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Biomedical subjects

I F Tannock

Publications and source records attributed to I F Tannock.

At least 91 records · Page 5Linked to original sources
PubMed1993

Regulation of intracellular pH in subpopulations of cells derived from spheroids and solid tumours.

Solid tumours are known to develop regions of extracellular acidity and survival of tumour cells in such regions depends on membrane-based mechanisms which regulate intracellular pH (pHi). We have therefore developed a method, based on dual staining of cells and flow cytometry, to study the regulation of pHi in subpopulations of tumours and spheroids. The activity of membrane-based pHi regulating transporters was studied in EMT-6 and MGH U1 cells grown in monolayer culture, spheroids, and tumours. pHi was measured with the fluorescent pH probe 2'7'-bis-(2-carboxyethyl)-5-(and-6)carboxyfluorescein, and Hoechst 33342 was used to identify cells from different regions of tumours and spheroids. In monolayer culture, incubation of cells for 18 h at pHe 6.6 led to a 1.3-1.5-fold enhancement in the activity of both the Na+/H+ exchanger and the Na(+)-dependent Cl-@HCO3- exchanger. This effect was prevented by the protein synthesis inhibitor cycloheximide. Cells from the centre of EMT-6 spheroids had increased activity of the Na+/H+ exchanger compared to cells from the periphery, when spheroids were grown in medium at pH 6.6, but not at 7.4. By contrast, in MGH U1 spheroids, cells from the centre had increased activity of the Na+/H+ antiport under both sets of conditions. There was no significant difference in the activity of the Na+/H+ exchanger in cells derived from different subpopulations of EMT-6 tumours or MGH U1 xenografts in nude mice. Although upregulation of Na+/H+ exchange occurs after exposure to acidic conditions in vitro, the microenvironmental conditions found within solid tumours do not appear to cause this effect. Our results suggest the feasibility of pharmacological inhibition of Na+/H+ exchange activity as an approach to therapy directed against nutrient-deprived tumour cells.

Animals↗
PubMed1993

Selective cellular acidification and toxicity of weak organic acids in an acidic microenvironment.

The mean extracellular pH (pHe) within solid tumours has been found to be lower than in normal tissues. Agents which cause intracellular acidification at low pHe might have selective toxicity towards cells in tumours. Weak acids (or their anions) with pKa values in the range of 4-6 have a higher proportion of molecules in the uncharged form at low pHe and can diffuse more rapidly into cells. The effects of organic acids including succinate, monomethyl succinate and malonate to acidify cells have been evaluated under conditions of different pHe in the acidic range. These weak acids caused intracellular acidification of murine EMT-6 and human MGH-U1 cells in a concentration and pHe dependent fashion. At concentrations of 10 mM and above, these acids also caused in vitro cytotoxicity to these cells at low pHe (< 6.5). The rate and extent of cellular acidification caused by these weak acids, and their cytotoxicity at low pHe, were enhanced by exposure to amiloride and 5-(N-ethyl-N-isopropyl)amiloride (EIPA), agents which inhibit Na+/H+ exchange, and hence the regulation of intracellular pH. Acid dependent cytotoxicity was also investigated in a murine solid tumour using the endpoints of growth delay and colony formation in vitro following treatment in vivo. Agents were tested alone or with 15 Gy X-rays to select a population of hypoxic (and presumably acidic) cells. Achievable serum concentrations of succinate were about 1 mM and no antitumour activity of succinate was detected when used in this way. It is concluded that weak acids are selectively taken up into cells, and can cause selective cellular acidification and toxicity, at low pHe in culture. Weak acids that are normal cellular metabolites are not toxic in vivo, but weak acids carrying cytotoxic groups offer the potential for selective uptake and toxicity under the conditions of low pHe that exist in many solid tumours.

Amiloride↗
PubMed1993

Therapeutic potential of analogues of amiloride: inhibition of the regulation of intracellular pH as a possible mechanism of tumour selective therapy.

The extracellular pH (pHe) in solid tumours is frequently lower than the pHe in normal tissues. Cells within an acidic environment depend on mechanisms which regulate intracellular pH (pHi) for their survival, including the Na+/H+ antiport which exports protons in exchange for Na+ ions. Amiloride and its analogues DMA (5-(N,N-dimethyl)amiloride), MIBA (5-(N-methyl-N-isobutyl)amiloride) and EIPA (5-(N-ethyl-N-isopropyl)amiloride) are known to inhibit the Na+/H+ antiport and therefore decrease the cells ability to regulate pHi. All three analogues were found to be potent inhibitors of the antiport in human MGH-U1 and murine EMT-6 cells, with DMA being approximately 20, MIBA 100 and EIPA 200-fold as potent as amiloride; EIPA also gave more complete suppression of the Na+/H+ antiport. These agents were not toxic to cells when used alone; however, in combination with nigericin, an agent which acidifies cells, all three analogues were toxic to cells at pHe < 7.0, and markedly enhanced the toxicity of nigericin alone. Cell killing was greatest for nigericin used with EIPA or MIBA. None of the agents were toxic to cells at pHe 7.0 or above. When used against variant cells lacking the Na+/H+ antiport (PS-120 cells) EIPA did not enhance the cytotoxicity of nigericin alone, suggesting that the observed effect was due to inhibition of Na+/H+ exchange, rather than due to non-specific effects. The combination of EIPA and nigericin gave similar cell killing in previously dissociated and intact MGH-U1 spheroids, suggesting that the agents have good penetration of solid tissue. Preliminary experiments using EMT-6 tumours in mice suggested that EIPA and nigericin were able to enhance the toxicity of radiation in vivo, presumably through selective effects against the hypoxic (and probably acidic) subpopulation of cells that is resistant to radiation.

Amiloride↗
PubMed1993

Phase II multicenter study of epirubicin for hormone-resistant prostatic cancer with measurable soft tissue disease.

Twenty-six patients with prostatic cancer were treated with courses of epirubicin at 3-week intervals, starting at an initial intravenous dose of 75 mg/m2. All patients had progressive disease after orchiectomy and/or antiandrogen therapy and had measurable soft tissue lesions. There were three partial responders (response rate: 12%; 95% confidence limits: 4-29%). Major toxicity was myelosuppression, and there were two drug-related deaths. Epirubicin in this dose and schedule cannot be recommended for treatment of prostatic cancer.

Aged↗
PubMed1992

Regulation of intracellular pH in tumor cell lines: influence of microenvironmental conditions.

The effect of microenvironmental factors on the regulation of intracellular pH (pHi) in MGH U1 cells and EMT-6 cells was studied using the fluorescent pH probe 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. Na+/H+ exchange and Na(+)-dependent Cl-/HCO3- exchange were found to be present in both cell types. The activity of both exchangers was dependent on pHi, with low levels of activity at neutral pH and an increase in activity as pHi fell. The level of extracellular pH (pHe) also influenced the operation of the exchangers, with a fall in activity as pHe was reduced over the range 7.4-6.6. This effect was more marked for the Na(+)-dependent Cl-/HCO3- exchanger than for the Na+/H+ antiporter, suggesting that under conditions of reduced pHe the Na+/H+ antiporter is the major mechanism for regulation of pHi. Neither 6 h of radiobiological hypoxia nor variations in the extracellular [Ca2+] over the range 1-6 mM had an effect on the regulation of pHi, while extracellular lactate (5-10 mM) caused a small, concentration-dependent decrease in the combined activity of both exchangers. We conclude that under the microenvironmental conditions found in some regions of tumors, Na+/H+ exchange may be the major method of regulation of pHi.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Some problems related to the design and analysis of clinical trials.

The evaluation of new cancer treatments requires demonstration of their efficacy in clinical trials. Many nonrandomized clinical series have suggested benefit of a new treatment compared with historical controls or with controls from other institutions that received standard treatment. Often, however, the new treatment is not found to be beneficial when evaluated in a subsequent randomized trial. The interpretation of clinical trials has been confounded by many problems, several of which were described or summarized in the writings of Raymond S. Bush: These include (a) invalid comparison of nonrandomized controls because of patient selection or stage migration, (b) inappropriate endpoints, and in particular the failure to evaluate quality of life and complications of treatment, (c) inadequate power to detect clinically meaningful differences in randomized trials, and (d) multiple comparisons and retrospective analysis used to make inappropriate conclusions from randomized trials. The present paper reviews briefly some of these methodological issues that may lead to inappropriate interpretation of clinical trials, with particular reference to trials of combined modality therapy.

Clinical Trials as Topic↗
PubMed1992

The fate of abstracts submitted to a cancer meeting: factors which influence presentation and subsequent publication.

Abstracts that are published in the proceedings of meetings receive minimal peer-review, but may be referenced or used to make decisions about management of patients. We have studied factors which influence the probability of acceptance for presentation, and of subsequent publication of articles, from abstracts included in the Proceedings of the American Society of Clinical Oncology (ASCO). From a random sample of 197 abstracts submitted to the 1984 meeting, 81 were accepted for presentation and a Cancerline computer search revealed 103 papers that were published subsequently in peer-reviewed journals. Communication with authors of the remaining abstracts led to identification of 12 additional articles that had been published. Major reasons for non-publication were insufficient priority or lack of time, funds or other resources. Abstracts which reported 'positive' results were more likely to be presented than those reporting 'negative' results (60% vs. 35%, p = 0.03) and to lead to subsequent publication (74% vs. 32%, p = 0.0001). Of the 81 abstracts in our sample that were selected for presentation at the meeting, 63 (78%) led to publications, compared to 45% (52/116) of those not selected (p = 0.00001). There were no significant differences in the frequency of citation of abstracts that did or did not lead to subsequent publications. We made detailed comparisons of abstracts and subsequent papers for 18 randomized phase III trials. For 15 studies (83%), there was good correlation between the conclusions of the article and of the abstract.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstracting and Indexing↗
PubMed1992

Assessment of study design in clinical trials for bladder cancer.

Physicians and surgeons who treat bladder cancer must be able to judge the validity and relevance of clinical trials if they are to make appropriate recommendations to their patients. To do so, they must be familiar with the design of clinical trials and with the many problems that may confound their results and limit their validity. The present article has reviewed aspects of the design, analysis, and reporting of clinical trials with particular reference to bladder cancer. Nonrandomized studies are important in establishing the feasibility of new treatments and in providing preliminary information about effectiveness. However, selection of patients, together with many other types of bias, prevents a useful comparison of the results obtained in such trials with those obtained using alternative treatment strategies. Establishment of the value of a new type of treatment will usually require the conduct of a large randomized trial in which patients receive experimental or standard therapy by random assignment. While such trials may influence practice in an appropriate way, they must likewise be reviewed critically to ensure the validity of the results and generalizability to patients seen in a nontrial setting.

Clinical Trials as Topic↗
PubMed1992

Use of a physician-directed questionnaire to define a consensus about management of breast cancer: implications for assessing costs and benefits of treatment.

The present study was designed to assess the preferred methods of treatment of early breast cancer by United States oncologists, to define the impact of published clinical trials on their practice, and to define questions related to clinical decision making that should be subjected to further research. A questionnaire was mailed to 405 oncologists of all three disciplines (medical, radiation, and surgical oncology) and to 60 oncology nurses who practice in the United States. The questionnaire included clinical scenarios of: (a) a patient with primary breast cancer; (b) a premenopausal woman with node-negative breast cancer; and (c) a postmenopausal woman with estrogen receptor (ER)-negative, node-positive breast cancer. Respondents were asked to describe their preferred management for each scenario. Our study demonstrates a consensus that modified radical mastectomy, or partial mastectomy plus radiation therapy, should be offered as equal options to selected patients with primary breast cancer; this consensus is supported by results of clinical trials. We also found agreement that adjuvant chemotherapy should be offered to premenopausal women with node-negative, ER-negative breast cancer. There was a similar consensus in favor of adjuvant chemotherapy for postmenopausal patients with ER-negative, node-positive breast cancer, despite the absence of improvement in overall survival in large, mature, controlled randomized trials (and in a meta-analysis). We suggest that further research be undertaken into factors that influence decision making by oncologists when they consider the administration of adjuvant chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
PubMed1991

Evaluation of the probability of spontaneous transfer of drug resistance between cells in culture.

Coculture of two different cell lines in monolayer or spheroids was used to investigate the spontaneous transfer of dominant genes determining drug resistance. MGH-U1 human bladder cancer cells (ouabain-sensitive, mitomycin C-resistant) were cocultured with UV-20 cells (a subline of Chinese hamster ovary cells which is ouabain-resistant and mitomycin C-sensitive). We investigated the possible transfer of mitomycin-C resistance from human to rodent cells by selection in both ouabain and mitomycin C. Regardless of coculture conditions, the frequency of surviving cells was at a similar level to that expected from studies of cell survival when cells were cultured alone. We found no evidence of spontaneous transfer of drug resistance between the two cell lines.

Animals↗
PubMed1991

The potential of lactate and succinate to kill nutrient deprived tumor cells by intracellular acidification.

We have investigated the ability of the weak acids, lactate, succinate, and the monomethylester of succinate, to cause intracellular acidification of EMT-6 and MGH-U1 cells. Each of the three substances caused a decrease of intracellular pH (pHi) when the cell lines were exposed at low extracellular pH (pHe) in the range 6.0-6.5. Only monomethylsuccinate caused intracellular acidification at neutral pHe. The fall in pHi increased with increasing dose of each agent and with decreasing pHe. The pHi recovered to almost normal values after exposure of 30 minutes to 50 mM lactate, but there was little or no recovery of pHi in the presence of succinate or monomethylsuccinate. Succinate and its methylester were toxic to cells at low pHe (less than 6.5), and cell killing increased with exposure time and with dose of the agents used. Lactate did not cause cell death at low pHe, and none of the three substances exhibited any cytotoxicity at neutral pHe. Solid tumors are known to have an acidic microenvironment, and pHe may be particularly low in regions of hypoxia. Succinate and its monomethylester may have the potential to kill cells in acidic regions of tumors and might therefore enhance the effect of radiation.

Acid-Base Equilibrium↗
PubMed1991

Bone metastases: pathophysiology and management policy.

The pathophysiology and options for management of bone metastases as well as criteria for determining response to therapy are reviewed. Bone metastases are frequently one of the first signs of disseminated disease in cancer patients. In the majority of patients, the primary tumor is in the breast, prostate, or lungs. Although almost all patients will die of their disease, a proportion of the patients will survive for several years. Treatment is primarily palliative: the intention is to relieve pain, prevent fractures, maintain activity and mobility, and, if possible, to prolong survival. Therapeutic options include local treatment with radiotherapy and/or surgery, and systemic treatment using chemotherapy, endocrine therapy, radioisotopes, agents such as diphosphonates, which inhibit resorption of bone, as well as analgesic and antiinflammatory drugs. The mechanisms by which pain is relieved by several of these therapies remain unclear but actions beyond a simple tumoricidal effect appear to be important. There have been few randomized trials comparing the therapeutic options, and the criteria for assessing response to therapy have, in general, been poorly defined. There is a need for rigorous clinical investigations that assess the efficacy of the various therapeutic possibilities by using well-defined and validated criteria of response.

Bone Neoplasms↗
PubMed1990

Effect of transient hypoxia on sensitivity to doxorubicin in human and murine cell lines.

Overreplication of DNA associated with gene amplification and drug resistance has been reported to occur after transient hypoxia of rodent cells. Because oxygen levels fluctuate in solid tumors, clinical drug resistance might be stimulated by this mechanism. We have therefore studied the effect of transient hypoxia on sensitivity to doxorubicin in human and murine cell lines. Exposure to hypoxia led to a decreased rate of cell proliferation, and most of the observed changes in sensitivity to doxorubicin were consistent with cell cycle-dependent cytotoxicity of this drug. After transient hypoxia, about 10% of the murine cells (EMT6/Ro and KHT-LP1) contained greater than four times the haploid DNA content (greater than 4C DNA), but only 0%-5% of the human cells (MGH-U1, A549, and Hey) had greater than 4C DNA content. Murine cells that had been exposed to hypoxia and reoxygenation, and which had greater than 4C DNA content, were separated by flow cytometry. For KHT-LP1 cells, but not for EMT6/Ro cells, this subpopulation was found to be more resistant to doxorubicin than the subpopulation with less than 4C DNA content and the aerobic control. When resistant KHT-LP1 clones were expanded in the presence of doxorubicin, six of six clones showed amplification of the P-glycoprotein gene family. The ability and efficiency of hypoxia to induce DNA overreplication, gene amplification, and drug resistance appears to be cell-line dependent.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Are treatment strategies of urologic oncologists influenced by the opinions of their colleagues?

In a previous study, urologists, radiation oncologists and medical oncologists in Britain, Canada and the United States were asked to state how they would wish to be treated if they had urologic cancer as described in six clinical scenarios and whether they would agree to be entered in randomised clinical trials. This study disclosed major controversy regarding treatment options for each scenario and reluctance by these experts to enter randomised clinical trials. In the present study a second questionnaire which included a summary of the treatments selected initially was sent to the same 227 oncologists. Respondents were asked, in view of these additional information, how they would wish to be treated and whether they would enter themselves (or their patients) on randomised trials comparing the two treatment options most favoured by their colleagues. Most respondents did not modify their treatment preference. There was still poor agreement to enter themselves on trials (29%), but a higher proportion would offer such trials to their patients (45%). Thus the demonstration of controversy about optimum treatment did not influence personal bias, but could facilitate the entry of patients into trials that address major controversies. We conclude that treatment strategies of urologic oncologists are influenced minimally by opinions of their colleagues, but that the method of using surrogate questionnaires is a valuable aid to the design of clinical trials.

Aged↗