In early afternoon trade, the S&P/ASX 200 Index (ASX: XJO) has found its legs after a subdued start and is pushing higher. At the time of writing, the benchmark index is up 0.4% to 8,235.3 points.

Four ASX shares that have failed to follow the market higher today and are ending the week in the red are listed below. Here's why they falling on Friday:

Appen Ltd (ASX: APX)

The Appen share price is down 3.5% to $2.72. This is despite there being no news out of the artificial intelligence data services company today. Though, with the company's shares up over 350% since this time last year, it is possible that some investors are taking profit today. Appen's shares were on fire last year thanks to a major improvement in its performance in FY 2024 after a couple of years of significant struggles.

Brainchip Holdings Ltd (ASX: BRN)

The Brainchip share price is down almost 2.5% to 42.5 cents. This is also likely to have been driven by profit taking from day traders after the semiconductor company's shares rocketed higher in December. The gains were so strong that Brainchip was issued a speeding ticket from the Australian stock exchange operator last week. However, the company was at a loss to explain the rise in its share price.

Liontown Resources Ltd (ASX: LTR)

The Liontown share price is down over 2.5% to 55.5 cents. This lithium miner's shares have been sold off over the last 12 months amid concerns over weak battery material prices. So much so, Liontown's shares are now down by approximately 66% since this time last year. It seems that the market doesn't believe that lithium prices are going to rebound in 2025 and are cutting their losses again today.

Mesoblast Ltd (ASX: MSB)

The Mesoblast share price is down over 4% to $3.21. Investors appear to have been taking profit off the table today after some incredible gains recently. For example, even after today's pullback, this biotechnology company's shares are up by 74% since this time last month. The catalyst for this has been Mesoblast receiving US FDA approval for one of its stem cell therapies at long last. In December, the US FDA approved its Ryoncil (remestemcel-L) product as the first mesenchymal stromal cell (MSC) therapy in the United States. It is also the only approved therapy for steroid-refractory acute graft versus host disease (SR-aGvHD) in children two months and older.