Chronic vaccination with a therapeutic EGF-based cancer vaccine: a review of patients receiving long lasting treatment

Therapeutic vaccines continue to be one of the most active fields in cancer research. However, despite clear evidence of antitumor effect in laboratory animals, and despite the ability of current vaccine candidates to elicit tumor specific antibodies and T-cells in humans, objective responses in the clinical trials are rare. The role of therapeutic vaccines in advanced cancer patients, if any, would be to decrease the rate of disease progression and to increase survival and quality of life. Due to the redundant regulatory loops contracting the immune response to antigens that cannot be eliminated, such a role would require chronic vaccination, which is at first sight at odds with the classic experience of vaccinology. During the last decade our team has been developing a therapeutic vaccine for advanced lung cancer, which consists in human recombinant Epidermal Growth Factor (EGF) chemically conjugated to a carrier protein from Neisseria meningitides. Several clinical trials have been carried out, showing increase in anti-EGF antibody titters, decrease in plasma EGF concentration and survival advantage in vaccinated patients. In the present paper we review data from 58 patients who were vaccinated monthly for more than one or two years. Long term vaccination was feasible and safe, and there was no evidence of cumulative toxicity. Patients kept high anti-EGF antibody titters during all the time of vaccination, without evidence of immune response exhaustion. Continued vaccination increased the probability to get a high antibody response, which has been previously shown to be, in turn, associated with a better survival. Observations done in this series of patients suggest that long term therapeutic vaccination is a feasible strategy, worth to be further explored in the aim of transforming advanced cancer into a chronic disease.

Cancer vaccines for hormone/growth factor immune deprivation: a feasible approach for cancer treatment

One of the older and most validated cancer treatments is endocrine therapy. Some tumors are dependent on hormone stimulation for growth, and therefore therapeutic interventions aiming to deprive the cells of the hormone are feasible and have been successful. Tumor growth also depends in some cases on growth factors, so that the concept of hormone-dependence can be extended to growth factors deprivation. Hormone deprivation has been therapeutically achieved up to now by surgical, radiation and chemical means. However, the immune system usually can be manipulated to recognize hormones and growth factors, and in fact some autoimmune diseases exists involving autoantibodies against hormones. The idea of inducing a deprivation of hormones and growth factors by active immunizations is appealing, and initial evidence about the feasibility of this approach is starting to appear in the literature. Clinical trials have been initiated using immunization with human chorionic gonadotrophin (hCG), gastrin, luteinizing hormone releasing hormone (LHRH) / gonadotropin releasing hormone (GnRH) and epidermal growth factor (EGF). Preliminary data already show that antibody titers can be elicited, which results in a decrease in the concentration of a given hormone or growth factor. Both the antibody titers and the decrease in the hormone level are related to survival. This immunological approach for hormone and growth factor deprivation creates the possibility of chronic management of advanced cancer patients.

Computational identification of beta-barrel outer-membrane proteins in Mycobacterium tuberculosis predicted proteomes as putative vaccine candidates

Mycobacterial porins and other beta-barrel outer-membrane proteins are represented by the structure of Mycobacterium smegmatis porin MspA. On the basis of existing knowledge of beta-barrel outer-membrane proteins, several state of the art prediction methods, as well as a new in-house program (PROB) were employed for the systematic exploration of Mycobacterium tuberculosis predicted proteomes for potential beta-barrel structures. PROB allowed parameter optimization while functioning with an adaptive algorithm for the detection of outer-membrane beta-barrel proteins in highly divergent proteomes. As a result of the predictions, 114 proteins in total were predicted to be beta-barrel structures; of these, 40 were PE-PPE proteins, 8 Mce proteins, 24 hypothetical, 11 probable membrane proteins, 10 transporters, 4 lipoproteins, and 14 classified as other. The congruence among three of the predictors, PROB, TMB-Hunt, and BOMP, was low with only three proteins (MT0318, MT0356, and MT2423) predicted by the three. Overall, 79 new proteins for which no previous experimental work has been performed are reported. At least 10 of these have high potential of being not only surface-exposed but also served as putative vaccine candidates as determined by in silico predictions of CD4T cell MHC-II restricted epitopes.

Therapeutic Cancer Vaccines: At Midway Between Immunology and Pharmacology

The pursuit of active specific immunotherapy of cancer re-emerged vigorously in the 90s. More than 50 vaccines are currently under clinical testing, and more than 400 clinical trials have been conducted. This wave of enthusiasm is rooted in fundamental immunology, as new paradigms, such as the dominant tolerance through T-regulatory cells and the instructive role of the innate immune system on the adaptive immune system, opened the possibility that an efficient cancer vaccination could be achieved even without the need of cancer neoantigens, provided that antigen presentation could be increased, and that regulatory circuits could be controlled. However, recent failures in some large trials have brought disappointment and have highlighted the differences between experiments in young, healthy mice with small transplanted tumours, and clinical testing in aged, ill patients with advanced spontaneous tumours, driving the attention to issues such as tumour editing, tumour-induced immunosuppression, and immunosenescence. The molecular basis of these phenomena is only partially known. Additionally, the inherent complexity of the immune system as a network of multiple interactions and redundant control loops among a huge diversity of components sets another barrier to the translation of in vitro reductionist knowledge into rationally designed clinical trials. All this calls for a new therapeutic paradigm in cancer vaccines, moving beyond the analogy with the classic drug-target approach, and targeting the immune system regulation as a whole, and its interaction with the tumour, in all its complexity. Early mathematical modelling of cancer immunotherapy has suggested how to go about it. This re-evaluation of the cancer vaccine landscape, suggests that future successful cancer immunotherapy will be combined immunotherapy, will be exquisitely schedule-dependent and will need new experimental models allowing for the exploration of the mechanisms of resistance and tumour escape, such as tumour editing and tumour induced immunosuppression, in the context of the physiology of the immune system of the elderly. These shifts will put cancer vaccines closer to pharmacology than to conventional preventive vaccinology, or at least at the midway. A change in the design and the ultimate goals of the clinical trials will also be needed, identifying long term stabilization of the disease and quality of life as main endpoints, again closer to the clinical management of most chronic noncommunicable diseases.

Changes in clinical and laboratory findings at the time of diagnosis of primary hyperparathyroidism in a University Hospital in São Paulo from 1985 to 2002

In contrast to most developed countries, most patients with primary hyperparathyroidism in Brazil are still symptomatic at diagnosis. However, we have been observing a change in this pattern, especially in the last few years. We evaluated 104 patients, 77 females and 27 males aged 11-79 years (mean: 54.4 years), diagnosed between 1985 and 2002 at a University Hospital. Diagnosis was made on the basis of clinical findings and of high total and/or ionized calcium levels, high or inappropriate levels of intact parathyroid hormone and of surgical findings in 80 patients. Patients were divided into three groups, i.e., patients diagnosed from 1985 to 1989, patients diagnosed from 1990 to 1994, and patients diagnosed from 1995 to 2002. The number of new cases diagnosed/year increased from 1.8/year in the first group to 6.0/year in the second group and 8.1/year in the third group. The first group comprised 9 patients (mean serum calcium +/- SD, 13.6 +/- 1.6 mg/dl), 8 of them (88.8%) defined as symptomatic. The second group comprised 30 patients (mean calcium +/- SD, 12.2 +/- 1.63 mg/dl), 22 of them defined as symptomatic (73.3%). The third group contained 65 patients (mean calcium 11.7 +/- 1.1 mg/dl), 34 of them symptomatic (52.3%). Patients from the first group tended to be younger (mean +/- SD, 43.0 +/- 15 vs 55.1 +/- 14.4 and 55.7 +/- 17.3 years, respectively) and their mean serum calcium was significantly higher (P < 0.05). All of symptomatic patients independent of group had higher serum calcium levels (12.4 +/- 1.53 mg/dl, N = 64) than asymptomatic patients (11.4 +/- 1.0 mg/dl, N = 40). Our data showed an increase in the percentage of asymptomatic patients over the years in the number of primary hyperparathyroidism cases diagnosed. This finding may be due to an increased availability of diagnostic methods and/or to an increased awareness about the disease.

Response to an oral calcium load in nephrolithiasis patients with fluctuating parathyroid hormone and ionized calcium levels

The response to an oral calcium load test was assessed in 17 hypercalciuric nephrolithiasis patients who presented elevated parathyroid hormone (PTH) irrespective of the ionized calcium (sCa2+) levels. Blood samples were collected at baseline (0 min) and at 60 and 180 min after 1 g calcium load for serum PTH, total calcium, sCa2+, and 1.25(OH)2D3 determinations. According to the sCa2+ level at baseline, patients were classified as normocalcemic (N = 9) or hypercalcemic (N = 8). Six healthy subjects were also evaluated as controls. Bone mineral density was reduced in 14/17 patients. In the normocalcemic group, mean PTH levels at 0, 60 and 180 min (95 +/- 76, 56 +/- 40, 57 +/- 45 pg/ml, respectively) did not differ from the hypercalcemic group (130 +/- 75, 68 +/- 35, 80 +/- 33 pg/ml) but were significantly higher compared to healthy subjects despite a similar elevation in sCa2+ after 60 and 180 min vs baseline in all 3 groups. Mean total calcium and 1.25(OH)2D3 were similar in the 3 groups. Additionally, we observed that 5 of 9 normocalcemic patients presented a significantly higher concentration-time curve for serum PTH (AUC0',60',180') than the other 4 patients and the healthy subjects, suggesting a primary parathyroid dysfunction. These data suggest that the individual response to an oral calcium load test may be a valuable dynamic tool to disclose a subtle primary hyperparathyroidism in patients with high PTH and fluctuating sCa2+ levels, avoiding repeated measurements of both parameters.

Autoimmunization to epidermal growth factor, a component of the immunological homunculus

Epidermal growth factor (EGF) is being tried as a vaccine in cancer immunotherapy with the aim of inducing neutralizing antibodies that might affect EGF-dependent tumors. Here we summarize our experience using the EGF self-molecule as an autoimmunigen. We report here that IgG anti-EGF antibodies are prevalent in healthy people and that augmentation of the response to EGF requires conjugation to an effective carrier and an adjuvant. Paradoxically, the response to EGF immunization could be enhanced by an 'immunosuppressive' treatment with cyclophosphamide, most probably by suppressing active control mechanisms. EGF is expressed in the thymus. Thus, EGF may be added to the immunological homunculus, the class of self-antigens to which there is both natural autoimmunity and natural regulation of the autoimmunity. The results using EGF as a vaccine can teach us about the homunculus and how to activate it.

Three-cell interactions in T cell-mediated suppression? A mathematical analysis of its quantitative implications

Aiming to further our understanding of T cell-mediated suppression, we investigate the plausibility of the hypothesis that regulatory T cells suppress other T cells (target cells), while both cells are conjugated with one APC. We use a mathematical model to analyze the proliferation inhibition scored during in vitro suppression assays. This model is a radical simplification of cell culture reality, assuming that thymidine incorporation is proportional to the number of target cells that would instantaneously form conjugates with APCs that are free of regulatory cells. According to this model the inhibition index should be mainly determined by the number of regulatory cells per APC and should be insensitive to the number of target cells. We reanalyzed several published data sets, confirming this expectation. Furthermore, we demonstrate that the instantaneous inhibition index has an absolute limit as a function of the number of regulatory cells per APC. By calculating this limit we find that the model can explain the data under two non-mutually exclusive conditions. First, only approximately 15% of APCs used in the suppression assays form conjugates with T cells. Second, the growth of the regulatory cell population depends on the target cells, such that the number of regulatory cells per APC increases when they are cocultured with target cells and overcomes its limit. However, if neither of these testable conditions is fulfilled, then one could conclude that suppression in vitro does not require the formation of multicellular conjugates.

Phase I clinical evaluation of a neutralizing monoclonal antibody against epidermal growth factor receptor in advanced brain tumor patients: preliminary study

High levels of growth factors and their receptors have been demonstrated in human tumors. Gliomas and meningiomas are characterized by overexpression of epidermal growth factor receptor (EGF-R). Ior egf/r3, is a neutralizing murine monoclonal antibody (MAb) against EGF-R, and was generated at the Cuban Institute of Oncology. The antibody recognizes EGF-R with high affinity, inhibiting tyrosine kinase activation. A clinical trial was conducted in brain tumor patients to evaluate toxicity, immunogenicity, and clinical benefit of escalating doses of the antibody. Nine patients with histologically confirmed gliomas or meningiomas, who had active or recurrent disease after receiving conventional treatment, received four intravenous doses of ior egf/r3. Total dosages ranged from 160 to 480 mg. As inclusion criteria, radioimmunoscintigraphy with the same MAb labeled with 99mTechnetium (99mTc) was performed. Immune response against the murine antibody was also evaluated. After four doses of ior egf/r3 MAb, no significant toxicity was found, except in one patient who developed a grade 4 allergic adverse event. This reaction was probably related with previous sensitization to the same MAb and the development of human anti-mouse antibodies (HAMA) response. Despite no major objective antitumor responses, eight patients had stable disease on the 6-month evaluation, and two patients remain alive after four years of MAb therapy.

Phase I clinical evaluation of a neutralizing monoclonal antibody against epidermal growth factor receptor

Ior egf/r3, a neutralizing monoclonal antibody (mAb) against Epidermal Growth Factor Receptor (EGFR) was generated at the Cuban Institute of Oncology. Immunoscintigraphic studies in 148 patients with this 99-m Technetium (99Tc) labeled mAb, showed a high sensitivity and specificity for in vivo detection of epithelial tumors. To study safety, pharmacokinetic and immunogenicity of ior egf/r3 at high doses, a phase I clinical trial was conducted. Nineteen patients with advanced epithelial tumors received 4 mAb intravenous infusions at 6 dose levels: from 50 to 500 mg. Previously, immunoscintigraphic images using the same mAb labeled with 99Tc were acquired. Blood samples were collected for pharmacokinetic analysis and HAMA response. After mAb therapy, objective response was classified according to WHO criteria. Ior egf/r3 was well tolerated in spite of the high-administered doses. Only a severe adverse reaction consisting of hypotension and lethargy was observed. In 13 patients, selective accumulation of 99Tc-labeled mAb was observed at the site of the primary tumor or the metastasis. Pharmacokinetic analysis revealed that elimination half-life and the area under the time-concentration curve increased linearly with dose. HAMA response was detected in 17 patients. After 6 months of mAb therapy, 4 patients had stable disease. One patient had a tumor partial remission after 3 cycles of ior egf/r3.

Modelling T-cell-mediated suppression dependent on interactions in multicellular conjugates

Tolerance to peripheral body antigens involves multiple mechanisms, namely T-cell-mediated suppression of potentially autoimmune cells. Recent in vivo and in vitro evidence indicates that regulatory T cells suppress the response of effector T cells by a mechanism that requires the simultaneous conjugation of regulatory and effector T cells with the same antigen-presenting cell (APC). Despite this strong requirement, it is not yet clear what happens while both cells are conjugated. Several hypotheses are discussed in the literature. Suppression may result from simple competition of regulatory and effector cells for activation resources on the APC; regulatory T cells may deliver an inhibitory signal to effector T cells in the same conjugate; or effector T cells may acquire the regulatory phenotype during their interaction with regulatory T cells. The present article tries to further our understanding of T-cell-mediated suppression, and to narrow-down the number of candidate mechanisms. We propose the first general formalism describing the formation of multicellular conjugates of T cells and APCs. Using this formalism we derive three particular models, representing alternative mechanisms of T-cell-mediated suppression. For each model, we make phase plane and bifurcation analysis, and identify their pros and cons in terms of the relationship with the large body of experimental observations on T-cell-mediated suppression. We argue that accounting for the quantitative details of adoptive transfers of tolerance requires models with bistable regimes in which either regulatory cells or effectors cells dominate the steady state. From this analysis, we conclude that the most plausible mechanism of T-cell-mediated suppression requires that regulatory T cells actively inhibit the growth of effector T cells, and that the maintenance of the population of regulatory T cells is dependent on the effector T cells. The regulatory T cell population may depend on a growth factor produced by effector T cells and/or on a continuous differentiation of effector cells to the regulatory phenotype.

Tumor-specific immunotherapy based on dominant models of natural tolerance

The assumption that cancer immunotherapy may be based on the existence of autoreactive lymphocytes recognizing self-antigens on cancer cells, obviously opens a new opportunity. Nevertheless this analysis, relying on a recessive model of natural tolerance, limits the approach to try to activate peripheral lymphocytes, by increasing co-stimulatory signals or using modified self-antigens for immunization. Here we hypothesize that, based on emerging dominant tolerance notions in autoimmunity, it would be possible to induce a specific autoimmunity against tumor cells and arrest their growth following the removal of regulatory T cells. These immunoregulatory cells suppress available immunocompetent autoreactive cells capable of destroying tumor cells. Therefore, in order to reach a complete tumor-specific autoimmunity it is necessary to combine the T cell immunosuppression which abrogates the regulatory cells, with the cancer vaccines, which induces extensive proliferation of lymphoid cells directed towards specificities on tumor cells.

Novel cross-reactive anti-idiotype antibodies with properties close to the human intravenous immunoglobulin (IVIg)

The most important link between the immune network theory and clinically useful therapies so far is the use of human intravenous immunoglobulin (IVIg) in the treatment of autoimmune diseases. Although still controversial, one of the main mechanisms that has been postulated for the in vivo effects of IVIg, is the selection of immune repertoires through idiotypic interactions. We describe here anti-idiotype IgG monoclonal antibodies (MAbs), which were obtained by immunization of syngeneic mice (Balb/c) with an anti-ganglioside antibody. These anti-idiotype MAbs show multiple idiotypic connections and share some of the properties of the IVIg pool. The antiidiotype (Ab2) MAbs B7 and 34B7 showed heterogeneous binding with the idiotypes of several anti-ganglioside antibodies, MAbs obtained from splenocytes of nonimmunized newborn mice, F(ab')2 fragments of IgG human myeloma proteins, and nonimmunoglobulin antigens. The recognition pattern of the B7 MAb to the idiotypes of human immunoglobulins was also studied using a phage display library obtained from the variable region genes of an asymptomatic AIDS patient and also F(ab')2 fragments obtained from an IVIg pool of healthy human donors. We also demonstrated that these MAbs produced some of the in vitro effects reported for the human IVIg pool, such as the inhibition of cell proliferation of human B and T cell lines and of normal human lymphocytes activated with different mitogens. Another striking property of the MAb B7 was its ability to induce a dose-dependent specific antibody T-cell response in vivo in syngeneic mice. Both anti-idiotype MAbs showed anti-metastatic effect in vivo when injected intravenously to mice inoculated with MB16-F10 melanoma cells. The antimetastatic effect of the antiidiotype MAbs was not observed in athymic mice inoculated with the same tumor. This kind of antibody can become an interesting tool for further exploration of the role of idiotypic network connections in the regulation of the immune system and to study the effects of interventions on network connectivity in experimental autoimmune disease, using a reagent better chemically defined than the IVIg pool.

Natural and induced tolerance in an immune network model

It has been proposed that the immune system can be partitioned into central and peripheral immune systems. Recently, Carneiro et al. (1996a, b) proposed a network, model incorporating B and T lymphocytes that explicitly accounts for that partition. This model however, had some limitations that are tackled here. Two main changes were introduced: the average idiotypic connectivity is now an explicit function of time based on empirical evidence; and the activation of T lymphocytes by antigen is described by a log-bell shaped dose response curve. The new model, which also accounts for the CIS and PIS distinction, shows more reasonable results since the frequencies of tolerant, immune or autoimmune responses to an antigen are now correct. The model provides a new interpretation for tolerance induction during the neonatal period, and for the adult tolerance by low or high doses of antigen. It predicts that natural tolerance for antigens available during the neonatal period can be kept indefinitely upon their removal, while tolerance induced in the adult stages is rapidly lost upon transient removal of the antigen. A semiquantitative analysis of the model provides a simple explanation for the different results in terms of the frequency at which a limited set of canonical connectivity structures emerge during ontogenesis.

A novel cancer vaccine composed of human-recombinant epidermal growth factor linked to a carrier protein: report of a pilot clinical trial

BACKGROUND

There is evidence of a relationship between epidermal growth factor (EGF) and tumor cell proliferation, such as the overexpression of EGF receptor (EGF-R) in different human tumors, which makes this system an interesting target for cancer treatment. Up to now, passive immunotherapy with monoclonal antibodies against the EGF-R has been assayed in clinics. Our approach consists of active immunotherapy with human EGF (hu-EGF). We conducted a pilot clinical trial to define the safety, toxicity and immunogenicity of vaccination with hu-EGF coupled to a carrier protein.

PATIENTS AND METHODS

Ten patients with histologically-proven malignant carcinomas (colon, lung, stomach and prostate) in advanced clinical stages were enrolled. Patients were immunized twice (on days 0 and 15) with hu-EGF linked to either tetanic toxoid (TT, five patients) or P64K Neisseria Meningitidis recombinant protein (P64k, five patients), intradermically, using aluminium hydroxyde as adjuvant.

RESULTS

In both groups 60% of patients developed anti-EGF antibody titers without evidence of toxicity. Secondary reactions were very mild, limited to erythema and itching at the site of injection, which disappeared without medication.

CONCLUSIONS

We conclude that the proposed vaccination with hu-EGF was well tolerated and that antibody titers against self EGF were developed. The results of this trial may be useful in the design of new clinical trials with higher dose immunization protocols and using more effective adjuvants.

Technetium-99m-labeled anti-EGF-receptor antibody in patients with tumor of epithelial origin: I. Biodistribution and dosimetry for radioimmunotherapy

Accurate estimation of biodistribution and absorbed dose to normal organs and tumors is important for immunoscintigraphic studies and radioimmunotherapy treatment planning.

METHODS

Four patients (3 men, 1 woman; mean age 54.8 +/- 9.2 yr; range 42-64 yr) were administered 3 mg of anti-human epidermal growth factor receptor (anti-hEGF-r) antibody (ior egf/r3), radiolabeled with 99mTc activity of 39.5 +/- 1.1 mCi (range 38.5 mCi-40.7 mCi) by intravenous bolus infusion. After administration, blood and urine samples were collected from three patients up to 24 hr after injection. Whole-body anterior and posterior scans were obtained at 5 min and 1, 3, 5 and 24 hr after injection. Using a computer program, regions of interest were drawn over the heart, liver, spleen, bladder and tumor to measure the activity in the source organs at each scanning time. Time-activity curves for each source organ were then fitted to monoexponential or biexponential functions by nonlinear least squares regression using the flexible polyhedrals method, which adequately fit our data with the correlation coefficient of 0.985 +/- 0.013, and were integrated to determine organ residence times. The mean absorbed doses to the whole body and various normal organs were then estimated from residence times and from blood and urine samples using the methods developed by the Medical Internal Radiation Dose Committee. The effective dose equivalent and effective dose were calculated as prescribed in ICRP Publication Nos. 30 and 60.

RESULTS

Plasma disappearance curves of 99mTc-labeled anti-hEGF-r antibody were best-fit by a two-compartment model in all patients with a distribution half-life (t(1/2alpha)) of 0.207 hr +/- 0.059 hr (mean +/- s.d., n = 3) and an elimination half-life (t(1/2beta)) of 13.9 hr +/- 2.2 hr. Among the various organs, significant accumulation of the radiolabeled antibody was found in the liver (48.5% +/- 4.4%, mean +/- s.d.), heart (3.50% +/- 0.17%) and spleen (3.1% +/- 1.8%) at 5 min postadministration. These values were reduced to 3.2% +/- 0.4%, 0.1% +/- 0.01% and 0.1% +/- 0.1%, respectively, at 24 hr. Mean cumulative urinary excretion of 99mTc-labeled anti-hEGF-r antibody was 4.6% +/- 0.6% at 24 hr postinjection. Estimates of radiation absorbed dose to normal organs in rad/mCi administered (mean +/- s.d., n = 4) were: whole body 0.017 +/- 0.002; gallbladder wall 0.074 +/- 0.007; spleen 0.136 +/- 0.076; and liver 0.267 +/- 0.036. The effective dose equivalent and effective dose estimates for adults were 0.041 +/- 0.008 rem/mCi and 0.027 +/- 0.004 rem/mCi administered.

CONCLUSION

This feasibility study indicates that 99mTc-labeled anti-hEGF-r antibody (ior egf/r3) can be used safely; this analysis provides a dosimetric framework for future studies. This monoclonal antibody, labeled with 188Re, could possibly permit a successful regional radioimmunotherapy of tumors of epithelial origin.

Growth inhibition of human lung adenocarcinoma cells by antibodies against epidermal growth factor receptor and by ganglioside GM3: involvement of receptor-directed protein tyrosine phosphatase(s)

Growth of the EGF receptor-expressing non-small-cell lung carcinoma cell line H125 seems to be at least partially driven by autocrine activation of the resident EGF receptors. Thus, the possibility of an EGF receptor-directed antiproliferative treatment was investigated in vitro using a monoclonal antibody (alpha EGFR ior egf/r3) against the human EGF receptor and gangliosides which are known to possess antiproliferative and anti-tyrosine kinase activity. The moderate growth-inhibitory effect of alpha EGFR ior egf/r3 was strongly potentiated by the addition of monosialoganglioside GM3. Likewise, the combination of alpha EGFR ior egf/r3 and GM3 inhibited EGF receptor autophosphorylation activity in H125 cells more strongly than either agent alone. A synergistic inhibition of EGF receptor autophosphorylation by alpha EGFR ior egf/r3 and GM3 was also observed in the human epidermoid carcinoma cell line A431. In both cell lines, the inhibition of EGF receptor autophosphorylation by GM3 was prevented by pretreatment of the cells with pervanadate, a potent inhibitor of protein tyrosine phosphatases (PTPases). Also, GM3 accelerated EGF receptor dephosphorylation in isolated A431 cell membranes. These findings indicate that GM3 has the capacity to activate EGF receptor-directed PTPase activity and suggest a novel possible mechanism for the regulation of cellular PTPases.

Effect of chewing rawhide and cereal biscuit on removal of dental calculus in dogs

The effect of chewing rawhide and cereal biscuit on removal of dental calculus was studied in 67 dogs. Two methods were used to measure supragingival calculus and calculus removal as a function of time and acceptability. Trial 1 used a quantitative method based on actual measurement of the area of calculus on a tooth, and trial 2 used a quantitative method based on an arbitrary grading system to establish a supragingival calculus index. Analysis was performed, using 2-factor (trial 1) and a 3-factor (trial 2) analysis of variance. Results indicated that dogs removed calculus from their teeth by chewing rawhide; some teeth were cleaned better than others. The optimal amount or frequency of rawhide treatment was not necessarily determined. It was determined that regular consumption of up to 3 rawhide strips/d for 3 weeks was safe. Processed biscuits were sometimes effective in removing calculus from dog's teeth; however, biscuits were not as effective as the rawhide in removing supragingival calculus.

A carcinoembryonic antigen-directed immunotoxin built by linking a monoclonal antibody to a hemolytic toxin

Hybrid molecules prepared by linking toxins to monoclonal antibodies (MAbs) are cytotoxic to cells bearing the target antigen. The toxin most widely used has been the plant toxin ricin as the toxic component, which inhibits protein synthesis at the ribosome level. Immunotoxins based on membrane-active, hemolytic toxins can be a useful alternative when directed towards antigens which do not mediate internalization, as is the case for most carcinoma antigens. We present an alternative for toxic components using a hemolytic toxin acting at the membrane level, due to its phospholipase activity. The hemolytic toxin (HT), isolated from the sea anemone Stoichactis helianthus, has been conjugated to a MAb directed against carcinoembryonic antigen (CEA), by means of an artificial disulphide bridge. The hybrid alpha CEA-HT exhibits no hemolytic activity unless it is reduced. It is toxic for cells (MDA-MB-134) expressing CEA and not toxic for cells (MDA-MB-231) not bearing CEA. An excess of free antibody reverses toxicity.

Biodistribution of radioactive epidermal growth factor in normal and tumor bearing mice

The biodistribution of iodinated epidermal growth factor in normal and tumor bearing mice was analyzed. The uptake of epidermal growth factor was high in the liver, skin and submaxillary gland, which all have detected receptors for the growth factor. Organs, such as lung, heart, spleen, intestine, bone and central nervous system, which lack the receptor, did not retain the growth factor. In tumor bearing mice, the growth factor accumulated in receptor positive tumors, but to a lesser extent than in the liver. This finding will probably prevent the use of epidermal growth factor as a carrier for radionuclides for a therapeutic purpose.

A new immunotoxin built by linking a hemolytic toxin to a monoclonal antibody specific for immature T lymphocytes

Hybrid molecules built by conjugation between monoclonal antibodies (MAbs) and toxins are currently being experimentally tested as potential new anti-cancer agents. These immunotoxins have mainly used the plant toxin ricin as the toxic component, which inhibits protein synthesis at the ribosome level. We present an alternative for toxic components using a hemolytic toxin acting at the membrane level, due to its phospholipase activity. The hemolytic toxin (HT), isolated from the sea anemone Stoichactis helianthus, has been conjugated to an antibody towards an antigen expressed on immature T lymphocytes (IOR-T6), by means of an artificial disulphide bridge. The hybrid IOR-T6-HT exhibits no hemolytic activity unless it is reduced. It is toxic for cells (CEM) expressing the IOR-T6 antigen and non-toxic for cells (K562) not bearing the antigen. An excess of unconjugated antibody reverses the toxicity. Immunotoxins based on membrane-active, hemolytic toxins can be a useful alternative when directed towards antigens which do not mediate internalization, as is the case for most carcinoma antigens.

Receptors for epidermal growth factor and estrogen as predictors of relapse in patients with mammary carcinoma

Analysis of the receptors for estradiol and epidermal growth factor was performed in tumors from 225 breast cancer patients. The tumor cell content of both receptors was independent of clinical stage and lymph node status. There was an inverse correlation between the epidermal growth factor receptor and the estradiol receptor. Either the presence of the epidermal growth factor receptor or the lack of the estradiol receptor was related to a high relapse rate. A combination of these two receptors leads to an increased prognostic predictive capacity. Patients whose tumors contain both the estradiol receptor and epidermal growth factor receptor had a relapse rate similar to those whose tumors were estradiol receptor poor, and are thus high risk patients. Patients whose tumors contain the estradiol receptor and lack the epidermal growth factor receptor belong to a good prognosis group.

Epidermal growth factor receptors in human breast cancer

The capacity for specific binding of 125I-epidermal growth factor (EGF) was studied in crude membrane fractions from 95 human breast carcinomas. About 42% of the samples showed saturable, high affinity, specific binding of EGF. In 21% of the tumors we were able to demonstrate high (above 10 fmoles/mg protein) binding capacity. Moreover, high EGF receptor values were associated with a low content of estradiol receptor. These studies are related to the definition of new biochemical markers in human breast cancer.

67Ga-citrate distribution in solid hepatoma 22

The intracellular distribution of 67Ga was studied in solid hepatoma 22 implanted in C3Ha/6 mice and in normal liver tissue from the same animals at different time intervals. The tissues were fractionated according to differential centrifugation principles, and subcellular fractions were isolated consecutively. The enzyme activities and the accumulation of 67Ga were determined in each fraction. The subcellular distribution of 67Ga in the tumor tissue was different compared with normal liver; in tumor it was found mainly in the nuclear fraction and this distribution was independent of time, but in normal liver the accumulation was mainly in the mitochondrial fraction, this was time-dependent and the maximal uptake was found 48 h after 67Ga administration.

Ureteral replacement with a new synthetic material: Gore-Tex

There are no currently accepted synthetic ureteral substitutes. When faced with the need for ureteral replacement, the urologist must resort to pedicle grafts of intestine or bladder. Based on encouraging preliminary work in Europe, we have used a new synthetic vascular substitute, Gore-Tex, to replace segments of ureter in the dog. This material is made of expanded (microporous) polytetrafluoroethylene. In vascular surgery it is currently the preferred material due to its non-wetting and non-clotting surface when used in the arterial and venous beds. Adult mongrel dogs underwent segmental replacement of the right ureter and subtotal replacement of the left ureter with segments of 5-mm. tubed Gore-Tex. All anastomoses were performed with running 6--0 prolene. Antibiotics were given routinely perioperatively. Data on 7 dogs are available. Results indicate that Gore-Tex is well tolerated as a ureteral substitute to bridge gaps between segments of ureter. Anastomoses of Gore-Tex to bladder were not successful, resulting in infection and migration of the prosthesis. Under proper circumstances, Gore-Tex can be a useful potential addition to the urologic armamentarium.