The relative distribution of gefitinib-related material in nude mice bearing s.c. human tumor xenografts and in an orthotopic rat lung tumor model was investigated following oral administration (50 mg/kg) of [14 C]-gefitinib. Selected tissue samples were monitored for radioactivity by liquid scintillation counting, whereas plasma and tumor extracts were assayed for gefitinib and its major metabolites (M523595 and M537194) by high-performance liquid chromatography with tandem mass spectrometric detection. Tissue distribution was also determined by whole body autoradiography. Gefitinib was extensively distributed into the tissues of tumor-bearing mice and unchanged gefitinib was shown to account for most of the tumor radioactivity. Concentrations of gefitinib in mouse s.c. tumor xenografts were similar to skin concentrations and substantially greater (up to 12-fold based on area under the concentration-time curve) than plasma. Concentrations of gefitinib-related material in an orthotopic rat lung tumor were similar to those in healthy lung tissue and were much higher than corresponding blood levels. Following treatment of breast cancer patients with oral gefitinib (Iressa) 250 mg/d for z z z14 days, gefitinib concentrations (mean, 7.5 A Ag/g, 16.7 A Amol/L) in breast tumor tissue were 42 times higher than plasma, confirming the preferential distribution of gefitinib from blood into tumor tissue in the clinical situation. These gefitinib tumor concentrations are considerably higher than those reportedly required in vitro to achieve complete inhibition of epidermal growth factor receptor autophosphorylation in both epidermal growth factor receptor mutant (0.2 A Amol/L) and wild-type cells (2 A Amol/L). [Mol Cancer Ther 2005;4(4):641 -9]

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Summary.-The relationship between tumour volume response and cell kill in B16 melanoma following treatment in vivo with cyclophosphamide (CY) and 1-(2-chloroethyl)-3-cyclohexyl-1 -nitrosourea (CCNU) was investigated. Tumour volume response, expressed as growth delay, was estimated from measurements of tumour dimensions. Depression of in vitro colony-forming ability of cells from treated tumours was used as the measure of tumour cell kill. The relationship between these parameters was clearly different for the two agents studied. CY produced more growth delay (7-5 days) per decade of tumour cell kill than CCNU (2 to 3-5 days). The possibility that this was due to a technical artefact was rejected in favour of an alternative explanation that different rates of cellular repopulation in tumours treated with CY and CCNU might be responsible. Cellular repopulation was measured directly, by performing cell-survival assays at various times after treatment with doses of CY and CCNU which produced about 3 decades of cell kill. The rate of repopulation by clonogenic cells was much slower after treatment with CY than with CCNU, and this appears to account for the longer duration of the growth delay obtained with CY.

Summary.-Cellular repopulation in Lewis carcinoma irradiated with 60Co y-rays was examined by performing sequential cell-survival estimations using an in vitro soft-agar-colony assay. Following local irradiation (15-35 Gy) two distinct types of colony were seen: compact colonies with tightly packed cells and diffuse colonies with widely dispersed cells. Maximal diffuse colony formation in vitro was only obtained in the simultaneous presence of adequate numbers of compact colonies. After wholebody irradiation only compact colonies were observed.Only cell-survival data from compact colony counts correlated with cell survival estimated by the lung colony assay and we conclude that compact colonies are produced by clonogenic tumour cells. Cytochemical and immunological evidence showed that diffuse colonies were composed of macrophages. After local irradiation the initial kill of clonogenic tumour cells was dose dependent. At each dose level, repopulation began immediately and proceeded with a doubling time of about 1 day. Macrophage colony-forming cells (macrophage progenitors) per tumour were initially reduced by about 3 decades, but recovered very rapidly to reach pretreatment levels within 2 days.We conclude that at least two populations of clonogenic cells are present in Lewis lung carcinoma, tumour cells that repopulate irradiated tumours by in situ proliferation and host-macrophage progenitors that repopulate locally irradiated tumours by infiltration. The hazards of confusing host and tumour cell colonies in in vitro assay systems are stressed.

Summary.-The "chemosensitizing" properties of the radiosensitizer misonidazole (MISO) were examined in 2 tumour systems, murine Lewis lung carcinoma and human pancreatic adenocarcinoma xenografted into immune-suppressed mice, using a soft-agar colony assay to measure tumour-cell survival.In mice bearing Lewis lung tumour, the administration of MISO simultaneously with melphalan, cyclophosphamide, CCNU, FU or vincristine gave substantial enhancement of cytotoxicity (DEFs from 15 to 3-5). However, no enhancement was seen with bleomycin, VP 16-213 or cis-Pt. The same level of enhancement of cyclophosphamide effect (DEF=2-0) was seen with both cell survival and growth delay end-points of tumour response.Enhancement was also seen in the human tumour xenograft with melphalan, cyclophosphamide and MeCCNU, using a cell survival assay, but cis-Pt was again not enhanced.