ABSTRACT
Metastatic castration-resistant prostate cancer is today incurable. Conventional imaging methods have limited detection, affecting their ability to give an accurate outcome prognosis, and current therapies for metastatic prostate cancer are insufficient. This inevitably leads to patients relapsing with castration-resistant prostate cancer. Targeting prostate-specific antigens whose expression is closely linked to the activity in the androgen receptor pathway, and thus the pathogenesis of prostate cancer, is a possible way to increase specificity and reduce off-target effects. We have humanized and evaluated radioimmunoconjugates of a previously murine antibody, m5A10, targeting PSA intended for theranostics of hormone-refractory prostate cancer. The humanized antibody h5A10 was expressed in mammalian HEK293 cells transfected with the nucleotide sequences for the heavy and light chains of the antibody. Cell culture medium was filtered and purified by Protein G chromatography, and the buffer was changed to PBS pH 7.4 by dialysis. Murine and humanized 5A10 were conjugated with p-SCN-Bn-CHX-A"-DTPA. Surface plasmon resonance was used to characterize the binding to PSA of the immunoconjugates. Immunoconjugates were labeled with either indium-111 or lutetium-177. Biodistribution studies of murine and humanized 5A10 were performed in mice with LNCaP xenografts. 5A10 was successfully humanized, and in vivo targeting showed specific binding in xenografts. The results thus give an excellent platform for further theranostic development of humanized 5A10 for clinical applications.
ABSTRACT
The mercury-sensing regulatory protein, MerR (Tn21), which regulates mercury resistance operons in Gram-negative bacteria, was subjected to directed evolution in an effort to generate a MerR mutant that responds to Cd but not Hg. Oligonucleotide-directed mutagenesis was used to introduce random mutations into the key metal-binding regions of MerR. The effects of these mutations were assessed using a vector in which MerR controlled the expression of green fluorescent protein (GFP) and luciferase via the mer operator/promoter. An Escherichia coli cell library was screened by fluorescence-activated cell sorting, using a fluorescence-based dual screening strategy that selected for MerR mutants that showed GFP repression when cells were induced with Hg but GFP activation in the presence of Cd. Two Cd-responsive MerR mutants with decreased responses toward Hg were identified through the first mutagenesis/selection round. These mutants were used for a second mutagenesis/selection round, which yielded eight Cd-specific mutants that had no significant response to Hg, Zn, or the other tested metal(loid)s. Seven of the eight Cd-specific MerR mutants showed repressor activities equal to that of wild-type (wt) MerR. These Cd-specific mutants harbored multiple mutations (12 to 22) in MerR, indicating that the alteration of metal specificity with maintenance of repressor function was due to the combined effect of many mutations rather than just a few amino acid changes. The amino acid changes were studied by alignment against the sequences of MerR and other metal-responsive MerR family proteins. The analysis indicated that the generated Cd-specific MerR mutants appear to be unique among the MerR family members characterized to date.
