US stocks end mostly lower, dragged by megacap tech; focus on Iran

STORY: Wall Street's main indexes closed mostly lower on Monday, with the exception of the Dow, which gained just under a third of a percent. The S&P 500 shed more than a third of a percent, while the Nasdaq dropped over 1.3%.Shares of Elon Musk's SpaceX weighed heavily on the Nasdaq, plummeting more than 16% for their biggest single-day decline. The rocket and AI company launched its first-ever debt offering on Monday and said it had roughly $100 billion in cash and cash equivalents as of last Friday. SpaceX's stock is still trading above its IPO price of $135.Optimism over AI has supported Wall Street's recent rally, but Melissa Brown, managing director of investment decision research at SimCorp, said the rally could be nearing its peak."Momentum tends to beget more momentum. So stocks do well, they continue to do well until something happens and they stop doing well. And then typically the market peaks at that point... I do think, though, that this kind of blowout, this huge surge of trading volume does suggest that the peak is closer than farther away."Among other tech names, shares of Alphabet fell 5% following news that Google DeepMind's senior research scientist and Nobel laureate John Jumper said he was leaving for AI startup Anthropic, the lab's latest high-profile exit.Shares of Meta, Amazon and Microsoft also closed lower Monday.The next test for the tech rally will be Micron Technology's quarterly results on Wednesday. Shares of the memory chipmaker are up nearly 300% this year.Among other movers, shares of Apogee Therapeutics soared nearly 47% after AbbVie said it would acquire the biotech company for $10.9 billion in cash. Shares of AbbVie rose more than 6%.Meanwhile, oil prices fell as peace talks between Washington and Tehran continued in Switzerland - though tensions persisted over Lebanon and the Strait of Hormuz.