SOUTH SAN FRANCISCO, Calif. (AP) — Biotechnology company Exelixis Inc. said Thursday it will collaborate with Sanofi-Aventis to develop cancer treatments in a deal that could be worth more than $1 billion. The companies will work together on drugs that block a type of enzyme called phosphoinositide-3 kinase, which is often found in tumors and leads to cell spreading, survival, and resistance to chemotherapy and radiation treatment. Exelixis will receive an upfront payment of $140 million, plus $21 million in guaranteed research funding over three years. Exelixis could get more than $1 billion if the drug candidates advance through testing and regulatory processes, and reach sales milestones. It could also receive royalties on sales. As part of the agreement, Sanofi-Aventis gains the worldwide license rights to XL147 and XL765, a pair of Exelixis drug candidates. Exelixis is running early human trials on the two drugs, and Sanofi-Aventis will be responsible for all future testing, regulatory submissions, sales and manufacturing. Exelixis is responsible for the ongoing trials, and it may conduct some of the future trials of drug candidates developed under the collaboration. South San Francisco, Calif.-based Exelixis in March predicted between $140 million and $170 million in revenue for all of 2009. It reported $29.6 million in revenue last year from collaborations with Bristol-Myers Squibb Co., Wyeth, and Genentech Inc. Shares of Exelixis spiked $1.33, or 29.5 percent, to $5.84 in premarket activity. Its shares have ranged from $2.11 to $7.35 over the past year.