A Phase I Trial Combining High-Dose ⁹⁰Y-Labeled Humanized Anti-CEA Monoclonal Antibody with Doxorubicin and Peripheral Blood Stem Cell Rescue in Advanced Medullary Thyroid Cancer

Antibody Preparation and Radiolabeling

Humanized MN-14 (Immu-14 or labetuzumab) IgG and DOTA-conjugated hMN-14 IgG were provided by Immunomedics, Inc. A minimum of 10 mg of the DOTA-hMN-14 was used in the preparation of the radiolabeled products with the initial ratio not exceeding 222 MBq/mg. For radiolabeling, the chelate-conjugate (in 0.25 mol/L sodium acetate buffer, pH 5.5) was added to the isotope vial supplied by radionuclide manufacturer. ¹¹¹InCl₃ and ⁹⁰YCl₃ were purchased from either Perkin-Elmer or IsoTex. Radiolabeling was performed at 43°C for 5–10 min followed by a brief incubation with an excess of DTPA at room temperature, to scavenge nonantibody-bound radiometal. The final product was sterilely filtered in a vial containing saline to meet the prescribed radioactivity dose for each patient (±10%). Quality-assurance testing included instant thin-layer chromatography (ITLC) for nonantibody-bound radionuclide (i.e., DTPA bound) and size-exclusion high-performance liquid chromatography (HPLC) (300 × 7.8 mm Bio-Sil SEC250 column with guard; Bio-Rad Laboratories) of the radiolabeled product alone and after addition of a 10-fold molar excess of CEA (Scripps Laboratories, Inc.) to assess the immunoreactive fraction. These studies showed that the final radiolabeled products had 2.6% ± 0.5% and 5.7% ± 3.1% unbound ¹¹¹In or ⁹⁰Y, respectively, by ITLC and 2.8% ± 2.7% and 2.8% ± 3.1% aggregates for the ¹¹¹In- and ⁹⁰Y-radiolabeled IgG, respectively, by size-exclusion HPLC. Other studies have shown that ¹¹¹In and ⁹⁰Y are both very stable when bound by DOTA-conjugated antibodies (19). The immunoreactive fraction was ≥90%.

Antibody Administration

Before injection of the ¹¹¹In- and ⁹⁰Y-labeled antibody, the patients first received a predose of unconjugated, unlabeled hMN-14 IgG with the intent to reduce the potential for complexation of the radiolabeled antibody with circulating CEA. The amount of unlabeled antibody administered equaled the total antibody protein (0.75 mg/kg) minus the amount of DOTA-hMN-14 IgG used to provide the radiolabeled antibody dose. The amount of unlabeled antibody given ranged from 21.6 to 72.5 mg, which represented 42.5%–93.8% of the total antibody administered dose. The amount of unlabeled antibody preinfused for the second injection was within 10% of the first injection for patients through patient 1799. Thereafter, the amount of unlabeled antibody preinfused for the second injection was 25%–65% less than that in the first injection because of the need to use additional DOTA-hMN-14 to provide the higher ⁹⁰Y-doses as well as the inclusion of patients who were coinfused with ¹¹¹In-DOTA-hMN-14. The unconjugated antibody was added to a buretrol containing 20–30 mL of saline and infused over approximately 30–50 min. The radiolabeled antibody was infused immediately at the conclusion of the unlabeled antibody infusion over another 15–30 min, except in 5 patients for whom there was a brief interval of 5–23 min between the 2 infusions. All antibody infusions were initiated without premedication, starting slowly with about 10% of the total dose infused over the first 5–10 min and then, as long as vital signs remained stable, the remaining dose was infused. Vital signs were then measured at 1, 2, and 24 h after the end of the radiolabeled antibody infusion.

Patient Selection and Registration

This clinical trial was conducted with Institutional Review Board approval and an investigator-initiated Investigational New Drug application from the Food and Drug Administration. Patients with histologic or cytologic diagnosis of MTC (sporadic or familial) were studied. Eligibility criteria included (a) unresectable locoregional MTC or distant metastases; (b) presence of measurable or evaluable disease by CT, with targeting of at least one cancer lesion seen on the CT scan in the diagnostic imaging study; (c) adequate PBSC or bone marrow harvest before receiving treatment; (d) white blood cells > 3,000/mm³, granulocytes > 1,500/mm³, and platelets > 100,000/mm³; (e) bilirubin ≤ 2 mg/dL and creatinine < 1.5 × the institutional upper limit of normal; (f) a cardiac ejection fraction of at least 50% and pulmonary function parameters (forced vital capacity [FVC] and diffusing capacity of lung for carbon monoxide [Dlco]) of at least 60% of predicted for their age; (g) age ≥16 y; and (h) Karnofsky performance status of ≥70 (Eastern Cooperative Group [ECOG] score 0–2). Patients who had known brain metastases or prior radiation therapy to >35% of their bone marrow, or who had received prior therapy with >240 mg/m² of Dox or who showed progression after prior Dox treatment, were excluded. All patients were mentally responsible and provided a written informed consent.

Table 1 lists some of the demographics of the patients enrolled in this trial, including their age, sex, sites of disease at enrollment, and baseline blood CEA and calcitonin levels. A total of 15 patients (11 men, 4 women; age range, 16–75 y) were enrolled and received a diagnostic imaging study, but only 14 received treatment, because the liver enzymes of 1 patient increased in the week before receiving the therapy dose, making him ineligible for the ⁹⁰Y-hMN-14 treatment.

Trial Design

The scheme in Figure 1 shows the treatment plan. All patients had PBSCs harvested after mobilization with granulocyte colony-stimulating factor (G-CSF). At least 2 × 10⁶ CD34⁺ cells/kg were required. Patients then received ∼222 MBq of ¹¹¹In-hMN-14 IgG. Scintigraphy and blood pharmacokinetics were obtained after the ¹¹¹In-hMN-14 infusion to predict the pharmacokinetics and radiation-absorbed doses for the subsequent ⁹⁰Y-hMN-14 infusion. These data also were used to predict when the total-body ⁹⁰Y radioactivity level would be <111 MBq/m² and, at this time, the PBSCs were reinfused. Treatment was given only when targeting of a confirmed tumor was established after the ¹¹¹In-hMN-14 injection and the predicted time for reinfusion of the PBSCs was ≤2 wk after receiving the ⁹⁰Y-hMN-14. In addition, dosimetry estimates had to show that the predicted absorbed dose to the liver would not exceed 3,000 cGy, or 2,000 cGy to the lungs and kidney at the prescribed ⁹⁰Y-hMN-14 dose level. Treatment with ⁹⁰Y-hMN-14 was given 6–8 d after ¹¹¹In-hMN-14 in most patients (12–13 d in 4 patients), and at least 14 d after the final G-CSF injection was given during the harvesting of the PBSCs. One day after the ⁹⁰Y-hMN-14 therapy infusion, a fixed dose of Dox (60 mg/m²) was given as an intravenous bolus. Dose escalation was based on body surface area (MBq/m²), with Table 1 listing the administered ⁹⁰Y-hMN-14 radioactivity in the 14 patients who received treatment. DLT was defined as grade 3 nonhematologic toxicity (except for alopecia, for which any grade was acceptable, or nausea and vomiting, for which grade 4 toxicity of 7 d was acceptable), grade 4 neutropenia or thrombocytopenia of >21-d duration, or anemia requiring transfusion support for >42 d. Toxicities were graded according to the National Cancer Institute Common Toxicity Criteria, version 2.0. Three patients were treated at each dose level, and only after all patients had completed 8 wk of follow-up with no DLT was the dose escalated to the next level. If any one of the 3 patients treated at a dose level developed DLT, up to 3 additional patients were to be studied at that dose level. However, if ≥2 patients at any dose level developed DLT, no further escalation was permitted. Patients were to be monitored for hematologic and nonhematologic toxicity for a minimum of 3 mo and, whenever possible, up to 5 y. Two patients had 2–3 mo of follow-up, whereas 4 patients had 3–6 mo, 5 had 6–9 mo, and 3 had >1-y follow-up.

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FIGURE 1.

Treatment plan. Each patient received a pretherapy imaging study with ¹¹¹In-hMN-14 IgG. This study was used to (a) confirm targeting of at least 1 index lesion, (b) estimate radiation-absorbed doses for ⁹⁰Y-hMN-14 to ensure that the dose to liver would not exceed 3,000 cGy and the lung and kidney dose would not exceed 2,000 cGy at prescribed ⁹⁰Y-hMN-14 administered dose, and (c) to verify that amount of ⁹⁰Y radioactivity remaining in the whole body would be ≤3 mCi/m² no later than 14 d in order to reinfuse PBSCs within this time. PBSCs were reinfused between 7 and 12 d, depending on dose level. G-CSF = granulocyte colony-stimulating factor; Mab = monoclonal antibody

Pharmacokinetics, Imaging, and Dosimetry

Whole-body (WB) clearance was determined after the ¹¹¹In-hMN-14 IgG infusion by serial WB γ-camera imaging, typically starting from within 1 h of the end of the infusion, but before voiding, until the ⁹⁰Y-hMN-14 therapy infusion 6–8 d later. The ¹¹¹In-IgG WB effective half-life (t_1/2) and residence times were computed from monoexponentially curve-fit data (6–8 time intervals). WB clearance was also estimated for ⁹⁰Y-hMN-14 using this same dataset by assuming the biologic clearance of the ¹¹¹In- and ⁹⁰Y-products was identical and then deriving the predicted effective data for ⁹⁰Y-hMN-14. Three patients received a second ¹¹¹In-hMN-14 dose (∼370 MBq) with the ⁹⁰Y-hMN-14 therapy infusion. This second ¹¹¹In-hMN-14 infusion was performed to compare the pharmacokinetics and biodistribution of the sequential injections and to obtain a preliminary assessment of how well the first ¹¹¹In-hMN-14 could be used to extrapolate the pharmacokinetics and dosimetry for a second injection given approximately 1 wk later (the therapy dose was administered 7–8 d after the first ¹¹¹In-hMN-14 injection in these 3 patients). In these 3 patients, serial WB imaging was performed at time points similar to those used after the first ¹¹¹In-hMN-14 infusion. These data were again fit with a monoexponential curve to describe WB clearance. In addition, urine was collected over 7 d in 2 patients and 3 d in 1 patient after the therapy injection, and the ¹¹¹In and ⁹⁰Y activities were determined. Comparisons were then made to WB clearance data derived from the pretherapy ¹¹¹In-hMN-14 injection by external scintigraphy, from external scintigraphy of the ¹¹¹In-hMN-14 given together with the ⁹⁰Y-hMN-14 dose, and from the urinary clearance of ¹¹¹In and ⁹⁰Y radioactivity measured after the second infusion.

Blood clearance was determined by counting the radioactivity in serial serum samples. Typically, 5–9 samples were collected over a 7-d period (a minimum of 5 samples was required). ¹¹¹In activity was determined by γ-scintillation counting, whereas ⁹⁰Y activity was determined using Cerenkov counting in a β-scintillation counter. In the case in which ¹¹¹In and ⁹⁰Y activities were coinfused, the ¹¹¹In activity was corrected for ⁹⁰Y scatter in the ¹¹¹In window. The volume of the serum sample was corrected to that of the whole blood using the baseline hematocrit of the patient, and then these data were processed using CONSAM (conversational SAAM version 3.0; Resource Facility of Kinetic Analysis) software examining both a monoexponential and a biexponential fit. Serum obtained within 1 and 24 h after each infusion was also examined in most patients by size-exclusion HPLC equipped with an in-line radiation detector or through the quantitation of radioactivity by a fraction collector in 0.2-mL fractions.

After each ¹¹¹In-hMN-14 infusion, anterior and posterior planar images of 3 or 4 regions (e.g., head/neck, chest, abdomen, and pelvis) were also obtained using a dual-head Solus camera (ADAC Laboratories) fitted with a medium-energy collimator. Planar images (5–10 min per view) were obtained starting 2–4 h after injection, with serial images done on at least 3 separate days between 1 and 5–7 d after the injection. One or 2 SPECT images were obtained typically between 48 and 72 h. SPECT was performed using a 64 × 64 matrix with 64 or 128 projections over 360° (average counts per projection = 60,000). Targeting sensitivity was assessed by side-by-side comparison of radioantibody scans and anatomic scans (usually CT).

Planar views were used for drawing regions of interest (ROIs) for the major organs, from which time–activity curves and radiation-absorbed doses were derived. ROIs were drawn for the kidneys, liver, lungs, and spleen. Dosimetry is reported only for those organs that were not involved with or masked by overlying or underlying tumor. ROIs for red marrow were based primarily on the lumbar spine, but the sacrum was used in the event of tumor involvement in the lumbar region. There were 2 patients in whom overlying tumor masked both the sacral and the lumbar regions. In this instance, the red marrow dose was calculated only from the serum clearance data, using the hematocrit to approximate the radioactivity in the whole-blood volume, and then applying a factor of 0.36, which represents an average red marrow-to-blood ratio (23). Activity quantitation from the images was determined by 2 methods—the buildup factor method (BFM) used in 10 patients (24) and the modified geometric mean method (MGMM) used in 5 patients (25). Because we had reported previously that radiation dose estimates derived from these 2 methods were similar for all normal tissues except the lungs (26), the radiation-absorbed dose for all organs, except the lungs, was averaged. Each set of organ time–activity data was fit to a mono-, bi-, or triexponential function using CONSAM, but most often a triexponential function was selected. For each method, dividing the area under the curve by the injected activity derived a residence time that was used in MIRDOSE3 (27) to calculate the radiation-absorbed dose. Absorbed doses were calculated for ⁹⁰Y from the ¹¹¹In-hMN-14 imaging study by using the biologic clearance curves for ¹¹¹In-hMN-14 and substituting the physical half-life of ⁹⁰Y to derive an effective clearance curve for ⁹⁰Y. Organ volumes were taken from MIRD (28). For tumor dosimetry, volumes were derived from bidimensional CT measurements, using the average of the 2 diameters to derive a radius, and, from this, a spheric volume was calculated. Time–activity curves for the tumors were fit by a trapezoidal model. The integral for the tumor time–activity curves was multiplied by the tumor S factor that was interpolated from S values of the nodule module in CONSAM software (27).

Toxicity and Tumor Response

Hematologic toxicity was monitored by complete blood counts performed approximately 3 times per week after reinfusion of PBSCs or bone marrow, until counts had recovered to ≤grade 2, at which time sampling was performed twice weekly until counts stabilized for at least 2 consecutive weeks. Nonhematologic toxicities were monitored, whenever possible, as follows: renal and hepatic toxicities were monitored by serum biochemistry profiles; cardiac and pulmonary toxicities were monitored by multiple gated acquisition (MUGA) scans and pulmonary function tests were performed at 8, 24, and 36 wk after treatment, and every 6–12 mo after that if the patient developed toxicity until recovery; neurologic and gastrointestinal (GI) toxicities were monitored by history and physical examination. Since all patients were referred to us from outside the local region, follow-up monitoring was performed primarily by the referring physician, and we maintained regular contact with the patients and their physicians and obtained copies of their medical records on a regular basis. Antitumor responses were assessed by serial CT at 1 and 3 mo after therapy and thereafter at 6-mo intervals or until progression occurred. Responses were judged according to ECOG criteria, using baseline studies obtained within 4 wk of the ¹¹¹In-hMN-14 study. Blood CEA and calcitonin levels were determined at 1 mo after treatment and at monthly intervals for 1 y whenever possible, or until progression.

Human Anti-Humanized Antibody (HAHA) Determination

A blood HAHA titer was determined for all patients at baseline. Follow-up testing was performed at 2, 4, 8, and 12 wk after treatment, whenever possible. The titer was determined by using 1 of 2 assays: the HPLC assay (n = 10), and later the enzyme-linked immunosorbent assay (ELISA) (n = 5). These methods were described in detail previously by Hajjar et al. (29)

Adverse Events During Antibody Infusions

A total of 29 infusions of radiolabeled hMN-14 were administered (14 patients received 2 infusions and 1 patient received only 1 infusion). No patient was premedicated for allergic reactions before the antibody infusion, and no antibody infusion was cancelled because of an adverse event. Two patients experienced mild-to-moderate allergic-type reactions: redness, pruritus, periorbital hives, chills, and mild hypertension (from 100/80 mm Hg at baseline to 120/90 mm Hg after infusion) after the first antibody infusion. These 2 patients then received the therapy infusion without premedication and without complications.

Pharmacokinetics

The WB effective t_1/2 for the ¹¹¹In-hMN-14 IgG was 62.1 ± 3.2 h (n = 15), which indicates that only a small portion of the total radioactivity injected was cleared from the body. Urine collection indicated that between 13% and 19% of the total injected ¹¹¹In or ⁹⁰Y radioactivity was excreted over 7 d (n = 2; collection over only 3 d in 1 patient accounted for 7% of the total injected radioactivity). Although the radioactivity in the urine was not analyzed, the amount of radioactivity in the first 24 h represented nearly 90% of what was determined as nonantibody bound (i.e., chelated with DTPA) ¹¹¹In or ⁹⁰Y from the ITLC results on the starting radiolabeled product. Since the majority of a chelated radiometal was expected to excrete quickly, it is likely that the elimination fraction over the first 24 h was almost entirely due to the nonantibody–bound fraction in the injected product. External scintigraphy did not reveal any substantial uptake or movement of radioactivity through the GI tract and, thus, urinary excretion was the major route of elimination. As shown in Table 2, the WB effective t_1/2 measured for ⁹⁰Y-hMN-14 based on urine collection in these 3 patients corresponded well to the predicted values obtained from external scintigraphy of the ¹¹¹In-hMN-14 given in either the first or second injections as well as to the clearance of the ¹¹¹In-hMN-14 based on urine.

The blood clearance data (both the effective and estimated biologic) for the ¹¹¹In- and ⁹⁰Y-hMN-14 IgG were adequately defined by a monoexponential function in all patients. One patient (injection 1 in patient 1818; plasma CEA was 3,650 ng/mL) had a sharp decline in the amount of radioactivity in the first blood sample (40 min) to the second sample taken at 85 min (23.2 to 14.0 %ID/L [percentage injected dose per liter]), but the remaining 6 samples collected from 85 min to 143 h were fit well by a monoexponential function. The only other indication that plasma CEA might have been affecting early blood clearance was the observation that in the 3 patients with plasma CEA levels ≥1,800 ng/mL, only ∼60% of the total injected dose was estimated in the total blood volume of the first sample taken with 1 h of the end of infusion, whereas >90% of the radioactivity could be accounted for in all other patients (i.e., plasma CEA ≤ 1,180 ng/mL). These data suggest that at higher plasma CEA concentrations, antigen-antibody complexes may have formed and were cleared from the blood by the time the first samples were collected. Size-exclusion HPLC showed no more than 15% of the radioactivity in a high-molecular-weight fraction when plasma CEA exceeded 1,000 ng/mL. Thus, the preinfusion of the unlabeled antibody before the radiolabeled antibody appeared to have minimized CEA-hMN-14 complex formation. Figure 2 shows the relationship between the predicted (based on the first ¹¹¹In-hMN-14 IgG) and observed (measured ⁹⁰Y-hMN-14) blood clearance of ⁹⁰Y-hMN-14 to that of the baseline plasma CEA. Plasma CEA was a significant contributing factor to the observed effective clearance t_1/2 but did not reach a statistically significant level for the predicted effective t_1/2 or the predicted or observed residence times. The proportion of variation that is explained by circulating CEA for each of these end points is relatively small (i.e., <35%).

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FIGURE 2.

Impact of plasma CEA on blood pharmacokinetic behavior of ⁹⁰Y-hMN-14 IgG (observed) and that predicted for ⁹⁰Y-hMN-14 IgG from ¹¹¹In-hMN-14 IgG injection given 1 wk earlier (predicted).

The mean blood biologic half-life (t_1/2) for the ¹¹¹In-hMN-14 (n = 15) was 81.2 ± 24.0 h (range, 44.8–115.4 h), whereas for the ⁹⁰Y-hMN-14 (n = 14) was 83.6 ± 22.9 h (range, 50.2–125.6 h), suggesting that both injections were cleared at a similar rate. Although a paired analysis of the effective half-lives of the predicted (from ¹¹¹In-hMN-14 injection 1) and measured ⁹⁰Y-hMN-14 from injection 2 were not significantly different (34.9 ± 5.1 h vs. 35.6 ± 4.5 h, respectively; P = 0.546), the predicted effective blood residence time for ⁹⁰Y-hMN-14 IgG based on the first ¹¹¹In-hMN-14 injection was significantly higher (9.3 ± 3.0 h/L; n = 14) than that measured for the ⁹⁰Y-hMN-14 in the second injection (7.2 ± 2.4 h/L; P = 0.002 for predicted vs. observed using a paired t test). These data suggest that if the red marrow dose for the ⁹⁰Y-hMN-14 were based on the blood clearance of ¹¹¹In-hMN-14 IgG given in the first injection, in many cases it would have been overestimated by about 20%. To further examine this issue, 3 patients were given a second injection of ¹¹¹In-hMN-14 IgG along with their ⁹⁰Y-hMN-14 therapy dose. Table 3 provides red marrow radiation-absorbed dose estimates by 4 different methods. The first method utilizes the blood and WB clearance from the direct measurement of ⁹⁰Y activity in the blood and urine of these patients after the ⁹⁰Y-hMN-14 IgG therapy dose and was considered the standard for comparison. Method 3 represents the use of a pretherapy study with ¹¹¹In-hMN-14 performed 1 wk in advance of the ⁹⁰Y-hMN-14 therapy study. In 2 of the 3 cases, this method overestimated the radiation-absorbed dose to the red marrow by nearly 35% when compared with the estimate provided by the directly measured ⁹⁰Y-hMN-14 IgG blood and urinary clearance data (method 1). Data generated from the clearance of the ¹¹¹In-hMN-14 coinjected with the ⁹⁰Y-hMN-14 (methods 2 and 4) more closely approximated the results found by direct measurement of the ⁹⁰Y activity. These data suggest that radiation dose estimates may be more reliably obtained from the ¹¹¹In-labeled antibody if it were coinjected with the ⁹⁰Y-labeled antibody. Using external scintigraphy of the sacrum or lumbar spine to derive red marrow dose may reduce some of this variability. For example, in 2 of the patients co-injected with ¹¹¹In-hMN-14, the red marrow dose for the first and second injections would be within 10% (e.g., 1.03 vs. 1.11 mGy/MBq and 2.70 vs. 2.97 mGy/MBq). The other patient had tumor involvement in the lumbar and sacral areas, preventing use of these regions for estimation of red marrow dose. Although this situation was not encountered frequently, it does illustrate the need to have alternate regions that could be used for external scintigraphy or reliable estimates provided from blood clearance data. Because radiation dose estimates can vary considerably when derived by different methods (i.e., imaging vs. blood clearance), it is important that the same method be used, particularly if the dosage assignment is to be based on red marrow dose estimates. For example, a review of the red marrow dose derived from blood clearance or external imaging of the ¹¹¹In-hMN-14 given in the first injection revealed that these estimates were within 25% of each other in 6 of 11 patients, but in 5 patients, the radiation dose derived from external scintigraphy was ≥50% higher compared with that derived from the blood clearance data (Fig. 3).

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FIGURE 3.

Frequency distribution shows number of patients for whom radiation-absorbed dose to red marrow (RM) by imaging was calculated to be lower (negative) or higher (positive) than dose derived from blood clearance data. Determination of RM dose by external scintigraphy was possible in 12 of 14 patients given ⁹⁰Y-hMN-14. Data from a 16-y-old subject were also not included in this analysis of adult patients. In this subject, dose derived from imaging study was 52.5% less than that derived from blood clearance data.

Biodistribution and Tumor Targeting

Table 4 summarizes the imaging sensitivity for the ¹¹¹In-hMN-14 IgG using CT as the standard comparator. A total of 156 lesions were documented by independent radiology review of the baseline CT. Seventy-nine of these lesions were noted in the bone of 3 patients. The ¹¹¹In-hMN-14 IgG identified 125 lesions (80% overall sensitivity; 78/79 of the bony lesions, for a sensitivity of 98.7%), but 16 additional lesions were documented on the ¹¹¹In-hMN-14 scan that were not seen even after further evaluation of the CT studies. Sensitivity was lowest in the lungs, but many of these lesions were ≤1.0 cm. Figure 4 shows the time course of WB images of a patient given 2 sequential injections of the ¹¹¹In-hMN-14 IgG to illustrate the similarity in targeting for both of these studies. This particular patient had diffuse nodular pulmonary disease, which was not seen on the ¹¹¹In-hMN-14 imaging study, but the multiple bony lesions were targeted and readily apparent within 24 h.

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FIGURE 4.

Anterior and posterior WB images of patient 1831 shows biodistribution of first injection of ¹¹¹In-hMN-14 IgG (top) and ¹¹¹In-hMN-14 IgG given with ⁹⁰Y-hMN-14 IgG injection 1 wk later (bottom).

Organ and Tumor Dosimetry

Table 5 provides the average radiation-absorbed dose for the ¹¹¹In- and ⁹⁰Y-hMN-14 in several of the major organs. Since the 2 methods used in this trial for quantitation of radioactivity provide similar estimates for all organs except the lungs, the radiation-absorbed dose to the lungs is not included in Table 5. The average absorbed dose for ⁹⁰Y-hMN-14 to the lungs using the BFM was 2.78 ± 0.76 mGy/MBq (n = 8; range, 1.84–4.19 mGy/MBq), whereas for the MGMM it was 1.92 ± 0.32 mGy/MBq (n = 5; range, 1.57–2.24 mGy/MBq). The highest dose was delivered to liver and, since CEA-anti-CEA complexes would most likely be transported to the liver, an examination was made to determine if the radiation dose to the liver increased in patients with higher plasma CEA levels. Interestingly, there appeared to be a trend for the predicted absorbed dose to the liver to decrease as CEA increased (Fig. 5), but there was not a significant correlation between the liver dose and plasma CEA (P = 0.132; R² = 0.234), primarily due to the variability in absorbed dose to the liver observed between 100 and 1,000 ng/mL of circulating CEA. However, there was a significant correlation between the effective residence time in the blood and the liver dose (P = 0.002; R² = 0.671), indicating that as the concentration of radioactivity was sustained in the blood, the radiation-absorbed dose to the liver increased. The highest total dose delivered to the organs based on scintigraphy was 963, 2,175, 1,185, and 893 cGy to the red marrow, liver, kidneys, and lungs, respectively. Organ dosimetry derived from the coadministered ¹¹¹In-hMN-14 was generally within 10% of the first ¹¹¹In-hMN-14 injection (n = 3), suggesting that there was not a significant deviation in distribution and clearance of the radioactivity in the organs between the 2 injections.

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FIGURE 5.

Potential factors contributing to radiation-absorbed dose to liver. RT-E = residence time, effective.

Radiation-absorbed doses were calculated in 29 well-defined tumors in 8 patients, using the first ¹¹¹In-hMN-14 injection data. Nearly half of these lesions were in the bone (15/29, with 13 bony lesions in 1 patient). The first ROI generation for tumor dosimetry was possible in 24 of 29 lesions within 24 h, with 5 lesions being clearly delineated within 2–3 h. Interestingly, the maximum effective uptake occurred within 48–72 h in 24 lesions, which indicates that uptake occurred progressively over this time. In fact, the radioactivity concentration in the tumor, as determined from the first ROI to the ROI obtained at the maximum uptake, increased an average of 42% ± 44% (range, 0%–209%). The average estimated radiation dose delivered to the tumor in these 29 tumors was 15.1 ± 10.8 mGy/MBq (55.8 ± 39.8 cGy/mCi) (range, 1.51–47.1 mGy/MBq; median, 11.0 mGy/MBq). The average tumor-to-red marrow, tumor-to-liver, tumor-to-lungs, and tumor-to-kidneys ratios were 15.0 ± 11.0, 5.1 ± 3.6, 6.9 ± 6.1, and 9.0 ± 8.7, respectively. Figure 6A illustrates a trend for the lower radiation doses to tumors of larger size. It was possible to estimate doses to several very small tumors (e.g., ≤5 g) because of the high contrast afforded by the uptake of the antibody, but also the anatomic positioning in less-vascularized regions of the body. Based on the total radioactivity injected, the majority of the tumors received >2,000 cGy, with 7 tumors, ranging in size from 0.7 to 33.5 g, receiving >5,000 cGy and with one 14.1-g bony lesion in the pelvis receiving 14,126 cGy (Fig. 6 B).

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FIGURE 6.

Tumor dosimetry shows distribution of radiation-absorbed dose delivered either on a per MBq basis (A) or total dose (B) based on size of tumor. B also lists total dose in each of 8 patients (4-digit patient numbers) and number of lesions per patient in parentheses.

Dose Escalation and Toxicity

Enrollment started at a dose level of 740 MBq/m². PBSCs were reinfused in this group of patients within 7–8 d of the ⁹⁰Y treatment, and none of the patients developed grade 4 hematologic toxicity. PBSCs were reinfused in the 3 patients receiving 1,110 MBq/m² within 9–10 d. Two patients developed grade 4 leukopenia/neutropenia starting 10 and 13 d after the ⁹⁰Y-hMN-14 IgG, lasting up to 5 d. At the 1,480 MBq/m² dose, PBSCs were reinfused within 9–12 d, and only 1 patient developed grade 4 leukopenia (with only grade 3 neutropenia) starting 12 d after the ⁹⁰Y-hMN-14 IgG, which lasted 4 d. None of these 9 patients developed a nonhematologic DLT.

Escalation proceeded to 1,850 MBq/m², with the first 3 patients all developing grade 4 leukopenia/neutropenia that lasted for up to 9 d, and 1 patient developing grade 4 thrombocytopenia lasting 1 d. PBSCs were reinfused in these patients within 10–12 d of treatment. One of these patients developed grade 4 cardiac toxicity manifested by cardiac tamponade, which required hospitalization and surgery. This patient had a moderate pericardial effusion and significant metastatic mediastinal lymphadenopathy at the baseline CT scans, which may have contributed to this toxicity. Therefore, the protocol was amended to exclude such patients, but only 2 patients were enrolled before closing the trial. One patient developed grade 4 leukopenia/neutropenia that lasted for up to 13 d and grade 4 thrombocytopenia lasting 1 d, but this patient also developed grade 4 shortness of breath and pneumonitis requiring long-term intubation and subsequently tracheostomy. Further analysis by independent medical reviewers of the conditions that led to the grade 4 respiratory toxicity in this patient revealed that multiple factors likely caused this toxicity, including infection, fluid overload, and the possibility that the patient had a central respiratory depression before intubation, secondary to significant doses of narcotics and hypnotics given to control pain. There was no clinical evidence to suggest that he developed radiation pneumonitis that contributed to his respiratory failure, and based on the ¹¹¹In-hMN-14 imaging study, the radiation-absorbed dose to the lungs for the ⁹⁰Y-hMN-14 dose administered was only 799 cGy. Nevertheless, with 2 patients treated at the 1,850 MBq/m² dose level experiencing DLT complications, further enrollment at this dose level was terminated. Thus, the trial was terminated with 1,480 MBq/m² of ⁹⁰Y-hMN-14 IgG when followed 24 h by Dox at the dose used in this protocol declared as the MTD.

Table 6 lists all nonhematologic adverse events recorded during the course of this trial, although several of these were not considered related to the treatment regimen. Many of these toxicities are commonly observed with Dox alone but, because of limited clinical experience with ⁹⁰Y-hMN-14 IgG, particularly at doses ≥1,110 MBq/m², it is not possible to gauge the incidence or severity that might be attributed solely to the ⁹⁰Y-hMN-14 IgG or the extent by which the combination affected the incidence or severity.

The most frequent nonhematologic toxicity observed was GI (n = 14) in the form of nausea (n = 13), vomiting (n = 9), and diarrhea (n = 10). All of these events were transient, with complete recovery in <2 wk, except in 1 patient who continued to have grade 2 vomiting for 19 d and grade 2 nausea for 63 d. There was no correlation between the administered radioactivity and the occurrence, severity, or duration of GI toxicity. Other nonhematologic toxicities included transient grade 1 hepatic toxicity in 3 patients, manifested by transient elevation in liver enzymes. Seven patients experienced grade 1 to grade 2 pulmonary toxicity and another patient had grade 4 pneumonitis that was considered DLT. The grade 1 (n = 2) and grade 2 (n = 5) pulmonary toxicities were manifested by decreases in the forced expiratory volume and/or Dlco (n = 3), or by mild/moderate shortness of breath (n = 4). Eight patients had cardiac toxicities. Four patients had grade 1 or grade 2 asymptomatic decreases in the left vertricular ejection fraction on the follow-up MUGA scan performed at 2–7 mo after treatment. One patient complained of palpitations 1 y after treatment, and another had atrial fibrillation or flutter 5 mo after treatment. A third patient was diagnosed with pleuropericarditis 3 mo after treatment when he was noted to have pericardial rub on cardiac auscultation. The other 2 cardiac events were considered DLTs and were described earlier.

In summary, the hematologic toxicities were moderate to severe, but with the aid of stem cells, all patients engrafted and recovered their blood counts to normal levels within 8–39 d. Cardiopulmonary toxicity was dose limiting at 1,850 MBq/m² and, because of the low incidence of severe toxicities at 1,480 MBq/m², it was chosen as the MTD for this treatment regimen.

HAHA

None of the 15 patients enrolled in the study was positive for HAHA before receiving the first infusion of hMN-14 IgG. Of the 14 patients who received treatment, 13 had at least 8 wk or more follow-up testing, whereas the other patient had testing available for only 4 wk after infusion. Four patients developed a detectable level of HAHA within 8–12 wk of infusion. Three of these met the criteria to be positive by the HPLC assay (29). The other patient was tested by the ELISA method and had a value of 727 ng/mL at week 12. The duration of these responses was not determined.

Antitumor Response

Of the 14 patients who received therapy, one patient was not assessable for tumor response, and another 7 patients showed disease progression on the follow-up CT scans, even though some of these patients had decreases or stabilization of tumor markers for a brief period of time before progressing. Four patients had stable disease on CT scans for 3, 3.5, 6, and 8.5+ mo. All of these patients also had stable tumor markers for at least the duration of the stabilization of the disease on CT scan. Two patients, patients 1779 and 1785, both treated at 740 MBq/m², had minor responses for 27+ and 10 mo, respectively. Circulating tumor markers (calcitonin or CEA) in these 2 patients were also stable for 12 and 10 mo, respectively. One patient (patient 1853), treated at 1,850 MBq/m², presented with multiple lesions in the neck, chest, and liver. Several index lesions decreased by >25% and the serum calcitonin level decreased by 55% (13,118 to 5,900 pg/mL) 1 mo after treatment, with a 62% overall reduction at 3 mo. The initial radiology review suggested that new lesions may have developed at 1 mo, indicating progression, but subsequent review by 3 other radiologists and an oncologist concluded that there were no new lesions and that there was a 68% overall reduction in tumor mass. Since there was no follow-up confirmatory CT scan, this was scored as an unconfirmed partial response. However, follow-up 4 mo after treatment indicated calcitonin and CEA levels had decreased 77% and 60%, respectively, but thereafter they began to increase, and medical notes indicated that the patient had progressed and ultimately died 8 mo after treatment. Figure 7 illustrates the response seen in 2 of the index lesions that were located in the liver. Other lesions in the neck and chest also had similarly significant decreases in their size.

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FIGURE 7.

Patient 1853, a 41-y-old man, presented with widely metastatic MTC in neck, chest, and liver and was treated at a dose of 1,850 MBq/m² with ⁹⁰Y-hMN-14 IgG + 60 mg/m² Dox 1 d later. Two index lesions selected in baseline CT images were in liver. (A and B) Sequential slices that show 1 index lesion as an irregularly shaped tumor in upper portion of left lobe of liver. (C and D) Two slices though lower portion of liver show another very large laterally positioned lesion that was apparent in 11 consecutive 7.0-mm slices. Extent of this lateral lesion can be better appreciated in nuclear images to the right, where its size was estimated to be 234 g. Regions are drawn around baseline lesions, since several tumors were poorly enhanced. Three-month CT scan shows considerable reduction in upper lesion with noticeable reduction and more necrosis in lateral lesion. WB and anterior planar nuclear images (E and G, respectively) taken 6 d after ¹¹¹In-hMN-14 IgG show very high accretion of radioactivity in lateral liver lesion as well as uptake in several other locations throughout liver. (H) Transaxial SPECT view of liver at 48 h also shows intense uptake in lateral lesion. (F) Antibody targeting of what proved to be 5 separate lesions in neck, with a sum of the product of their perpendicular diameters at baseline equaling 9.64 cm², decreasing to a sum of 3.28 cm² at 3 mo (66% reduction).

Dosimetry estimated 2,916 cGy was delivered to the larger (estimated mass size = 234 g) tumor mass in the liver of this patient. The index lesion in the upper portion of the liver was not readily identifiable on planar views and, therefore, radiation-absorbed doses were not determined. In the other patients with soft-tissue masses for whom dosimetry was obtained, there was no trend for lesions receiving higher doses to have any greater evidence of stabilization or reduction in size than those receiving lower doses. Many lesions that were amenable for dosimetry determinations were in the bone, but measures were not taken to assess response of these lesions.