No abstract

Many cancer cells have an unusual ability to grow in hypoxia, but the origins of this metabolic phenotype remain unclear. We compared the metabolic phenotypes of three common prostate cancer cell models (LNCaP, DU145, PC3), assessing energy metabolism, metabolic gene expression, and the response to various culture contexts (in vitro and xenografts). LNCaP cells had a more oxidative phenotype than PC3 and DU145 cells based upon respiration, lactate production, [ATP], metabolic gene expression, and sensitivity of these parameters to hypoxia. PC3 and DU145 cells possessed similar Complex II and mtDNA levels, but lower Complex III and IV activities, and were unresponsive to dinitrophenol or dichloroacetate, suggesting that their glycolytic phenotype is due to mitochondrial dysfunction rather than regulation. High passage under normoxia converted LNCaP from oxidative to glycolytic cells (based on respiration and lactate production), and altered metabolic gene expression. Though LNCaP-derived cells differed from the parental line in mitochondrial enzyme activities, none differed in mitochondrial content (assessed as cardiolipin levels). When LNCaP-derived cells were grown as xenografts in immunodeficient mice, there were elements of a hypoxic response (e.g., elevated VEGF mRNA) but line-specific changes in expression of select glycolytic, mitochondrial and fatty acid metabolic genes. Low oxygen in vitro did not influence the mRNA levels of SREBP axis, nor did it significantly alter triglyceride production in any of the cell lines suggesting that the pathway of de novo fatty acid synthesis is not directly upregulated by hypoxic conditions. Collectively, these studies demonstrate important differences in the metabolism of these prostate cancer models. Such metabolic differences would have important ramifications for therapeutic strategies involving metabolic targets.

Hypoxic tumor cells are likely to be resistant to conventional chemotherapy, in large part because many anticancer drugs are unable to penetrate into poorly oxygenated tumor tissue. Here, we used quantitative immunofluorescence to study the distribution of mitoxantrone and AQ4N in tumor tissue. AQ4N is a prodrug activated under hypoxic conditions to AQ4, which is structurally similar to mitoxantrone and inhibits topoisomerase II. We characterized the penetration of mitoxantrone and AQ4N/AQ4 through multilayered cell cultures (MCC) and in relation to blood vessels and hypoxic regions in human tumor xenografts. We also studied tumor growth delay after treatment with each agent alone and with the combination. In both MCC and xenografts, mitoxantrone is taken up by proximal cells and penetrates slowly to distant regions. In contrast, AQ4N rapidly penetrates MCC and tumor tissue in vivo, and AQ4N (or its reduced form AQ4) is detected at high concentration within hypoxic regions. The targeting of mitoxantrone to oxygenated regions and AQ4N/AQ4 to hypoxic tumor regions results in effective drug exposure over the entire tumor after combined treatment and increases tumor growth delay compared with either drug alone. The combination of a clinically used anticancer drug with limited tissue penetration and a structurally related drug activated in regions of tumor hypoxia is an effective strategy to overcome chemoresistance due to the tumor microenvironment. This study supports clinical evaluation of AQ4N in combination with conventional anticancer agents, such as mitoxantrone.