Hypoxia is an important selective force in the clonal evolution of tumours. Through HIF-1 and other transcription factors combined with tumour-specific genetic alterations, hypoxia is a dominant factor in the angiogenic phenotype. Cellular adaptation to hypoxia is an important requirement of tumour progression independent of angiogenesis. The adaptive changes, insofar as they alter hypoxiainduced apoptosis, are likely to determine responsiveness to antiangiogenic strategies. To investigate this adaptation of tumour cells to hypoxia, we recreated in vitro the in vivo situation of chronic intermittent exposure to low-oxygen levels. The colon carcinoma cell lines HT29 and HCT116 were subjected to 40 episodes of sublethal hypoxia (4 h) three times a week. The resulting two hypoxiaconditioned cell lines have been maintained in culture for more than 2 years. In both cell lines changes in doubling times occurred: in HT29 an increase, and in HCT116 a decrease. Cell survival in response to hypoxia and to DNA damage differed strikingly in the two cell lines. The HT29 hypoxia-conditioned cells were more resistant than the parental line to a 24 h hypoxic challenge, while those from HCT116 surprisingly were more sensitive. Sensitivity to cisplatin in vitro was also significantly different for the hypoxiaconditioned compared with the parental lines, suggesting a change in pathways leading to apoptosis following DNA damage signaling. The growth of both conditioned cell lines in vivo as xenografts in immunodeficient (SCID) mice was more rapid than their parental lines, and was accompanied in each by evidence of enhanced vascular proliferation as a consequence of the hypoxia-conditioning. Thus the changes in apoptotic susceptibility were independent of altered angiogenesis. The derivation of these lines provides a model for events within hypoxic regions of colon cancers, and for the acquisition of resistance and sensitivity characteristics that may have therapeutic implications for the use of antiangiogenesis drugs.

Pulmonary resection for colorectal metastases is well accepted. However, the main cause of death after pulmonary resection is recurrence in the lung. The aim of this study was to clarify whether a repeat pulmonary resection was warranted in patients with recurrent lung metastases. The records of 76 patients undergoing initial pulmonary resection, including 14 patients undergoing a repeat operation for lung metastases, were reviewed for survival, operative morbidity, and mortality. Overall, pulmonary resection was performed 96 times in this group of patients. The operative mortality was 0%, morbidity involved only one case of major postoperative hemorrhage associated with the first operation. The cumulative 5-year survival rate for the 76 patients was 32%. After the second pulmonary operation, recurrence was identified in 79% (11 of 14) of the patients. In 10 patients with isolated lung recurrence after a first pulmonary resection, who showed no extrapulmonary disease before or at the time of first thoracotomy, the 3-year, and 5-year-survival rate after the second pulmonary resection was 67%, and 33%, respectively, comparing favorably with the survival rate in those who underwent primary pulmonary resection. In contrast, all 4 patients with extrapulmonary disease before or at the time of thoracotomy had poor prognosis. Repeat pulmonary operation for isolated recurrent colorectal metastases to the lung yielded results comparable to those after the first pulmonary resection in terms of operative mortality and survival in the absence of hilar/mediastinal lymph node or extrathoracic involvement.

Hypoxia contributes to cytotoxic chemotherapy and radiation resistance and may play a role in the efficacy of antiangiogenesis cancer therapy. We have generated a series of cell lines derived from the colon adenocarcinoma models HT29 and HCT116 by exposing cells in vitro to repeated sublethal periods of profound hypoxia. These cell lines have altered sensitivity to hypoxia-induced apoptosis: those derived from HT29 are resistant, whereas those from HCT116 are more susceptible. We used cDNA selected subtractive hybridization to identify novel genes mediating sensitivity to hypoxia-induced apoptosis and isolated macrophage migration inhibitory factor (MIF) from the hypoxia-conditioned cell lines. MIF expression correlates with susceptibility of the cell lines to apoptosis. In hypoxia-resistant cells, the induction of apoptosis by hypoxia can be restored by the addition of exogenous recombinant MIF protein, suggesting that resistance may result in part from down-regulation of MIF production possibly through an autocrine loop. Inhibition of MIF using small interfering RNA in the susceptible lines conferred resistance to hypoxia-induced cell death. The relative expression of MIF in the hypoxia-conditioned cells implanted s.c. in severe combined immunodeficient mice in vivo was similar to that observed in vitro. In an analysis of 12 unrelated colon tumor cell lines, MIF expression and response to hypoxia varied widely. Cell lines in which MIF was inducible by hypoxia were more sensitive to oxaliplatin. In human colon tumor specimens analyzed by immunohistochemistry, MIF expression was similarly variable. There was no detectable expression of MIF in normal colon mucosa or adenoma but positive staining in all carcinomas tested. Taken together, these data indicate that MIF may be a determinant of hypoxia-induced apoptosis in vitro and that its variable expression in human colon cancers may indicate a functional role in vivo. We suggest that MIF expression in colorectal cancer may be a marker of susceptibility to therapies that may depend on induction of hypoxia, possibly including antiangiogenic therapy.Colon cancer is characterized by regions of variable hypoxia, known to be a consequence of disordered vasculature (1). Cells in these hypoxic regions are resistant to radiation and to cytotoxic drugs (2). We have shown previously that hypoxia induces increased expression of genes involved in the detoxification of cytotoxic drugs (3), an effect exerted in part by activation of transcription factors, including activator protein-1 and nuclear factor-nB (4, 5). Hurwitz et al. have shown recently that antiangiogenic therapy adds to the efficacy of chemotherapy in colorectal cancer (6), whereas Willett et al. showed that bevacizumab alone in rectal cancer markedly decreased blood flow to the tumor (7). These findings raise the possibility that apoptosis as a result of oxygen or nutrient withdrawal contributes to the therapeutic effect and prompted an investigation of the resistance of hypoxic cancer cells to apoptos...

A mitochondrial outer membrane protein of ϳ22 kDa (1C9-2) was purified from Vero cells assessing immunoreactivity with a monoclonal antibody, and the cDNA was cloned based on the partial amino acid sequence of the trypsin-digested fragments. 1C9-2 had 19 -20% sequence identity to fungal Tom22, a component of the preprotein translocase of the outer membrane (the TOM complex) with receptor and organizer functions. Despite such a low sequence identity, both shared a remarkable structural similarity in the hydrophobicity profile, membrane topology in the Ncyt-Cin orientation through a transmembrane domain in the middle of the molecule, and the abundant acidic amino acid residues in the N-terminal domain. The antibodies against 1C9-2 inhibited the import of a matrix-targeted preprotein into isolated mitochondria. Blue native polyacrylamide gel electrophoresis of digitonin-solubilized outer membranes revealed that 1C9-2 is firmly associated with TOM40 in the ϳ400-kDa complex, with a size and composition similar to those of the fungal TOM core complex. Furthermore, 1C9-2 complemented the defects of growth and mitochondrial protein import in ⌬tom22 yeast cells. Taken together, these results demonstrate that 1C9-2 is a functional homologue of fungal Tom22 and functions as a component of the TOM complex.Most mitochondrial proteins are encoded by the nuclear genome and are synthesized in the cytosol as preproteins. They are guided to the mitochondrial surface by cytoplasmic chaperones (1) and are then transported to the intramitochondrial compartments by the preprotein import machinery of the outer and inner membranes: the TOM 1 and TIM complexes, respectively (2-8). Extensive genetic and biochemical studies in Saccharomyces cerevisiae and Neurospora crassa have identified components of these complexes. The S. cerevisiae TOM complex is composed of at least nine proteins, Tom71, Tom70, Tom40, Tom37, Tom22, Tom20, Tom7, Tom6, and Tom5. Tom70, Tom37, Tom22, and Tom20 function as import receptors. Tom71 has strong similarity to Tom70 and is weakly associated with the TOM complex (9), although its function is unclear. Tom40 is deeply embedded in the outer membrane in a predicted ␤-barrel structure and functions as the central component of the translocation channel (10 -14). Tom6 and Tom7 modulate the dynamics of the TOM channel (15, 16). Tom5 is tightly associated with Tom40 and represents the connecting link between import receptors and the translocation channel (17). Thus, Tom40, Tom22, and three smaller Tom proteins form the general preprotein import pore (the TOM core complex) of ϳ400 kDa (14, 18). A recent study revealed that Tom22 not only functions as the import receptor, but also regulates the TOM complex organization (19). The mitochondrial inner membrane has at least two separate import machineries. The Tim23-Tim17 system mediates, in conjunction with Tim44 and mHsp70 in the matrix, mitochondrial transport of matrix-targeted preproteins (8,20). The Tim54-Tim22-Tim18 system acts with the small Tim proteins in the inter...

It is important to identify factors that are predictive of outcome after a curative resection in colon cancer in order to optimize adjuvant therapy. To investigate these prognostic factors we conducted a retrospective analysis of our clinicopathological data. A total of 190 patients with a pathological stage II or III colon cancer underwent potentially curative resection with lymphadenectomy at our hospital between 1990 and 1998. These patients received no preoperative chemotherapy, immunotherapy or radiotherapy. Postoperative adjuvant chemotherapy using oral fluoropyrimidines was performed in 127 patients, and the other 63 patients underwent surgery alone. Univariate and multivariate analyses for prognostic factors were carried out. The univariate analysis revealed that invasion to adjacent organs, N1-2, positive mesenteric lymph node metastasis (MLN+), lymphatic permeation (ly)1-3, venous invasion (v)1-3, and v2-3 were each significant factors indicating worse disease-free survival, and that N1-2, MLN+, ly1-3, v1-3 and v2-3 were each significant factors for worse overall survival. In the multivariate analysis, MLN+ and vl-3 were significant factors for worse disease-free survival, and for worse overall survival. In conclusion, stage II or III colon cancer patients positive for mesenteric lymph node metastasis or for venous invasion have a greater risk of recurrence and death after potentially curative resection. Postoperative adjuvant chemotherapy using oral fluoropyrimidines did not significantly reduce the risk of recurrence and death in these patients. More effective adjuvant chemotherapy than oral fluoropyrimidine should be considered, especially in such high-risk patients.