Etoposide (VP16-213) and teniposide (VM26) comparative in vitro activities in human tumors

Bromocriptine has little direct effect on murine lymphocytes, the immunomodulatory effect being mediated by the suppression of prolactin secretion

We investigated whether the immunosuppressive effect of bromocriptine in mice is due to its direct effect on lymphocyte functions or through inhibition of prolactin secretion. Incubation of mouse Babl/c splenic lymphocytes with bromocriptine in vitro at a concentration of around 0.5 to 1 microgram/mL causes an inhibition of antigen- or mitogen-induced proliferation. However, bromocriptine in vitro has no effect on lymphokine production (gamma-interferon and interleukin-2), expression of interleukin-2 receptor or lymphocyte cytotoxic function. Furthermore, treatment of Babl/c mice with bromocriptine inhibits the mixed lymphocyte reaction and mitogen stimulation, as well as primary and secondary antibody production. However, we postulated that the inhibition of ex vivo functional activity could not account for a direct cytostatic or cytotoxic effect of bromocriptine. This is supported by the in vitro data, which shows that bromocriptine has no effect on proliferating P-815 mastocytoma tumor cells. Finally, (NZB/NZW) F1 mice spontaneously develop a disease similar to systemic lupus erythematosus. In both non-autoimmune Babl/c mice and (NZB/NZW) F1 lupus-mice, the serum level of bromocriptine achieved by a treatment with 5 mg/kg on average is 2-6 ng/mL. On the one hand, this dose is sufficient to significantly alter the ex vivo functional tests in Babl/c mice and to show a beneficial effect in the in vivo model of female lupus-mice. On the other hand, the lowest concentration which could have an inhibitory effect on antigen- and mitogen-induced proliferation in vitro is 200 ng/mL, ie 50 times more than that required in vivo to obtain significant reductions of proteinurea, glomerular membrane proliferation and immune deposits in lupus-mice. The serum levels of gamma-interferon and interleukin-2 are reduced in lupus-mice when compared with Babl/c mice. The treatment with bromocriptine does not influence these parameters. In conclusion, our data demonstrate that the major immunosuppressive activity of bromocriptine is probably dependent on its hypoprolactinemic effect.

Comparison of in vitro activity of epipodophyllotoxins with other chemotherapeutic agents in human medulloblastomas

Surgical specimens from 15 medulloblastoma patients were used to establish early passage cultures. In vitro sensitivity to a battery of cytotoxic agents, including some in current medulloblastoma treatment protocols, was measured. Drug sensitivity was assessed at clinically relevant drug concentrations using the 3H-thymidine uptake method. Tumours were predicted to be sensitive if greater than 37% were killed by exposure to drugs at clinically achievable levels. A poor response to vincristine (Vcr), cis-platin (CDDP), hydroxyurea (HU) or diaziquone (AZQ) (no responders), and cytosine arabinoside (AraC) (1/12), was seen. Nine of ten tumours tested were sensitive to mafosfamide (Mfs); seven out of 12 were sensitive to carmustine (BCNU), 12 of 13 to teniposide (VM-26) and seven of 13 to etoposide (VP16-213). VM-26 was the best of the agents tested with most tumours responding to very low concentrations of drug, suggesting that the role of epipodophyllotoxins in treatment of brain tumours be further investigated. Despite the marked sensitivity of the medulloblastomas to the epipodophyllotoxins, three early passage cultures were much more resistant to these drugs than the average for the group. The basis of this resistance was investigated. Deficient cellular uptake of drug was excluded as a cause of resistance. One resistant early passage culture displayed low cellular activity of topoisomerase II and decreased levels of drug induced enzyme-DNA strand break activity. This was not the case for the other resistant early passage cultures: the basis of resistance in these cells does not appear to be due to any previously reported mechanism.

Clinical pharmacology of cancer chemotherapy in children

The pharmacokinetics of most anticancer drugs are highly variable in children, and are commonly different when children are compared to adults. Several recent studies have demonstrated that variability in systemic exposure due to interpatient pharmacokinetic variability, may be related to the probability of oncolytic effects or toxicity for some anticancer drugs. This review has exemplified differences in the clinical pharmacology of several anticancer drugs, when children are compared to adults. Such age-related differences in the pharmacokinetics and pharmacodynamics of these drugs, together with biologic differences between pediatric and adult cancers, provide the rationale for systematically conducting pediatric phase I through IV studies of anticancer drugs and denote the risks of relying on adult trials to identify new therapeutic strategies for childhood cancers.

The clinical pharmacology of etoposide and teniposide

Etoposide and teniposide are semisynthetic derivatives of podophyllotoxin and are increasingly used in cancer medicine. Teniposide is more highly protein-bound than etoposide, and its uptake and binding to cells is also greater. Etoposide and teniposide are phase-specific cytotoxic drugs acting in the late S and early G2 phases of the cell cycle. They appear to act by causing breaks in DNA via an interaction with DNA topoisomerase II or by the formation of free radicals. Teniposide is more potent as regards the production of DNA damage and cytotoxicity. Most studies show a biexponential decay following intravenous administration of etoposide and teniposide. The terminal elimination half-life of etoposide is less than that of teniposide, and the plasma and renal clearances of etoposide are greater. The peak plasma concentrations of drug and the area under the concentration versus time curve are linearly related to the intravenous dose of both drugs. Considerable interpatient variability of pharmacokinetic parameters exists following intravenous etoposide and teniposide. Various metabolites of etoposide and teniposide have been identified but their detection and quantitation are disputed. Approximately 30 to 70% of a dose of etoposide is accounted for by excretion, whereas the figure appears to be only 5 to 20% for teniposide. The bioavailability of oral etoposide is about 50% but its absorption is not linear with increasing dose within the range in clinical use. There is considerable inter- and intrapatient variability in the pharmacokinetics of oral etoposide. There is no evidence of accumulation of etoposide and teniposide after multiple consecutive doses by the intravenous or oral routes. The exact roles of the liver and kidney in metabolism and excretion of etoposide and teniposide are uncertain. Etoposide has been shown to be a highly schedule-dependent drug in clinical studies. This together with the phase-specific action of etoposide and teniposide and their increasingly widespread use in cancer medicine make the clinical pharmacology of these drugs of great clinical importance.

Chemical and biological stability of anticancer drugs used in a human tumor clonogenic assay

Human tumor clonogenic assays (HTCA) are being used to evaluate the chemosensitivity of human cancers to both standard and experimental anticancer drugs as well as to predict clinical tumor response and resistance to these agents. To enable us to design and accurately interpret drug assay data we quantitated the chemical and biological stability characteristics of various cell cycle-specific and cell cycle-nonspecific drugs commonly used in our laboratory for chemosensitivity testing in the HTCA. Aliquots of the culture media were obtained immediately after drug addition and after 6 and 24 h and 2, 4, and 10 days of incubation, and then frozen in liquid nitrogen for later chemical (HPLC or RIA) and biological (HTCA) assay. Adriamycin, actinomycin D, bisantrene, bleomycin, and vinblastine retained 80-100% of their biological activity against human tumor colony-forming units even after 10 days of incubation in culture media. In contrast, etoposide lost 60% of its in vitro antitumor activity over the same period. There was no loss in the chemical concentration of actinomycin D. bisantrene, bleomycin, or vinblastine in the culture media, but etoposide concentrations as measured by HPLC decreased to zero over 10 days. We conclude that the HTCA can be used as a simple test for biological stability of new investigational agents prior to the development of adequate chemical assay methodology, and that it can help clarify whether a drug's in vitro antitumor activity is due to the parent compound or to a degradation product.

Skin ulceration potential without therapeutic anticancer activity for epipodophyllotoxin commercial diluents

The epipodophyllotoxin derivatives, etoposide (VP-16) and teniposide (VM-26), are highly lipophilic anticancer drugs supplied with novel commercial solvent systems. A BALB/c mouse skin toxicity model was used to evaluate the ulcerative potential of intradermal (ID) VP-16 and its lipophilic solvent system along with the main ingredient of the VM-26 solvent, polyethoxylated castor oil (PECO). ID VP-16 caused dose-dependent ulceration following 0.17 mg, 0.33 mg (50 mg/M2) or 1.0 mg (150 mg/M2). Both normal saline (0.05 ml ID) and hyaluronidase (7.5 u ID) were effective as local VP-16 antidotes, presumably by diluting out the extravasated drug. The VP-16 solvent alone was as toxic as the 1.0 mg (undiluted) ID VP-16 injection. ID PECO was mildly ulcerative in mouse skin. When given to P-388 lymphocytic leukemia-bearing mice, both VP-16 (24 mg/kg IP for 3 doses) and VM-26 (8 mg/kg IP for 2 doses) were active, producing increased life spans (ILS) of 160% and 90%, respectively. The solvents, given IP at the same schedule, did not increase or decrease the life span of tumor-bearing mice, but did increase morbidity. In an in vitro human tumor clonogenic assay (WiDr colon carcinoma and HEC-1A endometrial carcinoma in soft agar), both VP-16 and VM-26 showed moderate to complete inhibition of tumor colony forming units (TCFUs) by continuous exposure. 1-h drug exposures were marginally active at reducing TCFUs. None of the epipodophyllotoxin diluents at clinical concentrations reduced TCFUs. At very high concentrations, both epipodophyllotoxins were cytotoxic. They were more effective at reducing TCFUs when plated as a continuous exposure rather than a 1-h exposure.