Minimum Viable Experiments with Imperfect Molecules: a Minipump Minireview
Optimizing lead compounds to have drug candidate-like qualities is time-consuming and expensive. Oftentimes, critical drug discovery project questions, such as on-target pharmacology or toxicology, can be answered more efficiently with compounds that are "good enough," saving teams time and further resource investment. This article discusses tools and strategies available to get desired in vivo pharmacology readouts when single agent oral administration isn't feasible. In particular, programmable minipumps have increasing data supporting their use in a range of settings, including understanding PK/PD for a recent “Molecule of the Month” targeting KRAS(G12C).
Introduction:
Make or break questions for a drug discovery project often come down to, “does modulating this target do what we want?” and, “what else does modulating this target do?” In order to answer those questions quickly and make drug discovery decisions with confidence, an understanding of target engagement and corresponding on- and off-target effects on biology is critical.
Genetic approaches such as inducible knockouts or knock-ins or "bump-hole" experiments can be useful but are not equivalent to pharmacological intervention, as countless studies have shown. Optimizing small molecules for ideal PK can be a significant investment and exceedingly challenging. During the drug discovery phase, one option is to modulate the PK (and hence, target engagement) through alternative methods.
There are several preclinical strategies commonly used to understand target biology with imperfect molecules including:
pharmacological approaches such as co-dosing with PK boosters (e.g. CYP inhibitors, PGP inhibitors)
changing formulations and dosing strategy:
SC, IM, IP extended release (e.g. (suspension, in situ depot)
oral formulations for improved bioavailability (e.g. solid dispersions, nanosuspensions) or extended release (e.g. capsule)
mechanical approaches using tools like minipumps to control drug exposure
Mechanical approaches leveraging tools such as iPRECIO's programmable minipumps to modulate target engagement can be ideal because they don’t require further optimization or significant characterization of the drug molecule. This method can be used to maximize or fine-tune drug exposure to the target while controlling the consistency of the exposure over the delivery time. In one recent “Molecule of the Month” publication, authors used minipumps to help understand whether covalent inhibitor pharmacology was driven by Cmax vs. AUC.
Here is a minireview on programmable minipumps as a method to improve artificially modulate drug exposures and target engagement in drug discovery, so you can ask your pharmacology team lead about it the next time you’re trying to make a go/no-go decision based on in vivo data.
Figure 1. Target engagement and its consequences are important to understand in early drug discovery, but challenging to achieve when working with new molecules. Sometimes it takes a TON of effort to optimize your compound further. If the results of an in vivo study could accelerate or “kill” a project, leading to a faster go/no-go decision, it may make sense to make an in vivo study work by modulating target engagement in ways other than further optimizing the molecule. IR, immediate release; ER, extended release
Pumps Are Well-Established Tools in Preclinical Drug Discovery
Minipumps were designed to deliver a wide range of test agents, from drugs to hormones, and can be used for systemic administration or for targeted delivery to a specific organ or tissue. Pumps allow for continuous and controlled drug delivery without the need for external connections or frequent handling. Once implanted, they can deliver drugs for durations ranging from one day to six weeks, eliminating the need for repeated dosing, even at night or on weekends by lab personnel.
The well-known ALZET Osmotic Pumps were initially developed by the ALZA Corporation during the 1970’s for internal company research and academic collaborators. Soon, word spread about the existence of a novel drug delivery system that allowed for continuous administration of test agents in laboratory animals. Increasing demand for a commercially available continuous drug delivery device for animal research led to introduction of ALZET pumps into the marketplace in 1977. In 2000, the ALZET product line was acquired by DURECT Corporation, which was founded in 1998 by several former ALZA scientists.
The first paper describing osmotic pumps was published in 1976, since then, there have been over 21,000 publications utilizing the technology. Research applications vary widely, from cancer, and cardiovascular, to neuroscience, and include academia and industry.
What Are iPRECIO Programmable Minipumps?
While the use of osmotic pumps is well-established, they are limited by the fact that they can only be used once and with a fixed quantity of drug determined at the beginning of a study. Programmable, implantable pumps, in contrast, allow for more control over drug delivery over the course of an experiment.
Because programmable pumps can be programmed to release a drug in a controlled fashion over preset schedules, chronic dosing regimens and quantitative pharmacology for PK/PD experiments may be scheduled and executed with minimal human intervention during the study and less animal stress. Utilizing an implantable device instead of repeated injection or oral dosing can reduce the impact of those important confounding factors, decrease data variability, reduce the total number of animals required, and make experiments less complex for the human pharmacology team. This can be especially important in neurology studies or any study that leverages a behavior, cardiovascular parameters, or metabolism as an endpoint. There is also evidence to suggest that stress can impact oncology studies, in which measurements are done in tumor cells.
Figure 2. Comparison of iPRECIO programmable minipumps and Alzet osmotic minipumps. The iPRECIO programmable minipump (right) is an advanced infusion device for drug delivery applications in mice, rats and larger animals. The iPRECIO pumps are programmable, refillable, and implantable, which enables full control over dosing studies. Since their introduction in 2007, there have been several applications using iPRECIO technology, including neuroscience, genetic, and cancer research applications. The advanced design of iPRECIO sets it apart from the traditional osmotic pumps, with many considerationswhen designing an experiment.
How Programmable Pumps Can Be Used to Make Drug Discovery Decisions
Programmable pumps are now used throughout the industry for drug discovery studies. According to Tsung Tan at iPRECIO, one pharmaceutical company uses close to one thousand of these pumps a year. Below are a few case studies of how these pumps have been used in preclinical pharmacology research, including from a very recent “Molecule of the Month” publication:
JDQ443 is a structurally unique covalent inhibitor of GDP-bound KRASG12C that forms novel interactions with the switch II pocket. JDQ443 potently inhibits KRASG12C-driven cellular signaling and demonstrates selective antiproliferative activity in KRASG12C-mutated cell lines, including those with G12C/H95 double mutations.
One key question was whether efficacy for this novel covalent inhibitor was driven by Cmax or AUC.
To assess the effect of continuous dosing on tumor growth, LU99 tumor–bearing nude mice were implanted subcutaneously with iPRECIO programmable microinfusion pumps (SMP310R).
Analysis of the antitumor responses and simulations of the PK/target occupancy model demonstrate that efficacy correlates with both the daily AUC of JDQ443 and KRASG12C target occupancy rather than other PK metrics, such as Cmax and time over threshold. Although the correlation of efficacy and target occupancy was expected, given the nature of the covalent mode of inhibition, the correlation to daily exposure was unexpected and presents the opportunity to utilize JDQ443 AUC as a readily measurable surrogate for target occupancy in preclinical and clinical studies.
Conclusion
Time is one of the most valuable resources in drug discovery; therefore, utilizing tools to save time when planning experiments is crucial. Optimizing small molecules for ideal PK could take several months to years, but fortunately there are alternative methods including programmable minipumps to modulate target engagement to get critical go/no-go experiments done when necessary.
We hope you found this article helpful and learned some new strategies for your team’s next in vivo pharmacology experiment.
If you found this article helpful, check out more resources in our resource library here.
Further Reading
Case Studies with Programmable Pumps
Angiotensin II (ANG II)-induced hypertension is a commonly studied model of experimental hypertension, particularly in rodents, and is often generated by subcutaneous delivery of ANG II using Alzet osmotic minipumps chronically implanted under the skin. In a subset of animals subjected to this protocol, mean arterial pressure (MAP) begins to decline gradually starting the second week of ANG II infusion, resulting in a blunting of the slow pressor response and reduced final MAP. The researchers hypothesized that this variability in the slow pressor response to ANG II was mainly due to factors unique to Alzet pumps.
To test this, they compared the pressure profile and changes in plasma ANG II levels during subcutaneous ANG II administration (150 ng·kg(-1)·min(-1)) using either Alzet minipumps, iPRECIO implantable pumps, or a Harvard external infusion pump.
Researchers determined that there were pump-dependent factors, with efficacy (as measured by MAP) being highest in the iPRECIO group (156 ± 3 mmHg) at the end of the experiment, followed by Harvard (140 ± 3 mmHg) and Alzet (122 ± 3 mmHg) groups.
Continuous Delivery of Lenalidomide and Other Immunomodulatory Agents (US 2020/0330445 A1)
This patent from Starton Therapeutics describes methods for continuously administering a formulation comprising an immunomodulatory imide compound.
Potential applications include treating multiple myeloma , transfusion-dependent anemia due to low- or intermediate-1-risk myelodysplastic syndromes, mantle cell lymphoma, hematologic cancers, or solid tumor cancers
Starton’s proprietary continuous delivery technology can increase efficacy of approved drugs, make them more tolerable, and expand their potential use.
The overall aim of this study was to test the effect and safety profile of 125I-UdR therapy in vitro and in vivo on immature Glioblastomas (GBMs) spheroid cultures (GSCs) and orthotopic xenografted GBM-bearing rats, respectively. One objective was to determine if further therapeutic effect was achieved when combining 125I-UdR therapy with the currently used first-line chemotherapeutic agent TMZ.
To assess this, pumps were initially loaded with isotone saline or 0.1 mM MTX. Two days later, residual saline or MTX was extracted from the pump reservoirs and refilled with 960μl of 0.3 μg/ml 125I-UdR or 127I-UdR.
Researchers found that the multidrug approach including CED of MTX and the AEE-compound 125I-UdR in combination with systematic TMZ was safe and very effective in the orthotopic xenograft GBM model, leading to 100% survival.
More Case Studies
A Novel Anti-Inflammatory d-Peptide Inhibits Disease Phenotype Progression in an ALS Mouse Model
Continuous Delivery of Lenalidomide and Other Immunomodulatory Agents
Reviews
iPRECIO Programmable Pump Resources
Additional Case Studies with Osmotic Pumps
Agents: Vascular endothelial growth factor, DNA
Vehicle: Glucose
Route: CSF/CNS (medula);
Species: Rat
Pump: 2001
Duration: 1 week
A Novel Anti-Inflammatory d-Peptide Inhibits Disease Phenotype Progression in an ALS Mouse Model (2021)
Agents: All-D-peptide RD2
Vehicle: Saline
Route: IP
Species: Mice
Pump: 1004
Duration: 28 days
Agents: Bleomycin
Vehicle: Saline, sterile
Route: SC
Species: Mice
Pump: 2010
Duration: 7 days
