Sensitivity of breast cancer cell lines to recombinant thiaminase I.
OBJECTIVE
We have previously shown that the expression of the thiamine transporter THTR2 is decreased sevenfold in breast cancer, which may leave breast cancer cells vulnerable to acute thiamine starvation. This concept was supported by the observation that MDA231 breast cancer xenografts demonstrated growth inhibition in mice fed a thiamine-free diet.


METHODS
We purified recombinant Bacillus thiaminolyticus thiaminase I enzyme, which digests thiamine, to study acute thiamine starvation in breast cancer.


RESULTS
Thiaminase I enzyme was cytotoxic in six breast cancer cell lines with IC(50)s ranging from 0.012 to 0.022 U/ml. The growth inhibitory effects of the combination of thiaminase I with either doxorubicin or paclitaxel were also examined. Over a wide range of drug concentrations, thiaminase 1 was consistently synergistic or additive with doxorubicin and paclitaxel in MCF-7, ZR75, HS578T and T47D cell lines, with most combinations having a calculated combination index (CI) of less than 0.8, indicating synergy. Although thiaminase I exposure did not stimulate the energy-sensing signaling kinases AKT, AMPK and GSK-3beta in MCF-7, ZR75, HS578T and T47D cell lines, thiaminase I exposure did stimulate expression of the ER stress response protein GRP78. In summary, thiaminase I is cytotoxic in breast cancer cell lines and triggers the unfolded protein response.


CONCLUSIONS
These findings suggest that THTR2 down-regulation in breast tumors may present a nutritional vulnerability that could be exploited by thiaminase I enzyme therapy.
Liu
Shuqian
S
Division of Pediatric Hematology-Oncology, Department of Pediatrics, University of Kentucky College of Medicine, 740 S Limestone Room J457, Lexington, KY 40536, USA.
Monks
Noel R
NR
Hanes
Jeremiah W
JW
Begley
Tadhg P
TP
Yu
Hui
H
Moscow
Jeffrey A
JA
D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D019883:Alkyl and Aryl Transferases / Q000008:administration & dosage / Q000627:therapeutic use*; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004317:Doxorubicin / Q000008:administration & dosage / Q000627:therapeutic use*; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D017239:Paclitaxel / Q000008:administration & dosage / Q000627:therapeutic use*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000627:therapeutic use; D013832:Thiamine Deficiency / Q000378:metabolism; D056811:Unfolded Protein Response / Q000187:drug effects
D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; C492291:SLC19A3 protein, human; D004317:Doxorubicin; D000255:Adenosine Triphosphate; D019883:Alkyl and Aryl Transferases; C022737:thiamin pyridinylase; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D055372:AMP-Activated Protein Kinases; D017239:Paclitaxel