Novartis AG agreed to buy Chinook Therapeutics Inc. for as much as $3.5 billion to add two promising treatments for a rare kidney disease that are currently in late-stage trials.

The Swiss drug company will pay $40 a share in cash for California-based Chinook, or 67% above the closing price on Friday, according to a statement Monday. Another $4 a share could be paid later based on achieving certain regulatory milestones.

Chinook has two treatments in late-stage trials to treat IgAN, a progressive, rare kidney disease that mostly affects young adults and currently lacks targeted treatment options.