Esbriet Shows Promising Phase II Results in HFpEF, Highlighted in Recent IPO Filing

Sino-American Drug Source Original

News Event

At the ongoing ACC Annual Scientific Session, Roche presented the Phase II clinical trial results for its idiopathic pulmonary fibrosis (IPF) drug, Esbriet, in a trial named Pirouette. The trial enrolled 94 patients with heart failure with preserved ejection fraction (HFpEF) and myocardial fibrosis. Results demonstrated that 52 weeks of Esbriet treatment significantly improved myocardial extracellular volume compared with placebo. This biomarker change is estimated to translate into a 9–28% reduction in the risk of hospitalization or death. The trial was funded by the University of Manchester, and Roche has not yet indicated whether it will fund a Phase III clinical trial to confirm this efficacy.

Drug Source Analysis

HFpEF is analogous to triple-negative breast cancer; it represents a heterogeneous "none-of-the-above" heart failure syndrome. Consequently, its etiology is complex, encompassing protein accumulation, inflammation, myocardial injury, toxins, and other factors, making it difficult to treat most patients with a single-mechanism drug. Although multiple drugs have been approved for HFrEF, therapeutic options for HFpEF remain limited. Recently, only Novartis’s combination drug Entresto has gained approval based on data from the PARAGON-HF trial, despite the trial failing to meet its primary endpoint and Entresto merely demonstrating comparable efficacy to valsartan. Currently, several agents with diverse mechanisms, including SGLT2 inhibitors and GLP-1 receptor agonists, are undergoing Phase III clinical trials. It is hoped that certain products, particularly SGLT2 inhibitors, will deliver meaningful clinical benefits to this patient population.

Esbriet is a compound with an exceptionally simple chemical structure. It was developed by InterMune for the treatment of idiopathic pulmonary fibrosis (IPF)—a condition that previously lacked any therapeutic options—after demonstrating antifibrotic efficacy in phenotypic screening. In 2014, Roche acquired InterMune for $8.4 billion. Later that same year, Esbriet and Boehringer Ingelheim’s Ofev were both approved by the FDA for IPF on the same day. The original team from InterMune founded Aligos Therapeutics, a hepatitis B-focused pharmaceutical company, a few years ago, and the company went public last year. Esbriet’s compound patent had long expired; its approval for IPF at the time was made possible by the FDA’s regulatory exclusivity framework. Designed to incentivize the development of older compounds with expired patents but newly discovered biological functions, this rule grants a five-year exclusivity period for the first approved indication. An additional two years may be awarded if orphan drug designation is obtained, with further extensions available for antibiotics. Furthermore, since the FDA only accepts ANDA submissions after the exclusivity period expires, and the ANDA review process itself takes one to two years, the combined effective market protection closely approximates that of a full patent term.

Esbriet can attenuate fibrosis, yet its molecular mechanism remains unknown. Given its structure, such a simple compound would be expected to exhibit very limited binding affinity for any protein, as protein-ligand interactions are mediated by weak intermolecular forces that have an inherent thermodynamic limit. Typically, even optimal binding contributes only about 0.3 kcal/mol of binding free energy per heavy atom. With the advancement of medicinal chemistry, scientific attention is increasingly shifting toward small-molecule functions beyond traditional enzyme inhibition and receptor signal transduction blockade. One emerging functional paradigm is the modulation of protein stability by small molecules, a mechanism that does not require high-affinity drug-protein binding. First, proteins may have evolved regulatory mechanisms analogous to an ignition switch, inherently designed to allow a minor perturbation to produce a disproportionately large effect. Second, such regulation is fundamentally a catalytic process; even if the drug-protein complex is high in energy, sufficient turnover can still drive the intended biological outcome. Ultra-small molecule drugs like Esbriet most likely operate through such mechanisms. The novel compound evaluation platforms currently under development should re-examine these agents, as they hold potential for optimization into superior next-generation therapeutics.

Of course, an unknown molecular mechanism does not necessarily preclude new drug development, particularly for a highly heterogeneous and complex disease like HFpEF. Even when partial mechanisms are elucidated, demonstrating significant efficacy in the overall population remains challenging, with clinical success often limited to biomarker-driven patient selection. Serelaxin may be the most mechanistically well-characterized drug in heart failure over the past two decades, yet it still failed to reach the market, even for the relatively straightforward HFrEF indication. Admittedly, it was primarily developed for acute heart failure. The currently highly anticipated SGLT2 inhibitors were likewise serendipitous clinical discoveries. At the time, Eli Lilly transformed a mandatory cardiovascular safety trial for diabetes into an efficacy trial. Unexpectedly, the results demonstrated that Jardiance’s cardiovascular benefits stemmed almost entirely from a reduced risk of heart failure, independent of its glucose-lowering effects. To this day, the precise mechanism by which Jardiance improves heart failure remains unknown. Ultimately, the discovery of most drugs owes as much to serendipity as it does to human ingenuity.