Date: 1st September 2020
It is estimated that around 422 million people worldwide are living with diabetes, and about 1.6 million deaths are directly attributed the condition each year. With its prevalence steadily rising, so are major risk factors such as overweight and obesity. In 2016, this accounted for more than 1.6 billion adults, and in 2019 around 380 million children were estimated to be overweight or obese.
Developing preventive and therapeutic strategies for obesity and diabetes is of great importance, current medications often only have transitory effects, and are frequently accompanied by weight gain rather than weight loss. Current advances in synthetic biology, gene editing and therapy, and biotherapeutics are paving the way for the next generation of novel treatments.
Last week saw two such advances published in the Science Translational Medicine journal. Yu-Hua Tseng and colleagues from the Joslin Diabetes Center, Harvard Medical School, US, in an international collaboration have delivered a proof of concept novel cell-based therapy using CRISPR engineering to combat obesity and diabetes. Whilst, biomedical engineers at Duke University, US, led by Ashutosh Chilkoti, have developed a single molecule, dual-drug therapy for the treatment of obesity and hyperglycemia.
In mammals, both brown adipose tissue (BAT) and white adipose tissue (WAT) contribute to systemic energy homeostasis although they have distinct functions. WAT is the main site for storing excess fuel, whereas BAT is specific for energy dissipation.
Brown fat can lower excessive levels of glucose and lipids in the blood that are linked to metabolic diseases such as diabetes, however this tissue is often diminished in obese or overweight people. BAT would make a good target for a potential therapy, however as it is located in small inaccessible regions of the body Tseng and the team wanted to genetically modify abundant WAT giving it the heat-generating properties of brown fat cells.
The team started by taking human white preadipocytes (precursor cells) and created human brown-like (HUMBLE) cells by using a variant of CRISPR-Cas9 to activate endogenous expression of uncoupling protein 1 (UCP1), a protein found in BAT which dissipates energy via heat. The variant they used was CRISPR-Cas9 Synergistic Activation Mediator (SAM) – an engineered protein complex where dCas9 was combined with a fusion protein consisting of two transcriptional activation domains to synergistically boost transcription.
The HUMBLE cells were then transplanted into immune deficient mice where they were able to reconstitute fat tissues in vivo that recapitulated the phenotypes of native brown fat cells.
Next the team wanted to test the HUMBLE cells activity with respect to obesity. Here the mice were fed a high-fat diet pre and post transplantation. Mice receiving HUMBLE cells gained less weight than mice receiving white control fat cells and also displayed about 30 to 35% improvements in glucose tolerance and insulin sensitivity than the control animals.
However, as diabetes is a long-term condition the team wanted to assess HUMBLE cell activity over a 12 week period (rather than 4 weeks for the above). Importantly, transplantation continued to display long-term metabolic benefits in the mice.
One surprising discovery was that the HUMBLE cells were able to activate endogenous murine BAT. This occurred via red blood cells, which carried nitric oxide (NO) secreted from HUMBLE cells to endogenous brown cells. Inhibition of NO production abolished HUMBLE cell–mediated metabolic benefits.
The work here demonstrated the preclinical therapeutic potential of the CRISPR-engineered HUMBLE cells in the prevention and treatment of obesity. Transplantation of HUMBLE cells significantly improved glucose homeostasis in mice, which was mediated at least in part by NO activating endogenous murine BAT.
The work offers exciting promise for new treatments for obesity and type-2 diabetes. The team are currently exploring several approaches for accelerating translation into the clinic. One option would be to create personalised therapies, using the patient’s own white fat cells. However, this would be a complex and expensive technique. The team are also considering using biomaterials to encapsulate the transplanted cells which would evade the immune system and thus bypass the need for personalisation. An alternative approach would be to edit endogenous white fat progenitor cells in vivo, activating the expression of UCP1.
Whilst Tseng and the team have opted for a reprogramming approach in their cell-based therapy there are currently a range of drugs licensed for use for diabetes that could be manipulated to enhance functionality and may offer an alternative strategy for treating the condition and obesity.
Incretin mimetics are a relatively new group of injectable drugs for treatment of type 2 diabetes. The drugs, also known as glucagon-like peptide 1 (GLP-1) receptor agonists, are normally prescribed for patients who have not been able to control their condition with tablet medication and they enhance glucose-stimulated insulin secretion and reduce food intake. However, these drugs are not entirely sufficient for chronic glucose control in patients with type-2 diabetes and weight loss induced by these drugs rarely corrects obesity furthermore, high doses can cause gastrointestinal distress.
To overcome these issues there is a growing effort to explore combination therapies that strategically pair GLP-1 with additional drugs to maximise glucose control, enhance weight loss but minimise side effects. In the main this has been restricted to drug combinations which incorporate small peptides from the same family as GLP-1.
However, Ashutosh Chilkoti and the team from Duke University wanted to combine structurally distinct drugs into a single molecule while maintaining the bioactivity and stability of each. They chose to combine FGF21, a metabolic hormone that regulates insulin sensitivity, energy expenditure and fat metabolism within body tissues, with GLP-1, hypothesising that that the two drugs would be complementary.
To create a single combination drug the team fused GLP-1 to FGF21 with an elastin-like peptide which acts as a heat-sensitive tether. This allowed the team to design a compound that was liquid at room temperature but formed a gel-like depot upon injection, allowing it to slowly dissolve releasing the drug over time and acting as a sustained release module.
The team then tested the dual-drug therapy in diabetic mice. They found that mice injected with a single dose of the dual-drug therapy were better able to recover from a glucose challenge compared to either GLP-1 or FGF21 alone. Furthermore, they were the only test group to lose weight during the trial – losing up to ~7% of their body weight (at the highest doses). The team also determined that the dual-drug tethered formulation had superior efficacy compared to a GLP-1 and FGF21 mixture administered in a single dose. The levels of drug circulating in the system remained steady while blood sugar levels were brought down to a healthy level, this was maintained for up to 10 days.
The data suggested to the team that by linking these two molecules with different modes of action, it allowed them to act in concert at the same time, creating a synergistic effect.
The Chilkoti team here describe the development of a biologic that fuses GLP-1 to FGF21 with a heat-sensitive linker that acts as a sustained release module. The dual-drug treatment facilitates greater weight reduction and enhanced glycemic control compared to current drug treatments or by mixing GLP-1 and FGF21 as individual molecules together.
The data presented here offers an exciting new approach to treating obesity and diabetes. In fact, the results are so compelling that it is currently driving the Duke’s Office of Licensing and Ventures to seek to license the therapy, believing that it is ready for a company to pursue this strategy commercially.
The two approaches here highlight the range and diversity of new and novel strategies for treating obesity and diabetes. They are likely to form part of a wider effort to accelerate efficient, effective treatments for these conditions that affect so many people globally. For example we have recently seen scientists engineer pancreatic cells to produce increased levels of insulin in response to high glucose levels in mice and the development of a low-cost, electronic-free, glucose-responsive gel technology as an in vivo insulin delivery system. In addition, from a manufacturing perspective we reported the generation of nanomachines; engineered enzymes created in order to yield a cleaner and quicker method of producing anti-diabetic drugs. It is clear that synthetic biology advances are powering the next generation of solutions that will hopefully translate into clinical application.
Whilst both the teams here are dedicated to improving the metabolism, body weight, quality of life and overall health of people with obesity and diabetes it is especially poignant given the current pandemic as these are people with a higher risk of serious outcomes if they are infected with SARS-CoV-2. Investing in diverse technologies may give us a better chance of successful outcomes.
Wang, C.-H., M. Lundh, A. Fu, R. Kriszt, T. L. Huang, M. D. Lynes, L. O. Leiria, F. Shamsi, J. Darcy, B. P. Greenwood, N. R. Narain, V. Tolstikov, K. L. Smith, B. Emanuelli, Y.-T. Chang, S. Hagen, N. N. Danial, M. A. Kiebish and Y.-H. Tseng (2020). “CRISPR-engineered human brown-like adipocytes prevent diet-induced obesity and ameliorate metabolic syndrome in mice.” Science Translational Medicine 12(558): eaaz8664.
Gilroy, C. A., M. E. Capozzi, A. K. Varanko, J. Tong, D. A. D’Alessio, J. E. Campbell and A. Chilkoti (2020). “Sustained release of a GLP-1 and FGF21 dual agonist from an injectable depot protects mice from obesity and hyperglycemia.” Science Advances 6(35): eaaz9890.