GlaxoSmithKline (GSK) is terminating its 5-year-old collaboration with Five Prime Therapeutics to develop the latter’s FP-1039 and returning its licensing rights to the cancer compound.

Word of GSK’s 180-day notice of termination—tucked in Five Prime’s announcement yesterday of fourth-quarter and full-year 2015 results—comes as FP-1039 is in a Phase Ib trial that according to Five Prime has shown encouraging preliminary data in mesothelioma. GSK has submitted mesothelioma data for presentation at the ASCO 2016 Annual Meeting, Five Prime noted. 

“Mesothelioma could represent a potentially attractive market opportunity for a company like Five Prime,” the company said in its statement. “Five Prime will base decisions on future development of FP-1039 on whether the quality and durability of responses in this population is maintained in this trial.”

FP-1039, also known as GSK3052230, is a ligand trap designed to intervene selectively in fibroblast growth factor (FGF) signaling. According to Five Prime, the compound is thought to bind to FGF ligands circulating in the extracellular space, thereby preventing these signaling proteins from reaching the receptor protein FGFR1 on the surface of tumor cells, where they would otherwise stimulate cancer cell division and/or angiogenesis.

Mesothelioma patients represented one of three treatment arms in the Phase Ib trial, conducted by GSK. The trial was designed to evaluate the safety, tolerability, dosage, response rate, and duration of response of FP-1039.

GSK and Five Prime agreed in January to enroll up to 30 mesothelioma patients at the expansion dose of 15 mg/kg in Arm C of the trial, which is assessing FP-1039 in combination with front-line pemetrexed and cisplatin.

The other two arms were designed to assess combination therapies, including FP-1039 in patients with metastatic squamous non-small cell lung cancer (sqNSCLC). Arm A studied FP-1039 plus paclitaxel and carboplatin in previously untreated metastatic sqNSCLC, while Arm B assessed FP-1039 in combination with docetaxel in metastatic sqNSCLC that has progressed after previous therapy.

Also in January, Five Prime and GSK agreed to stop enrolling sqNSCLC patients, citing the change in treatment paradigms due to approvals of immuno-oncology agents and the prospect of additional competition as other products reach the market. Immuno-oncology agents approved in recent years include Merck & Co.’s Keytruda (pembrolizumab) and Bristol-Myers Squibb’s Opdivo (nivolumab).

Five Prime sold license rights to FP-1039 for all indications in the U.S., Canada, and European Union back in March 2011 to Human Genome Sciences, which GSK acquired the following year for $3 billion. Under the deal, Five Prime won $50 million upfront, and was eligible to receive up to $445 million in future development, regulatory, and commercial milestone payments. The agreement also called for tiered double-digit percentage royalty payments on net sales.

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