Aplidin synergizes with cytosine arabinoside: functional relevance of mitochondria in Aplidin-induced cytotoxicity.

Aplidin (plitidepsin) is a novel marine-derived antitumor agent presently undergoing phase II clinical trials in hematological malignancies and solid tumors. Lack of bone marrow toxicity has encouraged further development of this drug for treatment of leukemia and lymphoma. Multiple signaling pathways have been shown to be involved in Aplidin-induced apoptosis and cell cycle arrest in G1 and G2 phase.

Sensitivity of soft tissue sarcoma cell lines to chemotherapeutic agents: identification of ecteinascidin-743 as a potent cytotoxic agent.

The cytotoxic effects of ecteinascidin-743(ET-743), a novel marine natural product, were evaluated and compared with that of clinically used anticancer agents methotrexate, doxorubicin, etoposide, and paclitaxel in eight human soft tissue sarcoma (STS) cell lines. HT-1080, a fibrosarcoma cell line, and HS-42, a malignant mesodermal cell line, were the most sensitive of the cell lines to methotrexate, doxorubicin, etoposide, and paclitaxel. Other cell lines (IC50s) varied considerably and were more resistant to these agents.

Defective transport is a common mechanism of acquired methotrexate resistance in acute lymphocytic leukemia and is associated with decreased reduced folate carrier expression.

Methotrexate (MTX) transport was examined in 27 patients with untreated acute lymphocytic leukemia (ALL) and 31 patients with relapsed ALL using a previously described fluorescent MTX analog (PT430) displacement assay (Blood 80:1158, 1992). Only 13% of untreated patients were considered to have impaired MTX transport, whereas more than 70% of relapsed patients had evidence of impaired MTX transport. To further characterize the basis for this defect, Northern analyses for the reduced folate carrier (RFC) were performed on the RNA available from the leukemic blasts of 24 patients in whom MTX transport had been measured.

Amplification of the dihydrofolate reductase gene is a mechanism of acquired resistance to methotrexate in patients with acute lymphoblastic leukemia and is correlated with p53 gene mutations.

Although dihydrofolate reductase (DHFR) gene amplification is a common mechanism of resistance to methotrexate (MTX) in tumor cell lines, with the exception of a few case reports, the incidence of this phenomenon as a mechanism of MTX resistance in the clinic has not been reported. We studied 38 untreated patients and 29 patients in relapse with acute lymphoblastic leukemia (ALL) for gene amplification and p53 gene mutations. Three patients were studied both at diagnosis and at each of two relapses after treatment with MTX.

Selective treatment of SCID mice bearing methotrexate-transport-resistant human acute lymphoblastic leukemia tumors with trimetrexate and leucovorin protection.

Impaired transport of methotrexate (MTX) is a common resistance mechanism of tumor cells to this drug. Trimetrexate (TMTX), a second-generation folate antagonist, is still active against MTX-transport-resistant cells because it enters cells by passive diffusion and does not use the reduced folate transport system for cell entry. Therefore, although leucovorin (LV) protects MTX-sensitive cells from TMTX toxicity, MTX-transport defective cells are poorly rescued by LV.