Heritable disorders of DNA repair: xeroderma pigmentosum and Fanconi's anemia

A new anticancer platinum compound, (-)-(R)-2-aminomethyl-pyrrolidine(1,1-cyclobutanedicarboxylato) platinum(II): DNA interstrand crosslinking, repair and lethal effects in normal human, Fanconi's anaemia and xeroderma pigmentosum cells

Interstrand cross-linking, repair and lethal effects of (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +) platinum(II) (DWA2114R) were studied in normal human. Fanconi's anaemia (FA) and xeroderma pigmentosum group A (XPA) cells. Interstrand crosslinking by DWA2114R was slower than that by cisplatin (CDDP), since DWA2114R produced mainly Pt(II)-monoadducts after 1 h treatment, followed by progressive interstrand crosslinking to a maximum 5 h post-incubation, while CDDP induced rapidly interstrand crosslinks in approximately 70% DNA during the 1 h treatment, followed by a approximately 30% residual increase. At the maximum rate, DWA2114R was 18 times less interstrand-crosslinking than CDDP on the 1 mM basis. FA cells were specifically defective in the first half-excision of DWA2114R and CDDP-induced Pt(II) interstrand crosslinks, but XPA cells were as proficient as normal cells (t1/2 = 5-7 h). On the contrary, XPA cells were deficient in excision repair of intrastrand crosslinks, but FA cells were normal. In clonogenic survival curves of all types of cells, mean lethal doses (Do) of DWA2114R were an order of magnitude greater than those of CDDP. FA cells were most (3.5 times) sensitive (Do = 25.1 +/- 0.96 microM) and XPA cells were 1.9 times more sensitive (Do = 47.1 +/- 0.17 microM) to DWA2114R than normal cells (Do = 87.6 +/- 5.65 microM). DWA2114R and carboplatin with a cyclobutanedicarboxylato group exhibited almost similar lethal effects on each of normal, FA and XPA strains. FA (Do = 3.44 +/- 0.44 microM) and XPA cells (Do = 3.84 +/- 0.17 microM) were similarly 3-fold more sensitive to CDDP than normal (Do = 9.97 +/- 0.15 microM). On the basis of a single lethal hit (Do), thus DWA2114R and carboplatin effectively killed more FA cells defective in interstrand crosslink repair than XPA cells defective in intrastrand crosslink repair.

Defective replication of psoralen adducts detected at the gene-specific level in xeroderma pigmentosum variant cells

Replication of damaged DNA is suspected to play an important role in cell cycle, genetic stability, and survival pathways. Using psoralen photoaddition as prototype DNA damage and the renaturing agarose gel electrophoresis technique to measure DNA cross-linking in individual genes, Vos and Hanawalt previously observed efficient bypass replication of psoralen monoadducts in human genes (J.-M. H. Vos and P. C. Hanawalt, Cell 50:789-799, 1987). To understand the mechanism of bypass replication in human cells, mutants affected in such a process would be useful. We now report that cells from individuals suffering from the hereditary recessive syndrome xeroderma pigmentosum variant (XPV) are hypersensitive to killing induced by photoactivated psoralen. In addition, analysis of psoralen-mediated DNA cross-linking in the rRNA genes indicated that although repair of psoralen adducts was similar to that of normal individuals, XPV cells were markedly deficient in the ability to bypass psoralen adducts during replication; in comparison with normal cells, approximately half as many monoadducts were bypassed during replication in XPV cells. Furthermore, in contrast to normal cells, replication of interstrand cross-links was not detected in XPV. This is the first demonstration of a deficiency in bypass replication detected at the gene-specific level in vivo. A model involving a strand-specific defect in recombinational bypass in XPV is proposed.

Defective replication of psoralen adducts detected at the gene-specific level in xeroderma pigmentosum variant cells

Replication of damaged DNA is suspected to play an important role in cell cycle, genetic stability, and survival pathways. Using psoralen photoaddition as prototype DNA damage and the renaturing agarose gel electrophoresis technique to measure DNA cross-linking in individual genes, Vos and Hanawalt previously observed efficient bypass replication of psoralen monoadducts in human genes (J.-M. H. Vos and P. C. Hanawalt, Cell 50:789-799, 1987). To understand the mechanism of bypass replication in human cells, mutants affected in such a process would be useful. We now report that cells from individuals suffering from the hereditary recessive syndrome xeroderma pigmentosum variant (XPV) are hypersensitive to killing induced by photoactivated psoralen. In addition, analysis of psoralen-mediated DNA cross-linking in the rRNA genes indicated that although repair of psoralen adducts was similar to that of normal individuals, XPV cells were markedly deficient in the ability to bypass psoralen adducts during replication; in comparison with normal cells, approximately half as many monoadducts were bypassed during replication in XPV cells. Furthermore, in contrast to normal cells, replication of interstrand cross-links was not detected in XPV. This is the first demonstration of a deficiency in bypass replication detected at the gene-specific level in vivo. A model involving a strand-specific defect in recombinational bypass in XPV is proposed.

A case of xeroderma pigmentosum group D determined by photobiological study

A case of xeroderma pigmentosum group D in 36-year-old woman (XP85TO) is reported. The patient had severe photosensitivity from age 4, and developed multiple basal cell epitheliomas and solar keratoses but exhibited no apparent neurological defects. A skin phototest by monochromatic ultraviolet light revealed a delayed peak of erythema 48 h after irradiation and lowered minimal erythemal doses. Unscheduled DNA synthesis induced in XP85TO cells was 36.0% in dermal fibroblasts and 32.6% in epidermal keratinocytes compared with normal cells. The XP85TO cells were sensitive to ultraviolet killing (n = 1.0, D0 = 0.80 J/m2). In complementation analysis, XP85TO cells did not complement with xeroderma pigmentosum group D cells. These results indicate that patient XP85TO had xeroderma pigmentosum group D. The Japanese group D patients including XP85TO case showed delayed onset of skin malignant tumors and neurological abnormalities, compared with the group D patients in Europe and the United States. These findings suggest a possible ethnic variation of the clinical phenotype, despite the similar repair defect and ultraviolet hyperssensitivity.

Repair of 254 nm ultraviolet-induced (6-4) photoproducts: monoclonal antibody recognition and differential defects in xeroderma pigmentosum complementation groups A, D, and variant

Repair kinetics of ultraviolet (UV) light-induced (6-4) photoproducts in xeroderma pigmentosum complementation group A, D, and variant cells were studied by the enzyme-linked immunosorbent assay (ELISA) using a specific monoclonal antibody raised against (6-4) photoproducts, together with unscheduled DNA synthesis (UDS) and loss of T4 endonuclease V-susceptible sites (ESS). Group AXP35KO cells completely failed to repair both ESS (cyclobutane pyrimidine dimers) and antibody-recognizing (6-4) photoproducts until tested 24 h after irradiation, and had 2% early-time UDS. Group DXP43KO cells showed about 10% removal of both (6-4) photoproducts and ESS in 24 h, despite showing a residually higher level of 40% early-time and cumulative UDS. Thus, the results substantiated the extreme UV hypersensitivity of XP group A and D cells. However, XP52KO variant cells exhibited the normal level of UDS and ESS loss, but a slightly reduced repair of antibody-recognizing (6-4) photoproducts at 6 and 12 h after irradiation, which may account for a small UV hypersensitivity of the XP variant cells.