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Session IV: CLINICAL STUDIES: SOLID TUMORS |
Departments of Otolaryngology/Head and Neck Surgery [P. K. E. B., D. R. C., R. d. B., G. B. S., G. A. M. S. v. D.] and Nuclear Medicine [J. C. R.], VU University Medical Center, 1081 HV Amsterdam, the Netherlands; Departments of Nuclear Medicine [E. J. P., W. J. G. O.] and Otolaryngology/Head and Neck Surgery [H. A. M. M.], UMC Nijmegen, 6500 HB Nijmegen, the Netherlands; Boehringer Ingelheim bv, 1802 KA Alkmaar, the Netherlands [M. H. v. S.]; and Boehringer Ingelheim Pharma KG, 88397 Biberach an der Riss, Germany [G. S.]
| ABSTRACT |
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Experimental Design: Twenty patients with inoperable recurrent and/or metastatic head and neck squamous cell carcinoma received a single dose of 186Re-labeled BIWA 4 in radiation dose-escalation steps of 20, 30, 40, 50, and 60 mCi/m2. Three patients received a second dose at least 3 months after the initial dose. After each administration, whole-body images as well as planar and tomographic images of the head and neck region were obtained, and the pharmacokinetics and the development of human antihuman antibody responses were determined. Radiation absorbed doses were calculated for whole body, red marrow, organs, and tumor.
Results: First and second administrations were all well tolerated, and targeting of tumor lesions proved to be excellent. The only significant manifestations of toxicity were dose-limiting myelotoxicity consisting of thrombo- and leukocytopenia and, to a lesser extent, oral mucositis (grade 2). Grade 4 myelotoxicity was seen in two patients treated with 60 mCi/m2. The MTD was established at 50 mCi/m2, at which level dose-limiting myelotoxicity was seen in one of six patients. Stable disease, varying between 6 and 21 weeks, was observed in three of six patients treated at the MTD level. The median tumor dose, recalculated to MTD level, was 12.4 Gy. The absorbed dose in red marrow was 1.82 ± 0.11 cGy/mCi for males and 2.35 ± 0.10 for females. Two patients experienced a human antihuman antibody response. Pharmacokinetics showed consistency across patients and within the three patients receiving 186Re-BIWA 4 on two occasions.
Conclusions: This study shows that 186Re-labeled BIWA 4 can safely be administered, also in a repeated way. The MTD was established at 50 mCi/m2. In comparison with the previously described anti-CD44v6 MAb U36, the humanized MAb BIWA 4 seems to be less immunogenic. The fact that antitumor effects were seen in incurable patients with bulky disease justifies the evaluation of RIT with 186Re-labeled BIWA 4 in an adjuvant setting.
| Introduction |
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Selective targeting of radionuclides to HNSCC by use of MAbs as in RIT might contribute to a more effective treatment of advanced-stage disease. Because HNSCC is relatively radiosensitive compared with other solid tumors, RIT can become a realistic option. To date, most successes in the field of RIT have been achieved in patients with hematological malignancies, such as non-Hodgkins lymphomas, where high rates of partial and complete responses have been observed (8) . In the treatment of B-cell non-Hodgkins lymphoma, most experience has been gained with iodine-131- and yttrium-90-labeled anti-CD20 MAbs such as tositumomab and ibritumomab, respectively (9, 10, 11, 12, 13) .
These successes have motivated us to explore the additional value of RIT against HNSCC. In the selection of a suitable target antigen in HNSCC, CD44 splice variants containing the v6 domain appeared to be the most promising thus far. The CD44 protein family consists of isoforms, encoded by standard exons and up to nine alternatively spliced variant exons (v2v10), which are expressed in a tissue-specific way and involved in physiological functions such as signal transduction, growth factor binding, cell adhesion, and cell migration. Expression of v6-containing CD44 variants has been related to aggressive behavior of various tumor types and was shown to be particularly high and homogeneous on the outer cell surface of HNSCC (14 , 15) .
In the past decade, the development of CD44v6-directed RIT in HNSCC has shown encouraging progress. For this purpose, two mMAbs became available, designated mMAb U36 and mMAb BIWA 1. Although BIWA 1 resembles U36, it binds to a different epitope with a 35-fold higher affinity (16) . According to the numbering of Kugelman et al. (17) , the epitope recognized by BIWA 1 consists of amino acids 360370, and the epitope recognized by MAb U36 consists of amino acids 365376.
Biodistribution studies with radiolabeled MAbs U36 and BIWA 1 in HNSCC patients undergoing surgery showed promising biodistribution patterns with selective tumor targeting and high tumor uptake for both MAbs (18 , 19) . Unfortunately, administration of BIWA 1 resulted in HAMA responses in 11 of 12 patients (19) , a problem also observed after injection of mMAb U36, although to a lesser extent (18) .
Subsequent Phase I RIT studies with chimeric (human/mouse) MAb U36 showed favorable targeting and (although not a primary objective) promising antitumor effects (20 , 21) . However, chimerization of MAb U36 had not resulted in a decrease of the immunogenicity because 5 of 12 patients showed development of HACAs (20) . Formation of HAMA or HACA should be eliminated to prevent allergic reactions and rapid clearance of the radioimmunoconjugate, especially when multiple administrations of the radioimmunoconjugate are anticipated. The engineering of hMAbs, being almost completely human apart from a small part of the antigen-binding sites, became the next approach to deal with this problem. In several studies, hMAbs showed excellent tumor targeting in combination with low or no immunogenicity (22 , 23) .
To reduce immunogenicity, two humanized BIWA versions were developed, called BIWA 4 and BIWA 8. The intermediate-affinity MAb BIWA 4 was selected for further clinical evaluation rather than the high-affinity MAb BIWA 8 because of its superior tumor targeting in HNSCC-bearing nude mice (16) .
In the present study, RIT with 186Re-labeled hMAb BIWA 4 was evaluated in 20 head and neck cancer patients with regard to safety, MTD, pharmacokinetics, immunogenicity, and preliminary therapeutic potential. Three of these patients received a second dose, which was the same or slightly different from the first dose.
| Materials and Methods |
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hMAb BIWA 4 (Bivatuzumab) and the v6 Domain of CD44.
mMAb BIWA 1 (Boehringer Ingelheim, Vienna, Austria), the parental MAb of BIWA 4, was generated by immunizing BALB/c mice with glutathione S-transferase fusion protein containing the human CD44 domains v3v10 (14)
. The epitope recognized by BIWA 1 has been mapped to the v6 domain of CD44. Homogenous expression of v6-containing CD44 isoforms has been observed in squamous cell carcinoma of the head and neck, lung, skin, esophagus, and cervix, whereas heterogeneous expression was found in adenocarcinomas of the breast, lung, colon, pancreas, and stomach. In normal tissues, expression has been found in epithelial tissues such as skin, breast, and prostate myoepithelium and bronchial epithelium (24)
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Generation, production, and characterization of BIWA 4 have been described previously (16)
. In short, mRNA was isolated from the BIWA 1 hybridoma cell line (Boehringer Ingelheim) using the QuickPrep mRNA Purification Kit (Pharmacia, Uppsala, Sweden). cDNA from heavy and light chain variable regions was generated by reverse transcription-PCR. Fragments were cloned into the TA cloning vector pCR II (Invitrogen, Groningen, the Netherlands) and sequenced. Two expression vectors derived from the plasmid pAD CMV1 (25)
were constructed, carrying the constant regions of human
-1 and of the human
light chain, respectively. Subsequently humanized versions of the BIWA 1 heavy and light chain variable regions (generated by CDR grafting) were cloned in front of the immunoglobulin constant regions of the above-mentioned expression vectors, resulting in the hMAb BIWA 4.
BIWA 4 was stably expressed in Chinese hamster ovary cells, whereas high producers were selected as described previously (16) . Cultivation was performed in proprietary serum-free medium TH-7 (Boehringer Ingelheim, Biberach an der Riss, Germany). Bulk substance from fermentation runs (titer after harvest, 90 mg/liter) was purified according to a generic downstream process for MAbs consisting of ultra/diafiltration, affinity chromatography on protein A-Sepharose, microwave treatment at 80°C, nanofiltration, ultra/diafiltration, anion exchange chromatography on Q-Sepharose, and ultra/diafiltration. The bulk substance was formulated in PBS (pH 7.4) containing 0.02% Tween 20, filter sterilized, and dispensed aseptically into vials. Each vial contained 5 ml of BIWA 4 at a concentration of 5 mg/ml.
Radiolabeling and Quality Controls.
For coupling of 186Re to BIWA 4, the chelate MAG3 was used as described previously (26)
. 186Re and MAG3 were obtained from Mallinckrodt, Inc. (Petten, the Netherlands). The mean specific activity of 186Re at the time of labeling was 0.31 ± 0.07 mCi/nmol. After synthesis of 186Re-MAG3, an esterification with tetrafluorophenol was performed. Subsequently, the ester was purified and conjugated to BIWA 4. Radiolabeled BIWA 4 was purified on a PD10 column (Pharmacia-Biotech, Woerden, the Netherlands) with 0.9% NaCl containing 5 mg/ml ascorbic acid (pH 5) as the eluent. Finally, the conjugates were filter sterilized. These procedures result in a sterile final product with endotoxin levels of <5 endotoxin units per ml, as demonstrated in five preceding validation runs. The molar ratio of 186Re-MAG3 to BIWA 4 was always <4. The radiochemical purity of the conjugates as assessed by high-performance liquid chromatography and thin-layer chromatography was always >95% (mean, 98 ± 1.3%). After each preparation of 186Re-BIWA 4, the immunoreactivity was determined by measuring binding to 0.1% paraformaldehyde-fixed cells of the HNSCC cell line UM-SCC-11B as described previously (16)
. The immunoreactive fraction of the 186Re-BIWA 4 preparations, as determined by a modified Lineweaver-Burk plot, ranged from 81% to 100% (mean, 90 ± 6.9%).
Prestudy Screening and Radiological Assessment.
The medical history and physical condition of all patients were examined, and routine laboratory analyses were performed, including complete blood cell counts, serum electrolytes, urine sediment, liver enzymes, and renal and thyroid functions. An electrocardiogram and a radiograph of the thorax were obtained. For all patients with locoregional tumor recurrence, a CT and/or MRI scan of the head and neck region was performed before treatment as has been described previously (18)
, and in cases with distant metastases, a CT scan of the region of interest was obtained. CT and/or MRI scans were also obtained at 6 weeks after administration for evaluation of RIT efficacy. To this end, perpendicular diameters of tumors were assessed by an experienced radiologist in both centers. In case of stable disease, follow-up assessments were, if possible, performed every 4 weeks.
For dosimetry, tumor volume was assessed by drawing regions of interest on consecutive CT or MRI slices with a VoxelQ system (Picker International, Highland Heights, OH), as described previously (20) . This system enables three-dimensional reconstruction and automated volume calculation.
Study Design.
RIT was performed with a starting activity dose of 20 mCi/m2, followed by escalation with 10-mCi/m2 increments of 186Re-labeled BIWA 4. All patients received 50 mg of BIWA 4, a dose that was found to result in optimal tumor uptake and tumor:nontumor ratios in a preceding MAb dose-finding study in which doses of 25, 50, and 100 mg BIWA 4 were evaluated (27)
. A complete pretreatment assessment was performed before the study, and blood samples were taken for pharmacokinetic analyses. Monitoring of vital functions (blood pressure, pulse rate, temperature, and breathing rate) was performed at the screening visit; before infusion; at 10, 60, 120, and 240 min after infusion; and 6 weeks after infusion. Patients who developed an objective response or stable disease after the first dose of 186Re-BIWA 4 were eligible for a second administration. They underwent the same visit schedule as for the first administration. As a safety precaution, all repeated administrations were conducted at least 3 months after the first administration, and the same inclusion/exclusion criteria were used as for the first dose.
Safety.
After treatment, patients were admitted for approximately 21 h in a special treatment room at the Department of Nuclear Medicine, and thereafter they stayed an additional 3 days in a single room at the Department of Otolaryngology/Head and Neck Surgery. Dose rates (in µSv/h) were measured 1 h after administration at a distance of 100 cm with a
-radiation dose rate counter [at VU University Medical Center, Berthold LB 1230 (EG&G, Wildbad, Germany); at UMC Nijmegen, Automess 6150 AD 2 (Automess GmbH, Ladenburg, Germany)]. The patients were discharged 4 days after administration of 186Re-BIWA 4, and the set of pretreatment laboratory analyses was repeated weekly for at least 6 weeks. The severity of toxicities was graded according to the National Cancer Institute CTC, version 2.0. The MTD was defined as the dose level at which grade 4 hematological or grade 3 nonhematological toxicity developed in not more than one of six patients.
Tumor Response.
Tumor response was assessed according to the WHO guidelines using physical examination or radiographic criteria. Stable disease was defined as a decrease of <50% or an increase of <25% of the sum of the perpendicular diameter products and no appearance of new lesions, which had to persist for at least 4 weeks. Progression was defined as a
25% increase in the size of one or more lesions or the appearance of a new lesion.
Imaging Studies.
Simultaneously acquired planar anterior and posterior whole-body scans were obtained within 1 h after administration of the radioimmunoconjugate; 21, 48, 72, and 144 h after administration of the radioimmunoconjugate; and, if feasible, for up to 2 weeks after administration of the radioimmunoconjugate. For all scintigraphic studies, a large field-of-view gamma camera [at VU University Medical Center, Dual Head Genesys Imaging System (ADAC Laboratories, Milpitas, CA); at UMC Nijmegen, Siemens Multispect 2 (Siemens, Erlangen, Germany)] equipped with low-energy high-resolution parallel-hole collimators and connected to a computer system [at VU University Medical Center, Pegasys (ADAC Laboratories); at UMC Nijmegen, ICON version 7.1 (Siemens)] was used. Camera quality control was performed at each imaging session. With the aliquot retained from the radioimmunoconjugate preparation for injection, a weighed dilution of the injected patient dose was prepared as standard, put in an Adams phantom, and measured simultaneously during whole-body imaging. Lateral, anterior, and posterior planar images of the head and neck region were acquired at 21, 48, 72, and 144 h. SPECT images were acquired at 72 h. Acquisition parameters for planar and SPECT images were as described previously (18)
, with a Hanning filter used for postfiltering (cutoff at 1 cycle/cm). In each of the study centers, all images were interpreted by one experienced examiner, who was unaware of the site of recurrence and/or the presence of distant metastases.
Dosimetry.
Dosimetry to assess dose delivery to whole body, bone marrow, organs, and tumor was performed as described previously (20)
. Patients 5 and 17 were excluded from dosimetric analysis due to insufficient data. In short, whole-body scintigraphy was used to draw regions around organs and sites of interest. Residence times in these organs and sites were calculated and entered in the MIRDOSE3 computer program, version 3.1 (Oak Ridge Associated Universities, Oak Ridge, TN). If CT/MRI scanning before treatment with 186Re-BIWA 4 showed a measurable tumor lesion, and if this lesion was visible on scintigraphy after RIT, dosimetry of the tumor was performed. The red marrow dose was calculated using a blood-derived method as described previously (20
, 28)
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Pharmacokinetics.
Serial blood samples were taken from a peripheral vein of the arm opposite to the infusion site at the following time points: preinfusion; at the end of the infusion; and at 5 and 30 min and 1, 2, 4, 16, 21, 48, 72, and 144 h after administration of 186Re-BIWA 4. Preliminary results obtained from the first four patients showed that blood sampling at additional time points in the second week after administration would improve the characterization of the 186Re-BIWA 4 pharmacokinetics. Therefore, for patients 520, blood samples were also taken at 240 and 336 h after administration. Plasma samples were prepared for determination of the concentration of immunoreactive BIWA 4 by validated ELISA methods, essentially as described previously (19)
. In this sandwich-type ELISA, microtiter plates were absorptively coated with the fusion protein GST-CD44v6. In a first step, BIWA 4 in the plasma sample bound to the immobilized antigen CD44v6. After incubation, unbound BIWA 4 and plasma components were removed by washing. In a second step, rabbit antihuman IgG labeled with horseradish peroxidase (DAKO, Copenhagen, Denmark) was used for detection of bound BIWA 4, and tetramethyl-benzidine (Kirkegaard & Perry, Gaithersburg, MD) was used for detection of enzyme activity.
In addition, whole-blood and serum samples were prepared and counted in a gamma counter [at VU University Medical Center, 1470 Wizard (Wallac, Turku, Finland); at UMC Nijmegen, 1480 Wizard (Wallac)], and radioactivity levels were expressed as %ID/kg. Background activity and decay were corrected for, and the %ID/kg was determined by comparison with an aliquot retained from the conjugate preparation for injection.
Human Anti-BIWA 4 Response.
Evaluation of the immunogenicity of the BIWA 4 radioimmunoconjugate was conducted by determination of human anti-hMAbs in serum samples taken before administration of 186Re-BIWA 4 and 1 and 6 weeks after administration, using a validated bridging ELISA. In short, BIWA 4 antibodies labeled with the chelator MAG3 were immobilized onto microtiter plates. Antibodies to BIWA 4-MAG3 present in the serum sample bound simultaneously to the solid phase and to biotinylated BIWA 4-MAG3 that was added at the same time in a fixed amount. Streptavidin coupled to horseradish peroxidase (Boehringer Mannheim, Mannheim, Germany) was used for signal generation by the peroxidase/tetramethyl-benzidine system. Due to the lack of a positive human anti-BIWA 4 serum, which would be desirable as a standard, the validation of the present assay was done with a rabbit antiserum from an animal that was previously immunized with nonradioactive 185Re-MAG3-BIWA 4. The assay only enabled the relative measurement of the HAHA titer in equivalents of the anti-BIWA 4 titer of the reference rabbit serum. For an easier handling of data, the dilution factors of the rabbit reference serum were converted into Boehringer Ingelheim titer units. The titer unit was defined as dilution of the rabbit reference serum (1:x) multiplied by 18,000. Assay performance during the study was assessed by back-calculation of calibration standards, tabulation of the standard curve fit function parameters, measurement of quality control samples, and construction of a precision profile. Triplicate determinations in three randomly assigned wells of a microtiter plate were used for unknown samples, calibration standards, and quality controls. The lower and upper limits of determination of the assay were 0.180 and 60 Boehringer Ingelheim titer units (1:100,000 to 1:300 dilution of the rabbit reference serum). A serum sample was considered HAHA positive only if all of the following criteria were met: (a) the measured titer was above the lower limit of determination/quantification; (b) the titer in the postinjection sample was at least two times higher than that in the preinjection sample; (c) the sample could be serially diluted with a strong correlation between titer and dilution factor; (d) the titer could be blocked by addition of BIWA 4; and (e) the titer could not be blocked by a nonspecific IgG MAb.
| Results |
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Febrile neutropenia occurred in patients 13 and 16 (both CTC grade 3) and in patient 17 (CTC grade 4), all of whom were treated at the 60-mCi/m2 dose level. All three patients received empirical antibiotic and antimycotic treatment until WBC counts had recovered and the patients were afebrile. CTC grade 3 fatigue occurred in patient 17 at approximately 4 weeks after administration of 60 mCi/m2 186Re-BIWA 4. The fatigue was most likely related to the aggravation of the pre-existing anemia. Main nonhematological toxicity consisted of mild (maximum CTC grade 2) mucositis (Fig. 1)
in two of the six patients treated at the 50-mCi/m2 dose level and in three of the five patients treated at the 60-mCi/m2 dose level. This form of toxicity is most likely drug related because the CD44v6 target antigen is known to be expressed in normal mucosa. The mucositis usually started 12 weeks after administration of the conjugate and disappeared 2 weeks after onset. Most other toxicity was not related to the conjugate, except for reversible loss of taste in one patient, observed after both injections of 186Re-BIWA 4.
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Hematological Toxicity.
The bone marrow appeared to be the dose-limiting organ. A significant decrease of platelet and WBC counts was observed for patients treated at the highest dose levels, with a nadir of 45 weeks after injection of the conjugate (Fig. 2)
. Hematological dose-limiting toxicity defined as drug-related CTC grade 4 was reported in three patients (Table 2)
. Reversible CTC grade 4 leukocytopenia and granulocytopenia were observed in two patients (patients 13 and 17) treated at 60 mCi/m2, at 4 and 5 weeks after injection, respectively. In addition, the anemia present before entering the study worsened slowly in patient 17 and finally resulted in a CTC grade 4 anemia, which was treated with blood transfusions. Reversible CTC grade 4 thrombocytopenia and grade 4 leukocytopenia were observed in one patient (patient 18) treated at 50 mCi/m2, who received concomitant treatment with methotrexate for rheumatoid arthritis. Clinical symptoms of thrombocytopenia in this patient consisted of mild petechiae. Patient received a total of two pooled donor units of platelets on day care basis. All three patients with grade 4 hematological toxicity received antibiotic and antimycotic treatment until WBC counts had recovered and the patient was afebrile. MTD was established at 50 mCi/m2. Nadirs of each individual patient are listed in Table 2
. Drug-related thrombocytopenia and leukocytopenia occurred about 21 days after start of RIT, and the patients started recovering from these conditions before 6 weeks postinjection.
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Human Anti-BIWA 4 Response.
HAHA analyses were evaluable for all patients. Two of the 20 patients (patients 10 and 17) showed a HAHA response (Table 3)
. For both patients, the titer of the week 6 sample was elevated and regarded as HAHA positive.
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Three of the six patients (patients 10, 11, and 12) treated with 50 mCi/m2 186Re-BIWA 4 developed stable disease after the first administration (Table 4)
. As a result, patients 11 and 12 received a second administration, and progressive disease was observed after a total of 18 weeks (patient 11) and 21 weeks (patient 12) after first administration of the trial drug.
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The overall time to progression for patients who did not respond to therapy ranged from 0 to 55 days, with a mean of about 56 weeks, irrespective of the treatment group. The survival time of the patients who did not obtain stable disease upon 186Re-BIWA 4 treatment ranged from 21 to 219 days. For the four patients with stable disease, the survival time ranged from 217 to 403 days.
| Discussion |
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Of great importance is the low immunogenicity of this humanized MAb directed against the CD44v6 antigen. Ten percent of the patients treated in the present study developed HAHAs. In the meantime, 28 more patients have been treated with 25100 mg of radiolabeled BIWA 4 in three parallel radioimmunoscintigraphy/biodistribution studies with HNSCC, non-small cell lung cancer, and breast cancer patients. HAHA responses were observed in none of these patients, resulting in an overall HAHA response rate of 4% for all four studies. This is considerably lower than the 40% HACAs as found with the cMAb U36 (20) and the 90% HAMAs as found with the parental mMAb BIWA 1 (19) . None of the three patients who received a second administration developed HAHAs, which illustrates the possibility for repeated treatment with BIWA 4.
Humanization of other MAbs has been performed with variable success. For instance, hMAb M195 elicited no immune response in a study group of 14 patients (23) , compared with 37% HAMAs found with mMAb M195 (29) . Furthermore, hMAb BrE-3 showed 14% HAHAs (22) , compared with mMAb BrE-3, which showed immunogenicity in 46.7% (30) and 83% (31) , respectively. On the other hand, hMAb A33 elicited HAHAs in 26 of 41 patients (32) . Although significantly lower as compared with its parental mMAb A33, for which HAMAs were found in all treated patients (33) , this example illustrates that humanization does not always solve the problem of immunogenicity.
A secondary objective in this Phase I study was to determine the therapeutic effects of RIT with 186Re-BIWA 4. Stabilization of tumor growth was observed in three of six patients treated at the MTD level, with durations ranging from 6 to 21 weeks. This is consistent with efficacy results obtained in previous Phase I RIT trials with 186Re-cMAb U36. In a first Phase I trial with 186Re-cMAb U36, stable disease was observed in one of six patients treated at MTD. In a second Phase I trial with 186Re-cMAb U36, reinfusion of granulocyte colony-stimulating factor-stimulated unprocessed whole blood was used to reduce myelotoxicity and to increase the MTD (21) . In this procedure, granulocyte colony-stimulating factor is administered s.c. at home during 5 days before the start of RIT. On day 0, just before administration of 186Re-labeled MAb, 1 liter of whole blood is harvested and kept unprocessed at 4°C until reinfusion after 72 h. Indeed, by using this facile procedure, the administered dose could be increased from 27 to 54 mCi/m2, without exceeding grade 3 myelotoxicity and grade 2 mucositis. In this particular study, stable disease was observed in five of nine patients, for a period ranging from 3 to 7 months. All three patients treated at the highest dose level showed stable disease. Whether such a procedure for further dose escalation is also applicable for 186Re-BIWA 4 remains to be established. It might well be that a second dose-limiting toxicity, most probably mucositis, will become manifest. Furthermore, it has to be considered that all HNSCC patients included in the Phase I RIT trials described above had a history of external beam irradiation, which had caused severe mucositis in some of the patients.
The observation of antitumor effects in patients with bulky disease offers opportunities for further development of RIT with single or multiple doses of 186Re-labeled BIWA 4 in an adjuvant setting. The tumor absorbed doses, recalculated to MTD level, ranged from 3.8 to 76.4 Gy, whereas the median absorbed dose was 12.4 Gy. The tumor with the highest absorbed dose of 76.4 Gy appeared to be a small lesion of 5.1 cm3, which remained stable in size upon RIT (patient 10). It is unlikely that antitumor effects are caused by immune modulating effects because BIWA 4 lacks antibody-dependent cell-mediated cytotoxicity or complement-dependent cytotoxicity-mediating activity in vitro. Recently, we reported on the relationship between HNSCC size and MAb accumulation (34) . Data for this report were obtained from several radioimmunoscintigraphy and biodistribution studies with the anti-HNSCC MAbs E48 and U36 in HNSCC patients. MAb uptake in small-volume tumors (1 cm3) was approximately 4 times higher than uptake in tumors with a large volume (>50 cm3). Therefore, in our view, these data justify evaluation of RIT with 186Re-BIWA 4 as a systemic adjuvant treatment.
In conclusion, this study shows that RIT with 186Re-BIWA 4 is safe. By using BIWA 4, a humanized anti-CD44v6 MAb, the rate of HAHA responses was reduced to a minimum, and repeated administrations appeared possible. The MTD was established at 50 mCi/m2, at which dose level stabilization of disease was observed in three of six inoperable HNSCC patients with bulky disease. The application of RIT with 186Re-BIWA 4 therefore holds promise, especially in an adjuvant setting.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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2 To whom requests for reprints should be addressed, at Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, the Netherlands. Phone: 31-20-4440953; Fax: 31-20-4443688; E-mail: gams.vandongen{at}vumc.nl ![]()
3 The abbreviations used are: HNSCC, head and neck squamous cell carcinoma; RIT, radioimmunotherapy; MAb, monoclonal antibody; mMAb, murine MAb; cMAb, chimeric MAb; hMAb, humanized MAb; MTD, maximum tolerated dose; HAMA, human antimouse antibody; HACA, human antichimeric antibody; HAHA, human antihuman antibody; SPECT, single photon emission computed tomography; CT, computed tomography; MRI, magnetic resonance imaging; MAG3, S-benzoylmercaptoacetyltriglycine; %ID/kg, percentage of injected dose/kilogram; CTC, Common Toxicity Criteria. ![]()
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