In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is out of form and dropping into the red. At the time of writing, the benchmark index is down 2% to 7,353.5 points.

Four ASX shares that are falling more than most today are listed below. Here's why they are dropping:

Mineral Resources Ltd (ASX: MIN)

The Mineral Resources share price is down 12% to $14.42. This morning, analysts at Goldman Sachs downgraded the mining and mining services company's shares to a sell rating with an $18.00 price target. The broker said: "Downgrade MIN to Sell (from Neutral) on valuation (and relative TSR vs. our coverage), high net debt and low FCF, and after downgrading EBITDA estimates after pushing out the Ashburton ramp-up and decreasing our near to medium term iron ore price forecasts. MIN continues to be highly geared, and we forecast net debt to further increase across FY25/26."

Polynovo Ltd (ASX: PNV)

The Polynovo share price is down 8.5% to 96 cents. This is despite the medical device company releasing a sales update this morning. Polynovo revealed that it achieved its first $11 million sales month in March. It reported record monthly sales of $11.9 million, up 71.1% on the prior corresponding period. This means that financial year to date, sales are up 31.1% to $64.4 million. Some investors may have been expecting even stronger growth. The chairman of PolyNovo, David Williams, remains positive on the future. He said: "We have an enviable array of ways to expand indications in existing markets, expand our international footprint, and introduce new products to drive revenue growth."

Regal Partners Ltd (ASX: RPL)

The Regal Partners share price is down 9% to $1.72. Investors have been selling the fund manager's shares following the release of its latest funds under management (FUM) update. Regal Partners reported quarterly FUM of $16.5 billion, which is down from $18 billion at the end of the December. This was driven largely by tough market conditions, which led to a negative investment performance for the period.

Santos Ltd (ASX: STO)

The Santos share price is down 5% to $5.36. The catalyst for this has been another sizeable decline in oil prices overnight. Concerns about production increases and tariff wars have put significant pressure on oil prices this month.