Role of P-glycoprotein in evolution of populations of chronic myeloid leukemia cells treated with imatinib.

Imatinib mesylate (imatinib) is a new generation preparation that is now successfully used for treatment of cancer, particularly for chemotherapy of chronic myeloid leukemia (CML). Imatinib inhibits the activity of chimeric kinase BCR-ABL, which is responsible for the development of CML. The goal of this study was to investigate the role of a multidrug resistance protein, P-glycoprotein (Pgp), in the evolution of CML treated with imatinib. We demonstrate here that although imatinib is a substrate for Pgp, cultured CML cells (strain K562/i-S9), overexpressing active Pgp, do not exhibit imatinib resistance. Studies of CML patients in the accelerated phase have shown variations in the number of Pgp-positive cells (Pgp+) among individual patients treated with imatinib. During treatment of patients with imatinib for 6-12 months, the number of Pgp-positive cells significantly increased in most patients. The high number of Pgp+ cells remained in patients at least for 4.5 years and correlated with active Rhodamine 123 (Rh123) efflux. Such correlation was not found in the group of imatinib-resistant patients examined 35-60 months after onset of imatinib therapy: cells from the imatinib-resistant patients exhibited efficient Rh123 efflux irrespectively of Pgp expression. We also compared the mode of Rh123 efflux by cells from CML patients who underwent imatinib treatment for 6-24 months and the responsiveness of patients to this therapy. There were significant differences in survival of patients depending on the absence or the presence of Rh123 efflux. In addition to Pgp, patients' cells expressed other transport proteins of the ABC family. Our data suggest that treatment with imatinib causes selection of leukemic stem cells characterized by expression of Pgp and other ABC transporters.

[Prognosis factors in imatinib mesilate therapy in patients with a chronic phase of Ph-positive chronic myeloid leukemia: data from a multicenter non-randomized trial in Russia].

AIM: To reveal prognostically significant factors affecting efficacy of glivek therapy in untreated (duration of the disease < or = 6 months) and pretreated (duration of the disease > 6 months) patients with chronic myeloid leukemia (CML) in a chronic phase. MATERIAL AND METHODS: A total of 338 patients (64 untreated and 274 pretreated) with a chronic-phase CML on glivek therapy entered the trial. RESULTS: Five-year survival on glivek was high (89, 98 and 88% in untreated and pretreated patients, respectively). Incidence of transformation in the acceleration phase and blast crisis was low both in untreated and pretreated patients (1.6 and 11%, respectively) and correlated with the rate of a complete cytogenetic response (CCR). Untreated patients had no factors affecting treatment efficacy negatively, CCR probability was 96%. Blastemia, thrombocytosis and splenomegaly reduced CCR probability significantly in pretreated patients. Slow reduction of the tumor mass, late achievement of a complete hematological response and a cytogenetic response decreased probability of CCR. CONCLUSION: Glivek is a drug of choice for patients with chronic-phase CML. High probability of CCR both in untreated and pretreated patients lowers the risk of the disease transformation into the phase of acceleration/blast crisis and raises overall survival in both groups.

[Cytogenetic response as a marker of efficacy of chronic myeloid leukemia therapy with a BCR-ABL thyrosine kinase inhibitor glivek].

AIM: Clinical practice with the drug glivek (imatinibe mesilate, ST1571) blocking activity of oncoprotein p210 shows that a cytogenetic response can be reached in 50-60% of patients with chronic myeloid leukemia (CML), in a late chronic phase (CP) in resistance to or intolerance of interferon alpha (IF-alpha) and in 24-43% of patients in the acceleration phase (AP). This study aimed at assessment of the rate and stability of a cytogenetic response (CR) and long-term results of survival in CML patients on glivek. MATERIAL AND METHODS: Glivek was given to 195 CML patients (median of the treatment duration was 42 months, 1-156 months, of the patients' age--46 years). 79 patients were in CP, 116--in AP. The doses were 400 mg/day and 116 mg/day, respectively. Karyotype was studied before the treatment and later after each 6 months. RESULTS: A considerable CR was achieved in 57% patients in CP and 44%--in AP. Of them complete CR was obtained in 48 and 35%, respectively. Marked CR is a favourable prognostic factor. Survival of patients with marked CR in CP (97% 0 and AP (89%) was significantly higher than without CR (58 and 47%, respectively, p < 0.05). Marked CR persisted in 95% cases in both phases of CML. In complete CR, a repeated study of karyotype revealed residual number of Ph+ cells both in CP and AP in 86% patients. This demonstrates necessity to take glivek continuously in achievement of a complete CR by karyotypic test. Glivek inhibits the disease progression, lowers annual lethality. 42-month (median of glivek treatment duration) overall survival reached 91 and 59% in CP and AP, respectively. CONCLUSION: CR is an integral index prognosticating CML course. Survival rose significantly in patients with marked CR both in CP and AP of CML. Marked CR is persistent in continuous glivek therapy. The rate of a CR depends much on the disease stage.