Reversal of multidrug resistance by novel verapamil analogs in cancer cells

Meyeroguilline E, a New Isoindolinone Alkaloid from the Poisonous Mushroom Chlorophyllum molybdites, and Identification of Compounds with Multidrug Resistance (MDR) Reversal Activities

Three isoindolinone alkaloids (1-3), including one new isoindolinone-type alkaloid, meyeroguilline E (1), and six other known compounds (4-9) were isolated from the poisonous mushroom Chlorophyllum molybdites (Agaricaceae). The structure of the new compound was determined using extensive spectroscopic analyses via one-dimensional (1D) and two-dimensional (2D) NMR data interpretation and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). To the best of our knowledge, compound 1 is the first example of a natural isoindolinone with a butanoic acid moiety, and this study is the first to detect the other known compounds (2-9) in C. molybdites. The isolated compounds (1-9) were examined for their multidrug resistance (MDR) reversal activity against MES-SA, MES-SA/DX5, HCT15, and HCT15/CL02 human cancer cells. Based on the results, 20 μM of compounds 3 and 6 slightly potentiated paclitaxel (TAX)-induced cytotoxicity in MES-SA/DX5, HCT15, and HCT15/CL02 cells; however, the compounds had no effect on the cytotoxicity against MES-SA and nonMDR cells.

Hexane fraction of adlay (Coix lachryma-jobi L.) testa ethanolic extract inhibits human uterine sarcoma cancer cells growth and chemosensitizes human uterine sarcoma cells to doxorubicin

BACKGROUND

Cancer has remained among the top ten causes of death in Taiwan since 1982. Uterine sarcoma is a rare gynecologic cancer, and chemotherapy is one type of cancer treatment. Doxorubicin (Dox) is widely used for treating several cancers, including uterine sarcoma, however, multidrug resistance (MDR) is a major clinical problem and a critical cause of treatment failure. The ethanolic extracts of adlay testa (ATE) exhibited significant anticancer activities against many cancer types.

PURPOSE

In this study we investigated the antitumor effects of the hexane fraction of the adlay testa ethanolic extracts (ATE-Hex) on the human uterine sarcoma cancer cell line MES-SA, as well as on the multidrug-resistant human uterine sarcoma cancer cell line MES-SA/Dx5.

METHODS

The MTT assay was performed to assess the effects of the extracts of different parts of the adlay on the proliferation of human uterine sarcoma cells (MES-SA and MES-SA/Dx5) and human uterine smooth muscle cells (HUtSMCs). To determine whether ATE-Hex has a chemosensitizing effect on drug-resistant uterine sarcoma cells, the MTT assay was performed to examine the synergistic effects of ATE-Hex, the chemotherapeutic drug Dox alone, and in combination. Rhodamine accumulation was analyzed using fluorescence detection. Apoptotic cells were analyzed via flow cytometry. In addition, employing a flame ionization detector (GC/FID) gas chromatography was also developed as the analysis platform for ATE-Hex.

RESULTS

The results demonstrated that ATE-Hex exhibited the best effects of inhibition on MES-SA and MES-SA/Dx5 cells. Co-treatment of ATE-Hex and Dox could synergistically inhibit the proliferation of cancer cells. ATE-Hex reduced the rhodamine efflux in MES-SA/Dx5 cells, indicating that ATE-Hex could reduce the expression of P-gp. In addition, our results showed that treatment with ATE-Hex alone or in combination with Dox significantly inhibited the growth of cancer cells and induced apoptosis by increasing the sub-G1 phase and poly(ADP-ribose) polymerase (PARP) being cleaved. Flow cytometry revealed that ATE-Hex induced apoptosis.

CONCLUSION

These results suggest that ATE-Hex can inhibit human uterine sarcoma cancer cells by inducing apoptosis and increasing the chemosensitivity of the multidrug-resistant human uterine sarcoma cancer cell MES-SA/Dx5 to Dox. Furthermore, the combination of ATE-Hex and Dox could decrease MDR and increase the synergistic effect.

Reversal of paclitaxel resistance in human ovarian cancer cells with redox-responsive micelles consisting of α-tocopheryl succinate-based polyphosphoester copolymers

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is a major obstacle in achieving the therapeutic benefits of paclitaxel (PTX) in the treatment of human ovarian carcinoma. This study is aimed to develop an efficient PTX drug delivery approach to overcome MDR. Redox-responsive micelles consisting of amphiphilic polymers containing disulfide linkages, ie, poly (phosphate ester)-SS-D-α-tocopheryl succinate (POPEA-SS-TOS, PSST) were prepared. PTX-loaded PSST micelles (PTX/PSST-M) designed to display synergistic functions, including reversible inhibition of P-gp, intracellular redox-sensitive release and potent anticancer activities. The average size of PTX/PSST-M was 68.1±4.9 nm. The encapsulated PTX was released quickly through redox-triggered dissociation of micelles. The inhibition of P-gp activity and enhanced cellular accumulation of the PSST micelles were validated. PTX/PSST-M showed significantly increased cytotoxicity against PTX-resistant human ovarian cancer A2780/PTX cells: when the cells were treated with PTX/PSST-M for 48 h, the equivalent IC₅₀ value of PTX was reduced from 61.51 to 0.49 μmol/L. The enhanced cytotoxic effects of PTX/PSST-M against A2780/PTX cells were attributed to their synergistic effects on reducing the mitochondrial transmembrane potential, ATP depletion, ROS production, and activation of apoptotic pathways. Furthermore, PTX/PSST-M significantly increased cell apoptosis/necrosis and cell cycle arrest at the G₂/M phase in A2780/PTX cells. These results demonstrate that the redox-responsive PSST micelles inhibit P-gp activity and have a good potential to effectively reverse PTX resistance in human ovarian carcinoma cells by activating intrinsic apoptotic pathways.

TPGS2k/PLGA nanoparticles for overcoming multidrug resistance by interfering mitochondria of human alveolar adenocarcinoma cells

In this study, we successfully synthesized d-α-tocopheryl polyethylene glycol 2000 succinate (TPGS2k) and prepared TPGS2k-modified poly(lactic-co-glycolic acid) nanoparticles (TPGS2k/PLGA NPs) loaded with 7-ethyl-10-hydroxycamptothecin (SN-38), designated TPGS2k/PLGA/SN-38 NPs. Characterization measurements showed that TPGS2k/PLGA/SN-38 NPs displayed flat and spheroidal particles with diameters of 80-104 nm. SN-38 was encapsulated in TPGS2k emulsified PLGA NPs with the entrapment efficiency and loading rates of SN-38 83.6 and 7.85%, respectively. SN-38 could release constantly from TPGS2k/PLGA/SN-38 NPs in vitro. TPGS2k/PLGA/SN-38 NPs induced significantly higher cytotoxicity on A549 cells and the multidrug resistance (MDR) cell line (A549/DDP cells and A549/Taxol cells) compared with free SN-38. Further studies on the mechanism of the NPs in increasing the death of MDR cells showed that following the SN-38 releasing into cytoplasm the remaining TPGS2k/PLGA NPs could reverse the P-gp mediated MDR via interfering with the structure and function of mitochondria and rather than directly inhibiting the enzymatic activity of P-gp ATPase. Therefore, TPGS2k/PLGA NPs can reduce the generation of ATP and the release of energy for the requisite of P-gp efflux transporters. The results indicated that TPGS2k/PLGA NPs could become the nanopharmaceutical materials with the capability to reversal MDR and improve anticancer effects of some chemotherapy drugs as P-gp substrates.

Disruption of vitellogenesis and spermatogenesis by triclabendazole (TCBZ) in a TCBZ-resistant isolate of Fasciola hepatica following incubation in vitro with a P-glycoprotein inhibitor

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Sligo TCBZ-resistant fluke isolate was used for these experiments and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. In the first experiment, flukes were initially incubated for 2 h in R(+)-VPL (100 μm), then incubated in R(+)-VPL+triclabendazole sulphoxide (TCBZ.SO) (50 μg mL−1, or 133·1 μm) until flukes ceased movement (at 9 h post-treatment). In a second experiment, flukes were incubated in TCBZ.SO alone and removed from the incubation medium following cessation of motility (after 15 h). In the third experiment, flukes were incubated for 24 h in R(+)-VPL on its own. Changes to the testis tubules and vitelline follicles following drug treatment and following Pgp inhibition were assessed by means of light microscope histology and transmission electron microscopy. Incubation of the Sligo isolate in either R(+)-VPL or TCBZ.SO on their own had a limited impact on the morphology of the two tissues. Greater disruption was observed when the drugs were combined, in terms of the block in development of the spermatogenic and vitelline cells and the apoptotic breakdown of the remaining cells. Sperm formation was severely affected and abnormal. Large spaces appeared in the vitelline follicles and synthesis of shell protein was disrupted. The results of this study support the concept of altered drug efflux in TCBZ-resistant flukes and indicate that drug transporters may play a role in the development of drug resistance.

Increased susceptibility of a triclabendazole (TCBZ)-resistant isolate of Fasciola hepatica to TCBZ following co-incubation in vitro with the P-glycoprotein inhibitor, R(+)-verapamil

A study was carried out to investigate whether the action of triclabendazole sulphoxide (TCBZ.SO) against the liver fluke, Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for this in vitro study and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. For experiments with the Oberon isolate, flukes were incubated for 24 h with either R(+)-VPL (1×10-4 m) on its own, TCBZ.SO (15 μg mL-1) alone, a combination of R(+)-VPL (1×10-4 m) plus TCBZ.SO (15 μg mL-1), TCBZ.SO (50 μg mL-1) on its own, or a combination of TCBZ.SO (50 μg mL-1) plus R(+)-VPL (1×10-4 m). They were also incubated in TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive; and in TCBZ.SO (50 μg mL-1) alone for a time to match that of the combination inactivity time. Flukes from the Cullompton isolate were treated with either TCBZ.SO (50 μg mL-1) alone or in combination with R(+)-VPL (1×10-4 m) until they became inactive, or with TCBZ.SO (50 μg mL-1) alone time-matched to the combination inactivity time. Morphological changes resulting from drug treatment and following Pgp inhibition were assessed by means of scanning electron microscopy. Incubation in R(+)-VPL alone had a minimal effect on either isolate. TCBZ.SO treatment had a relatively greater impact on the TCBZ-susceptible Cullompton isolate. When R(+)-VPL was combined with TCBZ.SO in the incubation medium, however, the surface disruption to both isolates was more severe than that seen after TCBZ.SO treatment alone; also, the time taken to reach inactivity was shorter. More significantly, though, the potentiation of drug activity was greater in the Oberon isolate; also, it was more distinct at the higher concentration of TCBZ.SO. So, the Oberon isolate appears to be particularly sensitive to efflux pump inhibition. The results of this study suggest that enhanced drug efflux in the Oberon isolate may be involved in the mechanism of resistance to TCBZ.

Influence of concurrent medications on outcomes of men with prostate cancer included in the TAX 327 study

OBJECTIVES

The TAX 327 trial was pivotal in establishing docetaxel in castration refractory metastatic prostate cancer. Various commonly prescribed and over-the-counter co-administered medications are thought to exhibit anti-neoplastic properties and/or could potentially have pharmacokinectic interactions with docetaxel lessening the effectiveness of chemotherapy.

METHODS

To examine the effect of on prostate cancer outcomes within this trial, we examined overall survival, prostate-specific antigen (PSA) response, percent PSA reduction, pain response and QOL responses for 14 families of medications including metformin, digoxin, verapamil, proton pump inhibitors, nitrates, statins, cox-2 inhibitors, warfarin, heparins, ascorbic acid, selenium, tocopherol, antidepressants and erythropoietin.

RESULTS

Our findings did not reveal any medication that had a significant additive or synergistic effect with docetaxel. We did note, however, that patients on digoxin or verapamil had poorer overall survival, possibly due to a trend of fewer cycles of administered chemotherapy being administered to the verapamil group, consistent with a pharmacokinectic interaction.

CONCLUSIONS

These data are only hypothesis-generating given the statistical limitations, but may form a basis for similar future analysis in other malignancies. The data suggest the need to be aware of pharmacokinectic interactions with medications that may interact with docetaxel.

Hydrocinchonine, cinchonine, and quinidine potentiate paclitaxel-induced cytotoxicity and apoptosis via multidrug resistance reversal in MES-SA/DX5 uterine sarcoma cells

Multidrug resistance (MDR) is one of important issues to cause the chemotherapy failure against cancers including gynecological malignancies. Despite some MDR reversal evidences of natural compounds including quinidine and cinchonine, there are no reports on MDR reversal activity of hydrocinchonine with its analogues quinidine and cinchonine especially in uterine sarcoma cells. Thus, in the current study, we comparatively investigated the potent efficacy of hydrocinchonine and its analogues quinidine and cinchonine as MDR-reversal agents for combined therapy with antitumor agent paclitaxel (TAX). Hydrocinchonine, cinchonine, and quinidine significantly increased the cytotoxicity of TAX in P-glycoprotein (gp)-positive MES-SA/DX5, but not in the P-gp-negative MES-SA cells at nontoxic concentrations by 3-(4,5-dimethylthiazol-2-yl)-2,5--diphenyltetrazolium bromide (MTT) assay. Rhodamine assay also revealed that hydrocinchonine, cinchonine, and quinidine effectively enhanced the accumulation of a P-gp substrate, rhodamine in TAX-treated MES-SA/DX5 cells compared with TAX-treated control. In addition, hydrocinchonine, cinchonine, and quinidine effectively cleaved poly (ADP-ribose) polymerase (PARP), activated caspase-3, and downregulated P-gp expression as well as increased sub-G1 apoptotic portion in TAX-treated MES-SA/DX5 cells. Taken together, hydrocinchonine exerted MDR reversal activity and synergistic apoptotic effect with TAX in MES-SA/DX5 cells almost comparable with quinidine and cinchonine as a potent MDR-reversal and combined therapy agent with TAX.

Quinoline derivative KB3-1 potentiates paclitaxel induced cytotoxicity and cycle arrest via multidrug resistance reversal in MES-SA/DX5 cancer cells

AIMS

The resistance to chemotherapeutic drugs is a major problem for successful cancer treatment. Multidrug resistance (MDR) phenotype is characterized by over-expression of P-glycoprotein (P-gp) on the cancer cell plasma membrane that extrudes drugs out of the cells. Therefore, novel MDR reversal agents are desirable for combination therapy to reduce MDR and enhance anti-tumor activity. Thus, the present study was aimed to evaluate the potent efficacy of novel quinoline derivative KB3-1 as a potent MDR-reversing agent for combined therapy with TAX.

MAIN METHODS

MDR reversing effect and TAX combined therapy were examined by Rhodamine accumulation and efflux assay and Confocal immunofluorescence microscopy, Western blotting, TUNEL assay, and cell cycle analysis.

KEY FINDINGS

The discovery of quinoline-3-carboxylic acid [4-(2-[benzyl-3[-(3,4-dimethoxy-phenyl)-propionyl]-amino]-ethyl)-phenyl]-amide (KB3-1) as a novel MDR-reversal agent. KB3-1 significantly enhanced the accumulation and retention of a P-gp substrate, rhodamine-123 in the P-gp-expressing MES-SA/DX5 uterine sarcoma cells but not in the P-gp-negative MES-SA cells at non-toxic concentrations of 1 microM and 3 microM. Similarly, fluorescence microscopy observation revealed that KB3-1 reduced the effluxed rhodamine-123 expression on the membrane of MES-SA/DX5 cells. Consistent with decreased P-gp pumping activity, confocal microscopic observation revealed that KB3-1 effectively diminished the expression of P-gp in paclitaxel (TAX)-treated MES-SA/DX-5 cells. Furthermore, Western blotting confirmed that KB3-1 reduced P-gp expression and enhanced cytochrome C release and Bax expression in TAX treated MES-SA/DX-5 cells. In addition, KB3-1 enhanced TAX-induced apoptotic bodies in MES-SA/DX5 cells by TdT-mediated-dUTP nick-end labeling (TUNEL) staining assay aswell as potentiated TAX- induced cytotoxicity, G2/M phase arrest and sub-G1 apoptosis in MES-SA/DX5 cells but not in MES-SA cells. Interestingly, KB3-1 at 3 microM had comparable MDR-reversal activity to 10 microM verapamil, a well-known MDR- reversal agent.

SIGNIFICANCE

KB3-1 can be a MDR-reversal drug candidate for combination chemotherapy with TAX.

The Effects of Crinum asiaticum on the Apoptosis Induction and the Reversal of Multidrug Resistance in HL-60/MX2

The present study investigated the anti-proliferative and chemosensitizing effects of Crinum asiaticum var. japonicum against multi-drug resistant (MDR) cancer cells. The 80% methanol extract, chloroform (CHCI3) fraction and butanol (BuOH) fraction of C asiaticum inhibited the growth of mitoxantrone (MX) resistant HL-60 (HL-60/MX2) cells. When HL-60/MX2 cells were treated with the CHCI3 and BuOH fractions, DNA ladder and sub-G1 hypodiploid cells were observed. Furthermore, the fractions reduced Bcl-2 mRNA levels, whereas Bax mRNA levels were increased. These results suggest that the inhibitory effect of C. asiaticum on the growth of the HL-60/MX2 cells might arise from the induction of apoptosis. Treatment of HL-60/MX2 cells with the fractions markedly decreased the mRNA levels of the multi-drug resistance protein-1 and breast cancer resistance protein. The CHCI3 fraction and hexane fraction increased MX accumulation in HL-60/MX2 cells. These results imply that the CHCI3 fraction of C asiaticum plays a pivotal role as a chemosensitizer. We suggest that components of C asiaticum might have a therapeutic potential for the treatment of MDR leukemia.

Multidrug reverting activity toward leukemia cells in a group of new verapamil analogues with low cardiovascular activity

The development of refractory disease is often associated with the overexpression of multidrug resistance (MDR) proteins, especially in several hematological malignancies, such as acute myeloid leukemias (AML), multiple myeloma (MM) and non-Hodgkin's lymphomas (NHL). Since the recognition of these proteins, several attempts have been made to modulate their expression and activity (protein kinase C inhibitors, anti-MDR-1 oligonucleotides, pharmacological competitors and transcriptional inhibitors). Six new compounds (MM 36, CTS 4, CTS 9, CTS 12, CTS 27 and CTS 41), derived from verapamil (VRP), were designed and synthesized to improve their MDR-reverting activity and reduce cardiovascular effects. Cytotoxicity (WST-1 methods) and functional (calcein-acetoxymethyl (Calcein-AM)) assays were performed on a resistant cell line K-562/doxR and on the mononuclear cells (MNCs) of patients with AML. Furthermore, the six molecules were tested for their vasodilator, inotropic and chronotropic activity on guinea pig aortic strip and isolated atrium preparations, respectively. Comparison between survival plots and relative ID50, obtained from the K-562/doxR cells treated with Idarubicin (IDA), in the presence or absence of inhibitors, showed that these compounds function well. All the resistance modifying agents potentiated IDA activity inducing a significant reduction (P<0.01) in ID(50) values in comparison to VRP at each of the concentrations tested, but MM 36, CTS 27 and CTS 41 demonstrated the strongest activity. Results obtained from the MNCs were superimposible to K-562/doxR. Further studies on pump functional analysis confirmed the cytotoxic test results: MM 36, CTS 27 and CTS 41 showed a striking inhibition of P-glycoprotein (Pgp) efflux in K-562/doxR and MNCs. Cardiovascular activity of MM 36, CTS 27 and CTS 41, that are the most interesting compounds as MDR inhibitors, followed this course: MM 36>CTS 27>CTS 41, the last one presenting no cardiovascular activity. Chemosensivity to IDA in K-562/doxR cells and AML blasts could be enhanced in vitro by the adjuvant use of the six new VRP analogues. Compared to VRP, all the new compounds presented good MDR-reverting- and reduced cardiovascular activities along with no vasorelaxant effects. The particularly favourable results in some cases (MM 36, CTS 27 and CTS 41) suggests that anti-MDR activity should be further evaluated in clinical trials in patients with myeloid malignancies.

Novel oral formulation of paclitaxel inhibits neointimal hyperplasia in a rat carotid artery injury model

BACKGROUND

Paclitaxel has been shown to inhibit vascular smooth muscle cell migration and proliferation contributing to neointimal formation. This study tested whether novel oral formulations of paclitaxel can prevent neointimal formation in a rat carotid artery injury model.

METHODS AND RESULTS

Oral formulations of paclitaxel (0, 5, 7.5, or 10 mg/kg) were administered to 40 rats by gavage for 5 days after injury. The peak plasma levels of paclitaxel administered at 5, 7.5, and 10 mg/kg were 61+/-16, 89+/-22, and 108+/-28 nmol/L, respectively. Treatment effects were assessed 11 days after injury. The angiographic minimum luminal diameters of the oral paclitaxel groups treated at 5, 7.5, and 10 mg/kg were 6.28+/-2.09, 6.97+/-1.79, and 7.97+/-1.57 AU, and these were significantly larger than that of the control group (4.67+/-1.45 AU). The oral paclitaxel groups (5, 7.5, 10 mg/kg; 0.05+/-0.05, 0.04+/-0.03, 0.05+/-0.03 mm2) showed significant neointimal formation reductions versus the control group (0.13+/-0.05 mm2). All rats survived to study completion. Only 2 animals in the 10 mg/kg group experienced weight loss ( approximately 10%) and loose stools between 4 and 6 days after injury. All other animals appeared healthy during the study. For comparison purposes, intraperitoneal formulations of paclitaxel (0 or 2 mg/kg) were administered by injection to 15 rats. We confirmed that the intraperitoneal administration of paclitaxel also effectively inhibited neointimal formation.

CONCLUSIONS

Oral formulations of paclitaxel provide an effective means of inhibiting proliferative response to vascular injury in the rat. Thus, oral formulations of paclitaxel may prevent human restenosis without significant toxicity.

Differential effects of the optical isomers of KR30031 on cardiotoxicity and on multidrug resistance reversal activity

The present study was performed to compare the cardiovascular adverse effects of verapamil, KR30031 and their optical isomers, and also to measure their ability to overcome multidrug resistance (MDR). The R-isomer of KR30031 (R-KR30031) was equipotent with the S-isomer of KR30031 (S-KR30031) and 25-fold less potent than the R-isomer of verapamil (R-verapamil) in relaxing the aorta isolated from rat (EC50: 11.8, 10.2 and 0.46 microM, respectively). The effect of R-KR30031 in decreasing left ventricular pressure of heart isolated from rat was 2- and 267-fold smaller than those of S-KR30031 and R-verapamil, respectively (EC50: 23.9, 9.4 and 0.089 mM, respectively). The hypotensive effect of R-KR30031 in rat was about 2- and 23-fold smaller than those of S-KR30031 and R-verapamil, respectively (ED20: 1.15, 0.60 and 0.05 mg/kg, respectively). On the other hand, R-KR30031 elicited potency similar to those of S-KR30031 and R-verapamil in enhancing the paclitaxel-induced cytotoxicity to HCT15/CL02 and MES-SA/DX5 cells that reveal high levels of P-glycoprotein expression (IC50: 3.11, 3.04 and 2.58 microM, respectively). In addition, the intrinsic cytotoxicity of R-KR30031 in HCT15/CL02 and MES-SA/DX5 cells was observed only at the very high concentration of 100 microM. All these results suggest that R- and racemic KR30031 are active modulators of MDR with potentially minimal cardiovascular adverse activity.

Effects of KR-30035, a novel multidrug-resistance modulator, on the cardiovascular system of rats in vivo and on the cell cycle of human cancer cells in vitro

The present study was performed to evaluate the adverse effects of KR-30035, a multidrug-resistance modulator, on the cardiovascular system in vivo, along with its effect on paclitaxel-induced cell cycle arrest in cultured cancer cells. In anesthetized rats, KR-30035 was about 10-fold less potent than verapamil in lowering blood pressure (i.v. ED20: 0.320+/-0.052 and 0.034+/-0.005 mg/kg, respectively) and in producing electrocardiogram changes. In conscious spontaneously hypertensive rats, verapamil caused a significant antihypertensive effects at the doses tested (p.o. ED20, 7.8+/-4.0 mg/kg), whereas KR-30035 did not significantly change either the blood pressure or the heart rate at any doses tested (up to 100 mg/kg). The estimated i.v. LD50 values in mice were 5.9 and 48.9 mg/kg for verapamil and KR-30035, respectively. In the presence of 10 microM KR-30035, paclitaxel (1 microM) when added to cultures of HCT15/CL02 human cancer cells greatly shifted the cell population from the G0/G1 phases towards G2/M phases (from 42.4, 30.3 and 27.3 to 14.6, 21.5 and 63.9% for the G0/G1, S and G2/M phases, respectively), with a similar magnitude to that of 10 microM verapamil (14.0, 15.7 and 70.3%, respectively). These results suggest that KR-30035 has weaker in vivo effects on the cardiovascular system compared with verapamil, while potentiating the G2/M arresting effect of paclitaxel on the cell cycle.