Targeting the Human Complement Membrane Attack Complex to Selectively Kill Prostate Cancer Cells.

摘要

The goal of this proposal is to develop a strategy to redirect the toxicity of a human protein to sites of prostate cancer. Ourhypothesis is that the human C5 complement protein can be modified to a form that is not activated by the normal complement pathways but is instead activated by the prostate cancer specific protease PSA. This strategy would allow us to selectively unleash the potent cytolytic activity of the human complement Membrane Attack Complex (MAC) within sites of metastatic prostate cancer while sparing normal host tissue due to the finely tuned regulation of complement activity in the circulation. A series of PSA-activated modified C5 proteins were generated and characterized for PSA activation. While initial studies suggested that wild type C5 was stable in the presence of PSA, further characterization demonstrated that both the wild type and modified C5 proteins were extensively cleaved and degraded by PSA. Thus, while PSA could cleave the engineered cleavage site within the modified protein, it also cleaved the protein at multiple off-target sites. PSA was able to inactivate complement fixation and MAC formation through degradation of wild type C5 suggesting a potential role for PSA in regulation of complement activity within prostate cancer. Based on the finding of PSA degradation of C5, we are now exploring whether alternative proteases selectively overexpressed in prostate cancers such as human glandular kallikrein 2, TMPRSS2 and fibroblast activation protein (FAP) can be targeted to activate a modified C5 protein using the same strategy we have outlined for the PSA studies. These new modified C5 proteins will be evaluated for appropriate cleavage at the engineered site and for selective toxicity.