Bortezomib Has No. Ex Vivo Activity in Chronic Myeloid Leukemia: Individual Tumor Response Testing Comparative Study in Pediatric and Adult Acute and Chronic Leukemia.

Resistance to imatinib is one of the most important issues in treatment of CML. Proteasome inhibitor, bortezomib, is known to be effective in therapy of various neoplasms. Preclinical studies demonstrate the ability of bortezomib in chemosensitization and overcoming of chemotherapy resistance.

Analysis of ex vivo drug resistance to bortezomib and another 23 drugs including tyrosine kinase inhibitors (TKI) in CML, in comparison to acute adult and pediatric leukemia.

A total number of 241 patients entered the study, including: 106 Ph(-)ALL and 53 AML children (age 0.1-18, median 7 years) and 46 AML and 36 CML adults (age 18-69, median 41 years). All children were diagnosed as de novo leukemia, AML adults as de novo (n=20) or relapsed/refractory (n=26). Due to similar drug sensitivity, all adult AML patients were pooled into one group (Gil et al, Anticancer Res, 2007;27:4021). Among CML patients 19 had advanced disease; 16 were resistant to imatinib and 6 had ABL-kinase domain mutations (M244V, E255K, Y253H, M351T and 2 with F317L). Ex vivo drug resistance profile was studied by the MTT assay with the use of following drugs: prednisolone, vincristine, idarubicin, daunorubicin, doxorubicin, mitoxantrone, etoposide, L-asparaginase, melphalan, cytarabine, fludarabine, cladribine, thiotepa, treosulfan, 4-HOO-cyclophosphamide, thioguanine, bortezomib, topotecan, clofarabine and busulfan. CML patients were also tested for sensitivity to TKI: imatinib, dasatinib and nilotinib.

CML cells were more resistant than AML blasts to following drugs: prednisolone (1.5-fold; p=0.037), vincristine (2.3-fold; p=0.004), doxorubicin (>6.9-fold; p<0.001), etoposide (7.4-fold; p<0.001), melphalan (5.9-fold; p=0.001), cytarabine (12.5-fold; p=0.005), fludarabine (2.6-fold; p=0.008), thiotepa (5.4-fold: p=0.001), 4-HOO-cyclophosphamide (2.3-fold; p=0.015), thioguanine (>4-fold; p<0.001), bortezomib (6.2-fold; p<0.001), topotecan (20-fold; p<0.001), and clofarabine (50-fold; p<0.001). No differences in sensitivity were found for idarubicin, daunorubicin, mitoxantrone, L-asparaginase, cladribine, and treosulfan, while CML cells were 2-fold more sensitive to busulfan (p=0.035). Adult and pediatric AML samples did not differ significantly in ex vivo drug resistance to all tested drugs. Pediatric AML samples were more resistant than pediatric ALL samples to most of tested drugs, however they had comparable sensitivity to cytarabine, thioguanine, bortezomib, and clofarabine. CML patients with mutation had higher ex vivo resistance to: vincristine (3.3-fold; p=0.044), idarubicin (7.9-fold; p=0.031), thiotepa (13.7-fold; p=0.044), and busulfan (21.6-fold; p=0.024). No significant differences were observed with respect to other drugs, including all 3 TKI's. CML patients resistant to imatinib had higher ex vivo resistance to: vincristine (2.5-fold; p=0.016), daunorubicin (3.1-fold; p=0.011), etoposide (2.2-fold; p=0.031), and busulfan (4.5-fold; p=0.032). No significant differences were observed in respect to other drugs, including all 3 TKI's. No significant differences were observed between CML patients with non-advanced and advanced disease to all tested drugs, including TKI's.

CML cells are ex vivo more resistant to most drugs than acute leukemia blasts. Bortezomib alone has no ex vivo activity in CML patients. No differences between CML subgroups in sensitivity to 3 various TKI was detected. These findings require further investigations.

This study was supported by grants: EC 2008/2009 ZPORR SPS.IV-3040-UE/217/2009; EFS 9/9/POKL/4.4.1/2008; UMK 09/2009 and MNiSW N407 078 32/2964.

No relevant conflicts of interest to declare.