OCI-AML-2

Isolation of Daunorubicin-Resistant AML-2 Sublines

An attempt was made to isolate resistant sublines of acute myelogenous leukemia (OCI-AML-2) cells by chronic exposure to gradually increasing concentrations of daunorubicin to determine the mechanism of its resistance to this drug. Five drug-resistant AML-2 sublines are developed from the wild-type AML-2 line. The resistant AML-2 sublines selected for resistance to daunorubicin were named AML-2/D100, /D250, /D500, and /D 1,000. These resistant sublines appeared to be similar to the wild-type AML-2 cell line in cell size, while they showed slightly increased doubling times of 30 h, 30 h, 43 h, and 43 h, respectively, as compared to 22 h in the parental cell line. The AML-2/D100, /D250, /D500, and /D1,000 were approximately 3-, 6-, 18-, and 23-fold resistant to daunorubicin in comparison to the AML-2 cell line in terms of IC50 (Fig. 1 and Table 1).

As shown in Table 1, the AML-2/D100 and/D250 sublines displayed low levels of cross-resistance to doxorubicin (4-fold), vincristine (26-fold), and VP-16 (10-fold). The AML-2/D500 showed an intermediate level of cross-resistance to doxorubicin (7-fold), vincristine (74-fold), and VP-16 (14-fold). The AML-2/D1,000 subline was resistant to doxorubicin (16-fold), vincristine (248-fold), and VP-16 (37-fold).

Fig. 1 Cytotoxicity of daunorubicin in the parental AML-2 cell line and its daunorubicin-resistant sublines. (Choi CH, Ling V, 1997)

Table 1. Relative resistance of daunorubicin-resistant AML-2 sublines to a variety of anticancer drugs. (Choi CH, Ling V, 1997)

In Vivo Anti-tumor Effects of either Free VTX or PEG-VTX on OCI-AML-2 Mouse Models

A novel polyethylene glycol (PEG)-drug conjugate of VTX (PEG-VTX) was evaluated for its cytotoxic effects on AML both in vitro and in vivo. In the OCI-AML-2 xenograft model, the clinical dosage was mimicked by orally administering free VTX daily for 2 weeks at a dose of 100 mg/kg/day: the total VTX dosage was 1400 mg/kg (Fig. 2 upper panel). PEG-VTX was intravenously administered at 100, 200, or 300 mg/kg once a week for 2 weeks: the total VTX dosages were 16, 32, and 48 mg/kg. Intravenous PEG-VTX showed a weaker growth-inhibitory effect even at the highest dose (300 mg/kg), compared with 100 mg/kg of oral-free VTX (Fig. 2 middle panel and Table 2). The doses of converted API and VTX, however, were much smaller in PEG-VTX (48 mg/kg) than in free VTX (1400 mg/kg). In addition, and most importantly, the treatments of intravenous PEG-VTX even at the highest dose (300 mg/kg) caused no body weight loss in the treated mice, while the treatments of oral-free VTX (100 mg/kg) caused >16% body weight loss (Fig.2 lower panel).

Fig. 2 In vivo anti-tumor effects of either free VTX or PEG-VTX on OCI-AML-2 xenograft mouse model. (Ando H, et al., 2022)

Table 2. TGI of free VTX and PEG-VTX on OCI-AML-2 xenograft mouse model. (Ando H, et al., 2022)