Presentation Title

Targeting mitochondrial DNA for development of novel antitumor drugs

Authors' Names

Sascha Stump

Presentation Type

Oral Presentation

Abstract

Mitochondria are responsible for the vast majority of energy metabolism in healthy cells and this is often considered their primary function. However, their role routinely changes in tumor cells where mitochondrial metabolism is no longer the major pathway used to produce energy; this shift in metabolism has been named the “Warburg effect”. This metabolic reprogramming has been suggested to also suppress another function of mitochondria in cells where they act as the gatekeeper to the intrinsic pathway of apoptosis, also known as programmed cell death. In order for tumor cells to survive, they must evade apoptosis and this is often referred to as a “hallmark of cancer”. With this in mind, targeting mitochondria for treatment of cancer is an emerging strategy suggested by several high impact reviews as a route to develop more selective therapies. Mitochondria possess their own separate genome, and mutations in mitochondrial DNA (mtDNA) are associated with various diseases including cancer. One strategy for inducing apoptosis in tumor cells involves disrupting transcription and/or replication of mtDNA. In the past decade, much research has been focused on a tertiary structure formed by DNA known as a guanine-quadruplex. Quadruplexes found in nuclear DNA have been demonstrated previously to effect expression of oncogenes and to inhibit telomerase activity, both of which contribute to the pathology of cancer. More recently however, quadruplexes have also been shown to form in mtDNA and are suspected to play a major role in mitochondrial genome homeostasis. A region of mtDNA known as conserved sequence block II (CSB II) has been reported to form a hybrid quadruplex (HQ) and to act as a switch that halts transcription, allowing formation of primers and initiation of mtDNA replication. Deletions in mtDNA have also been shown to occur in close proximity to quadruplexes and these structures are believed to act as “breakpoints”, or regions of increased DNA instability. These reports in the literature have informed the development of a novel class of antitumor compounds, the anthracenyl isoxazole amides (AIMs), which we have reported previously to inhibit the growth of SNB-19 glioblastoma cells at low micromolar to high nanomolar concentrations (10’BiPhenOxy AIM IC50 = 0.67 µM). The AIMs were originally designed to target quadruplexes found in nuclear DNA, however our laboratory has demonstrated that the majority of the AIMs do not enter the nucleus and rather concentrate in the mitochondria of SNB-19 cells. This has lead us to begin examining potential quadruplex targets found in mtDNA. Using a previously published quantitative PCR assay, we have shown the AIMs cause an increase in mtDNA damage following treatment at multiple time-points (3, 6, 12, & 24 hours) preceding the induction of apoptosis. Our laboratory is also working to crystallize the CSB II HQ in the presence and absence of the AIMs. This work will allow us to develop a structure-activity relationship to aid in further synthetic refinement of the AIMs to selectively target the CSB II HQ as a method to prevent mtDNA replication and induce apoptosis in tumor cells.

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Apr 27th, 1:05 PM Apr 27th, 1:20 PM

Targeting mitochondrial DNA for development of novel antitumor drugs

UC Ballroom, Pod #2

Mitochondria are responsible for the vast majority of energy metabolism in healthy cells and this is often considered their primary function. However, their role routinely changes in tumor cells where mitochondrial metabolism is no longer the major pathway used to produce energy; this shift in metabolism has been named the “Warburg effect”. This metabolic reprogramming has been suggested to also suppress another function of mitochondria in cells where they act as the gatekeeper to the intrinsic pathway of apoptosis, also known as programmed cell death. In order for tumor cells to survive, they must evade apoptosis and this is often referred to as a “hallmark of cancer”. With this in mind, targeting mitochondria for treatment of cancer is an emerging strategy suggested by several high impact reviews as a route to develop more selective therapies. Mitochondria possess their own separate genome, and mutations in mitochondrial DNA (mtDNA) are associated with various diseases including cancer. One strategy for inducing apoptosis in tumor cells involves disrupting transcription and/or replication of mtDNA. In the past decade, much research has been focused on a tertiary structure formed by DNA known as a guanine-quadruplex. Quadruplexes found in nuclear DNA have been demonstrated previously to effect expression of oncogenes and to inhibit telomerase activity, both of which contribute to the pathology of cancer. More recently however, quadruplexes have also been shown to form in mtDNA and are suspected to play a major role in mitochondrial genome homeostasis. A region of mtDNA known as conserved sequence block II (CSB II) has been reported to form a hybrid quadruplex (HQ) and to act as a switch that halts transcription, allowing formation of primers and initiation of mtDNA replication. Deletions in mtDNA have also been shown to occur in close proximity to quadruplexes and these structures are believed to act as “breakpoints”, or regions of increased DNA instability. These reports in the literature have informed the development of a novel class of antitumor compounds, the anthracenyl isoxazole amides (AIMs), which we have reported previously to inhibit the growth of SNB-19 glioblastoma cells at low micromolar to high nanomolar concentrations (10’BiPhenOxy AIM IC50 = 0.67 µM). The AIMs were originally designed to target quadruplexes found in nuclear DNA, however our laboratory has demonstrated that the majority of the AIMs do not enter the nucleus and rather concentrate in the mitochondria of SNB-19 cells. This has lead us to begin examining potential quadruplex targets found in mtDNA. Using a previously published quantitative PCR assay, we have shown the AIMs cause an increase in mtDNA damage following treatment at multiple time-points (3, 6, 12, & 24 hours) preceding the induction of apoptosis. Our laboratory is also working to crystallize the CSB II HQ in the presence and absence of the AIMs. This work will allow us to develop a structure-activity relationship to aid in further synthetic refinement of the AIMs to selectively target the CSB II HQ as a method to prevent mtDNA replication and induce apoptosis in tumor cells.