Study of breast cancer adaptation to anti-­angiogenic therapies by molecular imaging on tissue slides

Breast   carcinoma   is   the   most   common   and   second   leading   cause   of   cancer   mortality   in   women1.   The   ␣␣␣␣␣␣␣␣␣␣␣␣ ␣␣␣ ␣␣␣␣ ␣␣␣␣␣␣␣␣␣␣␣␣ ␣␣␣␣␣␣␣␣ ␣␣␣ ␣␣ ␣␣␣␣-­‐limiting   secondary   step   in   tumorigenesis   led   to   extensive   pre-­‐clinical   researches   on   angiogenesis   and   finally   the   approval   of   VEGF-­‐neutralizing   antibodies   (bevacizumab)  and  VEGF  receptor  tyrosine  kinase  inhibitors  (RTKs:sunitinib).  The  Sunitinib  has  been  used   clinically   in   patients   with   breast   cancer   refractory   to   other   therapeutic   agents2.   Unfortunately,   like   the   cytotoxic   therapies,   these   drugs   do   not   produce   lasting   effects   and   resistance   to   treatment   appeared   clinically3.   Recently,   independent   laboratories   have   reported   experimental   data   demonstrating   that   anti-­‐ angiogenic   treatments   inhibit   tumor   growth,   but   also   stimulate   the   formation   of   lung   metastases   after   treatment   discontinuation4.   The   field   of   imaging   mass   spectrometry   provides   new   tools   to   visualize   and   study  the  profiles  of  proteins  and  small  molecules  associated  with  biomedical  problems5.  
To  this  aim,  we  conducted  a  series  of  experiments  to  setup  a  reproductible  model  of  resistance  to  sunitinib.   The   cells   MDA-­‐MB-­‐231   triple   negative,   from   human   breast   cancer   and   expressing   luciferase   are   injected   subcutaneously  into  mice  RAG1-­‐/-­‐.  The  mice  were  divided  into  four  experimental  groups  including,  on  the   one  hand,  control  mice  treated  with  placebo  (Carboxymethyl  cellulose,  CMC)  sacrificed  on  day  30  (group  1)   or  when  the  tumor  reached  a  volume  of  300  mm3  (group  2).    On  the  other  hand,  Sunitinib-­‐treated  mice  (LC   Laboratories,   40mg/kg/day),   sacrificed   at   day   30   (group   3),   or   when   the   tumor   reached   a   volume   of   300   mm3  (group  4).  MALDI  mass  spectrometry  imaging  was  performed  on  tissue  sections  of  tumors  and  organs   subsequently   colonized   by   metastases.   Matrix   sublimation   was   used   to   coat   tumor   sections   (14   μm-­‐tick)   with   1.5   Diaminonaphthalene   (1.5   DAN)   for   lipids   analysis   and   Sinapinic   acid   (SA)   for   entire   proteins   analysis.   Ion   cartographies   were   recorded   with   a   Solarix9.4T   FTMS   instrument   for   lipids   and   with   an   Ultraflex   II   TOF-­‐TOF   instrument   for   entire   proteins   (BrukerDaltonics,   Bremen,   Germany)   with   a   spatial   resolution  of  100  μm.    
The  analysis  of  differential  protein/lipid  profiles  with  high  mass  accuracy  and  broadband  resolution  allows   detection   of   intense   signals   from   lipid   families   such   as   Phosphatidylcholine   (PC),   Triglyceride   (TAG),   Sphingomyelin   (SM)   and   precise   lipid   droplets   or   tumor   cells   differentiated   location   in   the   Sunitinib   resistant   tumor   cells   compared   to   control   cells.The   protein   profiles   of   the   4   groups   of   mice   show   differences   in   intensity   and   location,   enabling   a   correlation   to   inflammatory   (highlighted   by   histological   staining)  and  angiogenic  phenomenon.