114 Exp. Mol. Med. Vol. 44(2), 109-120, 2012 (Kroemer and Levine, 2008). However, several other reports, have demonstrated concrete examples of autophagic cell death in response to certain agents, further showing that the inhibition or knockdown of essential regulators of autophagy could prolong cell survival. Some cancer cells (especially those lacking essential apoptotic modulators, such as BAX, BAK or caspases) were found to show autophagic cell death in vitro when treated with certain chemothe- rapeutic agents, such as etoposide, fenretinide and dexamethasone (Shimizu et al., 2004; Fazi et al., 2008; Grander et al., 2009; Laane et al., 2009). Certain phytochemicals, including fisetin and resveratrol, have also been shown to induce autophagic cell death in certain types of cancer cells (Puissant et al., 2010; Suh et al., 2010). Furthermore, we recently reported that sodium selenite induces mitophagic cell death (cell death by excessive mitophagy) selectively in malignant glioma cells, but not in normal astrocytes (Kim et al., 2007; Kim and Choi, 2008), suggesting that selenite may prove useful for cancer therapy via a mitochondria-selective type of autophagic cell death. Table 2 lists other examples of autophagic cell death in cancer cells. Autophagic cell death seems to be induced in a cell type-, genetic background-, and stimulus-specific manner. Future studies will be needed to clarify whether the induction of autophagic cancer cell death will prove useful in the clinic. Remaining tasks Requirement for a novel and reliable method for measuring dynamic autophagic processes Our current understanding of autophagy is undoub- tedly incomplete. While we have a fairly good understanding of the regulatory mechanisms governing the early steps of autophagy, including autophagosome formation (initiation, nucleation and elongation) (Mizushima and Yoshimori, 2007), those governing the later steps of autophagy, such as autophagosomal maturation and lysosomal degra- dation, are less well understood. The widely used LC3-based autophagic assay primarily measures the early phases of autophagic activity, which control autophagosome formation (Kabeya et al., 2000). Recently, several different assays have been used to monitor autophagic flux, including the LC3 turnover assay, measurements of the total levels of autophagic substrates (e.g., LC3, p62 and GFP-LC3) (Mizushima and Yoshimori, 2007), analysis of the mRFP-GFP-LC3 color change (Kimura et al., 2007), and measurement of free GFP generated from GFP-LC3 (Hosokawa et al., 2006). However, the utilities and limitations of these assays may vary somewhat in different cell types and experimental contexts (Mizushima et al., 2010). For us to clearly understand the entire dynamic process of autophagy and identify therapeutic targets for its modulation, we need to develop new assays that can be used to examine autophagic activity all the way to the final lysosomal step. In addition, it would be useful to quantitatively measure activity changes among key autophagic effectors, and we should seek to generate standard autophagic assays suitable for routine clinical use. Currently, there are no available data on auto- phagic markers in biopsies obtained before and after treatment, which further indicates that we need new techniques for assessing autophagy in clinical samples, such as tumor biopsies and peripheral-blood mononuclear cells. Rational therapeutic design based on the functional status of autophagy in cancer cells Although only some of the links between autophagy and cancer have been elucidated in detail, pharmacological modulation of autophagy based on its functional status in tumors may provide novel opportunities for cancer management. However, the complex roles of autophagy in tumorigenesis and treatment responses make it difficult to decipher how we should modulate autophagy for maximum therapeutic benefit, given that context- and cell type-specific approaches may be required. Chronically autophagy-deficient tumors may be particularly sensitive to genotoxic and/or metabolic stress-inducing anticancer agents, such as DNA- damaging and anti-angiogenic drugs, due to the absence of autophagy-mediated survival mechanism (Chen and Karantza, 2011). In autophagy-competent tumors, concurrent autophagic inhibition would be expected to increase the efficacy of many anti- cancer modalities (Amaravadi et al., 2011). However, in autophagy-competent tumor cells with particular genetic backgrounds (for example, those having high thresholds of apoptosis), sustained or over- stimulation of autophagy can lead to cell death, and enhanced treatment efficacy (Buytaert et al., 2006; Yang et al., 2011). Therefore, gaining detailed information on the cellular functional status of autophagy (together with apoptosis) in certain cancer types may facilitate the rational design of therapeutic regimens via the modulation of autophagy (Table 3). Context-specific pharmacological mo- dulation of autophagy thus holds great promise as a novel therapeutic approach against cancer.