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KS99 alone or in combination in AML
CD123. Altogether, it indicated that KS99 targets LSC in AML.
Study of 21 primary human AML cases with KS99 showed a higher sensitivity of cases with mutations asso- ciated with poor prognosis compared to cases with favor- able prognosis. NPM1 mutation is linked to better progno- sis and responds well to traditional chemotherapy, but is relatively insensitive in vitro to KS99. In contrast, AML with poor prognosis MDS-RC49-54 were killed by KS99 at lower concentrations. AML with MDS-RC represents 25-35% of all AML, and, given its poor prognosis, calls for better therapies. Currently, experimental and investiga- tional agents are available to target different subgroups of AML, but few address AML with MDS-RC. Our study suggests that KS99 not only targets LSC, but has potential activity against AML with MDS-RC.
Finally, our preclinical animal data are clear evidence of the therapeutic potential of KS99 in immunocompromised and immunocompetent AML xenograft models. In addi- tion, KS99 augmented the efficacy of standard of care agent, Ara-C. Although KS99 has shown in vivo AML inhibitory potential in this study, the activity has been modest. We believe that these findings are expected given the PK profile of this agent. The plasma concentrations achievable at the MTD were well below the IC50 deter- mined from in vitro studies and, together with the relative- ly rapid decay in these levels, provide data explaining less than robust in vivo activity. Current efforts are directed at the study of different formulations for drug delivery and structural variants of KS99 which may yield similar in vitro activity with improved toxicity and pharmacokinetic characteristics.
In summary, we demonstrate that KS99 inhibits ALDH, pSTAT3, and pBTK in AML and decreases cell prolifera- tion and clonogenicity while increasing apoptosis. BTK
phosphorylation is also inhibited, though the evidence presented here suggests that this may not be the primary target of drug inhibition. We believe that in silico data sug- gest that ALDH may be such a primary target. Almost all human AML cases, including those with MDS-RC, have been sensitive to KS99. This agent targets LSC and pro- genitors with limited toxicity towards normal HSPC. Our study offers a comparative validation of KS99 to the stan- dard agent Ara-C in specific targeting of AML-LSC. This study advances KS99 alone or in combination as a candi- date agent for therapeutic development after reformula- tion or chemical modification of KS99 or its derivatives which may prove active in clinical trials of AML.
Acknowledgments
The authors thank those who generously provided cell lines for our studies: Drs. HG Wang and Kenichiro Doi, Penn State Hershey (MV4-11, MV4-11-Luc2-IRES-YFP, and MOLM- 13), Drs. Barbara Miller and Su Jen Chen, Penn State Hershey (U937 and U937-Luc2-P2A-tdTomato). Dr. Ahmad R. Safa, NCI, Bethesda, (HL-60/vincristine resistant). We also thank Dr. Malcolm Moore (Memorial Sloan Kettering, New York, NY) for pUltra-Chili-Luc plasmid. The authors thank the staff of the Penn State Cancer Institute, Organic Synthesis Core, Flow Cytometry, Mass Spectrometry & Proteomics Core, and Preclinical Therapeutic core facility at Penn State University College of Medicine. We thank Daniel Brosius, Christina Gareis, Shreya Thakur and Zheng Zeng for technical assistance.
Funding
This study was funded by the Kenneth F Noel Memorial Fund (DFC), Delbert J. McQuaide Cancer Research Fund (AS), The Penn State Cancer Institute and the National Institutes of Health under the National Cancer Institute Award Number P01CA171983.
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