Discovery of Dihydroartemisinin and Dasatinib Drug Combination to Cure Pooroutcome BCR-ABL+ Acute Lymphoblastic Leukemia

<p>Oncogenic signaling by the Philadelphia chromosome-encoded BCR-ABL fusion kinase initiates and drives both Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) and chronic myelogenous leukemia (CML). Food and Drug Administration (FDA)- approved BCR-ABL-specific kinase inhibitors (BCR-ABL–KIs) imatinib, dasatinib and nilotinib induce prolonged remissions in CML but poor leukemia-reduction and relapse-control in Ph+ ALL. The relative primary BCR-ABL–KI-resistance in Ph+ ALL patients carrying predominantly BCR-ABLWT disease cannot be attributed to drug-resistant BCR-ABL mutations (BCR-ABLMUTANTS), and remains poorly understood.</p> <p>We established a cell-based platform to evaluate the modulation of anti-Ph+ ALL activity of drugs by both tumor-extrinsic cytokines normally present in the leukemia microenvironment and tumor-intrinsic vector-mediated alteration of candidate genes. We identified that BCR-ABLWT-driven Ph+ ALL cells are rendered significantly resistant against all FDAapproved BCR-ABL–KIs by 1) Several host-cytokines, but most dominantly by Interleukin7 (IL7), and 2) Cell-intrinsic functional-loss of IKAROS. Utilizing IL7-deficient recipient mice, we demonstrated that physiological levels of IL7 significantly attenuate the survival benefit derived from dasatinib monotherapy against Ph+ ALL. Follow-up mechanistic studies using cell signaling and gene expression comparisons indicated that IL7 imparts chemo-refractoriness by initiating IL7-pSTAT5-c-MYC signaling. Interestingly, IKAROS haploinsufficiency, which has been previously associated with poor clinical prognosis in patients with Ph+ ALL, was recently demonstrated to directly de-repress c-MYC expression. This suggested that both cell-extrinsic IL7 and cell-intrinsic IKAROS loss converge on c-MYC, which may act as node of leukemia BCR-ABL–KI-refractoriness. We confirmed that vector-mediated modifications imitating IL7 induction of STAT5 activity, functional-loss of IKAROS, and c-MYC over-expression, all selectively enrich Ph+ ALL cells during prolonged exposures to imatinib and dasatinib, thus revealing new chemo-refractory phenotypes.</p> <p>Contemporary medicine advocates co-treatment with agents of complementary mechanism of drug-action to tackle drug resistance. To identify combination agents that could overcome the dasatinib-resistant phenotypes of Ph+ ALL, we screened a library of 3200 agents including known anti-infective and chemotherapy drugs. We discovered that a well known antimalarial drug dihydroartemisinin (DHA) killed host-IL7-protected BCR-ABLWT, c-MYC-overexpressing BCR-ABLWT and BCR-ABLMUTANT Ph+ ALL cells in vitro. In vivo, DHA displayed weak activity as a single agent but its addition synergistically augmented the leukemia reduction by dasatinib, relative to either of the two drugs alone. Remarkably, DHA and dasatinib combination regimen eliminated host-protected dasatinib-refractory persistent leukemia and improved long-term survival from 0 to >90% in a murine model that faithfully captures the BCR-ABL–KI drug-refractoriness of human Ph+ ALL.</p> <p>This study: 1) Uncovers novel mechanisms of clinical drug-resistance against BCR-ABL–KIs, 2) Identifies increased levels of IL7, pSTAT5 and c-MYC protein, and IKAROS haploinsufficiency as potential biomarkers of BCR-ABL-targeted drug-resistance, 3) Strongly supports clinical exploration of the BCR-ABL–KI and DHA combinations for treating patients with Ph+ ALL, and 4) Establishes a paradigm for investigating frequently overlooked host-tumor-drug interactions.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biomedical Sciences

Year dc:date.available

2012

Author dc:creator

• Singh, Harpreet

Contributors dc:contributor

• Gerard P. Zambetti, Ph.D. (for Richard T. Williams, M.D., Ph.D.)

• High Throughput Drug Screening
• Tumor Microenvironment
• Ph+ Acute Lymphoblastic Leukemia
• BCR-ABL Kinase Inhibitors
• Dasatinib
• Dihydroartemisinin
• Chemicals and Drugs
• Diseases
• Medical Sciences
• Medicine and Health Sciences
• Neoplasms
• Pharmaceutical Preparations
• Pharmaceutics and Drug Design
• Pharmacy and Pharmaceutical Sciences

Repository record dc:identifier

https://dc.uthsc.edu/dissertations/249

OAI identifier oai:identifier

oai:dc.uthsc.edu:dissertations-1245