Biohaven seeks IPO cash to fund trials of AstraZeneca, Bristol-Myers castoffs

Biohaven plans to IPO to fund phase 3 trials of an ex-Bristol-Myers migraine drug.

Biohaven Pharmaceutical has filed to raise up to $100 million in an IPO. The money is earmarked for clinical trials of drugs Biohaven picked up from AstraZeneca and Bristol-Myers Squibb, including two phase 3 studies of a candidate the latter shelved after pitting it against a generic in phase 2.

New Haven, CT-based Biohaven began life in 2013 as a Yale University spinout focused on the glutamatergic system. That interest in modulating the neurotransmitter glutamate lives on, most notably in phase 2/3-ready asset trigriluzole. But Biohaven’s near-term focus has shifted away from using such drugs to treat depression and anxiety.

Instead, the three-pronged glutamate pipeline is looking at types of ataxia, amyotrophic lateral sclerosis and Rett Syndrome. And Biohaven moved further away from its initial focus by licensing two CGRP receptor antagonists from Bristol-Myers.

Rimegepant, one of Bristol-Myers’ drugs, is at the leading edge of Biohaven’s attempts to bring a product to market. Biohaven plans to put the small-molecule CGRP receptor antagonist through two phase 3 trials for the acute treatment of migraine. With Biohaven aiming to start the phase 3 trials later this year, management expects to have top-line data in the first half of 2018. That gives Biohaven a program with the sort of near-term prospects that could attract investors.

The snag is Bristol-Myers dropped the drug on the back of phase 2 data that raised doubts about its ability to best sumatriptan, a generic 5-HT receptor agonist.

Bristol-Myers said it included a sumatriptan arm in the trial to provide an active control for assay sensitivity and the study wasn’t powered to enable comparison between the generic and rimegepant, then known as BMS-927711. But the fact that the sumatriptan cohort featured a larger proportion of patients who met the primary and secondary pain endpoints than any of the rimegepant arms is unlikely to have bolstered the CGRP receptor antagonist’s prospects.

Biohaven must also allay the FDA’s concerns about the safety of the candidate. Bristol-Myers reported an asymptomatic and mild increase in certain hepatic enzymes in one patient in the phase 2. And very high doses of the drug affected the liver in preclinical tests. With the FDA wary about the effect of CGRP antagonists on the liver, it wants Biohaven to run a safety study looking at patients who take the drug most days for three months or more.

As Biohaven presents it, these issues are outweighed by phase 2 data showing rimegepant beats placebo. And it has secured financial support from investors willing to bankroll the revised vision for the company enabled by rimegepant. Portage Biotech got Biohaven started in 2014 when it bought a 54% stake in the business for $3.5 million. But the current iteration of the company is built upon an $80 million round that attracted backers including Venrock, RA Capital Management and Vivo Capital late last year.

These investors, none of which are listed as planning to buy IPO stock in the SEC filing, are now looking for new financiers to come on board to help push rimegepant over the finish line. In parallel, Biohaven will take glutamate modulator trigriluzole through a phase 2/3 in spinocerebellar ataxia. And perform earlier-stage R&D on other prospects, including the NMDA receptor antagonist it picked up from AstraZeneca.