Selective killing of preneoplastic and neoplastic cells by methotrexate with leucovorin

Mechanisms, Management and Prevention of Pemetrexed-Related Toxicity

Pemetrexed is a cytostatic antifolate drug and a cornerstone in the treatment of lung cancer. Although generally well tolerated, a substantial part of the patient population experiences dose-limiting or even treatment-limiting toxicities. These include mucositis, skin problems, fatigue, renal toxicity, and neutropenia. Several studies confirmed that pemetrexed pharmacokinetics can serve as a prognostic factor for the development of toxicity, especially for neutropenia. Preventing and managing toxicity of pemetrexed can help to ensure durable treatment. Several evidence-based strategies are already implemented in clinical care. With the introduction of standard vitamin supplementation and dexamethasone, the incidence of hematological toxicity and skin reactions substantially decreased. In the case of high risk for toxicity, granulocyte colony-stimulating factor can be used to prevent severe hematological toxicity. Moreover, high-dose folinic acid can resolve severe pemetrexed-induced toxicity. There are several experimental options to prevent or manage pemetrexed-related toxicity, such as the use of standard folinic acid, hemodialysis, antidotes such as thymidine, hypoxanthine, and glucarpidase, and the use of therapeutic drug monitoring. These strategies still need clinical evaluation before implementation, but could enable treatment with pemetrexed for patients who are at risk for toxicity, such as in renal impairment.

Folinic acid attenuates methotrexate chemotherapy-induced damages on bone growth mechanisms and pools of bone marrow stromal cells

Chemotherapy often induces bone growth defects in pediatric cancer patients; yet the underlying cellular mechanisms remain unclear and currently no preventative treatments are available. Using an acute chemotherapy model in young rats with the commonly used antimetabolite methotrexate (MTX), this study investigated damaging effects of five once-daily MTX injections and potential protective effects of supplementary treatment with antidote folinic acid (FA) on cellular activities in the tibial growth plate, metaphysis, and bone marrow. MTX suppressed proliferation and induced apoptosis of chondrocytes, and reduced collagen-II expression and growth plate thickness. It reduced production of primary spongiosa bone, volume of secondary spongiosa bone, and proliferation of metaphyseal osteoblasts, preosteoblasts and bone marrow stromal cells, with the cellular activities being most severely damaged on day 9 and returning to or towards near normal levels by day 14. On the other hand, proliferation of marrow pericytes was increased early after MTX treatment and during repair. FA supplementation significantly suppressed chondrocyte apoptosis, preserved chondrocyte proliferation and expression of collagen-II, and attenuated damaging effects on production of calcified cartilage and primary bone. The supplementation also significantly reduced MTX effects on proliferation of metaphyseal osteoblastic cells and of bone marrow stromal cells, and enhanced pericyte proliferation. These observations suggest that FA supplementation effectively attenuates MTX damage on cellular activities in producing calcified cartilage and primary trabecular bone and on pools of osteoblastic cells and marrow stromal cells, and that it enhances proliferation of mesenchymal progenitor cells during bone/bone marrow recovery.

Anticancer and cytotoxic properties of the latex of Calotropis procera in a transgenic mouse model of hepatocellular carcinoma

AIM: To evaluate the anticancer property of the dried latex (DL) of Calotropis procera, a tropical medicinal plant, in the X15-myc transgenic mouse model of hepatocellular carcinoma and to elucidate its mechanism of action in cell culture.

METHODS: The young transgenic mice were orally fed with the aqueous suspension of DL (400 mg/kg for 5 d/wk) for 15 wk and their liver was examined for histopathological changes at 20 wk. Serum levels of vascular endothelial growth factor (VEGF) were also measured in these animals. To characterize the active fraction, DL was extracted with petroleum ether followed by methanol. The methanolic extract was sub-fractionated on a silica gel G column using a combination of non-polar and polar solvents and eleven fractions were obtained. Each fraction was analysed for cytotoxic effect on hepatoma (Huh7) and non-hepatoma (COS-1) cell lines and non-transformed hepatocytes (AML12) using tetrazolium (MTT) assay. Finally, the mechanism of cell death was investigated by measuring the levels of Bcl2, caspase 3 and DNA fragmentation.

RESULTS: DL treatment of mice showed a complete protection against hepatocarcinogenesis. No adverse effect was observed in these animals. The serum VEGF level was significantly lowered in the treated mice as compared to control animals. Cell culture studies revealed that the methanolic extract of DL as well as its fraction 8 induced extensive cell death in both Huh-7 and COS-1 cells while AML12 cells were spared. This was accompanied by extensive fragmentation of DNA in Huh-7 and COS-1 cells. No change in the levels of canonical markers of apoptosis such as Bcl2 and caspase 3 was observed.

CONCLUSION: DL of C. procera has the potential for anti-cancer therapy due to its differentiable targets and non-interference with regular pathway of apoptosis.

Cytogenetic toxicity of methotrexate in mouse bone marrow

Methotrexate (MTX), a widely used anticancer drug, was tested for its cytogenetic toxicity in mouse bone marrow after a single intraperitoneal treatment with three different doses i.e. at the rate of 2, 10 and 20 mg/kg b.w. of mice. The end points selected were chromosomal aberrations and mitotic index study at 24-h post-treatment and micronucleus (MN) test at 30-h post-treatment. The induction of statistically significant number of chromosomal aberrations, percentage of aberrant metaphases and highly significant number of MN per thousand polychromatic erythrocytes by all the doses of MTX indicated it as highly clastogenic. MTX was found more clastogenic in male mice than the females and the intermediate dose tested (10 mg/kg) was found more effective than the other doses. In mitotic index study, none of the doses of MTX inhibited cell proliferation during the first post-treated cell cycle. The results were compared with the earlier reports on the clastogenicity and cell proliferation inhibition of MTX only after multiple treatments. The possible mechanism of the cytogenetic effects of MTX has been discussed.

Liquid chromatographic analysis and preliminary pharmacokinetics of methotrexate in cancer patients co-treated with docetaxel

A new HPLC method has been developed for the quantitative determination of methotrexate (MTX) and its 7-hydroxyl metabolite in human plasma. Samples were purified by protein precipitation with acetone and methanol, and a sample clean-up with a mixture of n-butanol and diethyl ether. The analytes were separated on an RP Inertsil ODS-80A column and eluted in a solvent system containing 5% (v/v) tetrahydrofuran in water (pH 2.0). UV absorption measurement was performed at 313 nm, and the detector response was linear in a concentration range of 10-10,000 ng/ml. The lower limit of quantitation of MTX was 10 ng/ml using 1 ml sample aliquots. Values for accuracy and (within-run and between-run) precision were between 95.5-111% and 3.69-11.0%, respectively, at four concentrations analyzed in quintuplicate on four separate occasions. The assay was applied to study the effects of docetaxel co-administration on the pharmacokinetics and metabolism of MTX in cancer patients.

Quantitative aspects of the selective killing of transformed cells by methotrexate in the presence of leucovorin

A quantitative study was made of the cytotoxicity of methotrexate (MTX) for nontransformed and transformed NIH 3T3 cells in the presence and absence of leucovorin. The study was preceded by an analysis of the growth rates of the cells at low and high population density combined with low and high concentrations of calf serum (CS). The reduced maximal growth rates of the transformed cells at low population densities relative to the nontransformed cells reinforced earlier evidence that heritable damage involving chromosome aberrations drives the process of transformation. When small numbers of transformed cells are cocultured with a large excess of nontransformed cells in the assay for transformed foci, the transformed cells were more readily killed by MTX than the nontransformed cells. The selectivity was increased when leucovorin (folinic acid) was present in the medium. The selective killing of the transformed cells actively multiplying in foci was most pronounced when the background of nontransformed cells had become confluent and their growth was inhibited. However, selectivity has also been demonstrated when transformed and nontransformed cells are growing at their maximum rates at low density despite the lower growth rate of the transformed cells under these conditions. The sensitivity of transformed cells in pure culture to MTX was lower during the first 3 d of subculture than in the following 6 d but decreased to zero a few d after net growth had ceased. The nontransformed cells were more susceptible to killing by MTX in Dulbecco's modified Eagle's medium (DMEM) than in MCDB 402, but the transformed cells were sensitive to MTX in both media. The high selectivity of MTX for transformed over nontransformed cells in MCDB 402 results from the presence of 1.0 microM leucovorin (5-formyltetrahydrofolate), a reduced form of the folic acid present in most other culture media. When leucovorin was added to DMEM with its high concentration of folic acid, the resistance to MTX of both nontransformed and transformed cells was greatly increased, but the selectivity of MTX for transformed cells was almost entirely lost. The results indicate that leucovorin protects nontransformed cells against concentrations of MTX that kill transformed cells, but the protection is dependent on the relative amounts of leucovorin to folic acid in the medium. The relative sensitivities of transformed and nontransformed cells in our system to MTX when both cell types are exhibiting their characteristic differential in growth behavior is similar to that described for tumor and normal cells in vivo. Since the unregulated growth behavior of the transformed, tumor-producing cells is efficiently and quantitatively measured in this system, it can be used to develop general principles of treatment and resolve questions of cytotoxic mechanism.

The cellular ecology of progressive neoplastic transformation: a clonal analysis

A comparison was made of the competence for neoplastic transformation in three different sublines of NIH 3T3 cells and multiple clonal derivatives of each. Over 90% of the neoplastic foci produced by an uncloned transformed (t-SA') subline on a confluent background of nontransformed cells were of the dense, multilayered type, but about half of the t-SA' clones produced only light foci in assays without background. This asymmetry apparently arose from the failure of the light focus formers to register on a background of nontransformed cells. Comparison was made of the capacity for confluence-mediated transformation between uncloned parental cultures and their clonal derivatives by using two nontransformed sublines, one of which was highly sensitive and the other relatively refractory to confluence-mediated transformation. Transformation was more frequent in the clones than in the uncloned parental cultures for both sublines. This was dramatically so in the refractory subline, where the uncloned culture showed no overt sign of transformation in serially repeated assays but increasing numbers of its clones exhibited progressive transformation. The reason for the greater susceptibility of the pure clones is apparently the suppression of transformation among the diverse membership that makes up the uncloned parental culture. Progressive selection toward increasing degrees of transformation in confluent cultures plays a major role in the development of dense focus formers, but direct induction by the constraint of confluence may contribute by heritably damaging cells. In view of our finding of increased susceptibility to transformation in clonal versus uncloned populations, expansion of some clones at the expense of others during the aging process would contribute to the marked increase of cancer with age.