Biomedical subjects

Rolf Larsson

Publications and source records attributed to Rolf Larsson.

At least 37 records · Page 2Linked to original sources

PubMed2005

Predictive value of in vitro assessment of cytotoxic drug activity in advanced breast cancer.

The predictive value of a short-term in vitro total cell kill assay was investigated in 37 patients with breast cancer (BC). Tumor cells were prepared from tumor samples from 17 patients with locally advanced and 20 with metastatic BC, which were treated with the FEC (5-fluorouracil, epirubicin, cyclophosphamide) regimen or a combination of epirubicin and taxane. The cells were then tested in the fluorometric microculture cytotoxicity assay (FMCA), which is based on the conversion by viable cells of fluorescein diacetate to fluorescent fluorescein, for sensitivity to the drugs given in vivo. The FMCA data were scored as low, intermediate or extreme drug resistance based on the median cell survival +/- SD for each drug and patient subset. The drug classification for each sample was then correlated to clinical outcome in terms of objective response and time to tumor progression. The FMCA significantly predicted objective tumor response with a sensitivity of 89% and a specificity of 53%. Furthermore, in patients with locally advanced BC, low drug resistance was significantly associated with longer time to progression. It is concluded that the FMCA seems to report clinically relevant cytotoxic drug sensitivity data in BC. The potential clinical role of the FMCA and similar tests is discussed.

Antineoplastic Agents↗

PubMed2005

In vitro activity of imatinib in cells from patients with adult acute lymphoblastic leukemia.

We evaluated the in vitro activity of imatinib on BCR-ABL-positive and -negative tumor cells from patients with adult acute lymphoblastic leukemia (ALL), and investigated in vitro interactions between imatinib and conventional agents. A non-clonogenic cytotoxicity assay was used to analyze p190 BCR-ABL-positive (n = 4), p210 BCR-ABL-positive (n = 2) and BCR-ABL-negative (n = 9) tumor cells from adult ALL patients. The in vitro cytotoxic effect of imatinib was studied alone, and in combination with the cytotoxic agents cytarabine, prednisolone, vincristine, daunorubicin, asparaginase and mercaptopurine. The BCR-ABL-positive samples were significantly (p < 0.05) more sensitive to imatinib than the BCR-ABL-negative at the concentrations 0.1, 1 and 10 muM. Interestingly, the two p210 samples were somewhat less sensitive to imatinib than the p190 samples. Daunorubicin, prednisolone and cytarabine showed the largest benefit from combination with imatinib compared to the most active single agent. The study confirms that drug sensitivity to imatinib is specific for BCR-ABL-positive samples. The results also suggest that combinations between imatinib and daunorubicin, predisolone or cytarabine may be advantageous for the treatment of Philadelphia-positive ALL.

Adult↗

PubMed2004

Anticancer agent CHS 828 suppresses nuclear factor-kappa B activity in cancer cells through downregulation of IKK activity.

CHS 828, a pyridyl cyanoguanidine, has been shown to exert a significant antitumor effect in preclinical tests in vitro and in vivo, and CHS 828 is in phase I/II clinical trials. We have investigated the effect of CHS 828 on the nuclear factor-kappa B (NF-kappa B) because of its well-known role in the control of cell division and apoptosis. CHS 828 is able to inhibit the lipopolysaccharide (LPS)-induced nuclear localization as well as the transcriptional activity of NF-kappa B in human THP-1 leukemia cells. Moreover, CHS 828 has also been shown to inhibit the LPS-induced degradation of the I kappa B alpha and I kappa B beta in THP-1 cells, leading us to identify the I kappa B kinase complex as a molecular target of CHS 828. The IKK activity is inhibited by CHS 828 with an IC(50) of 8 nM. The inhibition of the IKK activity by different CHS 828 analogues correlates well with the inhibition of NYH small cell lung cancer cell proliferation in vitro and in vivo. Moreover, the inhibition of NF-kappa B transcriptional activity in different cancer cell lines by CHS 828 correlates to some extent with the reduction by CHS 828 of the size of the corresponding xenografts. Activation of NF-kappa B has been shown to induce expression of antiapoptotic proteins, and cancer cells have been shown to have high levels of constitutively active NF-kappa B. Therefore, we hypothesize that the anticancer activity of CHS 828 is due to inhibition of the IKK activity by which the antiapoptotic protection of NF-kappa B is removed, leading to the promotion of apoptosis.

Animals↗

PubMed2004

Cytotoxic activity of a new paclitaxel formulation, Pacliex, in vitro and in vivo.

BACKGROUND: The paclitaxel formulation, Taxol (Bristol-Myers Squibb), is one of the most effective anticancer agents used today. However; it is associated with serious side effects believed to be caused by the Cremophor EL used for its formulation. AIM: To evaluate the cytotoxic activity of a new paclitaxel formulation, Pacliex (developed by Oasmia Pharmaceutical, Uppsala, Sweden), a mixed micelles preparation in which an amphiphilic synthetic derivative of retinoic acid replaced Cremophor EL/ethanol vehicle. METHOD: In this study, three model systems were used to evaluate the cytotoxic activity of Pacliex and other paclitaxel preparations. The cytotoxic activities of Pacliex, Taxol and paclitaxel in ethanol were investigated against a panel of ten human tumor cell lines using the fluorometric microculture cytotoxicity assay (FMCA). Low- and high- proliferating in vitro hollow fiber model of two cell lines, the leukemia CCRF-CEM and the myeloma RPMI 8226/S cell lines, were used to assess the cytotoxic activity of the three formulations. The in vivo hollow fiber model of the two cell lines was used for assessment of Pacliex and Taxol activity. The [3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to analyze the in vitro and in vivo hollow fiber data. RESULT: Pacliex was somewhat more effective than Taxol in the more sensitive cell lines. The activity of Taxol was more pronounced in the resistant cell lines due to an additive effect of the vehicle used. The three formulations showed similar activity in both the low- and high-proliferating in vitro hollow fiber cultures. The in vivo hollow fiber cytotoxic activity of Pacliex was similar to that of Taxol. Putting all the results together, it was found that all the three formulations had similar in vitro and in vivo activity. CONCLUSION: The three in vitro and in vivo models confirmed the similarity of the cytotoxic activities of Pacliex and Taxol. Considering the above, Pacliex could be an interesting alternative Cremophor EL-free formulation of paclitaxel.

Antineoplastic Agents, Phytogenic↗

PubMed2004

Cytotoxicity and pharmacokinetics of cladribine metabolite, 2-chloroadenine in patients with leukemia.

The nucleoside analog 2-chlorodeoxyadenosine (Cladribine, CdA) is used in the treatment of patients with several hematological malignancies. After administration of CdA, the major catabolite measured in plasma and urine is 2-chloroadenine (CAde). This study was performed to determine the pharmacokinetics after oral and intravenous (iv) infusion of CdA in patients treated for chronic lymphocytic leukemia and to evaluate the toxicity of CAde to leukemia cells in vitro. CdA and CAde were also determined in plasma from 31 patients and in urine from 16 patients with reversed-phase high-performance liquid chromatographic. The toxicity of CdA and CAde was also determined in leukemic cells from 7 patients by fluorometric microculture cyotoxicity assay. Five times more CAde was quantified after oral treatment compared with an iv infusion of CdA. After iv infusion, the half-life was the same for CdA and CAde, but after oral administration the half-life was doubled for CAde. Excreted amount of CAde in urine constituted about 1.1% after iv infusion and 4.7% after oral CdA treatment. In vitro exposure of leukemia cells to CAde showed that it was eight times less toxic as compared to CdA. We conclude that CAde has a lower cytotoxic effect than CdA but may contribute significantly to the cytotoxicity after oral administration.

Adenine↗

PubMed2004

Translocation t(12;21) is related to in vitro cellular drug sensitivity to doxorubicin and etoposide in childhood acute lymphoblastic leukemia.

The t(12;21) (p13;q22) translocation resulting in ETV6/RUNX1 (previously named TEL/AML1) gene fusion is present in about 25% of children with precursor B-lineage acute lymphoblastic leukemia (B-ALL). We successfully tested 275 precursor B-ALL samples from children aged 1 to 17 years to determine the relation between t(12;21) and in vitro cellular drug resistance, measured by the fluorometric microculture cytotoxicity assay (FMCA). Samples from 83 patients (30%) were positive for t(12;21). The ETV6/RUNX1(+) samples were significantly more sensitive than ETV6/RUNX1(-) samples to doxorubicin, etoposide, amsacrine, and dexamethasone, whereas the opposite was true for cytarabine. After matching for unevenly distributed patient characteristics, that is, excluding patients with high hyperdiploidy (> 51 chromosomes), t(9; 22), t(1;19), or 11q23 rearrangement, the ETV6/RUNX1(+) samples remained significantly more sensitive to doxorubicin (P = .001) and etoposide (P = .001). For the other drugs tested (amsacrine, cytarabine, dexamethasone, prednisolone, vincristine, 6-thioguanine, and 4-hydroperoxy-cyclophosphamide), no significant difference in cellular drug sensitivity was found. In conclusion, we found that the presence of the t(12;21) translocation in childhood precursor B-ALL is associated with a high tumor cell sensitivity to doxorubicin and etoposide. High throughput techniques should now be used to elucidate the cellular mechanisms by which ETV6/RUNX1 gene fusion is linked to increased sensitivity to these drugs.

Adolescent↗

PubMed2004

Cytotoxic cyclotides from Viola tricolor.

A crude fraction of Viola tricolor rich in small lipophilic proteins was prepared and subjected to fractionation guided by bioactivity, using RP-HPLC and a fluorometric cytotoxicity assay. Two human cancer cell lines, U-937 GTB (lymphoma) and RPMI-8226/s (myeloma), were used in this study. The most potent compounds isolated, that is, the compounds showing the lowest IC(50) values, were shown to be three small proteins: vitri A (IC(50) = 0.6 microM and IC(50) = 1 microM, respectively), varv A (IC(50) = 6 microM and IC(50) = 3 microM, respectively), and varv E (IC(50) = 4 microM in both cell lines). Their sequences, determined by automated Edman degradation, quantitative amino acid analysis, and mass spectrometry, were cyclo-GESCVWIPCITSAIGCSCKSKVCYRNGIPC (vitri A), cyclo-GETCVGGTCNTPGCSCSWPVCTRNGLPVC (varv A), and cyclo-GETCVGGTCNTPGCSCSWPVCTRNGLPIC (varv E), of which vitri A is described for the first time. Each forms a head-to-tail cyclic backbone, with six cysteine residues being involved in three disulfide bonds, characteristic of the family of small proteins called the cyclotides. This is the first report on cyclotides from the species V. tricolor and the first report on the sequence of the cytotoxic cyclotide vitri A.

Amino Acid Sequence↗

PubMed2004

Antitumor efficacy and acute toxicity of the novel dipeptide melphalanyl-p-L-fluorophenylalanine ethyl ester (J1) in vivo.

The novel alkylating dipeptide melphalanyl-p-L-fluorophenylalanine ethyl ester (J1) was evaluated for acute toxicity and antitumor activity in mice, with melphalan as a reference. To determine a safe and tolerable dose for efficacy studies the acute toxicity following intravenous injection in the tail vein was monitored using a 14-day schedule with up to four doses. The highest tested dose, 25 micromoles/kg, was considered close to this level, with minor effects on body weight gain but significant effects on hematological parameters. Melphalan and J1 appeared equitoxic with no statistically significant differences. Subsequently a mouse hollow fiber model was employed with subcutaneous implantation of fibers containing human tumor cells. Three different human tumor cell lines as well as two samples of primary human tumor cells (ovarian carcinoma and chronic lymphatic leukemia) were used as tumor models. At the dose level tested there was a marked and statistically significant decrease in both T-cell leukemia CCRF-CEM and small cell lung cancer NCI-H69 tumor cell growth and viability in response to J1 as compared with both placebo and melphalan treated groups. In primary ovarian carcinoma cells only J1 treatment resulted in significant tumor regression (net cell kill). In summary the results indicate that, despite an expected short half time in the blood circulation, the promising in vitro data from the previous studies of J1 seems translatable into the in vivo situation. At equal doses of alkylating units J1, compared to melphalan, was more active in the mouse hollow-fiber model, but showed similar general toxicity.

Animals↗

PubMed2004

Development and characterization of two human tumor sublines expressing high-grade resistance to the cyanoguanidine CHS 828.

The cyanoguanidine CHS 828 has shown promising antitumor properties and is currently in early clinical trials, although the mechanism of action still is largely unknown. In this study, resistant sublines of the histiocytic lymphoma cell line U-937 GTB and the myeloma line RPMI 8226 were developed by culturing under gradually increasing concentrations of CHS 828 until reaching 25 times the parental line EC50s. The new phenotypes demonstrate more than 400-fold resistance to CHS 828 and cross-resistance to six cyanoguanidine analogs, but no resistance to nine standard drugs of different mechanistic classes or to the cytotoxic guanidines m-iodobenzylguanidine and methylglyoxal-bis(guanylhydrazone). The resistant phenotypes were stable for several months even if cultivated in drug-free medium and no difference in proliferation, ultrastructural or morphologic appearance in the sublines could be detected. Neither was decreased accumulation of tritium-labeled CHS 828 observed. Furthermore, the new U-937 phenotype was not accompanied by changes in differentiation or an altered cell-cycle distribution. In the myeloma cell line, esterase activity was shown to be moderately enhanced. Two-dimensional protein electrophoresis was undertaken to unmask possible resistance-mediating proteins and/or the target molecule(s) for CHS 828. In the myeloma cell line, lambda light chain immunoglobulin (down-regulated) and a fatty acid-binding protein (up-regulated) were identified. The findings presented here indicate that development of specific cellular alterations is responsible for the gained CHS 828 resistance.

Antineoplastic Agents↗

PubMed2004

Cytotoxic effect in vivo and in vitro of CHS 828 on human myeloma cell lines.

CHS 828 is a pyridyl cyanoguanidine with promising antitumor activity both in vitro and in vivo, and has previously been found especially active against tumor cells obtained from patients with B cell chronic lymphocytic leukemia. In the present study the cytotoxic effect in vitro of CHS 828 was investigated on a panel of 10 human myeloma cell lines using the fluorometric microculture cytotoxicity assay. CHS 828 induced a concentration-dependent, but variable decrease in tumor cell survival in the cell line panel with inhibitory concentrations 50% (IC50) in the range 0.01-0.3 microM. These concentrations are below those achievable in vivo. There was no detectable dependence on P-glycoprotein-mediated or GSH-associated drug resistance and the drug showed low to moderate cross-resistance with standard drugs, including melphalan, vincristine and doxorubicin. Furthermore, sensitivity to CHS 828 showed no apparent relationship to growth factor dependence, tumor progression or phenotypic variability. CHS 828 was also tested in vivo using a hollow fiber model in rats with three of the cell lines. The results indicate a high cytotoxic activity of CHS 828. Overall, the results show a high cytotoxic activity of CHS 828 in the myeloma models, which might warrant its further development against myeloma.

Animals↗

PubMed2004

VH gene mutation status and cellular drug resistance in chronic lymphocytic leukaemia.

OBJECTIVE: B-cell chronic lymphocytic leukaemia (B-CLL) can be divided into two clinical entities based on the immunoglobulin variable heavy chain (VH) gene mutation status, as cases with unmutated VH genes display a more aggressive disease with shorter survival time than mutated cases. The aim of this study was to investigate whether differences in cellular drug resistance could give an explanation for these divergent clinical courses. METHODS: The VH gene mutation status was analysed in patients with previously untreated B-CLL using VH gene family-specific PCR amplification and nucleotide sequencing. In vitro sensitivity to cytarabine, fludarabine, cladribine, doxorubicin, idarubicin, vincristine, cyclophosphamide, melphalan and prednisolone was assessed using the non-clonogenic in vitro assay, fluorometric microculture cytotoxicity assay. RESULTS: The VH genes and in vitro drug resistance were successfully analysed in 46 cases, revealing that 25 (54%) cases showed unmutated and 21 (46%) cases mutated VH genes. Interestingly, the unmutated group generally tended to be more chemosensitive than the mutated group with significant differences for cytarabine and prednisolone (P < or = 0.01). CONCLUSION: The propensity of inferior drug response in mutated B-CLL may reflect a more differentiated disease than in unmutated B-CLL. We conclude that the difference in prognosis between B-CLL cases with unmutated and mutated VH genes could not be explained by difference in cellular drug resistance.

Antineoplastic Agents↗

PubMed2004

Multiparametric evaluation of apoptosis: effects of standard cytotoxic agents and the cyanoguanidine CHS 828.

A multiparametric high-content screening assay for measurement of apoptosis was developed. HeLa cells and lymphoma U-937 cells were exposed to cytotoxic drugs in flat-bottomed optical microtiter plates. After incubation, the DNA-binding dye Hoechst 33342, fluorescein-tagged probes that covalently bind active caspases and chloromethyl-X-rosamine to detect mitochondrial membrane potential (MMP) were added. Image acquisition and quantitative measurement of fluorescence in a defined number of cells per well was performed using the automated image capture and analysis instrument ArrayScan. The usefulness of the assay was tested in cells exposed to standard cytotoxic drugs as well as in experimental cytotoxic cyanoguanidine CHS 828. A time- and dose-dependent activation of caspase-3, decrease in MMP, and increase in nuclear fragmentation and condensation were observed for the standard drugs, with the ability to correlate the parameters on a single cell basis. CHS 828 induced caspase-3 activation and reduction in MMP with modest changes in nuclear morphology. The method described was considered to be a rapid and information-rich apoptosis assay suitable both for correlating morphological and biochemical apoptotic events in single cells as well as for screening and evaluation of novel substances with apoptosis-inducing capabilities.

Antineoplastic Agents↗

PubMed2003

Optimal heparin surface concentration and antithrombin binding capacity as evaluated with human non-anticoagulated blood in vitro.

Contact between blood and a biomaterial surface takes place in many applications and is known to activate the coagulation and complement systems. Heparin surface coatings have been shown to reduce blood activation upon contact with artificial surfaces. To establish the optimal heparin surface concentration, blood was incubated in a tubing loop model at 37 degrees C. The tubing was coated with different surface concentrations of heparin and rotated at three different velocities. We demonstrate that the blood compatibility of a surface with regard to coagulation, complement, and platelet activation can be improved by increasing the heparin surface concentration in the 6-12 pmol antithrombin/cm2 concentration interval. The binding of factor H is not influenced by the increased heparin surface concentration, suggesting that this factor is not the primary regulator of complement on heparin surfaces. In addition, the heparin coating has no effect on the complement activation that occurs on gas surfaces in extracorporeal circuits.

Antithrombins↗

PubMed2003

Increased in vitro cellular drug resistance is related to poor outcome in high-risk childhood acute lymphoblastic leukaemia.

We determined the in vitro cellular drug resistance in 370 children with newly diagnosed acute lymphoblastic leukaemia (ALL). The resistance to each of 10 drugs was measured by the fluorometric microculture cytotoxicity assay (FMCA) and was related to clinical outcome. The median follow-up time was 41 months. Risk-group stratified analyses indicated that in vitro resistance to dexamethasone, doxorubicin and amsacrine were each significantly related to the probability of disease-free survival. In the high-risk (HR) group, increased in vitro resistance to dexamethasone (P = 0.014), etoposide (P = 0.025) and doxorubicin (P = 0.05) was associated with a worse clinical outcome. Combining the results for these drugs provided a drug resistance score with an independent prognostic significance superior to that of any other factor studied, with a relative risk of relapse in the most resistant group 9.8 times that in the most sensitive group (P = 0.007). The results in the intermediate-risk (IR) and standard-risk (SR) groups were less clear cut. In conclusion, our data indicate that in vitro testing of cellular drug resistance can be used to predict the clinical outcome in HR ALL, while the final evaluation of the results in IR and SR patients must await longer follow-up.

Adolescent↗

PubMed2003

Activity of hydrolytic enzymes in tumour cells is a determinant for anti-tumour efficacy of the melphalan containing prodrug J1.

Recently, we presented a series of melphalan containing di- and tripeptides with high cytotoxic activity and J1 (l-melphalanyl-p-l-fluorophenylalanine ethyl ester) was identified as one of the most interesting compounds. It was speculated that the increased activity compared to melphalan itself, demonstrated both in vitro and in vivo, resided in increased transport over the tumour cell membrane and/or hydrolytic cleavage and liberation of melphalan inside the cells. Indeed, overexpression of hydrolytic enzymes like peptidases, esterases and proteases has been described in several types of human malignancies, thus providing a target for selective chemotherapy. In this work, the details of the increased activity was further investigated and potential tumour selectivity is discussed. The intracellular delivery of melphalan is investigated in detail using peptidase resistant dipeptide derivatives, by enzyme inhibitors and probes for enzymatic activity and by studying the time dependency of drug effect as well as intracellular drug concentrations (cellular pharmacokinetics). The results show that the activity of the dipeptide mustards is highly dependent on intracellular hydrolysis, which result in rapid intracellular release of the alkylating unit (i.e. free melphalan) in cells with high enzymatic activity. The maximum intracellular melphalan concentration following J1 exposure was reached already after 15 min, thereafter declining with a half-life of approximately 1 h. This rapid intracellular loading resulted in less reduction of activity for J1 than for melphalan and six other standard drugs when human tumour cell lines were exposed to the drugs for a limited time (simulating short half-life in vivo). Peptidase inhibitors inhibited the activity and intracellular release of melphalan, and dipeptide derivatives designed to resist the action of peptidases was less active than the corresponding normal dipeptide.

Antineoplastic Agents, Alkylating↗

PubMed2003

Antitumor activity of the alkylating oligopeptides J1 (L-melphalanyl-p-L-fluorophenylalanine ethyl ester) and P2 (L-prolyl-m-L-sarcolysyl-p-L-fluorophenylalanine ethyl ester): comparison with melphalan.

Peptichemio, a mixture of six short oligopeptides all comprising the alkylating amino acid m-L-sarcolysin, has shown clinical activity in several malignancies. Previous studies have suggested that activity mainly resides in one of the peptides, P2 (L-prolyl-m-L-sarcolysyl-p-L-fluorophenylalanine ethyl ester). In the present study the in vitro activity of P2 was further investigated and compared to melphalan and the novel alkylating dipeptide J1 (L-melphalanyl-p-L-fluorophenylalanine ethyl ester), which is structurally related to P2 and melphalan. Cytotoxic activity was studied using patient tumor cells in a non-clonogenic cytotoxicity assay, whereas cellular response, and kinetics thereof, were studied in the lymphoma cell line U-937 GTB. Cellular metabolism was studied using microphysiometry, kinetic effects on macromolecular synthesis by radiolabeled substrate incorporation and, finally, the microculture kinetic assay of apoptosis was used to monitor morphologic changes following drug exposure. The assays compared P2 favorably with melphalan. Interestingly J1 was even more cytotoxic, and produced more pronounced effects in the kinetic assays for macromolecular synthesis, metabolic activity and apoptosis. The results indicate that the delivery properties of J1 are improved compared to those of melphalan and P2.

Antineoplastic Agents, Alkylating↗

PubMed2003

Structure-activity relationship for alkylating dipeptide nitrogen mustard derivatives.

The strategy of using small peptides for effective targeting of tumor cells in chemotherapy has proven beneficial. Recently we showed that J1 (L-melphalanyl-p-L-fluorophenylalanine ethyl ester), an alkylating nitrogen mustard-containing dipeptide, exhibited strong cytotoxic activity in fresh human tumor samples in addition to rapid and pronounced inhibition of macromolecular syntheses and cellular respiration in the human tumor lymphoma cell line U-937 GTB. In this study, an additional series of 17 nitrogen mustard-containing dipeptides has been synthesized and analyzed for cytotoxic activity in a panel of 10 human tumor cell lines. The results were compared to the single amino acid mustard derivative melphalan and its ethyl and isopropyl esters. Also P2 (L-prolyl-m-L-sarcolysyl-p-L-fluorophenylalanine ethyl ester), a tripeptide that previously has shown impressive effects in human tumor cells, was used as reference. The tested compounds displayed various activities in the different cell lines but also showed a high correlation, indicating a similar mechanism of action. Factors like amino acid composition, amino acid sequence, modifications of the C- and N-termini, and to a minor extent the lipophilicity of the dipeptide derivatives appear to influence the in vitro activity. The results indicate that the activity of these compounds not only relies on their chemical reactivity, but also on active biological interactions such as transport across membranes and/or enzymatic liberation of reactive molecular entities.

Alkylation↗

PubMed2003

Antitumor activity of the novel melphalan containing tripeptide J3 (L-prolyl-L-melphalanyl-p-L-fluorophenylalanine ethyl ester): comparison with its m-L-sarcolysin analogue P2.

Peptichemio (PTC), a mixture of six oligopeptides all containing m-L-sarcolysin, has previously shown impressive results in clinical trials. The tripeptide P2 (L-prolyl-m-L-sarcolysyl-p-L-fluorophenylalanine ethyl ester) has been suggested as the main contributor to PTC activity. In contrast to its analogue melphalan, m-L-sarcolysin never reached clinical use. To allow a direct comparison, the corresponding melphalan containing tripeptide J3 (L-prolyl-L-melphalanyl-p-L-fluorophenylalanine ethyl ester) was synthesized and its activity was compared with that of P2; the activities of melphalan and m-L-sarcolysin were studied in parallel. Cytotoxic activity in human tumor cell lines and some fresh human tumor specimens were analyzed as well as effects on cellular metabolism, macromolecular synthesis, and preliminary evaluation of the cell death characteristics. The results show that melphalan and m-L-sarcolysin display similar activity in these systems and that the tripeptides were more active than their parent monomers. Surprisingly however, the melphalan containing tripeptide J3 demonstrated a significantly more rapid and stronger activity than the m-L-sarcolysin analogue P2. Finally, the in vivo toxicity and activity of melphalan and J3 were investigated in mice bearing human leukemia cells in s.c. fibers. The in vitro results seem translatable into the in vivo situation, demonstrating better antileukemic effect of J3 but similar side effects as melphalan.

Antineoplastic Agents, Alkylating↗