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Solidus Biosciences Thinks it Can Change ADME/Tox Screening; Hopes Pharma Agrees

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Nascent biotechnology firm Solidus Biosciences is developing a cell-based assay chip that it says can perform rapid and inexpensive assessment of ADME/tox early on in the drug-development process, thereby eliminating unsuitable small-molecule candidates from further investigation.

The technology, which has been dubbed MetaChip, combines an array of sol-gel encapsulated cytochrome P450 metabolizing enzymes with a monolayer of cells on a micro-scale glass slide that can be read using any standard microarray scanner, fluorescent microscope, or combination thereof.

Douglas Clark, a co-founder of Solidus and a professor of chemical engineering at the University of California, Berkeley, told Inside Bioassays last week that the company is “just getting started,” and that it will still be some time before a product hits the market.

Solidus, however, does have a prototype version of MetaChip available, the development of which was in part supported by a phase 1 two-year $500,000 Small Business Technology Transfer grant for a special program on innovative toxicology models awarded to the company last year from the National Institutes of Health, Clark said. The company is now in the process of applying for phase II funding — worth a possible $2.4 million — to further refine MetaChip and ready a product for market.

Clark and Jonathan Dordick, a co-founder of the company and professor of chemical engineering at Rensselaer Polytechnic Institute, published a paper demonstrating the efficacy of MetaChip in the January 25 edition of the Proceedings of the National Academy of Sciences.

In the proof-of-principle paper, the researchers demonstrated how they used the P450 MetaChip prototype in combination with a breast cancer cell line to accurately mimic the activation of anticancer drugs Cytoxan and Tegafur, as well as generate cytotoxic metabolites from acetaminophen.

As described in the paper, the chip consists of a sol-gel microarray containing one or more human P450 isoforms used to generate biologically active metabolites of a lead compound. The volume of the sol-gel spots can be varied from five to 100 nanoliters and arrayed in various ways.

“The chip can accommodate any metabolizing enzyme of interest,” Clark told Inside Bioassays. “The P450 just happens to be the most prominent.” According to Clark, most drugs that the liver metabolizes undergo an enzymatic reaction with P450 complexes to create a variety of byproducts — some of which are harmless, but some of which are toxic to any number of cells in the body.

“There are some other enzymes involved, as well,” Clark said. “There are so-called phase 2 metabolizing enzymes that come from a variety of different classes. We can also add those to the MetaChip, and in fact, our intent is to produce MetaChips that include those, too.”

The researchers then added a lead compound to the sol-gel spots, and subsequently stamped a slide with a cell monolayer onto the array. After incubating the cells and allowing metabolites to form and react with them, they removed the cell monolayer slide, stained the cells, and determined the percentage of dead cells using both an epifluorescent microscope and a GenePix microarray scanner from Axon Instruments (now Molecular Devices).

As described in the paper, sol-gel spots prepared with the anticancer drugs produced 99-percent and 97-percent cytotoxicity in breast cancer cells, as would be expected, depending on which P450 complex — either CYP3A4 or CYP2B6, respectively — was used. Meanwhile, minimal toxicity was noted in control sol-gel spots. The researchers obtained similar validation in experiments for acetaminophen byproduct toxicity.

Alternative to Hepatocytes?

Solidus estimates that the total potential market for in vitro analysis of drug metabolism and toxicology — including the pharmaceutical, agrochemical, biotechnology, and chemical industries; as well as university and government laboratories — is approximately $4 billion.

According to Clark, the main competition in early-stage toxicity testing will come from live-cell assays using cultured human hepatocytes or liver tissue preparations. But, he said, the MetaChip would provide several advantages over these approaches.

“One area is controllability and reliability,” Clark said. “With hepatocytes, you have varying levels of P450, and the levels can vary from passage to passage. The level is often low to begin with unless it’s induced with a chemical compound.

“The MetaChip allows us to control the activity and the level of P450 very precisely, and to look at different p450 combinations, which can represent the different p450 levels in different sub-populations,” he added.

In addition, culturing hepatocytes is time-consuming and expensive. Although Clark did not disclose a potential cost for the MetaChips, he said they would be more cost-efficient than live hepatocyte assays, as the chips comprise only glass microscope slides, sol-gel, and the necessary cells and reagents.

Ian Mehr, senior director of business development at ADME /tox company Qualyst — which markets its own biochemical assays for P450 toxicity testing and hepatocyte-based assays — told Inside Bioassays last week that there would be little direct competition for a product like Solidus’.

“There are [many] assays out there that will allow you to do high-throughput toxicity screening in vitro, but they are typically looking at a parent compound,” Mehr said. “Maybe in the case of hepatocyte suspensions you’d be able to get an idea of whether the parent and/or metabolites are having a toxic effect. But typically, you’re not going to have that luxury.

“But here, if it does what [Solidus] says it can do — to generate metabolites and you don’t necessarily have to know what they are — then you can ask that question and get a conclusion that either the parent compound or the metabolites are having this effect that you’re seeing on this cell culture.”

But, Mehr said, Solidus would likely face significant hurdles in marketing such an early-stage toxicity testing product to pharmaceutical companies.

“There are two schools of thought when you go into a pharmaceutical company with a tool like that,” Mehr explained. “You’re either telling a company you’re going to help them kill their compounds and not advance ones they don’t want to, or you’re going to help them design the better ones. This seems like it’s a killing type of assay.

“There’s a negative aspect to that,” he added. “There’s a lot of talk about failing faster, but typically a pharmaceutical company doesn’t like to fail at all. That might be one particular challenge of getting this onto the marketplace — you’re asking them to change their perspective in several ways from the traditional aspect of doing screening.”

Eventually, Clark said, Solidus hopes to exploit the chips’ ease of use to tackle challenges beyond early-stage drug screening.

“What we’re very excited about is the prospect of generating individual MetaChips that correspond to the P450 levels of individual patients,” Clark said. “This would tie in with personalized medicine, where we can generate MetaChips that basically mimic [different] metabolisms by reproducing the levels of P450s that are in our individual bodies.

“This would allow specific side reactions, or possible side effects of drugs or drug combinations, to be tested for individual patients,” he added. “Everybody has individual tolerances, and everyone responds to drugs in different ways, so hopefully this would be a way of predicting those responses before they cause problems.”

Reading the Chips

As Solidus considers the angle from which it would like to market MetaChip, it is also considering whether it needs to sell a turnkey product complete with instrumentation and software.

“The idea would be to create a benchtop device that incorporates … microscopy, imaging, and scanning … that would allow a user to insert a MetaChip, apply the compound of interest — through injection, for example — and then all the subsequent steps and manipulations would be carried out within the device,” Clark said. “The output to the user would be a measure of toxicity — for example, an IC50 value for the compound of interest.”

Clark said that Solidus is already in discussions with several undisclosed instrument makers about what would be involved in building such an instrument.

“Some companies are very good about putting the final package together, but they basically get the components from somebody else,” Clark said. “There are lots of companies that do this. We don’t see this as a big hurdle. We think that with some kind of automated, user-friendly, bench-top device, we’ll be able to achieve market penetration and popularize the MetaChip much earlier.”

But the possibility remains, Clark added, of selling the chip without an associated instrumentation platform and letting users select their own microscope, plate reader, or combination thereof.

“We sort of go back and forth on this, and think maybe we ought to do that, just as the MetaChip was used in [the PNAS paper],” he said. “Even without the devices, it’s very easy to use, very simple, and the components that are necessary to analyze the chip are becoming more standard in the kinds of labs that would have an interest in the chip in the first place. So yes, we’re still thinking about that possibility.”

The company has also contacted pharma companies in hopes of snagging a beta-tester and gaining feedback on both the MetaChip’s performance, as well as the instrumentation question.

In terms of generating more capital, Solidus will wait and see if it wins further STTR funding, but Clark said the company has also begun to make some initial calls to venture capital companies. “We certainly have some people interested,” he said.

— BB

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