QSAR of Molecular Structure and Cytotoxic Activity of Vitamin K 2 Derivatives with Concept of Absolute Hardness

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1 QSAR of Molecular Structure and Cytotoxic Activity of Vitamin K 2 Derivatives with Concept of Absolute Hardness MARIKO ISHIHARA 1 and HIROSHI SAKAGAMI 2 Divisions of 1 Basic Chemistry and 2 Phamacology, Meikai University School of Dentistry, Sakado, Saitama , Japan Abstract. The correlation between the cytotoxicity of seven vitamin K 2 (menaquinone) derivatives and thirteen chemical descriptors determined by CONFLEX5/CAChe Worksystem 4.9 (PM3) was investigated. After determination of the conformation of the seven vitamin K 2 derivatives and approximation to the molecular form present in vivo (biomimetic) by CONFLEX5, the most stable structure was then determined by CAChe Worksystem 4.9 MOPAC (PM3). The vitamin K 2 derivatives with one to three isoprenyl units [1-3] showed an extended form, whereas those with four to seven isoprenyl units [4-7] displayed a spherical form. The human hepatocellular carcinoma HepG 2 cells displayed a good correlation between cytotoxicity and all the descriptors except for the electron affinity and lowest unoccupied molecular orbital energy (E LUMO ). The absolute hardness (Ë) absolute electron negativity ( ) activity diagram determined by this calculation method may be useful for estimating the cytotoxic activity of vitamin K 2 derivatives against HepG 2 cells. The human squamous cell carcinoma HSC-2 and HSC-3 cells showed similar correlation. The human promyleocytic leukemia HL-60 cells showed the good correlation between cytotoxicity and molecular length. The present study demonstrates for the first time the best correlation between cytotoxic activity and molecular shape or molecular weight of vitamin K 2 derivatives, regardless of the type of target cells. Vitamin K 2 (menaquinone) represents a series of compounds in which the phytyl side chain of phytonadione has been replaced by a side chain built up of 1 to 14 isoprenyl units. It has been reported that vitamin K 2 with four isoprenyl units [4] induced the monocytic differentiation of human myeloid Correspondence to: Mariko Ishihara, Division of Basic Chemistry, Department of Oral Biology and Tissue Engineering, Meikai University School of Dentistry, Sakado, Saitama , Japan. Tel: ex 563, 690, Fax: , mariko@dent.meikai.ac.jp / sakagami@dent.meikai.ac.jp Key Words: Vitamin K 2, cytotoxicity, semiempirical molecularorbital method. leukemia cell lines (1), or apoptosis in isolated osteoclast (2) and human ovary cancer cells (3). We have recently found that vitamin K 2 derivatives [1-3] induced some tumor-specific cytotoxicity and non-apoptotic cell death in oral carcinoma (4). As an extension of the search for the tumor-specific substances targeted against human oral squamous, hepatocellular carcinoma and promyelocytic leukemia cell lines, the quantitative structure-activity relationship (QSAR) of seven vitamin K 2 derivatives [1-7] (Figure 1) was investigated, by conventional and recent techniques of the computation chemistry including the concept of absolute hardness (5-7). Materials and Methods Calculation. The most stable conformation of thirteen imidazole derivatives was calculated by CONFLEX 5 (Confluex Co. Ltd., Tokyo, Japan). The optimization of the structure was done by semiempirical molecular-orbital method (PM3), using CAChe Worksystem 4.9 MOPAC (PM3) (Fujitsu Co. Ltd., Tokyo, Japan). The following descriptors were used: heat of formation (non- COSMO), ionization potential, electron affinity, molecular weight (M.W.), length of molecule, highest occupied molecular orbital energy (E HOMO ), lowest unoccupied molecular orbital energy (E LUMO ), absolute hardness (Ë), absolute electron negativity ( ) and reactivity index (ˆ) (5). The Ë, and ˆ were determined by the following equations: Ë= (E LUMO E HOMO )/2 = (E LUMO + E HOMO )/2 ˆ= 2/2Ë The octanol-water distribution coefficient (log-p) was determined by ACD/Log P DB6.0 (Fujitsu). The QSAR between 50% cytotoxicity (CC 50 ) and each descriptor derived from the molecular structure was investigated by CAChe Worksystem 4.9 project reader. The seven vitamin K 2 derivatives [1-7] were provided by Eisai Co. Ltd. Tokyo, Japan). HSC-2, HSC-4 (supplied by Prof. M. Nagumo, Showa University), HSC-3 (supplied by Prof. Y. Ohmori, Meikai University) and HepG 2 (supplied by Prof. T. Tobe, Showa University) were cultured in DMEM medium supplemented with 10% heat-inactivated FBS in a humidified 5% CO 2 atmosphere. HL-60 cells (supplied by Prof. K. Nakaya, Showa University) were cultured in suspension in RPMI 1640 medium supplemented with /2007 $

2 Figure 1. The structure of vitamin K 2 derivatives used. Figure 2. The most stable conformation of vitamin K 2 derivatives used. Figure 3. continued 4060

3 Ishihara and Sakagami: Estimation of Cytotoxicity of Vitamin K 2 by QSAR Figure 3. continued 10% heat-inactivated FBS. The cytotoxicity assay and determination of CC 50 against these cell lines were performed as described in our recent paper (4). Results and Discussion By determining the conformation of the seven vitamin K 2 derivatives with CONFLEX5, their structure was approximated to the molecular form present in vivo (biomimetic). The most stable structure was next determined by CAChe Worksystem 4.9 MOPAC (PM3) (Figure 2). The 3-dimensional structure of these seven compounds could be roughly separated into two groups: a more extended form [1-3] and a spherical form [4-7]. The molecular length of compounds [4-7] was approximately 10Å, although the isoprenyl unit in the side chain was increased from [4] to [7]. The CC 50 values (determined by experiments) against the HSC-2, HSC-3, HSC-4 and HepG 2 and HL-60 cells, and the chemical descriptors (determined by calculations) are listed in Table I. Using these values, any possible correlations between CC 50 and each of these descriptors were investigated (Figure 3). In the HSC-2 and HSC-3 cells, there was some correlation between CC 50 and eleven of the descriptors (Table II). In the HepG 2 cells, there was close correlation between the CC 50 and the descriptors except for electron affinity and E LUMO (Figure 3B1-11). In the HL-60 cells, there was good correlation only between CC 50 and heat of formation, M.W. and molecular length (Figure 3E1-3). It should be noted that a straight line was obtained when the CC 50 value was plotted vs. log-p for the HepG 2 cells (Figure 3B11) (r 2 =0.696), in contrast to the parabolic curves reported for gallic acid- (8) and coumarin- (9) derivatives. There was also a good correlation between CC 50 and the absolute hardness (Ë) (r 2 =0.755), electron negativity ( ) (r 2 =0.883) and reactivity index (ˆ) (r 2 =0.694). Since ˆ reflects the extent of reactivity, this result suggests a correlation between the reactivity and cytotoxicity of vitamin K 2 derivatives. 4061

4 Figure 3. Correlation between CC 50 value and each descriptor of vitamin K 2 derivatives against HSC-2 (A-1 ~ A-11), HepG 2 (B-1 ~ B-11), HSC-3 (C- 1 ~ C-4), HSC-4 (D-1 ~ D-3) and HL-60 cells (E-1 ~ E-3). Table I. CC 50 and chemical descriptors for vitamin K 2 derivatives. Compd. HL-60 HSC-2 HSC-3 HSC-4 HepG 2 Heat of Electron Ionization log-p E HOMO E LUMO Ë ˆ M.W. Length cells cells cells cells cells formation affinity potential (ev) (ev) (A) CC 50 CC 50 CC 50 CC 50 CC 50 (Kcal/mol) (ev) (ev) (ÌM) (ÌM) (ÌM) (ÌM) (ÌM) [1] [2] [3] [4] [5] [6] [7] log-p, octanol-water distribution coefficient; E HOMO, highest occupied molecular orbital energy; E LUMO, lowest unoccupied molecular orbital energy; Ë, absolute hardness;, absolute electron negativity; ˆ, reactivity index; M.W. molecular weight. 4062

5 Ishihara and Sakagami: Estimation of Cytotoxicity of Vitamin K 2 by QSAR Table II. Correlation coefficients between CC 50 and each chemical descriptor in five different cell lines. Chemical Regression analysis (r 2 ) descriptor HSC-2 HSC-3 HSC-4 HepG 2 HL-60 Heat of formation Elecrton affinity Ionization potential E HOMO E LUMO Ë ˆ Ë- No No No Good No correlation correlation correlation correlation correlation M.W Length log-p E HOMO, highest occupied molecular orbital energy; E LUMO, lowest unoccupied molecular orbital energy; Ë, absolute hardness;, absolute electron negativity; ˆ, reactivity index; M.W. molecular weight; log-p, octanol-water distribution coefficient. The correlation between the electron structure and the cytotoxicity of the vitamin K 2 derivatives, using the absolute hardness (Ë) vs. absolute electron negativity ( ) is shown in Figure 4. Only the HepG 2 cells showed clear-cut correlation in the Ë- activity diagram, where the cytotoxic activity of the vitamin K 2 derivatives depended on both Ë and. When the compounds were within the box (Ë<4.068 and <5.294) (Figure 4), no cytotoxicity was detected. The Ë- activity diagram determined by this calculation method may be useful to estimate the cytotoxic activity of vitamin K 2 derivatives against HepG 2 cells. The best correlation with the cytotoxic activity against any of the cells used in this study was with the molecular shape or molecular weight of the vitamin K 2 derivatives. Acknowledgements This study was supported in part by a Grant-in-Aid from the Ministry of Education, Science, Sports and Culture of Japan (Ishihara, No ). References 1 Sakai I, Hashimoto S, Yoda M, Hida T, Ohsawa S, Nakajo S and Nakaya K: Novel role of vitamin K 2 : a potent inducer of differentiation of various human myeloid leukemia cell lines. Biochem Biophys Res Commun 205: , Kameda T, Miyazawa K, Mori Y, Yuasa T, Shiokawa M, Nakamura Y, Mano H, Hakeda Y, Kameda A and Kumegawa Figure 4. Ë- activity diagram of vitamin K 2 derivatives in HepG 2 cells. Ë, absolute hardness;, absolute electron negativity. M: Vitamin K 2 inhibits osteoclastic bone resorption by inducing osteoclast apoptosis. Biochem Biophys Res Commun 220: , Shibayama-Imazu T, Sonoda I, Sakairi S, Aiuchi T, An W-W, Nakajo S, Itabe H and Nakaya K: Production of superoxide and dissipation of mitochondrial transmembrane potential by vitamin K 2 trigger apoptosis in human ovarian cancer TYK-nu cells. Apoptosis 11: , Sakagami H, Hashimoto K, Suzuki F, Ishihara M, Kikuchi H, Katayama T and Satoh K: Tumor-specificity and type of cell death induced by vitamin K 2 derivatives and prenylalcohols. Anticancer Res: in press. 5 Kobayashi S, Tanaka A and Sameshima K: Relationship between electron structure toxicity and biological activity of environmental hormones (in Japanese). Chemistry and Chemical Industry 52: 41-44, Kobayashi S, Sameshima K, Ishii Y and Tanaka A: Toxicity of dioxins: role of absolute hardness-absolute electronegativity diagram (Ë- diagram) as a new measure in risk assessment. Chem Pharm Bull 43: , Kobayashi S, Hamashima H, Kurihara M, Miyata N and Tanaka A: Hardness controlled enzymes and electronegativity controlled enzymes: role of an absolute hardness-electronegativity (Ë- ) activity diagram as a coordinate for biological activities. Pharm Bull 46: , Ishihara M and Sakagami H: Application of semiempirical method to estimate the cytotoxic activity of gallic acid and its related compounds. Anticancer Res 23: , Ishihara M, Yokote Y and Sakagami H: Quantitative structurecytotoxicity relationship analysis of coumarin and its derivatives by semiempirical molecular-orbital method. Anticancer Res 26: , Received July 30, 2007 Revised October 9, 2007 Accepted October 22,