Simpson Thacher & Bartlett and Sullivan & Cromwell have lead roles on an upcoming $1.2 billion equity offering by Japanese advertising group Dentsu Inc.

Dentsu, which is listed on the Tokyo Stock Exchange, plans to sell a mix of 37 million current and new shares in order to pay down part of the debt it incurred in its $4.8 acquisition last year of British ad agency Aegis Group Plc.