PNC

The anti-cancer activity and mechanism of PNC-27, which carries a p53 aa12-26-leader sequence connected on its carboxyl terminal end to a trans-membrane-penetrating sequence or membrane residency peptide (MRP), was studied against p53-null K562 leukemia cells. Murine leukocytes were used as a non-cancer cell control. Necrosis was determined by measuring the lactate dehydrogenase (LDH) release and apoptosis was determined by the detection of Caspases 3 and 7. Membrane colocalization of PNC-27 with HDM-2 was analyzed microscopically using fluorescently labeled antibodies against HDM-2 and PNC-27 peptides.

Results found that K562 cells strongly express HDM-2 protein in their membranes and that PNC-27 co-localizes with this protein in the membranes of these cells. PNC-27, but not the negative control peptide PNC-29, is selectively cytotoxic to K562 cells, inducing nearly 100 percent cell killing with LDH release. In contrast, this peptide had no effect on the lymphocyte control cells.

The results suggest that HDM-2 is expressed in the membranes of non-solid tissue tumor cells in addition to the membranes of solid tissue tumor cells. Since K-562 cells appear to be in the stem cell family, the results suggest that early developing tumor cells also express HDM-2 protein in their membranes. Since PNC-27 induces necrosis of K-562 leukemia cells and co-localizes with HDM-2 in the tumor cell membrane as an early event, we conclude that the association of PNC-27 with HDM-2 in the cancer cell membrane results in trans-membrane pore formation which results in cancer cell death, as previously discovered in a number of different solid tissue tumor cells. Since K562 cells lack p53 expression, these effects of PNC-27 on this leukemia cell line occur by a p53-independent pathway.

What Is PNC-27 ?

PNC-27 is a lab-made peptide designed to target and destroy cancer cells specifically. It belongs to a group of experimental proteins called the PNC set, which attach to abnormal (cancerous) cells and cause them to die through cell necrosis. This process leaves normal, healthy cells untouched and unharmed.

The PNC-27 peptide includes an HDM-2 binding part that matches amino acids 12-26 of p53 and a domain that penetrates cell membranes. This allows the peptide to bind to cancer cells and kill them by disrupting the cell membrane.

Studies on animals have shown that PNC-27 effectively targets many types of cancer, including pancreatic cancer, breast cancer, leukemia, melanoma, and others.

Molecular formula: C₁₈₈H₂₉₃N₅₃O₄₄S
CAS Number: 1159861-00-3
Molar Mass: 4031.7g/mol

How it Works

PNC proteins were first developed in 2000 by Drs. Matthew Pincus and Joseph Michl at SUNY Downstate Medical Center in New York. They were originally meant to fight HIV, but PNC-27 proved excellent at binding to cancer cells and killing them while sparing healthy ones.

The PNC-27 cancer peptide is nontoxic and only affects cancer cells, leaving healthy cells alone. It does this by attaching to the membranes of cancer cells and creating holes in them. These holes cause the cells to implode quickly due to the difference in pressure inside and outside the tumor cells.

PNC-27 works because it binds strongly to a protein called HDM-2. Cancer cells have HDM-2 in their membranes. When PNC-27 is given, it goes straight to the HDM-2 in cancer cell membranes. By binding to it, the peptide forms pores or holes in the membrane, leading to membranolysis and the death of the cancer cell.

Clinical Studies

In a 2010 paper from the American Association for Cancer Research, Drs. Ehsan Sarafraz-Yazdi and colleagues explained how PNC-27 works and what its unique action means for cancer research. The authors reported that the peptide forms oligomeric pores in the plasma membrane of tumor cells. These pores do not form in normal, non-tumor cells. They also noted that using MDM2 as a target makes PNC-27 selective for cancer cells because MDM2 is misplaced in their plasma membranes.

Researchers concluded that these findings show the unique location of MDM2 variants in cancer cell membranes. They suggested that this points to great potential for PNC-27 as a future anti-cancer drug, pending clinical trials.

PNC-27 has even been featured in a TED Talk by Dr. Sarafraz-Yazdi, an Assistant Professor in Gynecologic Oncology at SUNY.

Reviews

In animal studies, when PNC-27 is given, certain changes occur in successful cases. Pain levels often drop within about a week. By three weeks, animals may show flu-like symptoms, which likely means their immune systems are reacting to dying cancer cells.

At six weeks, levels of lactate dehydrogenase and bilirubin usually rise. Major tumor breakdown is often seen around ten weeks, when tumors become softer and more flexible.

Tumors might grow slightly at this point due to inflammation from the immune response. By the end of three months, animals typically show more energy and fewer cancer symptoms.

Side Effects

In animal studies, PNC-27 has caused side effects like skin and nose inflammation, watery eyes, dry skin, high blood pressure, headaches, back pain, nosebleeds, rectal bleeding, changes in taste, and excess protein in the urine.

Clinical Trials

In a 2009 study, researchers found that the 3D structure of PNC-27's p53 part matched exactly with the same part bound to HDM-2. This suggested PNC-27 could target HDM-2 in cancer cell membranes.

Cancer cells have high levels of HDM-2 in their membranes, while normal cells do not. This lets PNC-27 target cancer cells selectively, sparing healthy tissue.

Further tests showed that normal cells made vulnerable by adding HDM-2 with a membrane signal became susceptible to PNC-27. This confirmed that PNC-27 targets HDM-2 in cancer membranes and destroys them via membranolysis, without harming healthy cells.

In a 2010 study in Cancer Chemotherapy and Pharmacology, researchers found that PNC-27 works as a whole peptide, not fragments. Knowing it forms pores in cancer membranes, they tested if fragments or the full peptide did this.

Results showed the full peptide creates the pores in cancer cells. Nearby normal cells stayed alive. This means PNC-27 targets specific markers in cancer membranes, and this action extends its lifespan.

Cancer Cells

In a 2006 study in the International Journal of Cancer, researchers saw that PNC-28, a precursor to PNC-27 with a similar structure and effects, stopped pancreatic cancer cell growth in live animals. It caused necrosis, not apoptosis, in various tumor lines, including a rat pancreatic cancer line called BMRPA1, but had no effect on normal cells.

They tested if it could block pancreatic cancer growth in live animals. When given, it completely stopped tumor growth during two weeks of treatment and two weeks after. Then, any regrowth was slow and stayed small compared to controls.

When PNC-27 was given after tumors grew at a distant site, tumor size decreased, followed by slow regrowth much slower than in controls. Researchers concluded it could treat cancer effectively, especially if applied directly to the tumor.

More Studies

In a 2014 study in Annals of Clinical & Laboratory Science, researchers found that the anti-cancer peptide PNC-27 causes tumor cell necrosis in a leukemia cell line that relies on HDM-2 in the plasma membrane.

Building on earlier work showing PNC-27 destroys solid tumor cells by binding HDM-2 in membranes, independent of p53, they tested non-solid tumor cells like leukemia.

They checked if these cells have HDM-2 in membranes and if PNC-27 could kill them the same way.

Results showed non-solid tumor cells do express HDM-2 in membranes. Even more important, PNC-27 induced necrosis through membranolysis via HDM-2 binding, independent of p53, just like in solid tumors.