The mitochondrial type IB topoisomerase drives mitochondrial translation and carcinogenesis

Mitochondrial topoisomerase IB (TOP1MT) is a nuclear-encoded topoisomerase, exclusively localized to mitochondria, which resolves topological stress generated during mtDNA replication and transcription. Here, we report that TOP1MT is overexpressed in cancer tissues and demonstrate that TOP1MT deficiency attenuates tumor growth in human and mouse models of colon and liver cancer. Due to their mitochondrial dysfunction, TOP1MT-KO cells become addicted to glycolysis, which limits synthetic building blocks and energy supply required for the proliferation of cancer cells in a nutrient-deprived tumor microenvironment. Mechanistically, we show that TOP1MT associates with mitoribosomal subunits, ensuring optimal mitochondrial translation and assembly of oxidative phosphorylation complexes that are critical for sustaining tumor growth. The TOP1MT genomic signature profile, based on Top1mt-KO liver cancers, is correlated with enhanced survival of hepatocellular carcinoma patients. Our results highlight the importance of TOP1MT for tumor development, providing a potential rationale to develop TOP1MT-targeted drugs as anticancer therapies.

Use of a MET-specific photoprobe to identify bladder tumors in an orthotopic xenograft model of bladder cancer

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Background: Met over-expression has been found in bladder cancer (CaB). Stage and grade increases in urothelial carcinoma have been found to correlate with increases in Met expression. To assess whether molecular optical imaging could enhance the detection of bladder tumors, we used a Met-specific soluble photoprobe in an orthotopic xenograft model of bladder transitional cell carcinoma (TCC).

Methods: An orthotopic xenograft murine model of CaB was developed with T24-Luciferase-positive bladder cancer cells. Presence of tumor was confirmed by luciferase optical imaging (Xenogen IVIS) of mice, 4 weeks after TCC cell implantation. Mice were euthanized and their bladders removed and bivalved. Bladders were incubated for 30 minutes with unbound fluorophore (Cy5**, Peak emission at 675 nM) and subsequently for another 30 minutes with Cy5** bound to a Met-specific peptide. Fluorescence imaging (Maestro) was performed before and after each incubation period. Following imaging, presence of tumor was confirmed histologically.

Results: Cy5**-Met- peptide bound in sufficient density to tumor tissue in bladders for visualization by optical imaging. The tumor to normal bladder imaging ratio ranged from 2:1 to 8:1. Bladder regions with high uptake of Cy5**-Met-peptide corresponded to tumor areas confirmed by histological analysis.

Conclusions: Cy5**-Met-peptide successfully targets Met in an orthotopic xenograft model of bladder cancer. Our results suggest that this agent maybe useful for the enhanced visualization of bladder cancer tumors during cystoscopy.

No significant financial relationships to disclose.

Effect of the orally available MET inhibitor PF-2341066 on tumor burden and metastasis in an orthotopic xenograft model of bladder cancer

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Background: Met over-expression has been found in bladder cancer (CaB). However, to date, the effects of Met inhibition in CaB have not been reported. We used a small, orally available, highly specific Met-inhibitor currently on phase 2 clinical trials, to assess its effects in an orthotopic xenograft model of bladder transitional cell carcinoma (TCC).

Methods: An orthotopic xenograft murine model of TCC of the bladder was developed with T24-Luciferase positive bladder cancer cells. NIH 3T3 cells producing human hepatocyte growth factor (hHGF) were implanted subcutaneously in mice to provide a source of hHGF. Animals were treated with the selective Met inhibitor (PF-2341066) intra-peritoneally after positive detection of bladder tumor primary and/or metatastatic disease. Fluorescence imaging (Xenogen IVIS) of mice was performed weekly. Mice were euthanized 4 weeks after the start of treatment and their tissues studied histologically.

Results: PF-2341066 was found to reduce tumor burden to below detectable levels in both primary and metastatic sites in all mice treated. No noticeable side effects were detected in treated mice secondary to drug administration.

Conclusions: This study is the first to test a small orally available Met-selective inhibitor in an orthotopic, HGF-driven model of human CaB. Our results demonstrate that Met-inhibition by PF-2341066 reduces TCC tumor burden supporting its potential use in patients with bladder cancer.

No significant financial relationships to disclose.