Abstract C131: Two-step strategy for efficient killing of multiple myeloma stem cells using Auger-electrons emitting nucleoside analogue 5-Iod-4'-thio-2'-desoxyuridin (I-125-ITdU).

Abstract

Abstract Background: Despite advances in treatment, multiple myeloma (MM) remains an incurable disease. Tumor relapse is at least in part due to the existence of drug resistant cancer stem cells (CSCs). A new therapeutic paradigm that effectively eradicates bulk MM cells and CSC needs to be developed. Auger-electrons emitting nucleoside analogues are attractive for nano-irradiation therapy when incorporated into the DNA. For this proposal, the quiescent CSCs need to be awaked. Although dormant hematopoietic stem cells (HSC) are mostly highly resistant to therapeutic regiments, they can be activated by pro-drug 5-FU to enter active cell cycle and to generate proliferative, therapy sensitive progenitor and mature cells. In analogy to HSC, the activation of highly resistant dormant CSC may present the crucial step for achieving long-term cure of cancers. Therefore in this study we evaluated the therapeutic potential of I-125-ITdU for targeting of multiple myeloma CSCs after priming with a potent thymidylate synthase (TS) inhibitor FdUrd, an active metabolite of 5-FU. Methods: For CSCs isolation, KMS12BM cells were incubated with CD138 and CD27 MicroBeads. The CD Marker expression was investigated by flow cytometry. For FdUrd treatment, cells were incubated with 0.1 μM FdUrd for 2 d. The expression level of aldehyde dehydrogenase (ALDH) was evaluated using Aldefluor assay by flow cytometry. Cell cycle was investigated by Nicoletti. The uptake and DNA incorporation of I-125-ITdU (50kBq/2*10∘4 cells) were assessed after 4 d using gamma counter. Apoptotic cells were identified using Annexin-V by flow cytometry. Results: The purity of isolated CSC was more than 97% (CD27+CD138−). FdUrd treatment of CD27+CD138− cells yielded a decreased ALDH activity (65.2% vs. 29.8%). Furthermore, FdUrd induced CSC to enter the cell cycle (48.5% vs. 18.7% and 29.2% vs. 47.7% of cells in G0/G1 and S phase, respectively) and increased the CD138 expression. The treatment with a non-toxic dose of FdUrd was essential for effective incorporation of ITdU and inducing of irreparable DNA damage. The activation with FdUrd increased the cellular uptake by a factor of 25. KMS12BM CSC incorporated 46.3% ± 2.8% of internalized activity into DNA. Most important, I-125-ITdU showed a potent antimyeloma effect on isolated CSC. More than 95% of treated cells were detected as apoptotic. Conclusion: This is the first report to demonstrate that DNA is a promising target for endo-radio-therapy of CSC of multiple myeloma using two-step-strategy: FdUrd for activating and Auger-radiation emitting thymidine analogue ITdU for eliminating of malign cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C131.