Autophagy Inhibition Using Hydrochloroquine in Breast Cancer Patients:a Pilot Study

In response to various stresses, cells can launch a process of "self-eating", termed autophagy. Thereby, components of the cell are catabolically digested via specific lysosomes called autophagosomes, to provide the cell with energy and other necessary factors to serve as a temporary survival mechanism (Chen et al. 2010).

Two major stressors that can be evaded by autophagy are important for cancer progression and treatment sensitivity:

1. cells can respond with autophagy to cytotoxic treatment such as chemo- or endocrine therapy, thereby leading to treatment insensitivity (Kondo et al. 2005; Chen et al. 2010), and
2. cells can survive severe hypoxia using autophagy (Rouschop et al. 2010), and hypoxic cells themselves are refractory to chemo-, endocrine and radiotherapy.

Thus, tumor cells evade treatment induced cell death by launching a temporary last survival mechanism. Inhibition of this pathway could lead to sensitization for a variety of cancer treatment regimen, or to specific cell killing of tumor associated hypoxic cells that would otherwise be refractory to radiotherapy. Chloroquine (CQ), N'-(7-chloroquinoline-4-yl)-N,N-diethyl-pentane-1,4-diamine, was discovered in 1934, and has widely been used as an effective and safe anti-malarial and anti-rheumatoid agent since 1947. Later, CQ has been rediscovered as a sensitizer of cytotoxic cancer therapies such as ionizing radiation and chemotherapeutics, although the precise mechanism behind this has remained largely unknown (Solomon and Lee 2009). Most recently, it was discovered that CQ inhibits the process of autophagy by impairment of autophagic vesicle clearance, as CQ accumulates in lysosomal vesicles. This has now lead to several investigators proposing that CQ or one of its analogs can be used to inhibit the autophagic pathway as an additive to other cytotoxic treatments. Hydrochloroquine (HCQ, Plaquenil) is a CQ derivative with fewer side effects than CQ, which has long been used as anti-malarial and antirheumatoid agent. It can be safely used at high doses for extended periods of time. Both CQ and HCQ are under investigation in clinical trials for glioblastoma, small and non-small cell lung cancer, breast cancer, prostate cancer, melanoma, renal cell carcinoma, and pancreatic cancer (for reviews see Solomon and Lee 2009 and Chen et al. 2010).

However, the effect of HCQ on tumor tissue, autophagy and/or oxygenation has of yet not been studied in human patients in vivo.