Jennifer Matthews: From desert predators to ocean creatures, scientists are uncovering unusual sources for new medicines.

Renee Relin: How did they figure that you go from a sea squirt to a drug that's going to work on this specific, esoteric kind of cancer?

Jennifer Matthews: Renee Relin was diagnosed 7 years ago with soft tissue sarcoma, a cancer that affects muscles and organs. When doctors discovered a third tumor, she volunteered for a clinical trial testing ET-743, a drug made from the toxins of a sea squirt.

Bruce Chabner: About 10 percent of the patients respond, that is, the tumors shrink significantly.

Jennifer Matthews: For Renee, it offered hope when there was none.

Jennifer Matthews: The Israeli yellow scorpion is the inspiration for another cancer drug, TM-601. A synthetic copy of the scorpion's venom is helping patients with brain tumors.

Adam Mamelak: There are a variety of compounds in nature which are known to specifically excite cells in very detailed ways, some of them being toxins that come from insects, snakes, things like that.

Jennifer Matthews: A Brazilian pit viper's venom is used to make captopril, an FDA approved drug that lowers blood pressure. ABT-594 is derived from the poisonous skin of a South American frog. It blocks pain 200-times better than morphine and is not addictive. This poisonous cone snail also helps people with chronic pain.

Edgar Ross: SNX-111 is a very promising drug. It has shown efficacy in patients where nothing else has worked.

Jennifer Matthews: Pharmacist Paul Doering advises patients considering venom therapy to proceed with extreme caution.

Paul Doering: If we're talking about snake venom, the margin of safety may be quite narrow, and you may be thinking you're given a therapeutic dose, but it may turn out to be a toxic or deadly dose. It's a matter of balancing the benefits against the risks.

Jennifer Matthews: Doering also worries that long-term venom treatments could trigger life-threatening allergies.

Paul Doering: They are foreign substances to the human body, and the human body's goal is to recognize them as foreign and get them the heck out of the body."

Jennifer Matthews: Doctor Bruce Chabner, who studies the sea squirt drug, is more optimistic about the future of these therapies.

Bruce Chabner: These marine organisms are very, very prolific and a good source of toxins for investigation. There are still huge numbers that could be collected and tested.

Jennifer Matthews: Renee hopes scientists continue looking under the sea.

Renee Relin: Thank God for whoever's got the patience to keep trying on stuff, but I think it's phenomenal.

Jennifer Matthews: Since her first treatment, she has been cancer-free, and credits the sea squirt with giving her extra time with her two sons. This is Jennifer Matthews reporting.