GALECTIN INHIBITORS – Is a Galectin-3 Inhibitor the Answer for Millions of Patients With Cirrhosis & Cancer?


INTRODUCTION

First described in 1971, the galectin-3 protein has since been implicated in the progression of a wide range of different human diseases, such as cancer and cirrhosis. For instance, galectin-3 plays a significant role in liver diseases, such as non-alcoholic steatohepatitis (NASH) and its complication, liver cirrhosis.1 Could development of a galectin-3 inhibitor become a treatment for the millions of people affected by these diseases? Galectin Thera­peutics has spent the past decade researching this very question. The company recently enrolled its first patient in a Phase 2B/3 clinical trial to test whether its novel galectin-3 inhibitor, be­lapectin, has the ability to prevent the development of esophageal varices in patients suffering with NASH cirrhosis.2

GALECTINS

Galectins are a class of proteins that act as a molecular glue in the body, bringing together molecules that have specific sugars on them. There are 15 galectin protein subtypes, all with the com­mon characteristic of binding to galactose-containing carbohy­drates and glycoproteins. The most relevant galectin for human diseases is galectin-3.3

While galectin-3 is normally expressed in small amounts in many different cell types, it is highly expressed in macrophages of the immune system and activated by tissue damage. Chronic inflammation in organs such as the liver, for example, can trigger galectin-3 to promote the development of scar tissue, which over time can interfere with organ function.3

Galectin Therapeutics set out to discover whether using a galectin-3 inhibitor, belapectin, could break this cycle of disease.

GALECTIN-3 & DISEASE

Medical science is recognizing the role that galectin-3 plays in a wide range of diseases. There were few scientific articles writ­ten about galectin-3 in the 1990s and 2000s, but nearly 150 in 2010 and more than 300 in 2018. These articles encompass the role of galectin-3 not only in liver fibrosis, cirrhosis, and cancer, but also diabetes, heart attacks, lung fibrosis, and many other diseases.1

Published data substantiating the importance of galectin-3 in the fibrotic process arises from gene knockout experiments in animal studies.4 Mice genetically altered to knock out the galectin-3 gene, and thus unable to produce galectin-3, do not develop liver fibrosis in response to toxic insult to the liver.

GALECTIN-3 & LIVER FIBROSIS & CIRRHOSIS

In the liver, fibrosis – or the excessive deposition of collagen – is the end result of multiple inflammatory conditions and infec­tions. Progressive liver fibrosis leads to cirrhosis, which is charac­terized by a disruption of the normal architecture of the liver, resulting in reduction of liver function, multiple medical compli­cations, and ultimately death. More than 500,000 patients have cirrhosis in the US, with close to 50,000 losing their lives each year.5

Scientific evidence strongly suggests that galectin-3 is essential for the develop­ment of liver fibrosis and, ultimately, NASH and NASH cirrhosis.

In non-alcoholic fatty liver disease (NAFLD) – the precursor to NASH – fat starts to build up in the liver. The fat buildup causes inflammation, an immune response of the body to protect against at­tack. In this stage, galectin-3 becomes highly expressed. The presence of galectin-3 triggers liver scarring, causing liver fibrosis. As the fibrosis displaces healthy liver cells, the cells begin to die. The continued scarring and liver cell death causes cirrhosis. At this stage, liver function is reduced, even to the point of failure.

Currently, there is no treatment for NASH cirrhosis short of a liver transplant, and only a fraction of the patients with cir­rhosis are able to get a liver transplant, a highly expensive procedure.6 As a result, there is an urgent need for treating NASH cirrhosis.

THE ROLE OF GALECTIN-3 IN CANCER

Galectin proteins, notably galectin-3, are also present in increased amounts in cancers of many types. In fact, expression of galectin-3 appears to be higher in the majority of solid tumors including skin (melanoma), head and neck cancer, and lung cancer (such as non-small cell lung cancer).3

Examining tumors for the presence of galectin-3 has gained some acceptance in clinical medicine. In thyroid cancers, pathologists routinely stain tumor biopsies for galectin-3 to distinguish malignant tis­sue from normal tissue, potentially reduc­ing unnecessary thyroid surgeries. It has also been shown that the amount of galectin-3 expressed in some cancers, such as lung cancers, correlates with the aggressiveness of the cancer and the ulti­mate prognosis of the patient, subject to confirmation, a finding that may be useful in clinical practice and help with the choice of treatment.7

Galectin-3 promotes the spread of cancer in the following three ways:

  • Invasiveness – Galectin proteins help cancer cells migrate and therefore favor the infiltration of the cancer cells into surrounding tissue.
  • Metastasis – In colon cancer, the highest levels of galectin-3 are found in tumors that have metastasized elsewhere in the body, while the lowest are in the cancer cells located in the original tumor.
  • Tumor Growth – Galectin-3 reduces cell death and promotes the growth of blood vessels that bring blood supply to the tumor.

Galectin-3 also inhibits the patient’s immune system, thereby preventing im­mune cells from killing tumor cells.8 This immune effect of galectin-3 in cancer is particularly interesting because of the ris­ing importance of cancer immunotherapy. Could a galectin-3 inhibitor play a role in fighting cancer? This hypothesis is cur­rently being tested in the clinic by combin­ing belapectin with an immune checkpoint inhibitor in patients with melanoma and head and neck cancer.9

FINDING THE RIGHT GALECTIN-3 INHIBITOR

It is one thing to recognize an oppor­tunity for a galectin-3 inhibitor, but it is an­other to take advantage of it. More than a decade ago, Galectin Therapeutics began researching molecules with the potential to act as inhibitors to the disease-causing properties of galectins, particularly galectin-3.

UNDERSTANDING THE GALECTIN-3 BINDING SITE

The first step was to understand the galectin-3 binding site, which is found in cells throughout the body. The binding sites internal to the cells were not useful to Galectin Therapeutics’ purposes, but the binding sites found on the external surface of cells and in free-floating galectin-3 mol­ecules were both potentially actionable.

Galectin Therapeutics began with a survey of the existing chemical literature on the galectin-3 binding site, soon expand­ing to undertake basic research at the Uni­versity of Minnesota to understand the chemical structure of the galectin-3 recep­tor.

The galectin-3 natural carbohydrate binding site (CBD) exhibits poor drugga­bility, making it an unsuitable target for the more typical small molecules used in phar­maceutical treatments. It is a big, diverse binding site when compared to more dis­crete receptors, where a small drug mole­cule might fit like a lock and key. The propensity of galectin-3 to bind to sugars, notably at other sites on the molecule (Fig­ure 1), suggests that a larger molecule de­rived from a carbohydrate might be better suited as a potential drug candidate.10

The galectin-3 molecule has a globular head attached to a slender long N-tail, presenting several potential binding sites. The canonical S-face binds to lactose and similar molecules, while larger molecules, such as Galectin Therapeutics’ belapectin galectin-3 inhibitor, bind to the non-canonical F-face and the H-domain of the N-tail.10 (Figure based on Suthahar N, et al. Theranostics 2018; 8(3): 593-609. doi: 10.7150/thno.22196)

IN SILICO MODELING

Much of the initial search for suitable molecules was done using state-of-the-art in silico methods, where computer models were used to screen drug candidates for their physical and chemical properties to interact with galectin-3 and the carbohy­drate recognition domain. Galectin Ther­apeutics began with existing molecules but soon went on to design de novo new mol­ecule structures that weren’t yet known.

Because of the poor druggability of the galectin-3 CBD site, Galectin Thera­peutics believed that carbohydrate chem­istry held the answer to creating a different type of galectin-3 inhibitor. Galectin-3 is a large molecule itself and offers other op­tions for binding sites in addition to the single CBD. The flexibility of a complex polycarbohydrate structure meant such a molecule might have greater interaction with multiple binding sites on the galectin-3 molecule.

Galectin Therapeutics set out to create such flexible molecules that would bind to galectin-3 and thereby prevent the devel­opment of scar tissue and the other dele­terious effects. Computer models were used to predict the chemical interactions of candidate molecules with the galectin re­ceptor itself.

The predictions of the in silico model­ing were confirmed with in vitro testing, the results of which were used to refine the computer models.

This was not a trivial effort. Nearly 1,000 molecules were examined, not only for their galectin-3 binding abilities but also for affinity to other galectins. Extensive studies were required to characterize the physical, chemical, and biological properties of potential drug candidates utilizing state-of-the-art analytical techniques and methodologies, some of which were devel­oped in collaboration with leading scientists in the academic field of carbohy­drate research. Galectin Therapeutics has patented many of these new molecules. The first molecules, such as belapectin, will be delivered as infusions, and oral follow-up compounds are currently early in the development process.

ANIMAL STUDIES

Ultimately, Galectin Therapeutics had to show that the molecule actually worked in vivo to change the disease process. That called for animal and, eventually, human testing.

To do that, Galectin Therapeutics had to first synthesize a large amount of be­lapectin, a kilogram or so. Working in vitro might require only micrograms of the mol­ecule, but animal and human testing re­quires much more. The process also requires good analytical test methods to ensure the purity and quality of the sub­stance, and it must be delivered in a form that can be given to an animal.

The endpoints of the study must also be chosen carefully. Because galectin-3 works at the tissue level, there wouldn’t be a demonstrable change in the levels of cir­culating galectin-3. The drug levels could be tracked, but there was no way of know­ing whether the drug was having an effect by looking at the amount of galectin-3 in circulation. Instead, Galectin Therapeutics had to undertake in-depth preclinical ex­periments, trying to induce a disease in a cohort of mice and seeing whether a can­didate molecule had any effect on the dis­ease progression. This takes time – around 8 months from start to finish – to dose the animals, give time for the disease progres­sion, then follow up with tissue analysis (histology) and data analysis.

Two drug candidates underwent ex­tensive animal testing for use in liver dis­ease, and one molecule, belapectin, showed such strong results in preclinical testing that in 2013, the FDA allowed it to enter into human clinical trials for NASH and gave it the coveted Fast Track status.

HUMAN CLINICAL TRIALS IN NASH CIRRHOSIS

After many years of research, Galectin Therapeutics recently launched its NAVIGATE study, an international, seam­less, adaptively designed Phase 2b/3 clin­ical trial of its galectin-3 inhibitor belapectin, the company’s lead com­pound, in NASH cirrhosis patients who have clinical signs of portal hypertension and are at risk of developing esophageal varices.11 A previous Phase 2 study, the NASH-CX clinical trial, had shown be­lapectin could prevent the development of new varices in this patient population. To the best of Galectin Therapeutics’ knowl­edge, belapectin is the first compound to demonstrate clinically meaningful positive effects in patients with NASH cirrhosis with­out esophageal varices.

Unlike most other ongoing clinical tri­als focused primarily on earlier stages of NASH, the NAVIGATE study population will comprise patients with compensated liver cirrhosis. NAVIGATE is focused on pa­tients who have not yet developed esophageal varices but are at increased risk of developing these potentially life-threatening complications. Consequently, patient selection for both Phase 2b and Phase 3 will be based on clinical signs of portal hypertension such as a depressed platelet count (thrombocytopenia), an en­largement of the spleen (splenomegaly), and evidence of collateral vessels.

The primary endpoint of the trial is to assess the effect of belapectin on the inci­dence of new varices. A centralized review system of video recording of esophagogastroduodenoscopy (EGD) has been put in place, and the primary endpoint will be adjudicated by expert EGD readers. Key secondary endpoints will assess the type of varices (sizes and/or bleeding) and other clinical events, such as ascites, hepatic encephalopathy, listing for liver transplantation, or death.

HUMAN CLINICAL TRIALS IN OTHER INDICATIONS

The potential of belapectin as a galectin-3 inhibitor attracted the attention of researchers working in cancer immunology. Galectin-3 is intimately in­volved in the progression of cancer, perhaps interfering with the immune sys­tems’ ability to find and destroy cancer cells. Providence Cancer Institute has been testing belapectin in a Phase 1B investiga­tor-initiated trial in combination with KEYTRUDA®, a checkpoint inhibitor (anti-PD-1) immunotherapy, to treat advanced melanoma as well as head and neck can­cer. Preliminary data from this open-label study shows a 50% objective response rate in advanced melanoma with belapectin in combination with KEYTRUDA. There is also a suggestion that the combination could reduce the incidence of auto-immune re­actions, a well known and sometimes problematic side effect.12 These results are encouraging, and additional data are expected soon.

KEY LEARNINGS

Galectin Therapeutics has validated the applicability of using a galectin-3 in­hibitor in treating fibrosis in liver cirrhosis, a validation that drug developers call the “proof-of-concept.”

Galectin Therapeutics scientists also made the compound available to col­leagues working in selected areas, gener­ating data showing the molecule worked in various models of renal fibrosis, pul­monary fibrosis, and even cardiac and se­lect forms of vascular fibrosis.

The ongoing work at the Providence Cancer Institute likewise shows the impact a galectin-3 inhibitor might have in mod­ifying the body’s immune response to can­cer when used in combination with a check-point inhibitor.13

For its part, Galectin Therapeutics continues its basic research on new mole­cules, targeting both galectin-3 and other galectins. These would be follow-on com­pounds for belapectin, notably to develop an oral formulation of a galectin-3 in­hibitor. To this end, the company estab­lished Galectin Sciences LLC as a joint partnership with SBH Sciences in Natick, MA, a contract research organization that had been involved in much of the earlier preclinical research that had led to be­lapectin. Galectin Sciences continues re­search to find non-carbohydrate small molecules that can inhibit galectin mole­cules, with the goal of developing oral therapies.

REFERENCES

  1. Shlevin H. Why Galectin-3 has emerged as a focus for drug research and development. PharmaIQ 2019. https://www.pharma-iq.com/pre-clinical-discovery-and-development/articles/why-galectin-3-has-emerged-as-a-focus-for-drug-research-and-development-1.
  2. Galectin Therapeutics, Inc. Galectin Therapeutics An­nounces Commencement of Patient Enrollment of the Adaptively-Designed Phase 2b/3 Trial of Belapectin in NASH Cirrhosis. https://investor.galectintherapeutics.com/ news-releases/news-release-details/update-galectin-thera­peutics-announces-commencement-patient.
  3. Sciacchitano S, Lavra L, Morgante A, et al. Galectin-3: One Molecule for an Alphabet of Diseases, from A to Z. Int J Mol Sci. 2018;19(2):379. Published 2018 Jan 26. doi:10.3390/ijms19020379.
  4. Henderson NC, Mackinnon AC, Farnworth SL, et al. Galectin-3 regulates myofibroblast activation and hepatic fibrosis. Proc Natl Acad Sci U S A. 2006;103(13):5060-5065. doi:10.1073/pnas.0511167103 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1458794.
  5. Scaglione S, Kliethermes S, Cao G, et al. The Epidemiol­ogy of Cirrhosis in the United States: A Population-based Study. J Clin Gastroenterol. 2015;49(8):690-696. doi:10.1097/MCG.0000000000000208.
  6. The National Institute of Diabetes and Digestive and Kid­ney Diseases, Health Information Center. Definition & Facts of Liver Transplant. https://www.niddk.nih.gov/ health-information/liver-disease/liver-transplant/definition-facts.
  7. Takenaka Y, Fukumori T, Raz A. Galectin-3 and metastasis. Glycoconj J. 2002;19(7-9):543-549. doi:10.1023/B:GLYC.0000014084.01324.15.
  8. Kouo T, Huang L, Pucsek AB, et al.Galectin-3 Shapes Anti­tumor Immune Responses by Suppressing CD8+ T Cells via LAG-3 and Inhibiting Expansion of Plasmacytoid Den­dritic Cells. Cancer Immunol Res April 1 2015 (3) (4) 412-423; DOI: 10.1158/2326-6066.CIR-14-0150.
  9. U.S. National Institutes of Health. GR-MD-02 Plus Pem­brolizumab in Melanoma, Non-small Cell Lung Cancer, and Squamous Cell Head and Neck Cancer Patients. https://clinicaltrials.gov/ct2/show/NCT02575404.
  10. Suthahar N, et al. Galectin-3 Activation and Inhibition in Heart Failure and Cardiovascular Disease: An Update. Theranostics 2018; 8(3): 593-609. doi: 10.7150/thno.22196.
  11. U.S. National Institutes of Health. Study Evaluating the Ef­ficacy and Safety of Belapectin (GR-MD-02) for the Pre­vention of Esophageal Varices in NASH Cirrhosis.https://www.clinicaltrials.gov/ct2/show/NCT04365868?term=NCT04365868&draw=2&rank=1.
  12. Galectin Therapeutics, Inc. Galectin Therapeutics, Inc. Announces Positive Preliminary Results from Phase 1b Clinical Trial of GR-MD-02 and KEYTRUDA® in Ad­vanced Melanoma and Expansion of the Trial. https://in­vestor.galectintherapeutics.com/news-releases/news-release-details/galectin-therapeutics-inc-announces-positive-preliminary-results.
  13. Cristina V, Herrera-Gómez RG, Szturz P, Espeli V, Siano M. Immunotherapies and Future Combination Strategies for Head and Neck Squamous Cell Carcinoma. Int J Mol Sci. 2019;20(21):5399. Published 2019 Oct 30. doi:10.3390/ijms20215399.

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Pol F. Boudes, MD, is Chief Medical Officer of Galectin Therapeutics. Dr. Boudes has more than 25 years of experience in clinical drug development in immunology, endocrine, metabolic, orphan, and liver-related diseases, and he has contributed to the approval of multiple drugs, both in the US and globally, across a variety of therapeutic indications. Before joining Galectin Therapeutics, Dr. Boudes was the Chief Medical Officer at CymaBay Therapeutics, where he worked on the company’s proprietary NASH compound and was instrumental in inventing and launching programs in rare liver diseases. Dr. Boudes earned his MD at the University of Marseilles, France. He completed his internship and residency in Marseilles and Paris, was an assistant professor of medicine at the University of Paris, and also participated in multiple clinical research programs as an investigator. He is certified by the Educational Commission for Foreign Medical Graduates (US) and board-specialized in endocrinology and metabolic diseases, internal medicine, as well as in geriatric diseases (Paris).