Female BDF mice bearing
estrogen-dependent MXT mouse
mammary cancers were treated for 4 weeks with a cytotoxic analog of
luteinizing hormone-releasing hormone (
LH-RH).
T-98 (agonist [D-Lys6]
LH-RH linked to glutaryl-2(hydroxymethyl)
anthraquinone). The effects of
T-98 were compared to those of equimolar amounts of the cytotoxic moiety
2-(hydroxymethyl)anthraquinone hemiglutarate (
G-HMAQ) and carrier
LH-RH agonist [D-Lys6]
LH-RH. Both
T-98 and [D-Lys6]
LH-RH significantly inhibited the growth of MXT
cancers, but
G-HMAQ had only a minor non-significant effect. Cytotoxic analog
T-98 and the carrier [D-Lys6]
LH-RH had similar inhibitory hormonal activities on the pituitary-gonadal axis, but
T-98 caused a larger reduction in
tumor volume and decreased proliferation characteristics such as mitotic activity and AgNOR numbers in
tumor cells to a greater extent than the carrier.
Tumor inhibition by
T-98, [D-Lys6]
LH-RH, and
ovariectomy was connected with a significant decrease in binding capacity of
EGF receptors in
tumor cell membranes. The concentration of
EGF receptors remained high in
tumors that continued to enlarge in spite of treatment and in all control untreated
tumors, even those of small size. Thus, the changes in
EGF receptors are likely to be the result of the
therapy. Treatment with
T-98 caused a greater reduction in the binding capacity of
EGF receptors in
tumors than [D-Lys6]
LH-RH. This could explain the higher inhibitory effect of the cytotoxic analog on
tumor growth. Since radiolabeled
T-98 was shown to accumulate in MXT
cancers 3 hours after a
subcutaneous injection, this indicates that specific targeting might play a role in the antitumor effect exerted by this cytotoxic analog.