- Shares in Rigel Pharmaceuticals Inc. fell more than 15% Tuesday morning as investors reacted to news of disappointing clinical results from a mid-stage trial of the biotech's lead drug candidate fostamatinib.
- Treatment with fostamatinib failed to meet the proof-of-concept study's primary objective, showing no statistical difference from placebo in its effect on proteinuria levels among patients with a kidney disease called IgA nephropathy (IgAN).
- In an April 3 release, Rigel highlighted a preplanned subgroup analysis which showed fostamatinib led to greater proteinuria reduction in patients with higher baseline levels of the biomarker. That finding, however, also failed to reach statistical significance.
In the near term, Rigel's hopes for fostamatinib hinge on whether the Food and Drug Administration decides to approve the oral spleen tyrosine kinase inhibitor for a separate condition called immune thrombocytopenia (ITP).
The biotech had pushed forward with a submission to the FDA last year despite the drug coming up short in the second of two Phase 3 studies for ITP.
The FDA is expected to rule on Rigel's New Drug Application by April 17. If it secures an OK, Rigel plans to launch fostamatinib in the second quarter of this year under the brand name Tavalisse.
A rejection, however, would compound the recent clinical setback and likely raise further questions about the viability of the company's fostamatinib clinical program.
In the IgAN study read-out Tuesday, fostamatinib failed to significantly reduce proteinuria, a key marker for disease severity.
Rigel tested two doses, 100 mg and 150 mg, versus placebo in the trial. Notably, there didn't appear to be a clear dose response among the intent-to-treat population, although a trend did emerge when analyzing data from only patients with greater than 1 gram/day of proteinuria.
While the subgroup analysis was also not statistically significant, Rigel painted the narrower results as reason for optimism.
"This study has provided valuable information on the potential benefit of fostamatinib in IgA nephropathy patients with significant need, those with greater than 1 gram/day of proteinuria," said Rigel CEO Raul Rodriguez in a statement.
Future study could, for example, test the drug only in patients with more advanced disease. But in that case, Rigel says it would turn to a pharmaceutical partner to help conduct any future trial of fostamatinib in IgAN.
No new safety signals were identified in the study. Two patients experienced treatment-related adverse events, and more patients discontinued treatment or withdrew from study in the fostmatinib arms than in the placebo group.
Rigel reported $116 million in cash and equivalents as of Dec. 31, 2017 — a sum it believes is sufficient to fund operations through the next 12 months, including any potential launch activities if the FDA clears fostamatinib.
Shares in the company fell as much as 25%, or $0.90, Tuesday morning before gaining back some of those losses.