International symposium on trisomy 21. Rome 21-24 mai 1989. In vitro sensitivity of trisomy 21 lymphocytes to chemotherapy implications for future research.

Marie PEETERS, Marie Odile RETHORE and Jérôme LEJEUNE

Institut of progenese


Sommaire

It is generally accepted that trisomy 21 cells (DS) are unusually sensitive to clastogenic agents (chemical, radioactive or viral agents) thought to result from a defect in DNA repair mechanisms. Using an in vitro lymphocyte culture system we studied five chemotherapeutic agents : methotrexate (MTX), 6 mercaptopurine (6MP), 5 fluorodeoxy-uridine (FudR), cytosine arabinoside (AraC), 5 azacytidine (5Aza), all cell-cycle, S phase specific. Peripheral blood lymphocytes from at least 6 patients with trisomy 21 and their age-matched control sibling were cultured according to standard methods in TC 199 medium supplemented with 25% human AB serum, PHA-C and antibiotics. Drugs were added on initiation of the 72 hours culture :

MTX : 0, 1,2x10-8M, 2,4x10-8M ; 6MP : 0, 1,4x10-8M, 2,1x10-8M, 2,8x10-8M, 35x10-8M ; FUdR : 0,0, lx, 10-8M, 2x10-8M, 20x10-8M ; AraC : 0, 0,7x10-8M, 1,5 x10-8M, 2.2x10-8M, 3x10-8M ; 5Aza : 0, 0,6x10-8M, 1,2x10-8M, 2,4x10-8M.

Results were analysed by comparing the mitotic index of each experiment to the patient's own control culture and expressed as the percentage increment or decrease in mitotic index. Statistical comparisons between DS patients and control sibs were based on two-tailed student's t-test. Lymphocytes from patients with trisomy 21 were markedly more sensitive than their normal controls to both methotrexate and 5-azacytidine (MTX : DS lymphocytes were twice as sensitive as normal controls ; the decrease of the mitotic index was proportionnal to the square of the dose of MTX (1) ; 5Aza : t = 3,94, y = 29, p << 0,001). The sensitivity to FUdR was the same in both groups. 6 mercaptopurine and low dose AraC significantly increased the mitotic index of DS lymphocytes (6MP : t = 6, y = 54, p <<< 0.001 ; AraC : t = 3,6, y = 20, 0,005 < p < 0,001). These findings indicate : 1) The cytotoxicity of various chemotherapeutic agents is highly specific and indicative of biochemical anomalies associated with DS. 2) DS are abnormally sensitive to agents that interfere with methylation. 3) Nucleotide pool imbalances exist in DS and may be responsible for its pathophysiology.


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Note

(1) LEJEUNE J : Ann Génét. 1986, 29 ; 16-19.