Recently, several radiometalated
peptides have been approved for clinical imaging and/or
therapy (
theranostics) of several types of
cancer; nonetheless, the primary challenge that most of these
peptides confront is significant renal uptake and retention, which is often dose limiting and can cause nephrotoxicity. In response to this, numerous methods have been employed to reduce the uptake of radiometalated
peptides in the kidneys, and among these is adding a linker to modulate polarity and/or charge. To better understand the influence of net charge on the biodistribution of radiometalated
peptides, we selected the clinically popular construct
DOTA-TATE (
NETSPOT/
LUTATHERA) as a model system. We synthesized derivatives using manual solid-phase peptide synthesis methods including mechanical and ultrasonic agitation to effectively yield the gold standard
DOTA-TATE and a series of derivatives with different net charges (+2, +1, 0, -1, -2). Dynamic PET imaging from 0 to 90 min in healthy female mice (CD1) revealed high accumulation and retention of activity in the kidneys for the net-neutral (0) charged [68Ga]Ga-
DOTA-TATE and even higher for positively charged derivatives, whereas negatively charged derivatives exhibited low accumulation and fast renal excretion. Ex vivo biodistribution at 2 h post injection demonstrated a significant retention of [68Ga]Ga-
DOTA-TATE (∼74 %ID/g) in the kidneys, which increased as the net positive charge per molecule increased to +1 and +2 (∼272 %ID/g and ∼333 %ID/g, respectively), but the -1 and -2 net charged molecules exhibited lower renal uptake (∼15 %ID/g and 16 %ID/g, respectively). Interestingly, the net -2 charged [68Ga]Ga-
DOTA-(Glu)2-PEG4-TATE was stable in blood serum but had much higher healthy organ uptake (lungs, liver, spleen) than the net -1 compound, suggesting instability in vivo. Although the [68Ga]Ga-
DOTA-PEG4-TATE derivative with a net charge of 0 also showed a decrease in kidney uptake, it also showed instability in blood serum and in vivo. Despite the superior pharmacokinetics of the net -1 charged [68Ga]Ga-
DOTA-Glu-PEG4-TATE in healthy mice with respect to kidney uptake and overall profile, dynamic PET images and ex vivo biodistribution in male mice (NSG) bearing AR42J (SSTR2 overexpressing) subcutaneous
tumor xenografts showed significantly diminished
tumor uptake when compared to the gold standard [68Ga]Ga-
DOTA-TATE. Taken together, these findings indicate unambiguously that kidney uptake and retention are significantly influenced by the net charge of
peptide-based radiotracers. In addition, it was illustrated that the negatively charged
peptides had substantially decreased kidney uptake, but in this instantiation the
tumor uptake was also impaired.