On the other hand, cells with dysfunctional autophagy due to a conditional knockout of the autophagy regulator, FIP200, seem to be more sensitive to environmental stimuli and release more chemokines and interferon, recruiting immune response and suppressing tumor growth and development [52]. and also minimizes toxicity. Here, the role of autophagy in the context of cancer and the interplay of this process with HDACs will be summarized. Identification of key HDAC isozymes involved in autophagy and the ability to target specific isozymes SB 743921 yields the potential to cripple and ultimately eliminate malignant cells depending on autophagy as a survival mechanism. resulted in very promising sensitization to anticancer treatment [11,40,41,42,43,44,45]. Hence, clinical trials have been initiated using regimens that combine conventional chemotherapy or other agents with autophagic flux-blocking agents, such as chloroquine, in an attempt to sensitize the tumors to therapy [39,46]. Chloroquine (CQ) and its hydroxylated derivative, hydroxychloroquine (HCQ), are lysosomotropic agents and inhibit Rabbit polyclonal to ABCA6 lysosomal functions through concentration in acidic vesicles and therefore block autophagic flux at the level of degradation [47,48]. However, CQ and HCQ have properties that are not limited to acidification. Their accumulation in lysosomes has been also linked to lipase inhibition and lysosomal destabilization, and they have also been shown to weakly intercalate with DNA, causing DNA damage, and, finally, CQ has been shown to induce p53 and p21WAF and cause cell cycle arrest [49]. Though they are effective autophagosome degradation inhibitors, these agents additionally affect a diversity of other cellular processes, which should be kept in mind when evaluating clinical trial results and reported treatment side effects. Most of the early clinical trials initiated for the combination of HCQ SB 743921 with anticancer therapy were dose-finding in nature and were not primarily designed to address clinical efficacy. However, in a study combining temozolomide and HCQ, evidence for impaired autophagic flux in peripheral monocytes and in several patients, stable disease or a partial response was achieved [39]. In one patient with advanced melanoma, a durable response of greater than one year was seen [39]. Also, a trial examining the effects of HCQ in combination with temozolomide and radiation therapy in glioblastoma found that HCQ treatment was able to block autophagic flux in peripheral blood mononuclear cells (PBMCs) [46]. However, the maximum tolerated dose of HCQ was rather low and no significant improvement in overall survival was observed with added HCQ [46]. In all of these studies, high grade toxicities were identified in patients receiving HCQ at the dose associated with the best outcomes plus chemotherapy [39,46]. The most common toxicities seen with combination treatment at all dose levels of HCQ, but with greater frequency at the highest dose levels, were anorexia and nausea. Other common toxicities that were observed, but were less severe, were fatigue, rash, stomatitis, lymphopenia, thrombocytopenia, diarrhea, dizziness, and constipation. The increased hematologic toxicities seen with continuous dosing in one study suggest that intermittent compared with continuous dosing may allow for dose escalation [46,50]. Thus new, less toxic and more specific autophagic flux inhibiting compounds, which create a larger therapeutic window are needed. In addition, identifying which patients would be most likely to benefit from therapy combining autophagy-inhibiting agents remains a challenge. The relationship between the effects of autophagy-modulating drugs in the context of a human tumor compared with cell culture and animal models is complex and not directly translatable [50]. One common method to identify candidates for targeted therapy is by gene mutation status. Indeed, SB 743921 oncogene and tumor suppressor gene status also affect the interplay between autophagy and tumorigenesis as well as tumor progression [51,52]. For example, mutations and constitutive autophagy upregulation are closely connected. Differential effects of autophagy inhibition have been observed in can stimulate autophagy activation under conditions of stress [54], thus examining levels of basal autophagy instead of mutation status may be warranted. 2.2. Pitfalls of Using Autophagic Flux Inhibitors as Adjunct Therapy to Anticancer Treatment Several factors hamper a clear interpretation of the outcomes of clinical trials investigating autophagic flux modulation as a part of anticancer treatment. Many studies investigate autophagic flux in PBMCs as a surrogate marker of on-target activity of autophagy inhibitors. However, autophagic flux changes in PBMCs do not always reflect the degree to which autophagy is affected in the tumor itself [50]. Further complicating the matter is that the observation SB 743921 of increased autophagic vacuoles in tumor samples does not allow one to distinguish between autophagy induction SB 743921 and inhibition [50], necessitating measurement of pre- and post-treatment biomarkers to assist in monitoring and interpreting treatment response. Thus, a reliable biomarker to recognize autophagic flux in.
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