Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease, affecting 25% of the global population. NAFLD includes nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH), the former with milder symptoms and the latter having an increased inflammatory response, which is characterized by hepatocellular damage (ballooning), inflammation and fibrosis in addition to hepatocellular steatosis.

Among them, 25% of NAFL patients may progress to NASH, and 35% to 50% of NASH patients may further develop liver cancer, eventually requiring liver transplantation. However, currently, there is only one drug approved for the treatment of NASH globally, Saroglitaza, which is only approved and available in India. The U.S. FDA has not yet approved any drugs for NASH treatment. In clinical trials, investigational drugs have shown adverse reactions such as itching, liver damage, and cardiovascular disease risks. The search for an effective and safe treatment for NASH is urgent.

Saroglitazar: World's First Therapy for NASH

Saroglitazar magnesium, developed by Zydus-Cadila Group, is the only NASH treatment approved for marketing globally, which was approved on March 6, 2020 in India. The drug is currently in Phase II clinical stage in the US for the NASH.

Figure 1. Mechanism of action of Saroglitazar [2]

Saroglitazar magnesium is a novel peroxisome proliferator-activated receptor (PPAR) agonist with predominant PPARα and moderate PPARγ activity with EC50 values of 0.65 pM and 3 nM in HepG2 cells, respectively. PPARα/γ are important transcription factors in the regulation of body metabolism and have important roles in lipid metabolism and insulin resistance. Saroglitazar has been approved in India for diabetic dyslipidemia and hypertriglyceridemia with T2DM not controlled by statin therapy (September 2013) and for type 2 diabetes mellitus (January 2020).

Challenges in NASH Drug Development

Given the huge clinical demand and treatment gaps for NASH, many pharmaceutical companies, including Gilead, Novartis, and Novo Nordisk, are actively researching NASH drugs, aiming to be the first to break through in NASH drug development. However, as of now, no company has achieved success. According to statistics, one-third of phase II or higher NASH drug pipelines have failed.

There are two chanlleges ahead in NASH drug development.

1) Complex Pathogenic Mechanisms: NASH is intricately linked to factors such as the accumulation of fatty acids, insulin resistance, abnormal immune signals, inflammation, and cell apoptosis. The dominant factors in these connections are still unclear.

2) Lack of Reliable Non-Invasive Endpoints: The FDA strictly regulates alternative endpoints for phase III clinical trials of NASH drugs, requiring liver tissue biopsy pathology evaluation, including a. improvement in fatty liver inflammation without worsening fibrosis, or b. improvement in fibrosis without worsening fatty liver inflammation, or c. simultaneous improvement in both fatty liver inflammation and fibrosis. Imaging and serum evaluations cannot serve as the primary endpoints for market approval, limiting the approval threshold for NASH.

Global Status of NASH Drug Development

Currently, NASH drug development focuses on three different pathogenic processes - steatosis, inflammation and fibrosis - and extends to four different therapeutic pathways from the pathogenic source species.

1. Targets of drugs that focus on the gut-liver axis, including regulating enterohepatic circulation of bile acids, and improving the composition of intestinal flora.

2. Targets of metabolic-improving drugs, including enhancing insulin sensitivity, inhibiting key enzymes in de novo lipid synthesis, or promoting fatty acid oxidation in mitochondria.

3. Targets of anti-inflammatory drugs, including inhibiting the recruitment of inflammatory cells or blocking inflammatory signal transduction, reducing oxidative stress and endoplasmic reticulum stress, and inhibiting hepatocyte apoptosis.

4. Targets of anti-fibrotic drugs, including targeting hepatic stellate cells, reducing liver collagen distribution, and enhancing fibrolysis.

Figure2. NASH treatment drugs currently in phase II and phase III development and relevant mechanisms. [1]

Therapeutic strategies primarily focused on improving glucose and lipid metabolism, which are categorized as Type 1 and Type 2, currently have a substantial amount of research. Additionally, most of these strategies are regulated by various nuclear receptors.

Targets of drugs that focus on the gut-liver axis

1. Farnesoid X receptor  (FXR) Agonists

Farnesoid X receptor (FXR) is a nuclear hormone  receptor primarily expressed in the liver, intestine, and kidneys. FXR regulates the expression of multiple genes involved in lipid metabolism, inflammation, and fibrosis. In the context of NASH, when bile acids bind to FXR, FXR is activated. Subsequently, it downregulates the expression of transcription factors such as SREBP1c, thereby reducing hepatic fat synthesis and enhancing the clearance of very low-density lipoprotein in peripheral tissues. Based on this series of metabolic effects, FXR has been identified as a crucial target for treating NASH.

FXR agonists can be categorized into two groups: compounds with a bile acid structure, such as obeticholic acid (OCA) developed by Intercept Pharmaceuticals; and non-steroidal compounds without a bile acid structure, such as Tropifexor, Cilofexor, TERN-101, EDP-305, and MET-409.

Obeticholic Acid (OCA)

Obeticholic Acid (OCA) is a semi-synthetic hydrophobic bile acid (BA) analoguethat is highly selective agonist of FXR. In May 2016, the U.S. FDA granted accelerated approval for Ocaliva (obeticholic acid) for the treatment of primary biliary cholangitis (PBC).

In preclinical studies, OCA can significantly reduce the total amount of bile acids and the content of hydrophobic bile acids, thereby significantly decreasing the absorption of intestinal triglycerides (TG) and cholesterol. OCA is the first NASH treatment drug globally to enter phase III clinical trials, but its path to market has not been smooth.

In the REGENERATE phase III clinical study, after 18 months of treatment, 22.4% of participants receiving once-daily oral OCA 25 mg achieved a >−1 stage improvement of fibrosis with no worsening of NASH compared with 9.6% of participants receiving placebo (p <0.0001), indicating a significant therapeutic effect. [3] However, OCA is prone to causing severe itching symptoms and can lead to an increase in low-density lipoprotein cholesterol (LDL-C) and a decrease in high-density lipoprotein cholesterol (HDL-C). Higher doses of OCA can also worsen liver function in advanced liver disease patients, significantly limiting its clinical application.

Figure 3. REGENERATE phase III clinical study [3]

In June 2020, the FDA determined that the therapeutic benefits of OCA did not outweigh the potential risks and rejected its approval for the treatment of liver fibrosis caused by NASH. In June 2023, the FDA once again rejected a new drug application for OCA to treat fibrosis before the onset of cirrhosis caused by NASH. They requested the completion of long-term follow-up clinical data to demonstrate its safety and efficacy.

Due to concerns that the adverse reactions of OCA may be associated with its bile acid structure, several other investigational FXR agonists currently under research have distinct structures from OCA and lack a steroid-like structure, in the hope of reducing adverse effects while maintaining efficacy.

2. Glucagon-like peptide1 receptor (GLP-1R) Agonists

GLP-1 is primarily secreted by L cells in the ileum and colon. By binding to GLP-1 receptors (GLP-1R) in tissues such as the pancreas, intestine, and brain, it triggers a series of physiological responses involving insulin secretion, delayed gastric emptying, appetite suppression, and improvement of glucose metabolism. GLP-1R is a mature target in the field of diabetes.

The expression of GLP-1R in the liver is relatively low. However, an increasing amount of data suggests that GLP-1R agonists can improve the histological characteristics of the liver in NASH patients through various pathways. The primary mechanisms include weight reduction, lowering glycated hemoglobin and lipotoxicity, improving insulin sensitivity, and inhibiting hepatic steatosis and inflammation. Currently, several GLP-1R agonists have entered clinical trials for NASH research.

Semaglutide

Semaglutide is a long-acting GLP-1R agonist developed by Novo Nordisk, used to treat adult type 2 diabetes and obesity. It has gained significant attention due to its excellent effects on lowering blood sugar and promoting weight loss. On October 30, 2020, the FDA granted it breakthrough therapy designation for the treatment of NASH. In patients with NASH and compensated liver cirrhosis, Semaglutide can improve liver enzymes, hepatic steatosis, weight, diabetes, and lipid parameters, although it does not significantly improve fibrosis.

Currently, besides monotherapy, semaglutide is being explored in combination therapy with empagliflozin (SGLT2) (Phase III), as well as in combination therapy with the acetyl-CoA carboxylase (ACC) inhibitor firsocostat and the FXR agonist cilofexor (Phase II).

Targets of metabolic-improving drugs

1. Thyroid hormone receptors (THR) Agonists

Thyroid hormone receptor (THR) is a nuclear receptor activated by thyroid hormones and is currently the most promising target in the field of NASH. Activation of the THRβ subtype in the liver contributes to reducing hepatic fat and lowering lipid parameters that lead to atherosclerosis. Currently, clinical experience with THR-β agonists suggests the therapeutic potential of this target for NASH and lipid abnormalities.

Resmetirom

Resmetirom is a first-in-class THRβ oral selective agonist developed by Madrigal Pharmaceuticals. It is the only investigational therapy for NASH that has achieved both fibrosis improvement and NASH resolution primary endpoints in a Phase 3 trial.

On Nov 2023, Madrigal Pharmaceuticals announced new data from the Phase 3 MAESTRO-NASH trial demonstrating broad treatment effects of resmetirom on noninvasive tests that may be used to monitor NASH with liver fibrosis. Resmetirom treatment helped patients with NASH with significant fibrosis (F2/F3) as diagnosed on liver biopsy achieve improvements in liver enzymes, magnetic resonance imaging-proton density fat fraction (MRI-PDFF), magnetic resonance elastography (MRE), FibroScan Vibration Controlled Transient Elastography (VCTE), FibroScan Controlled Attenuation Parameter (CAP), and the Enhanced Liver Fibrosis (ELF) test. Resmetirom also reduced levels of LDL cholesterol and other lipids that are associated with heart disease. [4]

In April 2023, the FDA granted breakthrough therapy designation for Resmetirom in the treatment of adults with NASH and liver fibrosis. In September 2023, the FDA accepted the New Drug Application (NDA) for Resmetirom and granted it priority review for the treatment of adults with NASH and liver fibrosis and assigned a Prescription Drug User Fee Act date for resmetirom of March 14, 2024..

2. Peroxisome proliferator activated receptor (PPAR) Agonists

PPAR (peroxisome proliferator-activated receptor) is a group of nuclear receptors that regulate glucose and lipid metabolism, inflammation, and fibrosis. Its subtypes include α, β (or δ), and γ. PPARα is mainly expressed in the liver, regulating processes such as fibroblast growth factor 21 (FGF21) secretion, fatty acid beta-oxidation, fatty acid absorption, lipoprotein lipase activity, and very low-density lipoprotein (VLDL) output. PPARβ is primarily expressed in skeletal muscle, adipose tissue, etc., regulating fatty acid oxidation and promoting insulin sensitivity. PPARγ is highly expressed in adipose tissue, mainly regulating the body's immune system, insulin resistance, and adipocyte differentiation.

IVA337 (Lanifibranor)

IVA337 (Lanifibranor) is a pan-PPAR agonist developed by Inventiva that can activate three subtypes of PPAR receptors within a certain dosage range, synergistically improving insulin resistance and lipid metabolism. Results from Phase IIb clinical trials show that Lanifibranor significantly reduces steatosis and fibrosis scores, improves NASH, and prevents worsening of fibrosis. Consequently, the FDA granted Lanifibranor the breakthrough therapy designation for the treatment of NASH. Phase III clinical trials are currently underway in multiple countries and regions.

3. FGF21 Analogs

FGF21 is a liver-derived hepatokine, a type of factor secreted by the liver. Such factors, once secreted, can exert effects both on the liver itself and on other tissues throughout the body. The expression of FGF21 is regulated by PPAR, primarily exerting its functions through its receptor, FGFR1. FGF21 serves as a fundamental metabolic messenger in regulating glucose and lipid metabolism, insulin sensitivity, and energy homeostasis. It also exhibits anti-inflammatory effects by inhibiting the c-JNK and NF-κB signaling pathways. The endogenous FGF21 has an extremely short half-life, and therapeutic drugs are generally obtained by chemical modification or genetic engineering to create analogs with a longer half-life.

AKR-001 (Efruxifermin)

AKR-001 (Efruxifermin), a derivative of FGF21 developed by Akero, has currently been granted fast-track designation by the FDA for the treatment of NASH. Efruxifermin is a long-acting FGF21 analog created by fusing the Fc fragment of human immunoglobulin G1 with FGF21. It has a longer half-life and stronger receptor affinity compared to natural FGF21.

On September 13, 2022, Akero announced positive data for Efruxifermin in the Phase IIb HARMONY study. Both the 28mg and 50mg doses of Efruxifermin achieved the primary endpoint of improving liver fibrosis and multiple secondary endpoints within a short 24-week period. Efruxifermin demonstrated good tolerability, with the most common adverse events being grade 1 or 2 gastrointestinal events.

However, in October 2023, Akero announced that the interim analysis results of the Phase IIb study for Efruxifermin in treating compensated cirrhosis in NASH patients did not meet expectations. At week 36, a trend towards improvement in the primary endpoint of liver fibrosis was observed, but it did not reach statistical significance. Nevertheless, statistically significant improvements were observed in non-invasive markers of liver injury and fibrosis, blood glucose control, and lipids. Long-term data will be further observed up to 96 weeks in the future.

Conlusion

The drug development for NASH faces multiple challenges due to its complex etiology and the concurrent metabolic disruptions associated with liver dysfunction. FXR agonist OCA and THRβ agonist Resmetirom are the most promising drugs expected to receive approval. Other potential medications include FGF21 derivative Efruxifermin, PPAR agonist Lanifibranor, and GLP-1 receptor agonist Semaglutide. It is anticipated that more drugs will enter clinical trials and receive approval in the future.

Huateng Pharma, founded in 2013, is a one-stop contract development and manufacturing organization (CDMO) to supply researchers and companies with PEG derivatives and products used across the pharmaceutical value chain including intermediates, excipients, APIs, and reagents. We can provide semaglutide intermediates from lab to large scale. Contact us at sales@huatengusa.com for more details. 

References:
[1] Nathani RR, Bansal MB. Update on Clinical Trials for Nonalcoholic Steatohepatitis. Gastroenterol Hepatol (N Y). 2023 Jul;19(7):371-381. PMID: 37771619; PMCID: PMC10524415.
[2] Goyal, O., Nohria, S., Goyal, P. et al. Saroglitazar in patients with non-alcoholic fatty liver disease and diabetic dyslipidemia: a prospective, observational, real world study. Sci Rep 10, 21117 (2020). https://doi.org/10.1038/s41598-020-78342-x
[3] Sanyal AJ, Ratziu V, Loomba R, et al. Results from a new efficacy and safety analysis of the REGENERATE trial of obeticholic acid for treatment of pre-cirrhotic fibrosis due to non-alcoholic steatohepatitis. J Hepatol. 2023;79(5):1110-1120. doi:10.1016/j.jhep.2023.07.014
[4] Madrigal Pharmaceuticals Presents New Data from the Phase 3 MAESTRO-NASH Trial Demonstrating Broad Treatment Effects of Resmetirom on Noninvasive Measures of Liver Health https://ir.madrigalpharma.com/news-releases/news-release-details/madrigal-pharmaceuticals-presents-new-data-phase-3-maestro-nash

Related Articles:
Semaglutide Indication Opportunity: From CDK, HFpEF to Alzheimer's disease