Molecular and biochemical characterization of the human trk proto-oncogene.

Molecular analysis of the human trk oncogene, a transforming gene isolated from a colon carcinoma biopsy, revealed the existence of a novel member of the tyrosine kinase gene family. This locus, which we now designate the trk proto-oncogene, codes for a protein of 790 amino acid residues that has several features characteristic of cell surface receptors. They include (i) a 32-amino-acid-long putative signal peptide, (ii) an amino-terminal moiety (residues 33 to 407) rich in consensus sites for N-glycosylation, (iii) a transmembrane domain, (iv) a kinase catalytic region highly related to that of other tyrosine kinases, and (v) a very short (15 residue) carboxy-terminal tail. Residues 1 to 392 were absent in the trk oncogene, as they were replaced by tropomyosin sequences. However, no other differences were found between the transforming and nontransforming trk alleles (residues 392 to 790), suggesting that no additional mutations are required to activate the transforming potential of this gene. The human trk proto-oncogene codes for a 140,000-dalton glycoprotein, designated gp140proto-trk. However, its primary translational product is a 110,000-dalton glycoprotein which becomes immediately glycosylated, presumably during its translocation into the endoplasmic reticulum. This molecule, designated gp110proto-trk, is further glycosylated to yield the mature form, gp140proto-trk. Both gp110proto-trk and gp140proto-trk proteins possess in vitro kinase activity specific for tyrosine residues. Finally, iodination of intact NIH 3T3 cells expressing trk proto-oncogene products indicated that only the mature form, gp140proto-trk, cross the plasma membrane, becoming exposed to the outside of the cell. These results indicate that the product of the human trk locus is a novel tyrosine kinase cell surface receptor for an as yet unknown ligand.

Isozymic composition and regulatory properties of phosphofructokinase from well-differentiated and anaplastic medullary thyroid carcinomas of the rat.

Acceleration of glycolysis is, in general, a characteristic of neoplasia. Previous studies have shown that this increase in glycolysis is achieved by quantitative increases in the activities of the key regulatory enzymes, hexokinase, phosphofructokinase (PFK) and/or pyruvate kinase, which are often accompanied by isozymic alterations that facilitate glycolysis. In this study, we investigated the alterations in the activity, isozymic profile, and kinetic-regulatory properties of PFK from the medullary thyroid carcinomas of the rat, which represent a model for the neuroectodermally derived tumors in humans. Contrary to the expected, we found that undifferentiated tumors showed a decrease in the enzyme activity as compared to the highly differentiated tumors. This decrease in PFK activity was accompanied by an increase in the expression of the liver-type isozyme of PFK. The enzymes from the 2 tumor types showed no significant differences in their affinity and cooperativity toward the substrates, fructose 6-phosphate and adenosine triphosphate (ATP). However, the tumor PFKs showed major differences with respect to their behavior toward the allosteric regulators of the enzymes, ATP, citrate, and fructose 2,6-diphosphate; the latter is a recently discovered activator of the enzyme. The enzyme from the undifferentiated tumor was less sensitive to citrate inhibition, which was more readily reversed by cyclic adenosine 3':5'-monophosphate. In addition, it was less sensitive to ATP inhibition at low fructose 6-phosphate concentrations. More importantly, the enzyme from the undifferentiated tumors was more sensitive to the activation by fructose 2,6-diphosphate especially when inhibited by citrate and ATP. The altered regulatory properties of the enzyme from the undifferentiated tumors most probably reflect its altered isozymic composition, i.e., increase in the liver-type isozyme. The preferential expression of the liver-type isozyme by undifferentiated and rapidly replicating cancer cells may be explained in terms of the unique regulatory properties of this isozyme. Although the concentrations of fructose 2,6-diphosphate were comparable in these 2 tumor types, the higher sensitivity of the liver-type PFK to activation by this compound may permit accelerated glycolytic flux observed in undifferentiated tumors, despite a decrease in total PFK activity.

Sequential administration of recombinant human interleukin-2 and dacarbazine in metastatic melanoma: a multicenter phase II study.

Twenty-five assessable patients with metastatic melanoma have been entered in a multicenter phase II study of two induction cycles of human recombinant interleukin-2(IL2), 18 x 10(6) IU/m2/d continuous intravenous (IV) infusion on days 1 to 5 and days 12 to 17. Dacarbazine (DTIC), 850 mg/m2 IV bolus was given on day 26. The cycle was repeated at 5 weeks. Maintenance therapy was scheduled 3 weeks after the completion of induction treatment, consisting of IL2, 18 x 10(6) IU/m2/d for 5 days alternating with DTIC, 850 mg/m2 IV every 3 weeks, for a total of 18 weeks. Six patients responded (24%); two complete and four partial. Stable disease was seen in five patients. None of the six patients with more than two sites of metastases responded. Maximum response was observed in the first 3 months of treatment. Progression-free periods of 6 months and longer were seen in the two complete responders (8 and 17+ months), in two of the four partial responders (7 and 12+ months), and in three of the five patients with stable disease (9+, 15, and 17+ months). Toxicity included fever, skin rash, fatigue, anorexia, and diarrhea in most patients. Two patients had a weight gain of more than 10%. Eight patients needed intensive care for the observation and treatment of a myocardial injury (one patient), ventricular tachycardia (one), hypotension and oliguria (four), and sepsis (two). Sequential treatment with IL2 and DTIC appears to be effective but not clearly better than could be expected of IL2 alone.

Subunit-specific phosphorylation of pyruvate kinase in medullary thyroid carcinomas of the rat.

Pyruvate kinase from anaplastic medullary thyroid carcinomas contains predominantly K-type subunits, whereas pyruvate kinase from differentiated medullary thyroid carcinomas consist of M- and K-type subunits in about equal proportion. In order to analyse the incorporation of phosphate in the respective isozymes after endogenous phosphorylation of cytosolic extracts with [32P]ATP, homotetrameric isozymes as well as heterotetrameric hybrids of differentiated tumors were resolved by affinity chromatography on Blue-Sepharose CL-6B and, if necessary, further purified by immunoprecipitation. SDS-polyacrylamide gel electrophoresis of purified isozymes and subsequent autoradiography showed the incorporation of phosphate in the K4-type isozymes, but not in the other isozymes. The phosphorylation appeared to be cAMP-independent and occurred on a serine residue.

A phase III study of recombinant interleukin-2, 5-fluorouracil and leucovorin versus 5-fluorouracil and leucovorin in patients with unresectable or metastatic colorectal carcinoma.

135 patients with locally advanced or metastatic colorectal cancer were entered into a phase III trial evaluating the efficacy of chemoimmunotherapy [recombinant interleukin 2 (rIL2)/5-fluorouracil (5-FU) and leucovorin (LV)] versus chemotherapy alone (5-FU/LV). A cycle of chemoimmunotherapy comprised a constant intravenous infusion of rIL2 at a dose of 18 x 10(6) U/m2/24 h for 120 h, followed by three bolus injections of 5-FU (600 mg/m2) and LV (25 mg/m2) at weekly intervals. Patients receiving chemotherapy alone received 5-FU/LV at the same dose at weekly intervals for 6 weeks followed by a rest period of 2 weeks, constituting one cycle of therapy. A maximum of 6 months therapy was given in both arms of the study. The response rates (complete and partial responses) were 17% in patients receiving rIL2/5-FU/LV versus 16% in those in the 5-FU/LV arm of the study. Median survival and progression-free survival were comparable for the two groups of patients, although there was a trend for a prolongation of survival in patients receiving chemoimmunotherapy compared with chemotherapy alone, beyond 12 months. Retrospective subgroup analyses revealed a significantly increased survival in poor prognosis patients (ECOG 1) treated with rIL2/5-FU/LV when compared to those receiving chemotherapy alone. Therefore, further studies evaluating the dose and duration of chemoimmunotherapy in patients with metastatic colorectal cancer seem warranted.

Differential responses to chemoimmunotherapy in patients with metastatic malignant melanoma.

An open, multicentre non-randomised study was performed to evaluate the activity and toxicity of combination chemoimmunotherapy, consisting of cisplatin, interleukin-2 and interferon-alpha, in metastatic malignant melanoma. Between March 1992 and September 1993, 28 patients with pathologically proven metastatic malignant melanoma, bidimensionally measurable disease and an Eastern Co-operative Oncology Group score < or = 1 were treated with the combination chemoimmunotherapy. The regimen consisted of cisplatin (100 mg/m2 on day 0), interleukin-2 (Proleukin, Chiron, Middlesex, U.K.) 18 x 10(6)IU/m2/d continuous intravenous infusion on days 3-7 and 17-22, with interferon-alpha (Roferon-A, Roche, Hertfordshire, U.K.) 9 x 10(6) U/d subcutaneously on days 3, 5, 7, 17, 19, 21 during the interleukin-2 infusions. The treatment cycle lasted 28 days. Among 27 assessable patients, 5 patients achieved partial responses, for an overall response rate of 18% (95% CI 6-37%). Median progression-free survival was 44 days (range 8-279) and median overall survival was 264 days (range 41-1432). Differential responses were noted in 41% of patients and responses were more frequent in non-visceral disease (skin, lymph node and soft tissue disease) (P = 0.04). These results indicate that differential responses to chemoimmunotherapy are common in patients with metastatic melanoma. This may account for the broad range of response rates reported in the literature.

Continuous infusion of recombinant interleukin-2 with or without autologous lymphokine activated killer cells for the treatment of advanced renal cell carcinoma.

Data have been analysed for 327 patients with advanced renal cell carcinoma receiving a continuous infusion of recombinant interleukin 2 (rIL-2) alone (225 patients) or rIL-2 plus lymphokine activated killer (LAK) cells (102) on a normal oncology ward. Eligibility criteria were uniform across protocols, all patients having advanced progressive disease, but with an ambulatory performance status. The baseline characteristics of patients receiving rIL-2 alone did not differ significantly from those receiving LAK, with the exception that the LAK treated patients had a better performance status. Despite similar treatment intensity, toxicity was more severe in the patients receiving LAK. The addition of LAK did not lead to higher response rates or to prolonged response duration, progression-free survival or survival. This review confirms the activity of rIL-2 for the treatment of advanced renal cell carcinoma and demonstrates that the addition of LAK cells does not lead to increased efficacy.

A phase II study of sequential recombinant interleukin-2 followed by dacarbazine in metastatic melanoma.

16 patients with disseminated malignant melanoma (1 with primary ocular melanoma) entered a multicentre phase II study of recombinant interleukin-2, (rIL-2) given by continuous intravenous infusion on days 1-5 at 18 x 10(6) IU/m2 per day, followed by dacarbazine 850 mg/m2 on day 8. After a 2 week rest, a second course was given. In the absence of disease progression, monthly maintenance cycles were given for up to four cycles. 16 patients received one cycle, 14 received two and 6 patients three or more. All 16 patients are evaluable for toxicity and 15 for response. 2 patients responded (13%). 1 patient with lung and pleural metastases achieved partial remission after two cycles and went off treatment after six cycles. 3 months later a complete response was noted lasting 396+ days. A second patient with lung metastases had a partial response lasting 153 days. 3 patients (20%) had stable disease. Mean rebound lymphocytosis (24-48 h after the end of rIL-2 therapy), cell count 4.9 x 10(9)/l (2.6-8.8 x 10(9)/l) was within the expected limits. Other toxicity was as expected. Thus sequential treatment with rIL-2 and dacarbazine is feasible but synergy did not occur.

An improved method of unit gravity sedimentation separation for murine peritoneal macrophage populations.

A new method for the separation of murine peritoneal macrophage populations is described. Different macrophage populations were separated by velocity sedimentation in a Percoll gradient. The macrophages were separated by size as was shown by a morphometrical analysis. The different macrophage populations differed in their enzyme cytochemical profile. The overall recovery of peritoneal cells is more than 95% and the macrophages adhered normally to glass surfaces after washing. This indicated that this l X g sedimentation separation of macrophages, which is relatively simple to perform, is suitable for the study of macrophage heterogeneity.

Recombinant interleukin 2 for acute myeloid leukaemia in first complete remission: a pilot study.

We treated nine patients in first remission from AML with rhIL-2. The toxic effects of rhIL-2 infusion were, malaise, pyrexia, and hypotension, which resolved rapidly on cessation of rhIL-2 infusion. No patient required transfer to an intensive care unit. Following rhIL-2 infusions patients developed eosinophilia, and a modest lymphocytosis, involving both NK cells, and T lymphocytes. Relapse occurred in six patients at a median of 39 weeks from remission. A particular concern was rapid relapse in the two patients with AML FAB type M5. There was no survival advantage from rhIL-2 treatment when compared to a similar group of chemotherapy only treated AML patients from this institution.

[Feasibility and tolerance evaluation of 2 routes of preoperative administration of interleukin 2]. / Faisabilité et évaluation de la tolerance de deux schémas d'administration préopératoire d'interleukine 2.

Preoperative interleukin 2 (IL2) administration has been performed, in order to diminish the post-operative immunodepression in cancer patients. The aim of this study was to compare two different ways of preoperative IL2 administration, ie, intravenous (iv) and subcutaneous (sc), in terms of feasibility and tolerance. Nineteen surgical procedures were performed in 18 patients: a) 10 following the administration of 12 IU/m2/24 hours IL2 IV, with a continuous infusion, from day 5 to day 3 before surgery; b) 9 following the administration of 18 IU IL2, in 2 SC injections per day, from day 4 to day 2 before surgery. Tolerance was evaluated by both clinical and biological parameters, before, during, and after surgery. Hyperthermia and capillary leak syndrome were more important in the iv versus sc injection group. Insomnia and digestive troubles were more frequent in the iv injection group as well. However, we noticed few and equivalent cutaneous and respiratory complications in both groups. In conclusion, the tolerance of IL2 was better after sc versus iv injection. However, the toxicity of iv infusion of IL2 was moderate and could be limited by preventive treatments; moreover there was no consequence on the scheduled surgical procedure.

Isoenzymes of phosphofructokinase in the rat. Demonstration of the three non-identical subunits by biochemical, immunochemical and kinetic studies.

In man and the rabbit, 6-phosphofructokinase (PFK, EC 2.7.1.11) exists in tetrameric isoenzymic forms composed of muscle (M or A), liver (L or B) and platelet or brain (P or C) subunits, which are under separate genetic control. In contrast, the genetic control of the rat PFK has not yet been conclusively established; it is unclear whether the P-type or C-type subunit exists in this species. To resolve this question, we investigated the enzyme from the skeletal muscle, liver and brain of rats of Wag/Rij strain. Our studies demonstrate that the rat PFK is also under the control of three structural loci and that the homotetramers M4, P4 and L4 exhibit unique chromatographic, immunological and kinetic-regulatory properties. Skeletal-muscle and brain PFKs consist of isolated M4 and P4 homotetramers respectively. Although liver PFK consists predominantly of L4 homotetramer, it also contains small amounts of PL3 and P2L2 species. All three PFKs exhibit allosteric properties: co-operativity with fructose 6-phosphate and inhibition by ATP decrease in the order P4 greater than L4 greater than M4. P4 and M4 tetramers are the most sensitive to citrate inhibition, whereas L4 tetramer is the least sensitive. More importantly, P4 and L4 isoenzymes are the most sensitive to activation by fructose 2,6-bisphosphate, whereas M4 isoenzyme is the least sensitive. These results indicate that the brain PFK in this strain of rat is a unique tetramer, P4, which also exhibits allosteric kinetics, as do the well-studied M4 and L4 isoenzymes. The reported differences in the number and nature of isoenzymes present in the rat brain and liver most probably reflect the differences in the strains studied by previous investigators. Since the nature of the rat PFK isoenzymes and nomenclatures reported by previous investigators have been now reconciled, it is proposed that, for the sake of uniformity, only well-established nomenclatures used for the rabbit or human PFK isoenzymes be used for the rat isoenzymes.

Enolase isozymes in differentiated and undifferentiated medullary thyroid carcinomas.

Enolase isozyme composition was studied using both electrophoretic and chromatographic methods in rat medullary thyroid carcinomas (MTC), differing in their degree of differentiation. In well-differentiated rat tumors (DMTC), both the alpha- and gamma-subunits of enolase were expressed, resulting in alpha alpha, alpha gamma, and gamma gamma isozymes. The relatively high amount of alpha gamma and gamma gamma isozymes (neuron-specific enolase [NSE] ) was indicative of the presumed neuroectodermal origin of these tumors. In contrast, highly undifferentiated or anaplastic tumors (AMTC) were characterized by a decrease in expression of the gamma-subunit. Hence, the majority of enolase isozymes were alpha alpha dimers, with only a few percent alpha gamma hybrids remaining. These shifts from neuron-specific to non-neuronal isozymes in rat MTC were compared with human MTC and discussed with respect to neuronal differentiation and the clinical significance of NSE measurements in serum as a marker for amine precursor uptake and decarboxylation cell-derived neoplasms.

Pyruvate kinase isozymes and dedifferentiation of (neuro-)ectodermal tumors.

This paper describes the isozyme composition and regulatory properties of pyruvate kinase (PK) from well-differentiated (DMTC) and undifferentiated (AMTC) medullary thyroid carcinomas of the rat. These tumors were chosen as an animal model for human (neuro-)entodermal neoplasms differing in their degree of differentiation. The results were compared with human medullary thyroid carcinomas (MTC) and phaeochromocytomas. AMTC were characterized by increased PK activity, a higher apparent S0.5 for phosphoenolpyruvate, enhanced inhibition by alanine, presence of predominantly M2-type isozyme and loss of M1-type-containing hybrids as compared to DMTC. The alterations in PK isozyme expression and hence kinetic behaviour could not be demonstrated in human MTC or phaeochromocytomas due to the apparently well-differentiated nature of these tumors and the presence of M2-type isozymes. These results are discussed with reference to the nature and significance of PK isozyme shifts found in other tumors. It is suggested that the determination of PK isozyme composition might prove useful in the diagnosis of nueroectodermal neoplasms originating from tissues not primarily expressing M2-type isozyme(s).

Frequent generation of oncogenes by in vitro recombination of TRK protooncogene sequences.

Transfection of NIH 3T3 cells with cDNA clones containing either the entire coding sequences or the tyrosine protein kinase domain of the human TRK protooncogene results in the frequent generation of transforming genes. Activation of most of these TRK oncogenes involves acquisition of DNA sequences. These sequences, unlike those present in the original human TRK oncogene, are not derived from tropomyosin genes. The products of these in vitro-generated TRK oncogenes retain the parental tyrosine protein kinase activity and contain an intact carboxyl terminus. However, they exhibit distinct biochemical properties. Whereas some of them are nonglycosylated cytoplasmic molecules, others were found to be transmembrane glycoproteins. These results suggest that TRK oncogenes may induce malignant transformation by allowing their tyrosine kinase to interact with various substrates depending on the nature of their activating sequences. If so, the TRK kinase may serve as a pleiotropic marker to identify various cellular proteins whose unscheduled phosphorylation on tyrosine residues contributes to neoplastic transformation.

Human resident peritoneal macrophages: phenotype and biology.

Macrophages represent the primary line of host defences in the peritoneal cavity. In order to study the metabolic activity and maturation stage of human resident peritoneal macrophages (PM phi). peritoneal fluid (PF) was taken by Douglas puncture from healthy hyperstimulated infertile women undergoing oocyte retrieval for in vitro fertilization. Peritoneal fluid and macrophage culture fluids were studied for different inflammatory mediators such as interleukin-1 (IL-1), tumour necrosis factor (TNF) and interleukin-6 (IL-6). The level of macrophage colony-stimulating factor (M-CSF), which represents a macrophage proliferation and differentiation factor, was determined in the PF and in the serum. Furthermore, the macrophage phenotypic profile was analysed, in particular the expression of sex steroid hormone receptors. IL-1. IL-6 and TNF were detectable in the PF and in the culture supernatants of PM phi whether stimulated or not by IFN-gamma and LPS. The mean level of M-CSF in the PF was 6.37 +/- 2.02 ng/ml as measured by RIA; this level did not correlate with the concentration of PM phi. The mean PF-M-CSF level was 1.4-fold higher than in the sera as measured by a EIA. Oestrogen and progesterone receptors could not be demonstrated on the PM phi analysed, so that a direct relationship between the ovarian steroid concentration in these women and the function of PM phi was unlikely. As compared to peripheral blood monocytes (Mo). PM phi showed a phenotypic profile, with some more mature features, e.g. increased expression of CD14, CD68, FcRII, FcRIII, CR3, CR4 and MHC class II determinants. These results indicate that resident PM phi have acquired in vivo a certain differentiation and/or activation state under micro-environmental factors where cytokines secreted by the M phi themselves or by other cells such as the mesothelium may play important roles.

Immune reactivity in SL2 lymphoma-bearing mice compared with SL2-immunized mice.

We have studied the rather paradoxical phenomenon of the growth of an antigenic tumor in an immunocomponent host. This phenomenon was studied by comparing the lymphocyte reactivity and the macrophage cytotoxicity, during SL2 growth in DBA/2 mice (SL2-bearing mice) and in DBA/2 mice immunized against SL2 tumor cells (SL2-immune mice). Immune mice rejected a challenge of tumor cells. The immune T-lymphocytes rendered macrophages cytotoxic (arming) and were able to transfer tumor resistance to naive animals. Nonimmunized mice did not reject a challenge of SL2 cells. In these tumor-bearing mice various forms of immune reactivity were tested. Lymphocytes with the capacity to arm macrophages could not be found in the lymphoid organs. However, lymphocytes isolated from the tissue directly surrounding the subcutaneous SL2 tumor could arm macrophages in vitro. Shortly after subcutaneous tumor grafting cytotoxic macrophages were found in the peritoneal cavity. In the serum macrophage arming factors were detected that rendered macrophages cytotoxic in vitro. This cytotoxicity of the peritoneal macrophages and the presence of macrophage arming factors in the serum showed a similar biphasic pattern. The first phase of cytotoxicity between day 3 and 8 after tumor grafting was tumor (SL2) specific. The second phase from day 12 and onwards was not tumor specific. During the first 4 days after SL2 grafting the DBA/2 mice expressed a specific concomitant immunity to a second tumor graft. Then 7 or more days after grafting the first SL2 tumor, the concomitant immunity was nonspecific as the growth of a second SL2 tumor graft and a L5178Y (DBA/2) tumor graft were inhibited. In addition, the immune suppressive activity of serum and lymphocytes was tested. Neither serum nor lymphocytes from SL2-bearing mice suppressed the macrophage arming capacity of SL2 immune lymphocytes. Lymphocytes from tumor-bearing mice did not inhibit the capacity of SL2-immune lymphocytes to transfer resistance to naive animals. On the contrary, lymphocytes obtained from SL2-bearing mice 14 days after SL2 grafting transfered tumor resistance in a Winn-type assay. These data suggest that the growth of an antigenic tumor is due to the inability of the immune system to mount an effective antitumor effector cell population during tumor growth, rather than an immune suppression of the antitumor reactivity, as a limited immune reactivity could be detected in tumor-bearing mice, whereas immune suppression could not be detected.

Prognostic factors for survival in patients with advanced renal cell carcinoma treated with recombinant interleukin-2.

A database of 327 patients with advanced Renal Cell Carcinoma (RCC) has been analyzed in order to identify potential baseline prognostic factors predicting for survival, following recombinant Interleukin-2 treatment (rIL-2). All patients received a continuous infusion (CIV). Eligibility criteria were uniform across studies, and included patients with an ambulatory performance status (PS), measurable disease, no CNS metastases, and no major organ compromise. Multivariate analyses identified baseline PS (ECOG 0 vs. 1), time from diagnosis to treatment (DTI greater than 24 months vs. less than or equal to 24 months), and the number of metastatic sites (1 vs. greater than or equal to 2, where lung, bone and other sites are considered as separate sites) as important predictors for survival. Patients can be classified into 4 subgroups, which are a function of the number of risk factors present. Median survival for each subgroup is 28, 17, 10 and 5 months, respectively. The model was validated in an independent cohort of 125 patients with RCC treated with subcutaneous (s/c) rIL-2, and predicted for survival accurately. By determining in which risk group category patients may fall, treating physicians may be better equipped to decide on patient management. The model may also be of value in order to stratify patients in randomized clinical trials.

A phase-III study of recombinant interleukin 2 and 5-fluorouracil chemotherapy in patients with metastatic colorectal cancer.

Sixteen patients with metastatic colorectal cancer have been treated with a regimen involving an 120 h continuous infusion of rIL-2, 18 x 10(6) iu m-2 day followed by three injections of 5FU 600 mg m-2 at weekly intervals. Entry criteria included no previous chemotherapy, ambulatory performance status, and a measurable lesion. In most cases side effects were easily manageable and only one patient required transfer to an intensive care unit with the capillary leak syndrome. In three patients persistent hypotension was found to be unrelated to treatment with rIL-2, being caused respectively by a line infection, pulmonary embolus, and bowel perforation. This last proved a fatal complication. Five patients (33%; [95% confidence limits, 11.8%-61.6%]) achieved a partial response, and two non-responders later achieved a partial response when treated with weekly 5FU. This regimen is currently being evaluated in a phase-III randomised controlled trial.

Hexokinase isoenzymes from anaplastic and differentiated medullary thyroid carcinoma in the rat.

The activity, isoenzyme distribution and compartmentation of hexokinase (ADP: D-hexose-6-phosphotransferase, EC 2.7.1.1) were compared in slowly growing, well-differentiated medullary thyroid carcinoma (DMTC) and rapidly proliferating anaplastic thyroid carcinoma (AMTC) in the rat. Individual isoenzymes from either soluble or particulate fractions after solubilization were obtained by fast protein liquid chromatography and were kinetically analyzed either in soluble form or after (re)binding to rat liver mitochondria. These studies were undertaken to test the hypothesis that the growth rate of tumors is correlated with the activity of mitochondrial-bound hexokinase in our tumor system. In contradiction to this hypothesis, we found no difference in either enzyme activity or compartmentation of both kinds of tumors. The major part of enzyme activity was soluble (73 and 78% in DMTC and AMTC respectively). In addition, no major differences were observed in the kinetic properties of the individual isoenzymes of both tumors. Only soluble type II hexokinase from AMTC had a slightly decreased apparent Km for glucose. There appeared to be some differences in isoenzyme composition: both tumors contained type I and type II hexokinase in the soluble as well as in the particulate fractions. However, the proportion was shifted in favor of type II hexokinase in the soluble fraction of AMTC. Additional findings of this study were the following: the affinity of type II hexokinase to both substrates glucose and MgATP2- was significantly less compared to type I hexokinase. However, the inhibition constant for glucose-1,6-diphosphate of both isoenzymes was exactly the same. The bound form of both isoenzymes had the same substrate affinities as the soluble form but was considerably less inhibited by glucose-1,6-diphosphate. In the latter respect, type I and type II hexokinase behaved in the same way.