Doctor of Philosophy (PhD), University of Toledo, 2020, Biomedical Sciences (Cancer Biology)

Chemoresistance is a major clinical concern in triple-negative breast cancer (TNBC) patients, leading to minimal residual disease and tumor relapse. Intrinsic chemoresistance is mediated by the surviving breast cancer stem-like cells (BCSCs) that self-renew and undergo multilineage differentiation to repopulate into a heterogeneous tumor. BCSCs are not only intrinsically chemo/radio resistant, but can also interconvert between BCSCs and bulk tumor cells. In addition to intrinsic therapy resistance, cancer cells can also acquire resistance when they are gradually exposed to therapy, which is the usual course of a treatment regimen. During this process, cancer cells continuously adapt and rewire or reprogram themselves and their microenvironment by upregulating drug transporter proteins and survival factors for their sustenance. Therefore, it is imperative to identify novel molecular targets and develop therapeutic strategies that could co-target BCSCs and bulk tumor cells to tackle both, intrinsic and acquired chemoresistance. Many oncogenic signaling pathways converge at the eukaryotic protein translation initiation machinery, the eIF4F complex which plays a key role in regulating the translatome. This complex plays a critical role in translation of several oncogenic mRNAs implicated in cellular proliferation, invasion, metastasis and chemoresistance. In our previous study, we demonstrated that the mRNA helicase eIF4A1 of the eIF4F complex, serves as a vulnerable node in inducing cell-death in TNBC cells. In our current study, we hypothesized that targeting eIF4A1 could be used as a strategy to overcome breast cancer chemoresistance. We developed two model systems; BCSCs and paclitaxel-resistant cells, reflective of intrinsic and acquired chemoresistance. Through pharmacological (Rocaglamide A) and genetic (CRISPR-Cas9) targeting of eIF4A1, we observed a statistically significant reduction in the self-renewal ability, pluripotency factors and drug transporter expres (open full item for complete abstract)

Committee: Dayanidhi Raman (Advisor); Kathryn Eisenmann (Committee Member); Saori Furuta (Committee Member); Nagalakshmi Nadiminty (Committee Member); Amit Tiwari (Committee Member) Subjects: Biomedical Research

Doctor of Philosophy (PhD), University of Toledo, 2020, Biomedical Sciences (Cancer Biology)

Triple-negative breast cancer (TNBC) remains clinically challenging as effective targeted therapies are still lacking. In addition, patient mortality mainly results from the metastasized lesions. Therefore, there is an unmet need to develop novel therapies against metastatic TNBC (mTNBC). CXCR4 has been identified to be one of the major chemokine receptors involved in breast cancer metastasis. Previously, our lab had identified LIM and SH3 Protein 1 (LASP1) to be a key mediator in CXCR4-driven invasion. To further investigate the role of LASP1 in this process, a proteomic screen was employed and identified a novel protein-protein interaction between LASP1 and components of the eukaryotic initiation 4F complex (eIF4F). We hypothesized that activation of the CXCR4-LASP1-eIF4F axis may contribute to the preferential translation of oncogenic mRNAs leading to an altered pro-oncogenic proteome that facilitates breast cancer progression and metastasis. To test this hypothesis, we first confirmed that the gene expression of CXCR4, LASP1, and eIF4A are upregulated in invasive breast cancer. Moreover, we demonstrate that LASP1 specifically associated with eIF4A, a mRNA helicase, in a CXCL12-dependent manner via a proximity ligation assay. We validated this finding through many approaches including co-immunoprecipitation and GST-pulldown assays. Furthermore, we showed an association with eIF4B, an ancillary protein that enhances the helicase activity of eIF4A. Activation of CXCR4 signaling by its ligand, CXCL12, increased the translation of oncoproteins downstream of eIF4A. Interestingly, genetic silencing of LASP1 interrupted the ability of eIF4A to translate oncogenic mRNAs into oncoproteins implicating a role for LASP1 in mediating the signaling from CXCR4. This impaired ability of eIF4A was confirmed by a previously established luciferase reporter assay which harbors a 5'-leader dependent on eIF4F. Finally, depletion of LASP1 sensitizes 231S cells to the pharmacological in (open full item for complete abstract)

Committee: Dayanidhi Raman (Committee Chair); Amit Tiwari (Committee Member); Ritu Chakravarti (Committee Member); Nagalakshmi Nadiminty (Committee Member); Saori Furuta (Committee Member); Shi-He Liu (Committee Member) Subjects: Biomedical Research; Oncology