Biomedical Engineering Reference
In-Depth Information
Figure 4
. Construct of a random aptamer library with 40 random bases providing 6 + 10
14
dif-
ferent aptamers. Different aptamers binding to tumor antigens are then selected and amplified
through successive rounds of selection to create a highly purified population.
acids of PSMA, termed xPSM. Six rounds of in vitro selection were performed,
enriching for xPSM binding as monitored by aptamer inhibition of xPSM N-
acetyl-alpha-linked acid dipeptidase (NAALADase) enzymatic activity. After
six rounds of selection, 95% of the remaining total aptamer pool consisted of
only two sequences. These two aptamers, termed xPSM-A9 and xPSM-A10,
were cloned and found to be unique, sharing no consensus sequences. The affin-
ity of each aptamer for PSMA was quantitated by its ability to inhibit the enzy-
matic activity of PSMA. Aptamer xPSM-A9 inhibits PSMA noncompetitively
with an average Ki of 11/9 nM. Distinct modes of inhibition suggest that each
aptamer identifies a unique extracellular epitope of xPSM. One aptamer was
truncated from 23.4 to 18.5 kDa and specifically binds LNcaP human prostate
cancer cells expressing PSMA, but not to PSMA-devoid PC-3 human prostate
cancer cells. These are the first reported RNA aptamers selected to bind a tumor-
associated membrane antigen and the first application of RNA aptamers to a
prostate-specific cell markers. These aptamers may be used clinically by modifi-
cation to carry imaging agents and therapeutic agents that are directed to pros-
tate cancer cells.
Within a single tumor, cells are heterogeneous. Just as important, tumor
types are heterogeneous between patients. This approach of selected aptamers is
