Aptorum Group (APM) shares were down 33% in recent Friday premarket activity, erasing Thursday's 235% gain.
Volaris (VLRS) stock was down 7.8% after Citigroup downgraded the Mexican airline to neutral from buy with a $7 price target.
Gap (GAP) shares were down 2.1% after Barclays downgraded the specialty apparel company to equalweight from overweight and lowered its price target to $19 from $24.
Nvidia (NVDA) stock was down 1.3%, a day after media outlets reported that the tech giant told some of its suppliers to suspend work on its H20 chip.