Pfizer has filed for approval of its third-generation ALK inhibitor lorlatinib, a follow-up to its first-generation Xalkori product which is facing increasing competition.

The pharma company has submitted lorlatinib in Europe, the US and Japan as a second-line treatment for AL-positive non-small cell lung cancer (NSCLC) patients that have already been treated with one or more other ALK-targeting drugs. If all goes to plan, Pfizer could get US approval for the new drug in August as it has both priority review and breakthrough designations.

The filing comes as sales of Xalkori have come under pressure, growing from $561m in 2016 to $594m last year but with US sales down 11% to $223m in the face of competitive pressure from Roche’s fast-growing rival Alecensa (alectinib), a second-generation inhibitor that is well-tolerated and has the added benefit of penetrating the brain, which can help improve the durability of responses.

Alecensa saw sales double to reach around $385m in 2017, and its ascendency also seems to have taken its toll on Novartis’ second-generation drug Zykadia (ceritinib). After recording sales of $91m in 2016, Zykadia’s growth seems to have stalled despite picking up approval for first-line use last May, which may be because the standard dose can be hard to tolerate and can lead to dosing interruptions.

Meanwhile another new entrant - Alunbrig (brigatinib) from Takeda - is also making headway after its first approval in 2017, making $13m by the end of the calendar year. The drug has a broad spectrum of activity and recorded on of the higher progression-free survival (PFS) rates among its peers in first-line clinical trials.

With four ALK inhibitors already jostling for market share in lung cancer, Pfizer’s entry to the category seems like it could face an uphill battle, although oncologists are now welcoming the possibility to use three ALK inhibitors in sequence in these patients - with the big question now the order in which they should be administered.

Pfizer notes that lorlatinib has shown activity in almost all known clinically acquired ALK mutations and has also been reported to re-sensitise tumours to Xalkori.

“Treatment resistance resulting in disease progression is a major challenge faced by patients with ALK-positive metastatic NSCLC,” said Pfizer’s chief development officer Mace Rothenberg. “Lorlatinib was developed by Pfizer scientists with the specific goal of overcoming resistance to first- and second-generation ALK-targeted therapies," he added.