Document Type

Dissertation - Open Access

Award Date

2021

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Advisor

Rachel Willand-Charnley

Keywords

Collateral sensitivity, Drug repurposing, Erlotinib, H69 and H69AR, MK-571 and Reversan, Small cell lung cancer

Abstract

Some cancers are capable of “spitting out” drugs being fed to them, metaphorically speaking, becoming resistant to what were previously effective chemotherapeutics. In small-cell lung cancer (SCLC), an overexpression of a membrane protein (MRP1) and its transport activity can lead to chemotherapy failure. However, this study showed that certain drugs are selectively cytotoxic (exhibit collateral sensitivity) to MRP1-overexpressed SCLC (H69AR) cells. In this study, three drugs (Erlotinib, Pyrimethamine, Fludarabine) were identified to exhibit a dose-dependent collateral sensitivity on H69AR with IC50 values of ~3.5 μM, ~2 μM, and ~20 μM respectively. Halting the transport activity of the MRP1 with 25 μM MK-571 or 5 μM reversan increased the percent cell viability of MRP1 cells that were treated with erlotinib and pyrimethamine. Thus, the collateral sensitivity induction by these drugs disappeared. Also, the collateral sensitivities of erlotinib and azd1480 were shown to depend on caspase (P < 0.005) when the pan caspase inhibitor (QVD- OPh) was used to inhibit caspase activation. In a GSH-depletion fluorescence assay using 40uM dibromobimane, the collateral sensitivities of erlotinib and azd1480 again were shown to deplete total thiols (GSH) when 30uM of the drug is added to cells that have been treated with 50 μM N-acetylcysteine (NAC) for 48hrs. In another experiment, three non-oncology drugs were identified to exhibit shared cytotoxicity on both H69 and H69AR. Using MTT cytotoxicity assay, alexidine HCl, ouabain and cetrimonium bromide (the three non-oncology drugs) induced a shared cytotoxicity on both H69 and H69AR with ic50 of ~1 μM, ~8 nM, and ~1 μM, respectively. Employing annexin V apoptosis assay, alexidine HCl, and cetrimonium bromide induced apoptosis in both H69 and H69AR. Ouabain on the other hand was necrotic on H69 but induced apoptosis in H69AR. These investigations unveiled the cytotoxic mechanisms and targets that could lead to a possible way to accelerate the development of new cancer drugs or repurpose an existing drug to treat cancer.

Number of Pages

75

Publisher

South Dakota State University

Included in

Biochemistry Commons

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Rights Statement

In Copyright