Accurate measurement of glomerular filtration rate (GFR) at the bedside is highly desirable in order to assess renal
function in real-time, which is currently an unmet clinical need. In our pursuit to develop exogenous fluorescent tracers
as GFR markers, various hydrophilic derivatives of 3,6-diaminopyrazine-2,5-dicarboxylic acid with varying molecular
weights and absorption/emission characteristics were synthesized. These include polyhydroxyalkyl based small
molecules and poly(ethylene glycol) (PEG) substituted moderate molecular weight compounds, which were further sub-grouped
into analogs having blue excitation with green emission, and relatively longer wavelength analogs having green
excitation with orange emission. Lead compounds were identified in each of the four classes on the basis of structure-
activity relationship studies, which included in vitro plasma protein binding, in vivo urine recovery of administered dose,
and in vivo optical monitoring. The in vivo optical monitoring experiments with lead candidates have been correlated
with plasma pharmacokinetic (PK) data for measurement of clearance and hence GFR. Renal clearance of these
compounds, occurring exclusively via glomerular filtration, was established by probenecid blocking experiments. The
renal clearance property of all these advanced candidates was superior to that of the iothalamate, which is currently an
accepted standard for the measurement of GFR.
Photodynamic therapy of tumors involving Type 2 photosenstizers has been conspicuously successful, but the Type
1 process, in contrast, has not received much attention despite its considerable potential. Accordingly, several classes of
molecules containing fragile bonds such as azido (-N=N=N), azo (-N=N-), sulfenato (-S-O-) and oxaza (-N-O-)
functional groups that produce reactive intermediates such as radicals and nitrenes upon photoexcitation were prepared
and tested for cell viability using U397 leukemia cell line. The azido photosensitizer was conjugated to leukemia cell
binding peptide, SFFWRLS, for targeted cell viability study. The cells were incubated with the photosensitizer at
various concentrations, and were illuminated for 5, 10, and 20 minutes. The results show that all the photosensitizers
caused cell death compared to the controls when exposed to both the photosensitizers and light. Most importantly,
selective cell death was observed with the azido peptide conjugate 6, which clearly demonstrates that these Type 1
sensitizers are useful for phototherapeutic applications.
Rapid assessment of glomerular filtration rate (GFR), which measures the amount of plasma filtered through the
kidney within a given time, would greatly facilitate monitoring of renal function for patients at the bedside in the clinic.
In our pursuit to develop exogenous fluorescent tracers for real-time monitoring of renal function by optical methods, N-alkylated
aminopyrazine dyes and their hydrophilic conjugates based on poly (ethylene glycol) (PEG) were synthesized
via reductive amination as the key step. Photophysical properties indicated a bathochromic shift on the order of 50 nm in
both absorption and emission compared to naked aminopyrazines which could be very useful in enhancing both tissue
penetration as well as easier detection methods. Structure-activity relationship (SAR) and pharmacokinetic (PK) studies,
and the correlation of in vivo optical data with plasma PK for measurement of clearance (and hence GFR) are focus of
the current investigation.
The ability to continuously monitor renal function via the glomerular filtration rate (GFR) in the clinic is currently an
unmet medical need. To address this need we have developed a new series of hydrophilic fluorescent probes designed
to clear via glomerular filtration for use as real time optical monitoring agents at the bedside. The ideal molecule should
be freely filtered via the glomerular filtration barrier and be neither reabsorbed nor secreted by the renal tubule. In
addition, we have hypothesized that a low volume of distribution into the interstitial space could also be advantageous.
Our primary molecular design strategy employs a very small pyrazine-based fluorophore as the core unit. Modular
chemistry for functionalizing these systems for optimal pharmacokinetics (PK) and photophysical properties have been
developed. Structure-activity relationship (SAR) and pharmacokinetic (PK) studies involving hydrophilic pyrazine
analogues incorporating polyethylene glycol (PEG), carbohydrate, amino acid and peptide functionality have been a
focus of this work. Secondary design strategies for minimizing distribution into the interstitium while maintaining
glomerular filtration include enhancing molecular volume through PEG substitution. In vivo optical monitoring
experiments with advanced candidates have been correlated with plasma PK for measurement of clearance and hence
GFR.
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