The S&P 500 and the Nasdaq indexes looked set to drop from record highs on Friday, as results from mega-cap firms Apple and Amazon.com reignited concerns of labor and supply shortages that have been at the forefront of this quarterly earnings season. Market participants have been closely watching how corporate America navigates through these challenges along with concerns about rising inflation, after largely upbeat earnings reports so far helped investors look past a mixed batch of macro-economic data. Apple slipped 3.5 percent in premarket trading after the iPhone maker warned the impact of supply chain disruptions will be even worse during the current holiday sales quarter, after supply woes cost $6 billion in sales in the last quarter. Amazon.com Inc. dropped 4.8 percent after the world’s largest online retailer forecast downbeat holiday-quarter sales, as higher pay to attract workers and other operational disruptions diminish the company’s windfall from online shopping. …