Caliper Life Sciences (www.caliperls.com) approaches drug repositioning both as a contract research organization—through Caliper Discovery Alliances and Services—and as a solutions provider. A platform initially designed to phenotypically characterize genetically modified animals, which began as a Pfizer collaboration, was leveraged to create a broader enterprise for characterizing compounds.
In the current use, mice are used to comprehensively characterize genetic targets and compounds. This helps Caliper efficiently validate genetic targets and position potential therapeutics much earlier in the drug discovery process, as well as uncover secondary indications opportunities for early-stage compounds and reposition existing therapeutics and compounds, according to David S. Grass, Ph.D., vp, scientific operations.
The strategy to characterize genetic targets is called serial phenotyping comparison technology (SPCT). Using a small group of animals, he says, researchers can see how, or whether, genetic modifications affect the mouse response in 60 different bioassays and challenge assays covering more than 450 different parameters, relevant to 15 therapeutic areas.
For example, one program involves 50 knock-out and 50 wild-type mice, on which 60 assays were conducted without compromising the average number of animals per assay. Conclusions are reached in 17 weeks for each cohort of mice. Competing, nonmultiplexed methods would require a total of 900 mice and three months to get comparable data, according to Dr. Grass. (The funds spent on breeding the mice accounts for about 25% of the research testing budget using SPCT, versus 75% of the research testing budget using nonmultiplexed methods.)
Because this approach covers most of the major therapeutic areas, researchers are more likely to uncover unanticipated results and, therefore, may better focus their compounds. They may even start new projects with different concepts or potential indications.
Caliper is working on augmenting its platform to also capture pharmacodynamics readouts by following the expression of genes in key pathways, using its in vivo biophotonic imaging technology, Dr. Grass adds. This technology is able to noninvasively detect light emitted through mammalian tissue, and can be applied to oncology and infectious disease studies.
“For example,” Dr. Grass says, “tumors genetically modified to express the luciferase gene can be tracked or monitored noninvasively through the body of the animal, allowing real-time, in vivo measurement of tumors, as well as their growth or regression. This approach enhances data quality and efficiency in orthotopic and metastatic tumor models, as well as subcutaneous tumor models.”
In one case involving the evaluation of a clinical development candidate in a subcutaneous tumor model, caliper measurements indicated the tumor wasn’t regressing in response to the compound. Yet, measuring the light emitted by the firefly luciferase-expressing tumor cells revealed a necrotic core, proving that the compound was, in fact, efficacious.
When it comes to targets, “GPCRs are still the most addressed target class in the drug development industry,” notes Keith Olson, Ph.D., vp of R&D for DiscoveRx (www.discoverx.com).
DiscoveRx has leveraged that situation by developing a panel of more than 120 GPCR assays for high-throughput screening and profiling. The panel consists of 80 high-value GPCRs and more than 40 uncharacterized GPCRs. Although GPCRs have many different signaling pathways, and some use multiple channels, virtually all bind with arrestin. “Consequently,” Dr. Olson says, “the PathHunter™ Arrestin Assay is about as universal a platform as you can get.”
This panel’s broad assay windows and robust performance make it possible to use as few as 1,000 cells in a 1,536-well format, making it particularly useful for GPCRs with poor signaling or limited cell quantities. Another benefit, Dr. Olson says, is that it measures direct interactions rather than detecting secondary messengers. The PathHunter Arrestin assay is based on DiscoveRx’ enzyme fragment complementation and generally yields readouts in about one hour.
“The single-addition assay is ideally suited for screening, without force coupling, against GI and orphan receptors,” Dr. Olson notes. With a growing list of GPCRs included in the panel, the PathHunter Arrestin platform identifies agonists, antagonists, and inverse agonists while providing information about signaling pathways.”