Nucleotide ectoenzyme activities of human and Chinese hamster fibroblasts in tissue culture

Resistance to chemotherapeutic antimetabolites: a function of salvage pathway involvement and cellular response to DNA damage

The inherent or acquired (induced) resistance of certain tumours to cytotoxic drug therapy is a major clinical problem. There are many categories of cytotoxic agent: the antimetabolites, e.g. methotrexate (MTX), N-phosphonacetyl-L-aspartate (PALA), 5-fluorouracil (5-FU), 6-mercaptopurine (6-TG), hydroxyurea (HU) and 1-beta-D-arabinofuranosylcytosine (AraC); the alkylating agents, e.g. the nitrogen mustards and nitrosoureas; the antibiotics, e.g. doxorubicin and mitomycin C; the plant alkaloids, e.g. vincristine and vinblastine; and miscellaneous compounds, such as cisplatin. There are also many mechanisms of drug resistance elucidated principally from in vitro studies. These include mutation of target genes, amplification of target and mutated genes, differences in repair capacity, altered drug transport and differences in nucleoside and nucleobase salvage pathways (Fox et al, 1991). The aim of the present review is to evaluate in detail the mechanisms of response of both normal and tumour cells to three chemotherapeutic antimetabolites, MTX, PALA and 5-FU, which are routinely used in the clinic either alone or in combination to treat some of the commonest solid tumours, e.g. breast, colon, gastric and head and neck. The normal and tumour cell response to these agents will be discussed in relation to the operation of the known alternative 'salvage pathways' of DNA synthesis and current theories of DNA damage response.

Assignment of the gene encoding the catalytic subunit C beta of cAMP-dependent protein kinase to the p36 band on chromosome 1

A cDNA for the human catalytic subunit (C beta) of cAMP-dependent protein kinase (PKA) has been cloned from a testis cDNA library. In the present study, we have determined the chromosomal localization of this gene using a cDNA for C beta as a probe. Southern blot analysis of genomic DNA from human/mouse cell hybrids revealed that the presence or absence of a 20-kb XbaI fragment, which hybridized with the C beta probe, was concordant with the presence of human chromosome 1. In situ hybridization to metaphase chromosome confirmed the somatic cell hybrid data and regionally mapped the C beta gene of PKA to the p36 band on chromosome 1.

Trophoblast glycoprotein recognised by monoclonal antibody 5T4 maps to human chromosome 6q14-q15

Human X rodent hybrids were stained by indirect immunofluorescence with 5T4, a murine monoclonal antibody that recognises a 72 kdalton glycoprotein expressed by human trophoblasts and a very restricted range of adult tissues; they were analysed by flow cytometry. Concordance analysis supported by segregation data allowed assignment of the gene controlling glycoprotein expression (M6P1) to chromosome 6. Similar analysis with translocation hybrids gave a regional assignment to 6q14-q15. M6P1 is distinct from NT5, coding for 5' nucleotidase, which maps to the same region.