A prostate-specific antigen-activated channel-forming toxin as therapy for prostatic disease.
BACKGROUND
Most men will develop prostatic abnormalities, such as benign prostatic hyperplasia (BPH) or prostate cancer, as they age. Prostate-specific antigen (PSA) is a serine protease that is secreted at high levels by the normal and diseased prostate. Therapies that are activated by PSA may prove effective in treating prostatic malignancies.


METHODS
We modified proaerolysin (PA), the inactive precursor of a bacterial cytolytic pore-forming protein, to produce a PSA-activated protoxin (PRX302). The viability of the prostate adenocarcinoma cell lines LNCaP, PC-3, CWR22H, and DU145 and the bladder cancer cell line TSU after treatment with PA or PRX302 in the presence or absence of purified PSA was assayed. Mice carrying xenograft tumors derived from LNCaP, CWR22H, or TSU cells were treated with intratumoral injection of PA or PRX302, and tumor size was monitored. To test the safety of PRX302, we administered it into the PSA-secreting prostate glands of cynomolgus monkeys. All statistical tests were two-sided.


RESULTS
Native PA was highly toxic in vitro but had no tumor-specific effects in vitro or in vivo. Picomolar concentrations of PRX302 led to PSA-dependent decreases in cell viability in vitro (PRX302 versus PRX302 + PSA: DU145 cells, mean viability = 78.7% versus mean = 1.6%, difference = 77.1%, 95% confidence interval [CI] = 70.6% to 86.1%; P<.001; TSU cells, mean = 100.2% versus mean = 1.4%, difference = 98.8%, 95% CI = 96.4% to 104.0%; P<.001). Single intratumoral injections of PRX302 produced substantial and often complete regression of PSA-secreting human prostate cancer xenografts (5 microg dose, complete regression in 6 of 26 mice bearing LNCap or CWR22H xenografts [23%]; 10 microg dose, complete regression in 10 of 26 mice [38.5%]) but not PSA-null bladder cancer xenografts. The prostates of cynomolgus monkeys injected with a single dose of PRX302 displayed extensive but organ-confined damage, with no toxicity to neighboring organs or general morbidity.


CONCLUSIONS
Our observations demonstrate the potential safe and effective intraprostatic application of this engineered protoxin.
Williams
Simon A
SA
Department of Oncology, The Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Merchant
Rosemina F
RF
Garrett-Mayer
Elizabeth
E
Isaacs
John T
JT
Buckley
J Thomas
JT
Denmeade
Samuel R
SR
D000230:Adenocarcinoma / Q000188:drug therapy*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001427:Bacterial Toxins / Q000494:pharmacology* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D006801:Humans; D007150:Immunohistochemistry; D015552:Injections, Intralesional; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D052899:Pore Forming Cytotoxic Proteins / Q000494:pharmacology* / Q000627:therapeutic use; D011355:Prodrugs / Q000494:pharmacology; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011470:Prostatic Hyperplasia / Q000188:drug therapy*; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D012107:Research Design; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy*; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; D001427:Bacterial Toxins; C518473:PRX302; D052899:Pore Forming Cytotoxic Proteins; D011355:Prodrugs; C107096:proaerolysin; D017430:Prostate-Specific Antigen