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Biomedical subjects

P G Kasprzyk

Publications and source records attributed to P G Kasprzyk.

At least 19 recordsLinked to original sources
PubMed2001

The homocamptothecin BN 80915 is a highly potent orally active topoisomerase I poison.

BN 80915, a lead compound of the homocamptothecin (hCPT) family, has entered clinical trials. BN 80915 is a difluoro-hCPT where the six-membered alpha-hydroxylactone ring of camptothecin (CPT) is replaced by a seven-membered beta-hydroxylactone ring. Preclinical data reported here show that in spite of the modification to the crucial E-ring of CPTs, BN 80915 retains topoisomerase I poisoning activity as shown in living HT29 cells as well as in cell-free assays, where BN 80915 always performs better than SN-38 or TPT. In antiproliferative assays BN 80915 is also very potent as evidenced by IC50s values consistently lower than those of SN38 in sensitive cell lines as well as in their related multidrug-resistant lines overexpressing P-glycoprotein or multidrug resistance-associated protein. Furthermore, in human plasma, in contrast to CPT analogs, the hydrolysis of BN 80915 is slow, leading to improved plasma stability, and irreversible, thus avoiding toxicity related to the accumulation of active principle during excretion in the urinary tract. These findings may account for the good in vivo efficacy observed in PC3 xenograft experiments where BN 80915 administered orally at very low doses doubled the tumor growth delay in comparison to CPT-11 administered i.p. Altogether, these results strongly support further development of BN 80915.

Adenocarcinoma↗
PubMed2000

Homocamptothecins: E-ring modified CPT analogues.

Homocamptothecins (hCPT) are modified camptothecins (CPT) with a seven-membered beta-hydroxylactone instead of the naturally occurring six-membered alpha-hydroxylactone. This E-ring modification fully conserves the ability to stabilize topo I-DNA single-strand breaks and stimulates high levels of DNA cleavage. A key feature is the irreversibility of E-ring opening, which should give reduced toxicity. Substituted hCPTs have been selected for their high antiproliferative activity on a panel of tumor cell lines, including those with cross resistance, and were found to be active at very low doses in a variety of human tumor xenografts when administered orally. BN 80915, a difluoro-hCPT, has entered clinical trials.

Animals↗
PubMed1999

Homocamptothecin, an E-ring modified camptothecin with enhanced lactone stability, retains topoisomerase I-targeted activity and antitumor properties.

Homocamptothecin (hCPT) is a semisynthetic analogue of camptothecin (CPT) with a seven-membered beta-hydroxylactone resulting from the insertion of a methylene spacer between the alcohol moiety and the carboxyl function of the naturally occurring six-membered alpha-hydroxylactone of CPT. This E-ring modification provides a less reactive lactone with enhanced stability and decreased protein binding in human plasma. Biological testing against CPT revealed that, instead of being detrimental, the modified lactone of hCPT has a positive impact on topoisomerase I (Topo I) poisoning properties. In vitro tests showed hCPT to fully conserve the ability to stabilize Topo I-DNA cleavage complexes and to stimulate a higher level of DNA cleavage than CPT. A similar trend toward improvement was also observed in antiproliferative assays with human tumor cell lines (including cells overexpressing P-glycoprotein). In two distinct in vivo models, using L1210 murine leukemia or human colon carcinoma HT29, hCPT was found to be more efficacious than CPT. The slow, but irreversible, hydrolysis of hCPT, instead of the fast equilibrium of CPT, may account for its good in vivo activity. Overall, these results provide evidence that a highly reactive lactone is not a requisite for the Topo I-mediated antitumor activity of CPT analogues, and that hCPT is an interesting pharmacological tool with improved solution behavior as well as a promising new template for the preparation of more efficacious Topo I poisons.

Animals↗
PubMed1998

Homocamptothecins: synthesis and antitumor activity of novel E-ring-modified camptothecin analogues.

Homocamptothecin (hCPT), a camptothecin (CPT) analogue with a seven membered beta-hydroxylactone which combines enhanced plasma stability and potent topoisomerase I (Topo I)-mediated activity, is an attractive template for the elaboration of new anticancer agents. Like CPT, hCPT carries an asymmetric tertiary alcohol and displays stereoselective inhibition of Topo I. The preparation and biological screening of racemic hCPT analogues are described. The 10 hCPTs tested were better Topo I inhibitors than CPT. Fluorinated hCPTs 23c, d,f,g were found to have potent cytotoxic activity on A427 and PC-3 tumor cell lines. Their cytotoxicity remained high on the K562adr and MCF7mdr cell lines, which overexpress a functionally active P-glycoprotein. Fluorinated hCPTs were more efficacious in vivo than CPT on HT-29 xenografts. In this model, a tumor growth delay of 25 days was reached with hCPT 23g at a daily dose of 0.32 mg/kg, compared to 4 days with CPT at 0.625 mg/kg. Thus difluorinated hCPT 23g warrants further investigation as a novel Topo I inhibitor with high cytotoxicity toward tumor cells and promising in vivo efficacy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Preclinical testing of an anti-erbB-2 recombinant toxin.

The performance of OLX-209 indicates it should enter phase I clinical testing. OLX-209 is a recombinant toxin targeting the erbB-2 oncoprotein. The design of OLX-209 takes advantage of improvements in immunotoxin technology to produce a molecule that is smaller and more potent than a conventional chemically linked antibody-toxin conjugate. The targeting portion of OLX-209 is a single chain antibody structure derived from the anti-erbB-2 hybridoma, e23. This antibody has unusual specificity in that it does not bind to most normal tissue including peripheral nerve or kidney tissue. Preclinical testing shows in vitro activity against breast cancer cell lines in the pM range. Efficacy testing in five models of human cancer indicates that a dose of 43 micrograms/kg causes reproducible tumor regressions. Efficacy can be achieved on a variety of schedules of administration. The effective dose results in no measurable change in serum liver enzymes when delivered to mice or primates. The LD10 is over twice the effective dose in mice. The pharmacokinetics indicate a t 1/2 of 50 minutes for both mice and cynomolgus monkeys. Serum concentrations of more than ten times those observed at the effective dose can be achieved in monkeys with no evidence of toxicity. Antigenicity of OLX-209 is surprisingly low. These results form the basis for the clinical testing phase for OLX-209.

Animals↗
PubMed1996

Activity of anti-erbB-2 recombinant toxin OLX-209 on lung cancer cell lines in the absence of erbB-2 gene amplification.

The recombinant oncotoxin OLX-209 [e23(Fv)PE38KDEL] has been developed to target cancers with erbB-2 expression and is nearing a clinical trial. Important in clinical planning is the selection of patients on the basis of tumor expression of erbB-2. ErbB-2 gene amplification occurs in cancers of the breast, stomach, and ovary. Patients with these diseases and evident overexpression are candidates for OLX-209 therapy. In lung cancer, overexpression of erbB-2 is also frequent, but in most cases, it is not caused by gene amplification. This study demonstrates that OLX-209 has activity on lung cancer cells with varying levels of erbB-2 expression in the presence and absence of gene amplification. In vitro sensitivity of cell lines to OLX-209 is related to erbB-2 expression level. Normal bronchial epithelial cells were not sensitive. Effective treatment of lung cancer cell lines growing as xenografts in nude mice was shown with Calu-3 (a lung adenocarcinoma line with high levels of p185(erbB-2) caused by gene amplification) and three other lung adenocarcinomas (A549, NCI-H1466, and 201T) with lower levels of p185(erbB-2) and no gene amplification. The 201T cell line was isolated recently from a lung tumor with erbB-2 expression in the original tumor. The results of this study indicate that patients with erbB-2-positive, non-small cell lung cancer should be included in clinical trials of OLX-209.

Adenocarcinoma↗
PubMed1994

Improved binding and antitumor activity of a recombinant anti-erbB2 immunotoxin by disulfide stabilization of the Fv fragment.

e23(dsFv)-PE38KDEL is a recombinant immunotoxin composed of the Fv region of anti-erbB2 monoclonal antibody e23 connected to a truncated form of Pseudomonas exotoxin (PE38KDEL), in which the inherently unstable Fv heterodimer (composed of VH and VL) is stabilized by a disulfide bond engineered between structurally conserved framework positions of VH and VL. We have now found that e23(dsFv)-PE38KDEL is considerably more cytotoxic to antigen-positive cell lines than the corresponding single-chain immunotoxin. The basis for the enhanced cytotoxic activity is that the e23 dsFv-immunotoxin binds to erbB2 with greater affinity than the single-chain counterpart. The dsFv-immunotoxin had 4-fold increased binding compared to the scFv and almost identical to the binding affinity of e23 Fab. e23(dsFv)-PE38KDEL was also considerably more stable at 37 degrees C than the single-chain immunotoxin. The therapeutic potential of the disulfide-stabilized immunotoxin was compared with its single-chain counterpart using two animal models of immunodeficient mice bearing subcutaneous tumor xenografts of human gastric tumor N87 cells or human A431 epidermoid carcinoma cells. The antitumor effect of e23(dsFv)-PE38KDEL was significantly better than that of the single-chain immunotoxin. e23(dsFv)-PE38KDEL caused complete regression of tumors at doses which caused no toxic effects in mice, whereas the single-chain immunotoxin did not cause complete regressions at the same doses.

ADP Ribose Transferases↗
PubMed1993

Effect of gastrin-releasing peptide on the pancreatic tumor cell line (Capan).

Gastrin-releasing peptide (GRP) has previously been shown to be an autocrine growth factor for small cell lung cancer, and our objective in the study presented here was to determine whether GRP has a similar role in pancreatic cancer. Using 125I-GRP, we demonstrated binding to specific, saturable, high-affinity sites (Kd = 1 nM; Bmax = 245 fmol/mg protein) in membrane preparations from the pancreatic tumor cell line Capan. The receptors were found to be biologically active. In whole cells, a GRP analogue bound to these receptors and stimulated rapid transfer of tritium from the tritiated lipid inositol pool to inositol triphosphates. Exogenous GRP addition stimulated incorporation of [3H]thymidine into DNA 20-60%. This stimulatory effect was blocked by the addition of a monoclonal antibody that complexed specifically with the receptor-binding portion of the peptide. In addition, the monoclonal antibody inhibited the growth of Capan cells in an in vitro growth assay without exogenous peptide. Bombesin receptor-specific antagonists also inhibited growth in a similar fashion. These data suggest that paracrine production of GRP may be important in pancreatic tumor growth, or that low-levels of a GRP-like peptide may play an autocrine role in this tumor.

Amino Acid Sequence↗
PubMed1992

A mitogenic peptide amide encoded within the E peptide domain of the insulin-like growth factor IB prohormone.

We have identified an amino acid sequence within the E peptide of the insulin-like growth factor IB (IGF-IB) precursor that is biologically active and designated this peptide insulin-like growth factor IB-(103-124) E1 amide (IBE1). Its existence was predicted by a flanking Gly-Lys-Lys-Lys, a signal sequence for sequential proteolytic cleavage and peptidyl C-terminal amidation. A synthetic analog of the predicted IBE1 peptide, designated Y-23-R-NH2, was generated with tyrosine added at position 0. This peptide at 2-20 nM had growth-promoting effects on both normal and malignant human bronchial epithelial cells. Y-23-R-NH2 bound to specific high-affinity receptors (Kd = 2.8 +/- 1.4 x 10(-11) M) present at 1-2 x 10(4) binding sites per cell. Ligand binding was not inhibited by recombinant insulin or recombinant IGF-I. Furthermore, a monoclonal antibody antagonist to the IGF-I receptor (alpha IR3) did not suppress the proliferative response induced by Y-23-R-NH2. In addition, C-terminal amidation was shown to be important in receptor recognition since the free-acid analog of IBE1 (Y-23-R-OH) did not effectively compete for binding and was not a potent agonist of proliferation. Immunoblot analysis of human lung tumor cell line extracts using an antibody raised against Y-23-R-NH2 detected a low molecular mass band of approximately 5 kDa, implying that a protein product is produced that has immunological similarity to IBE1. Extracts of human, mammalian, and avian livers analyzed on an immunoblot with the anti-Y-23-R-NH2 antibody contained proteins of approximately 21 kDa that were specifically recognized by the antiserum and presumably represent an IGF-I precursor molecule. This implies that in species where an IGF-I mRNA with homology to the human IGF-IB E domain has not yet been described, an alternate mRNA must be produced that contains a sequence similar to that of the midportion of the human IGF-IB E domain. Our findings demonstrate that IBE1 is a growth factor that mediates its effect through a specific high-affinity receptor and is most likely conserved in many species.

Amides↗
PubMed1992

Recombinant anti-erbB2 immunotoxins containing Pseudomonas exotoxin.

Immunotoxins were made using five different murine monoclonal antibodies to the human erbB2 gene product and LysPE40, a 40-kDa recombinant form of Pseudomonas exotoxin (PE) lacking its cell-binding domain. All five conjugates were specifically cytotoxic to cancer cell lines overexpressing erbB2 protein. The most active conjugate was e23-LysPE40, generated by chemical crosslinking of anti-erbB2 monoclonal antibody e23 to LysPE40. In addition, a recombinant immunotoxin, e23(Fv)PE40, was constructed that consists of the light-chain variable domain of e23 connected through a peptide linker to its heavy-chain variable domain, which in turn is fused to PE40. The recombinant protein was made in Escherichia coli, purified to near homogeneity, and shown to selectively kill cells expressing the erbB2 protooncogene. To improve the cytotoxic activity of e23(Fv)PE40, PE40 was replaced with a variant, PE38KDEL, in which the carboxyl end of PE is changed from Arg-Glu-Asp-Leu-Lys to Lys-Asp-Glu-Leu and amino acids 365-380 of PE are deleted. The e23(Fv)PE38KDEL protein inhibits the growth of tumors formed by the human gastric cancer cell line N87 in immunodeficient mice.

ADP Ribose Transferases↗
PubMed1992

Therapy of an animal model of human gastric cancer using a combination of anti-erbB-2 monoclonal antibodies.

Amplification and/or overexpression of the erbB-2 gene have been demonstrated in 20-30% of adenocarcinomas of the breast, ovary, lung, and stomach and are associated with aggressive clinical course and poor prognosis. Interference with erbB-2 function by the use of monoclonal antibodies is a promising approach to the treatment of these diseases. In this study we demonstrate that a combination of two anti-erbB-2-specific antibodies inhibited the growth of human gastric tumor cells in vitro. This combination antibody therapy also inhibited the growth of human tumor cell lines growing as xenografts in nude mice and was able to dramatically reduce established tumors. This is the first reported observation of tumor regression induced by anti-erbB-2 monoclonal antibodies. Treatment was not curative in that tumors regrew after 6 weeks. Treatment with either single antibody alone did not inhibit cell growth or tumor formation. Pulse chase and tyrosine kinase activity experiments were used to investigate the activity of the erbB-2 gene product (gp185erbB-2). The formation of complexes by two antibodies was found to interfere with receptor function and mimic some properties of a typical receptor ligand. Selective interference of the erbB-2 receptor by combination antibody therapy may be advantageous for the treatment of human cancers.

3T3 Cells↗
PubMed1991

Preclinical evaluation of an anti-autocrine growth factor monoclonal antibody for treatment of patients with small-cell lung cancer.

We have evaluated an anti-autocrine growth factor monoclonal antibody for potential use in the treatment of patients with small-cell lung cancer. The monoclonal antibody, designated 2A11, binds to the C-terminal region of the autocrine growth factor gastrin-releasing peptide and neutralizes its growth-promoting effects in vitro and in vivo. Equilibrium-binding analysis demonstrated that the peptide binds to the antibody (dissociation constant = 1.5 x 10(-10) at least as avidly as it binds to the tumor peptide receptor. Pharmacokinetic studies in normal BALB/c mice demonstrated an initial clearance half-life (alpha t1/2) of 24.3 +/- 4 hours and a secondary clearance half-life (beta t1/2) of 1039.6 +/- 309 hours, and biodistribution studies revealed a distribution pattern which generally reflected blood flow. Single intravenous infusions of 2A11 (20 mg/20-25-kg dogs) into normal mongrel dogs with surgically created gastric fistulas antagonized the stimulatory effects of exogenously infused gastrin-releasing peptide or bombesin on plasma gastrin release and gastric acid secretion. Toxicology studies in normal dogs (with gastric fistulas) infused with 50 mg 2A11 intravenously three times a week for 4 weeks failed to reveal any adverse behavioral, clinical, or pathological effects. Four of six dogs developed an immune response to 2A11. Anti-idiotypic antibodies elicited in two cases did not mimic the functional effects of the peptide. We conclude that the concept of immunoblockade of an autocrine growth factor appears feasible in vivo.

Animals↗
PubMed1991

Alpha-amidation of peptide hormones in lung cancer.

Small-cell lung cancer (SCLC), the most common neuroendocrine tumor in humans, provides an excellent model system for analyzing the role of growth factors in lung cancer. SCLCs secrete a wide range of peptide hormones, including some that stimulate tumor cell growth, such as gastrin-releasing peptide and insulin-like growth factor I. Many of these peptides are synthesized as prohormones that acquire biological activity only after specific post-translational modifications. Here, we review our current understanding of the biological role of neuroendocrine peptides in lung carcinogenesis and consider how a mechanistic knowledge of one particular modification, carboxy-terminal alpha-amidation, may permit identification of novel growth factors for lung cancer cells. We also describe potential applications of this knowledge as a basis for prevention-oriented approaches to the disease.

Amides↗
PubMed1991

Lung cancer: rational strategies for early detection and intervention.

The current mortality rate for lung cancer, which approaches 90% at two years, is not decreasing despite intensive clinical trials attempting to improve systemic therapy. New drug discoveries and dose intensification approaches have not resulted in more effective anti-tumor control. An alternative approach using sputum immunocytology for early lung cancer detection was recently reported. The proposed basis for this early detection reflects the underlying biology of immunodominant carbohydrate tumor-associated antigens, which are recognized as a class of oncofetal antigens. The process of bronchial epithelial carcinogenesis is associated with an evolution of carbohydrate display which reverses the sequence originally associated with fetal organ development. By elucidating this pattern of fetal carbohydrate display, a precise map of stage of bronchial carcinogenesis may emerge.

Antigens, Neoplasm↗
PubMed1990

Implications of erbB-2 overexpression for basic science and clinical medicine.

Overexpression of the Epidermal Growth Factor (EGF) Receptor gene and the related erbB-2 gene has been identified in human cancers derived from a variety of tissues. The overexpression of the encoded growth factor receptor proteins is functionally related to the development of the tumor. This observation has important potential consequences for the improved diagnosis and treatment of cancer. Overexpression of these proteins also provides experimental systems that facilitate the study of growth factor signal transduction.

Animals↗