LONDON (AP) — GlaxoSmithKline PLC signed a potential $1 billion deal with U.S. biotech company Concert Pharmaceuticals on Tuesday to access deuterium-containing medicines, a deal that will beef up its pipeline of early stage drugs. Glaxo will gain the rights to three research programs by privately held Concert — a protease inhibitor for HIV due to start Phase I clinical trials this year, a preclinical drug for chronic kidney disease and a third unspecified product. Deuterium is a safe, non-radioactive relative of hydrogen that can be isolated from sea water and has been used extensively in human metabolic and clinical studies. As deuterium is heavier than hydrogen, it forms a stronger chemical bond to a carbon atom of a molecule, which may substantially improve a drug’s metabolic properties, potentially resulting in better efficacy. Patrick Vallance, senior vice president of drug discovery at Glaxo said that Concert’s approach to deuterium modification of medicines “has broad potential to enhance certain drug properties and result in innovative new medicines.” Lexington, Massachusetts-based Concert said it would receive $35 million upfront, including a $16.7 million equity investment. The company is also eligible to receive milestone payments and tiered, double-digit royalties based on deuterium-containing products arising from the Concert pipeline programs and from any Glaxo pipeline compounds. Combined with the upfront payment, Concert said it has the potential to receive in excess of $1 billion. Concert will retain full rights to further develop and commercialize its product candidates in any program that Glaxo chooses not to license.