Positive anticalcitonin immunoscintigraphy in patients with medullary thyroid carcinoma.

A cocktail of three monoclonal F(ab')2 fragments against three distinct epitopes of calcitonin or PDN 21 was labelled with either 111In or 131I. These F(ab')2 fragments, a control 125I-F(ab')2 fragment and 99mTc-pertechnetate were injected into four patients suffering from medullary thyroid carcinoma. Scintigraphy data were processed by energy factor analysis for an optimal separation of images corresponding to each isotope. The best tumor detection was obtained 1-3 days after injection of the 111In-F(ab')2 cocktail which clearly labeled the thyroid tumors in the four patients (smallest tumor detected, 0.6 cm) as well as lymph node and bone metastases. In the liver, positive detection was only successful with the 131I-labeled cocktail. These results were confirmed by counting rates of resected specimens which provided average specificity indices ranging from 3.3 to 13.1. Anticalcitonin antibodies could be particularly useful for immunoscintigraphy detection of residual or recurrent medullary thyroid carcinoma in patients with elevated calcitonin serum level.

Physiological studies of human chorionic gonadotropin (hCG), alpha hCG, and beta hCG as measured by specific monoclonal immunoradiometric assays.

Several libraries of monoclonal antibodies have been produced against epitopes that reside on hCG, alpha hCG, and beta hCG. Having characterized them physically, we explored their use in the construction of highly specific and sensitive immunoradiometric assays. There were several important immunochemical considerations with respect to developing assays that accurately detect low levels of free subunits in serum in the presence of high concentrations of the native hormone. These include physical properties and specificities of the monoclonal antibodies, choice of capture antibody on the solid phase support, assay design, and purity of hormone standards. Using such assays, we found early pregnancy (in vitro fertilization) to be characterized by the sequential appearance of hCG, followed by beta hCG and then alpha hCG. Molar ratios of beta hCG to alpha hCG and beta hCG to hCG were highest in early gestation. However, there was a reversal of the beta hCG to alpha hCG ratio at 12-13 weeks gestation, and an excess of free alpha hCG was observed thereafter. Except for values obtained in very early pregnancy, the beta hCG to hCG ratio remained remarkably constant at approximately 0.5% throughout gestation. In contrast, choriocarcinoma was distinguished by absolute serum beta hCG concentrations 3-100 times greater than the maximum values observed during pregnancy and, more importantly, by exceedingly high beta hCG to hCG ratios. For comparison, we studied hCG, alpha hCG, and beta hCG levels in an additional 178 patients with nontrophoblastic tumors. Ectopic production of alpha hCG and beta hCG was rare (3%), and thus far, we have been unable to demonstrate the presence of hCG in such patients. Therefore, hCG and the free subunits appear not to be useful as serological markers for nontrophoblastic tumors.

A new 123I-MIBG whole body scan scoring method--application to the prediction of the response of metastases to induction chemotherapy in stage IV neuroblastoma.

A new semi-quantitative scoring system is proposed, especially designed for the comparative interpretation of sequential whole-body meta-iodo-benzyl-guanidine (MIBG) scans in stage IV neuroblastoma children. This method was applied to assess whether MIBG scan at mid-course of induction chemotherapy could predict the final response. 27 newly diagnosed children were investigated by three sequential 123I-MIBG scans performed at the beginning, at mid-course (6 weeks) and at the end of neoadjuvant chemotherapy (12 weeks). Whole body scans were divided into nine regions in which the extension of bone metastases was separately quoted (score range: 0-3). The overall absolute scores were obtained by adding the scores of the nine regions. Relative scores were calculated by dividing the absolute score at each time by the corresponding pretreatment score. The score at mid-induction correctly predicted the overall response of metastases at the end of induction (P < 0.0001) in most cases. This method is easy to use, reproducible, subject to little inter-investigator variation, and thus well adapted to multicentric trials.

Immunoscintigraphy of Hodgkin's disease: in vivo use of radiolabelled monoclonal antibodies derived from Hodgkin cell lines.

The Hodgkin associated monoclonal antibody (Mab) HRS-1 reacts with Hodgkin and Reed-Sternberg cells (HR-S) in all HD subtypes. HRS-1 Mab was labelled with radioiodine and injected into 10 patients for immunoscintigraphy (IS). Seven patients were injected with HRS-1 Mab radiolabelled with 131I and three patients were injected with HRS-1 Mab labelled with 123I. A control anti-alpha-fetoprotein (anti-AFP) Mab was radiolabelled with another iodine isotope and was injected simultaneously in five cases. Six out of eight patients with proven HD had a true positive scan (nodal, splenic and bony involvement). Imaging was equivocal or failed in the two other patients. In the last two patients IS imaging was truly negative due to the absence of residual HD in one patient and to an erroneous histological diagnosis of HD in another patient. These results, although preliminary, demonstrate that IS with radioiodine-labelled HRS-1 Mab is feasible and may prove to be informative in the staging of HD.

Evaluation of protocols for purification of mouse monoclonal antibodies. Yield and purity in two-dimensional gel electrophoresis.

Protocols for purification of mouse monoclonal antibodies (MAbs) from nude mice ascites were investigated in order to assess the yield and to compare the purified products in two-dimensional gel electrophoresis (2DGE). Three MAbs (one IgG2 and two IgG1), selected for their differing behaviours towards protein A, were purified by ammonium sulphate precipitation and/or gel filtration, anion exchange (DEAE), hydroxylapatite and affinity (protein A) chromatography, or by a combination of these methods. Protein A constantly provided the highest purity whatever the IgG subclass. The best results in terms of yields and purity were a function of the optimization of the protein A protocol. In our study, they were obtained in a 3 h protocol (IgG2), a 16 h protocol with discontinuous pH gradient method (IgG1 with sufficiently high affinity for protein A) or a multi-step protocol involving DEAE and protein A (IgG1 with low affinity for protein A). DEAE chromatography alone provided a slightly better yield, but only moderate purity. Hydroxylapatite chromatography appeared to be less potent in terms of yield, purity and day-to-day reproducibility. Salt precipitation and gel filtration enabled only relative enrichment of the MAb solution. Some degradation products of both heavy and light chains clearly appeared in the 2DGE patterns of antibodies purified by different protocols, and seem to be partly related to the elution pH and to the duration of the purification procedure. Finally, this work highlights considerable heterogeneity not only between two different MAbs of the IgG1 subclass but also within a monoclonal population of immunoglobulins.

Indium-111-pentetreotide scintigraphy in children with neuroblast-derived tumors.

UNLABELLED: The somatostatin analog 111In-pentetreotide was evaluated in 11 children with sympathetic embryonic cell-derived tumors. METHODS: Six neuroblastomas, four ganglioneuroblastomas and one ganglioneuroma (benign) were imaged 4 and 24 hr after injection of 111In-pentetreotide (5 MBq/kg) and 24 hr after administration of 123I-metaiodobenzylguanidine (MIBG) (3.7 MBq/kg). RESULTS: Primary tumor was detected with both tracers in four of the five patients studied before surgery (one Stage III neuroblastoma, one Stage IV neuroblastoma, one Stage IVs neuroblastoma, one ganglioneuroblastoma), but the ganglioneuroma was not localized. Detection of bone marrow metastases was clearly better with 111In-pentetreotide in two patients, similar or slightly better with MIBG in six and (true) negative with both procedures in three. The positivity rate of 111In-pentetreotide for imaging of metastases was higher in undifferentiated malignant tumors (six neuroblastomas: two very positive, three positive, one true-negative) than in histologically well-differentiated tumors (four ganglioneuroblastomas: three weakly positive, one true-negative). All patients with positive 111In-pentetreotide imaging results had elevated urinary catecholamine levels, and the two most 111In-pentetreotide-positive metastases were found in neuroblastomas from children with an aneuploid primary tumor. The 111In-pentetreotide and MIBG results were only partly correlated with bone marrow status, as assessed by immunocytological and histological studies at the time of scanning. CONCLUSION: Abnormalities detected in 111In-pentetreotide uptake were slightly different from those seen with MIBG as a first-line routine method in neuroblast-derived tumors. However, some MIBG as a first-line routine method in neuroblast-derived tumors. However, some MIBG-negative tumor sites were detected by 111In-pentetreotide in patients with neuroblastomas. Thus, 111In-pentetreotide could provide novel information on the biology and prognosis of tumors whose clinical significance remains to be defined.

Increased cytotoxicity of nanoparticle-carried Adriamycin in vitro and potentiation by verapamil and amiodarone.

The cytotoxicities of free cyanoacrylic nanoparticles, free Adriamycin, Adriamycin-loaded nanoparticles and a mixture of Adriamycin and nanoparticles are compared in cancer cell cultures. Increased cytotoxicity was observed in the sensitive (DC3F) subline when Adriamycin was in particulate form rather than free. In the derived pleiotropic resistant subline (DC3F AD/AZA), sensitivity to Adriamycin was completely restored with the conjugate. Addition of verapamil or amiodarone allowed an enhancement of efficiency of tenfold for free Adriamycin and between two- and fourfold for its conjugate form. Vectorization by nanoparticles and pharmacological modulation of cell membrane can act in synergy in synergy to overcome the resistance to Adriamycin in vitro.

Isobutyl cyanoacrylate nanoparticles as a solid phase for an efficient immunoradiometric assay.

The interaction of monoclonal antibodies and seric proteins with cyanoacrylic nanoparticles was investigated. A high binding capacity, rapid kinetics of adsorption as well as a good stability of the linkage were found. Furthermore, the immunoreactivity was conserved after coating antibody to nanoparticles. A new competitive immunoradiometric assay was also proposed for determination of alpha-fetoprotein amounts as low as 0.1 ng per assay.

Radiolabeled monoclonal antibodies against Reed-Sternberg cells for in vivo imaging of Hodgkin's disease by immunoscintigraphy.

The Hodgkin Reed-Sternberg (HRS-1) monoclonal antibody (Mab) was raised against the L 428 Hodgkin's disease (HD) cell line. The HRS-1 Mab was labeled with radioactive iodine and injected into six patients with Hodgkin's disease of varied histological subtypes for immunoscintigraphic imaging. In five patients, the HRS-1 Mab was labeled with 131I; a control anti-alpha-fetoprotein (AFP) Mab was injected simultaneously in two of these five cases. Four of five patients had a positive scan (nodal, splenic and hepatic involvements), the results in the fifth patient being equivocal. In the sixth patient, the HRS-1 Mab was labeled with 123I in order to utilize tomoscintigraphy instead of linear scintigraphy. Although the immunoscintigraphy (IS) was performed secondary to effective chemotherapy, images of bony disease were demonstrated. These preliminary results demonstrate that IS with iodine-labeled HRS-1 Mab is feasible and informative in Hodgkin's lymphoma. The real clinical value and the specificity of IS deserves confirmation in a larger series of patients. Several techniques such as the use of Fab or F(ab')2 fragments should further improve the results.

169Erbium-citrate synoviorthesis after failure of local corticosteroid injections to treat rheumatoid arthritis-affected finger joints.

OBJECTIVES: Intra-articular injection of 169Erbium-citrate (169Er-citrate; radiosynoviorthesis or radiosynovectomy) is an effective local treatment of rheumatic joint diseases. However, its efficacy in corticosteroid-resistant rheumatoid arthritis-affected joints has not been clearly demonstrated. METHODS: A double-blind, randomised, placebo-controlled, international multicentre study was conducted in patients with rheumatoid arthritis with recent (< or = 24 months) ineffective corticosteroid injection(s) into their finger joint(s). Eighty-five finger joints of 44 patients were randomised to receive a single injection of placebo (NaCl 0.9%) or 169Er-citrate. Results of evaluation 6 months later were available for 82 joints (46 metacarpophalangeal and 36 proximal interphalangeal joints) of 42 patients: 39 169Er-citrate-injected joints and 43 placebo-injected joints. Efficacy was assessed using a rating scale for joint pain, swelling and mobility. RESULTS: Intent-to-treat analysis of the results of the 82 joints showed a significant effect of 169Er-citrate compared to placebo for the principal criteria decreased pain or swelling (95 vs 79%; p = 0.038) and decreased pain and swelling (79 vs 47%; p = 0.0024) and for the secondary criteria decreased pain (92 vs 72%; p = 0.017), decreased swelling (82 vs 53%; p = 0.0065) and increased mobility (64 vs 42%; p = 0.036). Per-protocol analysis, excluding 18 joints of patients who markedly changed their usual systemic treatment for arthritis, gave similar percentages of improvement but statistical significance was lower owing the reduced power of the statistical tests. CONCLUSION: These results confirm the clinical efficacy of 169Er-citrate synoviorthesis of rheumatoid arthritis-diseased finger joints after recent failure of intra-articular corticotherapy.

Better results with rhenium-186 radiosynoviorthesis than with cortivazol in rheumatoid arthritis (RA): a two-year follow-up randomized controlled multicentre study.

OBJECTIVE: The aim of this international multicentric randomized phase 3 clinical trial was to compare prospectively radiosynoviorthesis (RSO) with rhenium-186-sulfide (186Re) to intra-articular corticotherapy in patients with clinically controlled rheumatoid arthritis (RA), but in whom one or a few medium-sized joints remained painful or swollen. METHODS: One hundred and twenty-nine joints in 81 RA patients [stratified into 2 groups: wrists (group 1, n = 78) and all the other joints (group 2, n = 51, including 18 elbows, 21 shoulders and 12 ankles)] were randomized to receive intra-articular injections of either 186Re-sulfide (64 +/- 4 MBq), or cortivazol (Altim) 3.75 mg. Clinical assessment was performed before and then at 3, 6, 12, 18 and 24 months after local therapy, using a 4-step verbal rating scale (VRS) and a 100 mm visual analog scale for pain, a 4-step VRS for joint swelling and mobility and a 2-step VRS for the radiological stage. The Mantel-Haenszel test was used for qualitative variables, analysis of variance (ANOVA) for quantitative pain analysis and Kaplan-Meyer survival test for relapse analysis. RESULTS: 186Re was observed to be statistically superior to cortivazol at 18 and 24 months while no statistical difference was seen for any criterion at 3, 6 and 12 months post injection. At 24 months, the difference in favor of 186Re was significant for pain (p = 0.024), joint swelling (p = 0.01), mobility (p = 0.05, non-wrists only), pain and swelling (p = 0.03) and pain or swelling (p = 0.02). "Survival" studies (Kaplan-Meyer) demonstrated a greater relative risk of relapse in corticoid treated joints, but only from the second year of follow-up. No serious side effect was observed in any patient, with only light and transient local pain and/or swelling occurring in 24% of cases, regardless of the treatment used. CONCLUSION: 186Re-sulfide and cortivazol had similar efficacy up to 12 months post-injection, but 186Re became clearly more effective at 18 and 24 months, for all criteria monitored and for RA outcome. Therefore, 186Re RSO can be recommended for routine clinical use.

Physical and biological dosimetry in patients undergoing radiosynoviorthesis with erbium-169 and rhenium-186.

Physical and biological dosimetry were investigated in 45 rheumatoid arthritis patients treated by radiosynoviorthesis (RSO) with 186Re-sulphide (medium-sized joints) and 169Er-citrate (digital joints). Biological dosimetry involved scoring dicentrics in lymphocytes, cultured from blood samples withdrawn just before and 6 h, 24 h and 7 days after treatment. Physical methods included repeated blood sample counts and scintigraphy data. For erbium-169 (pure beta emitter), only bremsstrahlung could be measured and solely in the injection area. For rhenium-186 (both beta and gamma emitter), whole body scans and static images of joints and locoregional lymph nodes were performed. Dosimetry calculations were in accordance with the MIRDOSE 3 software and tables. For erbium-169 (21 patients), either metacarpophalangeal (30 MBq) or proximal interphalangeal (20 MBq) joints of the hands were treated (one joint per patient); 18 patients (out of 21) were interpretable for biological dosimetry, 10 (out of 11) for physical dosimetry and six (out of 10) for both. For rhenium-186, 23 wrists, nine elbows, three shoulders and two ankles were injected in 24 patients, with a maximum of three joints per patient (70 MBq per joint); 20 patients (out of 24) and 10 (out of 10) were interpretable for biological and physical dosimetry, respectively, and eight (out of 10) for both methods. Erbium-169 biological dosimetry was negative in all interpretable patients, and physical dosimetry gave a blood dose of 15 +/- 29 microGy and an effective dose lower than 1 mSv/30 MBq. For rhenium-186, biological results were negative in 16 patients (out of 20), but showed a blood irradiation around 200 mGy in the last four. A significant cumulative increase of dicentrics 7 days after injection (16/10,000 instead of 5/10,000 prior to treatment; p < 0.04) was also noted. Gamma counts gave a blood dose of 23.9 +/- 19.8 mGy/70 MBq and the effective dose was found to be 26.7 +/- 5.1 mGy/70 MBq, i.e. about 380 microGy.MBq-1. Erbium-169 RSO is very safe from both physical and biological dosimetry standpoints. Rhenium-186 leak is greater, as demonstrated by the higher blood activity and the measurable, although limited, dicentrics induction in blood lymphocytes. However, the effective dose remains moderate, i.e. 30 times lower than in 131I therapy in benign thyroid diseases.

[Immunoradionuclide localization of human neuroblastoma xenografted in nude mice using anti-GD2 labelled with I125]. / Localisation immunoscintigraphique de neuroblastomes humains greffés sur souris nude à l'aide d'anticorps anti-GD2 radio-iodés (125I).

Neuroblastoma is the most frequent tumour of the childhood under the age of 5. The staging and the follow up are achieved by MIBG scintigraphy, considered as the method of reference, but sometimes difficult to interpret . The availability of monoclonal antibodies against the ganglioside GD2, expressed on the cell membrane of neuroblastoma and neuro-endocrine cancers offers novel tools that deserve to be carefully explored. We investigated four mouse monoclonal antibodies (3 IgG3: BW704, 7A4, 60C3, and the IgG1 variant of BW704: MAK704), on nude mice xenografted with a human neuroblastoma (REM). Sixty one nude mice were included. The three former MAbs provided tumour imaging, the best results being obtained with BW704, followed by 7A4 and 60C3. MAK704 was disappointing. A control antiphosphorylcholine antibody (P51-1) did not give any tumour image in the three tested mice. Scintigraphy ratios tumour/liver and tumour/muscle reached 20 and 100 with BW704, respectively, on the 10th day. Good imaging quality was already obtained from the 24th h. The tumour uptake, calculated from radioactivity countings of resected samples, reached 22 +/- 3% of injected dose per gramme. These results let us hope that these antibodies could also provide highly contrasted images in humans and could open the way for therapeutic applications.

Could somatostatin scintigraphy be superior to MIBG scan in the staging of stage IVs neuroblastoma (Pepper's syndrome)?

A 4-month-old infant suffering from Stage IVs neuroblastoma (NB IVs; Pepper's syndrome) was repeatedly examined by I-123 MIBG and somatostatin analog in-111 pentetreotide (SMS) scintigraphy, during a 2-year period. Treatment was restricted to surgery of the primary tumor. I-123 MIBG and SMS scan results were positive in the primary tumor and liver, but I-123 MIBG yielded very poor images and failed to reliably detect bone marrow metastases in the lower limbs and skull, whereas SMS precisely visualized these lesions. Six months after diagnosis, the infant was in complete clinical remission. I-123 MIBG and SMS images had returned to normal at 1 year. The prognostic implication of positive SMS imaging, in combination with positive or negative I-123 MIBG scan results, is not known in NB IVs and requires further investigation.

[Monoclonal anti-AFP immunoscintigraphy of human hepatocellular carcinoma. Influence of biological, anatomical and vascular factors]. / Immunoscintigraphie monoclonale anti-AFP du carcinome hépatocellulaire humain. Influence des facteurs biologiques, anatomiques et vasculaires.

The actual interest of immunoscintigraphy for the detection of alphafetoprotein-producing liver tumors was investigated by both visual examination and quantitative analysis in 61 patients with either hepatocellular carcinoma (39 patients, group I), secondary liver cancer (11 patients, group II), or non tumoral liver (9 cirrhosis, 2 healthy liver, group III): All patients received injections of 123I-anti-alphafoetoprotein monoclonal antibodies and planar scans were performed after 28 hours. Only 18 out of 39 hepatocellular carcinoma-bearing patients had a positive scan (46 p. 100). Such a moderate sensibility was due to a striking inhibitory influence of cirrhosis: the positivity rate was 6/24 and 12/15 respectively when hepatocellular carcinoma was and was not associated with cirrhosis (p less than 0.01). Specificity was also moderate (55 p. 100) for detection of hepatocellular carcinoma in tumor-bearing patients (group I and II). In the absence of cirrhosis, the intensity of the tumoral uptake was highly correlated with high serum alphafoetoprotein level (p less than 0.001) and tumor arterial hypervascularization (p less than 0.01). Anti-alphafoetoprotein monoclonal antibody uptake by the extratumoral liver was found to be very specific of hepatocellular carcinoma since it was high in 23 out of 39 patients of group I but in only 1 out of 22 in groups II and III (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute renal toxicity of doxorubicin (adriamycin)-loaded cyanoacrylate nanoparticles.

Acute doxorubicin-loaded nanoparticle (DXNP) renal toxicity was explored in both normal rats and rats with experimental glomerulonephritis. In normal rats, 2/6 rats given free doxorubicin (DX) (5 mg/kg) died within one week, whereas all control animals and all rats having received free NP or DXNP survived. A 3 times higher proteinuria appeared in animals treated with DXNP than in those treated with DX. Free NP did not provoke any proteinuria. Two hr post-injection, DXNP was 2.7 times more concentrated in kidneys than free DX (p < 0.025). In rats with immune experimental glomerulonephritis, 5/6 rats given DX died within 7 days, in contrast to animals treated by DXNP, NP, or untreated, which all survived. Proteinuria appeared in all series, but was 2-5 times more intense (p > 0.001) and prolonged after doxorubicin treatment (400-700 mg/day), without significant difference between DXNP and DX. Rats treated by unloaded NP behaved as controls. These results demonstrate that, in these experimental conditions, DXNP killed less animals than free DX, despite of an enhanced renal toxicity of the former. Both effects (better survival and nephrosis) are most probably related to an enhanced capture of DXNP by cells of the mononuclear phagocyte system, including mesangial cells.

Strong uptake of 111In-pentetreotide by an MIBG-negative, xenografted neuroblastoma.

We investigated the distribution of 111In-pentetreotide (Octreoscan, Mallinckrodt) in nude mice xenografted with a human neuroblastoma cell line (SKLAN, derived from the LAN1 line). These cells develop into solid tumours in nude mice and can be grafted repeatedly in grafts of 10(8) cells. Animals were sequentially explored by scintigraphy 2, 4, 24 and 48 hr after i.v. injection of 2.5-4 MBq of the tracer and killed at various times up to 48 hr. 111In-pentetreotide was rapidly and strongly taken up by all tumours, with a tumour/muscle (T/M) ratio on resected samples of 20.0 +/- 5.7 at 2 hr, 23.7 +/- 3.0 at 4 hr, 75.6 +/- 12.6 at 24 hr and 78.7 +/- 12.4 at 48 hr, for tumours ranging from 0.5 to 8 g. Scintigraphy results were quantitatively in agreement. Pre-injection of a 15-20 times larger quantity of unlabelled octreotide s.c. reduced the tumour uptake by a factor of 2. For comparison, nude mice xenografted with the same cell line were also studied with 123I-MIBG (4 MBq). At 24 hr, the T/M ratio was 0.62 +/- 0.18. Two other cell lines (glioblastoma ROM and small-cell lung carcinoma SC41) which were similarly tested with 111In-pentetreotide (2.5-4 MBq) gave T/M ratios at 24 hr of 4.8 +/- 2.8 and 38.4 +/- 21.8, respectively. Pentetreotide seems to have a high affinity for this MIBG-negative neuroblastoma cell line, which exhibited a clearly higher tumour uptake than the 2 other lines. This work provides new experimental arguments in favour of the particular interest of somatostatin analogues in neuroblastoma and confirms our first clinical results.

Significant variation in mouse-skin aryl hydrocarbon hydroxylase inducibility as a function of the hair growth cycle.

An easy, rapid and improved technique for homogenizing whole skin is described. This technique consists of reducing skin to a powder in liquid N2 by using a metallic mortar, and homogenizing the powder in a Potter-Elvehjem tube. Using this homogenizing method, we have shown that skin AHH activity in C57BL/6K and C3H/Ico mice can be induced by i.p. injected or topically applied methylcholanthrene during a defined period of the hair growth cycle, i.e. between the 8th and 14th days after depilation (Stage 6 of the anagen period). In each experimental model, there is an optimal methylcholanthrene concentration which yields a maximum induction. Topical methylcholanthrene is also responsible for a smaller aryl hydrocarbon hydroxylase (AHH) induction when the chemical is applied the same day that the club hairs are plucked. On the other hand, skin AHH activity is never induced by methylcholanthrene in DBA/2J mice, a genetically non-responsive strain. No clear-cut segregation of skin AHH inducibility levels is found among the offspring from the back-cross between (C57BL/6J X DBA/2J)F1 and non-inducible DBA/2J mice.