AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA 4401 PSA is an important biomarker for diagnosis of and prognosis assessment in prostate cancer. We have previously demonstrated that calcium-independent PLA2 (iPLA2) controls the secretion of PSA and inhibition of iPLA2 causes apoptosis in LNCaP cells. Addition of the PLA2 product arachidonic acid or its eicosanoid derivatives had no discernable effect on iPLA2-mediated apoptosis in LNCaP cells. However, addition of PSA together with iPLA2 inhibitor restored survival and addition of neutralizing antibody to PSA resulted in apoptosis. Addition of neutralizing antibody alone to LNCaP cells is sufficient to cause activation of caspases, indicative of apoptosis. Based on these data, we hypothesized that PSA plays an autocrine role that affects the survival of prostate cancer cells. Since the PI3K/Akt pathway plays a major role in prostate cancer cell survival, we tested whether PSA could activate the PI3K/Akt. Investigation of PSA signaling by western analysis shows that PSA causes the activation of Akt through phosphorylation at both Ser-473 and Thr-308 in LNCaP cells in a dose and time-dependent fashion. Phosphorylation of Akt was initiated within 2 hr by PSA at concentrations between 200 and 700 ng/ml and incubation at 3 hr required 25 to 200 ng/ml PSA. Treatment with PI3K inhibitors LY294002 and wortmannin in combination with PSA completed inhibited Akt activation. These data indicate that PSA participates in autocrine signaling that contributes to the regulation of survival of prostate cancer cells. While PSA is one of the best biomarkers for the early detection of any cancer, its effect on patient survival is under question. A role for PSA in cancer progression could explain its minimal impact on patient survival while acting as an early warning signal for the disease.

Colostrinin (CLN), a mixture of proline-rich polypeptides, has shown a stabilizing effect on cognitive function in Alzheimer’s patients measured by the Alzheimer’s disease Assessment Scale-cognitive (ADAS-cog) and in Instrumental Activities of Daily Living (ILDL) in recently conducted clinical trials. The aim of this study was to elucidate a possible mode of action of CLN in the treatment of Alzheimer’s disease. Here, we report that CLN prevents the aggregation of β-amyloid peptide Aβ (1–40) in vitro. The impact of CLN on the fibril formation was monitored by optical and electron microscopy. The electron micrographs illustrate that, at 25μM, Aβ (1–40) peptides formed fibrils after 24–48h of incubation. The presence of 0.25μM CLN completely abolished the fibril formation. Aβ (1–40) peptides grow into dense fibers when examined at the 20th day. In the presence of CLN, however, the fibrils are much shorter and less dense. Addition of CLN as late as the 17th day can still dissolves the preformed fibrils. These observations were compared to the effect of CLN on the neurotoxic activity of β-amyloid peptides in the cell culture model (SHSY-5Y). The β-amyloid peptides were pre-incubated with CLN at various times and used to treat SHSY-5Y neuroblastoma cells for up to 4 days. The cytotoxic effect was monitored by trypan blue exclusion. We demonstrated that 24–48h treatment was the onset of toxicity of 10–50μM of β-amyloid peptides. Pre-incubation of 0.0025–0.25μM of CLN with 25μM of β-amyloid peptides leads to near-complete abolition of cytotoxicity. Low doses of CLN (2.5nM) can attain cytotoxic protection levels similar to those of highest doses (0.25μM). Thus, the time course for the appearance of β-amyloid fibrils coincides with that for cytotoxicity, and that the reduction of fibrils of β-amyloid peptides by CLN is concomitant with the reduction of the cytotoxic effects of β-amyloid on SHSY-5Y neuroblastoma cells. Our studies suggest that the neuroprotective effects exerted by CLN are related to the reduction of β-amyloid fibrils.

793 Serum prostate specific antigen (PSA) levels are elevated in prostate cancer patients and serve as a diagnostic marker for the disease. Prostate cancer is generally responsive to androgen ablation therapy and produces a drop in PSA levels. In time, hormone-refractory disease often develops and PSA levels once again rise. Under normal circumstances PSA is deposited in the lumen of prostatic ducts, whereas PSA secreted from malignant cells gains access to the circulation. The underlying biochemical mechanisms for the aberrant control of PSA secretion in prostate tumors are not well-known. Regulation of peptide secretion by iPLA2-β has recently been reported in non-prostatic tissue. In prostate tissue, both iPLA2-β and PSA expression are reportedly under androgen regulation. We therefore investigated whether iPLA2-β plays a role in PSA secretion in normal prostate epithelial RWPE-1 cells and in LNCaP prostate cancer cells. We observed an increase in iPLA2 activity in LNCaP cells that corresponded with an increase in expression of the two active isoforms, LH-iPLA2 and SH-iPLA2, as well as a decrease in the inhibitory ankyrin-iPLA2 isoform. We further demonstrated that treatment with the iPLA2-specfic inhibitor, BEL, inhibited PSA secretion from LNCaP cells and subsequently resulted in cell death. While BEL treatment triggered an apoptotic response in LNCaP cells, normal prostate RWPE-1epithelial cells were not vulnerable to BEL-induced cell death. Addition of exogenous PSA to LNCaP cultures suppressed BEL-induced cell death and addition of anti-PSA antibody reversed the survival effect of PSA. These data demonstrate that iPLA2 plays a role in regulating PSA secretion from cells and the release of PSA provides an autocrine survival function for LNCaP cells. The mechanism by which PSA imparts its survival effect is not currently understood.