Rigel gets bad news ahead of its biggest date yet

After more than a decade in development Rigel Pharmaceuticals’ fostamatinib is on the verge of commercial launch if in the next two weeks the US FDA gives its blessing for treating idiopathic thrombocytopaenic purpura. So news that the kinase inhibitor missed in a phase II trial in another indication that could have meaningfully expanded its patient population is not the sort of thing investors want to hear.

While the sellside has so far ascribed none of fostamatinib’s sales to the IgA nephropathy indication, the subject of the failed phase II, the 22% tumble in Rigel’s share price today suggest that investors had higher hopes. Fostamatinib had once been tested in rheumatoid arthritis, but was repurposed for orphan indications, and increasing the number of eligible patients would have a substantial effect on sales.

Showing effectiveness in multiple indications had become even more important for the project, branded Tavalisse, because in ITP it will be going up against Amgen’s incumbent, Nplate, as well as facing competition from Ablnyx’s caplacizumab, soon to be in Sanofi’s hands. An FDA approval decision on fostamatinib in ITP is due by April 17, and investors will no doubt hope this might trigger deal making.

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But the failure in IgA nephropathy will probably not help draw big pharma. The phase II trial was designed to show that versus placebo Tavalisse, a Syk inhibitor, could reduce proteinuria, a sign that the autoimmune-driven inflammation of kidney tissue had impaired the organ’s ability to filter blood.

Tavalisse missed at two doses, 100mg and 150mg. A subgroup of patients with greater than 1 gram per day of proteinuria demonstrated a numerical benefit, which could give the project a route forward in nephropathy – however, Rigel made clear that any further development here would need to be done by a partner.

This outcome is unfortunate for Rigel in that IgA nephropathy has no targeted therapy available for it; patients receive ACE inhibitors to reduce high blood pressure, a complication of the disease, and steroids to dampen immune response. The lack of competition for an estimated 160,000 patients would have made nephropathy a much more promising indication than ITP.

Three's a crowd

As it stands now, launch in ITP will see Tavalisse go against the might of Amgen and, assuming caplacizumab wins approval, Sanofi, for a population estimated at about 50,000.

Thus it is not surprising to see that the Tavalisse has the smallest 2022 forecasts in this indication, $114m, versus $717m for Nplate and $334m for caplacizumab, according to EvaluatePharma’s sellside consensus, even though Tavalisse could be on track to beat caplacizumab to the US market by a year or more.

Rigel has additional opportunities, however. Tavalisse passed an early test in warm antibody autoimmune haemolytic anaemia, successfully raising haemoglobin levels in patients whose immune systems have begun destroying red blood cells. Those data in patients who had failed at least one line of treatment, announced in October, caused a 33% share price jump and allowed the California-based company to raise $70m through a secondary offering.

Sellsiders have penciled in about $106m in haemolytic anaemia sales, a number that will be reviewed as the phase II trial continues. This, of course, is also a small patient population of 40,000, and 75% of subjects respond to treatment with steroids and Rituxan.

Rigel is busy preparing for a solo US launch in ITP in mid-2018, but it knows that it could use a hand in overseas markets. Missing an opportunity to expand into a less crowded space will not help that courtship.

To contact the writer of this story email Jonathan Gardner in Virginia at [email protected] or follow @ByJonGardner on Twitter