Hypoglycemic/hypoxic condition in vitro mimicking the tumor microenvironment markedly reduced the efficacy of anticancer drugs

Abstract

Tumor tissues are often hypoxic because of defective vasculature. We previously showed that tumor tissues are also often deprived of glucose. The efficacy of anticancer drugs is affected by the tumor microenvironment, partly because of the drug delivery and cellular drug resistance; however, the precise mechanisms remain to be clarified. In the present study, we attempted to clarify whether hypoglycemic ⁄ hypoxic condition, which mimics the tumor microenvironment, might induce drug resistance, and if it did, to elucidate the underlying mechanisms. Pancreatic cancerderived PANC-1 cells were treated with serial dilutions of anticancer drugs and incubated in either normoglycemic (1.0 g ⁄ L glucose) or hypoglycemic (0 g ⁄ L glucose) and normoxic (21% O 2 ) or hypoxic (1% O 2 ) conditions. The 50% inhibitory concentration of gemcitabine was 1000 times higher for PANC-1 cells incubated under the hypoglycemic ⁄ hypoxic condition than for those incubated under the normoglycemic ⁄ normoxic condition. Conventional anticancer drugs target rapidly growing cells, so that non-proliferating or slowly proliferating cells usually show resistance to drugs. Though the cell cycle was delayed, sufficient cellular uptake and DNA incorporation of gemcitabine occurred under the hypoglycemic ⁄ hypoxic condition to cause DNA lesions and S-phase arrest. To overcome hypoglycemic ⁄ hypoxia-induced drug resistance, we examined kinase inhibitors targeting Chk1 or cell-survival signaling pathways. Among the compounds examined, the combination of UCN-01 and LY294002 partially sensitized the cells to gemcitabine under the hypoglycemic ⁄ hypoxic condition. These findings suggested that the adoption of suitable strategies may enhance the cytotoxicities of clinically used anticancer drugs against cancer cells. (Cancer Sci 2011; 102: 975-982) I t is widely accepted that solid tumors are heterogeneous in structure as a result of unregulated cancer cell proliferation, presence of several cell types and aberrant vessel formation. Among these, the tumor vasculature has a major impact on the tumor microenvironment. In normal tissue, vascular networks generally develop in a well-ordered hierarchal fashion, so that an insufficient blood supply seldom occurs. In contrast, tumor vascular networks undergo continuous remodeling, because unregulated cell proliferation destroys the existing tissue structures. Previous structural analyses had clearly shown that tumors exhibit aberrant and poorly organized vasculature without any hierarchy.(1-4)As a consequence of the poorly organized vasculature in tumors, the delivery of oxygen is extremely limited. Direct measurement of the oxygen tension in cancer tissues has demonstrated the presence of severely hypoxic regions in many types of cancers.(5) Although hypoxia is also toxic to cancer cells, cancer cells adapt through genetic and epigenetic changes that allow them to survive and even proliferate in hypoxic environments.(6-9) Hypoxia-inducible factor-1a (HIF-1a) is a key transcription factor for downstream hypox...

Selective Enhancing Effect of Early Mitotic Inhibitor 1 (Emi1) Depletion on the Sensitivity of Doxorubicin or X-ray Treatment in Human Cancer Cells

“…6D), we are planning to examine the synergistic effect of Emi1 knockdown in combination with other anticancer drugs that interfere with DNA synthesis. Recent study showed that the hypoxic condition induced multidrug resistance (22). Interestingly, Emi1 siRNA enhanced the sensitivity of anticancer drugs under hypoxia condition (Fig.…”

“…Recent study showed that the hypoxic condition induced multidrug resistance (22). To mimic hypoxia conditions, we used cobalt chloride (CoCl 2 ).…”

Altered cellular redox homeostasis and redox responses under standard oxygen cell culture conditions versus physioxia

“…However, cells treated under these conditions were often compared to cells cultured under air, incorrectly inferring that this oxygenation was representative of "healthy" tissues, and studies have often used short-term decreases in O 2 concentration [4,5], rather than longer periods associated with disease. Additionally, air has been used to represent post-reperfusion oxygenation when modelling reperfusion events in vitro [55,56].…”

“…There is extensive literature on the effects of O 2 concentration on the efficacy of drug and radiation treatments in cancer cell killing, both in vivo and in vitro [4][5][6][7][8][9]. However, most studies have characterized these effects in vitro in cells that have been cultured, long-term, in a hyperoxic environment (i.e.…”

“…air) with subsequent short-term exposure to different O 2 concentrations during various treatments (drugs, photodynamic irradiation, hypoxia-reperfusion, etc.) [4,5,7,[9][10][11][12]. The consequences of long-term exposure to hyperoxic or physioxic environments on the subsequent cell killing effects of cancer treatments (e.g.…”