From: cpsigd01@ulkyvx.louisville.edu
Newsgroups: sci.med.physics
Subject: Re: cancer
Date: 2 Oct 92 20:08:39 GMT
Organization: University of Louisville

In article <1992Sep30.224138.5853@sjsumcs.sjsu.edu>, b5249-23@mathcs.sjsu.edu (Kurt Stocklmeir) writes:
> 
>     A photoactive dye called haematoporphyrin is used in photoradiation.
> Photoradiation is a method used to kill cancer cells.  This dye is absorbed by
> almost all cells.  But cancer cells keep this dye in them for a much
> longer time as compared to normal cells.  After this dye has left
> the normal cells, and while it is still in cancer cells, red light
> is used to put it into an excited state.  The dye goes into an
> excited state, and transfers energy to oxygen molecules.  The oxygen
> molecules then go into an excited state and kill the cell they are
> in.  The problem with this method is that red light will go through
> only about 1/3 in. of a person.
>     Red light has an energy of about 1.8 ev.  Because a molecule is
> photoactive, does not mean there are not other methods to put it in an excited
> state.  For example, collisions with other particles can cause a molecule to
> go into an excited state.  This method and others could maybe excite
> haematoporphyrin in all parts of a body.
>     Since people are mostly made of water, many molecules are in a
> form of ions.  Positive ions and protons tend to be around the cell wall on
> the inside of cells.  Most of the positive ions are K+.  Negative ions are
> on the outside of the cell wall.  Theories state that cancer cells
> may have a larger negative charge on the outside of cell walls as
> compared to normal cells and because of this there is an imbalance
> between forces of negative charges and forces associated with
> molecules.  This maybe is why cancer cells can move to different
> parts of a body.
>     Charged particles can be accelerated using electric fields.  I
> am not saying the following can be done, but I am saying it maybe
> can be done.  Alternating electric fields can accelerate charged
> particles in cells and outside of cells.  As the charged particles
> are accelerated, they will have various amounts of kinetic energy.
> Some of the particles could maybe have about 1.8 ev of kinetic energy while
> most will not.  [Stuff Deleted]

>If that is true, then those particles with 1.8 ev
> can collide with molecules of haematoporphyrin and excite them.
> If a reasonable amount of this dye is excite in a cell, the cell
> will then be killed.  Even if this happened only a small amount
> of the time, this method could be used to kill cancer cells.
> In my opinion, it would be better if the above only happened a
> small amount of the time, since killing all cancer cells in a person
> at 1 time could kill the person.
>
Its a great idea but won't work.  Hematoporphyrin has absorption spectrum
which actually peaks in the Blue-Green wave lengths- but because 630 nM
has the best penetration they use a smaller absorption band at that wave
length.  There will be not absorption spectrum for particulate radiations.
  One thing you didn't mention with regard to photodynamic therapy (PDT)
 is that the patient is often left photosensitive for up to 6 weeks after
 injection of HpD.  They have to live in reduced light and avoid direct
 sunlight or suffer severe 'sun burn'.  Keep thinking!
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