Currently many breast cancer patients with localized breast cancer undergo breast-conserving therapy consisting of local excision followed by radiation therapy. of autophagy inhibitors to increase radiosensitivity of breast cancer and to target radioresistant breast cancer stem cells. and to accumulate less DNA breaks after radiation [56]. Therefore it is hypothesized that the traditional cancer therapies reduce tumor bulk but the inability to completely eradicate BCSCs results in the failure of complete remission [54 56 57 Several contributing mechanisms for BCSC radioresistance have been reported in the literature. Radioresistance of BCSCs has been linked with genes involved in glutathione synthesis such as glutamate cysteine ligase glutathione synthetase and FoxO1 [8]. Furthermore depletion of glutathione has resulted in radiosensitization [8]. BCSCs in p53 null mutant mice have an increased capacity for DNA damage repair following radiation and this effect is accompanied by down-regulation of PTEN and activation of Akt and Wnt/beta-catenin signaling BMS-582949 pathways [58]. Inhibition of Akt has led to radiosensitization of BCSCs [58]. All together these evidences support the need for future clinical investigations to target BCSCs to increase the efficacy of radiation therapy in breast cancer patients. Autophagy in Breast Cancer Stem Cells Although numerous factors contribute to the characteristics of BCSCs autophagy has been linked to BCSCs survival and resistance to therapy [57]. Previously breast tumors injected with serum-deprived mesenchymal stem cells have demonstrated higher cellularity and decreased apoptosis with increased levels of autophagic activity in the surrounding areas [59]. Furthermore BCSCs are seen to secrete various paracrine factors to support growth in the setting of serum deprivation in parallel with upregulation of key autophagy regulators such as beclin-1 ATG10 and ATG12 [59]. Another study has demonstrated high expression of autophagy markers Atg5 Atg12 and LC3-B in breast BCSCs in associated with upregulation of JNK1 [60]. Inhibition of autophagy with 3-methyladenine can reverse the dormant phenyotpes of BCSCs [60]. Overexpression of beclin 1 and increased starvation-induced autophagy flux are also evident in mammospheres derived from breast cancer cells [61]. In addition beclin1 is found to be essential in BCSC maintenance and tumorigenesis [61]. Recently chloroquine has shown to inhibit autophagy and eliminate BCSCs in preclinical Mouse monoclonal antibody to Protein Phosphatase 3 alpha. and clinical settings via inhibition of the JAK2-STAT3 pathway [62]. BMS-582949 Therefore targeting BCSCs via inhibition of BMS-582949 autophagy may effectively increase radiosensitivity of breast cancers. Clinical Trials Chloroquine and hydroxychloroquine two pharmacologic autophagy inhibitors are currently being investigated in several BMS-582949 clinical trials (Table 1) for breast cancer BMS-582949 treatment [63]. In the ongoing CAT clinical trial 250 mg daily oral dose of chloroquine is being given in combination with taxane or taxane-like chemotherapy to advanced or metastastic breast cancer patients who have failed anthracycline based therapy. Overall response rates will be measured and BCSCs will be quantified pre- and post-therapy. In the CuBiC clinical trial patients waiting for surgery are receiving 500 mg oral chloroquine daily. Changes in proliferative and apoptotic responses based on Ki67 and TUNEL assays as well as autophagy markers of pre- and post-treatment biopsies are being assessed. In the PINC trial patients are receiving either standard dose chloroquine 500 mg per week or low dose chloroquine 250 mg per week for 1 month prior to the excision of the breast tumor. The tumor response to treatment will be evaluated by Response Evaluation Criteria in Solid Tumors (RECIST) criteria using tumor measurements obtained from breast MRI immediately preceding drug treatment and prior to surgery. There is yet another trial currently recruiting metastatic estrogen receptor positive breast cancer patients with progression of disease despite hormonal therapy for hydroxychloroquine treatment in combination with hormonal therapy. The level of the autophagy marker LC3b will be evaluated in pre- and post-treatment.