Screening, identification, purification and homologous modeling of marine cold-active alpha-amylase

BACKGROUND

Cold-active α-amylase is essential in industrial production. However, the number of cold-active α-amylases available for use is limited. Screening microbial strains would lay the groundwork for the future development of the food and pharmaceutical industries.

OBJECTIVE

To screen microbial strains for cold-active α-amylase based on physiological and biochemical identification, as well as homology modelling.

MATERIALS AND METHODS

Cold-active α-amylase strains were screened from water and mud obtained from the Yellow Sea. Colony morphology, Gram staining, scanning electron microscopy and transmission electron microscopy, physiological and biochemical identification and 16S rRNA gene analysis were used to identify strains. A series of steps, including DEAE-anion exchange column chromatography, SephadexG-100 column chromatography, and SDS-PAGE electrophoresis, were used to produce cold-active α-amylase of relatively high purity. Finally, the homology of amylase was modeled to explore the structure and activity site of the enzyme.

RESULTS

The named dsh19-1 strain of cold-active α-amylase was screened and identified as Bacillus. The cold-active α-amylase produced by Bacillus was named AmyD-1. The protein with PDB sequence number 5A2B was found to have 40.6% homology with AmyD-1. The verification score of the 3-D model was 137.07 points. We discovered that the six sites are potential sites for amylase to decompose starch by building a 3-D AmyD-1 model. AmyD-1 has a molecular weight of 1515 bp, and hydrogen bonding may be the primary interaction force between AmyD-1 and glucose molecules.

CONCLUSION

A cold-active α-amylase produced by Bacillus strain dsh19-1 was successfully obtained and named AmyD-1. This enzyme has potential uses in the food and pharmaceutical industries.

[Interference of long noncoding RNA FOXCUT inhibits epithelial-mesenchymal transformation and induces mitochondrial injury in nasopharyngeal carcinoma cells]

OBJECTIVE

To investigate the effects of RNA interference of long noncoding RNA FOXCUT on epithelial mesenchymal transformation and mitochondrial function in nasopharyngeal carcinoma (NPC) cells.

METHODS

FOXCUT expression levels were detected by RT-PCR in tumor tissues and adjacent tissues from 50 patients with NPC and in NP69, CNE1, CNE2, SUNE2, HER2 and 5-8F cell lines. CNE1 cells were transfected with a short hairpin RNA (shRNA) targeting FOXCUT or a negative control RNA construct (shRNA-NC), and the changes in cell proliferation and morphology were assessed with CCK8 assay, clone formation assay and microscopic observation. An immunofluorescence assay was used to examine the vimentin-positive cells, and the levels of SOD, MDA and LDH in the cells were detected. The changes of mitochondrial membrane potential were detected with flow cytometry, and the expression levels of E-cad, N-cad, vimentin, Bax, Bcl-2, caspase-3 and c-Myc in the cells were detected with Western blotting.

RESULTS

The expression level of FOXCUT was significantly increased in NPC tissues as compared with the adjacent tissues (P < 0.001). Compared with NP69 cells, CNE1, CNE2, SUNE2, HER2 and 5-8F cells all exhibited significantly increased expressions of FOXCUT (P < 0.001). In CNE1 cells, transfection with FOXCUT shRNA significantly inhibited cell proliferation and clone formation (P < 0.001), and caused obvious changes in cell morphology. FOXCUT knockdown significantly decreased the expressions of N-cad and vimentin, increased E- cad expression and the contents of MDA and LDH (P < 0.05), reduced vimentin- positive cells and the activity of SOD, and caused a shift of red fluorescent cells to green fluorescent cells and an increased percentage of green fluorescent cells. FOXCUT knockdown also resulted in significantly increased expressions of Bax/Bcl2 and cleaved Cas3/Cas3 and a lowered expression of c-Myc.

CONCLUSIONS

Interference of FOXCUT can inhibit the proliferation and epithelial-mesenchymal transformation, enhance oxidative stress, induce mitochondrial function injury, and promote apoptosis in NPC cells, suggesting the potential of FOXCUT interference for targeted treatment of NPC.

Ruminococcus gnavus E1 modulates mucin expression and intestinal glycosylation

AIMS

The molecular cross-talk between commensal bacteria and the gut play an important role in the maintenance of the intestinal homeostasis and general health. Here, we studied the impact of a major Gram-positive anaerobic bacterium of the human gut microbiota, that is, Ruminococcus gnavus on the glycosylation pattern and the production of intestinal mucus by the goblet cells.

METHODS AND RESULTS

Our results showed that R. gnavus E1 specifically increases the expression and the glycosylation level of the intestinal glyco-conjugates by goblet cells in the colonic mucosa of mono-associated mice with R. gnavus E1 as well as in human HT29-MTX cells. Such an effect was mediated through induction of the level of mRNA encoding for the major intestinal gel-forming mucin such as MUC2 and various glycosyltransferase enzymes.

CONCLUSIONS

This study demonstrates for the first time that R. gnavus E1 possess the ability to modulate the glycosylation profile of the glyco-conjugate molecules and mucus in goblet cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Furthermore, we demonstrated that R. gnavus E1 modified specifically the glycosylation pattern and MUC2 expression by means of a small soluble factor of peptidic nature (<3 kDa) and heat stable in the HT29-MTX cell.

Novel DNA Polymer for Amplification Pretargeting

In this Letter, different from conventional pretargeting, an additional novel DNA polymer with multiple copies of a target was first designed to be administrated between the antitumor antibody, and the labeled effector served as an amplification pretargeting strategy. Two phosphorothioate DNA strands, a bridging and a target strand, were hybridized to form a polymer. Polymer size, as a function of molar ratios, was then monitored by size exclusion HPLC and electrophoretic mobility shift assay. Moreover, binding efficiency of polymers with the radiolabeled effector and polymer size after hybridization were measured by HPLC as well. As the polymer was expected to produce more binding sites that would be targeted by effectors, amplification pretargeting can greatly improve accumulation of effectors in tumor. This novel proof-of-concept was then well demonstrated by the in vitro test of signal amplification in antibody-binding protein L coated plate and LS174T cells. Compared to conventional pretargeting, significantly increasing radioactive signal was observed in this designed amplification pretargeting, which would serve as a useful paradigm of the potential of oligomer polymers to improve pretargeting and other related approaches.

A feasible approach to evaluate the relative reactivity of NHS-ester activated group with primary amine-derivatized DNA analogue and non-derivatized impurity

Synthetic DNA analogues with improved stability are widely used in life science. The 3'and/or 5' equivalent terminuses are often derivatized by attaching an active group for further modification, but a certain amount of non-derivatized impurity often remains. It is important to know to what extent the impurity would influence further modification. The reaction of an NHS ester with primary amine is one of the most widely used options to modify DNA analogues. In this short communication, a 3'-(NH2-biotin)-derivatized morpholino DNA analogue (MORF) was utilized as the model derivatized DNA analogue. Inclusion of a biotin concomitant with the primary amine at the 3'-terminus allows for the use of streptavidin to discriminate between the products from the derivatized MORF and non-derivatized MORF impurity. To detect the MORF reaction with NHS ester, S-acetyl NHS-MAG3 was conjugated to the DNA analogue for labeling with (99m)Tc, a widely used nuclide in the clinic. It was found that the non-derivatized MORF also reacted with the S-acetyl NHS-MAG3. Radiolabeling of the product yielded an equally high labeling efficiency. Nevertheless, streptavidin binding indicated that under the conditions of this investigation, the non-derivatized MORF was five times less reactive than the amine-derivatized MORF.

Quantitative Correlation of in Vivo Properties with in Vitro Assay Results: The in Vitro Binding of a Biotin-DNA Analogue Modifier with Streptavidin Predicts the in Vivo Avidin-Induced Clearability of the Analogue-Modified Antibody

Quantitative prediction of in vivo behavior using an in vitro assay would dramatically accelerate pharmaceutical development. However, studies quantitatively correlating in vivo properties with in vitro assay results are rare because of the difficulty in quantitatively understanding the in vivo behavior of an agent. We now demonstrate such a correlation as a case study based on our quantitative understanding of the in vivo chemistry. In an ongoing pretargeting project, we designed a trifunctional antibody (Ab) that concomitantly carried a biotin and a DNA analogue (hereafter termed MORF). The biotin and the MORF were fused into one structure prior to conjugation to the Ab for the concomitant attachment. Because it was known that avidin-bound Ab molecules leave the circulation rapidly, this design would theoretically allow complete clearance by avidin. The clearability of the trifunctional Ab was determined by calculating the blood MORF concentration ratio of avidin-treated Ab to non-avidin-treated Ab using mice injected with these compounds. In theory, any compromised clearability should be due to the presence of impurities. In vitro, we measured the biotinylated percentage of the Ab-reacting (MORF-biotin)⊃-NH2 modifier, by addition of streptavidin to the radiolabeled (MORF-biotin)⊃-NH2 samples and subsequent high-performance liquid chromatography (HPLC) analysis. On the basis of our previous quantitative understanding, we predicted that the clearability of the Ab would be equal to the biotinylation percentage measured via HPLC. We validated this prediction within a 3% difference. In addition to the high avidin-induced clearability of the trifunctional Ab (up to ∼95%) achieved by the design, we were able to predict the required quality of the (MORF-biotin)⊃-NH2 modifier for any given in vivo clearability. This approach may greatly reduce the steps and time currently required in pharmaceutical development in the process of synthesis, chemical analysis, in vitro cell study, and in vivo validation.

Differentiation between temporary and real non-clearability of biotinylated IgG antibody by avidin in mice

Although an increasing number of antibody conjugates are being used in the clinic, there remain many unmet needs in antibody targeting. Normal tissue background is one of the key issues that limits the therapeutic efficacy and the detection sensitivity. Background reduction coupled with dose increase may provide the required target accumulation of the label or toxin at an acceptable normal tissue background. However, the knowledge about the in vivo interaction between antibody and a clearing agent is currently inadequate for designing a rational clearance regimen or system. The current investigation focuses on the clearability of antibody for background reduction, an important topic to antibody targeting in general. The investigation employs pretargeting as a research tool and avidin as a model clearing agent. By comparing the effects of natural clearance at a longer post-injection time and avidin clearance, we demonstrated that avidin clearance is much more effective. By directly attaching avidin to a biotinylated antibody prior to injection, we found that the biotinylated antibody in blood, once bound to the clearing agent, can be removed from the circulation immediately and completely, while the real non-clearable antibody without biotin stays. The study of multiple avidin injections confirmed that the presence of clearable biotinylated antibodies after an avidin injection is due to their temporary inaccessibility and subsequent return from tissue compartments. The collective clearance efficiency of 91% by three avidin injections indicates a continuous IV infusion would be recommended to remove all of the biotinylated IgG molecules. In conclusion, the use of antibody pretargeting as a tool in this study has improved understanding of the incomplete clearance by avidin and can aid in overcoming this obstacle.

Comparison between two labeled agents in mice using a coinjection-ratio approach in contrast to a conventional group approach

INTRODUCTION

The differences between two agents often need to be accurately defined in vivo. Usually they are injected respectively into two groups of subjects. However, if the two agents do not interact with each other in vivo, a coinjection would serve the same purpose. We believe some individual differences in biodistribution may be circumvented through this approach by calculating organ level ratios.

METHODS

A model system of MORF/cMORF pretargeting (MORF/cMORF is a complementary pair of DNA analogues) was employed in connection with an on-going tumor therapeutic project. Human LS174T cells were implanted into the flank of severely immuno-compromised NOD-scid IL2rg(null) mice. The tumor was confirmed to express TAG-72 antigens. At 16 days post tumor inoculation, mice received IV 60 μg of MORF-conjugated CC49 (an antiTAG-72 antibody), followed 2 days later by a low-mass-dose IV coinjection containing 2.5 μg of (90)Y-cMORF and 2.5 μg of (99m)Tc-cMORF. At 3 h post radioactivity injection, the distribution of (99m)Tc was imaged on a SPECT/CT camera and then organs were excised and counted for (90)Y and (99m)Tc. Because the two labeled cMORFs do not react or interact with each other in vivo, the two groups of (90)Y and (99m)Tc data enabled a conventional group comparison. In a new effort, (90)Y/(99m)Tc ratios were calculated. Student's t-test and retrospective power analysis were performed for both approaches. In the new approach, the ratios were set at 1 as the null hypothesis.

RESULTS

The Student's t-test in the conventional group approach indicated that the two labeled cMORFs distributed similarly, but significant differences were observed in salivary gland and large intestines. The coinjection-ratio approach certainly did not subvert the results of the conventional approach but revealed subtler differences. The P values were reduced, the powers were increased in most organs, and more significant differences were observed. The increased sensitivity was due to the reduced CV%s (SD/average*100%) of the (90)Y/(99m)Tc ratios. Therefore, some individual differences were circumvented and notably the ratio approach differentiated individual differences into ratio-correctable and ratio-uncorrectable.

CONCLUSIONS

Although the conventional approach is reliable, the coinjection-ratio approach using organ level ratios is more sensitive and therefore is recommended whenever possible. In addition, it differentiates individual differences into "coinjection correctable" and "coinjection uncorrectable".

(99m)Tc-MORF oligomers specific for bacterial ribosomal RNA as potential specific infection imaging agents

PURPOSE

Radiolabeled oligomers complementary to the 16S rRNA in bacteria were investigated as bacterial infection imaging agents.

METHODS AND RESULTS

Identical sequences with backbones phosphorodiamidate morpholino (MORF), peptide nucleic acid (PNA), and phosphorothioate DNA (PS-DNA) were (99m)Tc-labeled and evaluated for binding to bacterial RNA. MORF binding to RNA from Escherichia coli strains SM101 and K12 was 4- and 150-fold higher compared to PNA and PS-DNA, respectively. Subsequently MORF oligomer in fluorescence in situ hybridization showed a stronger signal with study MORF compared to control in fixed preparations of two E. coli strains and Klebsiella pneumoniae. Flow cytometry analysis showed study MORF accumulation to be 8- and 80-fold higher compared to the control in live K. pneumoniae and Staphylococcus aureus, respectively. Further, fluorescence microscopy showed increased accumulation of study MORF over control in live E. coli and K. pneumonia. Binding of (99m)Tc-study MORF to RNA from E. coli SM101 and K12 was 30.4 and 117.8pmol, respectively, per 10(10) cells. Mice with K. pneumoniae live or heat-killed (sterile inflammation) in one thigh at 90min for both (99m)Tc-study MORF and control showed higher accumulation in target thighs than in blood and all other organs expect for kidneys and small intestine. Accumulation of (99m)Tc-study MORF was significantly higher (p=0.009) than that of the control in the thigh with sterile inflammation.

CONCLUSION

A (99m)Tc-MORF oligomer complimentary to the bacterial 16S rRNA demonstrated binding to bacterial RNA in vitro with specific accumulation into live bacteria. Radiolabeled MORF oligomers antisense to the bacterial rRNA may be useful to image bacterial infection.

Intraperitoneal injection is not always a suitable alternative to intravenous injection for radiotherapy

Abstract Intraperitoneal (IP) injection is frequently reported to be as effective as intravenous (IV) injection. Because it allows administering a larger volume with more radioactivity, we have investigated this route and the possibility of using it to circumvent the volume constraint we earlier experienced with pretargeting radiotherapy. Using (99m)Tc as the label, the pharmacokinetics (PK) of the cMORF effector (a DNA analogue) was evaluated after IP or IV injection in normal mice by necropsy and SPECT/CT imaging. In another experiment, nude mice bearing tumors were used and they received MORF-CC49 pretargeting antibody IV 2 days earlier than labeled cMORF IV or IP. Tumor accumulations of cMORF were measured at 6 hours after its injections. The absorbed radiation doses for (188)Re or (90)Y pretargeting were estimated using the (99m)Tc data and a self-absorbed model. Although the absorbed radiation doses to other organs were comparable, the dose to intestines after IP injection was 30-fold higher than IV injection due to the slow entry into the circulation. It had reached such a level as high as the dose to the kidneys that cleared the radioactivity and usually were at the highest level. Nevertheless, the slow entry did not reduce the tumor accumulation. In conclusion, using IP in place of IV led to an unacceptably high absorbed radiation dose to the intestines although the tumor accumulation was not compromised. This effect may be applicable to other radiotherapeutic agents as well.

Detection of Aspergillus fumigatus pulmonary fungal infections in mice with (99m)Tc-labeled MORF oligomers targeting ribosomal RNA

PURPOSE

Invasive aspergillosis is a major cause of infectious morbidity and mortality in immunocompromised patients. The fungus Aspergillus fumigatus (A. fumigatus) is the primary causative agent of invasive aspergillosis. However, A. fumigatus infections remain difficult to diagnose particularly in the early stages due to the lack of a rapid, sensitive and specific diagnostic approach. In this study, we investigated (99m)Tc labeled MORF oligomers targeting fungal ribosomal RNA (rRNA) for the imaging detection of fungal infections.

PROCEDURES

Three phosphorodiamidate morpholino (MORF) oligomer (a DNA analogue) probes were designed: AGEN, complementary to a sequence of the fungal 28S ribosomal RNA (rRNA) of Aspergillus, as a genus-specific probe; AFUM, complementary to the 28S rRNA sequence of A. fumigatus, as a fungus species-specific probe; and cMORF, irrelevant to all fungal species, as a control probe. The probes were conjugated with Alexa Fluor 633 carboxylic acid succinimidyl ester (AF633) for fluorescence imaging or with NHS-mercaptoacetyl triglycine (NHS-MAG3) for nuclear imaging with (99m)Tc and then evaluated in vitro and in vivo.

RESULTS

The specific binding of AGEN and AFUM to fungal total RNA was confirmed by dot blot hybridization while specific binding of AGEN and AFUM in fixed and live A. fumigatus was demonstrated by both fluorescent in situ hybridization (FISH) analysis and accumulation in live cells. SPECT imaging of BALB/c mice with pulmonary A. fumigatus infections and administered (99m)Tc labeled AGEN and AFUM showed immediate and obvious accumulation in the infected lungs, while no significant accumulation of the control (99m)Tc-cMORF in the infected lung was observed. Compared to non-infected mice, with sacrifice at 1h, the accumulation of (99m)Tc-AGEN and (99m)Tc-AFUM in the lungs of mice infected with A. fumigatus was 2 and 2.7 fold higher respectively.

CONCLUSIONS

In vivo targeting fungal ribosomal RNA with (99m)Tc labeled MORF probes AGEN and AFUM may be useful for A. fumigatus infection imaging and may provide a new strategy for the noninvasive diagnosis of invasive aspergillosis and other fungal infections.

Pretargeting vs. direct targeting of human betalox5 islet cells subcutaneously implanted in mice using an anti-human islet cell antibody

INTRODUCTION

We previously demonstrated MORF/cMORF pretargeting of human islets and betalox 5 cells (a human beta cell line) transplanted subcutaneously in mice with the anti-human islet antibody, HPi1. We now compare pretargeting with direct targeting in the beta cell transplant model to evaluate the degree to which target/non-target (T/NT) ratios may be improved by pretargeting.

METHODS

Specific binding of an anti-human islet antibody HPi1 to the beta cells transplanted subcutaneously in mice was examined against a negative control antibody. We then compared pretargeting by MORF-HPi1 plus 111In-labeled cMORF to direct targeting by 111In-labeled HPi1.

RESULTS

HPi1 binding to betalox5 human cells in the transplant was shown by immunofluorescence. Normal organ 111In backgrounds by pretargeting were always lower, although target accumulations were similar. More importantly, the transplant to pancreas and liver ratios was, respectively, 26 and 10 by pretargeting as compared to 9 and 0.6 by direct targeting.

CONCLUSIONS

Pretargeting greatly improves the T/NT ratios, and based on the estimated endocrine to exocrine ratio within a pancreas, pretargeting may be approaching the sensitivity required for successful imaging of human islets within this organ.

90Y labeled phosphorodiamidate morpholino oligomer for pretargeting radiotherapy

While (188)Re has been used successfully in mice for tumor radiotherapy by MORF/cMORF pretargeting, previous radiolabeling of the amine-derivatized cMORF with (90)Y, a longer physical half-life nuclide, was not very successful. After developing a method involving a prepurification heating step during conjugation that increases labeling efficiency and label stability, the biodistribution of (90)Y-DOTA-Bn-SCN-cMORF ((90)Y-DOTA-cMORF) was measured in normal mice and in MORF-CC49 pretargeted mice that bear LS174T tumors. Absorbed radiation doses were then estimated and compared to those estimated for (188)Re. The pharmacokinetics of the (90)Y-DOTA-cMORF in normal mice and in the pretargeted nude mice was similar to that observed previously with (99m)Tc- and (188)Re-MAG(3)-cMORFs. While the (90)Y-DOTA-cMORF cleared rapidly from normal tissues, tumor clearance was very slow and tumor radioactivity accumulation was constant for at least 7 days such that the tumor/blood (T/B) ratio increased linearly from 6 to 25 over this period. Therefore, by extrapolation, normal tissue toxicities following administration of therapeutic doses of (90)Y may be comparable to that observed for (188)Re in which the T/B increased from 5 to 20. In conclusion, radiolabeling of DOTA-cMORF with (90)Y was improved by introducing a prepurification heating step during conjugation. The (90)Y-DOTA-cMORF provided a similar T/B ratio and biodistribution to that of (188)Re-MAG(3)-cMORF and was retained well in the tumor pretargeted with MORF-CC49. Because of the longer physical half-life, the T/NT absorbed radiation dose ratios were improved in most organs and especially in blood.

A preclinical 188Re tumor therapeutic investigation using MORF/cMORF pretargeting and an antiTAG-72 antibody CC49

The utility of MORF/cMORF pretargeting for the radiotherapy of cancer requires further validation in tumored mice before clinical trials. We now report on a therapeutic study in mice pretargeted with MORF-CC49 (an anti-TAG-72 antibody CC49 conjugated with MORF, a phosphorodiamidate morpholino oligomer) and then targeted by 188Re-cMORF (a 188Re labeled complementary MORF). Before the dose-escalating therapeutic study, a pretargeting study in LS174T tumored mice was performed at tracer levels. By both necropsy and imaging, the tracer study showed that the whole body radioactivity was largely restricted to tumor in the mice pretargeted 48 h earlier with MORF-CC49 and the tumor radioactivity was retained over 90 h. After decay correction, a best-fit to the biodistribution provided the areas under the radioactivity curves (AUCs) used for the radiation dose estimates. The tumor to normal organ AUC ratios in all cases were greater than unity and ranged from 3 (kidneys) to 48 (muscle). Tumor growth was inhibited in the therapy study. At the highest 188Re dose of 1.40 mCi, a complete but temporary tumor remission was evident in 3 out of the 5 animals. Histological examination of tissues from these animals showed no evidence of cytotoxicity to normal tissues but obvious radiation damage to tumor. In conclusion, effective radiotherapy was achieved in a mouse model by MORF/cMORF pretargeting using 188Re as the therapeutic radionuclide and CC49 as the pretargeting antibody.

Adding a clearing agent to pretargeting does not lower the tumor accumulation of the effector as predicted

Clearing agents are often used in pretargeting despite the potential for decreased tumor accumulation of the effector. However, according to the authors' semiempirical model, a clearing agent should not necessarily decrease tumor accumulation. In this study, the authors have added a clearing step to their model-morpholino phosphorodiamidate oligomer (MORF)/complement MORF (cMORF) pretargeting system-to confirm this prediction. The CC49 antibody was conjugated with both biotin and an 18 mer MORF. The influence of avidin on antibody clearance was first evaluated in normal mice in which each animal received 30 μg of MORF-CC49-biotin, 0-70 μg of avidin 1 day later, and 1.2 μg of ⁹⁹(m)Tc-cMORF 3 hours later, with sacrifice at 3 hours. Thereafter, a pretargeting study in mice bearing an LS174T tumor was performed at a 34 μg avidin dosage. In normal mice, the blood level of ⁹⁹(m)Tc-cMORF fell by 60% at an avidin dosage of 10 μg or higher. In tumored mice, avidin produced a similar reduction in blood but had no influence on tumor level, which remained at 6.30% ID/g as predicted. In conclusion, in addition to the expected reduced effector levels in blood and normal tissues, a reduction in tumor accumulation was avoided when adding a clearing agent as predicted.

Human islet cell MORF/cMORF pretargeting in a xenogeneic murine transplant model

Noninvasive measurement of human islet cell mass in pancreas or following islet transplantation by nuclear imaging has yet to be achieved. It has been shown using mouse tumor models that pretargeting imaging strategies are sensitive and can greatly increase target to nontarget signal ratios. The objective now is to demonstrate the specific pretargeting of human islet cells in mice. Our pretargeting strategy uses an anti-human islet cell antibody HPi1, conjugated to a phosphorodiamidate morpholino oligomer (MORF) that binds specifically to a (99m)Tc labeled complementary MORF (cMORF). Sensitivity and specificity of the pretargeting were first validated in culture using a human beta cell line (betalox5) and a negative control human cell line (HEK293). Pretargeting was then used to target and visualize these two cell lines and human islets transplanted subcutaneously in NOD-scid IL2rγ(null) mice. In culture, (99m)Tc accumulation on the betalox5 cells pretargeted by MORF-HPi1 was 100-fold higher than on untreated betalox5 cells or following treatment with native HPi1 and much higher than on the MORF-HPi1 pretargeted control HEK293 cells. Small animal imaging readily localized the transplanted betalox5 cells and human islets, but not the HEK293 cells. Ex vivo counting demonstrated 3-fold higher (99m)Tc accumulation in the transplanted betalox5 cells and human islets than in the control HEK293 cells. The target accumulation was also shown to increase linearly with increased numbers of the implanted betalox5 cells. These results demonstrate specific binding of radioactivity and successful imaging of human betalox5 cells and human islets transplanted in mice. Thus MORF/cMORF pretargeting may be useful to measure noninvasively human islet cell mass within the pancreas or following islet transplantation.

Identification of a high affinity TAG-72 binding peptide by phage display selection

PURPOSE

Phage display was used to select novel peptides that specifically bind the TAG-72 antigen and with properties suitable for imaging TAG-72 positive cancers.

RESULTS

After three rounds of selection against TAG-72 and using two different elution conditions including a long elution, the consensus sequences FRERCDKHPQKCTKFL and DPRHCQKRVLPCPAWL were expressed on phages G3-15 and T3-15 respectively. ELISA, fluorescence-activated cell sorting analysis and fluorescence microscopy provided evidence that both phages specifically bound TAG-72 in vitro. Both peptides are stable in 37oC serum. By a cell binding competition assay, the IC50 for T3-15 was measured as 0.29 nM and therefore 36-fold higher affinity than G3-15 at 10.32 nM. The biodistribution in mice carrying LS-174T tumors in one thigh were similar for both 99mTc-peptides at 30 min, but at 90 min the 99mTc-T3-15 peptide accumulated almost three times higher in the tumor. The SPECT/CT images were consistent with the biodistribution results.

PROCEDURES

The f88-4/Cys6 phage library and two different elution conditions were used to identify two new higher affinity binding peptides for the TAG-72 antigen. One, was a single brief elution with pH 2.2 glycine buffer, and the second began with the glycine elution but was followed with a longer elution with Tris buffered saline (TBS) at pH 7.4. The phages that bound TAG-72 were evaluated by fluorescence-activated cell sorting analysis using TAG-72 positive LS-174T cells and confirmed by immunofluorescence imaging. The consensus peptides displayed on the selected phages were synthesized and conjugated with NHS-MAG3 for radiolabeling with 99mTc. The IC50 for TAG-72 binding was evaluated by cell binding competition in vitro while binding affinity was evaluated in vivo by necropsy and SPECT/CT imaging in a tumor mouse model.

CONCLUSION

We have identified a peptide with a sub nanomolar inhibition constant for the TAG-72 antigen that may have application in cancer imaging.

Affinity enhancement pretargeting: synthesis and testing of a 99mTc-labeled bivalent MORF

Pretargeting with bivalent effectors capable of bridging antitumor antibodies (affinity enhancement pretargeting) has been reported to provide superior results by affinity enhancement. Phosphorodiamidate morpholinos (MORFs) and other DNA analogues used for pretargeting are ideally suited as bivalent effectors since they are easily synthesized and the distance between binding regions, a determinant of binding, may be adjusted simply by lengthening the chain. We have shown by surface plasmon resonance that bivalent MORFs will provide superior affinity enhancement provided that suitable spacing exists between the binding regions. The goals of this study were to synthesize a bivalent MORF with a MAG(3) group attached for technetium-99m ((99m)Tc) radiolabeling, investigate whether the bivalent MORF showed improved cell accumulation in culture compared to its corresponding monovalent MORF and compare biodistributions in normal mice and in pretargeted tumored mice. An excess of an amine derivatized 18 mer MORF with 6 nonbinding bases for spacing was reacted with Fmoc-l-beta-homoglutamic acid to form duplexes via their carboxylate groups and, after deprotection, conjugated with NHS-MAG(3) to attach the chelator. The anti-CEA antibody MN14 was conjugated with a 12 mer complementary MORF (i.e., cMORF). The binding behavior between radiolabeled monovalent and bivalent MORFs was compared in LS174T tumor cells at 4 degrees C pretargeted with MN14-cMORF. Biodistributions of radiolabeled monovalent and bivalent MORFs at 3 h postadministration were measured in normal mice and in tumor mice pretargeted with MN14-cMORF. In the pretargeted cells in culture, the accumulation of the bivalent MORF was significantly higher than the monovalent MORF (p = 0.002), thus providing strong evidence for affinity enhancement. In normal mice, whole body clearance of the bivalent and monovalent MORFs was equally rapid. In tumored mice, tumor accumulation of the radiolabeled bivalent MORF was significantly higher than that of the monovalent MORF. In conclusion, a bivalent MAG(3)-MORF was successfully synthesized and radiolabeled with (99m)Tc. While a pharmacokinetic effect for the higher tumor accumulations in pretargeted mice of the radiolabeled bivalent MORF cannot be excluded, the results may be best explained by affinity enhancement. Thus two monovalent MORFs were covalently conjugated into a bivalent MORF effector to improve tumor targeting by both pharmacokinetics and affinity enhancement influences.

Unexpected side products in the conjugation of an amine-derivatized morpholino oligomer with p-isothiocyanate benzyl DTPA and their removal

In connection with pretargeting, an amine-derivatized morpholino phosphorodiamidate oligomer (NH(2)-cMORF) was conjugated conventionally with p-isothiocyanate benzyl-DTPA (p-SCN-Bn-DTPA). However, after (111)In radiolabeling, unexpected label instability was observed. To understand this instability, the NH(2)-cMORF and, as control, the native cMORF without the amine were conjugated in the conventional manner. Surprisingly, the (111)In labeling of the native cMORF conjugate was equally effective as that of the NH(2)-cMORF conjugate (>95%) despite the absence of the amine group. Furthermore, heating the radiolabeled NH(2)-cMORF and native cMORF conjugates resulted in a 35% loss and a complete loss of the label, respectively. Since the (111)In labeled DTPA is known to be stable, the instability in both cases must be due to some unstable association of DTPA to the cMORF, presumably unstable association to some endogenous sites in cMORF. Based on this assumption, a postconjugation-prepurification heating step was introduced, and labeling efficiency and stability were again investigated. By introducing the heating step, the side products were dissociated, and after purification and labeling, the NH(2)-cMORF conjugate provided a stable label and high labeling efficiency with no need for postlabeling purification. The biodistribution of this radiolabeled conjugate in normal mice showed significantly lower backgrounds compared with the labeled unstable native cMORF conjugate. In conclusion, the conventional conjugation procedure to attach the p-SCN-Bn-DTPA to NH(2)-cMORF resulted in side product(s) that were responsible for the (111)In label instability. Adding a postconjugation-prepurification heating step dissociated the side products, improved the label stability and lowered tissue backgrounds in mice.

Tumor pretargeting in mice using MORF conjugated CC49 antibody and radiolabeled complimentary cMORF effector

AIM

Using the antiCEA antibody MN14, a LS174T mouse tumor model has been successfully targeted with (⁹⁹m)Tc for imaging and ¹⁸⁸Re for radiotherapy by phosphorodiamidate morpholino oligomers (MORF)/complementary MORF (cMORF) pretargeting strategy. This investigation evaluated the antiTAG-72 antibody CC49 as an alternative to MN14 for this application.

METHODS

Both CC49 and MN14 were labeled with ¹¹¹In via SCN-benzyl-DTPA and their biodistributions were compared to that of MN14 labeled via DTPA anhydride. Since the accessibility of the antibody to the effector is required for optimization of pretargeting, the internalization of both MORF-CC49 and MORF-MN14 antibodies in LS174T cells were evaluated in culture. In addition, the accessible concentration of MORF-CC49 antibody in tumor was determined in a series of pretargeting studies with escalating dosages of the [(⁹⁹m)Tc]cMORF effector. Finally, using these results and our semi-empirical model, an imaging study was performed under optimal pretargeting conditions.

RESULTS

The biodistribution of ¹¹¹In to trace the MN14 antibody depended significantly on the labeling method. Furthermore, both MORF-CC49 and MORF-MN14 antibodies showed rapid internalization in culture. Fortunately, the accessibility in tumor was found to be less seriously reduced in vivo. In a pretargeting study under optimal conditions, both by imaging and by necropsy, the [(⁹⁹m)Tc]cMORF effector accumulated predominantly in the tumor of pretargeted mice. Normal tissue accumulations were minimal except in kidneys, liver, and a segment of intestines.

CONCLUSION

MORF pretargeting with CC49 was equally successful in the LS174T tumor model to the MORF pretargeting with MN14. The MORF-CC49 antibody may therefore be considered for future investigations toward early clinical trials.

Preparation of (111)In-DTPA morpholino oligomer for low abdominal accumulation

An ability to quantitate the beta cell mass by noninvasive nuclear imaging will be very useful in the prevention, diagnosis, and treatment of diabetes. However, to be successful, radioactivity from the pancreas must not be obscured by the background radioactivity in the abdomen. Pretargeting offers the promise of achieving high target organ to normal tissue ratios. In preparation for pancreas imaging studies by pretargeting using morpholino oligomers (MORF/cMORF), it was necessary to develop a simple and efficient method to radiolabel the cMORF effector. Because we have shown that labeling the cMORF with (111)In via DTPA reduces excretion into the intestines compared to labeling with (99m)Tc via MAG(3), the conjugation of DTPA to cMORF was investigated for (111)In labeling. The amine-derivatized cMORF was conjugated with DTPA using 1-ethyl-3(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) as an alternative to the conventional cyclic anhydride. The conjugation efficiency (represented by the number of DTPA groups attached per cMORF) was investigated by changing the EDC, DTPA, and cMORF molar ratios. Different open columns were considered for the purification of DTPA-cMORF. Before conjugation, each cMORF molecule was confirmed to have an amine by trinitrobenzene sulfonic acid (TNBS) assay using the omega-amino butyric acid as positive standard and the non-amine derivatized cMORF as negative standard. The average number of DTPA groups per cMORF was 0.15-0.20 following the conjugation over a cMORF/DTPA molar ratio of 0.5-5 and over a cMORF/EDC molar ratio of 20-60. The conjugation efficiency was lower than expected probably due to steric hindrance. A 1 x 50cm P-4 column using ammonium acetate as eluting buffer provided an adequate separation of DTPA-cMORF from free DTPA. The (111)In labeling efficiency by transchelation from acetate exceeded 95%, thus avoiding the need for postlabeling purification. Despite the lower than expected conjugation efficiency in which no more than one-fifth of the cMORF were DTPA-derivatized, a specific radioactivity of at least 300microCi/microg or 1.90Ci/micromol of cMORF was achieved. In conclusion, a protocol is described for (111)In-DTPA-cMORF that provides the high specific activity favorable to beta cell imaging because of the low mass fraction of beta cells in pancreas (1-2%) and obviates the need for postlabeling purification.

The ratio of maximum percent tumour accumulations of the pretargeting agent and the radiolabelled effector is independent of tumour size

Our previous studies have indicated that the optimal dosage ratio of pretargeting antibody to effector is proportional to their maximum percent tumour accumulations (MPTAs). This study quantitatively describes how both MPTAs and their ratio change with tumour size, to simplify pretargeting optimisation when tumour size varies. The CC49 antibody dosages below saturation of the tumour antigen level were first examined for the LS174T tumour mouse model. Then the MPTAs of the antibody in mice bearing tumours of different sizes were determined, always at antibody dosages below antigen saturation. Historical data from this laboratory were used to collect the MPTAs of the (99m)Tc-cMORF effector for different tumour sizes, always at effector dosages below that required to saturate the MORF in tumour. The MPTAs versus tumour sizes for both the antibody and the effector were fitted non-linearly. The best fit of the antibody MPTA (Y(antibody)) with tumour size (x) in grams was Y(antibody)=19.00 x(-0.65) while that for the effector was Y(effector)=4.51x(-0.66). Thus, even though the MPTAs of both vary with tumour size, the ratio (Y(antibody)/Y(effector)) is a constant at 4.21. In conclusion, the MPTA ratio of the antibody to the effector was found to be constant with tumour size, an observation that will simplify pretargeting optimisation because remeasurement of the optimum dosage ratio for different tumour sizes can be avoided. Theoretical considerations also suggest that this relationship may be universal for alternative antibody/effector pairs and for different target models, but this must be experimentally confirmed.

Optical antisense tumor targeting in vivo with an improved fluorescent DNA duplex probe

Fluorescent conjugated DNA oligonucleotides for antisense targeting of mRNA has the potential of improving tumor/normal tissue ratios over that achievable by nuclear antisense imaging. By conjugating the Cy5.5 emitter to the 3' equivalent end of a 25 mer phosphorothioate (PS) antisense major DNA and hybridizing with a shorter 18 mer phosphodiester (PO) complementary minor DNA (cDNA) with the Black Hole inhibitor BHQ3 on its 5' end (i.e., PS DNA25-Cy5.5/PO cDNA18-BHQ3), we previously achieved antisense optical imaging in mice as a proof of this concept. In a process of optimization, we have now evaluated the stability of a small series of duplexes with variable-length minor strands. From these results, a new study anti-mdr1 antisense duplex was selected with a 10 mer minor strand (i.e., PS DNA25-Cy5.5/PO cDNA10-BHQ3). The new study duplex shows stability in serum environments at 37 degrees C and provides a dramatically enhanced fluorescence in KB-G2 (pgp++) cells when compared with KB-31 (pgp+/-) as evidence of antisense dissociation at its mdr1 mRNA target. The duplex was also administered to KB-G2 tumor bearing mice, and when compared to the duplex used previously, the fluorescence from the tumor thigh was more obvious and the tumor-to-background fluorescence ratio was improved. In conclusion, by a process designed to optimize the duplex for optical antisense tumor targeting, the fluorescence signal was improved both in cells and in tumored mice.

A convenient thiazole orange fluorescence assay for the evaluation of DNA duplex hybridization stability

OBJECTIVE

A simple and rapid method for measuring the hybridization stability of duplexes of DNAs and other oligomers in different environments is described. When added to an oligomer duplex, the thiazole orange (TO) dye intercalates and in this state is fluorescent. Therefore, when duplex dissociation occurs, the release of TO results in a detectable change in fluorescence intensity. This assay was developed primarily to screen antisense oligomer duplexes that are stable in serum and in the cytoplasm but unstable in the presence of their target messenger RNA (mRNA).

METHODS

The two antisense oligomers of this investigation were both 25 mer phosphorothioate (PS) DNAs, one directed against the RIalpha mRNA and the other directed against the mdr1 mRNA. The former duplex was first used in the solution studies, in most cases duplexed with a 16 mer phosphodiester (PO) complementary DNA (i.e., PS-DNA25/PO-cDNA16). Both duplexes were then tested in a series of cell studies using SK-BR-3 (RIalpha+), KB-G2 (mdr1++), and KB-31 (mdr1+/-) cells.

RESULTS

Preliminary measurements in solution showed that maximum fluorescence was achieved when more than ten TO molecules were bound to each duplex. When a 25 mer PO-DNA or PO-RNA with the base sequence of the RIalpha mRNA was added, the dramatic change in fluorescence intensity that followed signified dissociation of the antisense DNA from the study duplex and reassociation with the target DNA. Kinetic measurements showed that this process was completed in about 3 min. Fluorescent measurements of SK-BR-3 (RIalpha+) cells incubated at 37 degrees C with the anti-RIalpha study duplex over time showed a maximum at the point where the loss of fluorescence due to dissociation of the study duplex, probably by an antisense mechanism, began to dominate over the increasing fluorescence due to continuing cellular accumulation. A similar result was observed in the KB-G2 (mdr1+) cells incubated with the anti-mdr1 study duplex.

CONCLUSIONS

When study duplexes shown to be stable in serum were incubated with their target cells, the assay successfully detected evidence of dissociation, most likely by an antisense mechanism. Thus, a TO fluorescence assay has been developed that is capable of detecting the dissociation of DNA duplexes.

Replacing 99mTc with 111In improves MORF/cMORF pretargeting by reducing intestinal accumulation

PURPOSE

To reduce accumulation in the abdomen by MORF/cMORF pretargeting, 111In was compared to 99mTc as the radiolabel.

PROCEDURES

After receiving either 99mTc (MAG3)-cMORF or 111In (DTPA)-cMORF, normal mice were imaged and killed for pharmacokinetics. Thereafter, tumored mice were pretargeted withMORF-antibody, 48 h later were given an injection of 99mTc- or 111In-cMORF, and finally were imaged repeatedly.

RESULTS

The cMORF biodistribution in both normal and pretargeted tumored mice was influenced by its radiolabel. While excretion of both 99mTc-cMORF and 111In-cMORF was rapid and mainly through the kidneys, about 2% of 99mTc accumulated in the intestines compared toessentially no intestinal accumulation for 111In at any time. Tumor accumulation was unchanged.

CONCLUSION

In applications of MORF/cMORF pretargeting intended to image organs deep within the abdomen such as the pancreas, radiolabeling with 111In may be superior to 99mTc.

Investigation of four (99m)Tc-labeled bacteriophages for infection-specific imaging

INTRODUCTION

This study investigated radiolabeled bacteriophages for specific detection of infection through gamma imaging. Previously, a (99m)Tc-labeled M13 phage demonstrated specific binding for its host Escherichia coli in vitro and in mice through imaging.

METHODS

This study was extended to phages P22, E79, VD-13 and phage 60. Each was radiolabeled with (99m)Tc using the chelator MAG(3), and were evaluated for binding to host and non-host bacteria in vitro and in a mouse infection model.

RESULTS

In vitro, each (99m)Tc-phage bound to its host at least 4-fold higher than to non-host bacteria. For example, (99m)Tc-E79 showed 10- to 20-fold greater binding to host Pseudomonas aeruginosa compared to non-host Escherichia coli and Salmonella enterica, and (99m)Tc-phage 60 showed 20-fold greater binding to host Klebsiella pneumoniae over non-hosts. Mice received host or non-host bacteria in one thigh, and 3 h later, the (99m)Tc-phages were administered intravenously. After a further 3 h, the tissues were counted. Liver accumulation was highest for (99m)Tc-E79, averaging 39% compared to an average of 13% for the other (99m)Tc-phages. Animals infected with host bacteria showed infected thigh/normal thigh ratios of 14.2 for (99m)Tc-E79, 2.9 for (99m)Tc-P22, 3.5 for (99m)Tc-VD-13 and 2.1 for (99m)Tc-phage 60.

CONCLUSIONS

Although specific host binding was observed in vitro for each of these four (99m)Tc-phages, only (99m)Tc-E79 showed specificity for its host in an in vivo model.

An experimental and theoretical evaluation of the influence of pretargeting antibody on the tumor accumulation of effector

In treating tumors by pretargeting, the antitumor antibody and the cytotoxic effector (e.g., toxins and radioactivity) are separately administered. Therefore, pretargeting is more complicated with many variables. We are conducting studies to understand the influence of each variable using a novel recognition pair of mutually complementary phosphorodiamidate morpholino oligomers (MORF/cMORF). Earlier we developed a semi-empirical model capable of accurately predicting the behavior of a radiolabeled cMORF effector with variations in dosages and timing. We have now extended the model to predict the effector behavior, in particular, its maximum percent tumor accumulation (MPTA) in mice pretargeted with three different MORF-conjugated antibodies (MN14, B72.3, and CC49). The MN14 and the CC49 target different antigens in the same tumor, whereas the CC49 and the B72.3 target the same antigen but with very different tumor accumulation. By comparing the pretargeting results of these three antibodies with our prediction, we confirmed that the MPTA of the radiolabeled cMORF effector in the LS174T tumor is independent of the antibodies. In conclusion, the MPTA cannot be improved through the use of different pretargeting antibodies, although different antibodies may improve the maximum absolute tumor accumulation, the heterogeneity, and/or the tumor-to-normal tissue ratios of the effector. This conclusion will apply equally well to effectors carrying a fluorescent probe, an anticancer agent, or a radioactive imaging agent.

Synthesis and in vitro characterization of a dendrimer-MORF conjugate for amplification pretargeting

Amplification pretargeting can play an important role in molecular imaging by significantly increasing the accumulation of signal in target tissues. Multiple-step amplification pretargeting offers the potential to greatly improve target localization of effector molecules through the intermediate use of polymers conjugated with multiple copies of complementary oligomers. In this study, PAMAM dendrimer generation 3 (G3) was conjugated with multiple copies of a phosphorodiamidate morpholino (MORF) oligomer. Characterization of the conjugate by native-PAGE and SE-HPLC demonstrated that the conjugation was successful. The average numbers of MORF groups in the G3-MORF conjugate, both attached and accessible to the (99m)Tc labeled complementary MORF (cMORF), were determined. The antitumor antibody CC49 was conjugated with both MORF and cMORF (collectively (c)MORF) at an average of about one group per molecule. Nine of the 32 carboxyl groups of the dendrimer were modified with MORF, of which 90% were accessible in solution to (99m)Tc-cMORF. After purification, the G3-MORF was radiolabeled with tracer (99m)Tc-labeled cMORF (i.e., G3-MORF/(99m)Tc-cMORF) and added to the antibody CC49 previously conjugated with cMORF (i.e., CC49-cMORF/G3-MORF/(99m)Tc-cMORF), the complex demonstrated a single peak on SE-HPLC as evidence of complete hybridization between G3-MORF/(99m)Tc-cMORF and CC49-cMORF. The CC49-(c)MORF were bound to both Protein G and Protein L coated plates, and G3-MORF was added to hybridize with CC49-cMORF before the (99m)Tc-cMORF was added to test amplification pretargeting. In comparison to conventional pretargeting without the G3-MORF, the signal was amplified about 6 and 14 times, respectively, showing that the G3-MORF participated in amplifying the signal. Further amplification studies using the CC49-(c)MORF for LS174T tumor cells in tissue culture also demonstrated clear evidence of signal amplification.

Evidence of specificity of radiolabeled phage display peptides for the TAG-72 antigen

The TAG-72 glycoprotein is highly expressed in many tumor types and has been considered a target for tumor imaging. In this work, we used the f88-4/Cys6 phage library of constrained 16 mer peptides to select those that demonstrate binding to TAG-72. Three consensus peptides were identified: NPGTCKD-KWIECLLNG (clone A); NLIWCRKEFARCTSDM (clone B); and LKNYCRKCSNRCTPTG (clone C). The phage of clones containing these peptides were radiolabeled with technetium-99m (99mTC) at 90% radiochemical purity and were incubated with TAG-72-positive LS174T colon cancer cells. The phage of clones A and B bound significantly higher by 4.5-fold and 1.5-fold than that of a nonspecific control phage. The 99mTc-labeled phage of clones A, B, and control were also administered intravenously to mice with LS-174T tumors. The accumulation of phages from clone A showed a slightly statistically higher accumulation in the tumor (0.51% ID/g), compared to phages of clone B and control phage (0.28% and 0.29% ID/g; p=0.049 for both). In conclusion, the peptide expressed by clone A phage showed evidence of significant specific binding when presented as the radiolabeled phage to tumor in vivo and especially in vitro with cells and solid tumor. The results suggest that this peptide when free of the phage may have potential for the imaging and possibly radiotherapy of TAG-72-expressing cancers.

Optical antisense imaging of tumor with fluorescent DNA duplexes

Antisense targeting of tumor with fluorescent conjugated DNA oligomers has the potential of improving tumor/normal tissue ratios over that achievable by nuclear antisense imaging. When administered as a linear duplex of two fluorophore-conjugated oligomers arranged in a manner that inhibits fluorescence as the duplex and designed to dissociate only in the presence of the target mRNA, the fluorescence signal should in principle be inhibited everywhere except in the target cell. Optical imaging by fluorescence quenching using linear fluorophore-conjugated oligomers has not been extensively investigated and may not have been previously considered for antisense targeting. We evaluated in cell culture and in KB-G2 tumor bearing nude mice a 25-mer phosphorothioate (PS) anti- mdr1 antisense DNA conjugated with the Cy5.5 emitter on its 3' equivalent end and hybridized as a linear duplex with a shorter 18-mer phosphodiester (PO) complementary DNA (cDNA) with the Black Hole inhibitor BHQ3 on its 5' end. In serum environments, 90% of the DNA25-Cy5.5 fluorescence was inhibited immediately following addition of the cDNA18-BHQ3 and showed only slight loss of inhibition over 24 h at 37 degrees C. As evidence of antisense specific binding, when incubated with the DNA25-Cy5.5/cDNA18-BHQ3 duplex, the fluorescence was lower in KB-31 (Pgp +/-) cells compared to KB-G2 (Pgp++) cells, but when incubated with the control cDNA18-Cy5.5/DNA25-BHQ3 duplex in which the fluorophores were reversed, the fluorescence of both cell types was low. As further evidence of specific binding, the fluorescent intensity of total RNA from KB-G2 cells incubated with the study duplex showed evidence of dissociation and hybridization with the target mRNA. Furthermore, the fluorescence microscopy images of KB-G2 cells incubated with DNA25-Cy5.5 as the singlet or study duplex show that migration in both cases is to the nucleus. The animal studies were performed in mice bearing KB-G2 tumor in one thigh and receiving iv the study or control duplexes. The tumor/normal thigh fluorescence ratio was clearly positive as early as 30 min postinjection in the study mice and reached a maximum at 5 h. By contrast, much lower fluorescence was observed in mice receiving the control duplex at the same dosage. Fluorescence microscope imaging showed that the Cy5.5 fluorescence was much higher in tumor sections from the animal that had received the study rather than control duplex. Thus combining a fluorophore-conjugated antisense DNA with an inhibitor-conjugated shorter complementary cDNA inhibited fluorescence both in cell culture and in tumored animals except in the presence of the target mRNA. This proof of concept investigation of optical antisense targeting therefore suggests that further studies including optimization of this approach are appropriate.

Pretargeting CWR22 prostate tumor in mice with MORF-B72.3 antibody and radiolabeled cMORF

PURPOSE

We have now applied our MORF/cMORF pretargeting technology to the targeting of CWR22 prostate tumor in nude mice.

METHODS

The antiTAG-72 antibody B72.3 was conjugated with an 18 mer MORF while the cMORF was radiolabeled with (99m)Tc. The specific binding of the antibody to the CWR22 cells was first confirmed in an assay placing the radiolabeled B72.3 antibody in competition with increasing concentrations of native B72.3. Thereafter, a group of four CWR22 tumored mice intravenously received the MORF-B72.3 and, 3 days later, the (99m)Tc-cMORF, and were killed at 3 h postradioactivity injection. The dosage of the labeled cMORF was selected on the basis of previous experience in LS174T tumored mice. As controls, four animals received only the radiolabeled cMORF and another four received only the (111)In-B72.3. The maximum percent tumor accumulation (MPTA) of the labeled cMORF was subsequently determined by a dosage study of labeled cMORF. Both a multipinhole SPECT image and a planar gamma camera image were obtained of a representative mouse.

RESULTS

The CWR22 tumor was confirmed to be TAG-72-positive. The MPTA of the labeled cMORF in the CWR22 tumor was 2.22%ID/g compared to only 0.12%ID/g in control mice without pretargeting. Both the planar and tomographic images confirmed the success of the CWR22 pretargeting.

CONCLUSIONS

The MORF/cMORF pretargeting approach has been successfully applied to tumor targeting of the prostate xenograft CWR22. However, the MPTA in this tumor model is lower than that in the LS174T tumor model investigated earlier, possibly due to a lower tumor blood supply.

A novel pretargeting method for measuring antibody internalization in tumor cells

A novel pretargeting method has been developed to quantitate antibody cellular internalization. In this study, the antibody was conjugated with a phosphorodiamidate morpholino oligomer (MORF) specific for the complementary MORF (cMORF) as an effector. Half the tumor cells were incubated with the MORF-antibody (pretargeting group) and the other half with the same MORF-antibody at the same concentration but radiolabeled (direct targeting group). After incubation, the same dosage of radiolabeled cMORF was added to the wells of the pretargeting group. The radioactivity of the direct targeting cells represented the sum of both internalized and cell-surface-bound antibodies, whereas the radioactivity of the pretargeting cells resulted only from the surface-bound antibodies, as the radiolabeled cMORF does not penetrate the cell surface. Therefore, the difference in radioactivity accumulation between pretargeting and direct targeting provides the internalized fraction. In this example, the internalization of a MORF conjugated anti-prostate-specific membrane antigen antibody, 3C6, in LNCaP cells was examined, and the average cell-surface residence time was determined as 2 hours. This method of measuring antibody internalization is directly applicable to pretargeting applications but can be a universal alternative to the conventional acid-wash method, with the advantage of leaving the cell membrane undamaged.

Predicting the biodistribution of radiolabeled cMORF effector in MORF-pretargeted mice

PURPOSE

Pretargeting with phosphorodiamidate morpholino oligomers (MORFs) involves administration of a MORF-conjugated anti-tumor antibody such as MN14 as a pretargeting agent before that of the radiolabeled complementary MORF (cMORF) as the effector. The dosages of the pretargeting agent and effector, the pretargeting interval, and the detection time are the four pretargeting variables. The goal of this study was to develop a semiempirical description capable of predicting the biodistribution of the radiolabeled effector in pretargeted mice and then to compare predictions with experimental results from pretargeting studies in tumored animals in which the pretargeting interval and the detection time were both fixed but the dosages of both the effector and the pretargeting agent were separately varied.

METHODS

Pretargeting studies in LS174T tumored mice were performed using the anti-CEA antibody MN14 conjugated with MORF and the cMORF radiolabeled with (99m)Tc. A description was developed based on our previous observations in the same mouse model of the blood and tumor levels of MORF-MN14, accessibility of MORF-MN14 to labeled cMORF, the tumor accumulation of labeled cMORF relative to MORF-MN14 levels therein, and the kidney accumulation of labeled cMORF. The predicted values were then compared with the experimental values.

RESULTS

The predicted biodistribution of the radiolabeled effector and the experimental data were in gratifying agreement in normal organs, suggesting that the description of the pretargeting process was reliable. The tumor accumulations occasionally fell outside two standard deviations of that predicted, but after tumor size correction, good agreement between predicted and experimental values was observed here as well.

CONCLUSION

A semiempirical description of the biodistribution of labeled cMORF was capable of predicting the biodistribution of the radiolabeled effector in the pretargeted tumored mouse model, demonstrating that the underlying pretargeting concepts are correct. We believe that the approach described herein may be applied to any of the alternative pretargeting approaches and animal tumor models currently under investigation. Furthermore, appreciation of the concepts may provide a rationale for selecting dosages and timings in human pretargeting studies as an alternative to pure empirical means.

Comparison of several linear fluorophore- and quencher-conjugated oligomer duplexes for stability, fluorescence quenching, and kinetics in vitro and in vivo in mice

A useful property of optical imaging is the potential to modulate the detectable signal to improve target/nontarget ratios. When administered as a dimer of a fluorophore- and a quencher-conjugated duplex arranged to inhibit fluorescence but designed to dissociate only in the presence of its target, the fluorescence signal should in principle appear only in the target. This laboratory has demonstrated the feasibility of this approach by using a duplex consisting of a linear oligomer conjugated with Cy5.5 (emitter) hybridized to another linear oligomer conjugated with Iowa Black (quencher) in a pretargeting optical study. Now eight duplexes consisting of combinations of 18 mer linear phosphodiester (PO) and phosphorothioate (PS) DNAs and phosphorodiamidate morpholinos (MORFs) conjugated with Cy5.5 (emitter) and Iowa Black (quencher) were variously screened for in vitro duplex stability. The MORF/PO duplex was selected for further study based on evidence of stability in 37 degrees C serum. Simultaneously, the kinetics of quenching were investigated in vitro and in vivo in mice. Thereafter, mice were implanted in one thigh with MORF/PO Cy 5.5 microspheres and the complementary PS Iowa Black administered iv to measure the extent and kinetics of duplex formation in the target. While all duplexes were stable in buffer, only the MORF/PO duplexes and possibly all PS containing duplexes were stable in 37 degrees C serum for at least 4 h. The kinetics of quenching were found to be rapid in vitro, with a 80-90% decrease in Cy5.5 fluorescence immediately following formation of a PS/PS homoduplex, and in vivo, with a 27 to 38% decrease in target thigh/nontarget ratio within 1 h following administration of the complementary PS Iowa Black complementary DNA but not the random control DNA to mice implanted with MORF/PO Cy5.5 microspheres. This investigation has provided additional evidence that Cy5.5 may be efficiently and rapidly quenched by Iowa Black when both are conjugated to complementary oligomers and that the resulting inhibition of fluorescence is sufficiently persistent for imaging.

An improved method for covalently conjugating morpholino oligomers to antitumor antibodies

Whether for conventional pretargeting, amplification pretargeting, or affinity enhancement pretargeting, it will be necessary to conjugate an antitumor antibody as the first injectate. This laboratory is investigating phosphorodiamidate morpholinos (MORFs) for pretargeting, and accordingly we are examining methods of attaching MORFs to antitumor antibodies that provide at least one group per molecule (gpm) without adversely influencing antibody properties. The aim of this investigation was to evaluate the commercial Hydralink for the conjugation of the anti-CEA MN14 antibody with an 18 mer amine-derivatized MORF. The conjugation was approached in both directions by first reacting MN14 with the NHS derivatives of 4-hydrozinonicotinate acetone hydrazone (SANH) or 4-formylbenzoate (SFB) and then combining with MORF that was previously reacted with SFB or SANH to yield MN14(SANH)-MORF and MN14(SFB)-MORF respectively. The storage stability, immunoreactive fraction, and the biodistribution in normal mice were compared for both conjugates. Thereafter, MN14(SANH)-MORF was used in a pretargeting study in tumored nude mice, and the results were compared to that obtained historically with MN14-MORF prepared by carbodiimide (EDC) coupling. Both new methods of conjugation provided between 1 and 2 gpm compared to 0.2 achieved previously by EDC. Furthermore, by repeat SE HPLC with and without CEA, both showed an unimpaired immunoreactive fraction. MN14(SANH)-MORF tolerated long-term storage best. More importantly, when labeled by hybridization with 99mTc-labeled complementary MORF (99mTc-cMORF), the biodistribution of MN14(SANH)-MORF was more favorable than that of MN14(SFB)-MORF in normal mice with lower liver (5.7 vs 9.4 %ID/g at 18 h) and spleen (3.5 vs 8.4 %ID/g) accumulations and higher blood levels (4.8 vs 3.4 %ID/g). Accordingly, only MN14(SANH)-MORF was used in a pretargeting study in tumored mice. When targeted with 99mTc-cMORF and at 2 days postinjection of antibody-MORF, the results obtained with 6 microg of antibody prepared in this way were essentially identical to that obtained previously with 30 microg of antibody prepared via EDC. Hydralink was used successfully to conjugate MORF to MN14 at higher gpm than that achieved earlier and without an obvious compromise of properties. Using MN14(SANH)-MORF, the influence of the higher gpm on pretargeting permitted lowering the dosages of MN14 administered and may permit administering higher levels of radioactivity in connection with therapy.

Optical pretargeting of tumor with fluorescent MORF oligomers

OBJECTIVE

Pretargeting with radioactivity has significantly improved tumor to normal tissue radioactivity ratios over conventional antibody imaging in both animal studies and clinical trials. This laboratory is investigating DNA analogues such as phosphorodiamidate morpholinos (MORFs) for pretargeting using technetium-99m ((99m)Tc) for detection. However, the unique properties of fluorescence activation and quenching combined with oligomers with their unique properties of hybridization may be particularly useful when used together for pretargeting with optical detection. The use of linear fluorophore-conjugated oligomer duplexes have been little used in animals, and to our knowledge, have not previously been considered for pretargeting applications.

METHODS

A MORF/cDNA pair was selected such that when hybridized, the fluorescence of the Cy5.5-conjugated 25 mer MORF (Cy5.5-MORF25) is inhibited with a BHQ3-conjugated 18 mer complementary DNA (BHQ3-cDNA18). The short BHQ3-cDNA18 was selected to dissociate in the presence of a long cMORF25 in the pretargeted tumor, thus releasing the inhibitor from the Cy5.5 emitter. In this manner, the Cy5.5 fluorescence will be inhibited everywhere but in the target. The dissociation was first examined in vitro by adding the duplex to the cMORF25 both in solution and immobilized on polystyrene microspheres and by surface plasmon resonance (SPR). Thereafter, biotinylated cMORF25 immobilized on streptavidin polystyrene microspheres were administered intramuscularly in one thigh of hairless SKH-1 mice as target while an identical weight of the identical microspheres but without the cMORF25 was administered in the contralateral thigh as control. The animals then received IV the Cy5.5-MORF25/BHQ3-cDNA18 duplex or equal molar dosage of single-chain Cy5.5-MORF25 and were imaged.

RESULTS

The SPR studies showed that the immobilized cDNA18 rapidly captured the flowing MORF25 to provide a duplex with a slow dissociation rate constant. Furthermore, when cMORF25 was next allowed to flow over the now immobilized duplex, the cDNA18 was unable to prevent dissociation of the heteroduplex and the formation and release of the cMORF25-MORF25 homoduplex. Images of animals obtained soon after receiving the Cy5.5-MORF25 singlet showed intense whole body fluorescence obscuring the target thigh. However, only 5 minutes after receiving the Cy5.5-MORF25/BHQ3-cDNA18 duplex, the target thigh was clearly visible along with only the kidneys.

CONCLUSIONS

This first study of optical pretargeting provides a proof of concept that oligomer pretargeting found to be useful with radioactivity detection is applicable with fluorescent detection as well. In addition, our results demonstrate that by using linear oligomers for optical pretargeting, chain lengths (and base sequences) may be manipulated to provide duplexes with stabilities and fluorescence inhibition optimized for pretargeting and other in vivo applications of optical imaging.

Successful radiotherapy of tumor in pretargeted mice by 188Re-radiolabeled phosphorodiamidate morpholino oligomer, a synthetic DNA analogue

PURPOSE

Pretargeting has been attracting increasing attention as a drug delivery approach. We recently proposed Watson-Crick pairing of phosphorodiamidate morpholino oligomers (MORF) for the recognition system in tumor pretargeting. MORF pretargeting involves the initial i.v. injection of a MORF-conjugated antitumor antibody and the subsequent i.v. injection of the radiolabeled complement. Our laboratory has reported on MORF pretargeting for diagnosis using (99m)Tc as radiolabel. We now report on the use of MORF pretargeting for radiotherapy in a mouse tumor model using (188)Re as the therapeutic radiolabel.

EXPERIMENTAL DESIGN

An initial tracer study was done to estimate radiation dose, and was followed by the radiotherapy study at 400 muCi per mouse with three control groups (untreated, MORF antibody alone, and (188)Re complementary MORF alone).

RESULTS

Tracer study indicated rapid tumor localization of (188)Re and rapid clearance from normal tissues with a tumor area under the curve (AUC) about four times that of kidney and blood (the normal organs with highest radioactivity). Tumor growth in the study group ceased 1 day after radioactivity injection, whereas tumors continued to grow at the same rate among the three control groups. At sacrifice on day 5, the average net tumor weight in the study group was significantly lower at 0.68 +/- 0.29 g compared with the three control groups (1.24 +/- 0.31 g, 1.25 +/- 0.39 g, and 1.35 +/- 0.41 g; Ps < 0.05), confirming the therapeutic benefit observed by tumor size measurement.

CONCLUSIONS

MORF pretargeting has now been shown to be a promising approach for tumor radiotherapy as well as diagnosis.