Cyclosporin A as a multidrug-resistant modulator in patients with renal cell carcinoma treated with teniposide

Patients with refractory metastatic renal cell carcinoma (RCC) were enrolled in a phase II study with teniposide (VM26) and cyclosporin A (CSA) to investigate (1) the effect of CSA on the response rate to VM26; and (2) the effect of CSA on the pharmacokinetics and pharmacodynamics of VM26. Sixteen patients initially received VM26 alone (200 mg m(-2) day(-1) i.v.). No objective responses were observed and all patients crossed over to receive at least an additional two courses (range 2-5) of VM26 plus CSA (5 mg kg(-1) 2h(-1) followed by 30 mg kg(-1) 48h(-1) i.v.). At the end of the 2-h loading dose of CSA, whole-blood CSA levels ranged from 2250 to 3830 ng ml(-1), whereas at the end of the 48-h CSA infusion, CSA ranged from 1830 to 4501 ng ml(-1). CSA significantly (P<0.01) increased the area under the curve (AUC) of VM26. The variation in the paired AUC of VM26 was 50%. Terminal half-life of VM26 was significantly (P<0.01) increased (1.72-fold) after CSA administration, whereas the systemic clearance of VM26 was decreased by 1.4-fold (P<0.01). The nadir neutrophil count after VM26 plus CSA (median 700 microl(-1), range <100 to 2860 microl(-1)) was lower than after VM26 alone (median 1900 microl(-1), range 200 to 6000 microl(-1)). Increased haematological toxicity after CSA could be explained by the increase in the VM26 AUC and by inhibition of P-glycoprotein (P-gp) activity in haematopoietic precursor cells. Bilirubin concentrations in the serum were increased after VM26 plus CSA compared with VM26 alone (P<0.01). Among the 15 patients evaluable for response, one had a minor response, eight had stable disease, and six had progressive disease. In conclusion, the dose of CSA we used achieved plasma concentrations within the effective range for P-gp inhibition. CSA affected both the pharmacokinetics and pharmacodynamics of VM26 in the patients, principally by increasing the plasma concentrations of the antineoplastic drug and VM26 haemopoietic toxicity.

Inhibition of Pgp activity and cell cycle-dependent chemosensitivity to doxorubicin in the multidrug-resistant LoVo human colon cancer cell line

To determine whether the cell cycle affects multidrug resistance (MDR) and its reversal, doxorubicin (DOX) cytotoxicity and the effect of inhibition of P-glycoprotein (Pgp) activity by verapamil (VER) were investigated in MDR LoVo cell lines (LoVo-R) in different phases of the cell cycle. Synchronised cells were obtained by exposing cells for 24 h to non-toxic concentrations (40 nmol/l) of methotrexate (MTX), which induced a reversible blockade in the S phase. DOX cytotoxicity was higher if cells were exposed to DOX shortly after the pretreatment with MTX, when most cells were in the S phase of the cell cycle. At that time, the DOX concentration inhibiting cell growth by 50% (IC10) was decreased by approximately 4-fold compared to non-synchronised cycling cells. DOX cytotoxicity remained high during the transition from the S to the G2M phase, but was reduced when the cells had shifted to the G2M phase. Inhibition of Pgp activity by VER (6 mumol/l) enhanced DOX uptake and resulted in an intracellular nuclear compartmentalisation of DOX in LoVo-R cells. These effects were not significantly different (P = NS) in the different phases of the cell cycle. However, similar increases in intracellular DOX uptake due to the inhibitory effect of VER on Pgp greatly potentiated DOX cytotoxicity in LoVo-R cells synchronised in the S or G2M phase compared with non-synchronised cycling cells. The ratio between DOX IC50 in the absence and presence of VER in LoVo-R cells synchronised in the S phase and in cycling cells was 11.1 and 4.1, respectively (P < 0.01). This greater potentiation could be explained by the increased chemosensitivity of the S- and G2M-phase cells to intracellular DOX concentration compared with the non-synchronised cells. Finally, the combination of synchronisation by MTX and of inhibition of Pgp activity by VER produced a considerable reduction in DOX IC50 (approximately 50-fold) in LoVo-R cells compared with the cells not treated with MTX and VER. In conclusion, this study demonstrates that, in LoVo-R cells, the effect of Pgp inhibition on DOX cytotoxicity is dependent on cell cycle phase. DOX cytotoxicity is maximal when inhibition of Pgp activity occurs during the S/G2M phases.

Cellular pharmacology of idarubicinol in multidrug-resistant LoVo cell lines

Idarubicin (IDA) is a daunorubicin (DAU) analog that is being used to treat a variety of human malignancies. The major circulating metabolite of IDA is idarubicinol (IDOL). After administration of IDA to patients, the systemic exposure to IDOL is greater than IDA. We investigated the cytotoxic effect of IDOL in the LoVo human colon-carcinoma cell line and its derivative multidrug-resistant (MDR) sub-lines. In LoVo-sensitive cells, the extracellular IDOL concentration inhibiting cell growth by 50% (IC50) was about 2-fold higher than IDA IC50 but lower than DAU IC50. After continuous exposure of the LoVo parental cells to 20 nM IDOL, 5 drug-resistant clones were obtained. All these clones exhibited an MDR phenotype, indicating that IDOL is involved in multidrug resistance. The resistance index (RI) to IDOL was investigated in LoVo MDR sub-lines obtained by IDOL (LoVo-IDOL-1), IDA (LoVo-IDA-1) and DOX (LoVo-DOX-1) selection. In spite of the drug used for their selection, all the MDR sub-lines exhibited an RI to IDOL lower than DAU and only 2-fold higher than IDA. In LoVo-IDOL-1 cells the RI was 5, 11 and 32 for IDA, IDOL and DAU respectively. Differences in the RI were explained by the greater intracellular tolerance exhibited by MDR cells to DAU than to IDOL and IDA. In the LoVo-IDOL-1 sub-line, the intracellular drug concentration inhibiting cell growth by 50% (IC50int) was higher than in the sensitive cells by 11.4-, 4.7- and 2.8-fold for DAU, IDOL, and IDA respectively. Differences in the intracellular tolerance were explained by the different intracellular distribution of DAU compared with IDOL and IDA. While DAU had a higher nuclear location in LoVo-sensitive cells than in resistant cells, IDOL and IDA maintained the same distribution both in sensitive and in resistant cells. In conclusion, contrary to what has been observed for other derivative metabolites of anthracyclines, the metabolism of IDA to IDOL must not be considered an inactivation pathway. IDOL is a potent inhibitor of cell growth and retains good activity in MDR cells.

Structure-activity relationship of verapamil analogs and reversal of multidrug resistance

We studied the relationship between the chemical structure and multidrug resistance (MDR) reversal activity of racemic verapamil (VER) and 14 VER analogs (VAs). The LoVo-R human colon carcinoma cell line was used as an experimental model. This cell line exhibited a typical MDR phenotype and overexpressed the MDR1 gene products. Key structural features were identified as being related to MDR reversal and cytotoxic activity. In particular, we demonstrated that the methoxy groups in the VER molecule structure [1.7-Bis-(3.4-dimethoxyphenyl)-3-methylaza-7-cyan-8-methyl-n onane] prevented cytotoxicity when the VAs were used alone, whereas the 7-cyan-8-methyl groups were important for MDR reversal activity and interaction with P-glycoprotein (P-gp). Among the VAs tested, the most active compounds were gallopamil, R-isomer of VER (R-VER), and nor-VER, which potentiated doxorubicin (DOX) cytotoxicity by 52.3 +/- 7.2 (n = 3 +/- SD), 38.9 +/- 6.4 (n = 4 +/- SD), and 35.4 +/- 4.3 (n = 3 +/- SD) times, respectively. The reversal activity of these compounds was similar to that of VER, which enhanced DOX cytotoxicity by 41.3 +/- 5.0 (n = 3 +/- SD) times. The potentiation of DOX cytotoxicity was associated with an increase in DOX uptake in LoVo-R cells and with an increased [3H]azidopine P-gp photolabeling inhibition. Some compounds that had a high reversal potency (i.e. R-VER and nor-VER) showed a lower calcium antagonist activity than VER, and seem useful candidates for the treatment of MDR in cancer patients.

Effect of cyclosporine on teniposide pharmacokinetics and pharmacodynamics in patients with renal cell cancer

Five patients with metastatic renal cell cancer (RCC) entered this study. The patients received two courses of teniposide (VM26) (200 mg/m2/24 h i.v.) after which no objective response was observed: three patients had stable disease (SD) and two had progressive disease. Cyclosporine (CsA) (5 mg/kg/2 h followed by 30 mg/kg/48 h i.v.) was then added (VM26/CsA) and at least another two courses were administered. Pharmacokinetic and pharmacodynamic parameters were analyzed. CsA increased the area under curve (AUC) of VM26 in four out of five patients; on average, the variation in the paired AUC of VM26 was 41%. Nadir granulocyte count was lower (average 650/mm3, ranging from < 100 to 1800/mm3) after VM26/CsA than after VM26 (average 1260/mm3, ranging from 200 to 2100/mm3) (p < 0.01). Bilirubin concentration in the serum was increased after VM26/CsA compared with VM26 (p < 0.05). Finally, after two courses of VM26/CsA, four patients had stable disease and one patient had a minor response. In conclusion, the ongoing pilot study indicates that CsA affects both the pharmacokinetics and the pharmacodynamics of VM26.

Percutaneous computed tomography-guided ethanol injection in aldosterone-producing adrenocortical adenoma

The feasibility, safety and effectiveness of percutaneous computed tomography-guided ethanol injection (PEI-CT) was investigated in a patient affected by aldosterone-producing adenoma (APA). A 42-year-old male patient with typical features of hyperaldosteronism presented a solitary left adrenal adenoma measuring 2 cm, with a normal contralateral gland, evidenced by both CT scan and adrenal [75Se-19]-nor-cholesterol scintigraphy. After normalization of potassium plasma levels, 4 ml of sterile 95% ethanol with 0.5 ml of 80% iothalamate sodium was injected. The procedure was completed in about 30 min. No severe pain or local complication was noted. Five hours after PEI, a fourfold and a twofold increase in aldosterone and cortisol plasma levels were observed, respectively. After 11 days on a normal sodium and potassium diet, normal potassium plasma levels and reduced aldosterone plasma levels were present, with reappearance of an aldosterone postural response. Plasma renin activity and aldosterone plasma levels normalized 1 month later, with reappearance also of a plasma renin activity postural response and maintenance of normal potassium plasma levels even on a high sodium and normal potassium diet. The patient has remained hypertensive, although lower antihypertensive drug dosages have been employed. After 17 months, normal biochemical, hormonal and morphological findings were still present. Thus, we suggest PEI-CT as a further alternative approach to surgery in the management of carefully selected patients with APA.

Pharmacokinetics of doxorubicin co-administered with high-dose verapamil

The potential for the modification of the pharmacokinetics of doxorubicin (DOX) concurrently administered with high-dose verapamil (VER) has been investigated in 17 patients with advanced neoplasms refractory to drugs belonging to the multidrug resistance spectrum. Steady-state concentration of DOX, systemic clearance and urinary excretion were analysed. No significant difference was found between the kinetic parameters estimated for DOX at different levels of VER and those reported for doxorubicin as single agent. It can be concluded that VER does not appear to modify DOX kinetics.

Comparison of mechanisms responsible for resistance to idarubicin and daunorubicin in multidrug resistant LoVo cell lines

Two human colon carcinoma drug resistant clones (LoVo-IDA-1 and LoVo-IDA-2) were selected by continuous pressure of LoVo parent cell lines to idarubicin (IDA). Both cell sublines exhibited a typical multidrug resistance (MDR) phenotype but, despite IDA selection, the resistance index (RIext) was higher for daunorubicin (DAU) (RIext = 101-112) than for IDA (RIext = 20-23). A similar pattern of cross-resistance was also observed in two (DOX) doxorubicin-selected LoVo cell lines (LoVo-DOX-1 and LoVo-DOX-2). All the MDR cell lines exhibited decreased drug accumulation and increased intracellular drug tolerance as evidenced by the greater intracellular amount of drug required to cause a 50% growth inhibition (IC50int) compared to their parent cell line. The differences between DAU and IDA RIext exhibited by MDR cells were a function of intracellular resistance. DAU IC50int was 13.9 and 14.9 times higher in LoVo-IDA-1,2 and 6.4 and 6.2 in LoVo-DOX-1,2 cell lines, respectively, than in LoVo-sensitive cells, whereas IDA IC50int was only 3.6 and 3.2 times higher in LoVo-IDA-1,2 and 2.2 and 2.3 in LoVo-DOX-1,2 cell lines, respectively. Conversely, variations in IDA accumulation between resistant and sensitive cells were similar to those observed for DAU [the ratios between DAU uptake in sensitive and resistant cells were almost identical (P = NS) to those observed for IDA]. Differences between IDA and DAU intracellular distribution accounted for the relatively higher DAU intracellular resistance. In fact nuclear/cytoplasmic (N/C) DAU fluorescence ratio was higher (P < 0.01) in sensitive (N/C = 3.4 +/- 2.7) than in MDR cells (N/C ranging from 0.31 +/- 0.2 to 0.41 +/- 0.1). In contrast, no significant (P = NS) differences were observed in IDA N/C ratios between sensitive and MDR cells (N/C ranging from 0.16 +/- 0.1 to 0.20 +/- 0.1). In MDR cells, 1-hr VER (10 microM) treatment partially reverted both DAU N/C ratios and intracellular DAU resistance but neither changes in IDA N/C ratios nor variation in intracellular IDA resistance were observed following VER exposure. In conclusion, the greater intracellular drug tolerance that MDR cells show for DAU compared to IDA makes IDA more effective than DAU in MDR cells overexpressing P-glycoprotein (P-gp).

Increased chemosensitivity to doxorubicin of intrinsically multidrug-resistant human colon carcinoma cells by prolonged exposure to verapamil

Resistance modifying agents (RMA) such as verapamil (VER) have proved effective in reversing multidrug resistance (MDR) in many in vitro experimental models, but clinical results with RMA have been disappointing. To clarify this apparent discrepancy we have evaluated the cytotoxic effects of doxorubicin (DOX) plus VER in four human colon carcinoma (HCOC) cell lines (LoVo, DLD-1, SW948, SW1116). These lines were selected on the basis of their levels of mdr1 mRNA being similar to those expressed by HCC obtained from non-drug-treated patients. In all cell lines the sensitising effect of VER on DOX cytotoxicity was schedule-dependent and maximal potentiation of DOX cytotoxicity was obtained by exposure to VER for a time > or = the cells' population doubling time.