Inhibition of autophagy stimulate molecular iodine-induced apoptosis in hormone independent breast tumors.
Estrogen receptor negative (ER(-ve)) and p53 mutant breast tumors are highly aggressive and have fewer treatment options. Previously, we showed that molecular Iodine (I(2)) induces apoptosis in hormone responsive MCF-7 breast cancer cells, and non-apoptotic cell death in ER(-ve)-p53 mutant MDA-MB231 cells (Shrivastava, 2006). Here we show that I(2) (3 μM) treatment enhanced the features of autophagy in MDA-MB231 cells. Since autophagy is a cell survival response to most anti-cancer therapies, we used both in vitro and in vivo systems to determine whether ER(-ve) mammary tumors could be sensitized to I(2)-induced apoptosis by inhibiting autophagy. Autophagy inhibition with chloroquine (CQ) and inhibitors for PI3K (3MA, LY294002) and H+/ATPase (baflomycin) resulted in enhanced cell death in I(2) treated MDA-MB231 cells. Further, CQ (20 μM) in combination with I(2), showed apoptotic features such as increased sub-G1 fraction (∼5-fold), expression of cleaved caspase-9 and -3 compared to I(2) treatment alone. Flowcytometry of I(2) and CQ co-treated cells revealed increase in mitochondrial membrane permeability (p<0.01) and translocation of cathepsin D activity to cytosol relative to I(2) treatment. For in vivo studies ICRC mice were transplanted subcutaneously with MMTV-induced mammary tumors. A significant reduction in tumor volumes, as measured by MRI, was found in I(2) and CQ co-treated mice relative to I(2) or vehicle treated mice. These data indicate that inhibition of autophagy renders ER(-ve) breast tumor cells more sensitive to I(2) induced apoptosis. Thus, I(2) together with autophagy inhibitor could have a potential tumorostatic role in ER(-ve) aggressive breast tumors that may be evaluated in future studies.
Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.
Preeti
P
Singh
Madan
M
Godbole
Geeta
G
Rao
Sanjay
S
Annarao
Kalyan
K
Mitra
Raja
R
Roy
Arvind
A
Ingle
Gaurav
G
Agarwal
Swasti
S
Tiwari
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D045744:Cell Line, Tumor; D002738:Chloroquine / Q000494:pharmacology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007455:Iodine / Q000494:pharmacology*; D051379:Mice; D008813:Mice, Inbred ICR; D051336:Mitochondrial Membranes / Q000187:drug effects; D010539:Permeability; D021381:Protein Transport; D011960:Receptors, Estrogen / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
D000970:Antineoplastic Agents; D004967:Estrogens; D011960:Receptors, Estrogen; D016159:Tumor Suppressor Protein p53; D002738:Chloroquine; D007455:Iodine; D053148:Caspase 3; D053453:Caspase 9; D002402:Cathepsin D