The Effect of Electromagnetic Fields on Rat Mammary Carcinoma
Douglas M. Evans, M.D., et al. The processes of cancer
cell invasion involve the many faces of the fibrinolytic system.
What was initially thought to be a mechanism to control the effects
of intravascular thrombus formation has been shown to be far more
complex. The fibrinolytic cascade is nearly as complex as the coagulation
cascade. A major role in the capability of cells to migrate through
tissue has been recognized to belong to this biologic system. The
aspects of this system that are important from the aspect of tumor
invasive and metastatic potential are the collagenolytic activities
indicated. The Fisher rat MATB
tumor cell line was chosen for this study because it is of mammary
origin, and has been shown previously in the laboratory to produce
uPA. The degree of tumor production can be readily reproduced from
a given size of the inoculum. In order to establish that uPA was
indeed essential to the care and feeding of these cells, a preliminary
study was done to establish that the inhibition of uPA would impair
the growth of this tumor. PAI 2, the uPA inhibitor, was graciously
donated by (name withheld) and was utilized as the inhibitory agent
of uPA. The tumor model used was the creation of lung metastases
by injecting the tumor cells into the external iuqular vein of the
Fisher rat and counting the number of metastases produced in standardized
lung sections. The inhibitor was given The results confirm that this tumor system is susceptible to uPA suppression and that the model is productive in creating metastases in predictable numbers. An in vitro assay of
uPA output of the cells in tissue culture was carried out under varying
levels of exposure to electrical, magnetic and electromagnetic fields.
uPA was assayed from the culture media. The levels obtained from Being forced to reconcile
the evidence that the treated cells consistently produced smaller
tumors in the face of what was deemed to be an increased production
of uPA it was recalled that the action in terms of tissue invasion
was via surface bound uPA/plasmin complexes. The assay was repeated
using both media and cellular homogenate and using plasmin as the
assay target rather than free uPA. These results suggest that significantly
less surface bound plasmin is produced by the treated cells than
that produced by the control cells. Those levels of plasmin correlate
roughly with the tumor sizes generated by the corresponding treated
cell groups. Referring back to the electron microscopic findings,
the appearance of the cell membranes of the treated cells could suggest
that the receptor sites for uPA may be either reduced in number or
otherwise defunctionalized by the field exposures, thereby resulting
in measurably less The apparent increase in free uPA demonstrated by the media assay would then be accounted for by having notably fewer binding sites for the uPA produced by the tumor cells with a larger fraction available in the free state while a proportionally smaller fraction is converted to the surface bound plasmin required for tissue matrix dissolution. This latter hypothesis is currently in the process of verification by monoclonal antibody labeling of the receptor sites for uPA. This line of inquiry
is obviously barely in its initial stages. At this point we have
only a suspicion of an iceberg. if indeed there is an iceberg here,
it is entirely submerged and a great amount of exploration will be
required to Abstract: EMF
exposure and MATB Effects of Exposure of MATB Rat Mammary Cancer Douglas M. Evans, M.D. , et al. EMF Effect on Induced Ca The implication of environmental
exposure of electromagnetic fields on the incidence of certain malignancies
is of continued interest. This study shows inhibitory effects of
exposure of rat mammary cancer cells to electrical, magnetic and
combined electromagnetic fields on tumor growth and cell invasive
capacity, while cell proliferation was enhanced. Tumor growth was
measured in Fisher 344 rats by direct intramuscular inoculation of
EMF exposed/unexposed MATB rat mammary cancer cells. Invasive capacity
was measured by incubating exposed/unexposed cells in Matrigel invasion
chambers. Cell proliferation was measured by thymidine uptake combined
with numerical counts of exposed/unexposed cells. Cell exposure in
each aspect of this study was identical in field strength and exposure
time to unexposed controls. While each field caused significant suppression
of tumor growth and invasive capacity, as well as cell proliferation
enhancement, the responses to the combined fields were somewhat greater.
The determinations demonstrated strong dose related inhibitory response.
Key words: Cancer Inhibition; Tumor Inhibition Environmental
and occupational electromagnetic field (EMF) exposure have been implicated
as a causese of certain malignancies. Leukemia and the lymphomas
have been the primary neoplasms in question [1,2,3,4,5,6,7] although
there are also reports of an increase in the incidence of breast
cancer in employees exposed to electrical fields in the workplace
[8,9,10,11], and questions of a link between brain cancer and occupational
exposure to EMF [12]. The basis for these reports in each instance
has been retrospective epidemiological data. Accurate retrospective
measurement of the intensity of field exposures in these studies
is not possible. While an approximation of field strength can be
made in some instances, i.e. proximity to power lines, the use of
household appliances, electric blankets etc., the
extent of exposure to these field sources is uncertain. There have
been recent Determination of the
effect of field exposure on tumor growth utilized cells exposed to
each field (E, M, and EM) for one hour periods twice daily for 48
hours. Ten Fisher 344 rats per exposure type were subsequently inoculated
by intramuscular injection with l0u viable exposed cells. An identical
inoculum of 10u unexposed cells was carried out on 10 Fisher 344
rats for controlled comparison. The central gluteal musculature was
selected as the inoculation site under direct vision by virtue of
a 3mm skin incision. The same inoculation schedule was followed for
two groups of The effect of field
exposure on the capability of MATB cells to invade was determined
using the synthetic basement membrane Matrigel (Collaborative Biomedical
Products, Bradford, MA), and standard invasion chambers. Matrigel The effect of field
exposures on cellular growth and proliferation was measured by both
H-thymidine incorporation and by cell counts following incubation
during field exposures. MATB cells were prepared, placed in Millicells
and intermittently exposed to E, M, and EM fields as with the tumor
growth and invasion experiments. The exposure length for this section
of the study was Z hours twice daily over a duration of 72 hours.
The media was removed from the outer portion of the petri dish and
replaced with serum-free media to quiesce the cells for 48 hours,
prior to exposure. The cells were removed from the exposure and control
chambers and counted with Trypan blue stain in ahemocytometer. MATB
cells were resuspended in media containing 10% fetal bovine serum
and 0.25 Ci/ml of H-thymidine (NEN Dupont, Boston MA). 10 viable
cells per well were aliquotted into 6 wells per exposure group and
incubated for 48 hours. The suspended cells from each well were transferred
to microcentrufuge tubes, centrifuged and media aspirated. The wells
and pellets were washed with media to remove non-specific binding.
MATB pellets and The results of the tumor
growth aspect at the study are depicted graphically in Figure 1. Comparison
of tumor weights showed significant reduction of tumor mass (all
comparisons p<0.02) in lesions produced by exposed cells over
those by controls. Tumors produced by unexposed MATB cells weighed
0.9766 -+10.16 grams, those receiving electrical exposure weighed
0.5334+/-0.10 gms., those receiving magnetic exposure weighed 0.43424+/-
0.07 gms. and those receiving combined exposure weighed 0.3597 -+0.06gms.
EMF significantly decreased the growth and local EMF effects on MATB
cellular proliferation by incorporation of 3H-thymidine and growth
by cell counts were compared to the indices of unexposed cells (100%).
Exposure to electrical fields increased cell proliferation to 150%
of control, exposure to magnetic fields increased proliferation to
160% of control and combined field exposure produced increases of
228%. All field exposures increased the cellular proliferation (P<0.001)
of the MATB cells. Furthermore, cell counts for the E, M and EM exposed
cells showed increased cell growth (Table
1) to 105% of control, 116% of control and 137% of control for respective
p values of 0.32, 0.053 and 0.005. The results confirm that the MATB
cells remain In support of the concept
of a promotional role for EMF exposures, Leung et al [22] reported
an increased number of rat mammary tumors produced in animals exposed
to both dimethylbenzanthracene (DMBA) and 60Hz electrical fields.
Bemiashvili [23] likewise showed promotional effects of both static
and variable magnetic fields imposed on rats previously injected
with nitrosomethyl urea (NMU). The results reported by Rannug [24,
25] in two separate studies of promotional effects of magnetic fields
on the production of liver tumors were inconclusive. Loscher [26]
studied the promotional influence of magnetic fields in DMBA treated
female rats. Varying ranges of magnetic field exposures were used
with equivocal results. Conversely, inhibition of expected growth
of spontaneous tumors In animals exposed The results of the present study, showing variable levels of response to changes in the length and duration of exposures, are supportive of this concept. Both electrical and
magnetic fields singly imposed on MATB rat mammary cancer cells produced
significant inhibition of tumor growth and cell invasiveness. Combined
electric and magnetic field exposures produced the most profound
change. EMF exposure of identical cells at identical energy levels
which demonstrated decreased cell invasiveness and tumor growth provoked
seemingly incongruent increase in cell growth and proliferation.
These results are consistent with the current understanding of the
regulatory pathways of cell proliferation vs those of invasion and
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