Recent reports on the effect of low doses of ionizing radiation and its dose–effect relationship

Recently, the risk associated with low doses of ionizing radiation has gained new interest. Here, we analyze and discuss the major differences between two reports recently published on this issue; the report of the French Academy of Sciences and of the French Academy of Medicine published in March 2005, and the BEIR VII—Phase 2 Report of the American National Academy of Sciences published as a preliminary version in July 2005. The conclusion of the French Report is that the linear no-threshold relationship (LNT) may greatly overestimate the carcinogenic effect of low doses (<100 mSv) and even more that of very low doses (<10 mSv), such as those delivered during X-ray examinations. Conversely, the conclusion of the BEIR VII report is that LNT should be used for assessing the detrimental effects of these low and very low doses. The causes of these diverging conclusions should be carefully examined. They seem to be mostly associated with the interpretation of recent biological data. The point of view of the French Report is that these recent data are incompatible with the postulate on which LNT is implicitly based, namely the constancy of the carcinogenic effect per unit dose, irrespective of dose and dose rate.     

Demonstration of a radiation-induced bystander effect for low dose low LET β-particles

Radiation-induced bystander mutagenesis at a relatively low dose range was investigated using low LET β-particles in a three-dimensional cell culture model. CHO cells were labeled with 0, 0.5, 1.0 or 5.0 μCi tritiated thymidine (³HdTTP) for 12 h and subsequently incubated with A_L cells for 24 h at 11°C. The cell mixture was centrifuged to produce a spheroid of 4 × 10⁶ cells of which there was five times more A_L than CHO cells. The short-range β-particles emitted by ³HdTTP result in self-irradiation of labeled CHO cells, thus biological effects on neighboring A_L cells can be attributed to the bystander response. To evaluate such response, non-labeled bystander A_L cells were isolated from among labeled CHO cells and studied independently for survival and mutagenesis. Treatment of CHO cells with ³HdTTP resulted in a dose-dependent increase in bystander mutation incidence among neighboring A_L cells compared to controls. In addition, multiplex PCR analysis revealed the types of mutants to be significantly different from those of spontaneous origin. These data provide evidence that low dose low LET radiation can induce bystander mutagenesis in a three-dimensional model. The results of this study will address the relevant issues of actual target size and radiation quality, and are likely to have a significant impact on our current understanding of radiation risk assessment.     

Thermoluminescence dose–response of synthesized and doped hydroxyapatite: effect of formed crystal phases

In this research work, pure and doped hydroxyapatite samples were synthesized using hydrolysis and hydrothermal methods to produce powder material. The crystal structure was carried out by producing data using the X-ray diffraction system and the Rietveld method using material analysis using diffraction software. Then the sample was irradiated with different radiation absorbed doses, and their thermoluminescence response was investigated from the dosimetry point of view. The results showed that the synthesis method, doping, and annealing temperature could significantly affect the crystal structure and thermoluminescence dosimetry response of hydroxyapatite samples, consequently. The results showed that the high-temperature annealing process and dopant could lead to the formation of the β-TCP crystal phase during or after the synthesis of hydroxyapatite, and the percentage of this formed phase increased when raising the temperature, and finally led to increase in the thermoluminescence response.     

Mathematical simulation of dose–effect relationships for fish eggs exposed chronically to ionizing radiation

A mathematical model which simulates the observed dose-effect relationships for fish eggs exposed to chronic irradiation is presented. The model assumes that the exposed fish eggs may exist in one of the following states: normally developing, reversibly damaged, and lethally damaged. Reversible damages may be recovered by repairing mechanisms which are spent for the repairing processes. The model was applied to describe the observed differences in effects of chronic exposure for quickly (2 weeks) and slowly (up to 20 weeks) developing fish eggs. Calculations were performed for dose rates of chronic irradiation ranging from 10 to 300 mGy/day. Two types of radiation effects were considered—the effect on eggs survival (percentage of survived eggs at time t), and the depletion of the repairing pool (in percentage of its maximal value). The model predictions have been compared with the experimental data from the EPIC database. This comparison showed that the model adequately describes the radiation effects in fish eggs of different species, within a wide range of chronic radiation exposures.     

Abdominal imaging dose in radiology and radiotherapy – Phantom point dose measurements,effective dose and secondary cancer risk

PurposeTo compare abdominal imaging dose from 3D imaging in radiology (standard/low-dose/dual-energy CT) and radiotherapy (planning CT, kV cone-beam CT (CBCT)).MethodsDose was measured by thermoluminescent dosimeters (TLD’s) placed at 86 positions in an anthropomorphic phantom. Point, organ and effective dose were assessed, and secondary cancer risk from imaging was estimated.ResultsOverall dose and mean organ dose comparisons yield significantly lower dose for the optimized radiology protocols (dual-source and care kV), with an average dose of 0.34±0.01 mGy and 0.54±0.01 mGy (average ± standard deviation), respectively. Standard abdominal CT and planning CT involve considerably higher dose (13.58 ± 0.18 mGy and 18.78±0.27 mGy, respectively). The CBCT dose show a dose fall-off near the field edges. On average, dose is reduced as compared with the planning or standard CT (3.79 ± 0.21 mGy for 220° rotation and 7.76 ± 0.37 mGy for 360°), unless the high-quality setting is chosen (20.30 ± 0.96 mGy). The mean organ doses show a similar behavior, which translates to the estimated secondary cancer risk. The modelled risk is in the range between 0.4 cases per million patient years (PY) for the radiological scans dual-energy and care kV, and 300 cases per million PY for the high-quality CBCT setting.ConclusionsModern radiotherapy imaging techniques (while much lower in dose than radiotherapy), involve considerably more dose to the patient than modern radiology techniques. Given the frequency of radiotherapy imaging, a further reduction in radiotherapy imaging dose appears to be both desirable and technically feasible.     

Active immunization of post-pubertal heifers against prostaglandin F2α to suppress oestrous behaviour: effect of adjuvant and dose of immunogen

Two experiments were performed to develop an effective prostaglandin F_2α immunization protocol to suppress oestrous behaviour in beef heifers. In Experiment 1, a 3 × 2 factorial plan (n=4–5 per treatment) was used to test three doses (3.3, 10 and 30 mg) of a prostaglandin F_2α- human serum albumin (PGF-HSA) conjugate as the immunogen and two adjuvants, GNE (proprietary product; Intervet, The Netherlands) and diethylaminoethyl (DEAE)-dextran. Heifers (n=5) in a control group were untreated. Booster immunizations were given on Days 42 and 145 after the primary immunization (Day 0) and data collection for statistical purposes ended on Day 297. After Day 42 the incidence of oestrous behaviour was: (1) greater (P < 0.05) for control than immunized heifers (4.3 and 2.2, respectively), (2) greater (P < 0.05) for heifers immunized using GNE than for heifers immunized using DEAE-dextran (2.6 and 1.9, respectively), and (3) greater for heifers immunized with 30 mg of immunogen than for those immunized with either 3.3 or 10 mg (3.1, 1.7 and 1.9, respectively). Suppression of oestrous behaviour was accompanied by formation of a persistent corpus luteum (CL). Persistent CL were formed in ten of the 28 immunized heifers and the mean (± standard error of the mean) duration of persistence was 397 ± 85 days. In Experiment 2, a 2 × 2 factorial plan (n=6–7 per treatment) was used to test two doses (1 and 10 mg) of the PGF-HSA conjugate as the immunogen and two adjuvants, non-ulcerative Freund's adjuvant (NUFA) and DEAE-dextran. A control group was untreated (n=6). Booster immunization was given on Day 183 after the primary immunization (Day 0) and the experiment finished on Day 384. Antibody titres were higher (P < 0.05) in NUFA-treated heifers than in DEAE-dextran-treated (1 mg) heifers in the 183- to 283-day period. After Day 183, oestrous behaviour was suppressed in 26 out of the 27 immunized heifers. Persistent CL were maintained for longer (P < 0.05) in NUFA-treated heifers (245 days) than in DEAE-dextran-treated heifers (166 days) but there was no difference due to dose of immunogen (208 and 203 days, 1 and 10 mg, respectively). It is concluded that immunization against PGF-HSA results in suppression of oestrous behaviour in heifers due to prolongation of the life-span of the CL; however, efficacy of response is dependent on the immunization regime used.     

The effect of 17β-estradiol treatment on the mass and the turnover of bone in ovariectomized rats taking a mild dose of thyroxin

We performed the dosing experiment to establish whether estrogen administration has any beneficial effects on the mass and the turnover of bone in ovariectomized rats taking a mild dose of thyroxin. Thirty-five Wistar rats, 28 weeks of age, received ovariectomies (OVX) or sham operations and were divided into five groups. Group I was the sham group, Groups 2–5 were ovariectomized. Group 2 was the OVX-control, Group 3 treated with thyroxin 30 μg/kg/day (T4), Group 4, 17β-estradiol 0.3 mg/kg/week (E2), and Group 5, the combination of T4 and E2. The duration of the experiment was 12 weeks. At the end of the experiment, serum chemistries were measured. Bone minerals in the femur were determined with single photon absorptiometry and bone turnover was assessed histomorphometrically. Alkaline-phosphatase increased in Group 3 (OVX-T4), but it reduced in Groups 4 (OVX-E2) and 5 (OVX-T4 + E2). Bone minerals decreased in Groups 2 (OVX) and 3. In Group 4, it was preserved at the same level as in Group 1. Group 5 showed a significant increase of bone mass compared with Group 1. Eroded surface and osteoid surface increased in Groups 2 and 3 and they were reduced in Groups 4 and 5. Bone volume and mineral apposition rate were at a maximum in Group 5. This study demonstrated that 17β-estradiol was capable of preventing the bone mass decrease by regulating the turnover in ovariectomized rats taking a mild dose of thyroxin. Osteoblast function appeared to be stimulated in combination with 17β-estradiol and thyroxin.     

A “quality-control-based correction method” for displayed dose indices on CT scanner consoles in patient dose surveys

PurposeA new quality-control-based (QC-based) method is introduced to obtain correction factors to be applied to displayed patient dose indices (CTDI_Vol and DLP) on CT scanner consoles to verify improvement of dose surveys for diagnostic reference levels (DRLs) determination.MethodAn available data-base of QC documents and reports of 57 CT scanners in Tehran, Iran was used to estimate CTDI_Vol, DLP and relevant correction factors for three CT examination types including head, chest and abdomen/pelvis. The correction factor is the ratio of QC-based estimated dose to displayed dose. A dose survey was performed by applying on-site “data collection method” and correction factors obtained in order to select CT scanners in three modes for determination of CT DRLs by inclusion of: (a) all CT scanners before displayed dose indices were corrected (57), (b) only CT scanners calibrated by QC experts (41) and (c) all CT scanners after displayed dose indices were corrected (57).ResultsFor the 41 CT scanners, correction factors of three examination types obtained in this study are within the acceptance tolerance of IAEA HHS-19. The correction factors range from 0.45 to 1.7 (average of 3 examinations) which is due to the change in the calibrated value of CTDI_Vol over extended time. The DRL differences in three modes are within ±1.0% for CTDI_Vol and ±12.4% for DLP.ConclusionsThe “QC-based correction method” applied to mode (c) has improved the DRLs obtained by other two modes. This method is a strong alternative to “direct dose measurement” with simplicity and cost effectiveness.     

Bladder dose–surface maps and urinary toxicity: Robustness with respect to motion in assessing local dose effects

The purpose of this study was to quantify the impact of inter-fraction modifications of bladder during RT of prostate cancer on bladder dose surface maps (DSM).Eighteen patients treated with daily image-guided Tomotherapy and moderate hypofractionation (70–72.8 Gy at 2.5–2.6 Gy/fr in 28 fractions and full bladder) were considered. Bladder contours were delineated on co-registered daily Megavoltage CT (MVCT) by a single observer and copied on the planning CT to generate dose–volume/surface histograms (DVH/DSH) and bladder DSMs. Discrepancies between planned and daily absorbed doses were analyzed through the average of individual systematic errors, the population systematic errors and the population random errors for the DVH/DSHs and DSMs.In total, 477 DVH/DSH and 472 DSM were available. DSH and DVH showed small population systematic errors of absolute surfaces (<3.4 cm²) and volumes (<8.4 cm³) at the highest doses.The dose to the posterior bladder base assessed on DSMs showed a mean systematic error below 1 Gy, with population systematic and random errors within 4 and 3 Gy, respectively. The region surrounding this area shows higher mean systematic errors (1–3 Gy), population systematic (8–11 Gy) and random (5–7 Gy) errors.In conclusion, DVH/DSH and DSMs are quite stable with respect to inter-fraction variations in the high-dose region, within about 2 cm from bladder base. Larger systematic variations occur in the anterior portion and cranially 2.5–3.5 cm from the base.Results suggest that dose predictors related to the high dose area (including the trigone dose) are likely to be sufficiently reliable with respect to the expected variations due to variable bladder filling.     

Is dose escalation achievable for esophageal carcinoma?

Aim

To investigate the feasibility of dose escalation using rapid arc (RA) and Helical Tomotherapy (HT) for patients with upper, middle and distal esophageal carcinomas, even for large tumor volumes.

Background

In esophageal cancer, for patients with exclusive radio-chemotherapy, local disease control remains poor. Planning study with dose escalation was done for two sophisticated modulated radiotherapy techniques: Rapid arc against Tomotherapy.

Materials and methods

Six patients treated with a RA simultaneous integrated boost (SIB) of 60 Gy were re-planned for RA and HT techniques with a SIB dose escalated to 70 Gy. Dose volume histogram statistics, conformity indices and homogeneity indices were analyzed. For a given set of normal tissue constraints, the capability of each treatment modality to increase the GTV dose to 70 Gy was investigated.

Results

Either HT or VMAT may be used to escalate the dose delivered in esophageal tumors while maintaining the spinal cord, lung and heart doses within tolerance. Adequate target coverage was achieved by both techniques. Typically, HT achieved better lung sparing and PTV coverage than did RA.

Conclusions

Dose escalation for esophageal cancer becomes clinically feasible with the use of RA and HT. This promising result could be explored in a carefully controlled clinical study which considered normal tissue complications and tumor control as endpoints.     

Reproductive studies of Brahman cattle V. The effect of various dose levels of estradiol-17β upon serum luteinizing hormone in ovariectomized Brahman cows

Twelve mature chronically-ovariectomized Brahman cows were randomly assigned to receive three of six different dosages of estradiol-17_b (E2) at three different time periods such that at the termination of the trial six animals received each E2 dosage. The E2 was suspended in 0, 1, 2.5, 5, 10 and 20 milligrams. A two week period was maintained between injections. The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 18 hr, every hr from 18 to 42 hr and every 2 hr from 42 to 48 hr postinjection. Blood was processed to yield serum and stored at ?20 Celsius. Serum luteinizing hormone (LH) was quantitated by validated radioimmunoassay. An LH surge was defined as a sustained elevation of LH at least two standard deviations above the level of LH prior to the rise and was observed in $\text{0}\text{6}$, $\text{3}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, and $\text{6}\text{6}$ cows administered 0, 1, 2.5, 5, 10, and 20 mg of E2, respectively. All animals injected with E2 responded with a significant initial decrease (independent of E2 dosage) in LH that persisted from 2 through 12 hr post E2 injection. No significant decrease in LH levels was recorded in animals injected with the corn oil vehicle. The time to the LH surge differed (P<.05) between 1 mg E2 (10 hr) vs 20 mg E2 (19.5 hr), 1 mg E2 vs 10 mg E2 (16.2 hr), and 2.5 mg E2 (12.4 hr) vs 20 mg estradiol-17_β. Luteinizing hormone concentrations at the onset of the surge did not differ (P>.10) between E2 dosages. The elapsed time from E2 injection to the peak LH value differed (P<.05) between 1 mg E2 (20.3 hr) vs 20 mg E2 (26.8 hr), and 2.5 mg E2 (21.2 hr) vs 20 mg estradiol-17_β. The peak LH value, the area under the LH curve and the duration of the LH surge did not differ (P>.10) with E2 dosage. The time to the end of the LH surge differed (P<.05) between 1 mg E2 (25.3 hr) vs 2.5 mg E2 (31.6 hr), 1 mg E2 vs 5 mg (34.4 hr), 1 mg E2 vs 10 mg E2 (34.8 hr), 1 mg E2 vs 20 mg E2 (37.3 hr), and 2.5 mg E2 vs 20 mg estradiol-17_β. Luteinizing hormone values at the termination of the surge did not differ (P>.10) between dosages nor did the LH values at the termination of the surge differ (P>.10) from LH concentrations observed at the onset of the LH surge.     

Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose–response relationships

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED_rad-ther) in the irradiated organs. The OED_rad-ther concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose–response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose–response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin’s disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin’s disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.     

Reproductive studies of Brahman cattle I. Behavioral effect of various dose levels of Estradiol-17β upon ovariectomized Brahman,Brahman × Hereford and Hereford cows

Six ovariectomized mature cows each of Brahman (B), Brahman × Hereford (BH) or Hereford (H) breeding were injected intramuscularly with Estradiol-17β (E). Dose levels of 1, 2, 4 and 8 mg E were given in 2 ml corn oil. Cows were allowed a 2 week recovery period between treatments. After injection the cows were placed with 18 epididymectomized bulls and observed constantly for 36 hours. B failed to accept the bulls at any E dose level. Proportions of BH accepting the bull were $\text{2}\text{6}$, $\text{6}\text{6}$, $\text{6}\text{6}$ and $\text{6}\text{6}$ and proportions of H accepting the bull were $\text{5}\text{6}$, $\text{6}\text{6}$, $\text{5}\text{6}$ and $\text{6}\text{6}$ at 1, 2, 4 and 8 mg E, respectively. BH were less responsive at 1 mg E than H (P<.10) and B were less responsive at any level (P<.005). The number of stances increased significantly with dose level (P<.005) and a breed × dose level interaction (P<.10) was found. The duration of standing estrus behavior was longer in H cows at 1 and 2 mg E than in BH (P<.05) but was identical at 4 and 8 mg E. Duration of estrus was shorter in B except at the 2 mg dose level. Breed (P<.005) and breed × dose level interactions (P<.05) were found. Response time (injection of E to stance event) did not differ between dosages of E within breed groups. However, response time was significantly longer in B (19.3 hrs, P<.05) versus the response time of either H (10.1 hrs) or BH (12.8 hrs). If homosexual stance behavior is accepted as estrus, B were less responsive at 1, 2, 4 and 8 mg E than were BH or H (P<.10).     

Nonopioid effect of β-endorphin

This review presents the generalized literature data and the results of our own research of the nonopioid effect of β-endorphin, an opioid neuropeptide interacting not only with opioid but also with nonopioid (insensitive to the opioid antagonist naloxone) receptors. The roles of the hormone and its receptors in regulation of the immune, nervous, and endocrine systems are discussed. The effect of neuromediator on the immune system mediated by both opioid and nonopioid receptors is considered in detail. The data on distribution and function of the nonopioid β-endorphin receptor in human and animal organisms are presented. All available data on the characteristics of the nonopioid β-endorphin receptor obtained by means of radioligand analysis are given. The discussed information is supposed to extend our conceptions of the role of β-endorphin in mammals and to be of extensive use in medicine and pharmacology.     

The effect of the β-emitting yttrium-90 citrate on the dose–response of dicentric chromosomes in human lymphocytes: a basis for biological dosimetry after radiosynoviorthesis

The production of dicentric chromosomes in human lymphocytes by β-particles of yttrium-90 (Y-90) was studied in vitro to provide a basis of biological dosimetry after radiosynoviorthesis (RSO) of persistent synovitis by intra-articular administration of yttrium-90 citrate colloid. Since the injected colloid may leak into the lymphatic drainage exposing other parts of the body to radiation, the measurement of biological damage induced by β-particles of Y-90 is important for the assessment of radiation risk to the patients. A linear dose–response relationship (α = 0.0229 ± 0.0028 dicentric chromosomes per cell per gray) was found over the dose range of 0.2176–2.176 Gy. The absorbed doses were calculated for exposure of blood samples to Y-90 activities from 40 to 400 kBq using both Monte Carlo simulation and an analytical model. The maximum low-dose RBE, the RBE_M which is equivalent to the ratio of the α coefficients of the dose–response curves, is well in line with published results obtained earlier for irradiation of blood of the same donor with heavily filtered 220 kV X-rays (3.35 mm copper), but half of the RBE_M relative to weakly filtered 220 kV X-rays. Therefore, it can be concluded that for estimating an absorbed dose during RSO by the technique of biological dosimetry, in vitro and in vivo data for the same radiation quality are necessary.     

The effect of a single high dose of PGF2α administered to dairy cattle 3.5 days after ovulation on luteal function, morphology, and follicular dynamics

A single treatment with PGF2α is assumed to have no luteolytic effect on cows with corpora lutea < 5 days old. The objective of this study was to determine the effect of a single high dose of PGF2α administered to dairy cattle on the morphology and function of the early CL. The study followed a crossover design with a treatment cycle in which 50 mg of dinoprost were administered 3.5 days postovulation and a control untreated cycle. Ultrasound examination and blood samples were performed during the two consecutive cycles. Corpus luteum (CL) diameter, progesterone concentration, and follicular dynamics characteristics were compared between control and treated cycles. Two of nine cows (22%) developed full luteolysis. The remaining seven cows (78%) had partial luteolysis with a decrease (P < 0.05) in progesterone concentration and CL diameter for two and 12 days post-treatment, respectively. The interovulatory interval of treated cycles (19.7 ± 2.4 days) was not different (P > 0.05) from that of controls (23.8 ± 0.9 days). The transient reduction in progesterone of cows with partial luteolysis had no effect on the proportion of cows with two or three follicular waves, follicle growth rate, or preovulatory diameter (P > 0.05). Two cows developed ovarian cystic degeneration during the PGF2α-induced cycle. In conclusion, the treatment of cows with a high dose of PGF2α 3.5 days postovulation induced some degree of luteolysis in all treated cows. This resulted in partial luteolysis in 78% of treated animals and in full luteolysis in the remaining 22%.     

Sunitinib versus imatinib dose escalation after failure of imatinib standard dose in patients with advanced Gastrointestinal stromal tumors – a real-world multi-center study

BackgroundWhether to escalate imatinib dosage or directly switch to sunitinib in gastrointestinal stromal tumors (GISTs) failing on standard dose 400 mg/d of imatinib is still controversial.MethodsWe evaluated progression-free survival (PFS), overall survival (OS), and time to sunitinib failure (TTSF) of patients selecting imatinib dose escalation or directly switching to sunitinib after the failure of imatinib 400 mg/d therapy from 3 tertery referring centers between January 2008 to December 2016.ResultsA total of 240 patients receiving sunitinib (37.5 mg continuous daily dose or 50 mg 4 weeks on with 2 weeks off) for at least 8 weeks were examined. After failure on imatinib 400 mg/d, 100 (49.3%) patients had dose escalation to 600 mg or 800 mg per day (IM group, imatinib group), and 103 (50.7%) directly switched to sunitinib (SU group, sunitinib group). The PFS in the SU and IM groups was 12 months and 5.0 months (P < 0.001), respectively. TTSF or OS in both groups was not statistically significantly different.ConclusionsAfter the progression of imatinib standard-dose treatment in recurrent/metastatic GISTs, the PFS of patients directly switching to sunitinib was significantly longer compared with the PFS of patients with imatinib dose escalation. However, when the patients continued with sunitinib therapy after the failure of IM dose escalation, TTSF and OS in the IM group were similar to those in the SU group. Further exploration of the characteristics of the population benefiting from imatinib dose escalation are warranted.     

Hill coefficients,dose–response curves and allosteric mechanisms

Hill coefficients (n _H) derived from four parameter logistic fits to dose–response curves were compared to calculated realistic reaction schemes and related to experimental data: (1) Hill coefficients may give information on the number of interacting sites but cannot distinguish between competitive, non-competitive or ortho-, iso-, or allosteric mechanisms. (2) For enzymatic dose–inhibition curves, Hill coefficients smaller than one do not indicate anticooperative binding but show that at least one ternary complex has enzymatic activity. (3) Hill coefficients different from one are proof for multiple ligand binding. The large variations of reported Hill coefficients corresponds to multiple allosteric binding, where induced conformational changes cause loss of the active conformation. Such a denaturation mechanism is in stark contrast to the desired specificity of drugs. The discussion is open.