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V R Pallela

Publications and source records attributed to V R Pallela.

7 recordsLinked to original sources
PubMed2000

A receptor-specific peptide for imaging infection and inflammation.

The chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP), when radiolabelled, continues to be an attractive agent for imaging infection or inflammation. Previously, several analogues of fMLP have been prepared and radiolabelled using a bifunctional chelating agent conjugation procedure that was relatively long and complex. We have prepared a new analogue of fMLP, TP765, by the addition of 4-aminobutyric acid (4-ABA) and a group of four amino acids, Gly-Gly-d-Ala-Gly, to the carboxy terminus (i.e. to the phenylalanine) of fMLP. The adduct -(4-ABA)-Gly-Gly-d-Ala-Gly- serves as a chelating moiety for strong chelation with 99Tcm. The use of a peptide as a chelating moiety greatly simplified the synthetic procedure and rendered the analogue ready for instant chelation with 99Tcm. HPLC analysis revealed that 99Tcm-TP765 was a single chemical entity that retained biological activity and neutrophil specificity. 99Tcm-TP765 was stable when challenged with strong chelating agents in vitro and had rapid but biphasic blood clearance (alphat1/2 = 7 min, betat1/2 = 45 min). Approximately 90% of the radioactivity had cleared from circulation within 45 min post-injection and the agent had accumulated in experimental bacterial or sterile abscesses in significantly (P<0.05) higher quantities than the analogues evaluated previously. Generally, the biodistribution pattern of 99Tcm-TP765 was similar to that of other analogues examined and its abscess uptake was independent of the abscess age. In conclusion, a new analogue of fMLP, 99Tcm-TP765, was prepared by a simple procedure. This new analogue has properties similar to those of previously examined analogues used as agents for imaging infection or inflammation.

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PubMed2000

Imaging vascular thrombosis with 99mTc-labeled fibrin alpha-chain peptide.

UNLABELLED: An agent that permits scintigraphic detection of chronic deep venous thrombosis (DVT) or pulmonary embolism (PE) would be a welcome addition to the armamentarium of nuclear medicine. Because fibrin is the integral part of each clot, old or fresh, we hypothesized that a 99mTc-labeled fibrin alpha-chain N-terminal peptide, Gly-Pro-Arg-Pro-Pro, that binds to the C-terminal portion of the gamma-chain of fibrin can detect DVT and PE. METHODS: The peptide was modified to Gly-Pro-Arg-Pro-Pro-Aba-Gly-Gly-(D)-Ala-Gly to permit efficient binding of 99mTc (99mTc-TP 850). The stability of the peptide was examined in vitro as well as in vivo. The ability of the agent to bind to rabbit, dog, and human fibrin and to inhibit adenosine diphosphate-induced platelet aggregation was examined. Blood clearance and 3-h tissue distribution were studied. DVT was induced in 8 rabbits using a stimulating electrode and in 2 rabbits by inserting a thrombin-soaked suture. PE was induced in 6 additional rabbits by introducing tantalum-impregnated blood clots into the right atrium, and the rabbits were radiographed to locate the emboli. 99mTc-TP 850 was then injected through a lateral ear vein, and each rabbit was imaged for up to 3 h. The rabbits were then killed, the heart and lungs were dissected and radiographed and the clots were harvested so that clot-to-blood radioactivity ratios could be determined. RESULTS: The peptide analog permitted efficient incorporation of 99mTc, which was stable in vitro and in vivo. The blood clearance was biphasic, with an alpha phase half-life of approximately 4 min (20%) and a beta phase half-life of approximately 13 min (88%). The mean binding of 99mTc-TP 850 to human, dog, and rabbit fibrin was 46% +/- 2%, 60% +/- 3%, and 56% +/- 2.5%, respectively, and the inhibitory concentration of 50% for dog and rabbit platelet aggregation was 236 pm and 167 pm, respectively. All clots, including 24-h-old pulmonary emboli, were delineated. The radioactivity associated with clots varied from 0.01 to 0.09 %ID/g, with clot-to-blood radioactivity ratios ranging from 1.2 to 12.0. However, 48-h-old pulmonary emboli had lysed and were seen neither by radiography nor by scintigraphy. CONCLUSION: A fibrin alpha-chain, N-terminal peptide that binds to the C-terminal portion of the gamma-chain of fibrin has been modified and labeled with 99mTc. The resultant peptide is stable in vitro and in vivo; binds to human, dog, and rabbit fibrin in large quantities; and inhibits platelet aggregation. The peptide clears rapidly from the blood and delineates experimental DVT and PE in rabbits. This agent is worthy of further investigation.

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PubMed2000

Interferon-alpha-2b immunoconjugate for improving immunoscintigraphy and immunotherapy.

UNLABELLED: A pretreatment with a single dose of an immunoconjugate (IC) that promises to enhance tumor uptake and decrease liver uptake of radiolabeled monoclonal antibodies (MAbs) might be of use in radioimmunodetection and radioimmunotherapy (RIT). We have shown previously that an interferon (IFN)-MAb (1:1) immunoconjugate (IC) enhances tumor uptake by a factor of 2 or more and reduces liver uptake by 50% in nude mice bearing human tumors. The aim of this study was to determine whether IFN modulates antigenic expression and to ascertain the most effective route of its administration, the optimal quantity to be administered, and the optimal duration of time to lapse between the administration of IC and the radiolabeled MAb. METHODS: IFN-alpha-2b and anticarcinoembryonic antigen-F6 (IgG2a) MAb were conjugated (1:1), and F(ab')2 of the MAb was labeled with 99mTc. Human colorectal tumors were grown in nude mice by implanting 5 x 10(6) LS174T confluent cells grown in culture. Mice, 5 in each group, received 20 x 10(3) IU intravenously, intramuscularly, or intraperitoneally and 40 x 10(3), 60 x 10(3), and 80 x 10(3) IU intravenously 30 min before the intravenous administration of 25.9 MBq 99mTc/20 microg F(ab')2. Mice in the control groups received 99mTc-F(ab')2 but not the conjugate. Twenty-four hours later mice were killed and imaged, and tissues were removed for quantitative (percentage injected dose/g [% ID/g]) distribution of 99mTc. RESULTS: In all conjugate-receiving mice, the tumor uptake was higher and the liver uptake was lower (P < 0.01) than that in the control mice with the exception of liver uptake, which was not significantly different in mice receiving 80 x 10(3) IU conjugate. The optimal results were apparent in mice pretreated with 40 x 10(3) IU conjugate in which tumor uptake was enhanced by a factor of 2.3 (4.8 +/- 0.5 %ID/g versus 11 +/- 0.7 %ID/g; P < 0.01). The renal uptake remained unchanged, and the tumor-to-muscle ratios increased from 11.5 +/- 6.8 to 14.6 +/- 3.9, and the tumor-to-blood ratios increased from 4.4 +/- 1.8 to 8.3 +/- 2.4. The liver uptake decreased from 9.5% +/- 1% to 5% +/- 1.6%. Results were attributed to enhanced tumor blood flow, increased antigenic expression, and blocking of hepatic nonspecific Fc receptors. CONCLUSION: A pretreatment with IFN-MAb conjugate is a worthwhile approach to consider in radioimmunoscintigraphy and RIT.

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PubMed1999

99mTc-labeled vasoactive intestinal peptide receptor agonist: functional studies.

UNLABELLED: Vasoactive intestinal peptide (VIP) is a naturally occurring 28-amino acid peptide with a wide range of biological activities. Recent reports suggest that VIP receptors are expressed on a variety of malignant tumor cells and that the receptor density is higher than for somatostatin. Our aims were to label VIP with 99mTc--a generator-produced, inexpensive radionuclide that possesses ideal characteristics for scintigraphic imaging--and to evaluate 99mTc-VIP for bioactivity and its ability to detect experimental tumors. METHODS: VIP28 was modified at the carboxy terminus by the addition of four amino acids that provided an N4 configuration for a strong chelation of 99mTc. To eliminate steric hindrance, 4-aminobutyric acid (Aba) was used as a spacer. VIP28 was labeled with 1251, which served as a control. Biological activity of the modified VIP28 agonist (TP3654) was examined in vitro using a cell-binding assay and an opossum internal anal sphincter (IAS) smooth muscle relaxivity assay. Tissue distribution studies were performed at 4 and 24 h after injection, and receptor-blocking assays were also performed in nude mice bearing human colorectal cancer LS174T. Blood clearance was examined in normal Sprague-Dawley rats. RESULTS: The yield of 99mTc-TP3654 was quantitative, and the yields of 125I-VIP and 1251-TP3654 were >90%. All in vitro data strongly suggested that the biological activity of 99mTc-TP3654 agonist was equivalent to that of VIP28. As the time after injection increased, radioactivity in all tissues decreased, except in the receptor-enriched tumor (P = 0.84) and in the lungs (P = 0.78). The tumor uptake (0.23 percentage injected dose per gram of tissue [%ID/g]) was several-fold higher than 125I-VIP (0.06 %ID/g) at 24 h after injection in the similar system. In mice treated with unlabeled VIP or TP3654, the uptake of 99mTc-TP3654 decreased in all VIP receptor-rich tissues except the kidneys. The blood clearance was biphasic; the alpha half-time was 5 min and the beta half-time was approximately 120 min. CONCLUSION: VIP28 was modified and successfully labeled with 99mTc. The results of all in vitro examinations indicated that the biological activity of TP3654 was equivalent to that of native VIP28 and tumor binding was receptor specific.

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PubMed1997

Radiolabeled somatostatin analogs in prostate cancer.

Vapreotide (RC-160), a somatostatin analog, was labeled with 99mTC by a direct method and also by using CPTA [1,4,8,11-tetraazacyclotetradecane] as a bifunctional chelating agent. The labeled compounds were evaluated in nude mice bearing experimental human prostate cancers. In these studies, 111In-DTPA-D-Phe-Octreotide (111In-DTPA-octreotide) served as a standard and 99mTc-oxytocin as a receptor-non-specific control. 99mTc-octreotide was also used. The 24 htumor uptake of 99mTc-RC-160 was nearly 400% higher, (p < 0.05), than that of 111In-DTPA-octreotide and diminished upon receptor blocking. In all tissues except the kidneys, the uptake of 99mTc-RC-160 was also higher than that of 111In-DTPA-octreotide. The uptake of 99mTc-RC-160 was influenced by the amount of peptide injected and the best tumor/muscle and tumor/blood ratios were obtained when only one micrograms of the peptide (200 Ci/mmol) was administered.

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PubMed1997

Improved antibody targeting with interferon-alpha-2b conjugate.

This investigation is based on a hypothesis that a biological response modifier, interferon-alpha-2b (IFN), when conjugated with a specific monoclonal antibody (mAb) and given to tumor-bearing animals before the administration of radiolabeled mAb, may not only augment the tumor uptake but may also impede the liver and blood uptake, because the mAb associated with the conjugate may block nonspecific hepatic binding sites and scavenge circulating antigens. ME 31.3 and anti-carcinoembryonic antigen (CEA) F-6 (IgG-2a) specific for human melanoma and colorectal carcinoma, respectively, were chosen as prototype mAbs and conjugated with IFN-alpha-2b for evaluation in athymic nude mice bearing respective experimental tumors. The mAb specificity for the tumor cell line was examined by binding assays and Kd values were determined to be 1.96 x 10(-9) M and 5.9 x 10(-9) M for ME 31.3 and anti-CEA F-6, respectively. Thirty micrograms of conjugate, prepared chemically and purified chromatographically (IFN-mAb:1:1), was administered intravenously to each animal and 3 h later followed by an intravenous injection of 20 micrograms F(ab')2 of corresponding mAb labeled with 300 muCi Tc-99m (1.5 Ci/mmol). Twenty-four hours later, in melanoma-bearing animals, not only did the tumor uptake increase, but also the liver uptake decreased by 75%. Tumor/muscle and tumor/blood ratios also enhanced by 200 and 500%, respectively. Consistent with ME 31.3, the tumor uptake with anti-CEA F-6 also increased (p = 0.00) and the liver uptake decreased (p = 0.01). Similarly, tumor/muscle (p = 0.01) and tumor/blood (p = 0.02) ratios also increased significantly. Results indicate that IFN:mAb conjugate may improve diagnostic and therapeutic potential of mAbs, and is worthy of further studies.

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