagues recently reported results with 139 patients. EPP was chosen for clinically fit patients with stage I disease, while patients with advanced disease or who were unfit for EPP underwent PD. “EPP may only have a limited role in diffuse MPM, particularly as neither operative procedure is curative. Ultimately, the place of EPP will only be determined by randomized trial in comparison to PD in stage I disease with both groups receiving adjuvant therapy,” the investigators concluded (Eur. J. Cardio-Thorac. Surg. 2010;37:552-6).

Whether such trials will ever be performed is an open question. Despite the recent Mesothelioma and Radical Surgery (MARS) trial, which demonstrated the possibility of randomizing patients to surgical vs. nonsurgical treatment, there will likely never be a randomized clinical trial powered enough to completely solve the puzzle, according to Dr. Tom Treasure of the University College of London (Eur. J. Cardio-Thorac. Surg. 2010;37:509-10).

Efforts continue to develop surgical alternatives with less mortality and morbidity than those of the standard EPP and PD procedures. For example, Dr. M.D. Kluger and colleagues at Columbia University, New York, reported the phase I and II results of a recent clinical trial on a two-stage operative cytoreduction procedure coupled with intraperitoneal chemotherapy (Eur. J. Surg. Oncol. 2010;doi:10.1016/j.ejso.2010.07.001). They found that their protocol offered median survival comparable to that of one-stage protocols; rates of morbidity, mortality, visceral resections were relatively low and length of stay was relatively short despite the need for two operations.

Ultimately, surgery might be totally immaterial in some cases. In two recent papers, the type of surgery was not found to be predictive of survival. The poor prognosis of sarcomatoid MPM was independent of the extent of surgery, unlike other cell types (Ann. Thorac. Surg. 2010;89:907-11), and the combination of several immunohistochemical markers was found to be the only valid prognostic indicator of survival, including type of surgery.

source: european journal of cardio thoiracic surgery

Oral 5-aminosalicylic acid for maintenance of surgically-induced remission in Crohn`s disease.

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The use of 5-aminosalicylates (5-ASAs) in Crohn`s disease (CD) is controversial. A recent Cochrane review found that 5-ASAs are not effective for the maintenance of medically-induced remission in CD, but their role in the maintenance of surgically-induced remission is unclear.
OBJECTIVES: The objectives were to evaluate the efficacy and safety of 5-ASA agents for the maintenance of surgically-induced remission in CD.
SEARCH STRATEGY: The search was standardised and not limited by language and included electronic searching (MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Inflammatory Bowel Disease Group Specialized Trials Register), reference searching of all included studies, abstracts from major meetings, personal contacts and drug companies.
SELECTION CRITERIA: Randomised controlled trials (RCTs) which compared 5-ASAs with either placebo or another intervention, with treatment durations of at least 6 months were considered for inclusion. Participants were patients of any age with CD in remission following surgery. Primary outcome measures were clinical relapse or endoscopic recurrence as defined by the primary studies. Secondary endpoints were the occurrence of adverse events.
DATA COLLECTION AND ANALYSIS: Relevant papers were identified and the authors independently assessed the eligibility of trials. Methodological quality was assessed using the Cochrane risk of bias tool.The Cochrane RevMan software was used for analyses. Patients with final missing outcomes were assumed to have relapsed. Odds ratio (OR) and 95% confidence intervals (95% CI) were calculated based on the fixed effects model. The chi square and I(2) statistics were used to assess statistical heterogeneity.
MAIN RESULTS: Nine RCTs were included in the review. Seven studies compared oral 5-ASA with placebo and two compared oral 5-ASA with purine antimetabolites (azathioprine or 6-mercaptopurine). 5-ASA was significantly more effective than placebo for preventing relapse (OR 0.68, 95% CI, 0.52 to 0.90). There was no statistically significant heterogeneity among the 8 trials comparing 5-ASA with placebo (P=0.47). No statistically significant difference in adverse events was found for 5-ASA versus placebo (OR 1.02, 95%CI, 0.60 to 1.76). No statistically significant difference was found between 5-ASA and purine antimetabolites for preventing relapses (OR 1.08 95% CI, 0.63 to 1.85).
AUTHORS’ CONCLUSIONS: The pooled analyses suggest that 5-ASA preparations may be superior to placebo for the maintenance of surgically-induced remission in patients with CD. The results of the pooled analyses should be interpreted with caution because adequately powered studies demonstrated no difference and publication bias (failure to publish negative studies) may be an issue. The potential benefit provided by 5-ASA drugs is modest with a number needed to treat of approximately 16 to 19 patients to avoid one relapse which raises issues about the cost-effectiveness of this therapy. However, 5-ASA drugs are safe and well tolerated. The incidence of adverse events was not different in patients receiving 5-ASA compared with those receiving placebo. There is insufficient evidence to allow any conclusions on how 5-ASA preparations compare with azathioprine or 6-mercaptopurine.

source: cochrane library

Pooled Testing for Virologic Monitoring?

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A study conducted in South Africa indicates that pooling strategies could substantially reduce the cost of virologic monitoring while preserving accuracy.

Viral-load testing is critical for detecting HIV treatment failure but is rarely used in resource-limited settings because of the high costs and the requirement for sophisticated laboratory infrastructure. Pooled HIV RNA testing might be a viable alternative, according to a recent study from South Africa. Such testing has previously proven accurate and efficient for screening blood donors, diagnosing acute HIV infection, and detecting virologic failure in patients on antiretroviral therapy.

In the first part of the study, the researchers sought to develop criteria for identifying individuals who had a low probability of virologic failure (<10%) and would thus be eligible for pooled testing. They retrospectively analyzed information that is routinely included on laboratory request forms and found two pertinent variables: age ≥15 years and treatment with a regimen containing a nonnucleoside reverse transcriptase inhibitor.

The researchers then used two different pooling strategies (matrix and minipools) to evaluate stored specimens from individuals deemed to be at low risk for virologic failure. Four hundred liquid plasma samples were tested in minipools, and 300 of them were tested by matrix. The two strategies reduced the number of tests required by 31% and 41%, respectively, compared with individual testing. Based on current South African costs, using these strategies could lead to a savings in reagent costs of up to US$1640 per 100 specimens. Dried specimens were also tested using minipooling, and use of dried plasma spots was found to be the most efficient of any strategy analyzed.

Comment: Given the poor performance of clinical and laboratory algorithms to identify virologic failure, as well as limitations in laboratory infrastructure and human resources, accurate detection of treatment failure in many developing countries will be possible only when inexpensive point-of-care tests become available. In the meantime, optimization of algorithms that identify patients with a low probability of virologic failure and the use of pooled testing on dried plasma spots from such individuals might allow for wider access to viral-load monitoring, without increasing the number of tests performed or requiring an expansion of the existing laboratory infrastructure.

— Mauro Schechter, MD, PhD

Dr. Schechter is a Professor of Infectious Diseases at Universidade Federal do Rio de Janeiro, Head of the AIDS Research Laboratory at Hospital Universitario Clementino Fraga Filho, and Principal Investigator of Projeto Praça Onze at Hospital Escola São Francisco de Assis in Brazil. He reports no conflicts of interest.

Published in Journal Watch HIV/AIDS Clinical Care January 31, 2011

Arsenic DNA’ would be amazingly unstable

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Nasa’s recent ‘arsenic life’ storm in a tea-cup controversy has been reheated to some extent by a new paper that undermines key claims controversially made at the end of last year.

The space agency’s announcement that its researchers had an amazing finding with implications for the search for extraterrestrial life quickly turned sour. Although the discovery of a strain of bacteria called Halomonadacea GFAJ-1 that can apparently use arsenic in place of phosphorous in its DNA was exciting, some complained that it had been hugely overhyped while others questioned the result itself (see: Microbe gets toxic response).

Even at the time it was pointed out that the arsenate ion that was being proposed as a phosphate substitute would be somewhat unstable. The authors of the original work – published in Nature’s rival Science – counter that the bonds in question could be reinforced.

Now a paper in ACS Chemical Biology looks at how stable – or unstable – arsenic DNA would actually be. (The paper came out on the 18th of this month, and has just been highlighted on the In The Pipeline blog.)

Kent Gates, of Cairo University, and his colleagues point out that arsenate and phosphate are in some chemical ways very similar. For example, they form bonds of (roughly) similar strength with oxygen. However, they point out that the phosphate diesters found in normal DNA have a “vastly different” stability in water than their arsenate equivalents.

Although there is little in the way of published data on the matter, they suggest that if exposed to water half the arsenic-based links in the genome of the bacteria in question would be cleaved in less than 0.1 seconds.

“The anticipated instability of the genetic material in an arsenate-utilizing organism would present a serious challenge to cellular operations,” they under-state. “…While some bacteria have evolved mechanisms for protecting their DNA under conditions of stress, overcoming such dramatic kinetic instability in its genetic material would be a significant feat for Halomonadacea GFAJ-1.”

source: nature in collaboration with NASA

CJD diagnosis just got easier

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Test for Creutzfeldt–Jakob disease raises hopes of speedier diagnosis.

 

human prionIn prion diseases such as CJD, an isomer of a prion protein takes on an abnormal shape.AP Photo/Professors Stanley Prusiner/Fred Cohen, University of California San Francisco Medical School

Invasive biopsy is currently the only sure way to diagnose the degenerative neurological condition Creutzfeldt–Jakob Disease (CJD). But a highly sensitive assay could change that, providing a fast, accurate alternative for early diagnosis of this rare but deadly condition.

In its most common form, known as sporadic CJD, the disease affects roughly one in a million people. Beginning in the 1990s, several cases of a variation of CJD known as vCJD were reported among people who had consumed beef from cows infected with another disease, bovine spongiform encephalopathy (BSE).

The findings, published online in Nature Medicine1, also suggest that the assay — developed by microbiologist Ryuichiro Atarashi of Nagasaki University, Japan, and his team — could pave the way for the screening of broad sectors of the population.

CJD is a prion disease, in which an isomer of a common protein known as the prion protein (PrP) takes on an abnormal shape and becomes an infectious variant called PrPSc. This variant is thought to trigger the subsequent malformation of other PrP proteins. Unlike their normal counterparts, PrPSc prions cannot be broken down, and instead accumulate — often clustering in brain tissue.

The pockets of abnormal tissue that result cause brain tissue to develop a sponge-like appearance, and because prion conditions can be spread by affected humans or animals, the diseases are often referred to as transmissible spongiform encephalopathies (TSEs). Humans can be affected by several such conditions, while in addition to BSE in cows, there are several other such disorders among animals, including a condition called scrapie in sheep and hamsters.

No false positives

One problem that has plagued developers of non-biopsy diagnostic techniques is that it is often difficult to avoid false positives among samples taken from patients with neurodegenerative disorders other than CJD.

So Atarashi and his colleagues used a new assay known as a real-time quaking-induced conversion (RT-QUIC) assay. ‘Quaking-induced’ refers to in vitro shaking, which researchers believe helps to accelerate the reactions, enabling the assay to produce results more quickly.

The team tested cerebrospinal fluid samples from 18 people with CJD and 35 people with other neurodegenerative diseases. This pilot group produced no false positives, and CJD was correctly diagnosed more than 83% of the time.

The researchers compared these results with those obtained using an existing assay that tests for levels of a protein known as 14-3-3, which is a marker for sporadic CJD. When tested on patient samples, the accuracy of 14-3-3 was 72.2%, whereas the specificity was 85.7%.

In a subsequent blind trial on 30 cerebrospinal fluid samples from Australia, RT-QUIC showed 100% specificity, resulting in no false positives among the 14 control samples, and correct diagnoses of 87.5%. 14-3-3 was equally accurate, but the rate of false positives was much higher.

“This technique allows definitive ante-mortem confirmation of CJD,” says Atarashi, adding that this is currently difficult because it demands the detection of PrPSc in patients’ biopsy specimens.

Supersensitivity

The RT-QUIC assay is also extraordinarily sensitive — detecting the presence of harmful prions at very high dilutions — and speedy, yielding results within 48 hours.

Atarashi first began developing RT-QUIC as a researcher at the National Institute of Allergy and Infectious Diseases, Rocky Mountain Laboratories, in Montana. In 2008, he and his team successfully used it to screen cerebrospinal fluid taken from scrapie-infected hamsters2.

In December, Atarashi co-authored a paper reporting the efficacy of the RT-QUIC assay on nasal secretions and cerebrospinal fluid from hamsters with prion disorders3.

Byron Caughey, chief of prion/TSE research at the Rocky Mountain lab and a co-author of the two hamster studies, is encouraged by the application of the assay to human cerebrospinal fluid samples. “Of course it will also be important to detect prion diseases in other species, but human diagnosis is of pre-eminent importance,” Caughey says.

And although the next step is to replicate the findings in a much larger sample, the promise shown by RT-QUIC in analysing substances other than spinal fluid in hamsters suggests a potentially fertile area for future research in humans. If RT-QUIC could be used to screen blood samples, or cheek or nasal swabs, for example, it could open up the possibilities of much earlier diagnosis and more widespread screening of donated blood.

“The earlier you’re able to detect the presence of an infection in humans or animals, the more chance you have of preventing transmission to others and treating the disease in those who are infected,” Caughey says.

source: nature medicine

Secondhand Smoke Raises Kids’ Ear Infection Risk

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Study Shows Higher Risk of Middle Ear Infection for Children in Homes Where Parents Smoke

 

young girl having ear examined

Jan. 28, 2011 — Children who live in homes where parents or others smoke have a higher risk of developing middle ear infections than kids whose houses are smoke-free, a new study shows.

Researchers at the Harvard School of Public Health and the Research Institute for a Tobacco Free Society in the Republic of Ireland say they found that a reduction in secondhand smoke in American homes was associated with fewer cases of otitis media, or what most people refer to as middle ear infections.

Smoke from a burning cigarette combined with exhaled smoke from a person who smokes has been shown to increase unhealthy particles in the air, including those of nicotine and other toxins, the researchers write.

Risks of Secondhand Smoke

The U.S. Surgeon General in 2006 said enough evidence existed to suggest a connection between parents and others smoking and ear infections in children.

Researchers of the news study used data from the National Cancer Institute and found that no-smoking rules in households nearly doubled from 45% in 1993 to 86% in 2006. This increase in smoke-free homes, the researchers say, most likely was the result of increased awareness of dangers of secondhand smoke.

In this same time period, outpatient visits by children with otitis media to doctors’ offices or clinics decreased 4.6%; hospitalizations decreased by 9.8%.

“Our study is the first to demonstrate the public health benefits to children of the increase in smoke-free homes across the nation,” study researcher Hillel Alpert, ScM, of the Harvard School of Public Health’s department of society, human development and health, says in a news release. “If parents avoid smoking at home they can protect their children from the disease that is the most common cause of visits to physicians and hospitals for medical care.”

High Cost of Middle Ear Infections

Middle ear infections are the leading cause of visits to medical practices and hospitals among children, costing $3 billion to $5 billion. Visits by children with otitis media increased from 9.9 million in 1975 to 24.5 million in 1990.

But researchers found that the average number of outpatient visits for otitis media in youths 6 and younger dropped 5%, and that hospital discharges fell 10% annually between 1993 and 2006, in large part, apparently, to increased awareness of dangers to kids of secondhand smoke. Another reason, however, may have been a vaccine for pneumonia that was introduced in 2000.

“Smoke-free rules in homes are extremely important to protect children,” Alpert says.

The researchers write their study is the first to quantify average annual decreases in pediatric visits by children with middle ear infections over the past decade and a half, a period in which the importance of having smoke-free homes has been stressed.

source: Tobacco Control.