A Novel Iodomethylene-dimethyl-dihydropyranone Induces G2/M Arrest and Apoptosis in Human Cancer Cells

Background: The putative pharmacophore of a naturally cytotoxic limonoid haperforin B1, E-5-iodomethylene- 6,6-dimethyl-5,6-dihydropyran-2-one (IDDP) was synthesized and its biological activity was investigated. Materials and Methods: The cytotoxicity of IDDP was assessed using human breast, lung, colorectal and epidermal carcinomas, chronic myeloid leukemia and glioblastoma cell lines. Cell cycle analysis was performed by flow cytometry. The induction of apoptosis was studied by a caspase assay and by annexin V- propidium iodide double staining. The organization of actin and tubulin microfilaments was analysed by immunocytochemical labeling. Results: IDDP was shown to inhibit the growth of a panel of human cancer cell lines independently of their p53 status with IC 50 ranging from 0.07 to 0.50 μM. All the treated cells were arrested in the G 2 /M phase in a time-dependent manner before cell death occurred through an apoptotic pathway. Immunocytochemical studies revealed that the normal organization of microfilaments and microtubules was disrupted in IDDP exposed cells. Conclusion: IDDP can be considered as a promising anticancer agent. Over the past decades, chemotherapy, either alone or in association with surgery and/or radiotherapy, has maintained major importance for the treatment of cancer. However, progressive neoplasic diseases still remain one of the leading causes of death in developed countries. The efficiency of many clinically used anticancer drugs is limited by their toxicities and by intrinsic or acquired drug resistance (1, 2). Thus, there is a critical need for new therapies with improved potency over current treatments, especially against refractory tumors. It has been reported that the antitumor efficacy of several chemotherapeutic molecules correlates with their apoptosis-inducing ability (3). Therefore, it appears essential to identify new compounds able to induce the apoptotic death of tumor cells and overcome the frequently developed tumor resistance to conventional anticancer drugs. The search for antitumor compounds is ongoing over the world. A great number of investigations have focused on the identification of phytochemicals able to inhibit the growth of cancer cells, and several in vitro and in vivo studies have shown that extracts from a number of medicinal plants have anticancer potential (4-8). Harrisonia perforata (Blanco) Merr. belonging to the family of Simaroubaceae is a common bush widely distributed in Southeast Asia. Chemical composition analysis of the leaves of this plant has revealed the presence of several limonoids belonging to the obacunol series (9). We have previously isolated nine new limonoids (10-12) from the leaves of Harrisonia perforata (Simaroubaceae) originated from Central Vietnam. The structure of haperforin B1 (Figure 1), one of the isolated limonoids, presents a complex ring-cleaved rearranged skeleton of the parent tetranortriterpenoid (9). Preliminary biological studies of haperforin B1 suggested its cytotoxic activity. During the course of chemical synthesis of haperforin B1, the intermediate product, E-5-iodomethylene- 6,6-dimethyl-5,6-dihydropyran-2-one (IDDP), which is more toxic to cancer cell lines than haperforin B1 was discovered. This unsaturated δ-lactone moiety of haperforin B1 bearing an acrylic side chain represents an unusual structural element and a possible pharmacophore. A short synthesis of IDDP is described and its in vitro anti-proliferative activity against several chemosensitive and resistant cancer cell lines as well as its ability to induce cell death by apoptosis was investigated.