Efficacy of acetyldinaline for treatment of minimal residual disease (MRD): preclinical studies in the BNML rat model for human acute myelocytic leukemia.

The efficacy of acetyldinaline [4-acetylamino-N-(2'-aminophenyl)-benzamide] for eradication of minimal residual disease (MRD), which is left after bone marrow transplantation, and the risk of a bone marrow graft being jeopardized by this treatment was studied in the Brown Norway rat acute myelocytic leukemia model (BNML). To mimic the clinical situation, MRD induction treatment was given to rats showing clinical signs of leukemia and consisted of 80 mg/kg cyclophosphamide and 7.0 Gy X-rays total body irradiation resulting in a 6-8 log leukemic cell kill leaving 10-1000 leukemic cells in the animals. Treatment was completed with a syngeneic bone marrow transplant. A high dose level (HD) treatment of 23.7 mg acetyldinaline/kg per day and a low dose level (LD) treatment of 11.85 mg/kg per day, each given orally for five consecutive days, were compared. The increase in the survival time, the cure rate, and the toxic death rate were evaluated. One 5-day course of LD treatment, started at a time interval of 10, 17, or 24 days following MRD induction, resulted in 44%, 11% or 0% cures. With two 5-day courses of LD treatment, 89%, 22%, or 0% cures were achieved. With LD treatment, maximally an 8 log leukemic cell kill was obtained and no toxicity-related deaths were observed (only less than a 1 log kill of normal hemopoietic stem cells). In contrast, a single course of HD treatment resulted in 56% of the rats (10/18) dying from intestinal tract toxicity, while from the remaining eight rats at risk for relapse, three (37%) showed a very late relapse and five were cured (63%). It was evident that the leukemic cell load at the start of the acetyldinaline treatment determined the probability of relapse. An important finding was that acetyldinaline did not interfere with bone marrow regeneration. The highly curative potential of acetyldinaline treatment in the BNML model during the phase of MRD warrants the introduction of this compound in clinical phase I/II studies.

In vivo development of an acetyldinaline resistant subline of the BN rat acute myelocytic leukemia (BNML).

The cytostatic drug acetyldinaline [ACD, CI-994, 4-acetylamine-N-(2-aminophenyl)-benzamide] shows an extreme antileukemic effect in the Brown Norway (BN) rate model for acute myelocytic leukemia (BNML) with only minor toxicity for normal pluripotent hemopoietic stem cells. So far, the mode of action is unknown. A resistant subline (BNML/ACD-R) was developed in vivo in the BNML model. Leukemic rats received repeated oral administrations of ACD. When the leukemia relapsed after initial remission-induction with ACD, the cells were transferred to new recipients which were again treated. In total, the animals received 247 oral administrations of ACD (33 x 2 mg/kg per day and 214 x 5 mg/kg per day) before full resistance was reached. The cell line was transferred 17 times in total. Treatment of the final resistant cell line with therapeutically highly active doses of 23.7 mg/kg per day and 11.85 mg/kg per day ACD for 5 days, that resulted in an increase of life span (ILS) of 57 and 18 days, respectively, when applied to the sensitive parent BNML line (BNML/S), resulted in only 10 and 3 days ILS, respectively. These results indicate that a significant degree of resistance has been achieved, which can be overcome partially by increasing the dose of ACD. Whether the development of a resistant subpopulation of the BNML is a result of acquired resistance or whether a naturally resistant subpopulation has been selected out after prolonged treatment with ACD remains to be established. The currently available resistant subline BNML/ACD-R now offers the possibility for further studies on the mechanism of action of ACD.

Acetyldinaline: a new oral cytostatic drug with impressive differential activity against leukemic cells and normal stem cells--preclinical studies in a relevant rat model for human acute myelocytic leukemia.

Acetyldinaline [CI-994; GOE 5549; PD 123 654; 4-acetylamino-N-(2'-aminophenyl)-benzamide] is the acetylated derivative form of the original compound Dinaline (GOE 1734; PD 104 208). The efficacy and toxicity of Acetyldinaline for remission-induction treatment of leukemia were evaluated and compared with those observed in previous studies of Dinaline in the Brown Norway acute myelocytic leukemia, as a preclinical model for human acute myelocytic leukemia. There were three treatment groups. Leukemic animals received either 1 or 2 courses of 5 daily p.o. administrations of Acetyldinaline with a "full dose" of 23.7 mg/kg once daily (first group), a twice daily "half dose" of 11.85 mg/kg with an interval of 8 h (second group), or a "half dose" of 11.85 mg/kg once daily (third group). The drug-free interval between the 2 courses was 2 or 9 days. With repeated daily p.o. administrations of 23.7 mg/kg either in a single daily dose or a split daily dose of 2 x 11.85 mg/kg for 1 course, at least an 8-log leukemic cell kill was achieved. In contrast, with these treatment schedules, less than a 1-log cell kill of normal pluripotent hemopoietic stem cells (CFU-S) in the femoral bone marrow was found. Split daily dose treatment was more effective resulting in 37.5% cures, while no cures were observed with the single daily treatment for one course. Treatment with single daily dose of 23.7 mg/kg or a split daily dose of 2 x 11.85 mg/kg for 2 courses, with either a 2- or 9-day interval in between, resulted in lethal toxicity in most of rats. This result was comparable with that previously observed after equimolar doses of Dinaline (20 mg/kg). The half-dose once daily treatment with Acetyldinaline (11.85 mg/kg) for 1 or 2 cycles resulted in about a 4.5 or > 8-log leukemic cell kill, respectively. Toxic side effects, i.e., damage to the gastro-intestinal tract and hemorrhages in the lungs, were more pronounced with full dose either in the single or the split daily dose regimen. No significant toxicity was observed at the half-dose treatment once daily. In conclusion, the impressive differential activity against leukemic cells and normal stem cells observed in this relevant rat model for human acute myelocytic leukemia warrants the introduction of this compound in clinical phase I/II studies.