Cytologic evidence for gene amplification in methotrexate-resistant cells obtained from a patient with ovarian adenocarcinoma.

Abstract

To analyze if methotrexate (MTX) resistance arises from gene amplification in a patient treated clinically with MTX, the cytogenetic and drug sensitivity profile of the tumor colony forming units (TCFUs) from a 58-year-old woman with stage III well-differentiated ovarian serous adenocarcinoma was studied. This patient had not received treatment directed against her tumor for nine months before this study, but had received oral-dose MTX (2.5 mg, twice weekly) for three years for the treatment of psoriasis. Analysis of TCFUs grown in nucleoside-free media demonstrated MTX resistance at concentrations of up to 100 micrograms/mL (2.2 X 10(-4)M). Cytologic evidence for dihydrofolate reductase (DHFR) gene amplification in TCFUs was determined by in situ hybridization, using radiolabeled cDNA to DHFR mRNA. Results localized the DHFR sequences to an abnormally staining region present on chromosome 4q. This study supports the notion that alterations in gene dosage (that is, gene amplification) play a role in the development of drug resistance in spontaneous human cancers.

Resistance to antifolates

“…The former type of amplification is much more stable as the latter is lost during cell division. Low-level gene amplification has been identified in tissue specimens from patients with acute lymphoblastic leukemia (ALL) and ovarian cancer (Trent et al, 1984) treated with MTX, indicating that this process plays a role in clinical drug resistance. The low-level amplification detected prior to treatment in human soft-tissue sarcomas suggests that this may be one basis for intrinsic resistance in this disease requiring high-dose therapies (Li et al, 1992b).…”

DHFR/MSH3 amplification in methotrexate-resistant cells alters the hMutSα/hMutSβ ratio and reduces the efficiency of base–base mismatch repair

“…However, human tumor cells can acquire resistance to Mtx, a phenomenon that has been demonstrated both in vitro and in vivo (5)(6)(7)(8). One well documented mechanism of resistance involves the amplification of a region of the human or rodent genome containing the DHFR gene (5)(6)(7)(8)(9)(10), an event that leads to elevated expression of DHFR, which effectively circumvents the metabolic block produced by this agent.…”

Scheduling Chemotherapy: Catch 22 between Cell Kill and Resistance Evolution

“…With many drugs, however, resistance in the clinical setting has been shown to evolve by gene amplification , Curt et 01. 1983, Trent et al 1984, Cardman et al 1984. Kellen 1994, Bodey et al 1997, and in these situations the double bind described here may apply.…”

“…Thus, low drug concentrations facilitated the evolution of resistance. A number of clinical studies have shown three-to sixfold amplification of DHFR genes in patients resistant to MTX, with cancers ranging from leukemia , Cardman et al 1984, to lung cancer (Curt et al 1983) and ovarian cancer (Trent et al 1984).…”