Abstract B19: Phenothiazines induce cytotoxicity and enhance chemotherapy-induced cell death signaling in acute myeloid leukemia.
Authors: Haag Petra , Zielinska-Chomej Katarzyna , Juntti Therese , Kanter Lena , Lewensohn Rolf , Stenke Leif , Viktorsson Kristina 
Published: August 2014

Abstract
Acute myeloid leukemia (AML) is a hematological malignancy characterized by a clonal proliferation of myeloid precursor cells. Acquired genetic aberrations have been linked to leukemogenic events such as blocked differentiation and deregulated proliferation. Conventional chemotherapeutic regimens used for AML typically involve anthracyclines and cytarabine, often resulting in complete remission (CR), although relapsing disease with a resistant phenotype is still common. Thus, novel therapeutic strategies are clearly needed. We have shown that the CD33-targeted drug gemtuzumab ozogamicin (GO) can induce significant DNA double strand break (dsbs) formation and activate pro-apoptotic signaling via Bak, Bax, and Caspase-3 in AML. The interest in using “old” FDA-approved drugs for new indications is increasing. We have previously reported that phenothiazines, compounds in clinical use for psychiatric disorders, have the capacity to increase chemotherapy-induced cell death by increasing DNA damage signaling and block DNA repair in solid tumor cells. Here we evaluated the effect of phenothiazines as mono therapy, and in combination with different classes of chemotherapeutics, on AML cells representing different leukemic subtypes.
A panel of structurally different phenothiazines (trifluoperazine, thiothixene, chlorpromazine, triflupromazine, fluphenazine, cis-flupenthixol, prochlorperazine, and hydroxyzine) was evaluated for induction of in vitro cytotoxicity in the AML cell lines HL60, Kasumi-1, KG1a, and NB4, representing different AML subtypes. When used as mono therapy trifluoperazine (TFP) was the most efficient cell death inducing phenothiazine. Next the effect of phenothiazines on chemotherapy-induced responses was examined. A sub toxic dose of TFP, causing a 10% reduction in cell viability, was used in combination with the chemotherapeutics daunorubicin or GO. Pre-incubating AML cells for 1h with TFP increased GO-induced cytoxicity by up to 45%. Interestingly, a greater sensitization of chemotherapy-induced cell kill was observed in GO-resistant Kasumi-1 cells than in responsive HL-60 cells. In line with previous results in solid tumor malignancies we found that TFP increased chemotherapy-induced DNA damage signaling, Bak/Bax and caspase-3 activation also in the AML cells examined, suggesting increased DNA damage signaling to be operative.
In conclusion, we show that AML cells are differentially sensitive to a panel of phenothiazines when used in mono therapy and can potentiate different classes of chemotherapeutics by increasing DNA damage response signaling. Thus, this may be a promising treatment option for AML which needs to be further explored by analyzing AML patient derived cells, studies which are ongoing within our group.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B19.
Citation Format: Petra Haag, Katarzyna Zielinska-Chomej, Therese Juntti, Lena Kanter, Rolf Lewensohn, Leif Stenke, Kristina Viktorsson. Phenothiazines induce cytotoxicity and enhance chemotherapy-induced cell death signaling in acute myeloid leukemia. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B19.