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Cetuximab (Erbitux®) targets the epidermal growth factor receptor (EGFR) and is approved for treatment of colorectal and head and neck cancer. Despite wide expression of EGFR, only a subgroup of cancer patients responds to cetuximab therapy. In the present study we assessed the cetuximab response in vivo of 79 human patient-derived xenografts originating from five tumour histotypes. We analysed basic tumour characteristics including EGFR expression and activation, mutational status of KRAS, BRAF and NRAS, the expression of EGFR ligands and the activation of HER3 (ErbB3) and the hepatocyte growth factor receptor MET. Based on these results, a cetuximab response score including positive and negative factors affecting therapeutic response is proposed. Positive factors are high expression and activation of EGFR and its ligands epiregulin or amphiregulin, negative factors are markers for downstream pathway activation independent of EGFR. In cetuximab resistant NSCL adenocarcinoma LXFA 526 and LXFA 1647, overexpression due to gene amplification and strong activation of MET was identified. Knock-down of MET by siRNA in the corresponding cell lines showed that anchorage-independent growth and migration are dependent on MET. MET knock down sensitized LXFA 526L and LXFA 1647L to EGF. Combined treatments of a MET inhibitor and cetuximab were additive. Therefore, combination therapy of cetuximab and a MET inhibitor in selected lung cancer patients could be of high clinical significance., (Copyright © 2011. Published by Elsevier Ltd.)

Pluripotent cells can be grown in clonogenic assays. The tumour stem-cell fraction, which accounts for <0.4% of the total cells, and which is considered the most relevant cell type in the development of metastases and recurrences, is able to divide and to form colonies in a semisolid matrix (agar or methylcellulose). Major applications of the tumour clonogenic assay (TCA) are chemosensitivity testing of tumours and xenografts, and for assessments within drug discovery programmes. Of critical relevance for the usefulness of the TCA is whether it can predict sensitivity or resistance towards clinically used agents. When we compared the response of human tumours established as xenografts in nude mice in the TCA in vitro to that of the clinical response, 62% of the comparisons for drug sensitivity, and 92% of the comparisons for drug resistance were correct. The same percentage of true/false observations was found when tumours were tested after serial passage in nude mice in the TCA in vitro and their response compared to in vivo activity in corresponding xenografts (60% and 90%, respectively). The highest correct predictive values were, however, found when the clinical response of tumours was compared to their explants established in the nude mouse and treated in vivo. Of 80 comparisons performed, we observed a correct prediction for tumour resistance in 97% and for tumour sensitivity in 90%. In our opinion, the TCA with established human tumour xenografts has an important role in current drug discovery strategies. We therefore included the TCA as secondary assay in our approach to anticancer drug discovery and found that a number of novel agents were active; these are now in advanced preclinical development or clinical trials. Thus, the tumour clonogenic assay has proven predictive value in the chemosensitivity testing of standard and experimental anticancer drugs.

The antitumour activity of vinflunine, 20',20'-dichloro-3',4'-dihydrovinorelbine, a fluorinated Vinca alkaloid obtained by reaction in superacid media, was evaluated in comparison with vinorelbine against a series of subcutaneously-implanted human tumour xenografts. The tumours studied were established from bladder (BXF1299), pancreas (PAXF546), kidney (RXF944LX), colon (DLD-1, HT-29, TC37), central nervous system (SF-295), small cell lung (NCI-H69) and prostate (PC-3). Vinflunine or vinorelbine was administered as four weekly intraperitoneal treatments, within dose ranges of 5-80 or 0.63-10 mg/kg/injection, respectively. The overall antitumour activity of vinflunine was superior to that of vinorelbine. Vinflunine showed high activity against RXF944LX and NCI-H69 xenografts and moderate activity against PAXF546, PC-3 and TC37 tumours, achieving an overall response of 64%. This contrasts with a 27% response with vinorelbine, which proved only moderately active against RXF944LX and TC37 xenografts. These results confirm and extend our previous report of the broad spectrum of in vivo antitumour activity of vinflunine and reinforce its potential as a valuable addition to current chemotherapeutic agents.

Twenty-three human xenografts, including five colon, five gastric, nine lung (three small cell lung cancer) and four breast carcinomas, were investigated for their sensitivity to nitrosoureas, dacarbazine (DTIC), cyclophosphamide (CTX) and cisplatin (DDP). In 12 cases, at least one of the drugs produced complete or partial remission, in 2, a minor regression was observed and in the other 9, treatment was ineffective. The level of sensitivity to each drug, using a score from 1 to 5, was correlated to three biochemical parameters reported to be involved in resistance to alkylating agents: glutathione (GSH), glutathione transferase (GST) and O6-alkylguanine-DNA-alkyltransferase (AGT). A wide variability was found in these parameters in the xenografts investigated. No correlation was found between any of the three parameters and sensitivity to the drugs used or between sensitivity to one drug and to any of the other drugs tested. These results illustrate the complexity of the question of resistance to alkylating agents and indicate that, at least in xenografts, the biochemical parameters examined are not predictive of response to alkylating agents.

The antitumour activity of the investigational agent N-L-leucyl-doxorubicin (Leu-DOX) was compared with that of doxorubicin (DOX) in human tumour xenografts growing subcutaneously in athymic nude mice. Leu-DOX was developed as a prodrug of DOX, and may be converted into the clinically active parent compound by hydrolytic enzymes present in or on tumour cells. It has been suggested that a better therapeutic index with a reduced cardiac toxicity and higher efficacy might be obtained. Both compounds were administered intravenously weekly for 2 weeks, each at maximum tolerated doses of 8 mg/kg and 28 mg/kg for DOX and Leu-DOX, respectively. The panel of xenografts represented three different tumour types. Leu-DOX showed antitumour activity, defined as tumour growth inhibition > 50% and specific growth delay > 1.0, in 10 of the 16 tumours, including two of five breast, five of seven small cell and three of four non-small cell lung carcinomas. In comparison, DOX was active in one breast, four small cell lung and two lung adenocarcinoma xenografts. In all the DOX sensitive lung tumours, Leu-DOX showed higher efficacy than the parent compound. Based on the results of the present study, and since phase I clinical trials with Leu-DOX have already been performed, phase II clinical evaluation of Leu-DOX in patients with breast and lung cancer is recommended.

TGF alpha-PE40 is a chimeric protein composed of transforming growth factor alpha (TGF alpha) linked to a modified Pseudomonas exotoxin (PE40). We tested the in vitro cytotoxicity of TGF alpha-PE40 on 23 different solid human tumour xenografts established in nude mice and human bone marrow cells from healthy donors, utilising a modified clonogenic assay. In order to distinguish non-specific toxicity from the targeted effects of TGF alpha-PE40, epidermal growth factor receptor (EGFR) expression of the tumours studied was assessed by Northern blot, slot blot and immunohistochemistry. TGF alpha-PE40 demonstrated differential cytotoxicity on human tumour xenografts in the clonogenic assay. No toxicity on human bone marrow cells was observed. In vitro activity of TGF alpha-PE40 showed a significant correlation with the expression of EGF receptors as determined by immunohistochemistry and slot blot. Further studies will be performed in order to determine the in vivo activity of this compound in tumour-bearing nude mice.

Cycloplatam is a novel platinum compound which has shown anti-tumour activity in murine tumour models. In this study, cycloplatam was found to have anti-tumour activity in vitro and in vivo in human tumour models. In 15 cell lines (mainly ovarian), cycloplatam showed similar cytotoxicity as cisplatin, using the sulphorhodamine B assay. Determination of the resistance factor (IC50 of cisplatin-resistant divided by IC50 of parental cell line) clearly showed lower values for cycloplatam than for cisplatin. In the parental ovarian cell line CH1 and the cisplatin-resistant CH1 cisR model, we observed no cross-resistance of cycloplatam and cisplatin. The in vitro anti-tumour activity was confirmed in human tumour xenografts using the clonogenic assay. Mean IC70 values of cycloplatam were 0.54 microgram/ml (1.25 microM) and of cisplatin 0.42 microgram/ml (1.4 microM), respectively. In the murine subcutaneously implanted ADJ/PC6 plasmacytoma in vivo cycloplatam showed less activity than cisplatin, with a 2-fold smaller therapeutic index than cisplatin. In ovarian cancer xenografts cycloplatam was less active than cisplatin. However, anti-tumour activity of cycloplatam in lung cancer xenografts was quite different from cisplatin. In LXFS 538, a model moderately sensitive to cisplatin, a partial remission was observed, but in LXFL 529, a cisplatin-sensitive model, cycloplatam was inactive, cycloplatam thus demonstrating a different spectrum of anti-tumour activity. Based on these results, further preclinical investigations with other tumours, such as cisplatin-sensitive and -resistant gastric cancer models, are warranted with cycloplatam.

EO9 is a novel and fully synthetic bioreductive alkylating indoloquinone. Although structurally-related to mitomycin C, EO9 exhibits a distinct preclinical antitumour profile and there are also differences in its biochemical activation. In this study, EO9 was found to demonstrate preferential cytotoxicity against solid tumours in vitro as compared to leukaemia cell lines both in the Corbett two-tumour assay and in the disease-oriented human tumour cell line panel of the U.S. National Cancer Institute. In the latter system activity was particularly apparent in colon, melanoma and central nervous system lines, together with some renal and non-small cell lung lines. Preferential cytotoxicity towards hypoxic versus aerobic EMT6 mouse mammary tumour cells was observed. In vivo, EO9 was inactive against the P388 murine leukaemia, while exerting significant antiproliferative effects against several murine and human solid tumours, including the generally resistant MAC mouse colon tumours and gastric, ovarian and breast xenografts. These results confirmed in vitro observations of preferential solid tumour activity. In animal toxicology studies, EO9 induced vascular congestion in the gastrointestinal tract, but no significant bone marrow toxicity. The LD10 value of EO9 after a single intravenous injection into mice was 9 mg/kg (27 mg/m2). A dose of one-tenth of the mouse equivalent LD10 (2.7 mg/m2), the recommended starting dose for clinical phase I studies, was found to be safe in rats. Considering its distinct mechanism of bioactivation as compared to mitomycin C, its preferential solid tumour activity, its excellent activity against hypoxic cells, and lack of significant bone marrow toxicity in animals studies, EO9 has been selected for clinical evaluation within the framework of the EORTC.

The antitumour activity of the investigational agent vinblastine-isoleucinate (V-LEU) was compared with vintriptol, another investigational agent of the same series of vinblastine-23-oyl amino acid derivatives, and vinblastine, their clinically active parent compound, in a panel of nine human tumour xenografts growing subcutaneously in nude mice. Compounds were administered intravenously at equitoxic doses twice weekly. As assessed by optimal tumour growth inhibition and tumour growth delay, vinblastine, V-LEU and vintriptol exhibited antitumour activity in 8/9, 7/9 and 4/7 human tumour xenografts, respectively. When growth curves and numbers of complete remissions were compared, V-LEU was the most active agent in two malignant melanoma lines (THXO and LOX p28) and two small cell lung carcinoma lines tested (LXFS 538 and WX 322), whereas vinblastine was more active against the two colorectal carcinomas (CXF 243 and CXF 280). Notably, the non small cell lung carcinoma (NSCLC) line AHXOL was resistant to the three agents. The results of this study suggest that V-LEU was as active as vinblastine in most tumour lines, exhibiting superior antitumour activity in malignant melanoma, SCLC and breast cancer lines. The decision to bring this compound into clinical trial shall await further confirmation of these preclinical results and the evaluation of its toxicity profile in relation to other vinca alkaloids.

The potential of evaluating the preclinical response of solid tumours was studied in human tumour xenografts in the clonogenic assay. Tumour specimens surgically removed from cancer patients were implanted subcutaneously into thymus-aplastic nude mice. Chemosensitivity of the mouse-grown tumours was tested with a modification of the double-layer soft-agar clonogenic assay. Tumour cells were tested against thirteen established cytostatic drugs at two dosages by continuous exposure. 62 retrospective in vivo/in vitro correlations were done. The clonogenic assay predicted correctly for clinical response in 16/27 (59%) and for resistance in 32/35 (91%). These correlation rates were similar to reported data for fresh solid human tumour specimens. The results support the clinical relevance of the nude mouse/clonogenic assay model.