Binding and cytotoxicity of conjugated and recombinant fusion proteins targeted to the gonadotropin-releasing hormone receptor.
Pokeweed antiviral protein (PAP) is a plant-derived, highly potent ribosome inactivating protein that causes inhibition of protein translation and rapid cell death. We and others have delivered this protein to various cell types, including cancer cells, using hormones to specifically target cells bearing the hormone receptor. Here, we compare binding and cytotoxicity of GnRH-PAP hormonotoxins prepared either by protein conjugation (GnRH-PAP conjugate) or through recombinant DNA technology (GnRH-PAP fusion). Although GnRH-PAP conjugate protein bound specifically to and caused cell death in cells bearing the gonadotropin-releasing hormone (GnRH) receptor, we could not detect binding or cytotoxicity using two different versions of the fusion protein in receptor-positive cells. We conclude that generation of an active GnRH-PAP fusion protein may not be feasible either because both ends of the GnRH molecule are required for receptor binding, but only the NH(2) terminus is free in the fusion protein and/or that more potent analogues of GnRH (inclusion of which is not feasible in the fusion protein) are needed for efficient targeting. In contrast, the GnRH-PAP conjugate shows promise as a novel anticancer agent, capable of targeting cancer cells expressing the GnRH receptor such as prostate, breast, ovarian, endometrial, and pancreatic cells. It may also be useful as a therapeutic agent to eliminate pituitary gonadotrophs, eliminating the need for chronic GnRH analogue administration to treat hormone-sensitive diseases.
Qi
Lin
L
Department of Medicine, Division of Medical Oncology, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262, USA.
Nett
Terry M
TM
Allen
Matthew C
MC
Sha
Xiaoming
X
Harrison
Gail S
GS
Frederick
Barbara A
BA
Crawford
E David
ED
Glode
L Michael
LM
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D016466:CHO Cells; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D006224:Cricetinae; D006801:Humans; D000922:Immunotoxins / Q000633:toxicity*; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects; D011966:Receptors, LHRH / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000633:toxicity*; D054789:Ribosome Inactivating Proteins, Type 1
D000922:Immunotoxins; D010940:Plant Proteins; D011966:Receptors, LHRH; D011993:Recombinant Fusion Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D009699:N-Glycosyl Hydrolases; C024275:pokeweed antiviral protein