RESUMO
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.
Assuntos
Imunotoxinas/toxicidade , N-Glicosil Hidrolases/metabolismo , Proteínas de Plantas/metabolismo , Receptores LHRH/metabolismo , Proteínas Recombinantes de Fusão/toxicidade , Animais , Apoptose , Western Blotting , Células CHO , Bovinos , Membrana Celular/metabolismo , Células Cultivadas , Ensaio de Unidades Formadoras de Colônias , Cricetinae , Humanos , Hipófise/metabolismo , Ligação Proteica , Biossíntese de Proteínas/efeitos dos fármacos , Proteínas Inativadoras de Ribossomos Tipo 1RESUMO
Pokeweed antiviral protein (PAP) is a plant-derived, highly potent ribosome inactivating protein that causes inhibition of protein translation and rapid cell death. We have previously described potent cytotoxic activity of a GnRH (gonadotropin-releasing hormone) receptor-targeted conjugate protein (GnRH-PAP) and demonstrated that cytotoxicity depended on the number of GnRH receptors and the duration of exposure. Here, we demonstrate that the GnRH-PAP conjugate was cytotoxic to three different prostate cancer cell lines, supporting the feasibility of using such hormonotoxins as novel therapeutics for hormone-responsive cancers such as prostate cancer.
