In the July 15th issue of G and D, Dr. Suzanne Baker (St. Jude Children’s Research Hospital) and colleagues report on their surprising discovery of cell-type specificity of PI3K signaling in the mammalian brain. This finding highlights the complexity of this clinically significant cell signaling pathway, and its relevance to the design of small molecule PI3K pathway inhibitors, to both maximize efficacy and minimize side effects.

The PI3K pathway is an intricate signaling cascade that regulates cell survival and growth under normal, as well as pathological conditions. In fact, the PI3K pathway is mutated in more cancer patients than any other. The signaling network is balanced by the PTEN tumor suppressor protein.

PTEN (Phosphatase and Tensin Homologue Deleted from Chromosome-10) is recognized as one of the most frequently mutated tumor suppressors in human cancer, and has also been associated with neurological diseases like autism. It functions primarily as a phosphatase (phosphate-group-cleaving enzyme) to antagonize PI3K signaling by dephosphorylating PIP3, the lipid second messenger that signals activation of the PI3K signaling cascade. Loss of PTEN results in the upregulation of PI3K signaling, through the increased phosphorylation of PI3K effectors such as the molecule, AKT. Thus, the PTEN/PI3K/AKT pathway represents an important target for drug discovery.

To study the role of the PI3K downstream effector molecule, PDK1, in mediating the effects of PTEN loss, Dr. Baker and colleagues generated a novel transgenic mouse strain deficient in both PDK1 and PTEN specifically in the brain. The researchers found that while some of the characteristic brain abnormalities arising from PTEN loss are corrected by the concomitant deletion of PDK1, others are not: Most notably, PDK1 did not rescue the migration defects associated with PTEN loss in neurons. PDK1-independent abnormalities in the brains of PTEN-deficient mice suggests that additional, alternate downstream effectors of the PI3K signal exist.

This finding underscores the consideration that, as Dr. Baker explains, “inhibitors that block downstream effectors in PI3K signaling may not correct all of the defects caused by loss of PTEN function.”

Dr. Baker’s team also observed differential feedback regulation of the PI3K pathway in different CNS cell types. Clinical evidence has shown that some human tumors achieve chemoresistance through the increased phosphorylation of the PI3K downstream component, AKT. Quite surprisingly, Dr. Baker and colleagues found that PDK1 deletion caused a selective, dramatic increase in the phosphorylation of AKT in glial cells, but not neurons, indicating unanticipated cell-type specificity in PI3K feedback regulation in the brain.

Further research will be needed to determine if PDK1, itself, represents a useful therapeutic target. However, this example of a cell type-specific response to PDK1 deletion supports the notion of personalized cancer treatment, in so far as emphasizing the relevance of tumor cell of origin and genotype to help predict which patients will respond positively to specific PI3K inhibitors.

Dr. Baker emphasizes that, likewise, “There may be profound differences in the effects of inhibitors on different types of normal cells, which could be relevant in terms of side effects induced by systemic treatment with a pathway inhibitor.”

Source:
Heather Cosel-Pieper
Cold Spring Harbor Laboratory

Researchers funded by the National Institutes of Health have completed a critical first step in the eventual development of a technique to retain fertility in women with cancer who require treatments that might otherwise make them unable to have children.

The researchers have developed a method to advance undeveloped human eggs to near maturity, in laboratory cultures maintained outside the body. The technique focuses on the follicle, a tiny sac within the ovary that contains the immature egg. The researchers were able to grow human follicles in the laboratory for 30 days, until the eggs they contained were nearly mature.

The research seeks to provide women who require a fertility-ending treatment with options for reproduction after their treatment is complete. Men facing such treatments can freeze their sperm for use at a later date. Female cancer patients have fewer options. Unlike sperm, eggs rarely survive freezing and thawing.

The accomplishment represents the successful completion of the first of three steps needed to preserve a woman’s fertility after radiation treatments or chemotherapy. For the next step, researchers will need to induce the egg’s final division, so that it contains only half the genetic material of its precursors. Finally, the researchers will have to demonstrate that they can freeze and thaw human follicles before growing them in culture.

“The new technique could provide an option for women and girls who have cancer and are not yet ready to start families,” said Duane Alexander, M.D., director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), which funded the research as part of the NIH Roadmap Interdisciplinary Research Consortium program. “An additional benefit is that it will allow researchers to more closely follow the process by which immature eggs grow and mature. In turn, these observations may lead to new advances for treating other forms of infertility.”

The best option currently for a female cancer patient to preserve fertility is to collect eggs, fertilize them with sperm, and freeze the resulting embryos. But that technique may not be acceptable to all female cancer patients.

Researchers have already identified experimental methods to freeze entire ovaries or strips of ovarian tissue and implant them in a woman’s body when she is ready to have children. This is a good option for some patients, but it is possible that some cancer cells may hitch hike on the ovarian tissue and result in a new cancer after treatment is completed.

Developed by Teresa K. Woodruff, Ph.D. and Lonnie D. Shea, Ph.D., of Northwestern University’s Feinberg School of Medicine, and their colleagues, the new technique would avoid both concerns.

The findings were published online in Human Reproduction.

The new findings build on earlier efforts by the research team, who grew mouse follicles in culture, induced the eggs they contained to mature, fertilized them with mouse sperm, and implanted them into female mice to establish pregnancy. The earlier research is described in an article that appeared in The NIH Record, here.

The researchers made the new advance by suspending the human follicle in a three-dimensional matrix of a gel-like material. They then flushed the follicle with the same hormones and growth factors that the follicle would be exposed to inside a woman’s body.

In previous attempts to grow follicles, researchers had set the follicles on a flat surface, which the study authors now believe does not mimic closely enough conditions inside the body. These earlier attempts failed to develop good quality eggs that were healthy enough for fertilization.

For the current study, the researchers started with so-called secondary follicles, which are at an intermediate stage of development. They collected them from the ovarian tissue of 14 cancer patients.

During the 30-day experiment, the follicle grew and produced hormones and the immature egg matured just as it would inside a woman’s body. The researchers found that the follicles would grow if injected into a gelatin mixture. The gelatin (called alginate) provided three-dimensional support for the follicle, much like the support it receives inside the body.

“The researchers have demonstrated that the technique produces healthy eggs,” said Charisee Lamar, Ph.D., M.P.H., R.R.T., director of the Fertility Preservation Program in NICHD’s Reproductive Sciences Branch. “The next step would be to investigate the viability of follicles from frozen tissue.”

Another component of the NICHD program is attempting to grow follicles of monkeys in culture. The ability to do research on mouse and monkey follicles might lead to advances that could later be used to perfect the technique’s use with human eggs.

Reference: “In vitro grown human ovarian follicles from cancer patients support oocyte growth.” Human Reproduction.

Source:
Robert Bock
NIH/National Institute of Child Health and Human Development

New research published in the July issue of the Journal of the American College of Surgeons reveals that African Americans with gastrointestinal stromal tumors (GIST), a rare cancer that begins in the wall of the gastrointestinal tract, now have survival rates equivalent to those of Caucasians. Prior to 2000, African Americans were more likely to develop GIST and less likely to undergo surgical treatment for this type of cancer.

Racial disparities in survival rates have been demonstrated for a number of cancers, typically due to unequal access to care. Through the National Institutes of Health and Healthy People 2010, a national health promotion and disease prevention initiative, the federal government has set forth goals to explore, account for and minimize these disparities.

“Over the last decade, racial gaps in the treatment of GIST appeared to have closed,” said Michael Cheung, MD, DeWitt Daughtry Family Department of Surgery, University of Miami, Miller School of Medicine. “Both perioperative and long-term survival have improved among African Americans.”

“Our study suggests that better diagnosis and increased use of surgery - which still provides the best chance for cure - have contributed to improvements in care for African Americans,” said Leonidas G. Koniaris, MD, FACS, associate professor of surgery, DeWitt Daughtry Family Department of Surgery, University of Miami Miller School of Medicine, and surgical oncologist at Sylvester Comprehensive Cancer Center at UM. “In addition, increased access to new targeted therapies through medication assistance programs may be helping to eliminate racial disparities in cancer treatment.”

A statistical analysis was performed using the Surveillance, Epidemiology and End Results (SEER) database that identified 3,795 patients diagnosed with GIST and other intestinal mesenchymal tumors between1992 to 2005. Patient demographics showed 72.2 percent Caucasians, 15.6 percent African Americans, and 9.1 percent Hispanics. Survival was calculated from the time of initial diagnosis to the date of last contact or death.

Both perioperative and long-term survival had improved among African Americans since 2000. In patients diagnosed before the year 2000, 30-day surgical mortality was higher in African Americans (0.56 percent versus 0.76 percent Caucasians, p=0.012). After 2000, 30-day surgical mortality was equivalent between races (0.46 percent versus 0.35 percent for Caucasians, p=0.517).

Before the year 2000, three-year disease specific survival was better in Caucasians than African Americans (79.3 percent versus 75.1 percent, p=0.025). There was no racial difference in tumor stage (p=0.446) or grade (p=0.495), and African Americans underwent surgical procedures less frequently than Caucasians (p=0.003). Multivariate analysis correcting for patient demographics, socioeconomic status and clinical data demonstrated African American race and failure to undergo surgical treatment were independent predictors of poor prognosis. In patients diagnosed after 2000, three-year disease specific survival was nearly equivalent between Caucasians and African Americans (82.1 percent versus 80.7 percent, p=0.680) and African Americans underwent surgical procedures just as often as Caucasians (p=0.153) did. Multivariate analysis for patients diagnosed after 2000 demonstrated no difference in survival by race (p=0.126).

Source:
Sally Garneski
Weber Shandwick Worldwide