The lytic peptide-βCG conjugates have now been shown to be effective in destroying primary tumor cells of prostate, breast, ovarian, Leydig and granulosa cell cancers. The animal models used include nude mice, transgenic mice, and diethylstilbestiol/dimethylbenz(a) anthracene treated rats. Both androgen and estradiol sensitive and insensitive cells are destroyed. Adequate numbers of LH/CG or LHRH receptors must be expressed by the cancer cells for effective targeting and membrane disruption to occur.
The most remarkable finding of these studies is the ability of the lytic peptide conjugates Phor14-βCG(ala), Hecate-βCG, and Phor21-βCG(ala) to seek out and destroy metastatic cells in lymph nodes, bones, lungs and other organs and tissues. The lytic peptide conjugates are not effective in killing cells, such as TM4 Sertoli and CHO cells, that do not express LH/CG receptors, nor are the lytic peptides effective when administered alone or as unconjugated compounds (Hecate + LHRH).
The fact that estrogens and FSH can increase LH/CG receptors and thus the effectiveness of the lytic peptide-βCG conjugates in vitro and in vivo suggests that the lytic peptide conjugates might be used in combination with estrogens or FSH, in cases where LH/CG receptors in the tumor are absent or few in number. MCF-7 cells had higher numbers of LHRH receptors, and were more sensitive to LHRH-Hecate than MDA-MB-435S cells. On the other hand, MDA-MB-435S cells had higher numbers of LH/CG receptors and were more sensitive to Hecate-βCG than MCF-7 cells. Thus, the treatment of choice for a given tumor may depend on the number and type of receptors expressed. Sequential or concurrent treatments with lytic peptide-βCG and LHRH-lytic peptides may also be feasible. The lytic peptides alone, although toxic to breast cancer cells in vitro are ineffective in vivo in tumor-bearing nude mice, and do not appear to have the potency or specificity to serve as useful chemotherapeutic agents. Histopathological studies revealed extensive necrosis of the primary tumor cells of the treated nude mice (Fig. 7). Recent studies indicate that apoptosis is not involved in the destruction process. The degrees of necrosis in tumor cells of Phor14-βCG, Hecate-βCG, and LHRH-Hecate treated mice were similar when minimally effective doses were given. Ultimately, the degree of damage produced in a given tumor depends on the relative numbers of LH/CG and LHRH receptors expressed by the tumor cells. Eventually, it may be possible to tailor the treatment to fit the profile of LHRH or LH/CG receptors expressed.
Histopathological studies also revealed no damage to other organs and tissues, except the testes and ovaries, organs which express the LH receptors. In males, spermatogenesis was impaired and the interstitial cells were pyknotic. In females, ovulation was inhibited. Both male and female mice recovered fertility 12 weeks after removal from treatment. Surprisingly, no adverse effects were seen in other non-reproductive tissues and organs reported to express CG/LH receptors. These include the adrenal, lymphocytes, blood vessels and skin, among others. Failure of the lytic peptide-βCG conjugates to damage these tissues may reflect the fact that low numbers of receptors are expressed or that the CG/LH receptors expressed lack the ability to bind the 15 amino acid segment of theβchain of CG used as a ligand for the lytic peptides.
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