Anti-Cancer Peptide PNC-27 Kills Cancer Cells by Unique Interactions with Plasma Membrane-Bound hdm-2 and with Mitochondrial Membranes Causing Mitochondrial Disruption.

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.

Ketone Bodies Induce Unique Inhibition of Tumor Cell Proliferation and Enhance the Efficacy of Anti-Cancer Agents.

The ketone bodies, sodium and lithium salts of acetoacetate (AcAc) and sodium 3-hydroxybutyrate (3-HB; commonly called beta-hydroxybutyrate) have been found to inhibit the proliferation of cancer cells. Previous studies have suggested that lithium itself may be an inhibiting agent but may be additive or synergistic with the effect of AcAc. We previously found that sodium acetoacetate (NaAcAc) inhibits the growth of human colon cancer cell line SW480. We report here similar results for several other cancer cell lines including ovarian, cervical and breast cancers. We found that NaAcAc does not kill cancer cells but rather blocks their proliferation. Similar inhibition of growth was seen in the effect of lithium ion alone (as LiCl). The effect of LiAcAc appears to be due to the combined effects of acetoacetate and the lithium ion. The ketone bodies, when given together with chemotherapeutic agents, rapamycin, methotrexate and the new peptide anti-cancer agent, PNC-27, substantially lowers their IC50 values for cancer cell, killing suggesting that ketone bodies and ketogenic diets may be powerful adjunct agents in treating human cancers.