Susan J. Fisher

18F-2-deoxy-2-fluoro-D-glucose uptake into human tumor xenografts. Feasibility studies for cancer imaging with positron-emission tomography

The positron‐emitting glucose analogue 18F‐2‐fluoro‐2‐deoxy‐d‐glucose (FDG) was evaluated for its accretion into the following subcutaneous human tumor xenografts in nude mice: B‐cell lymphoma (Namalwa or Raji), ovarian carcinoma (HTB77), colon cancer (SW948), choriocarcinoma (BEWO), bladder cancer (UM‐UC‐2), renal cell carcinoma (UM‐RC‐3), neuroblastoma (Mey), melanoma (HTB63), and small cell lung carcinoma (NCI69). Two hours postinjection, tumor uptakes ranged from 0.027 (colon cancer) to 0.125% kg injected dose/g (melanoma); and was greater than 0.085 in the Namalwa lymphomas and the renal cell carcinomas. Tumor‐blood ratios of up to 23:1 were seen 2 hours postinjection (melanoma) with a mean tumor‐blood ratio for all tumors of 12.3 ± 1.8. Uptake in the other tumors was intermediate. When evaluated, tumor uptake was slightly greater at 1 than at 2 hours postinjection, although target‐background ratios were generally higher at 2 hours postinjection. This compound, FDG, may have broad applicability as a tracer for positron‐emission tomographic imaging of many human malignancies.

Preclinical and clinical studies of bone marrow uptake of fluorine-1-fluorodeoxyglucose with or without granulocyte colony-stimulating factor during chemotherapy.

PURPOSE To evaluate the effect of granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) on bone marrow glucose metabolism in rodents and in patients, as assessed by 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) uptake measured directly or by positron-emission tomography (PET) scanning. MATERIALS AND METHODS Groups of three rats received either daily saline, G-CSF, or GM-CSF injections for 7 days. After treatment, FDG was injected and F-18 activities in tissues measured 1 hour later. Twenty-two breast cancer patients treated with multiagent chemotherapy were sequentially studied with PET. Eleven patients received G-CSF therapy as an adjunct to chemotherapy, while 11 received chemotherapy only. The standardized uptake value-lean (SUL) of bone marrow FDG uptake was measured and compared. RESULTS In rats, bone marrow F-18 activity was significantly higher in both CSF groups than in the saline group (G-CSF, 0.44 +/- 0.08; GM-CSF, 0.33 +/- 0.02; saline, 0.18 +/- 0.02% injected dose [ID]/g x kg; P < .05), but the other normal tissues had comparable biodistributions to controls. In breast cancer patients, the FDG uptake of bone marrow did not change with chemotherapy alone; however, marrow uptake was increased after treatment with G-CSF. The dose of G-CSF and duration of treatment were correlated with the extent of increase in FDG uptake. The SUL of bone marrow was as follows: baseline, 1.56 +/- 0.23; after one cycle, 3.13 +/- 1.40 (P < .01); after two cycles, 2.22 +/- 0.85 (P < .05); and after three cycles, 2.14 +/- 0.79 (P < .05), respectively. Although the FDG uptake of bone marrow declined after G-CSF treatment was completed, it was higher than the baseline level for up to 4 weeks postcompletion of G-CSF and the elevated marrow FDG uptake was sustained longer than the period of blood neutrophil count elevation. CONCLUSION Substantial increases in bone marrow FDG uptake are rapidly induced by CSF treatments and should not be misinterpreted as diffuse bone marrow metastases.

Bone marrow cell trafficking following intravenous administration

To address trafficking of transplanted marrow cells immediately after intravenous infusion, we examined the early fate of infused non‐adherent, low‐density donor bone marrow cells in a syngeneic mouse model. The presence of infused donor cells, marked with indium‐111 oxine (111In), with the fluorescent dye PKH26, or by a detectable transgene marker, was evaluated at 3–48 h in a variety of tissues, including peripheral blood. All three cell‐marking methods indicated a rapid (< 4 h) influx of cells into the bone marrow, liver, spleen, muscle and other tissues. Moreover, these tissues remained positive for the 48 h observation period. Interestingly, analysis of PKH26‐positive cells in non‐myeloablated animals demonstrated that approximately 17% of infused donor marrow cells localized to the marrow space within 15 h, whereas a smaller proportion of donor cells (~ 1–2%) localized to the marrow in recipients preconditioned by irradiation. In an effort to enrich for cells that specifically home to the bone marrow, PKH26‐labelled donor marrow cells were recovered from the first host and infused into a secondary recipient. Although this was a phenotypically undefined population of cells, no increase was observed in the relative fraction of PKH26‐labelled cells returning or ‘homing’ to the marrow of the second recipient. Taken together, these data suggest both that marrow engraftment may be mediated by non‐specific ‘seeding’ rather than a specific homing signal, and that efficient targeting of transplanted cells to the marrow is a complex multifaceted process.

The intraperitoneal delivery of radiolabeled monoclonal antibodies: studies on the regional delivery advantage

SummaryThe i.p. delivery of murine monoclonal antibody was compared with i.v. delivery in normal mice and rats, in normal nude mice and in those with i.p. human ovarian carcinoma xenografts. In normal rats, all classes of antibodies and antibody fragments evaluated were cleared from the peritoneal cavity at comparable rates. The regional delivery (Rd1) advantage to the peritoneal cavity following i.p. delivery was thus most dependent on the rate of clearance of the antibody or fragment from the blood stream. Determining the exact i.p. delivery advantage was problematic due to the difficulty in reliably obtaining peritoneal fluid later than 9–10 h after i.p. injection in normal animals. During the first 9 h following i.p. injection, the Rd(0–9/0–9) was, for a murine IgG2ak Fab>F(ab′)2>IgG (at 13.6>10>7.9). Two murine IgMs evaluated differed in Rd(0–9) at 27.1 and 9.2 respectively. When blood levels were extrapolated to infinity, these Rd (0–9/∞) values were considerably lower with the Fab having the highest Rd at 4.67. The i.p. Rd advantage was almost solely due to the i.p. antibody levels seen in the first 24 h after injection, as after that time, blood levels become comparable to those seen following i.v. injection. Normal tissues obtained at sacrifice 5–7 days after i.p. injection. Normal tissues obtained at sacrifice 5–7 days after i.p. or i.v. injection in rats showed comparable levels of radioantibody activity, whether the injection was i.p. or i.v. (except for higher diaphragmatic levels following i.p. delivery). In nude mice with i.p. human-derived ovarian tumors, intact IgG clearance from the peritoneal cavity to the blood was considerably slower than in normal animals, and early i.p. tumor uptake of specific antibody was significantly higher than that following i.v. antibody delivery. With higher early tumor uptake and lower systemic exposure, early tumor/nontumor ratios were significantly greater than those for i.v. delivery, though not beyond 48 h after i.p. injection. This study demonstrates the pharmacokinetic rationale for i.p. monoclonal antibody delivery, especially for agents cleared rapidly from the blood, such as antibody fragments. In addition, definite i.p. delivery benefit for antibody specific to i.p. tumors in the i.p. ovarian cancer system was shown soon after injection. These data regarding i.p. antibody delivery should be useful in rationally planning diagnostic and therapeutic studies involving the i.p. delivery of unmodified and immunoconjugated monoclonal antibodies.

Uptake of 2-deoxy-2-[18F]fluoro-d-glucose in the normal testis: Retrospective PET study and animal experiment

Our retrospective PET and animal studies were conducted on a total of eight patients with normal testes and five male Sprague-Dawley rats. All the rats were necropsied at 60 minute post-injection of FDG, and the organs were removed and counted. The human testes were visualized on 60–70 minute FDG-PET images and whole- or partial-body images in all of the patients. The correlations between patient age over 50 years old and testis-to-muscle ratios, and patient age and SUVs were statistically significant, r = − 0.755, p < 10−6 (n = 7), r = − 0.900, p < 0.007 (n = 4), respectively. FDG uptake of the rat testes was 0.162 ± 0.004% kg injected dose/g (n = 5). The uptake was approximately 6.0 and 3.6 times as high as muscle and blood levels, respectively. In conclusion, there is substantial uptake of FDG into the normal testis which declines with age. The normal levels of FDG uptake in the testis relative to the patient’s age should be considered in the interpretation of FDG scans of the inguinal and lower pelvic regions.

Intratumoral microdistribution of [131I]MB-1 in patients with B-cell lymphoma following radioimmunotherapy

Intratumoral microdistribution of radiolabeled anti-CD37 murine monoclonal antibody, [131I]MB-1, in lymph nodes from five patients with non-Hodgkins B-cell lymphoma following radioimmunotherapy were evaluated by microautoradiography and image analysis of macroautoradiographs. Microdistribution of radioactivity was highly heterogeneous: silver grain counts varied from 28-70 to 8-10 per 400 X field, and the coefficients of variations calculated by image analysis ranged between 42.5 and 79.3%. Variable radiation doses delivered could have contributed to the limited durability of tumor regression.

Animal studies on the reduction and/or dilution of 2-deoxy-2-[18F]fluoro-d-glucose (FDG) activity in the urinary system

To evaluate two methods for decreasing and/or diluting the FDG activity in the urinary system, five rats were intraperitoneally given 1,000 μg/g ofl-lysine 4 times, starting from 60 minutes before iv injection of FDG, and then at 30-minute intervals for 90 minutes. Five rats were used as controls. In a furosemide study, 12 rats were allocated to three groups. Group 1 received iv injection of FDG alone. Group 2 received saline before iv injection of FDG. Group 3 received furosemide (7 mg/kg) and saline (1/30 of body weight). Neither renal uptake nor urinary excretion of FDG had a statistically significant difference: renal uptake; 0.179 ± 0.011 (l-lysine) vs. 0.119 ± 0.003 (control) % kg injected dose/g. The % dose excreted and total urine volume were: 15.0 ± 2.5 to 15.5 ± 2.5 with 2.98 ml (l-lysine), 22.9 ± 1.8 to 24.2 ± 1.5 with 1.41ml (control). The furosemide study revealed a statistically significant difference: Group 1; 7.57 ± 4.73, Group 2; 0.686 ± 0.638, Group 3; 2.37 ± 2.33% kg injected dose/g (p < 0.01 for Group 1 vs. Group 2, p < 0.05 for Group 1 vs. Group 3). While pretreatment withl-lysine or furosemide failed to decrease renal activity of FDG, saline injection without furosemide markedly decreased urinary activity.

The effect of specimen processing on radiolabeled monoclonal antibody biodistribution

Monoclonal antibodies are assuming increasing importance in experimental and clinical medicine. Generally, tissue biodistribution studies in animals precede human studies. To investigate a concern of ours that varying methods of sample handling in these studies could result in apparent alterations in tissue-binding levels, we compared two methods of tissue processing after the administration of labeled antibodies: one including only blotting away of blood, the other involving several washing steps. The unwashed, blotted specimens were found to have significantly more radioactivity per gram of tissue than the washed, ranging from 22% more in the spleen to 52% more in the lungs and left ventricle. Since in vivo imaging is dependent on the total mount of radioactivity in an organ, we believe the most meaningful determination of tissue radioactivity should be based on unwashed samples. Awareness of this problem is suggested to allow meaningful extrapolations from measured tisue localization data to imaging and therapy.

99Tcm-MDP uptake by lymph nodes following tracer infiltration: clinical and laboratory evaluation

Uptake of bone scanning agents in non-osseous sites has been described in a variety of pathologic conditions including tumor metastases. We have seen several patients in which such uptake was proximal and ipsilateral to the injection site of 99Tcm-methylene diphosphonate, apparently in normal lymph nodes. To further investigate this phenomenon, it was studied in a rat model. Activity in popliteal nodes ipsilateral to the injection site was over 60-fold greater in the animals that received subcutaneous (s.q.) footpad injection compared to femoral IV injection. Ipsilateral popliteal node activity in the s.q. group was 159 times that of contralateral popliteal nodes, with an ipsilateral node to liver ratio of 184:1. In summary, dramatically increased uptake of 99Tcm-MDP in normal lymph nodes ipsilateral and proximal to an extravasated injection has been demonstrated. An awareness of this phenomenon in the clinical setting can avoid confusion with pathologic forms of soft tissue uptake.

In Vitro and Ex Vivo Evaluation of Cyclic Aminoalkyl Benzilates as Potential Emission Tomography Ligands for the Muscarinic Receptor

A series of muscarinic antagonists were screened as potential receptor imaging agents. (+)2 alpha-tropanyl benzilate (TRB), N-methyl-4-piperidyl benzilate (NMPB) and several analogs amenable to labeling with positron emitting isotopes were evaluated for muscarinic binding to mouse brain tissue in vitro and ex vivo using [3H]quinuclidinyl benzilate as the probe. The in vitro assay directly compared the innate binding affinities of the compounds. The rank order of binding (IC50) was TRB (0.7 nm), QNB (0.8 nm), scopolamine (1.3 nm) and NMPB (1.6 nm). The ex vivo assay was used to gain information regarding the pharmacokinetics and brain penetration of the compounds in live animals. Ex vivo results demonstrated that TRB was rapidly taken up into the brain and was equipotent with QNB in occupying muscarinic binding sites at early time points, but TRB binding decreased twice as fast over time as QNB binding. The results suggest TRB would be a good candidate for radiolabeling and further study.