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Biotech / Medical : CLTR COULTER PHARMACEUTICAL -- Ignore unavailable to you. Want to Upgrade?

To: RWReeves who wrote (406)	11/29/1999 4:39:00 AM
From: Gordon James	Read Replies (1) \| Respond to of 666

RWR, I think they are using a Holmium 166 Beta emitter which might be better than a gamma source and the dosimetry involved. I believe that Bexxar's gamma radiation and associated dosimetry process are a positive factor for Bexxar, probably helping Bexxar to be a safer and more effective treatment for the patient than alternatives which do not intend to utilize gamma emissions. One of the ways that Bexxar differs from Zevalin is that Zevalin's 90Y only emits beta particles, while Bexxar's 131I emits beta, gamma and other particles as well (not sure offhand whether the Holmium 166 being used by NERX emits other particles in addition to the beta particles). In fact, it is Bexxar's beta emissions that are understood to be the therapeutic particles - the gamma emissions are not believed to provide any therapeutic benefit. So Bexxar, Zevalin and NERX's Pretarget therapy are all alike in that they are all designed to deliver therapeutic benefit via the beta particles of their radioisotopes. While not of any direct therapeutic benefit, the gamma radiation of 131I is nonetheless a net positive factor for Bexxar - instead of requiring dosimetry, the gamma particles enable Bexxar's dosimetry, which provides a very accurate patient-specific dosing, the likes of which cannot be done (exactly) with Zevalin. Unlike beta particles, gamma emissions can be detected outside the body and captured with a gamma camera. To recap for those not familiar - the Bexxar treatment regimen takes advantage of the gamma radiation in the following way: a small tracer dose of Bexxar is administered first, then the individual patient's biodistribution and clearance are documented via gamma camera. The Bexxar researchers claim that this is very important because individual patients will differ in terms biodistribution and clearance. Then, the subsequent therapeutic dose for each patient is individually modified based on the findings of the tracer study for that patient, so that a consistent whole-body radiation dose (generally 75 cGy) can be administered to each patient. So the gamma radiation is used to help tailor the dose that is delivered by the beta particles. Thus, unable to image a 90Y-labeled Zevalin tracer dose, the Zevalin researchers have utilized a 111I-labeled tracer dose (Indium 111 is a gamma emitter), but with a somewhat different purpose - rather than intending to adjust the therapeutic dose based on tracer studies, they intend to use the results of their tracer studies to show that a tracer/dosimetry process would not provide safer administration of Zevalin, and thus can be dispensed with altogether. This may be true, or may be a position that IDEC is forced into because of Coulter's dosimetry patents. I called this gamma radiation a "net positive" for Bexxar - downside of the long range of gamma emissions is concern about how long a treated patient should be isolated for safety of others. Looked like a plus for Zevalin for awhile, until updated NRC regulations awhile back (a few years ago?) made clear that most Bexxar treatments could be done on an outpatient basis as well and still comply with the regulations. As far as NERX goes, their Pretarget approach is an interesting idea, but I recall being disappointed in early results when I took a look awhile back, and I'll probably remain pretty skeptical until they prove it works. I don't usually have the constitution for "under a buck" type plays, so I didn't spend much time looking at them, but they might be worth more of a look from you braver souls... Cheers, Gordon