NEW YORK — The insurer Cigna will spend about $52 billion to acquire the nation’s biggest pharmacy benefit manager, Express Scripts, the latest in a string of proposed tie-ups as health care’s bill payers look to grow and gain better leverage to deal with rising costs.

Including $15 billion in debt, the proposed $67 billion acquisition follows a deal announced late last year in which the drugstore chain CVS Corp. said it will spend around $69 billion on the insurer Aetna Inc.

Health insurers and pharmacy benefit managers — which run drug plans for insurers, employers and other big clients — have been struggling to corral spiraling prescription drug prices and other health care costs. Their sector also has been jolted by the Affordable Care Act, which reshaped the individual insurance market and expanded the state- and federally funded Medicaid program.

And early this year, the ultimate disruptor, Amazon.com, said it wanted to get involved in health care in a collaboration with billionaire Warren Buffett and JPMorgan Chase. No one knows what that means, but it sent a shudder through the sector.

The deal announced Thursday consists of $48.75 in cash and a portion of stock in the combined company for each share of St. Louis-based Express Scripts Holding Co. Cigna Corp. CEO David Cordani will lead the combined company, with his Express Scripts counterpart, Tim Wentworth, staying on as a president.

The boards of both companies have approved the deal, which is expected to close at the end of this year.

Cigna, based in Bloomfield, Connecticut, was the target of an acquisition bid by the Blue Cross-Blue Shield insurer Anthem Inc. But Anthem ended that $48 billion offer last spring, accusing Cigna of sabotaging that deal. Cigna, in turn, said Anthem “willfully breached” its obligation to get regulatory approval.

A federal judge and an appeals court had rejected the combination after antitrust regulators sued to stop it.