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ESTEVA, MILLER, AND TEICHER<br />

TARGETS AND ANTIBODIES<br />

In selecting cell surface protein targets, whether on malignant<br />

cells, on malignant disease–associated cells (e.g., tumor<br />

endothelial cells), or in the tumor microenvironment, it is<br />

important that the antigen expression is abundant on the target<br />

cells or in the tumor region and is very limited on all other<br />

cells and normal tissues. 5-9 The patient whose tumor expresses<br />

high levels of the target antigen is most likely to benefıt<br />

from treatment. ADCs are targeted, potent cytotoxic<br />

agents. Most of the proteins being targeted with antibody<br />

conjugates are normal proteins, as opposed to mutant proteins;<br />

therefore, some antigen expression on normal cells is<br />

possible and even likely. Technologies for antibody discovery,<br />

development, and engineering are well established.<br />

Phage display libraries and humanized mice can<br />

produce fully human antibodies, and mouse antibody humanization<br />

can result in highly specifıc nonimmunogenic<br />

antibodies (Fig. 1). In most cases, the most appropriate<br />

antibody for ADC therapeutics requires that the antibodytarget<br />

complex internalize into the target cells where the<br />

drug is released.<br />

DRUGS<br />

The drugs most widely conjugated to form ADCs target tubulin<br />

or DNA and are uniformly highly potent cytotoxic<br />

agents with 50% inhibitory concentration (IC 50 ) values in the<br />

picomolar range in cell culture.<br />

Though ADCs are among the most tumor-selective anticancer<br />

therapeutics developed to date, only a small fraction of the<br />

drug reaches the intracellular target. The maytansinoids and dolastatin<br />

analogs target tubulin, and both suppress microtubule<br />

dynamics. 10 The duocarmycins and calicheamicins target the<br />

minor groove of DNA. The amatoxin analogs inhibit RNA polymerase<br />

II and III, and SN-38 targets toposiosmerase I, which<br />

results in DNA double-strand breaks. 11 These molecules have in<br />

KEY POINTS<br />

<br />

<br />

<br />

<br />

<br />

Most antibody-drug conjugate (ADC) targets are cell<br />

surface proteins that are much more abundant on tumor<br />

cells than on normal cells/tissues.<br />

ADCs selectively deliver targeted chemotherapy and could<br />

be important components of combination treatment<br />

regimens.<br />

ADCs are being targeted to solid tumors and to<br />

hematologic malignancies.<br />

The three components of ADCs, antibody, linker, and drug,<br />

must be stable in circulation for days or weeks.<br />

T-DM1 and brentuximab vedotin are the first two ADCs to<br />

gain regulatory approval for HER2-positive metastatic<br />

breast cancer and Hodgkin lymphoma, respectively. Patient<br />

selection and understanding about the toxicity profiles of<br />

these agents are critical for integration of ADCs into<br />

inpatient care.<br />

TABLE 1. ADCs in Clinical Development<br />

Conjugate Name Target Company<br />

Gemtuzumab ozogamicin, CD33<br />

Pfizer<br />

Mylotarg<br />

Trastuzumab emtansine, T-DM1 HER2 Roche-Genentech<br />

Brentuximab vedotin, Adcetris CD30 Seattle Genetics-<br />

Takeda<br />

Inotuzumab ozogamicin, CD22<br />

Pfizer<br />

CMC-544<br />

CDX-011, Glembatumumab GPNMB<br />

Celldex Therapeutics<br />

vedotin<br />

SAR3419, huB4-DM4 CD19 Sanofi<br />

Lorvotuzumab mertansine, CD56 (NCAM) ImmunoGen<br />

IMGN901<br />

Vorsetuzumab mafodotin; SGN-75 CD70 Seattle Genetics<br />

PSMA ADC PSMA Progenics<br />

Pinatuzumab vedotin; RG7593 CD22 Roche<br />

Polatuzumab vedotin; RG7596 CD79b Roche<br />

RG7450 STEAP1 Roche<br />

AGS-5ME AGS-5 (SLC44A4) Astellas<br />

AGS-22M6E Nectin-4 Astellas<br />

SAR566658, huDS6-DM4 CA6 (Muc1) Sanofi<br />

Indatuximab ravtansine; BT-062 CD138 (syndecan-1) Biotest<br />

Milatuzumab-DOX CD74 Immunomedics<br />

BAY 94-9343 Mesothelin Bayer Pharma<br />

IMGN529 CD37 ImmunoGen<br />

IMGN853 FOLR1 ImmunoGen<br />

Labetuzumab-SN-38; IMMU-130 CEACAM5 Immunomedics<br />

MLN0264 Guanylyl cyclase Millennium-Takeda<br />

IMMU-132 Trop-2 Immunomedics<br />

AMG-595 EGFR vIII Amgen<br />

AMG-172 CD70 Amgen<br />

AGS-15E SLITRK6 Astellas<br />

AGS-16C3F ENPP3 Astellas<br />

RG-7458 MUC16 Roche<br />

GSK2857916 BCMA GSK<br />

IMMU-132 Trop-2 Immunomedics<br />

HuMax-TF Tissue factor Genmab<br />

IMGN-242 CanAg ImmunoGen<br />

IMGN-289 EGFR ImmunoGen<br />

IMGN-388 Alpha v-integrin ImmunGen<br />

IMGN-633 CD33 ImmunoGen/Sanofi<br />

MEDI-547 EphA2 MedImmune<br />

MLN-0264 GCC Takeda<br />

MLN-2704 PSMA Takeda<br />

PF-06263507 5T4 Pfizer<br />

SAR-566658 huDS6 (Mucin 1) Sanofi<br />

SC16LD6.5 SC-16 Stem CentRx<br />

SGN-19A CD19 Seattle Genetics<br />

SGN-CD33A CD33 Seattle Genetics<br />

SGN-LIV1A LIV1 (ZIP6) Seattle Genetics<br />

Abbreviations: ADC, antibody-drug conjugate; DOX, doxorubicin; EGFR, epidermal growth<br />

factor receptor.<br />

e118<br />

2015 ASCO EDUCATIONAL BOOK | asco.org/edbook

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