False-positive results in clinical trials: multiple significance tests and the problem of unreported comparisons.
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Clinical Trials as Topic↗
Biomedical subjects
I F Tannock
Publications and source records attributed to I F Tannock.
The effect of heat on Na+/H+ antiport function and survival in mammalian cells.
PURPOSE: Because intracellular pH (pHi) is a determinate of thermosensitivity, it is important to understand the relationship between heat cytotoxicity and the mechanisms responsible for pHi regulation, such as the Na+/H+ antiport. The objective of this study is to elucidate the relationship between heat damage and Na+/H+ antiport activity. METHODS AND MATERIALS: Various cell lines, EMT6, RIF-1, and its thermoresistant variant TR-4, and CCL39, and its variant that lacks the Na+/H+ antiport (PS120), were all heated using a water bath. Parallel assessments of antiport function and pHi were made using the fluorescent dye 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). RESULTS: Exposure of EMT6 cells to 43-46 degrees C for 30-60 min caused progressive decline in antiport activity, in parallel with cytotoxicity. When the same degree of cytotoxicity was induced by ionizing radiation, no alteration in Na+/H+ antiport function was observed. Despite a 10-fold lower survival in RIF-1 compared to TR-4 cells after heating, there was no difference in the thermosensitivity of their antiports. Antiport activity in the TR-4 cells, however, was higher than that of RIF-1 cells both before and during heating. Intracellular pH for TR-4 cells decreased minimally during heating, in contrast to a decline of 1 pH unit in RIF-1 cells despite similar relative levels of antiport activity, suggesting that in this pair of cell lines, antiport activity does not play a major pHi regulatory role. PS120 and CCL39 cells and similar survival levels when heated at pHe 7.2 in the presence of NaHCO3, which allows function of the other major regulator of pHi, the Na+ -dependent HCO3-/Cl- exchanger. This occurred despite a drop in pHi in the PS120 cells during heating. A reduced survival was observed, however, in PS120 cells after 43 degrees C for 30-60 min at either pHe 6.5 or pHe 7.2 in the absence of NaHCO3. Intracellular pH was consistently greater for PS120 than CCL39 cells. CONCLUSION: We demonstrated that damage to the Na+/H+ antiport likely reflects early heat-induced change in membrane function, but is not a primary target for heat cytotoxicity. Although there is an association between survival, antiport function, and pHi level under most treatment conditions, the precise role of the Na+/H+ antiport in mediating thermal cytotoxicity remains uncertain.
Animals↗
The chronic administration of drugs that inhibit the regulation of intracellular pH: in vitro and anti-tumour effects.
Mean values of extracellular pH (pHe) in tumours tend to be about 0.5 pH units lower than in normal tissues, whereas values of intracellular pH (pHi) in tumours and normal tissues are similar. Previous studies have shown that drugs that acidify cells at lower pHe such as nigericin, used alone or with agents that inhibit the regulation of pHi, have toxicity to cultured cells at pHe < 6.5 in short-term exposure; these agents also lead to modest anti-tumour effects in mice when given acutely. To evaluate the long-term effects of these drugs at levels of pHe that might occur commonly in tumours, we exposed cells for up to 72h at pHe 6.8 or 7.2 in vitro. Nigericin (0.033 microM) caused time-dependent cell killing of murine KHT and EMT-6 cells at pHe 6.8 (but not at pHe 7.2) with a surviving fraction approximately 5 x 10(-3) after 72 h exposure. Cell killing was increased in the presence of 4,4-diisothiocyanstilbene 2,2-disulphonic acid (DIDS), an inhibitor of Na+-dependent HCO3-/CI- exchange, and to a lesser extent in the presence of 5-(N-ethyl-N-isopropyl) amiloride (EIPA), an inhibitor of Na+/H+ exchange. Cell killing was exquisitely sensitive to the level of pHe. Osmotic pumps were used to obtain a 72 h continuous infusion of nigericin in mice; this led to dose-dependent killing of cells in KHT tumours with surviving fraction of approximately 0.1 at maximum tolerated doses. Hydralazine, which may cause tumour hypoxia and lower pHi as well as pHe, caused cytotoxity when given alone by chronic infusion, and enhanced the cytotoxicity due to nigericin. The addition of DIDS and/or EIPA (using two pumps) further enhanced anti-tumour toxicity, with a surviving fraction of approximately 0.002 at tolerated doses of the four drugs used to treat KHT tumours. The experiments demonstrate the activity of drugs that inhibit the regulation of pHi against murine tumours when delivered by chronic infusion.
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
Improved local control of invasive bladder cancer by concurrent cisplatin and preoperative or definitive radiation. The National Cancer Institute of Canada Clinical Trials Group.
PURPOSE: A prospective randomized trial was conducted to determine whether the addition of concurrent cisplatin to preoperative or definitive radiation therapy in patients with muscle-invasive bladder cancer improved local control or survival. PATIENTS AND METHODS: Ninety-nine eligible patients with T2 to T4b transitional cell bladder cancer participated, 64% with cT3b or cT4. Patients and their physicians selected either definitive radiotherapy or precystectomy radiotherapy; patients were then randomly allocated to receive intravenous cisplatin 100 mg/m2 at 2-week intervals for three cycles concurrent with pelvic radiation, or to receive radiation without chemotherapy. Patients were stratified by clinical tumor stage and by radiation plan. The median follow-up duration is 6.5 years. RESULTS: The occurrence of distant metastases was the same in both study arms. However, 25 of 48 control patients have had a first recurrence in the pelvis, compared with 15 of 51 cisplatin-treated patients (P = .036). The pelvic relapse rate in the two groups was significantly reduced by concurrent cisplatin (P = .038, log-rank test) and this effect was preserved in a stepwise Cox regression model of prognostic factors (hazards ratio, 0.50; 90% confidence interval [CI], 0.29 to 0.86; P = .036). The hazard reduction was similar for both radiation plans. Pretreatment leukocytosis and high clinical stage were independent adverse factors in a Cox model of overall survival, but the effect of cisplatin was not significant. CONCLUSION: Concurrent cisplatin may improve pelvic control of locally advanced bladder cancer with preoperative or definitive radiation, but has not been shown to improve overall survival. The use of concurrent cisplatin had no detectable effect on distant metastases.
Adult↗
Treatment of cancer with radiation and drugs.
PURPOSE: To review the current status and future prospects of combined treatment of cancer with radiation and drugs. DESIGN: A review of (1) mechanisms whereby combined use of radiation and drugs might lead to improved therapeutic benefit for the treatment of cancer; (2) problems related to the design and analysis of clinical trials that evaluate combined modality treatment; and (3) clinical results of larger randomized trials that have compared combined versus single modality treatment for various types of cancer. RESULTS: Improvement in the therapeutic index depends on exploitation of the biologic properties that differ between tumors and normal tissues; such properties may include mechanisms of resistance to radiation and drugs, tissue microenvironment, and cell proliferation or repopulation during radiotherapy. To detect or rule out the small but clinically important differences in outcome that might occur will require the performance of large, randomized, controlled trials or patient-based meta-analyses; single-arm studies, small randomized trials, and subgroup analyses of larger trials can generate hypotheses. Clinical gains from combined treatment have been demonstrated in a few sites, with disappointing results in others. In general, more promising results have accrued from concurrent treatment, despite greater toxicity, than from sequential use of drugs and radiation. CONCLUSION: Clinical gains from combined treatment with radiation and drugs have been small. New, mechanistically based approaches to combined treatment are required.
Clinical Trials as Topic↗
Chemotherapy with mitoxantrone plus prednisone or prednisone alone for symptomatic hormone-resistant prostate cancer: a Canadian randomized trial with palliative end points.
PURPOSE: To investigate the benefit of chemotherapy in patients with symptomatic hormone-resistant prostate cancer using relevant end points of palliation in a randomized controlled trial. PATIENTS AND METHODS: We randomized 161 hormone-refractory patients with pain to receive mitoxantrone plus prednisone or prednisone alone (10 mg daily). Nonresponding patients on prednisone could receive mitoxantrone subsequently. The primary end point was a palliative response defined as a 2-point decrease in pain as assessed by a 6-point pain scale completed by patients (or complete loss of pain if initially 1 +) without an increase in analgesic medication and maintained for two consecutive evaluations at least 3 weeks apart. Secondary end points were a decrease of > or = 50% in use of analgesic medication without an increase in pain, duration of response, and survival. Health-related quality of life was evaluated with a series of linear analog self-assessment scales (LASA and the Prostate Cancer-Specific Quality-of-Life Instrument [PROSQOLI]), the core questionnaire of the European Organization for Research and Treatment of Cancer (EORTC), and a disease-specific module. RESULTS: Palliative response was observed in 23 of 80 patients (29%; 95% confidence interval, 19% to 40%) who received mitoxantrone plus prednisone, and in 10 of 81 patients (12%; 95% confidence interval, 6% to 22%) who received prednisone alone (P = .01). An additional seven patients in each group reduced analgesic medication > or = 50% without an increase in pain. The duration of palliation was longer in patients who received chemotherapy (median, 43 and 18 weeks; P < .0001, log-rank). Eleven of 50 patients randomized to prednisone treatment responded after addition of mitoxantrone. There was no difference in overall survival. Treatment was well tolerated, except for five episodes of possible cardiac toxicity in 130 patients who received mitoxantrone. Most responding patients had an improvement in quality-of-life scales and a decrease in serum prostate-specific antigen (PSA) level. CONCLUSION: Chemotherapy with mitoxantrone and prednisone provides palliation for some patients with symptomatic hormone-resistant prostate cancer.
Adenocarcinoma↗
Overview of Canadian trials in hormonally resistant prostate cancer.
There is no consensus about the best systemic treatment for hormonally resistant prostate cancer. Several regimens have been examined; none of them have demonstrated a consistent increase in overall survival. The treatment of hormonally resistant prostate cancer is therefore palliative. Recent studies in Canada have taken the approach that the best way to measure disease palliation is to assess the effects of therapy on disease-related symptoms and quality of life. Studies with mitoxantrone and prednisone confirm that this regimen is well tolerated and leads to symptomatic improvement in approximately 40% of patients, with a median duration of improvement of more than 10 months. This is greater than that achieved with prednisone alone. Treatments that have greater activity against hormonally resistant disease are urgently needed, although improvements probably will be gradual and modest. While it may be appealing to intensity treatments to obtain greater efficacy, there is a real risk that the toxicity will nullify any benefits. This approach of directly measuring the ability of systemic therapies to provide palliation is an appropriate way to assess newer therapies for hormonally resistant prostate cancer.
Antineoplastic Agents↗
Reduction of tumour intracellular pH and enhancement of melphalan cytotoxicity by the ionophore Nigericin.
Nigericin is an ionophore which permits the influx of H+ ions into cells down a concentration gradient, thus reducing intracellular pH (pHi) when extracellular pH is low. The effects of nigericin on the pHi of solid murine tumours in vivo were examined using 31P magnetic resonance spectroscopy. Nigericin at 2.5 mg/kg i.p. reduced pHi by 0.2-0.3 pH unit in the KHT and RIF-I tumours but had no effect on pHi in the SCCVII/Ha tumour. In vitro studies have shown that reduced pH can increase the toxicity of melphalan. Therefore, the anti-tumour effect of combining nigericin with melphalan was also examined. Nigericin at 2.5 mg/kg i.p. given before various doses of melphalan resulted in substantial delay in growth of the RIF-I tumour over that induced by melphalan alone. This observation was confirmed by an in vivo/in vitro excision assay, where nigericin given before melphalan produced a 30-fold increase in cell killing. By contrast, no enhancement of melphalan-induced cell killing by nigericin was observed in the KHT and SCCVII/Ha tumours, using growth delay and in vivo/in vitro excision assays, respectively.
Animals↗
The recruitment of patients into clinical trials.
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Humans↗
New perspectives in combined radiotherapy and chemotherapy treatment.
Strategies for developing combined modality treatment for lung cancer have, until now, depended largely on empirical approaches whereby drugs with some activity against advanced disease have been combined with radiation. Survival gains have been modest. The present article emphasizes the need for new approaches that are based on mechanisms of interaction or cooperation between radiation and drugs, such that there is a selective increase in killing of tumour cells. Potential interactions include the use of radiation and drugs to eliminate cell populations which are shown in predictive assays to have differing mechanisms of resistance to the two modalities, selective inhibition of repopulation of tumour cells during radiotherapy by using drugs or biological agents, and selective killing of cells in hypoxic or acidic regions of tumours. The feasibility and potential of such approaches should be evaluated initially in small single-arm studies where outcome in individual patients is related to biological studies of mechanism. Such treatment may need to be individualized (e.g. depending on markers of drug resistance or growth factor receptors). Ultimately, the value of such treatments will need to be evaluated (whether individualized or generic) against standard treatment in large randomized trials. Guidelines for the conduct of such trials are indicated with emphasis on quality of life, assessment of costs and benefits, and involvement of patients in clinical decision making.
Animals↗
Inhibition of the regulation of intracellular pH: potential of 5-(N,N-hexamethylene) amiloride in tumour-selective therapy.
The viability of cells within the acidic microenvironment found in solid tumours is expected to depend on the regulation of intracellular pH (pHi). 5-(N,N-hexamethylene) amiloride (HMA) is a potent inhibitor of the Na+/H+ antiport, a major mechanism for the regulation of pHi. We have therefore studied the cytotoxicity of HMA in combination with nigericin, a cell-acidifying agent, for EMT-6 cells in monolayer cell culture, in spheroids and in a murine tumour model. The combination of nigericin and HMA was toxic to cells in tissue culture at extracellular pH (pHe) < or = 6.8 (as may be found in tumours) but not at pH 7.0 or above (as in most normal tissues). Compared with amiloride, the relative potency of HMA in causing in vitro cytotoxicity (approximately 100-fold) was similar to that for inhibition of the Na+/H+ antiport. The fluorescent probe Hoechst 33342 was used with flow cytometry to study the cytotoxicity of HMA and nigericin at different depths in multicellular tumour spheroids. Only small differences in the level of cell survival were observed, but higher concentrations of HMA were required as compared with those giving equal levels of survival in monolayer culture. The pharmacokinetics of HMA in mice was studied by using high-performance liquid chromatography: after intraperitoneal injection of 20 micrograms g-1, the plasma level of HMA peaked at 8 microM after about 15 min and decreased to 1 microM at 120 min; the half-life was 35 min. Nigericin and HMA, at doses of 1.25 micrograms g-1 and 10 micrograms g-1 respectively, failed to cause significant cell killing in the EMT-6 murine tumour, but the surviving fraction was reduced to approximately 0.004 when hydralazine was administered with nigericin and HMA. Local tumour irradiation (15 Gy), followed by treatment with these drugs, led to cell killing that was additive to the effects of drugs and radiation alone, so that hypoxic cells which survived radiation did not appear more sensitive to pH-dependent drug treatment. Acid-mediated therapy can lead to cell death in murine solid tumours, but further measures will be required before the strategy can be exploited clinically.
Amiloride↗
Use of palliative end points to evaluate the effects of mitoxantrone and low-dose prednisone in patients with hormonally resistant prostate cancer.
PURPOSE: This phase II study was designed to assess the effects of mitoxantrone with prednisone in patients with metastatic prostate cancer who had progressed on hormonal therapy. The methods of assessment included quality-of-life analyses, pain indices, analgesic scores, and the National Prostatic Cancer Project (NPCP) criteria. PATIENTS AND METHODS: Patients received mitoxantrone 12 mg/m2 intravenously every 3 weeks plus prednisone 10 mg orally daily. All had a castrate serum testosterone and Eastern Cooperation Oncology Group (ECOG) performance status < or = 3, and had not received prior chemotherapy. Every 3 weeks, analgesic intake was scored, and a present pain intensity (PPI) record and visual analog scale (VAS) describing pain were collected. Every 6 weeks, the European Organization for Research and Treatment of Cancer (EORTC) core quality-of-life questionnaire plus a prostate-specific module were completed. A palliative response was defined as a decrease in analgesic score by > or = 50% or a decrease in PPI by > or = two integers without any increase in the other. RESULTS: Twenty-seven patients were entered onto the study. Nine of 25 (36%) assessable patients achieved a palliative response maintained for > or = two cycles (range, two to eight or more). Improvements in mean PPI and VAS pain scores after each cycle of therapy (P < .05) were seen. Quality-of-life analysis showed improvements in social and emotional functioning, and in pain and anorexia. Using NPCP criteria, one patient achieved a partial response (PR) and 12 had stable disease; one of seven patients with measurable disease had a PR. No serious nonhematologic toxicity was experienced, and there were no episodes of febrile neutropenia. CONCLUSION: Mitoxantrone with low-dose prednisone is a well-tolerated treatment regimen that has some beneficial effects on disease-related symptoms and quality of life for patients with advanced prostate cancer.
Aged↗
Adjuvant chemotherapy for breast cancer: discordance between physicians' perception of benefit and the results of clinical trials.
PURPOSE: Decisions about management of patients depend on the perception of physicians about the results of clinical trials. We therefore determined whether physicians would recommend adjuvant chemotherapy for specified patients with breast cancer, and whether the perceived levels of benefit that led to these decisions were supported by the results of clinical trials. METHODS: We mailed a questionnaire that presented two clinical scenarios to 515 American and European oncologists. Scenario A depicted a premenopausal woman with node-negative, estrogen receptor-negative (ER-) breast cancer, and scenario B depicted a post-menopausal woman with node-positive, ER- disease. Respondents were asked about the evidence that they required from clinical trials to recommend adjuvant chemotherapy for these patients. RESULTS: Replies were received from 307 oncologists. American respondents were more likely to recommend adjuvant chemotherapy than Europeans (A, 93% v 68%; B, 85% v 67%; P < .001 for both comparisons). Opinion was evenly divided as to whether improvement in the relapse-free survival (RFS) rate was sufficient to recommend treatment, or whether improvement in overall survival was necessary. Mean values of 12.9% to 14.6% improvement in RFS at 3 years, or 10.7% to 12.4% improvement in overall survival at 5 years, were required to offer treatment. An overview analysis of clinical trials suggests that adjuvant chemotherapy achieves absolute improvements of 6% to 9% in RFS rates at 3 years and 3% to 4% in overall survival rates at 5 years for patients in these scenarios. CONCLUSIONS: Most oncologists recommended treatment in these scenarios, but require a level of treatment effect that has not been demonstrated in clinical trials. Our results suggest that oncologists' perceptions of the results of clinical trials overestimate the therapeutic gain from use of adjuvant chemotherapy for breast cancer.
Adult↗
Clinical relevance of breast cancer biology.
Biological properties of breast cancer are reviewed in relation to their ability to provide information about etiology, prognosis, or response to therapy. The authors suggest guidelines for the rigorous and systematic evaluation of biologic factors in relation to the prognosis and treatment of breast cancer.
Breast Neoplasms↗
Antitumor activity of nigericin and 5-(N-ethyl-N-isopropyl)amiloride: an approach to therapy based on cellular acidification and the inhibition of regulation of intracellular pH.
The extracellular pH (pHe) in solid tumors is frequently lower than the pHe in normal tissues, but the intracellular pH (pHi) is regulated to physiological levels. Cell killing can be achieved in an acidic environment in tissue culture by nigericin, which acidifies cells by transporting H+ from the extracellular space into the cytoplasm; this cell killing can be enhanced when used with 5-(N-ethyl-N-isopropyl)amiloride (EIPA), a potent inhibitor of membrane-based Na+/H+ exchange, which plays a major role in the regulation of pHi (R. P. Maidorn; E. J. Cragoe; I. F. Tannock, Br. J. Cancer 67:297-303; 1993). We have therefore assessed the ability of nigericin and EIPA to kill cells in two murine solid tumors (the KHT fibrosarcoma and the EMT-6 sarcoma). Hydralazine, which reduces tumor blood flow, or glucose, which stimulates glycolysis leading to accumulation of lactate, were also administered to mice to lower pHe in the tumors. We observed only a small decrease in the surviving fractions of cells in the tumors when tolerated doses of nigericin and EIPA were given IP to tumor-bearing mice. When nigericin and EIPA were combined with administration of hydralazine, the surviving fraction of cells in both tumors was reduced by a factor of 0.01, but there were minimal effects on growth delay. Administration of glucose with nigericin and EIPA led to a smaller reduction in surviving fraction of the KHT tumor (by approximately 0.1), although glucose was more effective than hydralazine in lowering the mean tumor pHe. When KHT tumors were treated with 15 Gy X-rays followed immediately by nigericin, EIPA, and hydralazine, a reduced surviving fraction as well as an increase in tumor growth delay was observed compared to radiation alone; however, there was little evidence to suggest that these agents were selectively toxic to the cells that survived radiation. Nigericin and EIPA, with or without hydralazine, had minimal effects on normal tissues, as assessed by changes in body weight, number of leukocytes, and serum creatinine levels. We conclude that pharmacological effects to acidify cells and to prevent regulation of pHi under the acidic conditions that exist in solid tumors can lead to moderate levels of cell killing, if additional strategies are used to lower tumor pHe.
Amiloride↗
A phase II study of methotrexate, vinblastine, doxorubicin and cisplatin plus recombinant human granulocyte-macrophage colony stimulating factors in patients with advanced transitional cell carcinoma.
The use of methotrexate, vinblastine, doxorubicin, and cisplatin (M-VAC) to treat transitional cell carcinoma is associated with high rates of granulocytopenia. To test whether the addition of recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF) would decrease the hematological toxicity of M-VAC 21 patients were treated with standard dose M-VAC (30 mg./m.2 methotrexate on days 1, 15 and 22, 3 mg./m.2 vinblastine on days 2, 15 and 22, 30 mg./m.2 doxorubicin on day 2 and 70 mg./m.2 cisplatin on day 2) plus 5 micrograms./kg. rhGM-CSF subcutaneously on days 4 to 13. On cycles 1 and 2 of therapy grade III or greater granulocytopenia (less than 1.0 x 10(9)/l.) was noted in 39% and 43% of the patients, respectively, and the majority were able to receive the day 15 and day 22 treatments as scheduled. This was an apparent improvement over our historical experience with M-VAC alone (p = 0.03). By cycle 3 of treatment this beneficial effect of rhGM-CSF was no longer apparent, with 80% of the patients experiencing grade III or greater granulocytopenia and thrombocytopenia also becoming apparent. Seven patients had to discontinue rhGM-CSF because of side effects. It is unlikely that clinically significant escalation of chemotherapy dosages can be achieved with M-VAC and rhGM-CSF.
Antineoplastic Combined Chemotherapy Protocols↗
Lysosomes, lysosomal enzymes, and cancer.
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Animals↗
pH dependent cytotoxicity of N-dodecylimidazole: a compound that acquires detergent properties under acidic conditions.
N-dodecylimidazole is a compound which acquires detergent properties under acidic conditions and might be useful in killing selectively cells in those regions of solid tumours which have a reduced extracellular pH (pHe). We have therefore studied the effects of N-dodecylimidazole against malignant cells in tissue culture. N-dodecylimidazole displayed pHe-dependent cytotoxicity against EMT-6 and MGH U1 cells; cell killing was dose dependent and was 100-fold greater at pHe 6.0 than pHe 7.0. Reduced toxicity of N-dodecylimidazole was observed at higher cell concentrations (> 10(6) cells ml-1), and only minor effects were observed against multicellular tumour spheroids. Potential mechanisms of action of N-dodecylimidazole include detergent-mediated lysis of the cell membrane at low pHe, and selective uptake into lysosomes where detergent activity leads to rupture of the lysosomal membrane and release of cytolytic enzymes. Inhibition of activity of cysteine proteases by the inhibitor E-64 did not protect cells against the toxicity of N-dodecylimidazole, suggesting that these lysosomal enzymes do not play a major role in the mechanism of action of this compound. Lysis of erythrocytes (which contain no lysosomes) was observed with low concentrations of N-dodecylimidazole. Dependence of cell lysis on cell concentration was similar to that observed for two other detergents that act on the plasma membrane, Triton X-100 and sodium dodecyl sulfate. We conclude that N-dodecylimidazole causes pHe dependent cell killing in two cultured tumour cell lines, and that its mechanism of action is probably due to acid mediated production of detergent activity which acts primarily on the cell plasma membrane.
Animals↗