Favorable therapeutic index of a p210(BCR-ABL)-specific tyrosine kinase inhibitor; activity on lineage-committed and primitive chronic myelogenous leukemia progenitors.
OBJECTIVE
In order to assess the effect of the tyrosine kinase inhibitor CGP57148B on lineage-committed and primitive chronic myelogenous leukemia (CML) progenitor cells, peripheral blood progenitor cells (PBPC) mobilized in chronic phase CML were exposed to this compound in vitro.


METHODS
Both short-term (</=1 week) and long-term exposure (>/=2 weeks) to CGP57148B were investigated using suspension culture, semisolid (methylcellulose) assay or stroma-dependent long-term culture (LTC). The proportion of bcr/abl-positive progenitors was determined after direct plating [2 weeks in colony-forming cell (CFC) assay] as well as after 2 or 6 weeks LTC (LTC always followed by CFC replates).


RESULTS
Incubation of CML PBPC over 48 h in suspension culture with 100 microM CGP57148B reduced the proportion of bcr/abl-positive colonies to 4.4 +/- 4.3% (n = 5) after direct plating, 6.6 +/- 4.2% (n = 5) after 2 weeks LTC and 5 +/- 5.6% (n = 2) after 6 weeks LTC. At this dose, survival of drug-exposed normal PBPC was 53 +/- 4.2%, 51 +/- 2.8% and 54.5 +/- 4.9% (n = 2), respectively. Incubation with CGP57148B at a concentration of 10 microM over 1 week under LTC conditions reduced the number of bcr/abl-positive colonies to 11.8 +/- 6.1% (n = 5) after direct plating, 12 +/- 6.4% (n = 4) after 2 weeks LTC and 14.3 +/- 11.4% (n = 3) after 6 weeks LTC; survival of normal PBPC was 84.5 +/- 2.1%, 93 +/- 4.2% and 86 +/- 1.4% (n = 2), respectively. Following long-term exposure to CGP57148B at a concentration of 1 microM, the proportion of remaining bcr/abl-positive colonies was 35%, 9% and 25% of untreated CML samples after direct plating as well as after 2 and 6 weeks LTC, respectively. The respective values for 10 microM CGP57148B were 10%, 11% and 19%. Long-term exposure of normal progenitors to CGP57148B yielded a survival of 98%, 100% and 93% (1 microM) or 77%, 86% and 80% (10 microM), respectively.


CONCLUSIONS
The results support the use of CGP57148B either for short-term exposure in vitro (e.g. purging) or for continuous treatment of CML in vivo.
Kasper
B
B
German Cancer Research Center (DKFZ), Diagnostics and Experimental Therapy, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
Fruehauf
S
S
Schiedlmeier
B
B
Buchdunger
E
E
Ho
A D
AD
Zeller
W J
WJ
D000970:Antineoplastic Agents / Q000633:toxicity*; D001549:Benzamides; D018920:Coculture Techniques; D003114:Colony-Forming Units Assay; D004354:Drug Screening Assays, Antitumor; D004791:Enzyme Inhibitors / Q000633:toxicity*; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000473:pathology*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000097:blood / Q000473:pathology*; D010879:Piperazines / Q000633:toxicity*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011743:Pyrimidines / Q000633:toxicity*; D017154:Stromal Cells / Q000166:cytology / Q000473:pathology; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D001549:Benzamides; D004791:Enzyme Inhibitors; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl