Natural zeolite clinoptilolite: new adjuvant in anticancer therapy

 

Numerous natural compounds are commonly used for the treatment of various diseases, including green tea and soybean extracts (for review see [20]). Recent findings indicate that dietetic products and antioxidant compounds also have a beneficial effect particularly in cancer patients. In many cases the exact mechanism of their action is not fully understood. In this report we studied the effect of Natural Clinoptilolite Zeolite particles on development of several cancer models in vivo and in vitro.We found that mechanically activated clinoptilolite zeolites act as anticancer therapeutic agents in in vivo animal studies and in tissue culture cell models. Clinoptilolite applied orally in mice and dogs suffering from a variety of tumor types led to a significant shrinkage of some tumors and improvement in overall health status in some animals.

 

The range of effects was diverse, ranging from negative antitumor response, to normalization of biochemical parameters, prolongation of life span, and decrease in tumor size. The best results in animal models were observed in the treatment of skin cancer in dogs, suggesting that adsorption of some active components is responsible for TMA-Z activity (direct contact action). Complementary studies performed in tissue culture indicated that TMA-Z treatment affects proliferation and survival of several cancer cell lines. Addition of TMA-Z inhibited cell proliferation in a concentration-dependent manner, in part due to induction of inhibitors of cycline dependent kinases, inhibition of B/Akt expression and induction of programmed cell death.

 

The work described here was performed with the nontoxic natural, high silica content zeolite, clinoptilolite. The zeolite particles were negatively charged in the entire pH range studied (pH 1–11). Electron microscopy showed the absence of fibers, and most particles were round with very rough surface (data not shown). The absence of fibrous, positively charged particles was encouraging since such particles are present in asbestos and erionite zeolites, which are highly carcinogenic and mutagenic. In addition, activated zeolite particles did not catalyze the production of hydroxyl radicals, unlike asbestos or erionite (data not shown). It seems that absence of fibrous particles capable of producing hydroxyl radicals makes this zeolite sample nontoxic and noncarcinogenic, at least when applied orally.

Silicate and aluminosilicate particulates can interact directly with specific cells and modify their intracellular pathways, leading to the regulation of gene expression. TMA-Z was particularly successful in inhibiting protein kinase B/Akt in in vitro experiments with cancer cells. Such inactivation resulted in growth inhibition and increase in apoptosis of cancer cells. Inhibition of Akt by TMA-Z treatment was shown only in the presence of serum. This indicated that adsorption of serum components can be one of the mechanisms of TMA-Z action in these experiments. Indeed, the addition of EGF to serum-free medium led to activation of Akt, which was also blocked by TMA-Z pretreatment.

 

Adsorption of molecules involved in signal transduction cascades, such as inositol phosphatides and calcium, might also contribute to its therapeutic efficiency. Preliminary lipid adsorption studies show that TMA-Z are strong lipid sorbents. Similar results are observed with adsorption of proteins. Modifications of membrane ordering and interactions of other proteins with membrane proteins might also be involved [21], since membrane translocation is needed for activation of protein kinase B/Akt. It has also recently been shown that the activation of phosphoinositide-3 kinase and Akt is responsible for the ability of transformed epithelial cells to survive without cell attachment. Recent results indicate that constitutive activation of phosphoinositide- 3 kinase in five small-cell lung cancers cell lines studied was responsible for fast growth and anchorage independence of small-cell lung cancer cells [22]. In accordance with this, TMA-Z treatment leads to inhibition of protein kinase B/Akt pathways and subsequent apoptosis in our cell model. Akt has recently been demonstated to inactivate an important cyclin inhibitor and tumor suppressor molecule, p27KIP1 [22].

 

Here we provide evidence that TMA-Z treatment increases levels of p21WAF1CIP1 and p27KIP1 in tumor cell models. It is not yet clear whether inhibition of Akt is involved in regulation of expression of p21WAF1CIP1 and p27KIP1 cell cycle inhibitors. Preliminary results also show that TMA-Z adsorbs and deactivates nitric oxide and other oxidants. In addition, it has recently been reported that antioxidants stimulate the activation of cyclin inhibitor p21WAF1/CIP1 [23]. This molecule is responsible for thearrest of cell growth, and its expression in adenocarcinomasof lung is positively correlated with optimistic survivalprognosis.

 

The present study observed that activated clinoptilolite induces tumor suppressor molecules (both p21 and p27). The mechanisms of action of MZ in vivo remain largely unknown at this time. The indicate that inhibition of proliferation and survival of cancer cells may be part of mechanisms involved in anticancer effect of TMA-Z compounds. More studies on several other aspects of their action including possible immunomodulatoryaction of TMA-Z will be performed in the future. Taken together, this report characterizes cellular effects of the TMA-Z compounds in tissue culture cell models and provides data supporting a role of natural zeolite as an anticancer therapeutic agent in in vivo tumor models.