A Note on Nanotech and Cancer Diagnostics

Does anyone else sense an increase in the rate at which nanotechnology is being rationally applied to cancer diagnostics? More and more, it seems, researchers are aligning new instrumentation with existing sample preparation and analysis, which should help accelerate commercialization.

In this month’s START-UP, for example, we wrote about a way to differentiate tumors cells from normal cells based on nanomechanical measurements of cell stiffness—a technique that could improve the accuracy of traditional cytology using standard tissue sample prep and may have an immediate opportunity to diagnose mesothelioma, which is not now possible using visual analysis. Now comes a report in the December 20 issue of Nature describing a nanofluidics chip-based method for identifying circulating tumor cells (CTCs).

To be able to capture and preserve the rare and fragile CTCs, the researchers, from Massachusetts General Hospital, fine-tuned the speed and force at which a blood sample passes through their CTC-chip. By so doing, they could consistently extract up to 1000 CTCs from a 10ml blood sample from a cancer patient (other methods max out at one to five CTCs, and can only do that 50% of the time).

The CTC-chip can measure whether the number of circulating tumor cells is rising or falling after therapy, to monitor drug response, and could make monitoring of blood for tumor cells a routine part of a medical exam. And because the analysis is done by placing whole blood onto the chip without the need for any labeling or processing, the chip preserves live intact cells for subsequent analysis, which could help select the best therapy based on the molecular characteristics of the tumor.

“It’s almost like a viral load measure,” says senior author Mehmet Toner of MGH’s Bioelectromechanical Systems (BioMEMS) Resource Center. “We’re always looking at ways to put cells through chips for different purposes. This application was within reach of the technology.” MGH is continuing to demonstrate the chip’s clinical utility. It has also licensed the technology to a California company, Cellpoint Diagnostics.

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Sirtris Strikes Again

In a short paper to appear in tomorrow’s Nature, scientists at Sirtris Pharmaceuticals describe the in vitro and in vivo data supporting the development of their next-generation activators of Sirt1, one of the members of the sirtuin family of proteins. It’s another opportunity for their persistent PR machine to talk up the company’s founding premise: that activating sirtuins, which appear to play a role in the aging process, may be useful in treating a variety of things, including diabetes.

Unlike its first drug, a formulation of resveratrol (a Sirt1 activator found in red wine, which is now in early-stage trials), Sirtris found the molecules analyzed in the Letter to Nature by specifically screening for activity against Sirt1. “From a pharmacological perspective, we’ve proved the mechanism,” Sirtris CEO Christoph Westphal said yesterday in a phone interview.

The next-generation Sirt1 program, along with its development of other sirtuin activators, puts Sirtris firmly in the lead in sirtuin field. So much so that Lenny Guarente, the scientific founder of rival company Elixir Pharmaceuticals (now in registration for an IPO), whose discovery that the sirtuin-expressing gene sir2 is an important regulator of life span in several species, has jumped from Elixir to the Sirtris Scientific Advisory Board.

For years, Guarente and Sirtris co-founder David Sinclair, a former member of the Guarente lab, were estranged. And while some news outlets cast Guarente’s bolting as validation for Sirtris -- and it IS a good story -- it’s at least as much a reflection of Elixir’s affirmative determination several years ago that sirtuin-related drug development was just too early to support a company, leading to the in-license of an oral diabetes drug from the Japanese pharma Kissei in March 2006 and an early-stage growth hormone stimulator (a ghrelin agonist) from Bristol-Myers, both of which Elixir’s S-1 rank ahead of its sirtuin program.

No doubt Elixir abandoned Guarente a long time before he actually split. And the circumstance could have been predicted as far back as 2004, when Vaughn Kailian, ex of Millennium Pharmaceuticals and Cor Therapeutics, became Elixir’s Chairman. Kailian, a general partner at MPM Capital who focuses on late-stage investments (and also – DISCLOSURE, DISCLOSURE -- is a director of Windhover Information, IN VIVO’s publisher), is well known for advocating the rapid build-up of commercial capabilities. Indeed, during his tenure at Millennium, the competing interests of research and commercialization created a duality of cultures: what IN VIVO described at the time as “The Two Millenniums.”

Sirtris continues to build its sirtuin platform and expects to bring the first next-generation Sirt1 activator into the clinic in the first half of 2008. It's also got the benefit of buzz from frequent scientific publications in the evolving sirtuin field -- including their link to cell survival/protection mechanisms, which we discussed in the Science Matters column in START-UP a few months back -- as well as the elucidation of the roles of other anti-aging genes/proteins.

That said, it'll be interesting to see if the momentum lasts as it approaches the challenges of later-stage clinical trials.

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Horse Sense

When orthopedists think of the biology of bone formation and remodeling, they think protein and protein signaling. They might slap platelet-rich plasma into a bone defect, insert a collagen matrix to help recruit proteins to a site of disease or injury, or for an added punch add a protein-containing matrix such as Wyeth's BMP bone graft material Infuse.

Sugar molecules have long been suspected of also playing a role in the process of bone mineralization, but there's been much less emphasis on research elucidating their role. A group at Cambridge University, however, has recently shown that the same complex sugars found in abundance in cartilage and other connective tissues may play an important regulatory role in the bone mineralization process. I’d meant to follow up on this pretty obscure paper, which appeared in late September in the American Chemical Society's Chemistry of Materials, and was reminded to do so last week when I saw kids dressed in skeleton costumes for Halloween.

Dave Reid, who led the research, explains that many of the attempts to culture and synthesize biomimetic materials are based around assumptions that collagen and proteins both direct the formation of bone mineral and, importantly, stabilize bone mineral once it is formed, preventing runaway crystalization and growth.

Reid recently joined Melinda Duer’s group at Cambridge University. Duer is an NMR expert and has with a long-standing interest in studying equine diseases. She had the idea to use NMR to look at how the organic matrix promotes bone mineralization.

So Reid did just that, using readily available horse bones.

When he compared NMR scans of bone with those of equine cartilage, he saw similarities in the signatures in both. “We realized that the best explanation for the signal was if these molecules were proteoglycans and glycosaminoglycans [GAGs],” he says, suggesting that these carbs -- yes, the same stuff that goes into many popular nutritional supplements sold as joint remedies – could play a significant role in bone diseases where the amount or quality of the mineral is compromised. “I don’t think anyone has made the association between the complex sugars and the potential that association has for changing the way we think about how bone mineralizes, how it is formed, and its stability,” he adds.

Families with genetic defects in GAG and minor glycan metabolism leading to connective tissue disorders also have bone malformations, Reid points out. “It leads one to wonder if the deficiencies in GAG metabolism are translating into defects in bone metabolism at the molecular level.”

Admittedly, such defects are rare. But using genomics to study inherited defects in glycan metabolism and defects in the enzymes responsible for assembling GAGs at specific anatomic locations could lead to the identification of new drug targets outside the realm of the signaling and structural proteins now associated with bone disease.

A logical next step is to do more definitive chemical analysis using mass spec. Combining that with a genomics study of families with inherited bone disorders could lead to a gene target specific to GAG's role in bone mineralization, and IP.

It's still a long shot, but it makes horse sense.

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Science Matters: A small personalized medicine bailout for Cox-2s?

There was little attention paid to last week's paper suggesting that PPAR delta agonists might be used to prevent the cardiovascular side effects of Cox-2 inhibitors (coxibs) such as Vioxx and Celebrex.

The study in the Journal of Experimental Medicine (JEM) showed that Cox-2 suppresses the expression of tissue factor (TF) -- the primary activator of blood clotting and a proximal cause of coxibs' CV problems -- via the activation of PPAR delta.

Of course, there are no approved PPAR delta drugs, although pharmas including GSK have tried developing them to treat cardiovascular disease. (One news outlet suggested GSK's drug could be an "unlikely savior" for Vioxx, but that's a far stretch.) And no one would think to couple a PPAR delta with a coxib for use as a combination analgesic--the risk/benefit ratio of that presumably is way off.

But there's another, intriguing aspect to this research result.

The problem with Vioxx is that it is associated with cardiovascular complications in a small number of patients. "We should look at these patients in terms of their TF levels and other clotting parameters," suggests Timothy Hla of the University of Connecticut Health Center and a principal author of the JEM paper. "Is the TF gene in these people somehow different? Is it regulated differently? Are they more sensitive or more resistant to the effects of the PPAR delta they produce? Instead of looking at the selectivity of Cox-2, let's look at patients' sensitivity."

Hla has a longstanding interest in Cox-2's role in normal blood vessel physiology and angiogenesis: he cloned the gene from human vascular cells in and named it Cox-2 in 1992, while at the American Red Cross Research Institute.

A first step would be to measure TF levels, which can be easily collected from plasma, in patients taking Celebrex and correlate them with treatment results. It's all well and good to talk about testing PPAR delta agonists for their therapeutic effects regulating the TF gene. (The most advanced may be GSK's GW 501516, which the Hla group used in its experiments. GSK in-licensed the compound from Ligand Pharmaceuticals, but its development has lagged at Phase II. Ligand's most recent 1o-K says the drug's development is 'on hold' pending the review of preclinical studies, and there is no mention of it on GSK's own clinical trials web site or in any recent publicity [clintrials.gov lists a 'completed' Phase II study], so for all we know it has been terminated.)

So that's a long way off. Most of the focus on the mechanism of Cox-2 has centered on its effect on platelets. A simple blood test might go a long way towards refining that effort.

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