Dec 22 (Reuters) - A blank-check company backed by private equity firm Oaktree Capital Management cut the size of its initial public offering to $225 million from $275 million, a regulatory filing showed on Wednesday. The special purpose acquisition company (SPAC), Oaktree Acquisition Corp III, is looking to sell 22.5 million units, made up of shares and warrants. Earlier, the company had planned to sell 27.5 million units, priced at $10 apiece. SPACs are publicly listed companies formed with the intention of merging with a private company at a later date. For the company going public, a SPAC merger serves as an alternative to a traditional IPO. Oaktree Acquisition Corp III will list its units on the New York Stock Exchange under the ticker symbol "OACC". Deutsche Bank Securities, Credit Suisse and Morgan Stanley are the lead underwriters for the offering. Reporting by Manya Saini in Bengaluru; Editing by Maju Samuel