Versartis Inc. fulfilled its vow to provide the requested "bioanalytical data" to the FDA around the end of this year's second quarter, but still isn't saying exactly what the agency wanted. "We're staying away from it for competitive reasons and other [ones]," CEO Jay Shepard told BioWorld Today.

What matters now is that U.S. regulators have accepted the data and lifted the partial clinical hold (PCH) on VRS-317, allowing the go-ahead with the phase III registrational trial called Velocity in growth hormone deficiency (GHD) in children.

Menlo Park, Calif.-based Versartis' stock (NASDAQ:VSAR) closed Monday at $18.92, up $4.30, or 29.4 percent. "We had an extension trial off our phase II that the FDA let us to continue to enroll," Shepard noted.

The Velocity experiment began in January with the compound, a long-acting, twice-monthly form of recombinant human growth hormone, which is designed to overcome the burden of daily injections that represent the current standard of care.

Versartis disclosed the PCH in May. During a conference call on earnings at the time, analysts tried to pry specifics out of Versartis officials regarding the agency's concerns. Ken Cacciatore from Cowen and Co. said he was "a little bit confused. You're willing to say what the request is not, but you're not willing to say what the request is, and [saying] that it's not appropriate to let us know. So is it not appropriate for competitive reasons? What would be the FDA's issue with not disclosing it?"

Chief Financial Officer Joshua Brumm replied that the matter was "pretty straightforward. As a company policy, it's not appropriate for us to be discussing our active communications with the FDA. But I think also you point to a good point there, which is [that] from a competitive standpoint, it wouldn't make sense either to disclose anything that we're working through with the FDA."

Shepard did say Monday that the data requested were of the kind that "they would ask from any kind of biologics manufacturer – pharmacokinetic, pharmacodynamic, efficacy, adverse-event data, antibody data. They asked us to do it with certain assays and tests, and measure in certain ways, and we've gotten ourselves lined up with them. They said it looks good. We're not getting into any more detail than that." Safety, he said, was never an issue, and the product is "extremely well tolerated."

Velocity is a randomized, open-label experiment in the U.S., Europe, and Canada. It's expected to enroll up to 136 naïve to treatment, pre-pubertal children with GHD and will include a 3:1 randomization of 3.5 mg/kg VRS-317 twice-monthly to daily recombinant human growth hormone at the highest approved dose on the labels of Genotropin (somatotropin rDNA origin, Pfizer Inc.) and Norditropin (somatotropin rDNA origin, Novo Nordisk A/S) 34 µg/kg/day.

The primary endpoint is non-inferiority between the two treatment groups for 12-month mean height velocity. After they finish the phase III trial, all patients will be offered the opportunity to continue treatment with VRS-317 in the ongoing pediatric extension study.

On track to report interim six-month mean height velocity (MHV) data by the end of 2016, the study should yield top-line data on the 12-month MHV primary endpoint by mid-2017, enabling a potential biologics license application submission, which could mean FDA approval by late 2018, Versartis said.

Brumm told BioWorld Today that a previous phase Ia experiment was done in adults, and a phase Ib/IIa in children evaluated weekly, twice-monthly, and monthly dosing. In the second half of this year, a phase II trial in adults will begin. CEO Shepard added that the lifting of the PCH "opens the door for all those trials. We're really pleased with the way everything seems to be moving." The company also kicked off a phase II/III trial in Japan for children with GHD in April 2015.

Cowen's Cacciatore wrote in a May research report that his firm's clinician consultants "agree that safety, efficacy, and formulation are likely not the cause" of the surprising PCH. "And while admittedly there is uncertainty as to why the agency is requesting additional bioanalytical data, it's important to note that this is a PCH, not a full clinical hold, and patients are still being administered with the 3.5 mg/kg semi-monthly VRS-317 dose – which was being employed in the phase III Velocity study that just got put on PCH – in the ongoing phase II extension study." The slight delay "does not change our view of the potential long-term value creation," Cacciatore wrote.

In March 2014, Versartis took the spotlight when the firm priced its IPO at $21 – the high end of a range expanded just two days earlier – to raise $126 million, then opened at $28 before making another growth spurt to reach a high of $36.30 before closing at $31.37 for a gain of 49.4 percent over the opening price. More than 6.1 million shares changed hands that day. (See BioWorld Today, March 24, 2014.)