The Forrest group is interested in the areas of cancer immunotherapy and chemotherapy, using dogs with cancer as models of human treatment, Alzheimer’s drug development, targeted drug delivery and pharmacokinetics. This is a wide range of targets, but intelligent design of drug formulations and consideration of the drug/biological interface are commons themes.
Alzheimer’s – Metabolic Engineering
Alzheimer’s disease is a degenerative brain disease and the most common form of dementia. It is progressive, with symptoms worsening over time that adversely affect memory, thinking and behavior.
- The 6th leading cause of death in the United States, killing more than breast cancer and prostate cancer combined
- 1 in 3 three seniors dies with AD or another dementia
- 5.8 million Americans are living with AD; by 2050, this number could rise to nearly 14 million
- In 2019, AD and other dementias will cost the United States $290 billion; this number is projected to rise to $1.1 trillion by 2050
- The last drug to be approved for Alzheimer’s was over 15 years ago!
- Over 150 drugs have failed in clinical trials since 1998, with 132 currently in trials (2019)
Most drugs in clinical trials either target tau, beta amyloid, or disease symptoms. Our mechanism is completely different from all of these.
Brain energy metabolism represents one high potential target that has been ignored. In fact, Alzheimer’s has been increasingly recognized as a metabolic disease. The brain requires a substantial energy flux that, under normal conditions, is provided by glucose. This energy demand is estimated to be 20% or more of total body energy. Alzheimer’s patients consistently exhibit reductions in cerebral glucose utilization, which correlates with the severity of cognition impairment.
We have developed OxaloAcetic Acid (OAA) Ketone-bodies -based drugs as potential therapeutics. Our goal is OAA-ketons, the intent is to enhances bioenergetic fluxes and cell energy production through multiple mechanisms. OAA uniquely fills this niche as exogenously supplied OAA accesses the cell cytosol, where its reduction to malate converts NADH to NAD+ (Figure 1a). Unlike pyruvate, the other major cytosolic molecule whose reduction converts NADH to NAD+, OAA is not a downstream glycolysis intermediate and it enhances rather than impedes glycolysis flux (Figure 1b). Malate produced in the cytosol accesses mitochondria, enters the Krebs cycle, oxidizes to OAA in a reaction that generates mitochondrial NADH, and increases respiration (Figure 1c). Figure 2D schematically summarizes this.
Figure 1. OAA effects on bioenergetics. (A) NAD+/NADH in SH-SY5Y human neuroblastoma cells. (B) Glycolysis effects in SH-SY5Y cells. (C) Respiration effects in SH-SY5Y cells. (D) Overall effect schematic. **Indicates key statistical relationships at p<0.01. Con=control. Summary: OAA increased NAD+/NADH and cellular respiration by ~50%, similar to glucose restriction; OAA increased glycolysis flux capacity ~50%.
OAA and the ketones we use a natural chemicals already produced in the body, but they are unstable in the gastric tract and unstable even on the shelf. We have developed novel prodrugs that allow these to be made into safe and efficacious pharmaceuticals. In early rodent studies these have shown dramatic increases in ketone levels, exceeding the levels obtained with strict ketogenic diets.
Immune Agonist Cancer Therapies
The immune system can kill cancer cells, but unfortunately, cancers have developed mechanisms to suppress this immune response. Promoting immune activation against cancers or mitigating immune suppression is a major goal for cancer immunotherapies. TLR7 is an endosomal receptor expressed primarily in the antigen presenting cells (APCs) of the immune system, and TLR7 activation can lead to stimulation of three major tumor- killing immune cell populations (CTLs, Th1 cells, NKs). TLR7-mediated activation of the two main types of APCs, dendritic cells (DC) and macrophages, promotes cell- and cytokine-mediated events leading to CTL and Th1 activation, which is critical for response to immune therapies, generation of memory T cells, and the Abscopal effect.
Our group is developing novel highly potent TLR7 and TLR7/8 dual agonists and biomaterials that localize these therapies to the tumor and draining lymph nodes, where the immune response to cancers is initiated.
A problem with immunotherapy is always off-target effects, where the immune system attacks normal tissues. For example, patients on “checkpoint” inhibitors such as anti-PD1, anti-PDL1, and anti-CTLA4 drugs can have transplant organ rejection, thyroid problems, and gasto-intestinal diseases.
We use a new biomaterial based off hyaluronan that localizes the drug to the tumor and draining injection area, so there is no systemic inflammation.
Figure 2 - Free drug (no HAT) shows robust systemic TNFα response, but no local reaction. Red: TLR7/8-HAT local inflammation (arrows) around injection site (purple circle), but no systemic TNF-α response.
This approach produces a significant influx of activated immune cells into tumors (fluorescence microscopy of tumor cross-sections in mice), which leads to a reduction in tumor growth without chemotherapy.
Pet Dogs as Models for Cancer Drug Development
Mouse models provide critical data about cancer etiology and treatment but are not sufficient to predict human outcomes. The NIH Comparative Oncology Program (63) has recognized dogs with naturally occurring cancers as promising preclinical translational models, which may be more predictive of human outcomes. Most human cancers are found in dogs with similar pathologies and oncogenic mutations. Importantly, major components of the immune system (e.g. CD8+ and CD4+ T cells, and DCs) are similar to humans. Therefore, success in our dog trial has a strong likelihood of impacting treatment of human cancers.
In collaboration with the University of Missouri veterinarian cancer center, Kansas State University animal cancer center, and local veterinarians we are translating new cancer treatments form mice to dogs.
Not only do we get to help dogs with otherwise untreatable cancers, but these data are directing the development of drugs that may one day be used in humans.
Figure 1 - Oral melanoma that had a complete response (effectively a cure) after immunotherapy.
Figure 2 - Dog with inoperable mast cell cancer on the ankle who had failed chemotherapy. Free of disease after immunotherapy.
Intestinal Immunomodulating Drugs
Ulcerative colitis (UC) is a chronic inflammatory bowel disease where inflammation and ulceration are localized to the colon and rectum. Current strategies for treatment of UC involve aminosalicylates, corticosteroids, and anti-TNFα therapies. Unfortunately, patients often become refractory toward treatment over time, with colectomy being a final option.
Our strategy is to develop potent immunosuppressants that are only activated in the unique microbiome prevalent in the area of active UC.
Pharmacokinetics and Physiologically Based Models
Disease state (vs. healthy) is now known to influence the pharmacokinetics for drugs. Laboratory models (e.g. mice) can have some value in predicting these issues. One of our areas of interest is to improve models of drug disposition using data on inflammatory responses, to create semi-physiologically based pharmacokinetic (PBPK) models of drug pharmacokinetics and metabolism.
Figure 1: Schematic of PBPK model
Figure 2: Predicted and actual changes in metabolism of the drug midazolam after induction of inflammation in mice (using glucose-6-phosphate isomerase [GPI] induced inflammation).
Along these lines we are also interested in incorporating the lymphatic system into advanced models for the pharmacokinetics of antibody / large molecule therapeutics.
Biomaterials to Enhance Fracture Healing
Approximately 6.3 million fractures occur in the U.S. annually, with 5–10% resulting in debilitating nonunions. A major limitation to achieving successful bony union is impaired neovascularization. To augment fracture healing, we are designing implantable drug delivery technologies that can chelate iron at the break site and enhance bone healing.
Figure 1: In vivo: HA-DFO restores mineralization and enhances biomechanical strength in irradiated fracture healing. a In vivo experimental timeline, normal peak fracture angiogenesis timing and schematic of the rat mandible depicting drug delivery methods and release kinetics. b Representative µCT images by treatment group. Notice the decreased bony bridging across the fracture site in the XFx sample that is restored in both iDFO and HA-DFO treated mandibles.