Apoptosis corrected proliferation fraction in childhood ALL is related to karyotype

Tumour doubling time, a parameter in drug sensitivity testing, reflects both cell proliferation and apoptosis. Variable apoptosis fractions may explain the poor correlation of S-fraction and drug response. DNA aneuploidy (reflecting intrinsic DNA instability) may, by increasing apoptosis, affect drug response.

To assess the relationship between apoptosis corrected proliferation fraction and DNA ploidy in childhood acute lymphoblastic leukemia (ALL).

1.3.1. Study Groups. Thirty two consecutive, unselected diagnostic cases of childhood ALL were included in the study. 1.3.2. Karyotype. A normal karyotype was found in 15 cases (7M, 8F, age 8 m-12 yrs); high hyperdiploid aneuploidy (DNA index > 1.5) was found in 7 patients (1M, 7F, age 3-12 yrs) whereas complex karyotypic anomalies, but with 2n or near 2n DNA were present in 10 patients (7M, 3F, age 1 y 7 m -16 yrs). 1.3.3. Proliferation Fraction Assessment. Immunocytochemical demonstration of S-phase associated nuclear expression of the Ki-67 antigen (MM1, NovaCastra, UK). 1.3.4. Apoptosis Fraction Assessment. Binding of a horse radish peroxidase labelled DNA probe for the 3'-OH ends of apoptosis derived Klenow fragments (Frag-EL, CalBiochem, USA). 1.3.5. Quantitation. Computer assisted image analysis (Quantimet 570C), of 10 systematically random fields of a minimum of 20 nuclei each. A nuclear size bias correcting counting frame and rule were used to correct for cell proliferation associated nuclear volume increase and for the expected nuclear volume reduction resulting from apoptosis.

Corrected for apoptosis, proliferation fraction was highest (mean 57.5%, range 1-100) in poor prognosis, complex karyotype anomalies. Good prognosis, high hyper diploidy showed significantly lower proliferation rates (mean 24.7%, range 12-40) (p < 0.01, t-test).

Apoptosis corrected cell proliferation rate in childhood ALL is not independent of karyotype abnormality which may partly explain a relation to therapy response and prognosis.