Is Lymphoid Leukemia Less Susceptible to Busulfan Than Myeloid Leukemia? Comparison of Cytotoxicities of Busulfan, Melphalan, Fludarabine, Clofarabine, Cytosine Arabinoside, and Etoposide in Human Myeloid and Lymphoid Leukemia Cell Lines

<Introduction>

Busulfan (BU), melphalan (MEL), fludarabine (FLU), clofarabine (CLO), cytosine arabinoside (Ara-C), and etoposide (VP-16) are widely used as conditioning regimens for hematopoietic stem cell transplant (HSCT) for myeloid and/or lymphoid malignancies. Among these agents, BU has been used more often for patients with myeloid malignancies.  To show the priorities or inferiorities of anti-tumor activities of both myeloid and lymphoid leukemia cells in vitro, cytotoxicities of these 6 compounds were compared between human myeloid and lymphoid leukemia cell lines.

<Materials and methods>

The following human cell lines were exposed to all 6 chemotherapeutic agents: promyelocytic leukemia cell HL60; chronic myelogenous leukemia cell K562; acute myelogenous leukemia cell KU-812; acute monocytic leukemia cell THP-1; acute lymphoblastic leukemia cells CCRF-CEM, MOLT-3, and MOLT-4; lymphoblastoid cell WIL2-NS. Each cell line was exposed to each agent for 72 hours at 4 digits varied concentrations in 96 well micro plate with triplicate wells containing 5,000 cells in each well. Cell viabilities were determined by adding WST-8 (Kishida Chemical Co., Ltd.) to each well and reading absorbance of 450 nm wave length using multi micro plate reader GloMax^®-Multi+ Detection System (Promega KK).

The drug concentration capable of 50% growth inhibitory concentration (IC₅₀) was calculated using GraphPad Prism 6 (GraphPad Software, Inc.).

<Results>

The anti-tumor activities of these 6 chemotherapeutic agents for both myeloid and lymphoid leukemia cell lines were determined as IC₅₀. K562 was resistant to all the agents having the highest IC₅₀ in all agents (high than 100, 101, 529, 0.46, higher than 10 and 11.7 micro M for BU, MEL, FLU, CLO, Ara-C and VP-16) and MOLT-4 was relatively sensitive to tested agents showing lowest or lower IC₅₀ than those of other cell lines (14.2, 0.89, 0.28, 0.021, 0.0044 and 0.017 micro M respectively).

BU, MEL, FLU, CLO and Ara-C showed similar activities against myeloid leukemia cells and lymphoid leukemia cells [Fig 1 A)-E)]. On the other hand, VP-16 showed more anti-leukemia activities against lymphoid leukemia cells than myeloid leukemia cells [Fig 1 F)].

<Conclusion>

Although the number of tested cell lines is limited, BU showed similar anti-leukemic activities against myeloid and lymphoid leukemia cell lines as is shown by MEL, FLU, CLO, and Ara-C. This data supports the use of busulfan as a preparative agent in patients with lymphoid malignancies. Further studies including combination of multiple chemotherapeutic agents would show more advanced scientific rationale for strategic conditioning regimen of HSCT for leukemia.

Figure legends and figures

Figure 1 �FIC₅₀ of A) BU, B) MEL, C) FLU, D) CLO, E) Ara-C, and F) VP-16 for myeloid (�Ÿ) and lymphoid (�œ) human leukemia cell lines.