STRUCTURAL ASPECTS OF FUSION PROTEINS DETERMINING THE LEVEL OF COMMERCIAL SUCCESS - Fusion Protein Technologies for Biopharmaceuticals: Applications and Challenges - page 44

that was no longer consider ed appropri ate. 5 The product is
no longer shown in the com pany's pipeline and as such, it
has not been included in the FP database . 6
Other delivery moiet ies such as recepto r fragments can be
used to deliver cyto kines. Al tor BioS cience's ALT-801 is in
Phase I/II developme nt for metas tatic melano ma. It consists
of IL-2 fused to a solub le T-cell receptor (TCR ) that
specifica lly binds to p53 on cancerous cells, includi ng those
that are not readily accessible to larger mA bs. In an alter na-
tive appro ach, MolMed has fuse d cytokine s and other
proteins to a tumor-targeting NGR (Asn-G ly-Arg)-contain-
ing peptide sequence. The NGR motif is a natural ligand for
certain CD13 recepto r isoforms that are select ively
expressed by endothelia l cells in newly formed tumor
vessels. NGR-hTN F is in Phase III developme nt for the
treatme nt of mes otheliom a. Both NGR -hTNF and ALT-801
are designed to offer convenient dosi ng of the partnered
cytokine with a com paratively low toxici ty p rofile. As well
as targeting, NG R binding also has a dir ect effect on CD13,
adding to the antit umoral act ivity of the attach ed cytokine
[26]. Sim ilarly, stud ies have found the sma ll molecu le drug
doxoru bicin coupl ed to an NGR peptide to display greater
potency but lower side effects com pared to the free drug
[27]. FP developers mus t be careful to ensure that their
approache s are not built-upon by o thers to create comme r-
cially stronger compet itor produc ts.
It shou ld b e n ote d that targeted ligan ds in earlier stage s o f
develo pm ent i nvolve a wider range of ligands than ju st
cytokines. Furthermo re, not a ll targete d cytokines are designed
to bring about c ell d eath . Products are also i n d eve lop men t
for n onon cology indicatio ns, in clu di ng F8-IL1 0 th at delive rs
IL-10, which i s an anti-inflammatory cy tok in e w ith a potential
role in the treatment of rh eumato id arthritis.

delivered to APCs using a bacterial ligand, flagellin. Toll-
like recepto rs on APCs have evolved to reco gnize a wide
variet y of micro bial proteins, or pathogen- associa ted molec-
ular patterns (PAM Ps). Using a viral antigen fused to
flagelli n, VaxInnate is developing an appro ach for tre ating
influe nza.

3.1.7 Ant ibody Fragm ent Fusions (6b and 7b)

A d van c e s i n p r o t e i n e n g i n e e r i n g h ave f a c i l i t a t e d t h e d evel -
opment of a range of Ab-fragm ent-based s truc tures offe r-
ing diffe rent properti es that are designed to overcome
some of the s hortcomings of traditional m Abs, or bring
about mechanisms of action that were previously not
possible. Although mAbs have achieved s i g n i fi c a n t c o m -
mercial s uccess, wi th total gl obal s al es of

$40 b il lion in
2 0 1 0 , t h e i r c o m p a r a t ivel y l a rg e s i z e c a n r e s t r i c t t i s s u e
pene tr ati on o r a cc es s to c el lula r t arg ets . 7 Full mAbs are
c o m p a r a t ivel y ex p e n s ive t o m a n u f a c t u r e , r e q u i r i n g m a m -
malian expression syst em s. Furt he rm ore , t he I P landsca pe
is com pl ex, wi th many key st eps for opti mizing designs
b e i n g c ove r e d b y s ever a l l a y e r s o f p a t e n t p r o t e c t i o n . T h e s e
f a c t o r s h ave i n c e n t iv i z e d d r u g d evel o p e r s t o s e e k a l t e r n a -
tive structures. FPs in groups 6b and 7b (Figure 3.2) consist
of Ab-binding domains f used to other Ab-bi nding

domains, or to an Fc effe ctor.

3.1.7.1 Bispe cific Abs : Ab-Bindi ng Domai n Fused to Ab-
Bindi ng Domai n (6b) Th ree of the FPs iden tified consist
of an Ab- binding doma in fused to anot her binding d omain
specific for a different target, to achi eve bisp ecific targeting.
Trion/Frese nius' mar keted produc t Removab 1 (catum axo-
mab) and University Hospital Tuebingen' s Phase I/II candi-
date rM28 , also include an Fc effector domain, giv ing a third
functi on. The structure of Removab rese mbles that of a
traditi onal mAb, with one binding doma in specifi c to
EpCAM that is assoc iated with the surf ace of certain cance r
cells. Through genetic fusion, the secon d-bindi ng doma in is
designed to target CD3 on T cel ls, while the Fc portion
accele rates the immu ne response by recrui ting accessory
immu ne syst em. Similarly, Micromet 's bispeci fic T-cell
engage r (BiTE 1 ) MT103 (blinatumom ab) also uses anti-
CD3 binding to bring T cel ls into the proxi mity of cance r
cells, but lacks an Fc doma in.
Bispe cific and trifu nctiona l FPs pote ntially allow for
novel mechani sms of action to b e emp loyed. However, a
range of com peting non-FP bisp ecific scaffol d tec hnologie s
has been developed. Ab-based structure s include dimerized
single- chain variable fragment (scFv) fragme nts known as
diabodies and F-star's mAb 2 technology which relates to full

3.1.6.3 Antigen-Mediated Cell Death (5a and 5b) Vaccin es
typicall y initiate an immun e resp onse after proce ssed by that
display the antigen ic com ponents on their surf ace via class II
MHC molecu les. These are then recogniz ed by T cells that
cannot otherwis e iden tify foreign antigen s. FP immu nothera-
pies in developme nt are designed to be mor e efficient by
interact ing dir ectly with the immu ne system machin ery.
Of the 43 FPs in Phase II or above, three act by delivering
antigen s to APCs. Ce lldex h as two FP APC -targeting candi -
dates in Phase II development for the treatme nt of cance rs.
Ab delivery com ponents bind to targets on the surf ace of
APCs that are internalize d via recepto r-m ediated endocy-
tosis. The fuse d antigen fragments are subseq uently proc-
essed and present ed to T cells, which results in an immune
response against cel ls expressing the antigen . Similarly,
VaxInn ate uses a non-Ab appro ach, with an antigen

5 http://clinicaltrials.gov/ct2/show/NCT00408967?term ¼ tucotuzumab þ
celmoleukin&rank ¼ 2
6 http://www.merckserono.net/en/science/pipeline/phase_ii/phase_2.html

7 http://www.datamonitor.com/store/News/fast_growth_mab_market_to_
offer_great_rewards_to_a_select_few_over_2009_15?productid ¼
A31659B5-E3F6-4C49-8C5B-DF524E8EB770