Publication Date

8-2017

Date of Final Oral Examination (Defense)

6-9-2017

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Chemistry

Department

Chemistry

Supervisory Committee Chair

Kenneth A. Cornell, Ph.D.

Supervisory Committee Co-Chair

Don Warner, Ph.D.

Supervisory Committee Member

Kristen A. Mitchell, Ph.D.

Abstract

Anthracyclines remain widely prescribed and successful anticancer agents, despite serious side effects. Doxorubicin (DOX) is the most prominent anthracycline used to treat many cancers, including hematologic malignancies, soft-tissue sarcomas, cancers of the head and neck, and breast cancer. However, the clinical application of DOX is limited by the development of life-threatening cardiomyopathy and congestive heart failure. The main mechanisms of cardiotoxicity are thought to be mediated through the C-13 carbonyl and quinone ring structures in DOX. To improve the anticancer activity and reduce the cardiotoxic side effects of DOX, two synthetic analogs (GPX-150 and GPX-160) were developed and tested for in vitro and in vivo activity against a panel of soft tissue sarcoma cells. The analogs were further subjected to an array of tests to examine drug stability, transport properties, topoisomerase inhibitory activity and metabolism by cytochrome P450 enzymes.

The two analogs were effective anticancer agents against an array of cancer cells. In particular, GPX-160 exhibited in vitro cytotoxicity against human soft tissue sarcoma (STS) cells that was similar to DOX. Importantly, GPX-160 functioned equally well against both DOX-sensitive and DOX-resistant sarcoma cell lines, suggesting that its structural modifications allowed it to resist P-glycoprotein mediated drug efflux. Moreover, in a murine xenograft model of human STS, both GPX-150 and GPX-160 treatment resulted in significant decreases in both fibrosarcoma tumor volume and weight relative to the vehicle-treated controls.

The stability of the DOX analogs in tissue culture media suggest that in the absence of drug metabolizing enzymes, GPX-150 (t1/2 = 55.9 hr) will persist approximately 8-fold longer than DOX (t1/2 = 6.8 hr) and 3-fold longer than GPX-160 (t1/2 = 20.7 hr). In vitro drug absorption studies across Caco-2 cell monolayers indicate that GPX-150 and GPX-160 have higher permeability coefficients than DOX in both apical-to-basolateral and basolateral-to-apical directions. However, the transport of the analogs is not as heavily polarized in the basolateral-to-apical direction, as is seen with DOX. Both analogs also inhibited human topoisomerase IIα at low micromolar concentrations, supporting the possibility that they share a similar primary mechanism of action with DOX. Finally, human liver microsome metabolism of the two analogs showed that they were insensitive to aldo-keto reductase activity, which was expected based on the loss of the C-13 carbonyl and quinone structures. However, GPX-150 and GPX-160 remained sensitive to CYP2C8 and CYP3A4 activity.

Overall, these studies serve as an initial characterization of two DOX analogs that appear to hold great promise as a next generation of anthracyclines that overcome problems of drug resistance, while mitigating the cardiotoxicity that has limited the use of DOX.

DOI

https://doi.org/10.18122/B2HX43

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