H.M. Pinedo

Taxanes: A New Class of Antitumor Agents

Taxanes belong to a new group of antineoplastic agents with a novel mechanism of action for a cytotoxic drug. They promote microtubule assembly and stabilize the microtubules. Paclitaxel, the first agent in this group to become available, was isolated from the Pacific yew, Taxus brevifolia, in 1971. In preclinical and clinical studies, paclitaxel and its semisynthetic analog docetaxel exhibit significant antitumor activity. This review deals with the physicochemical properties, pharmacology, and results of preclinical and clinical trials of the taxanes.

Cortisol is transported by the multidrug resistance gene product P-glycoprotein

The physiology of the multidrug transporter P-glycoprotein (Pgp) is still poorly understood. We now show evidence that cell lines with a high expression of Pgp display a reduced accumulation of cortisol and an ATP-dependent outward transport of the hormone. Cortisol efflux from Pgp negative cells does not have such an active component. Further we show that the steroid hormones cortisol, testosterone, and progesterone cause an immediate, dose-dependent increase of daunorubicin accumulation in Pgp overexpressing cells. These effects are particularly apparent for the more lipophilic steroids. These results demonstrate that Pgp may function as a transporter for cortisol and suggest a physiological role of the protein in steroid handling by organs such as the adrenal.

High-performance liquid chromatographic procedure for the quantitative determination of paclitaxel (Taxol) in human plasma.

An isocratic high-performance liquid chromatographic method has been developed and validated for the quantitative determination of paclitaxel (Taxol), a novel antimitotic, anticancer agent, in human plasma. The analysis required 0.5 ml of plasma, and was accomplished by detection of the UV absorbance of paclitaxel at 227 nm following extraction and concentration. The method involved extraction of paclitaxel from plasma, buffered with 0.5 ml of 0.2 M ammonium acetate (pH 5.0), onto 1-ml cyano Bond Elut columns. The eluent was evaporated under nitrogen and low heat, and reconstituted with the mobile phase, acetonitrile-methanol-water (4:1:5, v/v/v) containing 0.01 M ammonium acetate (pH 5.0). The samples were chromatographed on a reversed-phase octyl 5 microns column. The retention time of paclitaxel was 10 min. The validated quantitation range of the method was 10-1000 ng/ml (0.012-1.17 microM) of paclitaxel in plasma. Standard curve correlation coefficients of 0.995 or greater were obtained during validation experiments and analysis of clinical study samples. The observed recovery for paclitaxel was 83%. Epitaxol, a biologically active stereoisomer, and baccatin III, a degradation product, were also chromatographically separated from taxol by this assay. The method was applied to samples from a clinical study of paclitaxel in cancer patients, providing a pharmacokinetic profiling of paclitaxel.

Ototoxicity of cis-diamminedichloroplatinum (II): Influence of dose, schedule and mode of administration

During and after 233 cycles of cis-diamminedichloroplatinum (II) (CDDP), 197 serial audiograms were obtained in 48 patients and compared with baseline audiograms. Use was made of three dose schedules (20 mg/m2, 25-50 mg/m2 and 70-120 mg/m2), two regimens (single-day or daily for 5 days) and three modes of administration (rapid infusion, 2- or 3-hr infusion, 24-hr infusion). Clinical hearing loss occurred in 12.5% and tinnitus in 25% of all patients. The incidence of audiographic changes (65% overall, 81% bilaterally) increased with increasing cumulative CDDP dose independent of treatment schedule. The incidence was correlated with the daily dose (P = 0.0037) and changes were more severe after single high doses. No difference was found between the single low dose and the daily for 5 days regimen. Rapid infusion of a single high dose was more ototoxic than a 24-hr infusion of the same dose (P = 0.0015). It is concluded that, compared with the single high-dose regimen, the daily low dose for 5 days is preferable in cases where the patient might be cured by a regimen including CDDP.

Response of peritoneal solid tumours after intraperitoneal chemohyperthermia treatment with cisplatin or carboplatin

The combination of heat and chemotherapy was studied in an intraperitoneal tumour model. Rats bearing peritoneal CC531 tumours (2-6 mm) were treated i.p. with cDDP or CBDCA [maximal tolerated dose (MTD)] in combination with regional hyperthermia (41.5 degrees C, 1 h) of the peritoneal cavity. The addition of hyperthermia to the i.p. treatment led to a decrease in the MTD of cDDP by 33.3% at 41.5 degrees C. This was due to increased nephrotoxicity. The MTD of CBDCA did not change as a result of hyperthermia treatment. The chemo-hyperthermia treatment resulted in more cDDP or CBDCA DNA adducts in peritoneal tumours after the combined treatment than after chemotherapy alone. The increased tumour platinum concentrations, rising from 1.3 micrograms Pt g-1 tumour at 37 degrees C to 5.4 micrograms Pt g-1 tumour at 41.5 degrees C for cDDP and from 0.2 microgram Pt g-1 tumor to 0.7 microgram Pt g-1 tumour at 41.5 degrees C for CBDCA, contributed considerably to the enhanced numbers of cDDP or CBDCA DNA adducts. As a result of the latter, i.p. chemotherapy combined with regional hyperthermia led to an increase in tumour growth delay (TGD) after increasing the temperature to 41.5 degrees C for cDDP and CBDCA (by 40 days for cDDP, 22 days for CBDCA). These data were in agreement with the in vitro findings, i.e. that higher temperatures led to increased cytotoxicity.

Cyvadic in advanced soft tissue sarcoma: A randomized study comparing two schedules: A study of the EORTC soft tissue and bone sarcoma group

Two hundred forty‐six adults with advanced progressive soft tissue sarcoma received combination chemotherapy with cyclophosphamide, vincristine, Adriamycin (doxorubicin), and DTIC. They were randomly allocated to receive the four drugs simultaneously every 4 weeks (S1: CYVADIC), or pairs of drugs (S2: ADIC‐CYV) alternating at 4 weekly intervals. One hundred sixty‐two patients completed 8 weeks of chemotherapy, and were considered to be evaluable for response. There were 18 complete remissions and 25 partial remissions, an overall response rate of 26%, with a highly significant difference between the two arms in favor of S1 (38% versus 14%, P = 0.001). There were no significant differences between S1 and S2 in terms of median duration of remissions (62 versus 39 weeks), and median survival of responders (85 versus 80 weeks) and of all evaluable patients (43 versus 45 weeks). Karnofsky index (KI) was the single most important prognostic factor. Patients with KI 90–100 showed a remission rate of 41% (56% on the S1 regimen) in contrast with 14% in those with KI 50–80. No patient with a KI of 50 responded to chemotherapy. The main toxicities were nausea, vomiting, anorexia, alopecia and myelosuppression, but did not differ significantly between the two regimens. Our findings suggest that stratification according to KI is essential for studies on chemotherapy for advanced soft tissue sarcomas in order to make a valuable comparison of treatment results.

A comparison of 5-fluorouracil metabolism in human colorectal cancer and colon mucosa

The metabolism of 5‐fluorouracil (5‐FU) was studied in biopsy specimens of primary colorectal cancer and healthy colonic mucosa obtained from previously untreated patients immediately after surgical removal. The conversion of 5‐FU to anabolites was measured under saturating substrate (5‐FU) and cosubstrate concentrations. For all enzymes, the activity was about threefold higher in tumor tissue compared with healthy mucosa of the same patient. The activity of pyrimidine nucleoside phosphorylase with deoxyribose‐1‐phosphate (dRib‐1‐P) was about tenfold higher (about 130 and 1200 nmol/hr/mg protein in tumors) than with ribose‐1‐phosphate (Rib‐1‐P), both in tumor and mucosa. Synthesis of the active nucleotides (5‐fluoro‐uridine‐5′‐monophosphate [FUMP] and 5‐fluoro‐2′deoxyuridine‐5′‐monophosphate [FdUMP]) was studied by adding physiologic concentrations of adenosine triphosphate (ATP) to the reaction mixture; the rate of FdUMP synthesis was 50% of that of FUMP (about 4 and 7 nmol/hr/mg protein in tumors). Direct synthesis of FUMP from 5‐FU in the presence of 5‐phosphoribosyl‐1‐pyrophosphate (PRPP) was about 2 nmol/hr/mg protein. With the natural substrate for this reaction, orotic acid, the activity was about 14‐fold higher. To obtain insight into the recruitment of precursors for these cosubstrates, the authors also tested the enzyme activity of pyrimidine nucleoside phosphorylase with inosine and ribose‐5‐phosphate (Rib‐5‐P, as precursors for Rib‐1‐P) and deoxyinosine (as a precursor for dRib‐1‐P); enzyme activities were approximately 7%, 7%, and 3%, respectively, of that with the normal substrates, both in tumors and mucosa. However, when ATP and Rib‐5‐P were combined, the synthesis of FUMP was about 70% of that with PRPP, but only in tumors. In normal tissues no activity was detectable. These data suggest a preference of colon tumor over colon mucosa for the conversion of 5‐FU to active nucleotides by a direct pathway; a selective antitumor effect of 5‐FU may be related to this difference.

Pharmacokinetics of 4′-epi-doxorubicin in man

SummaryThe pharmacokinetics of 4′-epi-doxorubicin (4′-epi-adriamycin, 4′-epi-DX) in man can be described by a three-compartment model with a rapid distribution phase and a very long elimination phase. Urine excretion amounts to a total of about 11% of the administered dose during 48 h after drug administration, and less than 1% during the following 48 h. In plasma 4′-epi-doxorubicin is rapidly converted to five metabolites (4′-epi-doxorubicinol, aglycones and glucuronides), the concentration of the aglycones sometimes exceeding that of 4′-epi-DX. In urine only three metabolites were found in addition to the parent drug; they were identified as 4′-epi-doxorubicinol (EOH), 4′-epi-doxorubicin-glucuronide (E-Glu) and 4′-epi-doxorubicinol-glucuronide (EOH-Glu). Comparison of the pharmacokinetics and metabolic profiles of 4′-epi-DX and doxorubicin (DX) in man revealed that 4′-epi-DX eliminates faster than DX.

Pharmacokinetics of free platinum species following rapid, 3-hr and 24-hr infusions of cis-diamminedichloroplatinum (II) and its therapeutic implications

The pharmacokinetics of free platinum species derived from cis-diamminedichloroplatinum (II) (cisplatin) was studied in three patients who received the drug as a single agent for the first time at equal doses (100 mg/m2) but with different infusion times. In rapid, 3-hr and 24-hr infusions, peak levels of free platinum were 8.62, 1.96 and 0.27 microgram Pt/ml respectively; half-lives of disposition calculated 0-30 min after the end of each infusion were 17.4, 22.7 and 26.2 min respectively. Free platinum availability, measured as the area under the curves of the free platinum concentration, was the same for the three modes of administration (290, 321 and 325 micrograms Pt/min/ml-1 respectively). This observation supports the clinical impression that antitumour activity of cisplatin is not dependent on the method of administration.

Inhibition of pyrimidine de novo synthesis by DUP-785 (NSC 368390)

The mechanism of action of NSC 368390 (DUP-785, 6-fluoro-2-(2′-fluoro-1, 1′-biphenyl-4-yl)-3-methyl-4-quinoline carboxylic acid sodium salt) was studied using three different approaches. First, we studied growth inhibition by DUP-785 in L1210 leukemia cells and M5 melanoma cells. The concentrations causing 50% growth inhibition after 48 hr of culture were 5.8 and 0.6 μM, respectively. DUP-785 had to be present continuously throughout culture. Growth inhibition by 25 μM DUP-785 could be prevented by addition of 1 mM uridine or orotic acid to cultures of these cell lines; in M5 cells cytidine was also able to prevent growth inhibition. Dihydro-orotic acid (DHO) and carbamyl-aspartate were not able to prevent growth inhibition by DUP-785. Second, we studied accumulation of orotic acid and of orotidine induced by incubation with 1 μM pyrazofurin, an inhibitor of the orotate phosphoribosyl-transferase-orotidine-monophosphate decarboxylase complex. Addition of DUP-785 to the culture medium prevented the orotic acid accumulation. Furthermore, DUP-785 prevented accumulation of H14CO3− into orotic acid of pyrazofurin-treated L1210 cells. Third, we measured the effect of DUP-785 on DHO-dehydrogenase (DHO-DH), since the results indicated that this enzyme was affected by DUP-785. DHO-DH was assayed in isolated rat liver mitochondria. The Km for L-DHO was about 12 μM. DUP-785 appeared to be a potent inhibitor of DHO-DH with an apparent Ki of about 0.1 μM and an apparent Ki′ of about 0.8 μM. The mode of inhibition appeared to be linear mixed type. After exposure of L1210 cells to 25 μM DUP-785 for 2 hr DHO-DH was almost completely inhibited. After suspension in fresh medium without drug, DHO-DH activity was recovered to about 60% after 24 hr. In conclusion, DUP-785 is a potent inhibitor of pyrimidine de novo biosynthesis, by inhibition of the mitochondrial enzyme DHO-DH.