Apigenin induces apoptosis through proteasomal degradation of HER2/neu in HER2/neu-overexpressing breast cancer cells via the phosphatidylinositol 3-kinase/Akt-dependent pathway

The scientific paper by Tzong-Der Way et al., titled Apigenin Induces Apoptosis through Proteasomal Degradation of HER2/neu in HER2/neu-Overexpressing Breast Cancer Cells via the Phosphatidylinositol 3-Kinase/Akt-Dependent Pathway, investigates the effects of apigenin, a natural compound, on HER2-positive breast cancer cells. HER2/neu is an overexpressed protein in approximately 30% of breast cancers, often leading to more aggressive tumors and resistance to chemotherapy. The authors focus on how apigenin promotes cancer cell death (apoptosis) by targeting HER2/neu, disrupting the protein's signaling pathways. This research is significant as it highlights a natural, low-toxicity option for treating breast cancers that overexpress HER2/neu, which could complement or provide an alternative to existing therapies like trastuzumab (Herceptin).

Apigenin is a natural compound found in foods like parsley, onions, and oranges and is known for its anti-cancer properties . It is non-toxic and doesn’t cause harmful mutations, making it a promising candidate for cancer treatments. In cancer research, apigenin has shown the ability to slow down the growth of cancer cells by targeting specific proteins involved in cancer development.

The HER2/neu protein (also called ErbB2) plays a significant role in aggressive breast cancers . In about 30% of breast cancer cases, HER2/neu is overproduced, leading to faster tumor growth and increased resistance to therapies. These HER2-positive breast cancers are typically more aggressive and more challenging to treat.

Scientists are interested in finding new ways to block HER2/neu and stop tumor growth. This study investigates how apigenin can induce cancer cell death (apoptosis) in breast cancer cells that overexpress HER2/neu, using apigenin as a natural therapeutic agent.

The study focused on different breast cancer cell lines that varied in their HER2/neu expression levels. The researchers used MDA-MB-453 cells, which have high HER2/neu levels, and MCF-7 cells, which have lower, normal levels of the protein. The main goal was to see if apigenin could slow down the growth of HER2/neu-overexpressing cells and push them into apoptosis.

Several laboratory techniques were used to measure the effects:

1. MTT Assay: This test measured how apigenin impacted the growth of cancer cells.
2. Western Blotting: The researchers studied protein levels, focusing on how apigenin affected HER2/neu.
3. Flow Cytometry: This method was used to detect whether the cells were undergoing apoptosis.

The researchers also examined how apigenin influenced the phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathway, a pathway that helps cancer cells survive and resist treatment. Apigenin’s potential to interfere with this pathway was a key focus of the study, as HER2/neu-positive breast cancer cells often rely on it to avoid cell death.

Apigenin was found to selectively block the growth of cancer cells that overexpress HER2/neu. The effect was dose-dependent: higher doses of apigenin (like 40 µM) resulted in more significant inhibition of cancer cell growth. For example, in MDA-MB-453 cells, apigenin blocked 48% of cell growth at this concentration. In contrast, the effect was weaker in MCF-7 cells with lower HER2/neu levels, with only 31% of growth inhibition. The researchers noted, "Apigenin preferentially suppresses growth of HER2/neu-overexpressing breast cancer cell lines."

Apigenin triggered apoptosis in the HER2/neu-overexpressing cancer cells in both a dose- and time-dependent manner. After 36 hours of treatment with 40 µM apigenin, more than half (55.37%) of the MDA-MB-453 cells were undergoing apoptosis. Lower concentrations, such as 20 µM, resulted in less cell death. The study explained that “apoptosis was observed in a significant number of HER2/neu-overexpressing breast cancer cells as early as 36 hours after treatment.”

A major finding was that apigenin caused the proteasomal degradation of HER2/neu, the protein that drives aggressive breast cancer growth. By promoting the breakdown of this protein, apigenin effectively removed a key factor that cancer cells rely on to grow and avoid death. The study noted, "Apigenin promoted the degradation of HER2/neu through polyubiquitination," meaning the protein was tagged for destruction within the cancer cells.

The research also showed that apigenin disrupted the PI3K/Akt signaling pathway. This pathway is often activated by HER2/neu to promote cancer cell survival. Apigenin inhibited PI3K activity and reduced the phosphorylation of Akt, which is essential for cell survival. The researchers noted, "Akt phosphorylation at serine 473 was inhibited in a dose- and time-dependent manner," highlighting how apigenin interferes with this critical cancer survival mechanism.

Apigenin prevented HER2 from forming a complex with HER3, another protein that helps activate the PI3K/Akt pathway. By blocking this interaction, apigenin further weakened the survival pathways of the cancer cells. The research stated, "Dissociation of HER2/neu from HER3 led to a decrease in PI3K docking," showing that apigenin disrupts the cancer cells' internal communication systems.

The study found that apigenin’s effects were linked to the proteasomal degradation. Apigenin tagged the HER2/neu protein with ubiquitin, marking it for breakdown in the cell’s proteasome, the structure responsible for degrading unneeded proteins. The authors observed, "Proteasomal degradation of HER2/neu by apigenin involved polyubiquitination and subsequent hydrolysis."

This study shows that apigenin could be an important natural treatment for breast cancer patients with HER2-positive tumors. The compound’s ability to specifically target and break down HER2/neu in cancer cells while sparing normal cells could make it a valuable tool in cancer therapy.

Currently, treatments for HER2-positive breast cancer, such as trastuzumab (Herceptin), focus on targeting HER2/neu but often come with significant side effects and the risk of drug resistance. Apigenin offers a more natural, less toxic option, as it selectively breaks down HER2/neu without affecting healthy cells. The researchers emphasized that "apigenin provides a low-toxicity alternative for targeting HER2/neu in breast cancer cells."

Since apigenin is found in many everyday foods, it may also have potential as a chemopreventive agent. Regularly consuming apigenin-rich foods could help reduce the risk of developing HER2-positive breast cancers. "Apigenin’s presence in common dietary sources offers a promising chemopreventive strategy for breast cancer," the study noted.

Apigenin’s effects on the PI3K/Akt pathway suggest it could be combined with other cancer treatments targeting different parts of cancer cell survival. Combining apigenin with existing therapies could make these treatments more effective, especially in cases where cancer cells have become resistant to drugs.

This scientific study provides strong evidence that apigenin, a natural compound found in everyday foods, can effectively target and degrade the HER2/neu protein in breast cancer cells. By interfering with the PI3K/Akt signaling pathway and breaking down HER2/neu, apigenin induces apoptosis in HER2-positive breast cancer cells, making it a potential game-changer in cancer treatment.

With its low toxicity and ability to selectively target cancer cells, apigenin presents an exciting opportunity for new breast cancer therapies, especially for patients with aggressive, HER2-overexpressing tumors. Furthermore, its potential as a chemopreventive agent opens new doors for cancer prevention through diet. This study suggests that apigenin could be developed as a natural, safe alternative to traditional cancer treatments like Herceptin, providing a gentler yet practical option for those battling breast cancer.