Bernard W Futscher

PMID: 8383009;Abstract:

Five cell lines selected for resistance to the cytotoxicity of inhibitors of DNA topoisomerase II have point mutations in the gene that codes for the Mr 170,000 form of this enzyme. In each case, the mutation results in an amino acid change in or near an ATP binding sequence of the Mr 170,000 isozyme of topoisomerase II. We used single-strand conformational polymorphism analysis to screen for similar mutations in other drug-resistant cell lines or in leukemic cells from patients previously treated with etoposide or teniposide. We also analyzed the region of the gene that codes for amino acids adjacent to the tyrosine at position 804 of topoisomerase II which binds covalently to DNA. CEM/VM-1, CEM/VM-1-5, and HL-60/AMSA human leukemic cell lines were used as controls; 3 of 3 known mutations were detected by migration differences of polymerase chain reaction products from the RNA extracted from these three lines. A previously unknown mutation was found in the tyrosine 804 region of the Mr 170,000 topoisomerase II expressed by CEM/VM-1 and CEM/VM-1-5 cells. Sequence analysis showed that substitution of a T for a C at nucleolide 2404 resulted in an amino acid change of a serine for a proline at amino acid 802. No mutations in any of the ATP binding sequences or in the tyrosine 804 region were detected in polymerase chain reaction products from RNA extracted from human leukemia HL-60/MX2 or CEM/MX1 cells (both cell lines selected for resistance to mitoxantrone) or in human myeloma 8226/Dox1V cells (selected for resistance by simultaneous exposure to doxorubicin and verapamil). No mutations were detected in polymerase chain reaction products from RNA extracted from blasts of 15 patients with relapsed acute lymphocytic leukemia, previously treated with etoposide or teniposide. We conclude that: (a) single-strand conformational polymorphism analysis is useful for screening for mutations in topoisomerase II; (b) resistance to the cytotoxicity of inhibitors of DNA topoisomerase II is not always associated with mutations in ATP binding sequences or the active site tyrosine region of Mr 170,000 topoisomerase II; and (c) mutations similar to those detected in drug resistant cells selected in culture have not been identified in blast cells from patients with relapsed acute lymphocytic leukemia, previously treated with etoposide or teniposide.

PMID: 15256060;PMCID: PMC1502109;Abstract:

The maspin gene functions as a tumor suppressor in human breasts, and its expression is frequently lost during breast cancer progression. In vitro models of human breast cancer indicate that the loss of maspin expression is closely linked to aberrant methylation of the maspin promoter. We conducted a study on 30 archival ductal carcinoma in situ (DCIS) specimens to determine if aberrant methylation of the maspin promoter occurred in vivo, and whether it occurred early in breast cancer evolution. Healthy tissue obtained from reduction mammoplasty was used as normal control. Results from immunohistochemical analysis indicate that maspin expression is lost in a substantial fraction of DCIS specimens (57%). Bisulfite sequencing of DNA isolated from laser capture-microdissected normal and neoplastic ducts showed that loss of maspin expression was often, but not always, linked to aberrant methylation of the maspin promoter, suggesting that other mechanisms, in addition to aberrant methylation, participate and/or cooperate to silence maspin gene expression. Taken together, these results indicate that aberrant methylation of the maspin promoter is an early event in human breast cancer.

Desmocollin 3 (DSC3) is a member of the cadherin superfamily of calcium-dependent cell adhesion molecules and a principle component of desmosomes. Desmosomal proteins such as DSC3 are integral to the maintenance of tissue architecture and the loss of these components leads to a lack of adhesion and a gain of cellular mobility. DSC3 expression is down-regulated in breast cancer cell lines and primary breast tumors; however, the loss of DSC3 is not due to gene deletion or gross rearrangement of the gene. In this study, we examined the prevalence of epigenetic silencing of DSC3 gene expression in primary breast tumor specimens.

PMID: 2534817;Abstract:

In this report we present evidence which suggests that pretreatment of a highly nitrosourea-resistant human colon tumor cell line with non-cytotoxic doses of streptozotocin (STZ) prior to, or simultaneously with, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) exposure produces synergistic increases in cytotoxicity of several logs over the cytotoxicity produced by exposure to BCNU alone. STZ pretreatment or simultaneous treatment with BCNU allowed BCNU-induced DNA interstrand crosslinks to form in this cell line, in which BCNU alone did not induce DNA interstrand-crosslinks. Reversal of the schedule (i.e., STZ following BCNU) was less effective in producing synergistic cell kill or increased DNA interstrand crosslinking. Replacement of BCNU with fresh BCNU was not effective in producing increased cell kill and produced no observable interstrand crosslinking. Direct assays for guanine O6-DNA alkyltransferase activity confirmed that more than 75% inhibition of this important DNA repair system occurred following exposure to 2.5 mM STZ and that the inhibition was virtually complete when STZ pretreatment was combined with BCNU exposure.