Radiopotentiation Profiling of Multiple Inhibitors of the DNA Damage Response for Early Clinical Development.

Radiotherapy is an effective anticancer treatment, but combinations with targeted agents that maximize efficacy while sparing normal tissue are needed. Here, we assess the radiopotentiation profiles of DNA damage response inhibitors (DDRi) olaparib (PARP1/2), ceralasertib (ATR), adavosertib (WEE1), AZD0156 (ATM), and KU-60648 (DNA-PK). We performed a radiotherapy combination screen and assessed how drug concentration and cellular DDR deficiencies influence the radiopotentiation ability of DDRi. We pre-selected six lung cancer cell lines with different genetic/signaling aberrations (including mutations in TP53 and ATM) and assessed multiple concentrations of DDRi in combination with a fixed radiotherapy dose by clonogenic assay. The effective concentration of DDRi in radiotherapy combinations is lower than that required for single-agent efficacy. This has the potential to be exploited further in the context of DDR deficiencies to increase therapeutic index and we demonstrate that low concentrations of AZD0156 preferentially sensitized p53-deficient cells. Moreover, testing multiple concentrations of DDRi in radiotherapy combinations indicated that olaparib, ceralasertib, and adavosertib have a desirable safety profile showing moderate increases in radiotherapy dose enhancement with increasing inhibitor concentration. Small increases in concentration of AZD0156 and particularly KU-60648, however, result in steep increases in dose enhancement. Radiopotentiation profiling can inform on effective drug doses required for radiosensitization in relation to biomarkers, providing an opportunity to increase therapeutic index. Moreover, multiple concentration testing demonstrates a relationship between drug concentration and radiotherapy effect that provides valuable insights that, with future in vivo validation, can guide dose-escalation strategies in clinical trials.

Repeatability of 18F-FDG PET in a multicenter phase I study of patients with advanced gastrointestinal malignancies.

UNLABELLED: (18)F-FDG PET is often used to monitor tumor response in multicenter oncology clinical trials. This study assessed the repeatability of several semiquantitative standardized uptake values (mean SUV [SUV(mean)], maximum SUV [SUV(max)], peak SUV [SUV(peak)], and the 3-dimensional isocontour at 70% of the maximum pixel value [SUV(70%)]) as measured by repeated baseline (18)F-FDG PET studies in a multicenter phase I oncology trial. METHODS: Double-baseline (18)F-FDG PET studies were acquired for 62 sequentially enrolled patients. Tumor metabolic activity was assessed by SUV(mean), SUV(max), SUV(peak), and SUV(70%). The effect on SUV repeatability of compliance with recommended image-acquisition guidelines and quality assurance (QA) standards was assessed. Summary statistics for absolute differences relative to the average of baseline values and repeatability analysis were performed for all patients and for a subgroup that passed QA, in both a multi- and a single-observer setting. Intrasubject precision of baseline measurements was assessed by repeatability coefficients, intrasubject coefficients of variation (CV), and confidence intervals on mean baseline differences for all SUV parameters. RESULTS: The mean differences between the 2 SUV baseline measurements were small, varying from -2.1% to 1.9%, and the 95% confidence intervals for these mean differences had a maximum half-width of about 5.6% across the SUV parameters assessed. For SUV(max), the intrasubject CV varied from 10.7% to 12.8% for the QA multi- and single-observer datasets and was 16% for the full dataset. The 95% repeatability coefficients ranged from -28.4% to 39.6% for the QA datasets and up to -34.3% to 52.3% for the full dataset. CONCLUSION: Repeatability results of double-baseline (18)F-FDG PET scans were similar for all SUV parameters assessed, for both the full and the QA datasets, in both the multi- and the single-observer settings. Centralized quality assurance and analysis of data improved intrasubject CV from 15.9% to 10.7% for averaged SUV(max). Thresholds for metabolic response in the multicenter multiobserver non-QA settings were -34% and 52% and in the range of -26% to 39% with centralized QA. These results support the use of (18)F-FDG PET for tumor assessment in multicenter oncology clinical trials.

MR in oncology drug development.

This article reviews the use of MR in preclinical and clinical experiments to aid drug development. In particular it concentrates on the use of MR to study tumor microvasculature following treatment with anti-vascular agents and the use of MRS to study tumor metabolism following treatment with a variety of anti-cancer agents. The advantages and disadvantages of a variety of techniques including contrast- and noncontrast-enhanced methods are discussed and the data from clinical trials using these techniques are reviewed. Despite the consensus documents produced to date for both dynamic contrast-enhanced MRI and MRS, most of the trials reported used alternative methods, and different nomenclature for the MR parameters used. This continues to inhibit the comparison between novel therapeutics and between different trials with the same compound. Comprehensive data from multicenter trials on the reproducibility of techniques is still lacking in the literature and the implications of the available data on clinical trial design is also discussed.

Phase I clinical trial of weekly combretastatin A4 phosphate: clinical and pharmacokinetic results.

PURPOSE: A phase I trial was performed with combretastatin A4 phosphate (CA4P), a novel tubulin-binding agent that has been shown to rapidly reduce blood flow in animal tumors. PATIENTS AND METHODS: The drug was delivered by a 10-minute weekly infusion for 3 weeks followed by a week gap, with intrapatient dose escalation. Dose escalation was accomplished by doubling until grade 2 toxicity was seen. The starting dose was 5 mg/m2. RESULTS: Thirty-four patients received 167 infusions. CA4P was rapidly converted to the active combretastatin A4 (CA4), which was further metabolized to the glucuronide. CA4 area under the curve (AUC) increased from 0.169 at 5 mg/m2 to 3.29 micromol * h/L at 114 mg/m2. The mean CA4 AUC in eight patients at 68 mg/m2 was 2.33 micromol * h/L compared with 5.8 micromol * h/L at 25 mg/kg (the lowest effective dose) in the mouse. The only toxicity that possibly was related to the drug dose up to 40 mg/m2 was tumor pain. Dose-limiting toxicity was reversible ataxia at 114 mg/m2, vasovagal syncope and motor neuropathy at 88 mg/m2, and fatal ischemia in previously irradiated bowel at 52 mg/m2. Other drug-related grade 2 or higher toxicities seen in more than one patient were pain, lymphopenia, fatigue, anemia, diarrhea, hypertension, hypotension, vomiting, visual disturbance, and dyspnea. One patient at 68 mg/m2 had improvement in liver metastases of adrenocortical carcinoma. CONCLUSION: CA4P was well tolerated in 14 of 16 patients at 52 or 68 mg/m2; these are doses at which tumor blood flow reduction has been recorded.

Combretastatin A4 phosphate has tumor antivascular activity in rat and man as demonstrated by dynamic magnetic resonance imaging.

PURPOSE: Combretastatin A4 phosphate (CA4P) is a novel vascular targeting agent. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) studies were performed to examine changes in parameters related to blood flow and vascular permeability in tumor and normal tissue after CA4P treatment. MATERIALS AND METHODS: Changes in kinetic DCE-MRI parameters (transfer constant [Ktrans] and area under contrast medium-time curve [AUC]) over 24 hours after treatment with CA4P were measured in 18 patients in a phase I trial and compared with those obtained in the rat P22 carcinosarcoma model, using the same imaging technique. Rats were treated with 30 mg/kg of CA4P; patients received escalating doses from 5 to 114 mg/m2. RESULTS: A similar pattern and time course of change in tumor and normal tissue parameters was seen in rats and humans. Rat tumor Ktrans was reduced by 64% 6 hours after treatment with CA4P (30 mg/kg). No significant reductions in kidney or muscle parameters were seen. Significant reductions were seen in tumor Ktrans in six of 16 patients treated at >or= 52 mg/m2, with a significant group mean reduction of 37% and 29% at 4 and 24 hours, respectively, after treatment. The mean reduction in tumor initial area under the gadolinium-diethylenetriamine pentaacetic acid concentration-time curve (AUC) was 33% and 18%, respectively, at these times. No reduction was seen in muscle Ktrans or in kidney AUC in group analysis of the clinical data. CONCLUSION: CA4P acutely reduces Ktrans in human as well as rat tumors at well-tolerated doses, with no significant changes in kidney or muscle, providing proof of principle that this drug has tumor antivascular activity in rats and humans.

ZD6126: a novel vascular-targeting agent that causes selective destruction of tumor vasculature.

Physiological differences between tumor and normal vasculature provide a target for drug discovery. In particular, the immature nature of tumor vasculature may render it intrinsically sensitive to disruption by agents affecting the endothelial cell cytoskeleton, including tubulin-binding agents. In this article, we report the synthesis of a water-soluble phosphate prodrug, ZD6126, of the tubulin-binding agent N-acetylcolchinol. In vitro studies demonstrate the comparative tubulin-binding properties of the prodrug and active drug, and show the induction of pronounced, reversible changes in endothelial cell morphology at subcytotoxic doses. Neither ZD6126 nor N-acetylcolchinol showed effects on the growth of human umbilical vein endothelial cells at concentrations below 100 micro M. In contrast, changes in endothelial cell morphology were seen at much lower, noncytotoxic concentrations (0.1 micro M) of ZD6126 and more pronounced effects were seen in proliferating versus confluent endothelial cell cultures. In vivo studies were carried out using a murine tumor model (CaNT) with single administration of a dose well below the maximum tolerated dose. These studies showed a large reduction in vascular volume, induction of extensive necrosis in tumors, and a reduced tumor cell yield in a clonal excision assay, consistent with vascular rather than cytotoxic effects. A viable rim of tumor remained after single-dose administration and minimal growth delay was observed. However, well-tolerated, multiple administration regimens led to pronounced tumor-growth delay. In the human xenograft FaDu, the growth delay given by a single dose of paclitaxel was enhanced by combination with a single dose of ZD6126, and the growth delay given by the combination was greater than the sum of the growth delays from the individual treatments. These findings show that ZD6126 is a promising antivascular agent for the treatment of solid tumors.

Effects of 5,6-dimethylxanthenone-4-acetic acid on human tumor microcirculation assessed by dynamic contrast-enhanced magnetic resonance imaging.

PURPOSE: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) causes vascular shutdown in preclinical models. Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) studies were performed in the phase I trials to examine changes related to blood flow and permeability in tumor and muscle. PATIENTS AND METHODS: Sixteen patients treated with DMXAA from 500 to 4,900 mg/m(2) had DCE-MRI examinations before and after treatment. The maximum gradient, the maximum enhancement, and the area under the signal-intensity-time curve (AUC) over the first 90 seconds were calculated for each pixel in regions of interest (ROIs) in muscle and tumor, and the median value for each ROI was obtained. Changes after treatment were compared with 95% limits of agreement for an individual and for groups using data from our reproducibility study. RESULTS: Nine of 16 patients had significant reductions in AUC 24 hours after the first dose of DMXAA, and eight of 11 patients had reductions of up to 66% in AUC 24 hours after the last dose. Mean reductions in gradient, enhancement, and AUC were 25%, 18%, and 31%, respectively, 24 hours after the last dose, significantly greater than the 95% limits of change for a group of 11 patients. Enhancement and AUC in muscle 24 hours after the first dose were significantly reduced, but no significant changes were seen 24 hours after the last dose. CONCLUSION: DMXAA significantly reduces DCE-MRI parameters related to tumor blood flow, over a wide dose range, consistent with the reported tumor vascular targeting activity. Further clinical evaluation of DMXAA is warranted.

Reproducibility of dynamic contrast-enhanced MRI in human muscle and tumours: comparison of quantitative and semi-quantitative analysis.

The purpose of this study was to determine the reproducibility of dynamic contrast-enhanced (DCE)-MRI and compare quantitative kinetic parameters with semi-quantitative methods, and whole region-of-interest (ROI) with pixel analysis. Twenty-one patients with a range of tumour types underwent paired MRI examinations within a week, of which 16 pairs were evaluable. A proton density-weighted image was obtained prior to a dynamic series of 30 T(1)-weighted spoiled gradient echo images every 11.9 s with an intravenous bolus of gadopentetate dimeglumine given after the third baseline data point. Identical ROIs around the whole tumour and in skeletal muscle were drawn by the same observer on each pair of examinations and used for the reproducibility analysis. Semi-quantitative parameters, gradient, enhancement and AUC (area under the curve) were derived from tissue enhancement curves. Quantitative parameters (K(trans), k(ep), v(e)) were obtained by the application of the Tofts' model. Analysis was performed on data averaged across the whole ROI and on the median value from individual pixels within the ROI. No parameter showed a significant change between examinations. For all parameters except K(trans), the variability was not dependent on the parameter value, so the absolute values for the size of changes needed for significance should be used for future reference rather than percentages. The size of change needed for significance in a group of 16 in tumours for K(trans), k(ep) and v(e) was -14 to +16%, -0.20 ml/ml/min (15%) and -1.9[?]ml/ml (6%), respectively (pixel analysis), and -16 to +19%, -0.23 ml/ml/min (16%) and +/- 1.9[?]ml/ml (6%) (whole ROI analysis). For a single tumour, changes greater than -45 to +83%, +/- 0.78 ml/ml/min (60%) and +/- 7.6 ml/ml (24%), respectively, would be significant (pixel analysis). For gradient, enhancement and AUC the size of change needed for significance in tumours was -0.24 (17%), -0.05 (6%) and -0.06 (8%), respectively for a group of 16 (pixel analysis), and +/- 0.96 (68%), +/- 0.20 (25%) and +/- 0.22 (32%) for individuals. In muscle, the size of change needed for significance in a group of 16 for K(trans), k(ep) and v(e) was -30 to +44%, +/- 0.81 ml/ml/min (61%) and +/- 1.7 ml/ml (13%). For gradient, enhancement and AUC it was +/- 0.09 (20%), +/- 0.02 (8%) and +/- 0.03 (12%). v(e), enhancement and AUC are highly reproducible DCE-MRI parameters. K(trans), k(ep) and gradient have greater variability, with larger changes in individuals required to be statistically significant, but are nevertheless sufficiently reproducible to detect changes greater than 14-17% in a cohort of 16 patients. Pixel analyses slightly improve reproducibility estimates and retain information about spatial heterogeneity. Reproducibility studies are recommended when treatment effects are being monitored.