PNC-27

OBJECTIVE: Despite an 80% response rate to chemotherapy, epithelial ovarian cancer has the highest case fatality rate of all gynecologic malignancies. Several studies have shown the efficiency of anticancer peptides PNC-27 and PNC-28 in killing a variety of cancer cells selectively in vitro and in vivo. The purpose of this study was to evaluate the efficacy of PNC-27 against human primary epithelial ovarian cancer. METHODS: We established primary cultures of freshly isolated epithelial ovarian cancer cells from patients with newly diagnosed ovarian cystadenocarcinomas. Two cell lines were obtained, one from mucinous cystadenocarcinoma, and the other from high-grade papillary serous carcinoma. The cancerous properties of these cells were characterized in vitro morphologically, by their growth requirements and serum independence. Treatment effects with PNC-27 were followed qualitatively by light microscopy, and quantitatively by measuring inhibition of cell growth using the MTT cell proliferation assay and direct cytotoxicity by measuring lactate dehydrogenase (LDH). RESULTS: PNC-27 inhibits in a dose-dependent manner the growth of and is cytotoxic to human primary cancer cells that had been freshly isolated from two ovarian epithelial cancers. The results further show that the control peptide PNC-29 has no effect on the primary cancer cells. Our results also show that PNC-27 is cytotoxic to cells from long-established and chemotherapy-resistant human ovarian cancer cell lines. CONCLUSION: These findings show, for the first time, the efficacy of PNC-27 on freshly isolated, primary human cancer cells. Our results indicate the potential of PNC-27 peptide as an efficient alternative treatment of previously untreated ovarian cancer as well as for ovarian cancers that have become resistant to present chemotherapies.

OBJECTIVE: The peptide PNC-27 has been found to kill many different endodermal solid tissue and hematopoietic cancer cells but has no effect on normal cells. The mechanism involves binding to the HDM-2 protein, which is expressed in the membranes of cancer cells but not in normal (untransformed) cells. Our objectives in the current study are to determine 1) if PNC-27 is lethal to squamous cervical epithelial cancer cells but not to untransformed squamous cervical cells; 2) if membrane-bound HDM-2 is expressed uniquely in cervical cancer cells; and 3) whether HDM-2 is stable for detection in different types of preservative solutions. METHODS: We determined dose response curves for incubation of PNC-27 with the human squamous cervical cancer cell line HTB-35 (also called SiHa cells) and with the untransformed human squamous cervical cell line, PCS-480. Cell viability was determined using the MTT and LDH release assays. Finally, slot blots and flow cytometry were used to determine membrane expression of HDM-2 using a polyclonal anti-HDM-2 antibody. RESULTS: We found that PNC-27 is cytotoxic even at low doses (IC50=12.4 μM) to the human HTB-35 cervical cancer squamous epithelial cell line but not to a counterpart normal human PCS-480 cell line. We found that HTB-35 cells express high levels of HDM-2 proteins in their membranes both in cell culture and in alcoholic preservative solutions but that the normal PCS-480 cells do not. Consistent with previous results, the data suggest that cervical cancer cells express HDM-2 in their membranes and that this is the target for PNC-27. CONCLUSIONS: PNC-27 kills cervical squamous cancer but not normal cervical cells due to the unique expression of HDM-2 in the cervical squamous cell membranes. Thus, PNC-27 may be an effective drug against this cancer. Our results further suggest that the expression of membrane-bound HDM-2 on cervical cancer cells is stable both in cell culture media and in alcoholic preservative fluid.

OBJECTIVES: Paclitaxel is widely used in the treatment of gynecologic malignancies. It targets tumor cells in the M phase of the cell cycle. Cells in other phases survive the insult and repopulate the tumor. PNC-27 is a peptide synthesized of amino acids of the p53-MDM-2 binding domain. It kills various cancer cell lines in a dose-dependent manner. The goal of this study is to assess ovarian cancer cells' sensitivity to PNC-27 after surviving exposure to paclitaxel and to investigate the potential for synergy between PNC-27 and paclitaxel in the treatment of ovarian cancer. METHODS: The impact of exposure to paclitaxel on the surface expression of MDM-2 was assessed with the use of flow cytometry. For measurement of cytotoxicity in vitro, ID8 cells were exposed to paclitaxel for 12 hours in various concentrations. At 12 hours, the drug containing media was removed and the cells were cultured in media containing various concentrations of PNC-27 for 24 hours. Viability was assessed with the use of an MTT assay. Survival fractions were plotted against drug concentrations and the data were fit to logistic dose-response curves. Isoeffective combinations were used to create isobolograms. The combined treatment with weekly paclitaxel and PNC-27 was tested in an intraperitoneal mouse model of ovarian cancer (ID8). RESULTS: Exposure to paclitaxel rendered incomplete time-dependent killing, while PNC-27 mediated comprehensive, dose-dependent killing of ID8 cells. The cytotoxic effect of PNC-27 was dependent on its binding to MDM-2. Blocking MDM-2 inhibited the killing by PNC-27. ID8 cells surviving paclitaxel demonstrated increased expression of MDM-2 and increased susceptibility to PNC-27. Isobologram for dose combinations that were isoeffective indicates synergistic effect between the 2 agents (Combination index <1). In an in vivo model of ovarian cancer (ID8), the addition of PNC-27 to weekly paclitaxel administration significantly reduces tumor growth. CONCLUSIONS: These data demonstrate synergism between PNC-27 and paclitaxel. PNC-27 could target cells surviving paclitaxel and improve its antitumor effect.

OBJECTIVES: Superparamagnetic iron oxide nanoparticles (SPIONs) have been considered promising non-invasive imaging tools in medicine. However, their high surface energy leads to NPs aggregation, while non-targeted SPIONs can cause cytotoxic effects on normal cells. In this work, we evaluated the in vitro potential of polyethyleneimine (PEI)-SPIONs targeted by PNC-27 peptide as a double targeting agent throughout early cancer diagnosis. MATERIALS AND METHODS: Initially, PEI was conjugated to PNC-27 with HDM-2-binding domain. Then, SPIONs were loaded into PEI-PNC-27 through the ligand exchange method. The physicochemical characteristics of the synthesized NPs were evaluated. The cytotoxicity and targeting efficiency were assayed against HT-29 and CT-26 cell lines along with NIH-3t3 as normal cells by MTT method and Prussian blue staining test, respectively. RESULTS: The mean diameter of synthesized carriers was obtained in the range of 86.6 - 116.1 nm with a positive charge. According to the cytotoxicity results, the binding and uptake abilities of the PNC-27 peptide by cancer cells were significantly higher than that of the NIH-3t3 cells. However, the results were indicative of the more toxic impacts of targeted synthesized NPs against CT-26 cancer cell line when being compared with HT-29 cells, which may be caused by the different cytotoxicity mechanisms of NPs. In addition, the targeted carriers and SPIONs were present inside and around the cells with HDM-2 expression along with only a few non-targeted vectors, while displaying no appearance throughout the normal cell. CONCLUSION: The results indicated the efficiency of targeted PEI-coated SPIONs for cancer diagnostic applications.

BACKGROUND/AIM: Anticancer peptide PNC-27 binds to HDM-2 protein on cancer cell membranes inducing the formation of cytotoxic transmembrane pores. Herein, we investigated HDM-2 membrane expression and the effect of PNC-27 treatment on human non-stem cell acute myelogenous leukemia cell lines: U937, acute monocytic leukemia; OCI-AML3, acute myelomonocytic leukemia and HL60, acute promyelocytic leukemia. MATERIALS AND METHODS: We measured cell surface membrane expression of HDM-2 using flow cytometry. Cell viability was assessed using MTT assay while direct cytotoxicity was measured by lactate dehydrogenase (LDH) release and induction of apoptotic markers annexin V and caspase-3. RESULTS: HDM-2 is expressed at high levels in membranes of U937, OCI-AML3 and HL-60 cells. PNC-27 can bind to membrane HDM-2 to induce cell necrosis and LDH release within 4 h. CONCLUSION: Targeting membrane HDM-2 can be a potential strategy to treat leukemia. PNC-27 targeting membrane HDM-2 demonstrated significant anti-leukemia activity in a variety of leukemic cell lines.

OBJECTIVE: We have previously shown that the anti-cancer peptide PNC-27 kills cancer cells by co-localizing with membrane-expressed HDM-2, resulting in transmembrane pore formation causing extrusion of intracellular contents. We have also observed cancer cell mitochondrial disruption in PNC-27-treated cancer cells. Our objectives are to determine: 1. if PNC-27 binds to the p53 binding site of HDM-2 (residues 1-109) in the cancer cell membrane and 2. if this peptide causes selective disruption of cancer cell mitochondria. METHODS: For aim 1, we incubated MIA-PaCa-2 human pancreatic carcinoma cells with PNC-27 in the presence of a monoclonal antibody against the amino terminal p53 binding site of HDM-2 to determine if it, but not negative control immune serum, blocks PNC-27-induced tumor cell necrosis. For the second aim, we incubated these cells with PNC-27 in the presence of two specific dyes that highlight normal organelle function: mitotracker for mitochondria and lysotracker for lysosomes. We also performed immuno-electron microscopy (IEM) with gold-labeled anti-PNC-27 antibody on the mitochondria of these cells treated with PNC-27. RESULTS: Monoclonal antibody to the p53 binding site of HDM-2 blocks PNC-27-induced cancer cell necrosis, whereas negative control immune serum does not. The mitochondria of PNC-27-treated cancer cells fail to retain mitotracker dye while their lysosomes retain lysotracker dye. IEM of the mitochondria cancer cells reveals gold particles present on the mitochondrial membranes. CONCLUSIONS: PNC-27 binds to the p53 binding site of HDM-2 (residues 1-109) inducing transmembrane pore formation and cancer cell necrosis. Furthermore, this peptide enters cancer cells and binds to the membranes of mitochondria, resulting in their disruption.