Ta ge ing euka yo ic ansla ion elonga ion wi h na u al p oduc s
Ma k B öns up1, 2, 3 and Flo enz Sasse1
1 Depa men o Chemical Biology, Helmhol z Cen e o In ec ion Resea ch, 38124 B aunschweig,
Ge many
2 Cen e o Biomolecula D ug Resea ch (BMWZ), Leibniz Uni e si y, 30159 Hanno e , Ge many
3 Ge man Cen e o In ec ion Resea ch (DZIF), pa ne si e Hanno e -B aunschweig, Ge many
E-mail: [email p o ec ed]
Abs ac
The ansla ion o mRNA in o p o eins is a p ecisely egula ed, complex p ocess ha can be di ided
in o h ee main s ages, i.e. ini ia ion, elonga ion and e mina ion. This con ibu ion is in ended o
highligh how na u al p oduc s in e e e wi h he elonga ion phase o euka yo ic p o ein
biosyn hesis. Cycloheximide, isola ed om S ep omyces g iseus, has been he p o o ype inhibi o o
euka yo ic ansla ion elonga ion o long. In he las h ee decades, a a ie y o na u al p oduc s
om di e en o igin we e disco e ed o also add ess he elonga ion s ep in di e en manne s,
including in e e ence wi h he elonga ion ac o s eEF1 and eEF2 as well as binding o A-, P- o E-si es
o he ibosome i sel . Recen ad ances in he c ys alliza ion o he ibosomal machine y oge he
wi h na u al p oduc inhibi o s allowed cha ac e izing simila i ies as well as di e ences o hei mode
o ac ion. Since abe a ions in p o ein syn hesis a e commonly obse ed in umo s, and mal unc ion
o o e exp ession o ansla ion ac o s can cause cellula ans o ma ion, he p o ein syn hesis
machine y has been ealized as an a ac i e a ge o an icance d ugs. The he apeu ic use o he
i s na u al p oduc s ha eached ma ke app o al, pli idepsin (Aplidin®) and homoha ing onine
(Syn ibo®), will be in oduced. In addi ion, we will highligh wo o he po en ial indica ions o
ansla ion elonga ion inhibi o s, i.e. i al in ec ions and gene ic diso de s caused by p ema u e
e mina ion o ansla ion.
1
Table o Con en
1 In oduc ion o euka yo ic p o ein biosyn hesis.............................................................................2
2 The elonga ion phase o he ansla ion sys em..............................................................................3
3 Na u al p oduc s as inhibi o s o he elonga ion phase..................................................................3
4 Inhibi o s o elonga ion phase as he apeu ics................................................................................7
5 Conclusion.......................................................................................................................................9
6 Re e ences.....................................................................................................................................10
This highligh is in ended o showcase how na u al p oduc s in e e e wi h he elonga ion phase o
euka yo ic p o ein biosyn hesis. A e an in oduc ion o euka yo ic p o ein biosyn hesis in gene al
and o he indi idual s eps in he elonga ion phase, we will p esen a selec ion o impo an
ansla ion inhibi o s om na u al o igin, wi h a ocus on hei binding modes and hei mechanisms
o ac ion. Finally, exis ing and po en ial u u e uses o elonga ion inhibi o s will be highligh ed.
1 In oduc ion o euka yo ic p o ein biosyn hesis
The ansla ion o in o ma ion s o ed by DNA in o p o eins is a i al p ocess in biological sys ems. In
b ie , he base sequence o he double-s anded DNA is ansc ibed and u he p ocessed in o a
single-s anded RNA molecule, he mRNA. The base sequence o he mRNA is ansla ed in o an
amino acid sequence o a p o ein on ibosomes in he cy oplasm o he cell.1-4 In he mRNA, h ee
consecu i e bases, a base iple , o m a codon o a speci ic amino acid. On he ibosome, he
codons a e ansla ed acco ding o hei sequence in o amino acids, and hese a e sequen ially linked
o o m a polypep ide. The s uc u al ela ionship be ween a codon and i s co esponding amino acid
is media ed by RNA molecules, ha ha e wo dis inc binding si es o he speci ic a achmen o he
amino acid (ca alyzed by aminoacyl- RNA syn he ases), and he speci ic binding o a codon (by a
complemen a y, so-called an icodon sequence). In o de o o m a pep ide bond be ween wo amino
acids, hey mus be b ough in o p oximi y o each o he . This ask is ul illed by he ibosomes,
composed o a small (40S) and a la ge subuni (60S) in Homo sapiens (Fig. 1). The 60S RNA uni has
h ee joining binding si es, called accep o si e (A-si e), pep idyl si e (P-si e), and exi si e (E-si e).
The ansla ion i sel is a highly egula ed and complex p ocess in ol ing many ac o s. I can be
di ided in o he h ee main s ages ini ia ion, elonga ion and e mina ion (Fig. 1). Fo i s ini ia ion, he
cell needs a special ini ia o RNA, he wo ibosomal subuni s and he mRNA. The ini ia o RNA
binds o he s a codon AUG, which ansmi s me hionine in euka yo es. In addi ion, a wide ange o
euka yo ic ini ia ion ac o s (eIF’s) a e in ol ed. A e o ma ion o a p eini ia ion complex o he
small ibosomal subuni and he ini ia o RNA wi h eIF-2 and o he ac o s, he mRNA is sc eened in
he 3' di ec ion o an AUG sequence. Once an AUG base iple o he mRNA is ound, he ini ia o
Me -loaded RNA will bind o i . A e he elease o eIF2, he 60S subuni is bound, c ea ing he
elonga ion-compe en 80S ini ia ion complex ( o de ailed in o ma ion abou he ini ia ion p ocess
see he con ibu ion by Pelle ie and collegues o his NPR special issue). The ini ia ion phase is
ollowed by he elonga ion o he amino acid chain as desc ibed in he nex chap e , ha con inues
2
un il a s op codon is eached, leading o he e mina ion o he pep ide o ma ion. The ibosomal
subuni s a e dissocia ed and ecycled o e-en e he ini ia ion phase.
2 The elonga ion phase o he ansla ion sys em
The elonga ion phase begins when he ini ia o Me - RNA is bound o he s a AUG codon and
posi ioned on he P-si e o he ibosome, lea ing he A-si e ee o he en y o he nex aminoacyl
RNA. A single elonga ion cycle in ol es h ee s eps: Amino acid inco po a ion (i.e. binding o he
amino acid-loaded RNA a he A-si e), o ma ion o he pep ide bond, and ibosome ansloca ion.
The i s s ep is media ed by he euka yo ic elonga ion ac o eEF1A (Fig. 2). Mammalian eEF1A is a
50 kDa p o ein ha possesses wo pa alogs, eEF1A1 and eEF1A2, wi h high amino acid sequence
homology (app oxima ely 90% iden i y). eEF1A, which is equi alen o bac e ial EF-Tu, binds amino
acyl- RNA in a GTP-dependen manne and di ec s he RNA o he A-si e o he ibosome. A codon
ecogni ion be ween mRNA and RNA causes GTP hyd olysis by eEF1A. eEF1A is eleased and he
aminoacyl- RNA can be accommoda ed in o he A-si e. The eEF1A-GDP is ecycled o eEF1A-GTP wi h
he help o he guanine exchange ac o (GEF) unc ion o he nucleo ide exchange ac o eEF1B
complex, which is composed o he subuni s α, δ, and γ.
The pep ide bond o ma ion be ween he amino acids loca ed a he P-si e and he A-si e is ca alyzed
by ibosomal pep idyl ans e ases. The deacyla ed RNA emains in a P/E hyb id posi ion. In his
s a e he accep o end is bound o he E-si e and he an icodon s em o he P-si e, whe eas he
pep idyl RNA ( he RNA on which he pep ide chain has been loaded) lies in an A/P hyb id posi ion.
To con inue wi h he nex cycle o elonga ion, a ansloca ion ha places he deacyla ed RNA
comple ely in he E-si e and he pep idyl RNA in he P-si e is equi ed. This ansloca ion is an ene gy
dependen p ocess ha employs eEF2, which s abilises he hyb id s a e. eEF2-GTP hyd olysis induces
a con o ma ional change in he complex and p omo es ansloca ion, he eby c ea ing an emp y A-
si e, whe e a new RNA can bind and ini ia e he nex cycle o pep ide chain elonga ion. Among all
h ee binding si es, he E-si e is he mos di e se ac oss species, showing di e en nucleo ides and
p o eins in bac e ia, a chaea and euka yo es.5, 6
3 Na u al p oduc s as inhibi o s o he elonga ion phase
Na u al p oduc s ha e played an ins umen al ole o s udy he ansla ion p ocess, because hey
demons a e how o in e e e wi h elonga ion a e y di e se s ages and posi ions. This includes
in e ac ions wi h p o eins in ol ed in he elonga ion p ocess o wi h he RNA o he ibosome. The
unde s anding o he unde lying molecula de ails has been g ea ly enhanced in he pas decade by
s uc u al biology s udies, ha p o ided high- esolu ion s uc u es o ibosomes om yeas s, a chaea
and humans in complexes wi h ansla ion inhibi o s.6, 7-10 The p e e en ial binding si es o euka yo e-
speci ic inhibi o s a he ibosome a e he RNA E-si e and he pep idyl ans e ase cen e (PTC) on
he 60S subuni . Rema kably, he a majo i y o co-c ys allized compounds is o na u al o igin. A
selec ion o he mos p ominen na u al p oduc s in e e ing wi h he elonga ion phase, ha a e
highly di e se om a s uc u al poin o iew, is gi en in Fig. 3 and Fig. 4.
Cycloheximide (CHX) ep esen s he p o o ype inhibi o o euka yo ic ansla ion elonga ion, as i
was he only known inhibi o o his p ocess o a long ime. I s isola ion om S ep omyces g iseus
was epo ed al eady in 1946. CHX inhibi s eEF2-media ed ansloca ion. Su p isingly, bound CHX s ill
3
allows one ansloca ion cycle o p oceed be o e he u he elonga ion is s opped.11 I binds o he
25S RNA and a euka yo e-speci ic p o ein eL42 a he E-si e on he la ge subuni o he ibosome,
and in e ac ion da a a a omic esolu ion a e a ailable o Saccha omyces ce e isiae (Fig. 5).6 Recen
c yo-EM expe imen s on human ibosomes wi h an a e age esolu ion o 3.6Å indica ed a simila
binding si e, bu addi ional molecula in e ac ions compa ed o he yeas ibosome.8 Thus, i is
possible ha he o e all mechanism o ac ion o CHX is no iden ical ac oss species.
CHX con ains a glu a imide moie y, a mo i ha is also p esen in he side chain o he mac olac one
lac imidomycin (LTM) isola ed om S ep omyces amphibiospo us.12 LTM inhibi s he elonga ion s ep
o euka yo ic ansla ion h ough binding o he E-si e o he 60S ibosome in a simila , bu no
iden ical ashion o CHX.13 The binding o CHX and LTM o he E-si e blocks eEF2-media ed RNA
ansloca ion, and he glu a imide g oups o CHX and LTM closely o e lap in he binding si e. CHX and
LTM di e in he abili y o bind he E-si e oge he wi h he E-si e RNA: Acco ding o a model o
Schneide -Poe sch e al.,13 he p esence o CHX a he E-si e does no s all ansloca ion, bu
occupa ion o he E-si e by bo h CHX and deacyla ed RNA does. Consequen ly, wo ansloca ion
e en s can occu be o e he p ocess s ops. While LTM binds o he same si e, he la ge LTM blocks
he access o deacyla ed RNA o he E-si e and p e en s he ibosome om lea ing he s a si e.
When LTM is bound o an emp y E-si e immedia ely a e ini ia ion, i allows pep ide bond o ma ion,
bu blocks he ansloca ion o he newly o med deacyla ed ini ia ing RNA om he P- o E-si e,
he eby a es ing he ibosome a he AUG s a codon. A e elonga ion has been s a ed and
deacyla ed RNA is bound o he E-si e, i is mo e di icul o LTM o ge access o he E-si e. Unlike
LTM, CHX can in e up he elonga ion p ocess a any ime, as i s binding o he E-si e is ega dless o
whe he he E-si e is occupied by deacyla ed RNA o no . The euka yo e-selec i e ac i i y o E-si e
inhibi o s is a ionalized by he p esence o wo bac e ia-speci ic RNA esidues (U2431 and A2432 in
E. coli) ha p e en d ug binding o he bac e ial ibosome.
The lissoclimides, which we e isola ed om shell-less mollusks, ca y a succinimide a he han a
glu a imide moie y. They we e also shown o in e e e wi h he elonga ion s ep o p o ein
biosyn hesis. De ailed in es iga ions ound ha chlo olissoclimide did no a ec he loading o
aminoacyl RNA on o ibosomes o he pep idyl ans e ase eac ion, bu in e e ed wi h ibosomal
E-si e unc ion.14 Recen X- ay co-c ys al s uc u e s udies showed a simila binding o lissoclimides o
he euka yo ic ibosome as ound o CHX and LTM.15
Phyllan hoside is a ansla ion elonga ion inhibi o i s isola ed om ex ac s o he Cen al
Ame ican ee Phyllan hus acumina us.16 Al hough chemically un ela ed, phyllan hoside was also
ound o bind o he same RNA nucleo ides and he eL42 p o ein as he glu a imide inhibi o s (Fig.
5); he elec on densi y in he c ys al s uc u e sugges s a co alen bond be ween C2764 and he
opened epoxide g oup o phyllan hoside.
Mycalamides A and B we e o iginally isola ed as cy o oxic compounds om he ma ine sponge
Mycale spec. om he coas o New Zealand. They we e shown o inhibi p o ein syn hesis,17 bu
hei molecula mechanism o ac ion emained unknown o long. In 2011 i was epo ed ha by
mycalamide B (MycB) inhibi s ansla ion elonga ion h ough blockade o eEF2-media ed
ansloca ion simila o CHX and LTM, in spi e o no s uc u al esemblance o he glu a imide-
con aining inhibi o s. MycB did no a ec he eEF1A-media ed loading o RNA on o he ibosome,
he AUG s a codon ecogni ion, o pep ide bond o ma ion, bu compe ed wi h deacyla ed RNA o
E-si e binding in a dose-dependen manne . As seen wi h LTM, MycB blocks RNA binding o he E-
si e and a es s he ibosome on he mRNA one codon ahead o CHX.18
4
C yp opleu ine is a phenan h oquinolizidine alkaloid which was isola ed om he ba k o C yp oca ya
pleu ospe ma ees. I was also shown o be an E-si e inhibi o and desc ibed o be euka yo e
speci ic.19 X- ay c ys allog aphic da a showed ha i binds o he mRNA channel a he 40S E-si e o
he small subuni . I sha es he same binding si e as pac amycine, an an ibio ic which also inhibi s
p oka yo ic ansla ion. The s uc u e o c yp opleu ine bound o yeas ibosome did no p o ide
hin s o i s speci ici y o euka yo es.6
So da ins a e ungal e penoid na u al p oduc s wi h a e acyclic co e embedding a no bo nene.
They inhibi p o ein syn hesis, bu exhibi a no able, selec i e an i ungal ac i i y. So da in binds o
eEF2 o Saccha omyces ce e isiae, bu no o eEF2 om plan s o mammals, hough he e is a high
le el o amino acid sequence conse a ion among hese p o eins. The e icacy o so da in di e s
g ea ly in di e en species o ungi. I could be demons a ed ha a “so da in speci ici y egion”
be ween amino acid esidues 517 and 525 wi hin eEF2 o S. ce e isiae accoun s o he special
bioac i i y p o ile o his class o compounds. A single subs i u ion o se ine a posi ion 523 by
glu amic acid, he co esponding esidue in human eEF2 a his posi ion, was su icien o ende S.
ce e isiae insensi i e o so da in.20
Mos elonga ion inhibi o s a ge he pep idyl ans e ase cen e (PTC) o he ibosome loca ed on
he la ge subuni , which is composed o highly conse ed RNA nucleo ides. Fo pep ide bond
o ma ion, he amino acyl- RNA and he pep idyl- RNA mus be p ope ly aligned in he A-si e and P-
si e o he PTC. The icho hecenes span a g oup o impo an myco oxins ha comp ises mo e han
150 membe s, including T-2 oxin, deoxyni alenol, and e uca in. They sha e a sesqui e pene co e
ha media es he majo in e ac ions wi h 25S RNA esidues in he binding pocke (Fig. 6a).6
Howe e , icho hecenes ha e also been shown o inhibi ansla ion ini ia ion and e mina ion, and
o ha e o he e ec s beyond p o ein biosyn hesis as well.21 A second, s uc u ally un ela ed g oup o
na u al p oduc s ha occupy he same binding si e is o med by plan alkaloids like lyco ine,
na ciclasine, and homoha ing onine, which sha e a dioxol-py oline g oup (Fig. 6b). These alkaloids
a e epo ed o be speci ic elonga ion inhibi o s. Lyco ine and na ciclasine we e isola ed om
Ama yllidaceae, and na ciclasine showed po en ial as an an icance o an i-in lamma o y d ug.
Howe e , clinical ials ha e no been conduc ed so a .22, 23 Homoha ing onine is an alkaloid wi h a
cephalo axine sca old ha was i s isola ed om Cephalo axus ha ing onii and C. o unei ees,
whose ba k ex ac s we e used in Chinese adi ional medicine o ea cance . Because
cephalo axine i sel is abundan in Cephalo axus lea es, homoha ing onine can be con enien ly
ob ained by a simple es e i ica ion om isola ed cephalo axine.
All A-si e inhibi o s block he access o he cha ged RNA and consequen ly pep ide bond o ma ion.
In con as o he E-si e inhibi o s men ioned abo e, hey do no in e ac wi h p o ein esidues, bu
only bind o he RNA nucleo ides o he ibosome. A-si e inhibi o s ha e been ob ained om e y
di e se sou ces, as exempli ied by anisomycin, an an ibio ic p oduced by S ep omyces g iseolus,
nagilac ones, di e penoid lac ones isola ed om Podoca pus nagi ees, o agelas a ins, b omina ed
alkaloids isola ed om he ma ine sponge Agelas dend omo pha. The po en an i umo ac i i y o
agelas a ins24 was only ecen ly aced back o he inhibi ion o p o ein syn hesis. Using a high-
h oughpu chemical oo p in ing me hod, he AglA-binding si e was mapped o he A-si e.9, 25
Aminoglycosides exe a unique mechanism o ac ion by pe u bing nucleo ides in he decoding
cen e ha disc imina es cogna e RNA om non-cogna e RNA. They bind wi hin a loop o helix 44
o 18S RNA, and hey s abilize he lip-ou con o ma ion o he wo essen ial and uni e sally
conse ed nucleo ides A1755 (A1492) and A1756 (A1493) in yeas (human numbe ing in b acke s).
5

Because his con o ma ional change is pa o he p oo eading p ocess, i s induc ion by
aminoglycoside binding lowe s he high ideli y o decoding, enables he binding o nea -cogna e
RNAs and he eby p omo es he inco po a ion o inco ec amino acids in o pep ide chains. While
mos aminoglycosides show selec i i y o bac e ial ibosomes, congene s like gene icin (G418) bind
wi h high a ini y o he euka yo ic ibosome (Fig. 7a). The s uc u al basis o his selec i i y has
been deciphe ed ecen ly by X- ay c ys allog aphy6 and asc ibed o he esidues G1645 and A1754,
ha a e speci ic o euka yo ic ibosomes (Fig. 7b) and ac as a ba ie ha p e en s he binding o
mos aminoglycosides.
The polyke ide my iapo one 3/4 was i s isola ed in 1995 om he alse co al My iapo a unca a.
The high cy o oxici y in he nanomola ange was a ibu ed o i s ac i i y as a ansla ion inhibi o .
My iapo one 3/4 also s alls p o ein syn hesis a he elonga ion phase by in e e ence wi h eEF-2
ac i i y, bu his is achie ed in an indi ec manne . eEF2 ac i i y is inhibi ed by phospho yla ion o
Th 56 by eEF2 kinase (eEF2K). eEF2K is a Ca2+-dependen kinase which is ac i a ed/deac i a ed by
a ious s imuli. Phospho yla ion o eEF2K a Se 359 leads o i s inac i a ion. The subsequen
dephospho yla ion o eEF2 hen induces he con inua ion o ansla ion. eEF2K ac i i y was shown o
be inc eased in se e al cance cell lines and epo ed as a po en ial a ge in cance ea men .26-28
My iapo one 3/4 was shown o bind o eEF2K, which in u n led o a phospho yla ion o eEF2 and an
inhibi ion o ansla ion elonga ion.29 Mycalamide (men ioned abo e) and my iapo one a e membe s
o a s uc u ally ela ed polyke ide amily, which also includes compounds like pede in, psymbe in,
edanolid, and gephy onic acid. All hese compounds a e ansla ion inhibi o s, bu each inhibi o
ac s in a di e en way.30-33 This polyke ide amily is he e o e an in e es ing example o he
di e si ica ion o bioac i i y associa ed wi h sub le s uc u al changes.
Didemnins and he ela ed amanda ins cons i u e ano he class o deeply s udied ansla ion
elonga ion inhibi o s. The cyclic depsipep ides we e i s isola ed om unica es and al eady
epo ed in 1981;34, 35 ecen s udies iden i ied he ma ine α-p o eobac e ia Tis ella mobilis and T.
bauzanensis as he p oduce o didemnins.36 The compounds showed ema kable an i umo , an i i al
and immunosupp essi e p ope ies. The analog didemnin B was shown o inhibi p o ein syn hesis
also by p e en ing he ansloca ion s ep, bu in con as o CHX and LTM, didemnin B binds o a
pocke o eEF1A ha is no mally used o bind ei he aa- RNA o eEF1Bα, a ac o ha is needed o
guanine nucleo ide exchange upon GTP hyd olysis. Since eEF1Bα and didemnin B a e mu ually
exclusi e, he p o ein syn hesis is inhibi ed by didemnin B because o i s compe i ion wi h his
nucleo ide exchange ac o . The ollowing mode o ac ion was p oposed: didemnin B binding o
eEF1A akes place ollowing deli e y o aa- RNA o he ibosome. The esul ing didemnin B-eEF1A
complex es s a he A-si e o he ibosome, because binding o eEF1Bα is p ecluded by didemnin B.
S abiliza ion o his complex a he A-si e p e en s displacemen o eEF1A by eEF2 causing
ansla ional a es .37-40
Nannocys ins a e mac ocycles isola ed om myxobac e ial Nannocys is sp.41 Mode o ac ion s udies
using haploinsu iciency p o iling (HIP) in yeas , mu a ional s udies in human HCT116 cells, and a ge
ishing wi h chemop o eomic p obes es ablished eEF1A as he p ima y a ge o his compound
class.42 Nannocys in A showed a ying ac i i ies in di e en cance cell lines, and he main
di e en ia ing ac o was ound o be he eEF1A exp ession le el. Biochemical and gene ic e idence
suppo an o e lapping binding si e o nannocys in wi h didemnin B on eEF1A. Al hough a c ys al
s uc u e is missing so a , s uc u al de e minan s o he ac i i y o nannocys ins could be p oposed
based on a ionally designed analogs om o al syn hesis.43-45
6
O he na u al compounds like he polyke ides cy o ienin and ansa ienin and he cyclic pep ide
e na in ha e been shown o compe e wi h didemnin binding o he e na y complex o eEF1A, GTP
and aminoacyl RNA.46
4 Inhibi o s o elonga ion phase as he apeu ics
Almos all inhibi o s o euka yo ic ansla ion isola ed om na u e we e ound o be cy o oxic in
assays wi h mammalian cell cul u es and we e p oposed o ha e po en ial an i umo ac i i y.
Abe a ions in p o ein syn hesis a e o en obse ed in es ablished cance s, and pe u ba ion by
mu a ion o o e exp ession o ansla ion ac o s can cause cellula ans o ma ion. The e o e, he
p o ein syn hesis machine y is a po en ial a ge o an icance d ugs. Howe e , as he ac i i y o
p o ein elonga ion ac o s in heal hy cells is ubiqui ous and essen ial, he inhibi ion o hese a ge s
leads o a delica e balance be ween an i umo e ec s and oxic side e ec s.
Se e al inhibi o s o euka yo ic p o ein syn hesis ha e s a ed o be de eloped as an icance d ugs,
and a ew ad anced o phase I and II clinical ials. Howe e , mos o he ansla ion inhibi o s ailed
in clinical ials, mos ly due o dose-limi ing oxici y.47 Howe e , he wo elonga ion inhibi o s
pli idepsin and homoha ing onine ha e ob ained ma ke au ho iza ion and will be in oduced in
mo e de ail.
Didemnin B, he mos ac i e among nine na u al didemnins, was he i s ma ine na u al p oduc ha
en e ed clinical ials as an an icance d ug. I has comple ed phase II clinical ials agains non-
Hodgkin's lymphoma, kidney adenoca cinoma, ad anced epi helial o a ian cance , and me as a ic
b eas cance , bu inally ailed o demons a e e ec i e an i umo ac i i y, while showing ca diac
and neu omuscula oxici ies.36,48 Though he p ima y a ge o didemnins is eEF1A, hey showed
pleio opic e ec s in cance cells. Using gene exp ession signa u es, didemnin B was iden i ied as a
pe sis en mTORC1 pa hway agonis , and palmi oyl-p o ein hioes e ase 1 (PPT1) could be iden i ied
as a second a ge . Didemnin induces cell-cycle a es and a caspase dependen apop o ic p ocess
h ough dual inhibi ion o eEF1A and PPT1.49
The closely ela ed compound pli idepsin (dehyd odidemnin B, aplidine, PLD) has an N- e minal
py u a e ins ead o a lac a e esidue (Fig. 4). Despi e he mino s uc u al di e ence, PLD was shown
o be mo e po en and less oxic, and has he e o e ou paced didemnin B in clinical de elopmen .50-
53. PLD binds o eEF1A2 and induces oxida i e s ess, Rac1 ac i a ion and JNK1 phospho yla ion,
which leads o a apid apop o ic p ocess in umo cells. While se e al clinical phase II s udies showed
only limi ed ac i i y in solid umo s, PLD had signi ican bene icial e ec s in hema ological cance s,
pa icula ly in mul iple myeloma, whe e eEF1A2 is o e exp essed.54 The phase III ial ADMYRE,
which ended in No embe 2017, showed ha a combina o ial he apy led o a longe p og ession-
ee and o e all su i al o pa ien s wi h mul iple myeloma. Ad e se e ec s like a igue, myalgia and
nausea we e usually ansien and manageable. Despi e he nega i e opinion adop ed by Eu opean
Medicines Agency's (EMA) commi ee, PLD ecei ed o phan d ug s a us o he ea men o mul iple
myeloma in Swi ze land in 2017 and has also been ecen ly app o ed by Aus alian egula o y
au ho i ies. PLD is ma ke ed by Pha maMa S.A. unde he ade name Aplidin.36, 52, 53, 55-61
Though i is p o en ha PLD inhibi s p o ein biosyn hesis, a seconda y, impo an unc ion o eEF1A
could con ibu e o i s bene icial e ec in myeloma pa ien s: eEF1A also in e ac s wi h polypep ides
a e hei elease om he ibosome. Speci ically, i is in ol ed in he elimina ion o mis olded
p o eins h ough he p o easome and agg esome p ocess.62 Inhibi ion o eEF1A by PLD led o an
7
inc ease in he le els o mis olded p o eins, while concomi an ly educing he au ophagic lux. These
e ec s p e en PLD- ea ed cance cells om educing p o eo oxic s ess and lead o apop osis.63 We
no e in passing ha mos mul iple myeloma he apies also a ge he p o easome.
The in e es in homoha ing onine s a ed ollowing he disclosu e o i s po en an ip oli e a i e
ac i i y agains mu ine P-388 leukemia cells wi h IC50 alues o 17 nM. Homoha ing onine o a
mix u e o cephalo axine es e s ha e been used o ea hema ological malignancies in China since
he 1970s.64 A e he de elopmen o he abo e-men ioned semisyn he ic p oduc ion,
homoha ing onine a ac ed a en ion o Wes e n medicine as well. The e icacy o he d ug is
aced back o he deple ion o p o eins wi h apid u no e ha a e essen ial o cance , such as he
sho -li ed oncop o eins BCR-ABL1 and an i-apop o ic p o eins (Mcl-1, Myc), which a e up egula ed
in leukemic cells.65 I was ecen ly shown ha homoha ing onine also a ec s signalling pa hways like
Jak-S a 5 by egula ing p o ein y osine kinase phospho yla ion66 and by ac i a ing he TGF-β
pa hway h ough phospho yla ion o smad3.67 Homoha ing onine was app o ed by he U.S. Food
and D ug Adminis a ion in 2012 o he ea men o ch onic myeloid leukemia in pa ien s wi h
esis ance and/o in ole ance o wo o mo e y osine kinase inhibi o s. Homoha ing onine is he
only na u al p oduc app o ed as a d ug o ea ch onic myeloid leukemia. I is ma ke ed by Te a
Pha maceu ical Indus ies unde he ade name Syn ibo.68
The disco e y o speci ic inhibi o s o euka yo ic ansla ion has imp o ed ou knowledge o he
simila i ies and di e ences be ween he ansla ional machine y o euka yo es and bac e ia. The
cha ac e iza ion o new ansla ion inhibi o s has also imp o ed ou knowledge o he changed
p o ein biosyn hesis in malignan cells, and u he s udies will open new pa hs – al hough hey
migh be na ow - o de elop he apeu ic agen s agains cance .
In addi ion o cance , wo po en ial medical indica ions o ansla ion elonga ion inhibi o s a e i al
in ec ions and gene ic diso de s. The an i i al spec um o CHX included se e al DNA and RNA
i uses,69 and LTM was iden i ied as be a po en inhibi o o dengue i us 2 in ec ion in cell cul u e
wi h an EC90 alue o 0.4 μM. An i i al ac i i y was obse ed a concen a ions ha do no a ec cell
iabili y. O he as eplica ing RNA i uses we e also ound o be sensi i e o LTM.70
Homoha ing onine showed a good (EC50 = 3.0 and 3.5 M) inhibi o y e ec agains wo di e en
i us s ains o oo -and-mou h disease (FMDVs) in swine kidney cells. The compound did no a ec
i us a achmen o en y, bu he ea ly phases o FMDV eplica ion - consis en wi h i s mechanism
o ac ion. Homoha ing onine has he po en ial o be an e ec i e an i-FMDV d ug bu u he s udies
o explo e he an i i al ac i i y in i o a e equi ed.71 Also mycalamides A and B ha e shown an i i al
ac i i ies agains co ona i uses, HSV and Polio i us, which ha e been asc ibed o hei ibosomal
inhibi ion.72 Howe e , analogues o mycalamides inhibi ed in luenza i us in i o by binding o he
i al nucleop o ein (NP), impeding i s associa ion wi h i al RNA.73 Thus, whe he mycalamides exe
hei an i i al ac ion by a ge ing p o ein ansla ion, i al componen s o bo h is no clea . To he
bes o ou knowledge, no ansla ion elonga ion inhibi o is in ad anced s udies as an an i i al d ug.
As men ioned abo e, aminoglycoside binding o ibosomes lowe s ideli y in cogna e RNA
ecogni ion and he eby p omo es he inco po a ion o inco ec amino acids in o pep ide chains.
This unique mode o ac ion has a po en ial he apeu ic use o he ea men o inhe i ed diso de s
caused by nonsense mu a ions.74, 75 In ac , s udies wi h issue cul u e as well as in i o models ha e
p o ided a p oo o concep ha aminoglycoside ea men can indeed induce eading h ough
p ema u e e mina ion codon mu a ions and he eby es o e he p oduc ion o ull leng h p o eins in
se e al gene ic diso de s. Fi s clinical s udies ha e been unde aken in pa ien s wi h Duchenne
8
muscle dys ophy and cys ic ib osis.76 Howe e , he long- e m use o aminoglycosides in his
indica ion is limi ed by he inhe en neph o oxic and o o oxic side e ec s o his class o na u al
p oduc s ha is (a leas pa ly) asc ibed o he inhibi ion o mi ochond ial ibosomes. The e o e, he
gene a ion o no el analogs ha ha e an inc eased p ema u e e mina ion codon (PTC) supp ession
a euka yo ic ibosome, bu a educed e icacy a bac e ial and/o mi ochond ial ibosomes, is a
subjec o cu en esea ch.77
5 Conclusion
Small molecule inhibi o s o bac e ial p o ein syn hesis ha e been shown o be powe ul ools in he
elucida ion o p oka yo ic p o ein biosyn hesis. Compa ed o p oka yo es, ewe compounds ha
inhibi euka yo ic ansla ion ha e been iden i ied. The s uc u al basis o hei e icacy has been
elucida ed only ecen ly, enabled by ad ances in he c ys alliza ion o he ibosomal machine y.
Na u al p oduc s ha e in o med cell biology ha in e e ence wi h p o ein ansla ion is possible by a
a ie y o mechanisms, in ol ing he wo elonga ion ac o s eEF1 and eEF2 as well as he A, P o E-
si es o he ibosome i sel . Aplidin and homoha ing onine a e he i s compounds inhibi ing
ansla ion elonga ion ha a e app o ed as an icance d ugs, albei in e y na ow indica ions o
ma ke s. Since ansla ion plays an essen ial ole in he p oli e a ion and su i al o as -g owing
umo cells, in pa icula o p o eins wi h a apid u no e ha a e essen ial o cance , i is well-
possible ha u he niches o ansla ion inhibi o s as new cance he apeu ics a e ca ed. This is
acili a ed by a mo e de ailed cha ac e iza ion mode o ac ion o ansla ion inhibi o s, including
seconda y e ec s o he pa icipa ing elonga ion ac o s and/o o - a ge e ec s o he na u al
p oduc s (e.g. p o ein deg ada ion o PPT1 inhibi ion, as men ioned abo e). The same holds ue o
o he indica ions like i al in ec ions o he amelio a ion o gene ic diso de s caused by p ema u e
e mina ion o ansla ion. Thus, he s udy o na u al p oduc in e e ing wi h euka yo ic ansla ion
o e s ample oppo uni ies o u u e disco e ies.
Con lic s o in e es
The e a e no con lic s o in e es o decla e.
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