NeoRx Corp. announced Tuesday that its "pretargeting" methodfor radioactive monoclonal antibody-based cancer therapyworks in mice.
The Seattle company (NASDAQ:NERX) reported these findings toits shareholders at last week's annual gathering. Not only didthe pretargeting approach cause complete tumor regressions,but it also apparently cured chemotherapy-resistant humanlung cancer tumors in mice.
Monoclonal antibodies tagged with tissue-damagingradioactivity or toxin molecules are theoretically attractivecandidates for cancer chemotherapy. But they haveencountered substantial technical difficulties. One of these is aphenomenon known as "innocent bystander" toxicity. When alabeled monoclonal is injected into a person's bloodstream, it'sradioactive emissions can damage non-targeted tissue --especially bone marrow -- as it finds its way to the targetedtissue.
But a new system, called pretargeting, is intended to eliminatethis problem. In pretargeting, the monoclonal of choice is firstinjected into the body, where it selectively binds to the targettissue. Any excessive unbound antibody is eliminated from thecirculatory system. The patient is then injected with theradionuclide, which either binds quickly to the antibody by anavidin-biotin reaction, or is itself rapidly removed from theblood stream.
NeoRx has licensed the pretargeting technology from StanfordUniversity. The company said that it has demonstrated a 300percent improvement in the therapeutic index -- the ratio ofdose delivered to tumor vs. the dose delivered to the bonemarrow -- compared with the "conventional" method.
"We've shown in nude mice and in patients that if we can get acertain level of radiation into a tumor there is a greater chanceof the tumor responding or completely disappearing," RobertLittauer, NeoRx's vice president and chief financial officer, toldBioWorld.
"We've announced previously that by using pretargeting it'spossible to get a better ratio of dose (of radioactivity, or rads)to tumor versus dose to bone marrow," Littauer explained, "andwe've also seen tumor regression in patients who don't showregression from normal treatment." But now the scientists havedemonstrated that they can actually achieve tumor regressionin mice at a much better tumor-to-background ratio than withconventional antibody therapy methods, Littauer toldBioWorld.
-- Jennifer Van Brunt Senior Editor
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