These were the worst performing ASX 200 shares last week

It was a disappointing five days for the S&P/ASX 200 Index (ASX: XJO) last week. The benchmark index ended the period 35.3 points or 0.5% lower at 7,273.3 points.

While a good number of ASX 200 shares tumbled last week, some fells more than most. Here's why these were the worst performers on the benchmark index:

PolyNovo Ltd (ASX: PNV)

The PolyNovo share price the worst performer on the ASX 200 last week with a 13.4% decline. This was despite there being no news out of the medical device company. However, the PolyNovo share price has been under a lot of pressure in 2021 due to concerns over slowing sales late in the first half. This latest decline means its shares are down 40% since the start of the year.

Nine Entertainment Co Holdings Ltd (ASX: NEC)

The Nine share price wasn't far behind with a 10.8% decline. This decline may have been driven by a broker note out of Macquarie. Last week the broker downgraded the entertainment company's shares to a neutral rating and slashed the price target on them to $3.00. The broker made the move on valuation grounds and due to concerns over short term headwinds.

Clinuvel Pharmaceuticals Limited (ASX: CUV)

The Clinuvel share price was a poor performer and sank 10.1% over the five days. Investors were selling this biopharmaceutical company's shares following the release of a change of director's interests notice. That notice reveals that the company's CEO, Philippe Wolgen, has sold 122,675 shares on-market recently. Dr Wolgen received a total consideration of approximately $3.75 million.

Appen Ltd (ASX: APX)

The Appen share price was out of form and dropped 9% last week. This decline appears to have been caused by news that a major shareholder has been selling down its holding shortly after building it up. According to a ceasing to be a substantial holder notice, the Capital Group Companies has been selling a significant number of shares just a month after buying them. Its most recent sale involved 583,170 shares for just a touch over $8 million on 1 July.