Figure 4

R clones are cross-resistant to nucleoside analogs, but remain sensitive to other classes of anti-lymphoma agents. (A-D) WST-8 cell proliferation assays of CTRL cells and R clones were carried out as described in Methods. Maximal absorbance obtained from the untreated cells during the particular experiment (MAX_u) was arbitrary set as 100%. Absorbance of medium without cells was used as background (B). For each cell population (both, unexposed and drug-exposed) and for each measurement (M₁, M₂, M₃…M_X) the proliferation curve was calculated as follows: (M_X - B)/(MAX_u - B). As a consequence, proliferation curves of untreated cells always peak at 100%, while proliferation curves of drug-exposed cells can terminate below or above 100%. One representative example of two independent experiments carried out both on JEKO-1 (A, C) and MINO (B, D) is shown. Data from the remaining three MCL cell lines (HBL-2, GRANTA-519 and REC-1) are not shown, because they did not significantly differ from those presented for the JEKO-1 and MINO cells. In summary, all 5 R clones were cross-resistant to the tested nucleoside analogs, but remained sensitive to other classes of anti-lymphoma agents with negligible differences between particular MCL cell lines. The only exception to the rule was markedly (>100-fold) increased sensitivity of REC-1 R clone to ibrutinib compared to REC-1 CTRL cells (see Additional file 3: Figure S2). The remaining 4 MCL cell lines (JEKO-1, MINO, GRANTA-519 and HBL-2) showed only approx. 2-fold increased sensitivity to ibrutinib compared to the corresponding CTRL cells. Standard deviations were < 5% for all measurements presented in Figure 4.