MEDICINE

New frontiers

Two anticancer substances show promise

ANNE STEACY July 24 1989
MEDICINE

New frontiers

Two anticancer substances show promise

ANNE STEACY July 24 1989

New frontiers

MEDICINE

Two anticancer substances show promise

In the battle against cancer, three approved forms of treatment are currently in use for dealing with malignant tumors: surgery, radiation therapy and chemotherapy. Surgeons, therapists and patients experience problems with all three techniques. Surgery can weaken the patient, while both radiation and chemotherapy—the therapeutic use of chemicals—are often painful and cause side effects that range from nausea to hair loss. Now, cancer researchers at two companies in Western Canada are experimenting with new substances that they say may cause fewer harmful side effects—and which, in the future, may be used to prevent tumors from spreading or recurring in certain patients.

Although both products are still undergoing testing—and are unlikely to be commercially available for several years—specialists say that the new treatments appear promising. In Vancouver, researchers at Quadra Logic Technologies Inc., a firm that is associated with the University of British Columbia (UBC), applied last month for Canadian government approval to market Photofrin, a light-activated substance developed in the United States and tested in Canada for use in a new form of cancer treatment called photodynamic therapy. After five years of tests on cancer patients in Canada, the United States, Europe,

China and Japan, Quadra Logic officials said that Photofrin was effective in bringing about remissions in 80 per cent of the cases treated for a form of cancer involving the bladder lining, called carcinoma in situ.

At the same time, scientists at Edmonton’s Biomira Inc. have developed a synthetic antigen (antigens are chemicals that act as signals to alert the body’s immune system to fight disease) that researchers say might be used to activate cancer patients’ immune systems to fight their tumors. Officials of Biomira, which is funding research at the University of Alberta, said that after tests on animals produced encouraging results, they are now ready to test the synthetic antigen on consenting human patients.

In the case of Photofrin, company officials said that tests involving about 4,000 patients with advanced tumors—including lung, bladder and esophageal cancers—have already shown that photodynamic therapy can play a valuable palliative role in sparing patients pain

and discomfort by reducing the size of tumors. So far, Photofrin, a burgundy-colored photosensitive liquid that is a derivative of cow’s blood, is the only substance approved for use in photodynamic therapy.

Injected into a cancer victim’s bloodstream, Photofrin disappears from most of the patient’s body after about two days, leaving concentrations in some organs—including the liver, skin and spleen—and in tumors. In photodynamic therapy, doctors can then insert a fibre-optic probe into the Photofrin-saturated tumor and fire a laser light beam along it to destroy cancer

cells. Researchers at Quadra Logic say that photodynamic therapy has only one known side effect: patients may become prone to sunburn for up to six weeks because of small amounts of Photofrin remaining in the skin.

Photofrin’s success to date results largely from the efforts of a small Canadian firm that took over and developed research carried out in the United States. Four UBC scientists formed Quadra Logic in 1981 and bought the rights to an early version of the compound from the New Brunswick, NJ.-based pharmaceutical manufacturer Johnson & Johnson. So far, doctors say that the main role of photodynamic therapy is in destroying enough cancer cells to reduce the size of tumors and, by doing that,

allowing patients to live more comfortably. But Dr. Julia Levy, an immunologist who helped found Quadra Logic, said that Photofrin, which glows when it is irradiated with ultraviolet light, has the potential to be used to detect— and then destroy—small, early tumors. And Dr. Norman Marcon, a gastroenterologist at Toronto’s Wellesley Hospital who has used photodynamic therapy on more than 25 patients suffering from esophageal tumors during the past two years, called the procedure a new frontier in cancer treatment. Said Marcon: “It is one of the most exciting developments in our field. It is still in its infancy, but it has great potential.”

The synthetic antigen developed at Edmonton’s Biomira Inc. is aimed at strengthening the human immune system. Because cancerous tumors suppress that system, a patient’s natural antigens are unable to stimulate antibodies to attack cancer cells. Biomira’s antigen—a clear liquid made of synthetic sugar compounds—is capable of mimicking antigens normally destroyed as cancer develops. Biomira officials said that when injected into mice, the synthetic antigen naturally drained into the animals’ lymph nodes where it encountered cells of the immune system and vigorously activated them to destroy tumors. In more than 10 recent experiments on mice, members of a team of 40 researchers transplanted mouse breast cancer tumors into two groups of rodents. All 10 animals in one group received the antigen, and 10 in a control group did not. Researchers said that after about 21 days, all of the rodents in the control group had died—but tumors in about 90 per cent of the mice immunized with the antigen disappeared.

Officials at Biomira now are seeking private funding to proceed with university-sponsored tests on patients who are in remission from skin and ovarian cancers, but whose cancer is likely to recur, at the Cross Cancer Institute in Edmonton and the Tom Baker Cancer Centre in Calgary. The researchers’ long-term goal: to develop specific antigens suitable for treating a variety of cancers, including colon, lung and breast tumors. Still, University of Alberta immunologist Michael Longenecker, who worked for nine years on the development of the antigen and who cofounded Biomira in 1985 with pharmacist Antoine Noujaim, said that initial trials would simply gauge the safety of the substance for human use.

Longenecker said that he anticipated no adverse side effects from the antigen, adding that there was no guarantee that a substance which works in animals will be effective in combatting cancer in humans. “I am very optimistic and excited,” said Longenecker, adding that a decisive medical breakthrough “is still years away.” Still, the new cancer treatments under development show that scientists are willing to chart venturesome new courses in their efforts to defeat the disease that will kill an estimated 52,500 Canadians this year.

ANNE STEACY