Positive data from FibroGen’s Phase II trial of pamrevlumab in idiopathic pulmonary fibrosis (IPF) provide the foundation for a Phase III program and the potential to become the third licensed drug in the IPF market. Clear opportunities are present, with pamrevlumab demonstrating synergistic properties with Esbriet and Ofev, opening room for potential collaborations as well as further freedom regarding its Phase III study design. Provided FibroGen adopts the appropriate study designs and collaborative choices, pamrevlumab is likely to be well received by physicians and patients.
On 8 August 2017, FibroGen announced positive topline results from its Phase II study of pamrevlumab in patients with idiopathic pulmonary fibrosis (IPF). Pamrevlumab is a first-in-class anti-connective tissue growth factor (CTGF) antibody being evaluated in fibrotic disease and related serious diseases. In this placebo-controlled study, pamrevlumab met the primary efficacy endpoint with an average decline in forced vital capacity percent predicted (ppFVC) from baseline to week 48 of 2.85%, compared to 7.17% in the placebo arm. Pamrevlumab-treated patients also had an average decrease in FVC of 129ml, compared to 308ml for placebo. FibroGen also reported pamrevlumab to be well tolerated, consistent with previous clinical studies.
The IPF treatment landscape comprises just two approved drugs, Esbriet (pirfenidone; Roche/Shionogi) and Ofev (nintedanib; Boehringer Ingelheim). These were approved almost simultaneously in the US in October 2014, and together generated impressive combined sales of nearly $1.5bn in 2016. Despite IPF being a rare disease with small patient numbers – approximately 100,000 US patients – there is a large potential market for new therapies. IPF is incurable and ultimately fatal, with patient outcomes typically being very poor. Patients have a median survival time of two to five years following diagnosis, with the five-year survival rate of 20–40% being lower than that of several malignant diseases. Any new therapeutic therefore has the potential to fill a real unmet clinical need, which was one of the drivers behind Roche’s acquisition of InterMune for $8.3bn in 2014 – in order to gain access to Esbriet. Accordingly, there is considerable excitement around pamrevlumab and its potential to be the third drug to enter the market.
The Phase II pamrevlumab data compare favorably with those of Esbriet and Ofev. Across Esbriet’s Phase III clinical trial program — ASCEND, CAPACITY 1, and CAPACITY 2 – there were inconsistent data on ppFVC, with placebo-subtracted differences of 1.9–4.8% after 52 weeks, although a pooled analysis demonstrated the drug’s overall effect and uniquely its ability to lower all-cause mortality. The INPULSIS 1 and 2 trials of Ofev showed 3.1–3.2% differences in ppFVC after 52 weeks, which are lower than the 4.33% noted for pamrevlumab against placebo. Similarly, the absolute decrease in FVC for pamrevlumab when compared to the placebo arm was numerically superior to those reported for Esbriet and Ofev over comparable treatment durations.
As an anti-CTGF antibody, pamrevlumab is not necessarily a direct competitor to Esbriet and Ofev. Indeed, some patients in the Phase II trial were randomized to receive one of the two approved therapies as background treatments in addition to either pamrevlumab or placebo, in order to demonstrate the safety of the combinations. Although Roche and Boehringer Ingelheim will clearly be interested in partnering with FibroGen to improve the competitive positioning of their own therapies, FibroGen is in a very strong negotiating position and has several strategic options. Indeed, the company could maximize its commercial opportunity if it continues alone with its current trial design, and allows for monotherapy use and combinations with both Esbriet and Ofev. This would keep competition at a minimum and increase exposure to as many patients as possible, at least until its clinical profile is characterized during pivotal Phase III trials. Nevertheless, partnering before initiating Phase III trials would de-risk the pamrevlumab development program considerably and provide significant investment for future research. FibroGen has previously shown its willingness to partner with large pharmaceutical companies for its pipeline, notably its involvement with AstraZeneca and Astellas for the anemia drug roxadustat.