REVIEW
published: 08 June 2016
doi: 10.3389/ pha .2016.00151
F on ie s in Pha macology | www. on ie sin.o g 1June 2016 | Volume 7 | A icle 151
Edi ed by:
F ancois X. Cla e ,
The Uni e si y o Texas MD Ande son
Cance Cen e , USA
Re iewed by:
Amedeo Columbano,
Uni e si y o Caglia i, I aly
Nelson Shu-Sang Yee,
Penn S a e Mil on S. He shey Medical
Cen e , USA
Jae-Sung Kim,
Uni e si y o Flo ida, USA
*Co espondence:
José L. Mau iz
[email p o ec ed]
Special y sec ion:
This a icle was submi ed o
Cance Molecula Ta ge s and
The apeu ics,
a sec ion o he jou nal
F on ie s in Pha macology
Recei ed: 14 Ma ch 2016
Accep ed: 26 May 2016
Published: 08 June 2016
Ci a ion:
P ie o-Domínguez N, O dóñez R,
Fe nández A, Ga cía-Palomo A,
Mun ané J, González-Gallego J and
Mau iz JL (2016) Modula ion o
Au ophagy by So a enib: E ec s on
T ea men Response.
F on . Pha macol. 7:151.
doi: 10.3389/ pha .2016.00151
Modula ion o Au ophagy by
So a enib: E ec s on T ea men
Response
Nes o P ie o-Domínguez1, 2, Raquel O dóñez1, 2, Anna Fe nández1, 2,
And es Ga cía-Palomo3, Jo di Mun ané1, 4, Ja ie González-Gallego1, 2 and
José L. Mau iz1, 2*
1Cen o de In es igación Biomédica en Red de En e medades Hepá icas y Diges i as (CIBERehd), León, Spain, 2Ins i u e o
Biomedicine (IBIOMED), Uni e si y o León, León, Spain, 3Se ice o Clinical Oncology, Complejo Asis encial Uni e si a io de
León (Hospi al o León), León, Spain, 4Depa men o Gene al Su ge y, “Vi gen del Rocío”-“Vi gen Maca ena” Uni e si y
Hospi al/IBiS/CSIC/Uni e sidad de Se illa, Spain
The mul ikinase inhibi o so a enib is, a p esen , he only d ug app o ed o he ea men
o hepa ocellula ca cinoma (HCC), one o he mos le hal ypes o cance wo ldwide.
Howe e , he inc ease in he numbe o so a enib umo esis an cells educes e iciency.
A be e knowledge o he in acellula mechanism o he d ug leading o educed cell
su i al could help o imp o e he bene i s o so a enib he apy. Au ophagy is a bulk
cellula deg ada ion p ocess ac i a ed in a b oad ange o s ess si ua ions, which allows
cells o deg ade mis olded p o eins o dys unc ional o ganelles. This cellula ou e can
induce su i al o dea h, depending on cell s a us and media signals. So a enib, alone
o in combina ion wi h o he d ugs is able o induce au ophagy, bu cell esponse o he
d ug depends on he complex in eg a i e c oss alk o di e en in acellula signals. In
cance ous cells, au ophagy can be egula ed by di e en cellula pa hways (Ak - ela ed
mammalian a ge o apamycin (mTOR) inhibi ion, 5′AMP-ac i a ed p o ein kinase
(AMPK) induc ion, dissocia ion o B-cell lymphoma 2 (Bcl-2) amily p o eins om Beclin-
1), o e ec s o some miRNAs. Inhibi ion o mTOR signaling by so a enib and diminished
in e ac ion be ween Beclin-1 and myeloid cell leukemia 1 (Mcl-1) ha e been ela ed
o induc ion o au ophagy in HCC. Fu he mo e, changes in some miRNAs, such as
miR-30α, a e able o modula e au ophagy and modi y sensi i i y in so a enib- esis an
cells. Howe e , al hough AMPK phospho yla ion by so a enib seems o play a ole in he
an ip oli e a i e ac ion o he d ug, i does no ela e wi h modula ion o au ophagy. In
his e iew, we p esen an upda ed o e iew o he e ec s o so a enib on au ophagy
and i s ela ed ac i a ion pa hways, analyzing in de ail he in ol emen o au ophagy on
so a enib sensi i i y and esis ance.
Keywo ds: so a enib, au ophagy, hepa ocellula ca cinoma, cance he apeu ic, dug esis ance
INTRODUCTION
Hepa ocellula ca cinoma (HCC) is he mos common ype o li e cance and he second mos
equen cause o cance - ela ed dea h wo ldwide (Fe lay e al., 2015; To e e al., 2015). The
s aging and ecommended ea men o pa ien s wi h HCC is ela ed o he li e unc ion, size and
numbe o nodules, gene al s a us o he pa ien , ascula in asion, and he p esence o ex ahepa ic
P ie o-Domínguez e al. So a enib and Au ophagy
me as asis. Cu a i e ea men s such as su gical esec ion, li e
ansplan a ion, and adio equency abla ion may be use ul
in he ea ly s ages o he disease. Howe e , only pallia i e
ea men s a e a ailable in ad anced s ages, in which di e en
chemo he apeu ics ha e been assayed wi h a iable e ec i eness
(Rossi e al., 2010; Fo ne e al., 2012). The de elopmen o
new diagnos ic me hods which can de ec small li e umo s is
essen ial o allow mo e agg essi e in e en ions and o imp o e
pa ien su i al a es (Gonzalez, 2014).
So a enib (BAY 43-9006, Nexa a R
), which was de eloped
in 1995 (Gau hie and Ho, 2013), is he only chemo he apeu ic
d ug which has demons a ed o imp o e su i al a e in
pa ien s wi h HCC (Llo e e al., 2008; Abdel-Rahman and
Fouad, 2014). Recen s udies ha e also p o en ha so a enib
has he apeu ic e ec s in o he cance ypes, such as hy oid
cance , acu e myeloid leukemia, ad anced enal cell ca cinoma
o p os a e cance (Escudie e al., 2007; Gollob e al., 2007;
Chi e al., 2008; An a e al., 2014; Luo e al., 2014; Alonso-
Go doa e al., 2015; Yamamo o e al., 2015). So a enib a ge s
he RAF se ine/ h eonine kinases, a amily o h ee membe s
(A-RAF, B-RAF, and C-RAF/Ra -1) ha play a key ole in
he ansduc ion o mi ogenic and oncogenic signals h ough
he Ra /Mi ogen-ac i a ed p o ein (MAP)/ex acellula signal-
egula ed kinase (ERK) kinase (MEK)/ERK signaling pa hway,
esul ing in a lowe cyclin D1 exp ession and in cell cycle
a es (Wellb ock e al., 2004; Adnane e al., 2006; Liu e al.,
2006). So a enib also po en ly inhibi s y osine kinase ecep o s
such as ascula endo helial g ow h ac o ecep o (VEGFR) 2,
VEGFR 3, pla ele -de i ed g ow h ac o ecep o -β(PDGFR-
β), Fl 3, and c-Ki , which p omo e angiogenesis (Wilhelm
e al., 2004, 2008; Ce ello e al., 2012). The ep ession
blocks a b oad spec um o di e en p ocesses in ol ed in
p oli e a ion, angiogenesis o apop osis, causing a educ ion in
blood essel a ea in he umo and s a ing cance ous cells (E be
e al., 2004; Gau hie and Ho, 2013). Fu he mo e, so a enib
enhances TRAIL-induced cell dea h h ough SH2 domain-
con aining y osine phospha ase (SHP-1)-dependen educ ion
o signal ansduce s and ac i a o s o ansc ip ion ype 3
(STAT3) phospho yla ion (Ty 705STAT3) and ela ed p o eins
Mcl-1 (myeloid cell leukemia 1), su i in, and cyclin D1 in
hepa oma cells (Chen e al., 2010). So a enib is also able o ep ess
Mcl-1 ac i i y h ough a MAPK-independen mechanism, which
inc eases he apop osis in insic pa hway in umo cells (Yu e al.,
2005; Uli i e al., 2009). Mo eo e , ecen s udies ha e claimed
ha eIF4E (euka yo ic ansla ion ini ia ion ac o 4E) migh be
implica ed in so a enib-dependen Mcl-1 inhibi ion (Rahmani
e al., 2005).
Nowadays, so a enib is he only Food and D ug
Adminis a ion (FDA)-app o ed HCC sys emic he apy,
expanding pa ien mean su i al om 7.9 o 10.7 mon hs (Llo e
e al., 2008; Guan and He, 2011). Despi e ini ial esponse, mos
pa ien s de elop disease p og ession p obably as a consequence
o umo esis an cells which do no espond o his molecule,
mainly due o up egula ion o some su i al pa hways which
may co e up he dea h signals induced by so a enib. The e o e, a
be e knowledge o hose cellula ou es is equi ed o o e come
unwan ed umo esis ance and consequen ly imp o e he
bene icial e ec s o so a enib he apy (Knie el e al., 2014; Sakai
e al., 2015; Togashi and Nishio, 2015).
Mac oau ophagy (he ea e e e ed o as au ophagy) is a
bulk deg ada ion sys em which ecycles un olded, damaged,
o useless cellula componen s, like p o eins o o ganelles, o
he main enance o cellula homeos asis in o de o p omo e
adap a ion and cell su i al (San-Miguel e al., 2014, 2015;
Vallejo e al., 2014). Howe e , excessi ely s imula ion may lead
o p og ammed cell dea h ins ead o su i al (Tsujimo o and
Shimizu, 2005). In ac , i s de egula ion has been associa ed
wi h some diseases such as neu odegene a i e diso de s, diabe es,
cys ic ib osis, C ohn’s disease, di e se myopa hies, hepa i is,
α-1 ypsin de iciency, ca diac hype ophy, and umo igenesis
(Mizushima and Koma su, 2011). Au ophagy is ini ia ed wi h he
o ma ion o a small memb anous esicle named phagopho e
ha elonga es and engul s a speci ic o unspeci ic po ion o
he cy oplasm, o ming a doubled-memb anous s uc u e named
au ophagosome. A e wa ds, his o ganelle uses wi h a lysosome
and o ms a combined esicle o au ophagolysosome, leading
o he deg ada ion o he inne ma e ial by lysosomal enzymes,
eleasing subs ances ha become a disposal o he syn hesis o
newly mac omolecules o ma ion o ene gy p oduc ion (Tanida,
2011).
Au ophagic p ocess in ol es a highly conse ed g oup
o mac omolecules which we e disco e ed in yeas s and
named as au ophagy- ela ed genes (A g) (Tanida, 2011). In
mammals, i e g oups o p o eins a e in ol e in au ophagosome
o ma ion (Tanida, 2011). The i s is ULK1 (unc-51-like kinase)
complex, whose unc ions a e he ec ui men o dis inc A g
componen s and he main enance o phagopho e in eg i y
(Mizushima, 2010). Nex , Beclin1-Vps34 ( acuola p o ein
so ing 34) complex allows memb ane nuclea ion wi h o ma ion
o PI3P (phospha idylinosi ol 3-phospha e) (Yuan e al., 2013).
A e wa ds, A g9 and WIPI-1 (WD- epea p o ein in e ac ing
wi h phosphoinosi ides) sys em b ings o phagopho e some
lipids and p o eins which a e necessa y o i s elonga ion
(O si e al., 2010). Finally, wo ubiqui in-like sys ems, A g5-
A g12-A g16L and LC3 (mic o ubule-associa ed p o ein 1 ligh
chain 3), ha conjuga ing wi h PE (phospha idyle hanolamine)
cons i u es LC3-II ( an de Veen and Ploegh, 2012), a e bo h
equi ed o au ophagosome o ma ion. The i s sys em plays
an impo an ole in he ac i a ion o he second one, and
LC3 p o ein is implica ed in he elonga ion o au ophagosome
memb ane and in i s closu e (Sou e al., 2008).
The e a e a ious ex acellula s imuli, such as nu ien
dep i a ion, g ow h ac o wi hd awal o hypoxia, which ha e
he abili y o induce au ophagy (He and Klionsky, 2009). S ess
si ua ions, such as eac i e oxygen species (ROS) accumula ion
o endoplasmic e iculum (ER) s ess can also modi y his
cellula p ocess (He and Klionsky, 2009). The mos impo an
pa hways in ol ed in au ophagy modula ion a e mTORC1
(mammalian a ge o apamycin complex 1) and AMPK (5′
AMP-ac i a ed p o ein kinase). The i s one abolishes au ophagy
in p esence o nu ien s o g ow h ac o s, h ough ULK1
complex inhibi ion, while he second one p omo es au ophagy
when cellula ene ge ic s a us is low (Sengup a e al., 2010;
Manwani and McCullough, 2013). On he o he hand, some
F on ie s in Pha macology | www. on ie sin.o g 2June 2016 | Volume 7 | A icle 151
P ie o-Domínguez e al. So a enib and Au ophagy
sphingolipids a e also able o igge au ophagy (Li e al., 2014;
O doñez e al., 2015). Speci ically, ce amide induces au ophagy-
associa ed cell dea h, whe eas sphingosine-1-phospha e induces
au ophagy-associa ed su i al (Li e al., 2014). The in e ac ion
be ween Beclin-1 and Bcl-2 p o ein amily, as well as he pos -
ansc ip ional egula ion by miRNAs ha e been ela ed o
egula ion o au ophagy (Zhou e al., 2011; Sui e al., 2015).
Au ophagy ac s as a double-edged swo d in cance cells
because emo es newly mu a ed cells and damaged mi ochond ia
in he ea ly s age o he disease, bu induces su i al in
hypoxia and ischemia condi ions, as well as p omo es esis ance
agains some chemo he apeu ic d ugs and umo p og ession
a he la e phases (Eskelinen, 2011; Choi, 2012). In animal
models o hepa oca cinogenesis i has been desc ibed ha
au ophagy could play a p o ec ing ole du ing dysplas ic phase
in no mal hepa ocy es, bu p omo es umo cells g ow h du ing
he umo - o ming s age (Sun e al., 2013). Those appa en ly
con o e sial esul s can be ela ed wi h he abili y o au ophagy
o educe oxida i e s ess and main ain heal hy mi ochond ia
p e en ing he ini ia ion o hepa oca cinogenesis, while i blocks
he exp ession o p53 and o he umo supp esso s du ing
la e phases o p omo e he de elopmen o HCC (Tian e al.,
2015). Fu he mo e, some d ugs used in cance ea men induce
au ophagy- ela ed cell dea h in cance cells (Sca la i e al., 2004).
Thus, i is in e es ing o e iew he e ec s o his an i umo agen
on he au ophagy p ocess in HCC cells, and he in luence o
au ophagy on so a enib- ela ed cell esis ance gene a ion (Liu
e al., 2016). A be e knowledge o he so a enib au ophagy-
ela ed mechanisms could con ibu e o imp o e i s he apeu ic
e iciency, inc easing cance pa ien su i al a es.
AUTOPHAGY INDUCTION BY SORAFENIB
Au ophagy is usually de egula ed in umo cells whe eas has
been ela ed o cell su i al and d ug esis ance. So a enib and
o he chemo he apeu ic d ugs ha e been shown o modula e
au ophagy in di e en in i o and in i o expe imen al models
(Gau hie and Ho, 2013). So a enib egula es au ophagy in
a ious hepa ocellula cell lines (Table 1). In pa icula , di e en
s udies ha e shown he p esence o acid esicles which a e ypical
ea u es o au ophagosomes in so a enib- ea ed cells (Table 1;
Pa k e al., 2008; Chiou e al., 2010; Shi e al., 2011; Shimizu
e al., 2012; Eum e al., 2013; Honma and Ha ada, 2013; Tai
e al., 2013; Fische e al., 2014; S iuso e al., 2015). Mo eo e ,
so a enib can also p omo e LC3 lipida ion, an ob ious sign o
au ophagy induc ion (Tai e al., 2013; Yuan e al., 2014; Zhai
e al., 2014). Fo example, i has been obse ed ha LC3-II
o ma ion by so a enib is dose-dependen and ime-dependen
in HepG2, MHCC97-L, Huh7, HLF, and PLC/PRF/5 HCC cells
(Shi e al., 2011; Shimizu e al., 2012). In addi ion, so a enib
modula es he exp ession o mul iple au ophagy ma ke s. Thus,
he d ug s imula es Beclin1, A g5, and A g12 exp ession in
HCC cells in i o (Yuan e al., 2014), Beclin-1 exp ession is
inc eased by so a enib in a ime-dependen ashion in Hep3B
cells (Ca e al., 2013), so a enib can mildly induce Beclin1
and A g-5 exp ession whe eas dec eases p62 exp ession in a
signi ican manne in PLC-5 cells (Tai e al., 2013), o inc eases
A g5, Vps34 and Beclin-1, dec eases p62 and does no a ec
UVRAG exp ession in Huh7 and HepG2 cells (Zhai e al., 2014).
Mo eo e , au ophagy induced by so a enib eaches he lysosome
deg ada o y phase, as demons a ed by using a mRFP-GFP-
LC3 combined luo escen - ag (Shimizu e al., 2012). Se e al
disc epancies in au ophagy induc ion ha e been also obse ed
in so a enib- ea ed HCC cells (Chiou e al., 2010; Fische
e al., 2014). This appa en ly pa adoxical disc epancy and o he s,
abou he e ec s o so a enib in he au ophagic mechanisms,
a e included in he Table 2. So a enib also egula ed au ophagy
in non HCC cance cells (Table 3) such as mac ophages,
os eosa coma, mul iple myeloma, colo ec al ca cinoma cells,
p os a e, mamma y, hy oid, and enal cance cells, (Walke
e al., 2009; Ullen e al., 2010; Ba e o d e al., 2011a,b; P is e e
e al., 2011; Kha aziha e al., 2012, 2013; Lin e al., 2013; Zheng
e al., 2015) h ough di e en pa hways which a e summa ized in
he Table 3.
Some s udies connec so a enib adminis a ion and au ophagy
modula ion in expe imen al HCC models in i o (Tables 1, 3).
In all esea ch done un il now, so a enib can inc ease
au ophagosome o ma ion and modi y au ophagy ma ke s
exp ession in a simila way o models in i o (Shi e al., 2011;
Shimizu e al., 2012; Tai e al., 2013). The only s udy analyzing
he po en ial link be ween so a enib and au ophagy in pa ien s
has been pe o med in e ac o y o elapsed lymphop oli e a i e
disease, demons a ing ha LC3-II base le els a e lowe in non-
esponsible pa ien s compa ed o esponde s, and ha pa ien s
who espond o so a enib show a highe educ ion o LC3
exp ession a e 1 mon h o ea men (Guide i e al., 2012).
Rego a enib, a s uc u al analog o so a enib, induces
au ophagosome o ma ion in HCC cells simila ly han so a enib
(Ca e al., 2013; Ta allai e al., 2015). In ano he s udy, wo
di e en so a enib analogs, -MTUCB and AUCMB, caused
au ophagosome o ma ion and LC3 lipida ion in a ious HCC
cell lines (Wecksle e al., 2014). Finally, sc-59, a kinase-
independen de i a e o so a enib showed a highe au ophagy
induc ion cha ac e ized by an inc eased abili y o induce LC3-
lipida ion and acid esicles o ma ion (Tai e al., 2013).
Some wo ks ha e es ablished ha so a enib induces
au ophagy as a cellula su i al mechanism in HCC because
when his pa hway is ep essed by a chemical d ug (like
chlo oquine o ba ilomycin A1) o by a small in e e ing RNA
(siRNA) agains Beclin-1 o A g5, so a enib kills mo e cance ous
cells and i s an ip oli e a i e abili y imp o es, which means ha
au ophagy induced by ha an i umo agen wo ks as a p o ec i e
pa hway (Pa k e al., 2010; Yuan e al., 2014). Mo eo e , simila
e ec s ha e been also desc ibed in o he non HCC cance cells
(Tables 1, 3;Ma in e al., 2009; Walke e al., 2009; Kha aziha
e al., 2012; Zheng e al., 2015). Howe e , o he s udies ha e
obse ed opposi e esul s in HCC (Tables 1, 3;Eum e al.,
2013; Tai e al., 2013; Ta allai e al., 2015) and non-HCC cells
(Lian e al., 2012; Lin e al., 2012). Tumo cell esis ance o
so a enib can also be ela ed o swi ch om au ophagy- ela ed
dea h o au ophagy- ela ed HCC cell su i al (Zhai e al., 2014).
Mo eo e , ano he di e en way o gene a e so a enib esis ance
consis s in he abolishmen o au ophagy induc ion. In ac ,
F on ie s in Pha macology | www. on ie sin.o g 3June 2016 | Volume 7 | A icle 151
P ie o-Domínguez e al. So a enib and Au ophagy
TABLE 1 | E ec o so a enib on au ophagy ma ke s in HCC in i o o in i o models.
Re e ences Model E ec s on au ophagy
ma ke s
Global e ec s Role o au ophagy
Ca e al., 2013 Rego a enib in Hep3B,
PLC/PRF/5, HepG2
↑LC3-II
↑Beclin-1
Inc ease apop osis on umo cells (i
inc eases caspase 3, 8, and 9 ac i i y, Bax
exp ession, and dec eases Bcl-2 p o ein
le els)
No assessed
Eum e al., 2013 Mul id ug- esis an Ras-NIH
3T3/Md cells
↑LC3-posi i e esicles So a enib aises HCC cell dea h h ough
he ac i a ion o au ophagy pa hway and
he inhibi ion o mTOR ac i i y
Cell dea h
Fische e al., 2014 Hep3B, HuH7 ↑LC3 lipida ion only in HuH7, bu
wi h no e ec s in Hep3B cells
Those cell lines ha e di e en au ophagy
esponsi eness o so a enib and ha
migh be linked o gene a ion o so a enib
esis an cells
No assessed
Shi e al., 2011 MHCC97-L, PLC/PRF/5, HepG2 ↑Au ophagosome o ma ion
↑LC3 lipida ion
↑A g5
IRE-1αsignaling pa hway o ER s ess is
necessa y o au ophagy induc ion by
so a enib
Cell su i al
Shi e al., 2011 Nude mice o o hopically
implan ed wi h MHCC97-L
↑CHOP Au ophagy inhibi ion dec ease umo
olume in so a enib and so a enib +
clo oquine ea ed mice
Cell su i al
Shimizu e al., 2012 HuH7, HLF, PLC/PRF/5 ↑LC3 lipida ion
↓p62
↑Au ophagosome o ma ion
=A g5 and Beclin-1
Inhibi ion o au ophagy inc eases cell
sensi i i y o so a enib
Cell su i al
Shimizu e al., 2012 Xenog a umo s o HuH7 cells
in nude mice
↑LC3 lipida ion Au ophagy inhibi ion dec ease umo
olume in So a enib ea ed mice
Cell su i al
Tai e al., 2013 PLC/PRF/5, Hep3B, Sk-Hep-1,
HepG2
↑LC3 lipida ion
↓p62
↑Beclin-1 and A g5
So a enib induces au ophagy h ough he
dis up ion o Beclin-1-Mcl-1 complex
Cell dea h
Tai e al., 2013 Nude mice injec ed wi h PLC-5 Au ophagy induc ion So a enib induces au ophagy in i o
h ough p-STAT inhibi ion and abolishes
cance p oli e a ion
Cell dea h
Zhai e al., 2014 So a enib- esis an and sensi i e
HepG2 and HuH7 cells.
↑LC3-II. A g5, Vps34, Beclin1
↓p62 in bo h, esis an and
sensi i e cells al hough esis an
cells show lowe le els o ha
ma ke s
Lack o so a enib-induced au ophagy in
HCC cells leads o gene a ion o
so a enib- esis an cells
P o ec ion in pa en al
cells, bu p omo ion o
cell dea h in esis an
cell lines
Zhai e al., 2014 Mice injec ed wi h HuH7
esis an cells
Resul s in acco dance o in i o
assay
Au ophagy beha io swi ch is able o
modi y cell sensi i eness o so a enib.
Resul s in acco dance
o in i o assay
i has been demons a ed ha so a enib esis an cells show
lowe le els o au ophagy ma ke s such as LC3, A g5, Vps34, o
Beclin1 (Zhai e al., 2014). Fo all hese easons, no maliza ion o
au ophagy may be one o he key mechanisms o a oid cellula
esis ance o ha an ineoplas ic agen (Zhai e al., 2014; Liu e al.,
2016).
EFFECTS ON AUTOPHAGY OF SORAFENIB
COMBINATION WITH OTHER DRUGS
Some s udies ha e analyzed changes in au ophagy modula ion
in HCC cells ea ed wi h di e en so a enib-based d ug
combina ions (Table 4). The adminis a ion o an inhibi o
o his one deace ylases (HDAC), enzyme implica ed in he
egula ion o gene ansc ip ion ela ed o p omo ion o
p og ession o cance (Dokmano ic e al., 2007; Giannini e al.,
2012), has been shown o supp ess umo cell p oli e a ion. The
mos impo an membe o ha g oup is o inos a , he i s
HDACi o be app o ed o human clinical use (Giannini e al.,
2012). When o inos a is combined wi h so a enib in HCC
cul u ed cells, cell iabili y dec eases mo e han in cells ea ed
wi h so a enib o , o inos a alone (Pa k e al., 2008, 2010).
Fu he mo e, d ug combina ion can induce a highe Beclin-1,
A g5, o A g12 exp ession and LC3 lipida ion han ea men
wi h only one chemo he apeu ic agen (Pa k e al., 2008; Yuan
e al., 2014). When A g5 o Beclin-1 we e silenced wi h siRNA
in hose s udies, iabili y dec eased mo e in cance cells han
in con ol cells, being he d op highe in he d ug combina ion
ea ed g oup (Pa k e al., 2008; Yuan e al., 2014). This esul is
compa ible wi h he p osu i al p ope ies o au ophagy du ing
he an ip oli e a i e syne gis ic e ec o hose d ugs (Table 4;
Pa k e al., 2008; Ma in e al., 2009; Yuan e al., 2014).
The low e icacy o doxo ubicin, as a single agen in HCC, has
led o e alua e i s ac i i y in combined ea men wi h so a enib
(Mano e al., 2011). Doxo ubicin belongs o an h acyclines
g oup, a ype o an ibio ic which we e i s isola ed om soil
bac e ia (Yang e al., 2014), ha can gene a e simul aneously
F on ie s in Pha macology | www. on ie sin.o g 4June 2016 | Volume 7 | A icle 151
P ie o-Domínguez e al. So a enib and Au ophagy
TABLE 2 | Disc epancies exis en be ween di e en so a enib ei he in i o o in i o s udies.
Condi ion Fi s si ua ion Second si ua ion
LC3 ↑Le els in Huh7 cells, inducing mo e d ug esponse (Fische e al.,
2014)
Mode a e ↑le els in Hep3B cells, inducing less d ug esponse (Fische
e al., 2014).
Au ophagy ↑Le els, p o ec ing cance ous cells om cell dea h bo h in i o an
in i o models (Shimizu e al., 2012)
↑Le els, p omo ing p og ammed cellula dea h in cance ous cells bo h
in i o an in i o models (Tai e al., 2013)
Au ophagy ↓Le els in d ug combina ion, educing side e ec s o bo h d ugs
(Mano e al., 2011)
↑Le els in d ug combina ion, leading o enhance d ug syne gism (Yuan
e al., 2014)
mTORC1 ↓Phospho yla ion, leading o au ophagy induc ion and cell dea h (Zhai
e al., 2014; Zhang e al., 2015)
No changes in phospho yla ion associa ed wi h so a enib cell esis ance
(Ramak ishnan e al., 2012)
mTORC1 ↓Phospho yla ion by some o he analogs o so a enib associa ed wi h
au ophagy (Ta allai e al., 2015)
No changes in phospho yla ion by some o he analogs o so a enib, no
being au ophagy induc ion dependen on ha pa hway (Wecksle e al.,
2014)
Ak ↓Exp ession associa ed wi h inc emen s in cellula dea h bo h in i o
and in i o expe imen s (Euli e al., 2010)
↑Le els bo h in i o and in i o models, leading o induc ion o su i al
au ophagy, su i al pa hways, and inc easing so a enib cell esis ance (Zhai
e al., 2014)
AMPK ↑Phospho yla ion due o he gene a ion o a educ ion o ATP cellula
le els (Teso i e al., 2015)
↑Phospho yla ion due o he elease o ROS om mi ochond ia (Pignochino
e al., 2015)
AMPK ↑Phospho yla ion wi hou au ophagy associa ed (Teso i e al., 2015) No changes in AMPK ac i a ion and no au ophagy associa ed (S i ipa e al.,
2013)
ER s ess ↑IRE-1αexp ession, leading o au ophagy induc ion (Shi e al., 2011)↑PERK exp ession, bu non-au ophagy induc ion associa ed (Shi e al.,
2011)
Sphingolipids ↑Ce amide o ma ion a in i o models, leading o induc ion o
au ophagy and p og ammed cell dea h (Pa k e al., 2010)
↓Sligh ly S1P le els a in i o models (Beljanski e al., 2011)
TABLE 3 | E ec o so a enib on au ophagy ma ke s in o he in i o o in i o cance ous models dis inc o HCC.
Re e ences Model E ec s on au ophagy
ma ke s
Global e ec s Role o
au ophagy
Lin e al., 2013 Human mac ophages ↑Au ophagic acuoles
↑LC3 lipida ion
So a enib s imula es au ophagy bu i inhibi s
phagocy osis and sec e ion o IL-10
No assessed
Kha aziha e al., 2012 Myeloma cell lines LP1, RPMI-8226 ↑LC3 lipida ion
↓p62
↑LC3-posi i e esicles
So a enib induces au ophagy which p o ec
agains caspase-dependen and
independen cell dea h
Cell su i al
Kha aziha e al., 2012 Myeloma pa ien samples ↑LC3 lipida ion I induces cell dea h and au ophagy Cell dea h
Kha aziha e al., 2012 Myeloma mice models ↑LC3 lipida ion So a enib inc eases mice su i al, educes
umo de elopmen and induces au ophagy
pa hway
Cell dea h
Walke e al., 2009 So a enib plus o inos a ea men in
a colo ec al cance cell line, HCT116
↑LC3
lipida ion ↑A g5
So a enib ea men induces a sligh ly
amoun o au ophagy which is cy op o ec i e
and is s imula ed by o inos a co ea men
Cell su i al
Ullen e al., 2010 P os a e ca cinoma cell lines DU145
and PC3
↑Au ophagosome o ma ion So a enib al e s mi ochond ial po en ial and
induces apop osis and au ophagy
No assessed
Ba e o d e al., 2011b Ful es an - esis an and sensi i e
MCF7 cell line (o igina ing om b eas
adenoca cinoma)
↑Au ophagosome o ma ion,
↑Beclin-1 ↑A g5-A g12
↑LC3-II
↓p62
So a enib induces au ophagy pa hway alone
o in combina ion wi h pe me exed, and ha
induc ion sensi izes ha cells o cell dea h
Cell dea h
P is e e e al., 2011 Human os eosa coma cell line U2OS ↑WIPI
↑Au ophagosome o ma ion
So a enib induces au ophagy in no mal and
s a ed cells and ha is induced by calcium
ion elease o cy oplasm
No assessed
Lin e al., 2012 Medulla y hy oid cance cell lines
MTG-1 and TT
↑LC3-II ↑A g5 So a enib induces bo h au ophagy and
apop osis in ha in i o model
Cell dea h
Zheng e al., 2015 Di e se enal ca cinoma cell lines like
786-0, A498 and SK-RC-44
↑Beclin-1
↑A g5
↓p62
↑LC3-II and LC3-II/I a io
So a enib induces a cy op o ec i e o m o
au ophagy in enal ca cinoma cells
Cell su i al
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P ie o-Domínguez e al. So a enib and Au ophagy
TABLE 4 | E ec o so a enib combined ea men wi h ano he d ug on au ophagy in HCC and o he cance ypes.
Re e ence Pa hophysiological
condi ion
Model D ug combined
wi h so a enib
So a enib alone
e ec s
D ug combina ion
e ec s
Global e ec o bo h
d ugs ea men
Yuan e al., 2014 Hepa ocellula
ca cinoma
In i o Vo inos a ↑Beclin-1
↑A g5
↑A g7
↑LC3-II
↑↑Beclin-1 ↑↑A g5
↑↑A g7
↑↑LC3-II
D ug combina ion enhances
Beclin-1-dependan
p o ec i e o m o
au ophagy
Mano e al., 2011 Hepa ocellula
ca cinoma
In i o Doxo ubicin ↑LC3-II ↓LC3-II So a enib ac s as an
an agonis o doxo ubicin
Ta allai e al., 2015 Hepa ocellula
ca cinoma
In i o Sildena il ↑Au ophagic acuoles
=LC3 =p62
↑↑Au ophagic
acuoles
↑LC3
↓p62
Sidena il p omo es so a enib
e ec s on au ophagy and
s imula e au ophagic cell
dea h
Lam e al., 2015 Hepa ocellula
ca cinoma
In i o PHY906 ↑LC3 ↓ULK1 ↑↑LC3
↑ULK1
PHY906 s imula e
so a enib- ela ed au ophagy
Ba e o d e al.,
2011b
B eas
adenoca cinoma
In i o Peme exed ↑Beclin-1
↑A g5-A g12
↑LC3-II
↓p62
↑↑Beclin-1
↑↑A g5-A g12
↓sligh ly LC3-II
↓p62
Pe me exed p omo es
so a enib- ela ed au ophagy
induc ion
Hamed e al.,
2015
Glioblas oma In i o Lapa inib ↑Au ophagic acuoles
=p62
↑Beclin-1
↑LC3-II/I
↓LAMP2
↑↑au ophagic
acuoles
↓p62 =Beclin-1
↓LC3-II/I
↓LAMP2
Lapa inib p omo es
so a enib cellula dea h
h ough au ophagy pa hway
Jakubowicz-Gil
e al., 2014
Glioblas oma
mul i o me and
anaplas ic as ocy oma
In i o Que ce in ↑Au ophagic esicles,
Beclin-1 and LC3-I/II
only in
glioblas omamul i o me
cell line.
↑↑Au ophagic
esicles, Beclin-1 and
LC3-I/II only in he
same cell line as
so a enib alone
Que ce in p omo es
so a enib cell dea h in bo h
cell lines bu only induces
au ophagy in one o hem
Lian e al., 2012 And ogen-independen
p os a e cance
In i o and
in i o
(–) gossypol ↑Au ophagic esicles
↑LC3-I/II
↓p62
↑↑Au ophagic
esicles
↑↑LC3-I/II
↓↓p62 P e e en ially
in one o he cell lines
es ed
(–) gossypol agonis s
so a enib au ophagy and
induces cellula dea h
opoisome ase II poisoning, DNA adduc o ma ion, ce amide
o e p oduc ion and oxida i e s ess (Yang e al., 2014). One
o he main p oblems o he use o doxo ubicin alone in
he apy is he high numbe o side e ec s (Yang e al.,
2014). In e es ingly, so a enib dec eases doxo ubicin- ela ed
au ophagy, wi h a educ ion o he exp ession o LC3 and i s
lipida ion (Table 4;Mano e al., 2011).
Sildena il is ano he agen which has been combined wi h
so a enib in HCC (Table 4;Ta allai e al., 2015). This d ug
is able o inhibi phosphodies e ase 5, an enzyme which
ans o ms cyclic GMP (cGMP) in o his inac i e o m (Das
e al., 2015). Sildena il is used mainly in he ea men o
e ec ile dys unc ion and o some ca dio ascula diseases because
i p oduces asodila a ion (Das e al., 2015). I has also been
pos ula ed ha sildena il is able o induce he in insic pa hway o
apop osis in colo ec al ca cinoma cells and lympha ic leukemia
cells (Boo h e al., 2014; Das e al., 2015). Sildena il inc eases
he an ip oli e a i e p ope ies o so a enib and ego a enib
(Table 4;Ta allai e al., 2015). The combined ea men inc eases
au ophagosome o ma ion ollowed by he accumula ion o
ed luo escence a 24 h in o GFP-RFP-LC3- ans ec ed HCC
cells. Mo eo e , he educ ion o cell dea h by ego a enib and
sildena il in cells ea ed wi h A g5, Beclin-1, o ULK1 siRNA
sugges s ha au ophagy may ac as a p o-dea h mechanism in
his se ing (Ta allai e al., 2015).
So a enib has also been combined wi h PHY906, an
he bal mix u e which consis s o ou dis inc componen s:
Glycy hiza u alensis,Paeonia lac i lo a,Scu ella ia baicalensis
oo s, and Ziziphus jujuba ui . This plan mix u e is based
on an old Chinese o mula ion used o he ea men
o a ious gas oin es inal diseases, like dia hea, e e , o
omi ing (Liu and Cheng, 2012; Rockwell e al., 2013).
Recen s udies ha e shown he e icacy o PHY906 as a
chemo he apeu ical adju an (Kumma e al., 2011). When
his he bal mix u e is combined wi h so a enib, exp ession o
au ophagy ma ke s inc eases. Paeonia lac i lo a and Scu ella ia
baicalensis a e he c i ical componen s o ha mix u e in ela ion
o au ophagy induc ion, because ollowing supp ession o hose
plan s om he he bal blend, LC3 is no lipida ed (Table 4;
Lam e al., 2015).
Simila ly, di e en combina ions o so a enib wi h o he
d ugs and an ioxidan s o he bal mix u es seem o be
able o modula e au ophagy in non-li e cance cells (see
Table 4).
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P ie o-Domínguez e al. So a enib and Au ophagy
AUTOPHAGY-RELATED CELLULAR
PATHWAYS AND SORAFENIB TREATMENT
The e a e some p o eins and cellula pa hways in umo cells
ha can be in ol ed in he egula ion o au ophagy by so a enib.
Those egula o y ou es ha e a changing e ec , because hey a e
dependen on he cell s a e, i s o igin o some medium ea u es.
The mos impo an a e desc ibed in de ail in he ollowing
sec ions (Figu e 1).
mTOR Pa hway
The mTOR pa hway is one o he main egula o s o cellula
me abolism in esponse o oxida i e s ess, un olded p o ein
esponse, hypoxia, nu ien s dep i a ion o g ow h ac o
de iciency (Neu eld, 2010; Yang and Ming, 2012; Sa ka , 2013).
The inhibi ion o mTOR signaling by so a enib is ela ed
o induc ion o au ophagy (Table 5,Figu e 1). Mos s udies
ha e shown ha so a enib is able o dec ease mTORC1
phospho yla ion, exp ession, and ac i i y bo h in cul u ed cells
in i o and in xenog a umo implan a ion in mice (Liu
e al., 2012; Zhai e al., 2014). In HCC in i o models, i has
been desc ibed ha so a enib inhibi s mTORC1 phospho yla ion
du ing pe iods om 24 o 48 h (Zhai e al., 2014; Zhang e al.,
2015). Fu he mo e, so a enib is able o dephospho yla e p70S6K
and 4E-BP1, which a e wo ob ious e idences o mTORC1
ac i i y inhibi ion in HCC cells (Liu e al., 2012) and o he
cance s (Euli e al., 2010; Gulha i e al., 2012; Kha aziha e al.,
2012; Tang e al., 2012; Eum e al., 2013; Hamed e al., 2015).
Howe e , i has been shown ha so a enib is no able o al e
phospho yla ion s a us o mTORC1 bu educes p70S6K and
4EBP1 phospho yla ion in cul u ed non-Hodgkin lymphoma cell
lines (Ramak ishnan e al., 2012). O he in i o s udies also
sugges ha so a enib is able o educe mTORC1 ac i i y in
HCC xenog a models ollowed by a dec eased phospho yla ion
o i s downs eam p o eins, p70S6K, 4E-BP1, and eIF-4E (Liu
e al., 2012; Zhai e al., 2014). I has been shown ha so a enib
educes in i o and in i o mTORC1 signaling and p70S6K
phospho yla ion, bu inc eases mTORC2 h ough inc easing
Se 2481mTOR, being his la e e ec abolished by e e olimus
co- ea men in os e osa coma p eclinical models (Figu e 1;
Pignochino e al., 2013).
Some esea che s ha e assessed i he induc ion o au ophagy
by so a enib is due o ep ession o mTOR signaling pa hway in
HCC (Shimizu e al., 2012; Zhai e al., 2015) and o he cance s
(Ba e o d e al., 2011a,b; Kha aziha e al., 2012; Eum e al., 2013).
Due o dual ole o au ophagy in cellula dea h, mTOR inhibi ion
migh lead o dea h o su i al o cance cells, depending on
whe he au ophagy ep essed by his p o ein wo ks, espec i ely,
as a cell dea h induce , o as a su i al mechanism in bo h
HCC and non-HCC cells (Kha aziha e al., 2012; Shimizu e al.,
2012; Ta allai e al., 2015). So a enib analogs ha e a di e en
abili y o abolish mTOR in cul u ed cell lines in i o. Some
o hem, such as ego a enib o SK-01105, a e able o induce
mTOR dephospho yla ion simila ly o so a enib, whe eas o he
compounds, like -AUCMB o -MTUCB, canno inhibi mTOR
ac i i y, so au ophagy induc ion media ed by hose so a enib
analogs is no modula ed by mTORC1 ac i i y (Wecksle e al.,
2014; Ta allai e al., 2015).
The majo ups eam induce o mTORC1 pa hways is
PI3K/Ak signaling (Sa ka , 2013). In so a enib- esis an cells,
Ak exp ession is usually o e -s imula ed, and ea men
wi h some speci ic ep esso s is able o inc ease so a enib-
ela ed cell dea h, which means ha combined ea men wi h
so a enib and an Ak inhibi o may be use ul because i
migh imp o e so a enib sensi i i y (Zhai e al., 2015). Di e en
epo s ha e shown ha so a enib inhibi s Ak ac i i y and
i s phospho yla ion in HCC and enal ca cinoma cells (RCC)
(Table 5;Euli e al., 2010; Gulha i e al., 2012; Se o a e al., 2013;
Hamed e al., 2015; Zhang e al., 2015). Howe e , o he s udies
ound ha so a enib induces Ak phospho yla ion, which will
TABLE 5 | E ec o so a enib on mTOR/Ak pa hway in umo cells.
Re e ences Cell lines Pa hophysiological condi ion E ec on ma ke s o mTOR/Ak
pa hway
Global e ec
Hamed e al., 2015 GBM12 Glioblas oma mul i o me ↓p-Ak
↓p-mTOR ↓p-p70
So a enib induces Ak /mTOR
pa hway inhibi ion when ha e passed
only 6 h o ea men
Liu e al., 2012 PLC/PRF/5, HepG2
and Hep3B
Hepa ocellula ca cinoma ↓p-mTOR ↓p-p70S6K ↓p-4E-BP1
↑p-Ak
Two hou s o ea men wi h so a enib
is able o down egula e mTOR and all
i s ela ed pa hways
Ramak ishnan e al., 2012 Dohh2 Non-Hodgkin lymphoma ↓p-p70 ↓p-4E-BP1 =p-mTOR So a enib ails in inac i a e mTOR
phospho yla ion a 8 h o ea men
Tang e al., 2012 GBM15 Glioblas oma mul i o me ↓p-p70 =p-mTOR Twen y-Fou hou s o ea men wi h
so a enib educes sligh ly mTOR
pa hway induc ion
Zhai e al., 2014 Huh7 and HepG2 Hepa ocellula ca cinoma ↓p-mTOR ↓p-p70S6K ↓p-4E-BP1
↑p-Ak
So a enib inhibi s mTOR pa hway
ac i i y and ha inac i a ion
s imula es au ophagy esponse
Zhang e al., 2015 SMMC-772l Hepa ocellula ca cinoma ↓Ak , PI3K and mTOR a 8 h o
ea men , a e wa ds hei le els
inc eases
So a enib induces a ansi o y
inac i a ion o Ak /mTOR pa hway
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P ie o-Domínguez e al. So a enib and Au ophagy
FIGURE 1 | So a enib induces au ophagy esponse h ough modula ion o he main downs eam ac o s and pa hways. In his scheme, some o he
media o s o au ophagy induc ion by so a enib in umo cells a e ep esen ed. So a enib may induce AMPK pa hway because i educes ATP le els and inc eases
ROS, which leads o inhibi ion o mTORC1 signaling pa hway. So a enib can also s imula e ER s ess, speci ically IRE-1αb anch and all i s downs eam genes, and
elease calcium ion o cy osol, which induces au ophagosome o ma ion. I may also dis up Beclin-1 and Bcl-2 complex, wi h Beclin-1 elease. O he non-p o ein
media o s which may be in ol ed in so a enib e ec s a e miRNA30αand sphingolipids, because he d ug can educe miRNA30αsignaling, which is a Beclin-1
ep esso , induce ce amide o ma ion, and educe S1P le els, leading o au ophagosome o ma ion.
lead o gene a e esis ance agains ha chemo he apeu ic agen
(Table 5;Liu e al., 2012; Zhai e al., 2015). Finally, a hi d g oup
o wo ks ha e epo ed ha so a enib has no in luence in he
phospho yla ion s a us o Ak (Gedaly e al., 2010).
In summa y, so a enib appea s o inac i a e mTORC1 ac i i y,
which would con ibu e o au ophagy induc ion. The mechanism
esponsible o hose e ec s emains unclea , bu , in some cases,
could in ol e he PI3K/Ak pa hway.
AMPK Pa hway
AMPK is a he e o ime ic complex ac ing as a senso o ene gy
s a us in euka yo ic cells (G ahame Ha die, 2014; No iko a
e al., 2015). AMPK ac i a o s may be used as adju an s in
a ious cance he apies, because i s s imula ion can induce
au ophagy o cell cycle s op in umo cell (Mo oshima e al.,
2006; Donadon e al., 2010; Rehman e al., 2014). So a enib
ac i a es AMPK being his e ec po en ially ele an du ing
induc ion o au ophagy in cance cells (Figu e 1;Eum e al.,
2013; Fische e al., 2014; Teso i e al., 2015). So a enib is able
o induce AMPK phospho yla ion in a ime-dependen ashion
and in a dose-dependen manne in expe imen al models in
i o, speci ically in cul u ed cells coming om di e en ypes
o human umo s (Eum e al., 2013; Fuma ola e al., 2013;
Pignochino e al., 2013, 2015; Fische e al., 2014; G oenendijk
e al., 2015; Teso i e al., 2015). I has been demons a ed ha he
incuba ion wi h 5 µM o so a enib in mul id ug esis an cells
cul u ed in i o can s imula e AMPK phospho yla ion in a ime-
dependen manne , s a ing a 0.5 h a e ea men (Eum e al.,
2013). So a enib also induces AMPK phospho yla ion (48 h) in
lung adenoca cinoma o non-small cell lung cance (G oenendijk
e al., 2015). The d ug is also able o induce AMPK ac i a ion
in a ious b eas cance cell lines (Fuma ola e al., 2013). On
he o he hand, he e a e some expe imen al models in which
so a enib is no able o induce AMPK phospho yla ion due o
he use o low concen a ions o he an i umo agen (S i ipa
e al., 2013). Cu iously, some di e ences in AMPK modula ion
by so a enib ha e been desc ibed be ween Huh7 and Hep3B
HCC cell lines, showing inc eases only in Huh7 cells bu wi hou
changes in Hep3B (Fische e al., 2014).
The e a e wo p incipal hypo heses which explain he
mechanism by which so a enib induces AMPK phospho yla ion
(Figu e 1). The i s one is ha so a enib gene a es a educ ion
F on ie s in Pha macology | www. on ie sin.o g 8June 2016 | Volume 7 | A icle 151
P ie o-Domínguez e al. So a enib and Au ophagy
in cellula ATP le els ha inc ease AMP/ATP a io and
AMPK ac i a ion (Fuma ola e al., 2013; Teso i e al., 2015).
An expe imen al s udy which co obo a es ha hypo hesis
demons a ed ha ATP le el in so a enib- ea ed lung
adenoca cinoma cells dec eases mo e han 50% compa ed
o he con ol g oup (Teso i e al., 2015). On he o he hand, he
con i ma ion o he ole o ROS bu s du ing so a enib-induced
AMP ac i a ion comes om a s udy in which AMPK- ela ed
apop osis was p e en ed by he ea men wi h a ROS sca enge
(Pignochino e al., 2013, 2015). The ac i a ion o ups eam
kinases, LKB1 and CAMKKβ, is in ol ed on so a enib-
ela ed AMPK ac i a ion in NSCLC cells in i o and in i o
(G oenendijk e al., 2015). Ne e heless, i seems ha he AMPK
pa hway could be no in ol ed in au ophagy-induc ion by
so a enib, because LC3II exp ession inc eases sha ply when
AMPK is inhibi ed in HCC cul u ed cells ea ed wi h so a enib.
Whe eby, i is possible ha AMPK modula ion by so a enib
pa icipa es in o he cellula p ocesses, di e en o au ophagy,
which can also ake pa in o i s an ip oli e a i e ac ion, such as
apop osis o glucose me abolism de egula ion (Pignochino e al.,
2013; Teso i e al., 2015).
Endoplasmic Re iculum S ess
Endoplasmic e iculum is he main cellula o ganelle whe e
p o ein syn hesis, modi ica ion, and olding a e ca ied ou
and whe e calcium is s o ed. In he p esence o di e en
s esses caused by physiological o pa hological changes, non-
olding o un olding p o eins accumula e in o he o ganelle,
gene a ing a new condi ion inside he cell called ER s ess.
ER s ess is nega i ely in e e ing wi h p o ein syn hesis and
a ec s o he unc ions o ha o ganelle, such as calcium
homeos asis, which inally may cause p og ammed cell dea h
(Tuñón e al., 2013; Kania e al., 2015). This si ua ion leads
o he ac i a ion o he un olded p o ein esponse (UPR),
which ies o eco e he ini ial si ua ion (Jheng e al., 2014).
Some o he s a egies ha his esponse uses o alle ia e ER
s ess a e educ ion o p o ein ansla ion, exp ession o di e se
chape ones, induc ion o p o ein deg ada ion p ocesses, such
as ubiqui in-p o easome sys em, and deg ada ion o po ions
o he endoplasmic e iculum h ough he au ophagy pa hway
(Ve aillie e al., 2010). The h ee essen ial p o eins in UPR
induc ion a e inosi ol equi ing enzyme 1α(IRE1α), p o ein
kinase R-like ER kinase (PERK) and ac i a ing ansc ip ion
ac o (ATF6) (C espo e al., 2012). These mac omolecules a e
loca ed in basal condi ions in o he ER memb ane and hey
a e inhibi ed by he chape one binding immunoglobulin p o ein
(BiP). In s ess si ua ions, BiP disassembles o hese molecules,
causing hei ac i a ion and he s imula ion o h ee di e en
p o ein cascades which p omo e he UPR (Malhi and Kau man,
2011).
So a enib igge s he UPR esponse in di e en expe imen al
in i o models, which may con ibu e o he so a enib- ela ed
induc ion o au ophagy and o i s an ip oli e a i e e ec s
(Table 6,Figu e 1). So a enib-induced UPR is un ela ed o
MAPK inhibi ion because ERK ep ession canno s imula e ER
s ess (Rahmani e al., 2007; Shi e al., 2011). Mo e in de ail,
so a enib is able o ac i a e wo o he h ee b anches implica ed
in he esponse agains ER s ess (Rahmani e al., 2007; Yi e al.,
2012). Speci ically, his d ug induces he exp ession o IRE1α
and PERK, whe eas ATF6 exp ession emains cons an wi hou
changes in he exp ession on downs eam p o eins such as BiP
(Table 6;Rahmani e al., 2007; Yi e al., 2012). In ac , i has
been pos ula ed ha he e ec i eness o ATF6 is consequence
o he p o ound al e a ion o he sec e o y pa hway induced by
so a enib (Yi e al., 2012). O he expe imen s ha e claimed ha
so a enib educes di ec ly BiP exp ession, chape one ela ed wi h
he induc ion o UPR media ed by his chemo he apeu ic agen
(Table 6;Rahmani e al., 2007; Jiang e al., 2014).
Di e en esea ch has demons a ed ha so a enib induces a
p onounced inc ease in he exp ession o PERK (Table 6), which
modi ies he ac i i y o all i s downs eam p o eins (Rahmani
e al., 2007; Pa k e al., 2008; Shi e al., 2011; Yi e al., 2012; Holz
e al., 2013). One o he mos impo an is eIF2α(euka yo ic
ansla ion ini ia ion ac o 2α), is a ipa i e p o ein complex
ha binds and hyd olyzes GTP du ing i s ole in ec ui ing
he ini ia o me hionyl- RNA o he 40S ibosome o begin
mRNA ansla ion in euka yo ic cells (Ve aillie e al., 2010).
Some s udies ha e shown ha so a enib is able o induce eIF2α
phospho yla ion on Se 51 when i has passed 2 h since he s a
o he ea men (Rahmani e al., 2007; Yi e al., 2012; Dixon
e al., 2014). The phospho yla ion o eIF2αp e en s binding o
GTP and consequen ly educes p o ein ansla ion in cance cells
(Rahmani e al., 2007; Yi e al., 2012).
The las o he UPR b anches which is modi ied by so a enib
is he IRE1αpa hway. Some s udies ha e sugges ed ha
his an i umo al agen is able o s imula e IRE1αexp ession,
inducing i s ac i a ion and changing he exp ession o di e en
downs eam ac o s (Table 6,Figu e 1;Rahmani e al., 2007; Shi
e al., 2011; Yi e al., 2012). In his way, IRE1αhas a key ole
in he splicing and subsequen ly ansla ion o xbp1 (Malhi and
Kau man, 2011), and so a enib s imula es he splicing o his gene
simila ly o he incuba ion wi h di e se ER s ess induc o s, such
as unicamycin o hapsiga gin (Yi e al., 2012). Cu iously, when
IRE1αo xbp1 a e knocked down, cell sensibili y o so a enib
inc eases (Rahmani e al., 2007).
The endoplasmic e iculum is he main ese oi o calcium
ion (Ca2+) (Kania e al., 2015). So a enib is able o dis up
e iculum homeos asis because i discha ges all he Ca2+
ion p esen in ha o ganelle and induces i s accumula ion
in o he cy osol (Rahmani e al., 2007). This educ ion o
Ca2+endoplasmic e iculum s o ages inc eases ROS p oduc ion,
inducing oxida i e s ess, and may con ibu e o he cance ous
cell dea h induced by so a enib (Figu e 1;Rahmani e al., 2007).
I ER s ess is p olonged o e ime, UPR migh be
o e whelmed because ha o ganelle may be ull o un olded
and useless p o eins, and ha si ua ion would gene a e
p og ammed cell dea h h ough CHOP (C/EBP homologous
p o ein) media o , which is a ansc ip ion ac o in ol ed in
he inc ease o he exp ession o a lo o genes ela ed wi h
apop osis pa hway (Ve aillie e al., 2010; Malhi and Kau man,
2011). So a enib is able o induce he exp ession o CHOP and
o some p o eases ela ed wi h ER s ess p og ammed cell dea h,
such as caspase-2 o -4 (Table 6). IRE1αhas also been shown
o induce caspase-12 oligome iza ion h ough associa ion wi h
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