San Francisco Chronicle - The Voice of the West, 901 Mission Street, San Francisco, CA 94119 - Thursday, July 11, 1996 - Page A6
David Perlman, Chronicle Science Editor

Researchers reported yesterday at the 11th International AIDS Conference that after six weeks of twice-daily use, the combination of two new and expensive drugs reduced levels of HIV, the virus that causes AIDS, by as much as 99.6 percent in a group of 43 patients. In addition, levels of disease- fighting immune system cells in their bodies, known as CD4 T-cells, increased by small but highly significant amounts, the researchers said. The report is the latest of a train of encouraging news since arrival on the AIDS scene of the protease inhibitor drugs just two years ago. Since then, continuing clinical trials have generally shown such good results that some scientists have begun hoping it may soon be possible to eradicate the AIDS virus from some patients, which would amount to a cure. But many profound questions and strong reservations remain, because no patients have been taking any of the three protease inhibiting drugs for more than a year.

Dosages have yet to be established. No one knows whether any of the new drugs could really wipe out even a single one of the deadly virus particles, which can go dormant in some tissues for years. The virus may find a way to mutate into resistant forms.

One of the drugs, called ritonavir and marketed as Norvir, is made by Abbott Laboratories. The other, saquinavir, is from Hoffmann-La Roche and has the trade name Invirase. The two fiercely competitive pharmaceutical companies, after learning from independent laboratory research that the drugs might multiply each other's effects, called in outside researchers for clinical trials. Yesterday's reports came from Dr. Martin Markowitz of the AIDS laboratory at the Aaron Diamond Institute in New York and Dr. William Cameron of Ottawa General Hospital and the University of Ottawa. "For the first time, we have data that support what we have predicted -- that certain protease inhibitors such as saquinavir and ritonavir can be used synergistically," said Markowitz. "This combination will become an important element of future HIV treatments."

The AIDS virus, although it is a wily beast, has vulnerable points as it commandeers the genetic machinery of the body's immune system to reproduce itself. The virus uses at least two enzymes to reproduce -- enzymes called reverse transcriptase, and protease. The new reports reinforce a growing conviction that the best way to fight HIV is with many drugs, used at once, making it nearly impossible for the virus to evolve simultaneous resistance to so many challenges. The results are the first to look at two protease inhibitors in combination.

Early drugs used in the AIDS epidemic, such as AZT, 3Tc, ddI and DDc, interrupt reverse transcriptase. Used in double and triple combinations, they have lowered the "viral load" of severely ill AIDS patients so much that many doctors use them as standard treatments.

Three protease inhibitors, Invirase and Norvir, plus a third called Indinavir and marketed by Merck & Co., have already been approved in the United States by the federal Food and Drug Administration. Two more, Auguron's nelfinavir and Glaxo Wellcome's VX-478 are on the way.

During the past year, clinical trials on tens of thousands of patients worldwide have showed that protease inhibitors, in combination with older reverse transcriptase inhibitors, can leave patients with virtually no viruses in the blood, where they do their most obvious damage. But the virus is known to hide in the body's lymph system -- in lymph nodes and tonsils, for example, and scientists do not yet know whether the virus might eventually escape from those hiding places and proliferate actively all over again after a treatment.
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