Assessment of near-infrared fluorophores to study the biodistribution and tumor targeting of an IL13 receptor α2 antibody by fluorescence molecular tomography

Non-invasive imaging using radiolabels is a common technique used to study the biodistribution of biologics. Due to the limited shelf-life of radiolabels and the requirements of specialized labs, non-invasive optical imaging is an attractive alternative for preclinical studies. Previously, we demonstrated the utility of fluorescence molecular tomography (FMT) an optical imaging modality in evaluating the biodistribution of antibody-drug conjugates. As FMT is a relatively new technology, few fluorophores have been validated for in vivo imaging. The goal of this study was to characterize and determine the utility of near-infrared (NIR) fluorophores for biodistribution studies using interleukin-13 receptor subunit alpha-2 antibody (IL13Rα2-Ab). Eight fluorophores (ex/em: 630/800 nm) with an N-hydroxysuccinimide (NHS) linker were evaluated for Ab conjugation. The resulting antibody-fluorophore (Ab-F) conjugates were evaluated in vitro for degree of conjugation, stability and target-binding, followed by in vivo/ex vivo FMT imaging to determine biodistribution in a xenograft model. The Ab-F conjugates (except Ab-DyLight800) showed good in vitro stability and antigen binding. All Ab-F conjugates (except for Ab-BOD630) resulted in a quantifiable signal in vivo and had similar biodistribution profiles, with peak tumor accumulation between 6 and 24 h post-injection. In vivo/ex vivo FMT imaging showed 17–34% ID/g Ab uptake by the tumor at 96 h. Overall, this is the first study to characterize the biodistribution of an Ab using eight NIR fluorophores. Our results show that 3-dimensional optical imaging is a valuable technology to understand biodistribution and targeting, but a careful selection of the fluorophore for each Ab is warranted.

Abstract 2092: Characterizing NIR dye-IL13RA2 antibody conjugates for biodistribution studies in xenograft tumor models by fluorescence molecular tomography (FMT)

Background: The antibody based therapies are promising anti-cancer therapeutic modalities with minimal toxicity and maximum efficacy. The efficacy of these agents is regulated by their biodistribution and targeting. The contemporary methods of testing the biodistriution of large molecule drugs are expensive and tedious. The development of simple and rapid methodology, such as optical imaging, can enable effective screening of a larger number of compounds. Here we have used Fluorescence Molecular Tomography (FMT), an optical imaging technique to study biodistribution and tumor targeting of IL3RA2 antibody (Ab). Methods: Different near infrared (NIR) fluorophores (λmax:650-800nm) were conjugated to the Ab. The fluorophore conjugation protocol was optimized to achieve a degree of labeling (DOL) of 1-3 for all the conjugates. The properties of Ab-fluorophore conjugate (Ab-F) were compared to unlabeled Ab using SEC-HPLC and cell binding assays in three cell lines with varying expression of IL13RA2: A375(+++), U87MG(+) and H460(-). For in vivo evaluation, Ab-F conjugates were administered intravenously at a dose of 2 nmol fluorophore to nu/nu mice bearing A375. Similar studies were also conducted in U87MG and H460 xenografts with selected Ab-F. The mice were imaged longitudinally (6 time-points) for up to 96 hrs using FMT4000 and the data were analyzed using TrueQuant software. Results: The SEC-HPLC and flow cytometry studies demonstrated that conjugation of Ab with most of the fluorophores did not change its stability or functionality. The in vivo fluorescence data from all the NIR dyes showed a peak tumor accumulation of the Ab-F at 6h and was maintained until 96 hrs. Quantitation of various Ab-F conjugated revealed that 2-6% of the injected dose was accumulated in the A375 tumors. In contrast to tumor profile, there was a steep decline in heart signal (a surrogate for blood/ plasma concentration), suggesting fast clearance from blood. The in vivo and ex vivo data suggested that there was 15-80pmol of Ab-F conjugate accumulated in the tumors at 96h. In addition, Alexa Flour® (AF)680 and AF750 showed minimal non-specific accumulation in other organs, whereas VivoTag® (VT)680 and BODIPY®630 showed a significantly higher non-specific accumulation in liver. Conclusions: These results show that the biological properties of Ab were not changed by conjugation with various NIR fluorophores at DOL <3. Optical imaging using fluorescent tags can effectively track and quantitate the tumor targeting/ biodistribution of large molecule drugs.

Citation Format: Parul Gupta, Dangshe Ma, Rachel Roach, Mary Spilker, Mauricio Leal, Cedo Bagi, Anand Giddabasappa. Characterizing NIR dye-IL13RA2 antibody conjugates for biodistribution studies in xenograft tumor models by fluorescence molecular tomography (FMT). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2092.

The effect of systemically administered rhIGF-I/IGFBP-3 complex on cortical bone strength and structure in ovariectomized rats

The action of systematically administered recombinant human insulinlike growth factor-I (rhIGF-I) complexed to its natural binding protein-3 (rhIGFBP-3) on cortical bone dynamic, structural, and mechanical properties was tested in previously ovariectomized (Ovx) rats. Bilateral ovariectomy or sham surgery was performed on 16-week-old female Sprague-Dawley rats. Eight weeks after surgery basal Sham and Ovx rats were killed to establish baseline cortical bone values before the initiation of treatment with rhIGF-I/IGFBP-3 complex. At that time, Ovx rats had increased body weight and body fat mass with reduced femoral BMC and BMD relative to basal Shams. Bone formation rates in Ovx rats were increased on both cortical envelopes relative to time-matched controls. The thickness of the inner lamellar bone layer and average cortical width were reduced due to increased endocortical erosion. A similar ratio between Sham and Ovx rats in body mass and composition and femoral BMC and BMD continued throughout the experiment. Sixteen weeks after surgery bone formation rates at both cortical envelopes in Ovx rats were reduced relative to Shams, but endocortical erosion remained high causing a further decrease in thickness of the inner lamellar layer. As a result of periosteal bone modeling. Ovx rats exhibited a larger femoral cross-sectional area and periosteal perimeter, as well as a thicker outer lamellar layer. Newly deposited periosteal bone increased ultimate torque values in the Ovx rats relative to Shams at 16 weeks. Treatment of Ovx rats with the rhIGF-I/IGFBP-3 complex increased body weight, lean body mass, and femoral BMC and BMD.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and bioavailability of rhIGF-I/IGFBP-3 in the rat and monkey

Circulating IGF-I exists primarily as part of a ternary 150 kDa complex comprising equimolar amounts of IGF-I, IGFBP-3 and acid labile subunit (ALS). It is also known that in contrast to IGF-I and IGFBP-3 there exists a substantial quantity of unbound ALS in the circulation. As part of our preclinical development program, we have investigated the pharmacokinetic properties of a complex of human recombinant IGF-I and IGFBP-3. Systematic administration of rhIGF-I/IGFBP-3 results in binding of this binary complex to endogenous free ALS and thus leads to increased circulating levels of 150 kD ternary complex (IGF-I/IGFBP-3/ALS). In contrast to the administration of free IGF-I, IGF-I/IGFBP-3 dosing leads to increased systemic IGF-I exposure (i.e. increased area under the time vs. serum concentration curve or AUC) and decreased clearance (CL). Upon administration of equimolar doses of IGF-I/IGFBP-3 to the rat and monkey, it was found that in the monkey AUC was increased and CL decreased when compared to the rat. In addition, the pharmacokinetic profile suggests that saturation of excess ALS occurs at considerably lower doses of rhIGF-I/IGFBP-3 in the monkey than in the rat. Finally, the bioavailability of rhIGF-I/IGFBP-3 was assessed in the rat and found to be approximately 85% and 50% after intramuscular and sub-cutaneous administration, respectively. It was concluded that the formation of the 150 kD ternary complex had a significant impact on increasing the systemic exposure to rhIGF-I when administered as the binary complex (rhIGF-I/IGFBP-3). In addition, IGFBP-3 increases the therapeutic index of rhIGF-I even at doses that significantly exceed the saturation of ALS.

Trace metal levels in fossil human bone from the Bezdanjaca necropolis in Croatia

Elemental analysis of prehistoric human bone for the reconstruction of past environmental conditions, diets and migrations is a relatively new concept and can be a helpful tool in palaeoanthropology. The contents of Pb, Cu, Cd, Zn, Ca, Sr and Ba in fossil and recent human bone were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and differential pulse anodic stripping voltammetry (DPASV). Some variation among the measured elements was established, but strontium was found to be a suitable tracer for such bioanthropological investigations. The applied analytical techniques are suitable for such investigations because of the comparatively small amount of material required and great analytical precision.

Mechanical stimulation by intermittent compression stimulates sulfate incorporation and matrix mineralization in fetal mouse long-bone rudiments under serum-free conditions

Mechanical stimulation evoked by intermittent hydrostatic compression (IC) in a closed culture system has been shown to stimulate calcification of fetal long-bone rudiments in the presence of serum [6]. We have studied effects of IC on sulfate metabolism and matrix mineralization under serum-free conditions, in short-term (24 hours) cultures of mineralizing long-bone rudiments in alpha minimum essential medium (MEM) + 0.2% bovine serum albumen (BSA). Exposure to IC for 24 hours stimulated radiosulfate incorporation into the papain-digestible pool in the noncalcifying epiphyses and, to a larger extent, in the calcifying diaphysis. The percentage release of 35S from prelabeled rudiments was stimulated in the epiphyses, but inhibited in the diaphyses. The changes in sulfate metabolism of matrix mineralization, in hypertrophic cartilage, and the diaphyseal bone collar, were judged from the increase in length of the diaphysis. This study shows that under serum-free conditions, mechanical stimulation by IC increases sulfate content while stimulating mineralization in calcifying cartilage of fetal long-bone rudiments. Mechanical stimulation seems to be an important regulator of cartilage calcification.

The influence of 1 alpha,25- and 24(R),25-dihydroxyvitamin D3 on bone constituents during early mineralization in the rat

The influence of vitamin D metabolites on intramuscular implants of bone matrix in rachitic rats was investigated. Recipient rats with rickets were injected daily with 1 alpha,25(OH)2D3,24(R),25(OH)2D3 or a combination of both metabolites. The presence of 1 alpha,25(OH)2D3 increased significantly the alkaline phosphatase activity, and slightly increased the activity of acid phosphatase. 24(R),25(OH)2D3 had no effect on the activity of the measured enzymes. The results of inductively coupled plasma emission spectrometric determination of bone elements revealed that: (a) 1 alpha,25(OH)2D3 stimulated the incorporation of magnesium and decreased the phosphorus content of bone implants when compared with rats given both vitamin D metabolites; (b) 1 alpha,25(OH)2D3 as well as 24(R),25(OH)2D3 had antagonistic effects on bone carbonate content. The values for 1 alpha,25(OH)2D3 treated animals were significantly higher, and 24(R),25(OH)2D3 treated rats had a significantly lower carbonate content of implants when compared to the controls. Time-dependent CO2-liberation diagrams indicated a differently bound bone carbonate in 1 alpha,25(OH)2D3 treated rats; (c) when plotted against time, the diagrams for both the values for zinc and the activity distribution of the measured enzymes had a similar appearance, indicating zinc incorporation into bone enzymes during early mineralization. It is concluded that 24(R),25(OH)2D3 should not be compared to 1,25(OH)2D3 on the basis of the same effects, since other effects of 24(R),25(OH)2D3 on the developing bone exist, opposite to those of 1,25(OH)2D3; and these could be important for protecting bone from different agents and in determining the nature of early mineral deposited.

1a,25-Dihydroxyvitamin D3 stimulates alkaline phosphatase activity and inhibits soft-tissue proliferation in implants of bone matrix

To test the importance of vitamin D metabolites on intramuscular implants of demineralized bone, four-month-old rats were given either 1a,25-(OH)2D3 or 24R,25-(OH)2D3, or a combination of both metabolites, and sacrificed at intervals ranging from five to 35 days after implantation. Histologically there was a reduced ingrowth of mesenchymal cells into the implanted matrix cylinders in the presence of 1a,25-(OH)2D3; the reduction was followed by decreased total DNA and protein values until the 16th experimental day. At 35 days postimplantation, the quantity of new bone was the same in all treated groups. However, 1a,25-(OH)2D3 increased the alkaline phosphatase activity 60%-110% (depending on the denominator used). The metabolite 24R,25-(OH)2R3 had no effect on cell growth or the alkaline phosphatase activity. These results provide evidence for the inhibitory effect of 1a,25-(OH)2D3 on mesenchymal cell growth and its stimulatory effect on osteoblasts, which are responsible for increased alkaline phosphatase activity and new bone formation in vivo.