San Diego’s Arena Pharmaceuticals (NASDAQ: ARNA) was trading just under $4 a share today, after the company priced its secondary public offering of 12.5 million shares yesterday at $4.17. Arena shares closed Tuesday at $4.67. Arena said last month that it had arranged $100 million in debt financing with Deerfield Management, a significant shareholder, that’s needed to complete final trials of its obesity drug, lorcaserin, and to carry the company through its new drug application review with the FDA. The company says its secondary stock offering was pursuant to a shelf registration filed in November. Arena is expected to raise approximately $52.1 million before expenses, with Piper Jaffray & Co. acting as sole underwriter.