Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5366_Библиотеки_им_академика_М_И_Перельмана.pdf
340
111. Lee JH, Jeong YR, Kim YG, Lee GM (2017) Understanding of decreased sialylation
of Fc-fusion protein in hyperosmotic recombinant Chinese hamster ovary cell culture:
N-glycosylation gene expression and N-linked glycan antennary prole. Biotechnol Bioeng
114(8):1721–1732
112. Lewis AM, Croughan WD, Aranibar N, Lee AG, Warrack B, Abu-Absi NR et al (2016)
Understanding and controlling sialylation in a CHO Fc-Fusion process. PLoS One 11(6):1–24
113. Liu J, Wang J, Fan L, Chen X, Hu D, Deng X etal (2015) Galactose supplementation enhance
sialylation of recombinant Fc-fusion protein in CHO cell: an insight into the role of galactosylation in sialylation. World J Microbiol Biotechnol 31(7):1147–1156
114. Chen X, Liu X, Xiao Z, Liu J, Zhao L, Tan WS etal (2019) Insights into the loss of protein sialylation in an fc-fusion protein-producing CHO cell bioprocess. Appl Microbiol
Biotechnol 103(12):4753–4765
115. Bora de Oliveira K, Spencer D, Barton C, Agarwal N (2017) Site-specic monitoring of
N-Glycosylation proles of a CTLA4-Fc-fusion protein from the secretory pathway to the
extracellular environment. Biotechnol Bioeng 114(7):1550–1560
116. Wang Q, Yang G, Wang T, Yang W, Betenbaugh MJ, Zhang H (2019) Characterization of
intact glycopeptides reveals the impact of culture media on site-specic glycosylation of
EPO-Fc fusion protein generated by CHO-GS cells. Biotechnol Bioeng 116(9):2303–2315
117. Schmidt SR (2017) Production challenges for complex biologics: fusion proteins. Am Pharm
Rev (February):1–4
118. Cordes AA, Platt CW, Carpenter JF, Randolph TW (2012) Selective domain stabilization as a
strategy to reduce fusion protein aggregation. J Pharm Sci 101(4):1400–1409
119. Fast JL, Cordes A, a, Carpenter JF, Randolph TW. (2009) Physical instability of a therapeutic Fc fusion protein: domain contributions to conformational and colloidal stability.
Biochemistry 48(49):11724–11736
120. Strand J, Huang C, Xu JIN (2013) Characterization of Fc-fusion protein aggregates derived
from extracellular domain disulde bond rearrangements. J Pharm Sci 102(2):441–453
121. Wang T, Fodor S, Hapuarachchi S, Jiang XG, Chen K, Apostol I etal (2013) Analysis and
characterization of aggregation of a therapeutic Fc-fusion protein. J Pharm Biomed Anal
72:59–64
122. Huang RY-C, Iacob RE, Krystek SR, Jin M, Wei H, Tao L etal (2016) Characterization
of aggregation propensity of a human Fc-fusion protein therapeutic by hydrogen/deuterium
exchange mass spectrometry. J Am Soc Mass Spectrom 28:795
123. Shukla AA, Gupta P, Han X (2007) Protein aggregation kinetics during Protein A chromatography. Case study for an Fc fusion protein. J Chromatogr A 1171(1–2):22–28
124. Xu X, Didio DM, Leister KJ, Ghose S (2010) Disaggregation of high-molecular weight
species during downstream processing to recover functional monomer. Biotechnol Prog
26(3):717–726
125. Bobst CE, Wang S, Shen W-C, Kaltashov IA (2012) Mass spectrometry study of a transferrinbased protein drug reveals the key role of protein aggregation for successful oral delivery.
Proc Natl Acad Sci USA 109(34):13544–13548
126. Amaral M, Hölper S, Lange C, Jung J, Sjuts H, Weil S etal (2020) Engineered technologies
and bioanalysis of multispecic antibody formats. J Appl Bioanal 6(1):26–51
127. Duivelshof BL, Murisier A, Camperi J, Fekete S, Beck A, Guillarme D et al (2021)
Therapeutic Fc-fusion proteins: current analytical strategies. J Sep Sci 44(1):35–62
128. Wu B, Sun YN (2014) Pharmacokinetics of peptide-Fc fusion proteins. J Pharm Sci
103(1):53–64
129. Wunder A, Stehle G, Sinn H, Schrenk HH, Hoff-Biederbeck D, Bader F etal (1997) Enhanced
albumin uptake by rat tumors. Int J Oncol 11(3):497–507
130. Schulte S (2009) Half-life extension through albumin fusion technologies. Thromb Res
124(Suppl):6–8
131. Zalevsky J, Chamberlain AK, Horton HM, Karki S, Leung IWL, Sproule TJ etal (2010)
Enhanced antibody half-life improves invivo activity. Nat Biotechnol 28(2):157–159
S. R. Schmidt
11 Fusion Proteins: Current Status andFuture Perspectives
132. Presta LG (2008) Molecular engineering and design of therapeutic antibodies. Curr Opin
Immunol 20(4):460–470
133. Suzuki T, Ishii-watabe A, Tada M, Kanayasu-toyoda T, Kawanishi T, Yamaguchi T et al
(2010) Importance of neonatal FcR in regulating the serum half-life of therapeutic proteins
containing the Fc domain of human IgG1: a comparative study of the afnity of monoclonal
antibodies and Fc-fusion proteins to human neonatal FcR.J Immunol 184:1968
134. Bitonti AJ, Dumont JA, Low SC, Peters RT, Kropp KE, Palombella VJ etal (2004) Pulmonary
delivery of an erythropoietin Fc fusion protein in non-human primates through an immunoglobulin transport pathway. Proc Natl Acad Sci USA 101(26):9763–9768
135. Mayle KM, Le AM, Kamei DT (2012) The intracellular trafcking pathway of transferrin.
Biochim Biophys Acta, Gen Subj 1820(3):264–281
136. Wang Y, Chen YS, Zaro JL, Shen WC (2011) Receptor-mediated activation of a proinsulintransferrin fusion protein in hepatoma cells. J Control Release 155:386–392
137. Park E, Starzyk RM, McGrath JP, Lee T, George J, Schutz AJ etal (1998) Production and
characterization of fusion proteins containing transferrin and nerve growth factor. J Drug
Target 6(1):53–64
138. Bai Y, Shen W-C (2006) Improving the oral efcacy of recombinant granulocyte colonystimulating factor and transferrin fusion protein by spacer optimization. Pharm Res
23(9):2116–2121
139. Chen YS, Zaro JL, Zhang D, Huang N, Simon A, Shen WC (2018) Characterization and oral
delivery of proinsulin-transferrin fusion protein expressed using expresstec. Int J Mol Sci
19(2):1–13
140. Xie C, Wang Z, Su Y, Wang J, Shen WC (2020) Discovery of an orally effective factor
IX-transferrin fusion protein for hemophilia B.Int J Mol Sci 21(1)
141. Schlapschy M, Theobald I, Mack H, Schottelius M, Wester H-J, Skerra A (2007) Fusion of
a recombinant antibody fragment with a homo-amino-acid polymer: effects on biophysical
properties and prolonged plasma half-life. Protein Eng Des Sel 20(6):273–284
142. Breibeck J, Skerra A (2017) The polypeptide biophysics of proline / alanine-rich sequences
(PAS): recombinant biopolymers with PEG-like properties. Biopolymers (July):1–12
143. Schellenberger V, Wang C, Geething NC, Spink BJ, Campbell A, To W etal (2009) A recombinant polypeptide extends the invivo half-life of peptides and proteins in a tunable manner.
Nat Biotechnol 27(12):1186–1190
144. Geething NC, To W, Spink BJ, Scholle MD, Wang CW, Yin Y etal (2010) Gcg-XTEN: An
improved glucagon capable of preventing hypoglycemia without increasing baseline blood
glucose. PLoS One 5(4):e10175
145. Brandl F, Merten H, Zimmermann M, Béhé M, Zangemeister-Wittke U, Plückthun A (2019)
Inuence of size and charge of unstructured polypeptides on pharmacokinetics and biodistribution of targeted fusion proteins. J Control Release 307(May):379–392
146. Egrie JC, Browne JK (2001) Development and characterization of novel erythropoiesis stimulating protein (NESP). Br J Cancer 84(s1):3–10
147. Fares F, Suganuma N, Nishimori K, LaPolt P, Hsueh A, Boime I (1992) Design of a longacting follitropin agonist by fusing the C-terminal sequence of the chorionic gonadotropin
beta subunit to the follitropin beta subunit. Proc Natl Acad Sci USA 89(10):4304–4308
148. Xu J, Okada S, Tan L, Goodrum KJ, Kopchick JJ, Kieliszewski MJ (2010) Human growth
hormone expressed in tobacco cells as an arabinogalactan-protein fusion glycoprotein has a
prolonged serum life. Transgenic Res 19(5):849–867
149. Betre H, Liu W, Zalutsky MR, Chilkoti A, Kraus VB, Setton LA (2006) A thermally responsive biopolymer for intra-articular drug delivery. J Control Release 115(2):175–182
150. Boado RJ (2022) IgG fusion proteins for brain delivery of biologics via blood–brain barrier
receptor-mediated transport of the transporting. Pharmaceutics 14(7):14071476
151. Liu Y, Wang HY, Zhou L, Su Y, Shen WC (2018) Biodistribution, activation, and retention of
proinsulin-transferrin fusion protein in the liver: mechanism of liver-targeting as an insulin
prodrug. J Control Release 275:186–191
341
342
152. Kim K-J, Malik AB (2003) Protein transport across the lung epithelial barrier. Am J Phys
Lung Cell Mol Phys 284(2):L247–L259
153. Hofmann C, Seefried L, Jakob F (2016) Asfotase alfa: enzyme replacement for the treatment
of bone disease in hypophosphatasia. Drugs Today 52(5):271–285
154. Zimran A, Wajnrajch M, Hernandez B, Pastores GM (2018) Taliglucerase alfa: Safety and
efcacy across 6 clinical studies in adults and children with Gaucher disease. Orphanet J Rare
Dis 13(1):1–10
155. LeBowitz JH, Grubb JH, Maga JA, Schmiel DH, Vogler C, Sly WS (2004) Glycosylationindependent targeting enhances enzyme delivery to lysosomes and decreases storage in
mucopolysaccharidosis type VII mice. Proc Natl Acad Sci USA 101(9):3083–3088
156. Maga JA, Zhou J, Kambampati R, Peng S, Wang X, Bohnsack RN etal (2013) Glycosylationindependent lysosomal targeting of acid a-glucosidase enhances muscle glycogen clearance
in pompe mice. J Biol Chem 288(3):1428–1438
157. Zhou Z, Austin GL, Shaffer R, Armstrong DD, Gentry MS (2019) Antibody-mediated
enzyme therapeutics and applications in glycogen storage diseases. Trends Mol Med
25(12):1094–1109
158. Correale P, Cusi MG, Tagliaferri P (2011) Immunomodulatory properties of anticancer monoclonal antibodies: Is the “magic bullet” still a reliable paradigm? Immunotherapy 3(1):1–4
159. Shapira A, Benhar I (2010) Toxin-based therapeutic approaches. Toxins (Basel)
2(11):2519–2583
160. Baldo BA (2014) Side effects of cytokines approved for therapy. Drug Saf 37(11):921–943
161. Sun Z, Ren Z, Yang K, Liu Z, Cao S, Deng S etal (2019) A next-generation tumor-targeting
IL-2 preferentially promotes tumor-inltrating CD8+ T-cell response and effective tumor
control. Nat Commun 10(1):3874
162. Klein C, Waldhauer I, Nicolini VG, Freimoser-Grundschober A, Nayak T, Vugts DJ etal
(2017) Cergutuzumab amunaleukin (CEA-IL2v), a CEA-targeted IL-2 variant-based immunocytokine for combination cancer immunotherapy: overcoming limitations of aldesleukin
and conventional IL-2-based immunocytokines. Onco Targets Ther 6(3):e1277306
163. Murer P, Neri D (2019) Antibody-cytokine fusion proteins: a novel class of biopharmaceuticals for the therapy of cancer and of chronic inammation. New Biotechnol 52(April):42–53
164. Hutmacher C, Neri D (2019) Antibody-cytokine fusion proteins: biopharmaceuticals with
immunomodulatory properties for cancer therapy. Adv Drug Deliv Rev 141:67–91
165. Lechner MG, Russell SM, Bass RS, Epstein AL (2011) Chemokines, costimulatory molecules
and fusion proteins for the immunotherapy of solid tumors. Immunotherapy 3(11):1317–1340
166. Schirrmann T, Krauss J, Arndt MAE, Rybak SM, Dübel S (2008) Targeted therapeutic
RNases (ImmunoRNases). Expert Opin Biol Ther 9(1):79–95
167. Arndt MAE, Vu BK, Newton DL, Rybak SM (2005) A dimeric angiogenin immunofusion
protein mediates selective toxicity toward CD221 tumor cells. J Immunother 28(3):245–251
168. Krauss J, Arndt MAE, Vu BK, Newton DL, Rybak S (2005) Targeting malignant B-cell
lymphoma with a humanized anti-CD22 scFv-angiogenin immunoenzyme. Br J Haematol
128(5):602–609
169. Jordaan S, Akinrinmade O, Nachreiner T, Cremer C, Naran K, Chetty S et al (2018)
Updates in the development of ImmunoRNases for the selective killing of tumor cells.
Biomedicine 6(1):28
170. Lilienthal N, Lohmann G, Crispatzu G, Vasyutina E, Zittrich S, Mayer P etal (2016) A novel
recombinant anti-CD22 immunokinase delivers proapoptotic activity of death-associated
protein kinase (DAPK) and mediates cytotoxicity in neoplastic B cells. Mol Cancer Ther
15(5):971–984
171. Hlongwane P, Mungra N, Madheswaran S, Akinrinmade OA, Chetty S, Barth S (2018)
Human granzyme B based targeted cytolytic fusion proteins. Biomedicine 6(72):1–11
172. Zhang DX, Zhao PT, Xia L, Liu LL, Liang J, Zhai HH etal (2010) Potent inhibition of
human gastric cancer by HER2-directed induction of apoptosis with anti-HER2 antibody and
caspase- 3 fusion protein. Gut 59(3):292–299
S. R. Schmidt
11 Fusion Proteins: Current Status andFuture Perspectives
173. Papadia F, Basso V, Patuzzo R, Maurichi A, Di Florio A, Zardi L etal (2013) Isolated limb
perfusion with the tumor-targeting human monoclonal antibody-cytokine fusion protein
L19-TNF plus melphalan and mild hyperthermia in patients with locally advanced extremity
melanoma. J Surg Oncol 107(2):173–179
174. Diaz Arguello OA, Haisma HJ (2021) Apoptosis-inducing tnf superfamily ligands for cancer
therapy. Cancers (Basel) 13(7):1543–1565
175. Wajant H, Gerspach J, Pzenmaier K (2013) Engineering death receptor ligands for cancer
therapy. Cancer Lett 332(2):163–174
176. Chura-Chambi RM, Bellini MH, Jacysyn JF, Andrade LN, Medina LP, Prieto-Da-Silva ARB
etal (2014) Improving the therapeutic potential of endostatin by fusing it with the BAX BH3
death domain. Cell Death Dis 5(8):1–10
177. Wang F, Ren J, Qiu XC, Wang LF, Zhu Q, Zhang YQ etal (2010) Selective cytotoxicity to
HER2-positive tumor cells by a recombinant e23sFv-TD-tBID protein containing a furin
cleavage sequence. Clin Cancer Res 16(8):2284–2294
343
Chapter 12
Development ofAntibody-Drug
Conjugates
DavidY.Jackson
Abstract Antibody drug conjugates (ADCs) are a rapidly growing class of targeted
cancer drugs in which a highly toxic small molecule (payload) is conjugated to a
tumor-selective antibody. Over the past two decades, a total of 11 ADCs have been
approved by the FDA in the United States; including: gemtuzumab ozogamicin
(Mylotarg™), brentuximab vedotin (Adcetris™), ado-trastuzumab emtansine
(Kadcyla™), inotuzumab ozogamicin (Besponsa™), polatuzumab vedotin
(Polivy™), enfortumab vedotin (Padcev™), trastuzumab deruxtecan (Enhertu™),
sacituzumab govitecan (Trodelvy™), belantamab mafodotin (Blenrep™), loncastuximab tesirine-lpyl (Zynlonta™), and tisotumab vedotin-tftv (Tivdak™). The
path to commercial success for these ADCs has been challenging however, and new
ADC approvals were rare prior to 2017 when only three ADCs had been approved
by the FDA. Then in 2019 three more ADCs were approved, followed by two
approvals in 2020 and two more in 2021. Dozens of ADCs are now in late-stage
clinical trials and new approvals are expected to remain consistent for the near
future. Following closely behind are over a hundred new ADCs in early clinical or
preclinical development. This chapter will summarize the history of currently
approved ADCs with emphasis on the challenges that were overcome during development and new technology that likely contributed to their success. The safety and
efcacy of each ADC will be discussed from a critical but honest perspective based
on personal experience. My intention in writing this chapter is to encourage readers
to educate themselves about the real benets and risks of ADC therapeutics so that
informed decisions can be made by cancer patients in collaboration with their
doctors.
Keywords Antibody-drug conjugate · Toxic payload · FDA approved · Cancer
drug · oncology · Targeted therapy
D. Y. Jackson (*)
DYJ Pharma, San Mateo, CA, USA
K. Gadamasetti, S. A. Kolodziej (eds.), Bioprocessing, Bioengineering
and Process Chemistry in the Biopharmaceutical Industry,
https://doi.org/10.1007/978-3-031-62007-2_12
345© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
346
D. Y. Jackson
12.1 Introduction
Antibody-drug conjugates (ADCs) are a rapidly growing class of targeted therapeutic agents for the treatment of cancer [1, 2]. Cancer is the second most prevalent
cause of death in the US and many other countries; only heart disease kills more
people. Most conventional drugs for the treatment of cancer are highly potent small
molecules that kill cells or inhibit cell growth and often have poor therapeutic windows due to their lack of selectivity for tumor cells [3]. In the last three decades
however, new monoclonal antibody (mAb) therapeutics that bind to specic antigens on tumor cells have demonstrated improved tumor selectivity and safety [4].
These mAbs, however, frequently lack sufcient potency for use as single-agent
drugs and are often used in combination with conventional chemotherapeutic agents
to improve patient treatment outcomes [5]. Although multidrug treatment regimens
have been moderately successful in treating some forms of cancer, the increased
costs associated with conventional chemotherapy, combined with complicated dosing schedules and potential toxicity due to adverse drug interactions, demonstrate a
need for safer more effective cancer drugs.
Antibody-drug conjugates combine the target specicity of a monoclonal antibody with the potency of a small molecule drug (payload) by connecting them into
a single ADC molecule that retains the properties of both [6]. The improved selectivity and potency of ADCs lead to superior safety and efcacy resulting in broader
therapeutic windows compared to conventional chemotherapeutic drugs (Fig.12.1).
In fact, ADCs have been described as the “smart bombs” of cancer therapy because
they deliver highly toxic payloads directly to tumor cells while minimizing “collateral damage” to the surrounding noncancerous or normal tissues [7]. The concept
is simple, but in reality, tumor cells are not easy to target because they are derived
from normal cells and express similar proteins on their cell membrane. Moreover,
cancer cells are usually very good at camouage by mimicking their surroundings;
making them difcult targets to hit, even for antibodies.
The key to developing an effective ADC therapeutic is to nd the optimal combination of components; target, antibody, linker, and payload for a specic cancer
Fig. 12.1 ADCs improve the safety (higher MTD) & efcacy (lower Rx) to broaden the therapeutic window of conventional cancer drugs
12 Development ofAntibody-Drug Conjugates
347
type. This chapter will discuss these components and their desired properties in
order to give the reader a better understanding of the benets and limitations of the
currently approved ADC therapeutics. Emerging new technologies such as sitespecic conjugation methods designed to improve the safety and efcacy of future
ADCs will also be discussed. ADCs do not yet offer a cure for cancer but they do
offer an alternative to conventional chemotherapeutic drugs and should continue to
be investigated as targeted therapeutic agents. Cancer may never disappear completely from the human condition, but each small step toward nding a cure might
eventually save the life of someone you care about.
12.2 ADC History
Most antibody-drug conjugates have experienced a rugged path to commercial success and have overcome numerous challenges along the journey. For example, the
rst ADC to reach the market (Mylotarg) was approved in 2000 butwas later discontinued due to lack of efcacy [8]. Nearly 10years elapsed before the second
ADC, Adcetris was approved in 2011; followed by a third ADC, Kadcyla, which
was approved in 2013. With only three approvals in the rst decade of ADC development, their approval rate was lower than that for small molecules and only a fraction of the approval rate for most antibody therapeutics [9]. Fortunately, this trend
was temporary and the rate of ADC approvals has increased dramatically in recent
years with seven new ADCs approved for cancer between 2017 and 2022 [10].
Given the rapid increase in approvals, one might conclude that the lessons
learned from early ADCs may have facilitated the development pathways of those
that followed. Closer analysis however, indicates that the increase in ADC approvals
likely reects the growing number of ADCs entering clinical trials, rather than new
breakthroughs in ADC technology. During the past decade (between 2011 and
2021), the number of clinical trials has steadily increased by nearly tenfold to over
300 trials in 2021 (Fig.12.2a), yet the number of new ADC approvals during the
same time period only doubled (Fig.12.2b). Although the number of new clinical
trials continues to grow each year, the discrepancy between the number of phase I/
II and phase III trials indicates that most ADCs fail to progress beyond the early
stages of clinical development.
The reasons for these clinical failures are difcult to assess and seldom reported,
even if they’ve been determined by the companies that sponsored them. Based on
the currently available information, however, most ADC researchers would probably agree that systemic exposures to toxic payloads and off-target toxicity are primary contributors to ADC failures in the clinic [11]. Methods for reducing ADC
toxicity would therefore be expected to improve the overall safety of ADCs and will
likely be a major focus for future research and development efforts.
In general, there are four major components (target, antibody, linker, and drug
payload) that impact the commercial success or failure of an antibody-drug
348
A)
# of trials
Year
2
0
B)
Year
D. Y. Jackson
300
250
200
150
100
50
0
2
2
2
0
0
0
0
0
0
1
3
2
2
2
2
2
2
0
0
4
2
0
0
0
0
0
0
0
0
0
0
8
7
9
5
6
2
2
0
1
0
2
2
2
2
2
2
0
0
1
1
1
2
2
0
0
0
0
0
0
1
1
1
1
1
1
7
4
5
6
3
8
50
45
40
35
30
25
20
15
# of trials
10
2
2
0
0
1
2
9
0
5
0
2
2
0
0
0
0
1
2
2
2
2
2
2
2
0
0
3
2
0
0
0
0
0
0
0
0
0
0
6
7
4
5
8
2
2
0
9
1
1
3
4
0
1
2
2
2
2
0
0
0
0
0
0
1
1
1
2
2
2
2
2
2
0
0
0
1
5
0
0
0
1
1
1
1
6
7
9
8
Fig. 12.2 (a) Number of ADC clinical trials by phase of development since 2001. (b) Number of
new clinical trials and approvals since 2001. (Source: clinical trials.gov)
Desired Properties
Target/antigen
Antibody
Linker
Payload
Fig. 12.3 Components and desired properties of an antibody-drug conjugate (ADC)
conjugate (Fig.12.3). Pharmaceutical companies focus signicant efforts on selecting components with optimal properties in order to improve the effectiveness of
ADCs. Ironically the component that likely has the greatest impact on the success
or failure of an ADC resides in the tumor and is not part of the ADC [12]. The selectivity of an ADC for killing tumor cells over normal adjacent tissues is almost solely
dependent upon the expression prole of the antigen target, so target selection is an
essential part of the ADC early development process.
12 Development ofAntibody-Drug Conjugates
349
12.3 Target Selection
ADC targets are often described as “tumor antigens,“ or they are said to be “overexpressed” on tumors, but these terms are misleading for a number of reasons. First,
there are currently over a hundred different antigens being targeted by ADCs in
clinical development, yet very few are differentially expressed on tumors at higher
levels than on normal tissues [13]. A majority of the data used to evaluate potential
tumor-associated antigens are derived from mRNA expression analysis, which is
known to be highly variable, irreproducible, and not suitable for accurate quantication of proteins. Researchers frequently use complimentary methods such as IHC to
conrm the expression of a selected antigen on tumor cells, but IHC also has signicant limitations for quantifying protein expression and the results are dependent on
the samples being tested.
Problems with cross-reactivity are common with IHC and other antibody-based
detection methods (ELISAs, FACs ...etc.), and heterogeneous protein expression in
tumors creates additional uncertainties when trying to analyze expression data.
Furthermore, the quantitation of specic antigens via protein isolation, purication,
and analysis is not practical in a clinical setting. In general, it is very difcult to
accurately measure protein expression in tumors because proteins and mRNA often
continue to degrade in tumor samples, even after they are removed from the patient,
Ideally, the expression levels of a specic antigen in tumors would be compared
with expression levels in normal tissue, and higher target expression in tumors than
in surrounding normal tissues would be considered desirable because it would
enable relatively more drug to be delivered to the tumors by the ADC.Unfortunately,
it is also very difcult to obtain truly normal tissue samples to use as controls, since
most people are reluctant to give away parts of their healthy organs. As a result, the
availability of normal tissue samples in the US relies on organs donated by people
who suffer untimely deaths.
The prevalence of target expression, or the number of tumors that express a specic target antigen also varies widely and is dependent on the type of cancer being
treated. To further complicate matters, target expression is often not uniform
throughout the tumor and is seldom restricted to specic organs or systems [14].
Consequently, the therapeutic windows of most ADCs are quite narrow, and selecting an optimal target is likely the most important step toward developing an effective ADC.
12.4 Antibody Selection
In addition to the target, the antibody component of an ADC can also signicantly
impact its commercial success (Fig.12.3). Factors such as afnity for the target, the
specic binding epitope, the internalization rate, and the antibody subtype can all
affect the success of an ADC.Processes used for antibody production, the species