Abstract B98: Chloroquin converts molecular iodine induced autophagy in MDAMB231 to apoptotic cell death: Implications for overcoming chemotherapeutic resistance
Authors: Singh Preeti , Godbole Madan , Rao Geeta , Saxena Vishwamohan , Annarao Sanjay , Roy Raja , Mitra Kalyan , Bajpai VK , Ingle Arvind 
Published: May 2012

B98

Autophagic mechanism is known to provide survival advantage and chemo-resistant in various cancers. Molecular iodine (I2) has been shown to cause apoptotic cell death independent of estrogen receptor and p53 status in breast cancer cell lines (MCF-7, MDA-MB-231, MDA-MB-453, ZR-75-1, T-47D). In MCF-7 cells apoptotic cell death has been shown to be independent of caspase activity and is mediated through AIF. Non-evident apoptosis in MDA-MB-231 in response to I2 treatment led us to investigate its cell death mechanism in detail. Electron microscopic observations and immunofluorescence performed in molecular iodine treated MDA-MB-231 cells showed increase in acidic vacuoles, autophagosome formation and subsequent autolysosome formation confirmed the autophagy. Blocking of various stages of I2 induced autophagy by PI3 kinase inhibitors (LY294002 and 3-MA), bafilomycin (lysosomal fusion inhibitor) resulted in enhanced cell death indicating that autophagy provides survival advantage to MDA-MB-231 cells. The evidence of autophagy is further supported by enhanced expression of Beclin, decreased Bcl-2, and increased LC-3 cleavage seen on western blot.

Recent evidence that anti-malarial drug chloroquin inhibits chemotherapeutic regimen induced autophagy leading to increased cell death in CNS lymphoma is promising. To know whether the chloroquin mediated increased therapeutic efficacy is drug/system specific or is more generalized phenomenon we investigated its effect in I2 treated MDA-MB-231 cells. Co-treatment with I2 and Chloroquin resulted in increased cytotoxicity, accumulation of sub-G1 cell fraction, nuclear fragmentation with enhanced caspase-9 activation and decreased pro-caspase-3 indicates that chloroquin redirects the cells undergoing autophagy under the influence of molecular iodine to dominant apoptotic mechanism of cell death. In vivo efficiency of molecular iodine and chloroquine combined treatment was assessed in mammary tumor implanted ICRC mice. Mammary tumors were implanted in 18-20 mice from spontaneous mammary tumors harboring mice. Volumes were measured by NMR spectroscopy. Once tumor volume reached 0.5 - 0.7 cm3, mice were divided in three groups of six mice each of control, I2 treatment and I2 plus chloroquin co-treatment (n=6). Tumor volume in untreated mice showed a significant increase over a period of 6 weeks, no increase in iodine treated group and a significant decreased on combination treatment protocol The evidence provided so far indicates that the chloroquin probably increases the therapeutic efficacy of drug regimen in a ubiquitous manner. This switch over ability from autophagy to apoptosis provided by chloroquin makes it a potential adjuvant to overcome the survival advantage conferred by molecular Iodine to MDA-MB-231 cells.

Supported by Department of Science & Technology, Government of India, Grant No SR/SO/HS/017/2003

Citation Information: Cancer Prev Res 2008;1(7 Suppl):B98.