Inhibition of cotranslational translocation by apratoxin S4: Effects on oncogenic receptor tyrosine kinases and the fate of transmembrane proteins produced in the cytoplasm.

Receptor tyrosine kinases (RTKs) have become major targets for anticancer therapy. However, resistance and signaling pathway redundancy has been problematic. The marine-derived apratoxins act complementary to direct kinase inhibitors by downregulating the levels of multiple of these receptors and additionally prevent the secretion of growth factors that act on these receptors by targeting Sec61α, therefore interfering with cotranslational translocation. We have profiled the synthetic, natural product-inspired apratoxin S4 against panels of cancer cells characterized by differential sensitivity to RTK inhibitors due to receptor mutations, oncogenic KRAS mutations, or activation of compensatory pathways. Apratoxin S4 was active at low-nanomolar to sub-nanomolar concentrations against panels of lung, head and neck, bladder, and pancreatic cancer cells, concomitant with the downregulation of levels of several RTKs, including EGFR, MET and others. However, the requisite concentration to inhibit certain receptors varied, suggesting some differential substrate selectivity in cellular settings. This selectivity was most pronounced in breast cancer cells, where apratoxin S4 selectively targeted HER3 over HER2 and showed greater activity against ER+ and triple negative breast cancer cells than HER2+ cancer cells. Depending on the breast cancer subtype, apratoxin S4 differentially downregulated transmembrane protein CDCP1, which is linked to metastasis and invasion in breast cancer and modulates EGFR activity. We followed the fate of CDCP1 through proteomics and found that nonglycosylated CDCP1 associates with chaperone HSP70 and HUWE1 that functions as an E3 ubiquitin ligase and presumably targets CDCP1, as well as potentially other substrates inhibited by apratoxins, for proteasomal degradation. By preventing cotranslational translocation of VEGF and other proangiogenic factors as well as VEGFR2 and other receptors, apratoxins also possess antiangiogenic activity, which was validated in endothelial cells where downregulation of VEGFR2 was observed, extending the therapeutic scope to angiogenic diseases.

Identification of a mitochondrial-binding site on the N-terminal end of hexokinase II.

Hexokinase II (HKII) is responsible for the first step in the glycolysis pathway by adding a phosphate on to the glucose molecule so it can proceed down the pathway to produce the energy for continuous cancer cell growth. Tumour cells overexpress the HKII enzyme. In fact, it is the overexpression of the HKII enzyme that makes the diagnosis of cancer possible when imaged by positron emission tomography (PET). HKII binds to the voltage-dependent anion channel (VDAC) located on the mitochondrial outer membrane (MOM). When bound to the MOM, HKII is blocking a major cell death pathway. Thus, HKII is responsible for two characteristics of cancer cells, rapid tumour growth and inability of cancer cells to undergo apoptosis. One method to identify novel compounds that may interfere with the HKII-VDAC-binding site is to create a molecular model using the crystal structure of HKII. However, the amino acid(s) responsible for HKII binding to VDAC are not known. Therefore, a series of truncations and point mutations were made to the N-terminal end of HKII to identify the binding site to VDAC. Deletions of the first 10 and 20 amino acids indicated that important amino acid(s) for binding were located within the first 10 amino acids. Next, a series of point mutations were made within the first 10 amino acids. It is clear from the immunofluorescence images and immunoblot results that mutating the fifth amino acid from histidine to proline completely abolished binding to the MOM.

Pazopanib combined with radiation: in vivo model of interaction.

OBJECTIVE: Assess interaction of pazopanib, an oral antivascular endothelial growth factor inhibitor, with radiation in tumor xenograft models. METHODS: Flank xenografts in female athymic nude mice of human lung cancer cell line, A549, and head and neck cancer cell line, UM-SCC-6, were allowed to grow to ∼5×5 mm. Groups were then treated with pazopanib and/or escalating doses of radiation and tumor measurements over time compared with untreated tumor-bearing controls. Pazopanib (100 mg/kg) began 7 days before radiation and continued for 28 days. Daily radiation was 0.5, 1, 2, or 3 Gy ×5 days. RESULTS: Tumors in the A549 control group reached >4× the original size by day 36 postradiation. All treatment groups had less robust tumor growth (p<0.05) and the group receiving pazopanib+3 Gy radiation/day had tumor regression to less than baseline. In the UM-SCC-6-tumor-bearing animals, tumors in all treatment groups had less robust growth than untreated controls after day 23 post-treatment. CONCLUSION: The combination of pazopanib and radiation resulted in a trend of superior tumor growth inhibition compared with either agent alone. All treatment groups had impaired tumor progression compared with untreated controls.

Treatment of small cell lung cancer with TRA-8 in combination with cisplatin and radiation.

BACKGROUND: Limited stage small cell lung cancer (SCLC) represents a minority of SCLC. Despite extensive clinical trials, standard treatment remains cisplatin-based chemotherapy and thoracic irradiation (TI). This study focused on the interaction of cisplatin/radiation with the anti-human DR5 monoclonal antibody TRA-8 in SCLC cells. TRA-8 binds specifically to DR5 and has been shown to activate apoptosis. METHODS: Four human SCLC cell lines were utilized for experimentation (SCLC-41, SCLC-58, SCLC-68, and SCLC-74). Immunoblot analysis was used to determine relative protein levels of DR5, DR4 and pro-caspase 8 for each cell line. Using a tetrazolium-based assay (XTT), the IC(50) values for cisplatin with or without TRA-8 were determined for the SCLC cell lines. Four SCLC lines were assayed with a combination of TRA-8 (10 µg/ml), 2 Gy radiation and various concentrations of cisplatin. Apoptosis was evaluated using Annexin V-FITC and cleaved caspase immunoblotting. Using a SCLC-58 subcutaneous xenograft model, treatment began 21 d after tumor cell injection. Treatment included weekly cisplatin (4 mg/kg) and radiation of 1 Gy (24 h after cisplatin) and TRA-8 (200 µg) was administered i.p. twice weekly for three weeks. RESULTS: Immunoblot analysis showed similar levels of DR5 for all cell lines with variable levels of DR4. Various concentrations of TRA-8 antibody (≤ 10 µg/ml) induced no significant cytotoxicity in the SCLC cell lines. The in vitro combination treatment with TRA-8 (10 µg/ml), 1.25 µg/ml cisplatin and 2 Gy radiation showed increased cytotoxicity when compared to combinations without TRA-8. Furthermore, the triple combination demonstrated the greatest amount of apoptosis as measured by Annexin V staining. The in vivo studies showed the combination of 1G y, cisplatin and TRA-8 extended the tumor doubling time to 44 d as compared to any doublet treatment groups that ranged from 12 to 20 d. Analysis of survival data showed 100% of the combination group (RT+cisplatin+TRA-8) were alive 65 d after treatment began whereas all doublet treatment groups showed 50% or less survival. CONCLUSIONS: These studies showed increased cytotoxicity when TRA-8 was added to radiation/cisplatin in SCLC. This effect was demonstrated in vitro and in vivo. TRA-8 represents a promising new agent in the treatment of SCLC.

Inhibition of STAT-3 results in greater cetuximab sensitivity in head and neck squamous cell carcinoma.

OBJECTIVE: The inhibition of epidermal growth factor receptor (EGFr) with the monoclonal antibody cetuximab reduces cell proliferation and survival which correlates with increased DNA damage. Since the signal transducer and activator of transcription-3 (STAT-3) is involved in the EGFr-induced signaling pathway, we hypothesized that depletion of STAT-3 may augment cetuximab-induced processes in human head and neck cancer cells. MATERIALS AND METHODS: Human head and neck squamous carcinoma cells (UM-SCC-5) were transfected with short hairpin RNA (shRNA) against STAT-3 (STAT3-2.4 and 2.9 cells). A mutated form of this shRNA was transfected for a control (NEG4.17 cells). Radiosensitivity was assessed by a standard colony formation assay. Proliferation was assessed by daily cell counts following treatment and apoptosis was assessed by an annexin V-FITC assay. The alkaline comet assay was used to assess DNA damage. RESULTS: The STAT-3 knockdown cells (STAT3-2.4 and STAT3-2.9 cells) demonstrated enhanced radiosensitivity compared to control NEG4.17 cells, which correlated with increased apoptosis. Also, the STAT-3 knockdown cells demonstrated decreased proliferation with cetuximab treatments compared to control cells (NEG4.17). The increased cetuximab sensitivity of the STAT-3 knockdown cells correlated with increased apoptosis and DNA damage compared to control cells (NEG4.17). CONCLUSION: These studies revealed that the greater anti-proliferative effects and increased cytotoxicity of cetuximab in the STAT3-2.4 and STAT3-2.9 cells compared to control NEG4.17 cells, may be a result of STAT3-mediated effects on cellular apoptosis and DNA damage.

Clotrimazole induces a late G1 cell cycle arrest and sensitizes glioblastoma cells to radiation in vitro.

Tumor cells are characterized by their high rate of glycolysis and clotrimazole has been shown to disrupt the glycolysis pathway thereby arresting the cells in the G1 cell cycle phase. Herein, we present data to support our hypothesis that clotrimazole arrests tumor cells in a radiosensitizing, late G1 phase. The effects of clotrimazole were studied using the glioblastoma cell line, U-87 MG. Flow cytometry was used to analyze cell cycle redistribution and induction of apoptosis. Immunoblots were probed to characterize a late G1 cell cycle arrest. Nuclear and cytoplasmic fractions were collected to follow the clotrimazole-induced translocation of hexokinase II. Clonogenic assays were designed to determine the radiosensitizing effect by clotrimazole. Our studies have shown a dose-dependent and time-dependent clotrimazole arrest in a late G1 cell cycle phase. Concurrent with the late G1 arrest, we observed an overexpression of p27 along with a decreased expression of p21, cyclin-dependent kinase 1, cyclin-dependent kinase 4, and cyclin D. Clotrimazole induced the translocation of mitochondrial-bound hexokinase II to the cytoplasm and the release of cytochrome c into the cytoplasm. Clotrimazole-induced apoptosis was enhanced when combined with radiation. Clotrimazole was shown to sensitize tumor cells to radiation when the cells were irradiated for 18 h post-clotrimazole treatment. The disruption of the glycolysis pathway by clotrimazole leads to cell cycle arrest of U-87 MG cells in the radiosensitizing late G1 phase. The use of clotrimazole as a radiosensitizing agent for cancer treatment is novel and may have broad therapeutic applications.

Synthesis and preliminary biological evaluation of high-drug-load paclitaxel-antibody conjugates for tumor-targeted chemotherapy.

The goal of this study was to design paclitaxel (PTX)-monoclonal antibody (mAb) prodrug conjugates (PTXMAbs) with the ability to deliver therapeutically significant doses of the drug to the tumor while avoiding the previously observed solubility limitations of conjugates with PTX:mAb molar ratios of >3. New PTX conjugates were synthesized using the discrete poly(ethylene glycol) (dPEG) as linkers. These compounds, PTX-L-Lys[(dPEG12)(3)-dPEG4]-dPEG6-NHS (9a and 9b, for L = GL or SX, respectively), were then conjugated to the antiepidermal growth factor receptor mAb, C225 at increasing PTX:C225 ratios, producing completely soluble conjugates. Unlike the earlier PTXMAbs, buffered solutions of these conjugates remained homogeneous for extended periods of time. Fluorescence-activated cell sorting (FACS) analysis indicated preserved immunogenicity of the conjugates at all four substitution ratios, while cytotoxicity studies in MDA-MB-468 breast cancer cells indicated preservation of drug cytotoxicity. These conjugates may have potential in the development of high-drug-load tumor-targeting taxanes.

Rational design and semisynthesis of betulinic acid analogues as potent topoisomerase inhibitors.

Chemical transformation studies were conducted on betulinic acid (1), a common plant-derived lupane-type triterpene. Eleven new rationally designed derivatives of 1 (2-5 and 7-13) were synthesized based on docking studies and tested for their topoisomerase I and IIalpha inhibitory activity. Semisynthetic reactions targeted C-3, C-20, and C-28 in 1. Structures of the new compounds were confirmed by spectroscopic methods (1D and 2D NMR and MS). Compound 9, 3-O-[N-(phenylsulfonyl)carbamoyl-17beta-N-(phenylsulfonyl)amide]betulinic acid, showed 1.5-fold the activity of CPT in a topoisomerase I DNA relaxation assay. Four out of 14 betulinic acid analogues (5, 9, 11, and 12) showed 1.5-fold the activity of etoposide in a topoisomerase II assay. The new analogues exhibited better cytotoxic activities against the human colon cancer cells SW948 and HCT-116 and the breast cancer cell line MDA-MB-231 compared to the parent (1). Betulinic acid (1) is a potential scaffold for the design of new topoisomerase I and IIalpha inhibitors.

Inhibition of STAT-3 results in radiosensitization of human squamous cell carcinoma.

BACKGROUND: Signal transducer and activator of transcription-3 (STAT-3) is a downstream component of the Epidermal Growth Factor Receptor (EGFr) signaling process that may facilitate the resistance of tumor cells to conventional cancer treatments. Studies were performed to determine if inhibition of this downstream protein produces radiosensitization. METHODS/RESULTS: A431 cells (human squamous cell carcinoma cells with EGFr overexpression) were found to be sensitized to radiation after treatment with STAT-3 small interfering RNA (siRNA). Therefore, a short hairpin RNA (shRNA) against STAT-3 was designed and cloned into a pBABE vector system modified for shRNA expression. Following transfection, clone 2.1 was selected for further study as it showed a dramatic reduction of STAT-3 protein (and mRNA) when compared to A431 parental cells or a negative control shRNA cell line (transfected with STAT-3 shRNA with 2 base pairs mutated). A431 2.1 showed doubling times of 25-31h as compared to 18-24h for the parental cell line. The A431 shRNA knockdown STAT-3 cells A431 were more sensitive to radiation than A431 parental or negative STAT-3 control cells. CONCLUSION: A431 cells stably transfected with shRNA against STAT-3 resulted in enhanced radiosensitivity. Further work will be necessary to determine whether the inhibition of STAT-3 phosphorylation is a necessary step for the radiosensitization that is induced by the inhibition of EGFr.

Synthesis and antiproliferative activity of benzyl and phenethyl analogs of makaluvamines.

Analogs of marine alkaloid, makaluvamine, bearing substituted benzyl and substituted phenethyl side chains have been synthesized and their antiproliferative activities have been evaluated. 4-Methyl, 4-chloro, and 4-fluoro substituted benzyl analogs possessed pronounced antiproliferative effects on the breast cancer cell line, MCF-7 at IC(50) values of 2.3 microM, 1.8 microM, and 2.8 microM, respectively. 4-Methyl, 4-chloro, and 3,4-methylenedioxy derivatives showed the best activity against MCF-7 among the phenethyl analogs with IC(50) values of 2.3 microM, 2.8 microM, and 2.4muM, respectively. In general, methoxy substitutions resulted in slight loss in activity in both benzyl and phenethyl series. Benzyl, 4-fluorobenzyl, 3,4-dimethoxyphenethyl, and 3,4-methylenedioxyphenethyl analogs were tested by NCI in their 60 cell lines in vitro human cancer cell screen. All four compounds showed excellent inhibition against several tested cancer cell lines. Benzyl and 4-fluorobenzyl analogs were relatively more active than 3,4-dimethoxy phenethyl and 3,4-methylenedioxy phenethyl analogs. In NCI assays, the best LogGI(50) values were shown by the fluorobenzyl analog against the renal cancer cell line RXF-393 (<-8.0M) and dimethoxy phenethyl analog against the CNS cancer cell line, SF-268 (<-8.0M). The best LogLC(50) value was shown by the fluorobenzyl analog against the breast cancer cell line MCF-7 (-6.01 M).

Design and development of water-soluble curcumin conjugates as potential anticancer agents.

Conjugates of curcumin to two differently sized poly(ethylene glycol) molecules were synthesized in an attempt to overcome the low aqueous solubility of this natural product with cytotoxic activity against some human cancer cell lines. The soluble conjugates exhibited enhanced cytotoxicity as compared to that of the parent drug. Synthesis, analyses of the rate of drug release, and cytotoxicity studies are herein reported. The water-soluble conjugates may provide information useful for the development of injectable curcumin conjugates.

Analogs of the marine alkaloid makaluvamines: synthesis, topoisomerase II inhibition, and anticancer activity.

Twelve analogs of makaluvamines have been synthesized. These compounds were evaluated for their ability to inhibit the enzyme topoisomerase II. Five compounds were shown to inhibit topoisomerase catalytic activity comparable to two known topoisomerase II targeting control drugs, etoposide and m-AMSA. Their cytotoxicity against human colon cancer cell line HCT-116 and human breast cancer cell lines MCF-7 and MDA-MB-468 has been evaluated. Four makaluvamine analogs exhibited better IC(50) values against HCT-116 as compared to control drug etoposide. One analog exhibited better IC(50) value against HCT-116 as compared to m-AMSA. All 12 of the makaluvamine analogs exhibited better IC(50) values against MCF-7 and MDA-MB-468 as compared to etoposide as well as m-AMSA.

Single-drug multiligand conjugates: synthesis and preliminary cytotoxicity evaluation of a paclitaxel-dipeptide "scorpion" molecule.

To improve the targeting properties of receptor-directed drug-peptide conjugates, a multiligand approach was proposed and a model "scorpion" conjugate (6, Figure 1), consisting of two peptide "claws" and a paclitaxel (PTX) "tail", was synthesized. The cell surface receptor-directed peptide used in this single-drug multiligand (SDML) model was a segment of the amphibian peptide bombesin (BBN) which had the Y6Q7W8A9V10G11H12L13M14-NH2 sequence, designated here as BBN[6-14] (2, Figure 2). Due to the lipophilic nature of both PTX and BBN[6-14], compound 6 had a low water solubility. To enhance the solubility, PEG derivatives of this conjugate were prepared with the polymer inserted either in the claws or in the tail regions. In a preliminary random screening, conjugate 6 showed superior cytotoxic activity in several GRPR-positive human cancer cell lines as compared to free PTX and two single-drug single-ligand (SDSL) conjugates. In a receptor blocking experiment, addition of excess unconjugated BBN[6-14] ligand reduced the cytotoxicity of conjugate 6, indicating the receptor-mediated mechanism of drug delivery. The PEG-derived conjugates showed activities which were intermediate between SDSL and the SDML congeners. Also, an increase in the number of the PEG segments lowered cytotoxicity, possibly due to steric hindrance against ligand-receptor binding. Taken together, these results demonstrate the potential of the multiligand approach in the design of receptor-targeting conjugates for tumor-specific drug delivery.

Epidermal growth factor receptor tyrosine kinase inhibitor, erlotinib, and concurrent 5-fluorouracil, cisplatin and radiotherapy for patients with esophageal cancer: a phase I study.

This phase I trial investigates the safety of combining radiation, 5-fluorouracil (5-FU) and cisplatin with the epidermal growth factor receptor tyrosine kinase inhibitor, erlotinib, in patients with esophageal carcinoma. From April 2000 to January 2005, 11 patients with squamous or adenocarcinoma of the esophagus were enrolled. Patients received either 50, 100 or 150 mg oral erlotinib/day beginning on the first day of radiation (three patients in each dose cohort). Concurrent cisplatin (75 mg/m2 i.v., days 8 and 36) and 5-FU (1000 mg/m2 i.v., days 8-11 and 36-39) were also given with 50.4 Gy thoracic radiation, delivered at 180 cGy/day, 5 days/week. Toxicity was evaluated using the National Cancer Institute Common Toxicity Criteria (version 3.0). Erlotinib with concurrent 5-FU, cisplatin and thoracic radiation was well-tolerated at 50, 100 and 150 mg/day. The major toxicities were diarrhea (grade 1=18%, grade 2=18%), skin rash (grade 4=54.5%), nausea (grade 1=18%, grade 2=54%, grade 3=9%) and dehydration (grade 3=27%). All patients experienced esophagitis during treatment (grade 1=55%, grade 2=32%, grade 3=9%, grade 4=9%). Two patients were discontinued from the study secondary to non-erlotinib-related toxicities. We conclude that the phase I study demonstrates the safety and tolerability of erlotinib delivered at 150 mg/day with concurrent 5-FU, cisplatin and thoracic radiation. The major toxicities encountered were grade 1-2 diarrhea, grade 1 skin rash, grade 1-3 nausea and grade 3 dehydration. A phase II study is planned.

Extracellular matrix metalloprotease inducer-expressing head and neck squamous cell carcinoma cells promote fibroblast-mediated type I collagen degradation in vitro.

Until recently, tumor progression has been considered a multistep process defined by tumor cell mutations and the importance of the surrounding stroma poorly understood. It is now recognized that matrix-degrading enzymes that promote tumor cell invasion are elaborated by both tumor cells and fibroblasts in vivo. To determine the relative role of tumor cell-derived proteases compared with fibroblast-derived proteases, coculture experiments were done with each cell type using an in vitro model of type I collagen degradation. Head and neck squamous cell carcinoma cells in coculture with normal dermal fibroblasts showed matrix degradation, but neither cell type alone produced this effect. Manipulating the in vitro coculture environment showed that collagenolysis in this model was a result of fibroblast-derived matrix metalloproteases (MMP). To explore the possible role of extracellular matrix metalloprotease inducer (EMMPRIN) in this interaction, transfection of EMMPRIN into a cell line with low endogenous EMMPRIN expression was done and showed a significant increase in collagenolysis. Inhibition of collagenolysis with a tissue inhibitor of metalloprotease-2 (TIMP-2) and a synthetic furin inhibitor was observed but not with TIMP-1, which suggested a possible role for membrane type-1 MMP. These results suggest that fibroblast-derived MMPs but not those from tumor cells are important for in vitro collagenolysis and that this process is promoted by tumor cell-expressed EMMPRIN.

Synthesis and biological evaluation of a paclitaxel immunoconjugate.

Targeted cancer therapy is a promising strategy for the treatment of this disease. In this approach, a cytotoxic agent (CA), such as a drug or a radionuclide, is attached, usually covalently, to a "targeting" vehicle (TV), which in turn is capable of recognizing specific receptor motifs on the surface of the tumor cells. Once administered systemically, the construct would localize on the tumor through the TV moiety and would release the CA cargo, resulting in the destruction of the malignant tissue. Small-molecule peptides as well as monoclonal antibodies have been used as TVs. The synthesis, antigen binding, and cytotoxicity of a covalent conjugate of the anticancer drug paclitaxel (taxol) to the anti-epidermal growth factor receptor (EGFR) monoclonal antibody C225 (IMC-C225; Erbitux, ImClone Systems, Somerville, NJ) are described in this chapter to illustrate the methods used for the construction and in vitro evaluation of these conjugates.

Site-specifically traced drug release and biodistribution of a paclitaxel-antibody conjugate toward improvement of the linker structure.

Tumor-directed drug delivery is a promising strategy in cancer treatment, and in this field, monoclonal antibodies constitute an important class of targeting vehicles. A critical issue in the design of targeting conjugates is the timing of the release of the cytotoxic payload, with the ideal situation being the release at the maximum tumor uptake of the targeting molecule. A site-specific radiolabeling technique was used to elucidate the biodistribution and in vivo drug release pattern of an antibody conjugate of paclitaxel (PTX, 1, Figure 1) in which the drug and the antibody moieties were connected by a succinate (SX) linker. In this new method, a metabolite of PTX, 3'-(4-hydroxyphenyl)paclitaxel (3'-OH-PTX, 2, Figure 1) was used as a tyrosine mimic for the synthesis of the drug site-labeled conjugate (DSL, [(125)I]-3'-OH-PTXSXC225). This was achieved by iodogen (125)I-labeling of 3'-OH-PTXSX and subsequent conjugation to C225. The antibody site-labeled conjugate (ASL, PTXSX-[(125)I]-C225) was prepared by direct radioiodination of PTXSXC225. Biodistribution of these compounds was studied in Balb/c nude mice bearing DU-145 human prostate carcinoma xenografts. While the 4 and 24 h tumor uptake (in percent injected dose per gram of tissue, %ID/g) for [(125)I]-3'-OH-PTXSXC225 were 3.3 +/- 1.5 and 1.7 +/- 0.6%ID/g, the PTXSX-[(125)I]-C225 showed tumor uptake values of 3.8 +/- 4.2 and 14.8 +/- 4.2%ID/g at these time points. This difference in the tumor uptake over time indicates an early cleavage of the drug with respect to the antibody tumor localization. This was further confirmed by an in vitro drug release kinetics study leading to a half-life of about 2 h for PTXSXC225 under physiological conditions. To increase the stability of the PTX-MAb bond, a new conjugate (PTXGLC225) with glutaric acid (GL) as the linker was synthesized. Under the same conditions, the PTXGLC225 showed a 16-fold increase in the half-life (t(1/2)) of the drug release. The effect of the increased t(1/2) of this compound on the antitumor activity of the conjugate was tested in a DU-145 human prostate tumor-implanted mouse model. In comparison to a previous similar experiment with PTXSXC225, better antitumor activity was observed for the PTXGLC225 conjugate as compared to controls. These results demonstrated the first time use of radioiodinated 3'-OH-PTX for in vivo tracing of a paclitaxel conjugate and application of the resulting information to the design of a therapeutically more useful PTX-MAb linker.

Anti-EGFR-mediated radiosensitization as a result of augmented EGFR expression.

PURPOSE: Elevated epidermal growth factor receptor (EGFR) expression has correlated with a poor prognosis after standard treatment of several malignancies. However, it is not clear whether the absolute level of EGFR expression affects the radiosensitizing properties of anti-EGFR treatments. A better understanding of this question would be helpful for the design of protocols that deliver these treatments. To explore this question, cells (LS174T) that did not display inherent anti-EGFR treatment-induced radiosensitization were selected for studies that could potentially enhance EGFR expression. MATERIALS AND METHODS: Human colon carcinoma cells (LS174T), which did not show radiosensitization by anti-EGFR treatments, were employed for these studies. (Also, these cells were not responsive to the antiproliferative effects of anti-EGFR treatment.) Using standard transfection techniques (eukaryotic expression vector) as well as an adenoviral construct to enhance EGFR expression, LS174T cells were transduced in a manner that resulted in enhanced expression of EGFR. Subsequently, standard proliferation studies were performed to test the radiosensitizing properties of anti-EGFR treatment (an anti-EGFR monoclonal antibody: IMC-C225). RESULTS: Studies were undertaken to stably transfect LS174T cells with EGFR. The stable transfectants, LS174T.EGFR cells, were responsive to the antiproliferative effects of anti-EGFR treatment, in contrast to the parent LS174T cells. Similar results were demonstrated when the cells were infected with AdEGFR. Additionally, the LS174T.EGFR cells were responsive to the radiosensitizing properties of anti-EGFR treatment (IMC-C225), whereas the parent cells were not. CONCLUSIONS: Although the level of EGFR expression is of prognostic significance in many tumor models, the response of cells to anti-EGFR treatment alone, or combinations of this treatment with radiation or chemotherapy, depends upon many factors that are not necessarily related to the inherent EGFR expression of the tumor cells. However, the studies reported herein, demonstrate that when LS174T cells were transduced to show increased EGFR expression, they became responsive to the radiosensitizing properties of anti-EGFR treatments.

Adenoviral vector-mediated augmentation of epidermal growth factor receptor (EGFr) enhances the radiosensitization properties of anti-EGFr treatment in prostate cancer cells.

PURPOSE: To determine whether an adenoviral vector approach to the augmentation of epidermal growth factor receptor (EGFr) expression results in increased antiproliferative and radiosensitization properties of anti-EGFr antibody therapy in prostate cancer cells. METHODS AND MATERIALS: DU145 and LNCaP human prostate cancer cells were used to test the above question in vitro. An adenoviral vector was utilized to transduce cells with an EGFr transgene (AdEGFr). Immunoblots were performed to measure EGFr expression and EGFr tyrosine phosphorylation. Radiolabeled ligand studies were employed to test binding of epidermal growth factor to EGFr. Scatchard analyses allowed for quantification of the number of EGFrs. Standard immunohistochemistry was performed to assess EGFr expression. Cellular proliferation was assessed after various combinations of treatment. RESULTS: Studies of prostate carcinoma cells infected with AdEGFr demonstrated an increase in EGFr expression. This increase in expression correlated with increased function of EGFr. Specifically, increased EGFr expression also resulted in increased ligand binding, ligand-induced internalization of EGFr, and ligand-induced EGFr tyrosine kinase activity that could be blocked with pre-exposure to IMC-C225 (an anti-EGFr monoclonal antibody). Transduction of the LNCaP cells with AdEGFr did not increase the antiproliferative effects of IMC-C225, but did significantly increase IMC-C225-induced radiosensitization as determined by cell proliferation. CONCLUSIONS: Augmentation of EGFr expression, through an adenoviral vector approach in prostate carcinoma cells, resulted in cells that demonstrated greater IMC-C225-induced radiosensitization compared to cells that were not treated with AdEGFr.

Differential responses by pancreatic carcinoma cell lines to prolonged exposure to Erbitux (IMC-C225) anti-EGFR antibody.

BACKGROUND: Pancreatic cancer remains a devastating disease, with 95% of all patients diagnosed with the disease dying within 2 years. The combined therapy using Erbitux, gemcitabine, and radiation caused complete tumor regression using a nude mouse model inoculated with pancreatic MiaPaCa-2 cells but only a delay in tumor growth with BxPC-3. We investigated the effect of prolonged Erbitux treatment to the sensitivity to gemcitabine and/or radiation and the epidermal growth factor receptor (EGFR) signal transduction pathway. METHODS: MiaPaCa-2 and BxPC-3 cells were cultured with or without Erbitux for 6 weeks. Cells were then treated with gemcitabine and/or radiation, harvested 48 h after treatment, and counted. Differences in EGFR expression after exposure to Erbitux were analyzed by FACS. Internalization rates of EGFR induced by Erbitux on these cell lines were determined using 125I-EGF binding assay after removal of Erbitux by acidic wash. Cell lysates were harvested after cells were stimulated with EGF, FGF, or IGF-1 respectively, and EGFR was immunoprecipitated using Erbitux. Samples were separated using SDS-PAGE and transferred to PVDF membrane. The membranes were probed with antibody against human growth factor receptor binding protein (Grb2) to detect the association of this Ras-MAPK upstream adaptor protein to EGFR. Cell lysates were also separated with SDS-PAGE and probed with rabbit anti-human PARP after samples were transferred to PVDF membrane. Expression of BAX and Bcl-(XL) were probed in the cells treated with or without Erbitux. RESULTS: Proliferation assays indicated that prolonged exposure to Erbitux increased the sensitivities of MiaPaCa-2 to gemcitabine and radiation therapy (41 +/- 16% vs 52 +/- 9% for gemcitation, 28 +/- 9 vs 39 +/- 9% for combination; P = 0.015) but not for BxPC-3. FACS analysis showed that the expressed EGFR level decreased by about 42% on MiaPaCa 2 whereas no loss was seen on BxPC-3. Expression of BAX was upregulated on MiaPaCa-2. Poly (ADP-ribose) polymerase cleavage indicated the killing was mediated by apoptosis. Immunoblots showed that Grb2 was co-immunoprecipitated with EGFR after EGF stimulation. Incubation with Erbitux blocked Grb2 binding in MiaPaCa-2 but not BxPC 3. FGF transactivated EGFR down stream Ras-MAPK in the presence or absence of Erbitux. Internalization of EGFR induced by Erbitux did not differ between MiaPaCa-2 and BxPC-3. CONCLUSIONS: 1) Association of Grb2 to EGFR in BxPC-3 induced by EGF in the presence of Erbitux indicates an alternate pathway of Ras-MAPK activation, which may be related with the tumor resistance to treatment; 2) transactivation of EGFR downstream Ras-MAPK pathway by FGF contributes the resistance to treatment; and 3) downregulation of EGFR may increase the response to therapy.