It is understood Weber Shandwick is working with Interpublic Group sister ad agency McCann-Erickson, while DuPont PR incumbent Rowland Communications is believed to be handling the PR for a pitch by Saatchi & Saatchi.
It is unclear which PR firms may have been hired to team up with the other advertising finalists, which include Foote, Cone & Belding, Ogilvy & Mather and Young & Rubicam.
The review is said to include several marketing areas, although ad agencies are heading the pitches.
The DuPont pitch has captured attention in the US due to the unusually high-profile role the company's procurement team is playing in the process.
The finalists were asked to participate in a competitive online auction, in which marketers bid on the DuPont business in a process similar to that used on auction site eBay.
The review was originally expected to finish in late April with the results announced soon after.
Those close to the process say the pitch is unusual and highlighted the fact that large multinational corporations are viewing creative marketing services agencies as a commodity business, where there is only a slight distinction between firms.
DuPont comms manager Julia Saia insisted that despite the auction mechanism, 'price was just one of several factors' that will play a role in the company's decision.
DuPont, which was founded in 1802, employs nearly 80,000 people and operates in 70 countries, with 75 research and development labs across the globe.
The Fortune 500 firm started as an explosives company, but now works in areas such as food and nutrition, healthcare, electronics and clothing.