What Yahoo shows as long term debt is wrong. Arena has leasehold obligations on their 4 properties that run until 2027 and the $74.6 million is the long term obligation on these, so there is no note that comes due. They just have to continue paying as they have always done. (they exercised a lease/buyback so they show these payments as interest - see footnotes under balance sheet)
The short interest in ARNA is 32% of total shares outstanding. That is huge short interest, just about as high as I've ever seen it in any stock. That's why stock has fallen. I wouldn't worry about the stock price. You're about to see the mother of all short squeezes here. This is loaded with rocket fuel and ready for takeoff.