1-Methyl-3-propyl-7-butylxanthine, a novel biochemical modulator, enhances therapeutic efficacy of adriamycin

Inhibitory effects of caffeine analogues on neoplastic transformation: structure-activity relationship

Some xanthine analogues, including 1,3,7-trimethylxanthine (caffeine) and 1,3-dimethylxanthine (theophylline), have been shown to exert anticancer activities in both cell culture and animal models. The present study focused on the relationship of structure and activity of 50 different caffeine analogues in preventing epidermal growth factor (EGF)-induced malignant transformation of mouse epidermal JB6 promotion-sensitive (P+) Cl41 (JB6 P+) cells. Results indicated that the inhibition of cell transformation by the 1,3,7-trialkylxanthines depends on the number of carbons at the alkyl groups R1 and R3, but not R7. Notably, 1-ethyl-3-hexylxanthine (xanthine 70) was the most effective compound for inhibiting EGF-induced neoplastic transformation among the 50 xanthine analogues tested. The 50% inhibition of cell transformation (ICT(50)) value for xanthine 70 was 48- or 75-fold less than the ICT(50) value of caffeine or theophylline, respectively. Further study revealed that xanthine 70 (5-40 muM) dose dependently inhibited EGF-induced transactivation of activator protein 1 (AP-1), whereas theophylline or caffeine (up to 500 muM) had no effect on AP-1 activity. In addition, xanthine 70 (10 muM) inhibited 12-O-tetradecanoylphorbol-13-acetate- or H-Ras-induced neoplastic transformation in JB6 P+ cells by 78.2 or 62.0%, respectively. Collectively, these results indicated that the number of carbons at R1 and R3 is important for the antitumor-promoting activity of the trialkylxanthines and xanthine 70 might be a promising anticancer agent.

Increased effects of MPDAX, a novel xanthine derivative, on antitumor activity of doxorubicin

To clarify the effect of 1-methyl-3-propyl-7-N,N-dimethylpropylamide-xanthine (MPDAX) on doxorubicin (DOX) transport, we examined the efficacy of MPDAX as an amplifier of the antitumor activity of DOX in mice bearing tumors with different properties as to DOX transport across cell membranes. MPDAX significantly enhanced the DOX-induced antitumor activity on DOX-sensitive tumors. It is expected that the increase in antitumor activity caused by MPDAX contributes to the increased DOX concentration in tumors due to the MPDAX-induced change in DOX transport via the transporter expressed in sensitive tumor cells. In contrast, in M5076, a lower sensitive to DOX, MPDAX decreased the tumor weight by half at an otherwise ineffective dose of DOX. Furthermore, in P388/DOX, DOX has no effect, but MPDAX caused an elevation of the DOX-induced antitumor activity with an increase in the DOX concentration in the tumors. The results suggested that MPDAX is a novel amplifier for antitumor agents as it significantly increased the antitumor activity toward tumors with different properties. The DOX concentrations in the MPDAX + DOX group for all tumor lines were about two-fold those in the DOX alone group. Furthermore, MPDAX and DOX exhibited significant inhibitory effects on uridine and thymidine uptake. It is known that nucleoside transporters increase the membrane permeability of DOX. We speculated that MPDAX inhibits the cell membrane transport of uridine and thymidine via nucleoside transporters. MPDAX, acting via nucleoside transporters, increases the DOX-induced antitumor activity toward many tumor types and is an useful biochemical modulator.

Modulation of doxorubicin sensitivity by a novel organic compound, oxalyl bis (N-phenyl) hydroxamic acid on acetyl aminofluorene-induced preneoplastic hepatocytes

Development of biochemical modulators and application of the same with anticancer drugs is a current approach of modern cancer chemotherapy. We report the effect of two novel hydroxamic acid derivatives, viz. oxaly bis (N-phenyl) hydroxamic acid (OBPHA) and succinyl bis (N-phenyl) hydroxamic acid (SBPHA) on doxorubicin sensitivity and on P-glycoprotein (P-gp) in acetyl amino fluorene (AAF) induced preneoplastic hepatocytes in vitro. OBPHA increases doxorubicin sensitivity in AAF induced preneoplastic hepatocytes compared to normal hepatocytes. SBPHA, with an additional -CH(2)-CH(2)- group than OBPHA does not modulate the sensitivity of doxorubicin. The mechanism of action of OBPHA and SBPHA and their in vivo toxicity on male Swiss mice has been studied. OBPHA in combination with doxorubicin (i.e. OBPHA+doxorubicin) has higher antitumour activity compared to doxorubicin alone group; in consequence, OBPHA may decrease the dose related side effect of doxorubicin.

Effects of xanthine derivatives on the influx and efflux of doxorubicin in P388 and DOX-resistant P388 leukemia cells

It was reported that xanthine derivatives (caffeine and 1-methyl-3-propyl-7-butylxanthine) enhanced the antitumor activity of doxorubicin (DOX) with increasing DOX concentrations in tumors in vivo in our previous papers. In addition, these actions were found to be related to the inhibitory activity toward DOX efflux from tumor cells in vitro. In this study, we searched for novel biochemical modulators of DOX among 3-n-propylxanthines with functional groups at the 1- or 7-position by using an assay system for their inhibitory effect on DOX efflux from P388 leukemia and DOX resistant P388 leukemia (P388/DOX) cells. 1-Substituted xanthines facilitated the DOX efflux from P388 cells. In contrast, among 7-substituted xanthines, XT-141 and XT-139 significantly inhibited the DOX efflux from P388 cells. In addition, XT-141 inhibited the DOX efflux from P388/DOX cells, and P-glycoprotein (P-gp) inhibitor facilitated DOX influx and inhibited DOX efflux from P388/DOX cells in a dose-dependent manner. These results indicated that the resistance of P388/DOX might depend on the over-expression of P-gp, and that XT-141 inhibited DOX efflux through its interaction with P-gp. We suspect that XT-141 is a useful biochemical modulator of DOX in DOX-resistant tumors with over-expression of P-gp in addition in DOX-sensitive tumors.

Structural basis for the binding affinity of xanthines with the DNA intercalator acridine orange

Caffeine (CAF), a methyl-substituted xanthine, interacts with polyaromatic DNA intercalators and has been hypothesized to interfere with their intercalation into DNA. Optical absorption spectroscopy was used to determine the binding affinities (K(assoc)) and structural effects of a series of methyl-substituted xanthines and a series of methyl-substituted uric acids (8-oxoxanthine) with the known DNA intercalator acridine orange (AO). There is evidence that complexation occurred (K(assoc) > or = 150 M(-1); binding curve saturation approximately > or =50%) between AO and 1,7-dimethylxanthine (155 M(-1)), 1,3-dimethylxanthine (theophylline, 157 M(-1)), 1,3,7-trimethylxanthine (CAF, 256 M(-1)), 1,3-dimethyl-8-chloroxanthine (413 M(-1)), 1,3,7,9-tetramethyl-8-oxyxanthine (tetramethyl uric acid or TMU, 552 M(-1)), and theophylline ethylenediamine (aminophylline, 596 M(-1)). No definitive evidence of complexation occurred between AO and 16 other substituted xanthines or purines, although there was some evidence of weak complexation (K(assoc) < 150 M(-1)) between AO and eight of the sixteen. Three common structural similarities were identified among those compounds found to form significant bonding with AO: (i) the N(1) or N(3) on the xanthine structure must be substituted with a methyl group; (ii) oxygen or chlorine substitution at C(8) increases binding affinity to AO when resonate states remain unchanged; and (iii) K(assoc) increases with an increase in number of methyl group substitutions on the 1- or 3-methylxanthine core structure. These results are explained on the basis of complex stabilization due predominately to hydrophobic attraction, with a contribution from charge transfer between donor and acceptor components. This information can be used in the manipulation of the physical or chemical characteristics of biologically active polyaromatic molecules.

Effects of 1-methyl-3-propyl-7-butylxanthine (MPBX) on idarubicin-induced antitumor activity and bone marrow suppression

The effects of 1-methyl-3-propyl-7-butylxanthine (MPBX), a xanthine derivative, on idarubicin (IDA)-induced antitumor activity against P388 leukemia cells (P388) and bone marrow suppression were examined. In P388 tumor-bearing mice, the combination of MPBX with IDA increased the antitumor activity of IDA. The IDA concentration in the tumors in the MPBX combination group increased by 2.0-fold compared to the level in the IDA-alone group. On the other hand, as regards IDA-induced bone marrow suppression, the combination of MPBX with IDA reduced the decrease in the bone marrow cell number by 30% compared to that in the IDA-alone group. In addition, the IDA concentration in the bone marrow cells was decreased by the combination of MPBX with IDA. An in vitro experiment showed that MPBX facilitated IDA influx and suppressed IDA efflux in P388 cells. In conclusion, the combination of MPBX with IDA increased the antitumor activity and decreased the bone marrow suppression. Therefore, we expect that the combination of MPBX with IDA will be useful for leukemia chemotherapy.

Enhanced efficacy of 1-methyl-3-propyl-7-butylxanthine on the antitumor activity of doxorubicin against doxorubicin-resistant P388 leukemia

The effects of 1-methyl-3-propyl-7-butylxanthine (MPBX), a xanthine derivative, on doxorubicin (DOX)-induced antitumor activity against DOX-sensitive P388 leukemia (P388) and DOX-resistant P388 leukemia (P388/DOX) have been examined. In P388-bearing mice, the combination of MPBX with DOX increased the antitumor activity of DOX 1.6-fold. In contrast, in P388/DOX-bearing mice, DOX alone did not decrease the tumor weight, whereas in combination with MPBX it significantly decreased the tumor weight in the control group by 50%. The increase in DOX-induced antitumor activity caused by MPBX was correlated with the DOX concentration in the tumors. The DOX concentration in the tumors of P388- and P388/DOX-bearing mice in the MPBX combination group increased by 1.3-fold and 2.2-fold, respectively, compared to the level in the DOX-alone group. On the other hand, there was no increase in the DOX concentration in the heart or liver in both types of tumor-bearing mice treated with MPBX. In vitro, the facilitated DOX influx and suppressed efflux by MPBX in both types of tumor cells were similar, suggesting that MPBX acts on the same site in both types of cells. P388/DOX overexpressed P-glycoprotein, i.e. the inhibitory order of DOX efflux caused by the inhibitor of P-glycoprotein was P388 < P388/DOX. However, the effect of MPBX was P388 > P388/DOX. Therefore, we expect that the site of attack by MPBX is not P-glycoprotein.