Two types of tumour sensitivity test compared for platinum derivatives

Prediction of antifolate efficacy in a rat sarcoma model

A methylcholanthrene-induced rat sarcoma propagated both in vitro and in vivo was used to examine the usefulness of a rapid biochemical in situ assay that measures thymidylate synthase (TS) activity in whole cells to predict sensitivity and resistance to the folate antagonists methotrexate (MTX), 10-ethyl-10-deazaaminopterin (10-EDAM) and trimetrexate (TMTX). There was an excellent correlation between the effects of these drugs on inhibiting TS and cytotoxicity as measured by a clonogenic assay, when the exposure time was 4 hr and those when the rat sarcoma cell line was employed (p less than 0.001). When tumor-cell suspensions were prepared from the rat sarcoma propagated in vivo, they were less sensitive to these antifolates, but the relative effectiveness of the 3 antifolates was similar: TMTX much greater than 10-EDAM greater than MTX. As expected, continuous exposure (10 to 12 days) produced cytotoxicity at a much lower dose of these drugs. When the 3 drugs were tested for anti-tumor effectiveness in rats bearing this tumor, the tumor regression measured was best with TMTX; 10-EDAM was intermediate in effectiveness as compared with MTX. These results indicate that the in situ TS assay and clonogenic assay may be used to predict anti-tumor efficacy of antifolates in vivo in this rat sarcoma.

Three tumor sensitivity tests evaluated with mouse tumors

The predictive value of three types of tumor sensitivity tests was evaluated using mouse tumors. Sensitivities of osteosarcoma C22LR, Lewis lung and M2661 carcinoma were determined for the following drugs: DNA interacting or alkylating agent (doxorubicin, cisplatin, 1,3-bis(2-chloroethyl)-1-nitrosourea, melphalan), antimetabolite (5-fluorouracil, methotrexate) and microtubule inhibitor (vinblastine, vincristine). Volume measurements of the subcutaneously growing tumors after treatment with the same drugs were considered to be the traditional reference system with which the results of the in vitro clonogenic assay, the labeled precursor incorporation assay and the subrenal capsule assay were compared. Results obtained with the in vitro clonogenic assay were highly reproducible. With the 1-h drug exposure technique the predictive accuracy was 71%. This result is in the same range as those found by others for human tumors. Predictive accuracy after continuous drug exposure was only 25%. Vinblastine, vincristine and cisplatin caused no inhibition of labeled precursor incorporation. However, the assay is too unreliable to use, due to the extreme variability when used with the other drugs. From 31 consecutively performed duplicate tests in the subrenal capsule assay, nine showed opposite results. This degree of disagreement between duplicate test results was considered too high to make reliable predictions of tumor sensitivity with this assay.

Cellular heterogeneity and drug resistance in two ovarian adenocarcinoma cell lines derived from a single patient

Two ovarian cell lines were derived from the ascites of a patient before and after the onset of resistance to chemotherapy involving cis-platinum, chlorambucil and 5-fluorouracil. Characterization of these lines shows them to have various features in common and some significant differences. Cytologically the lines cannot be distinguished and they both contain high concentrations of oestrogen receptor. However, they do differ with respect to their growth characteristics, karyotype, glutathione content and sensitivity to cis-platinum. The karyotypes of the 2 lines show several marker chromosomes in common but the resistant line contained a chromosome 8 and a 17 which were absent from the earlier sensitive line. This suggests a clonal origin with subsequent divergence to a heterogeneous population.