By Maggie Fick and Ludwig Burger

ZURICH (Reuters) -Roche has acquired rights to an obesity therapy by Denmark's Zealand Pharma in a collaboration deal worth up to $5.3 billion, as the Swiss drugmaker seeks to boost its prospects in the booming weight-loss market.

The agreement covering the compound petrelintide, announced by Roche on Wednesday, marks renewed efforts to catch up with weight-loss market leaders Novo Nordisk and Eli Lilly.

Under the accord, Zealand will receive $1.65 billion upfront with the possibility of milestone payments taking the total sum to $5.3 billion, depending mainly on phase 3 trials and sales development, Roche said.

After the announcement, Zealand shares leapt 45% before easing. They were last up 28% at 0828 GMT. Roche shares gained 3.8%.

Zealand is currently testing petrelintide in overweight or obese individuals without type 2 diabetes in a mid-stage study.

Petrelintide belongs to a class of drugs known as long-acting amylin analogues, which mimic a hormone called amylin that is co-secreted with insulin during meals.

The first wave of weight-loss drugs was based mainly on the gut hormone GLP-1, but Novo Nordisk is banking on a dual mode of action that includes amylin for its next generation of drugs, with experimental compounds called amycretin and CagriSema.

Disappointing clinical trial read-outs from CagriSema, however, have dragged Novo's shares lower. Zealand shares have also suffered on scepticism about the Danish firm's amylin approach.

Other companies in early stages of work with amylin, which is believed to better preserve lean mass than GLP-1-based drugs, include AstraZeneca.

Shares in Novo Nordisk fell 3.4% in early trading on Wednesday.

Zealand and Roche will jointly commercialise petrelintide in the United States and Europe, and the Swiss company will obtain exclusive commercialisation rights in the rest of the world.

Profits and losses for petrelintide, as well as a fixed-dose combination with Roche's CT-388, will be shared on a 50/50 basis in the U.S. and Europe, said Roche.

The transaction is expected to close in the second quarter.

Roche, which in late 2023 agreed to buy drug developer Carmot, said in September three early-stage obesity and diabetes drug candidates from that acquisition have a combined potential of more than 3 billion Swiss francs in annual sales.

Zealand CEO Adam Steensberg said Roche's development efforts had helped qualify the Swiss drugmaker for the partnership.

"They have already started making strong steps in the obesity and cardiometabolic disease area. Roche has a strong history of coming and redefining disease care," Steensberg told Reuters.

(Writing by Miranda Murray, Dave Graham and Ludwig Burger, Additional reporting by Maagie Fick, Editing by Rachel More and Kate Mayberry)