Resistance to Cancer Treatment: The Role of Somatic Genetic Events and the Challenges for Targeted Therapies

Therapeutic resistance remains a major cause of cancer-related deaths. Resistance can occur from the outset of treatment or as an acquired phenomenon after an initial clinical response. Therapeutic resistance is an almost universal phenomenon in the treatment of metastatic cancers. The advent of molecularly targeted treatments brought greater efficacy in patients whose tumors express a particular target or molecular signature. However, resistance remains a predictable challenge. This article provides an overview of somatic genomic events that confer resistance to cancer therapies. Some examples, including BCR–Abl, EML4–ALK, and the androgen receptor, contain mutations in the target itself, which hamper binding and inhibitory functions of therapeutic agents. There are also examples of somatic genetic changes in other genes or pathways that result in resistance by circumventing the inhibitor, as in resistance to trastuzumab and BRAF inhibitors. Yet other examples results in activation of cytoprotective genes. The fact that all of these mechanisms of resistance are due to somatic changes in the tumor’s genome makes targeting them selectively a feasible goal. To identify and validate these changes, it is important to obtain biopsies of clinically resistant tumors. A rational consequence of this evolving knowledge is the growing appreciation that combinations of inhibitors will be needed to anticipate and overcome therapeutic resistance

QUANTITATIVE EVALUATION OF THERAPEUTIC RESPONSE BY FDG PET-CT IN METASTATIC BREAST CANCER

Purpose To assess the therapeutic response for metastatic breast cancer with 18F-FDG PET, this retrospective study aims to compare the performance of 6 different metabolic metrics with PERCIST, PERCIST with optimal thresholds and an image-based parametric approach.MethodsThirty six metastatic breast cancer patients underwent 128 PET scans and 123 lesions were identified. In a per-lesion and per-patient analysis, the performance of 6 metrics: SUVmax (maximum Standardized Uptake Value), SUVpeak, SAM (Standardized Added Metabolic activity), SUVmean, metabolic volume (MV), TLG (total lesion glycolysis) and a parametric approach (SULTAN) were determined and compared to the gold standard (defined by clinical assessment and biological and conventional imaging according RECIST 1.1). The evaluation was performed using PERCIST thresholds (for per-patient analysis only) and optimal thresholds (determined by the Youden criterion from the Receiver Operating Characteristic curves).ResultsIn the per-lesion analysis, 210 pairs of lesion evolutions were studied. Using the optimal thresholds, SUVmax, SUVpeak, SUVmean, SAM and TLG were significantly correlated with the gold standard. SUVmax, SUVpeak and SUVmean reached the best sensitivity (91 %, 88 % and 83% respectively), specificity (93%, 95% and 97% respectively) and negative predictive value (NPV, 90%, 88% and 83% respectively). For the per-patient analysis, 79 pairs of PET were studied. The optimal thresholds compared to the PERCIST threshold did not improve performance for SUVmax, SUVpeak and SUVmean. Only SUVmax, SUVpeak, SUVmean and TLG were correlated with the gold standard. SULTAN also performed equally: 83% sensitivity, 88% specificity and NPV 86%.ConclusionsThis study showed that SUVmax and SUVpeak were the best parameters for PET evaluation of metastatic breast cancer lesions. Parametric imaging is helpful in evaluating serial studies

Improvement of radioimmunotherapy using pretargeting

During the past two decades, considerable research has been devoted to radionuclide therapy using radiolabelled monoclonal antibodies and receptor binding agents. Conventional Radioimmunotherapy (RIT) is now an established and important tool in the treatment of hematologic malignancies such as Non-Hodgkin lymphoma. For solid malignancies, the efficacy of RIT has not been as successful due to lower radiosensitivity, difficult penetration of the antibody into the tumor and potential excessive radiation to normal tissues. Innovative approaches have been developed in order to enhance tumor absorbed dose while limiting toxicity to overcome the different limitations due to the tumor and host characteristics.Pretargeting techniques (pRIT) are a promising approach that consists of decoupling the delivery of a tumor monoclonal antibody (mAb) from the delivery of the radionuclide. This results in a much higher tumor-to-normal tissue ratio and is favorable for therapy as well and imaging. This includes various strategies based on avidin/streptavidin-biotin, DNA-complementary DNA and bispecific antibody-hapten bindings. PRIT continuously evolves with the investigation of new molecular constructs and the development of radiochemistry. Pharmacokinetics improve dosimetry depending on the radionuclides used (alpha, beta and Auger emitters) with prediction of tumor response and host toxicities. New constructs such as the Dock and Lock technology allow production of a variety of mABs directed against tumor-associated antigens. Survival benefit has already been shown in medullary thyroid carcinoma. Improvement in delivery of radioactivity to tumors with these pretargeting procedures associated with reduced hematologic toxicity will become the next generation of RIT. The following review addresses actual technical and clinical considerations and future development of pRIT

CLINICAL AND SURVIVAL IMPACT OF FDG PET IN PATIENTS WITH SUSPICION OF RECURRENT OVARIAN CANCER: A 6-YEAR FOLLOW-UP

Background: The aim of this retrospective study was to evaluate the contribution of FDG PET to the clinical management and survival outcome of patients (pts) suspected of recurrent ovarian carcinoma, with the hypothesis that early diagnosis of recurrent ovarian cancer may improve overall survival. Methods: 53 FDG PET/CT scans were retrospectively analyzed for 42 pts. CT and PET/CT findings were confirmed by imaging and clinical follow-up, and/or pathology which was considered as the gold standard diagnosis. The treatment plan based on CT staging was compared with that based on PET/CT findings. Medical records were reviewed for pts characteristics, progression free survival (PFS) and overall survival (OS). Progression-free survival (PFS) and overall survival (OS) were analyzed using the Cox proportional hazards regression model. Results: The final diagnosis of recurrence was established pathologically (n=16), or by a median clinical follow-up of 6.5 years (range 0.5-7.5) after the PET/CT (n=37). PET/CT provided a higher detection sensitivity (92.2%, 47/51) than CT (60.8%, 31/51) (p<0.001). Globally, PET/CT modified the treatment plan in 56.6% (30/53) of and in 65,2% (14/23) when the CT was negative prior to PET/CT. In 30 cases, that benefited from a modified treatment plan, these changes led to the intensification of a previous treatment procedure in 83.3% (25/30), and to a reduction in the previous treatment procedure in 16.6% of cases (5/30). The Cox regression multivariate analysis showed that the number of lesions visualized by CT, and presence of lung lesions detected by PET/CT, were significantly associated with PFS (p=0.002 and p = 0.035, respectively). Conclusion: On account of its impact on treatment planning, and especially patient outcome, FDG PET is a valuable diagnostic tool for cases of suspected ovarian cancer recurrence

Physician recruitment of patients to non-therapeutic oncology clinical trials: ethics revisited

Tailoring medical treatment to individual patients requires a strong foundation in research to provide the data necessary to understand the relationship between the disease, the patient, and the type of treatment advocated for. Non-therapeutic oncology clinical trials studying therapeutic resistance require the participation of patients, yet only a small percentage enroll. Treating physicians are often relied on to recruit patients, but they have a number of ethical obligations that might be perceived as barriers to recruiting. Concepts such as voluntariness of consent and conflicts of interest can have an impact on whether physicians will discuss clinical trials with their patients and how patients perceive the information. However, these ethical obligations should not be prohibitive to physician recruitment of patients—precautions can be taken to ensure that patients’ consent to research participation is fully voluntary and devoid of conflict, such as the use of other members of the research team than the treating physician to discuss the trial and obtain consent, and better communication between researchers, clinicians and patients. These can ensure that research benefits are maximized for the good of patients and society

Focus on the controversial aspects of 64Cu-ATSM in tumoral hypoxia mapping by PET imaging

Mapping tumor hypoxia is a great challenge in Positron Emission Tomography (PET) imaging as the precise functional information of the biological processes is needed for many effective therapeutic strategies. Tumor hypoxia has been widely reported as a poor prognostic indicator and is often associated with tumor aggressiveness, chemo and radio resistance. An accurate diagnosis of hypoxia is a challenge and is crucial for providing accurate treatment for patients’ survival benefits. This challenge has led to the emergence of new and novel PET tracers for the functional and metabolic characterization of tumor hypoxia non-invasively. Among these tracers, copper semicarbazone compound, [64Cu]- diacetyl-bis(N4 methylthiosemicarbazone) (=64Cu-ATSM) has been developed as a tracer for hypoxia imaging. This review focuses on 64Cu-ATSM PET imaging and the concept is presented in two sections. The first section describes its in vitro development and pre-clinical testing and particularly its affinity in different cell lines. The second section describes the controversial reports on its specificity for hypoxia imaging. The review concludes that 64Cu-ATSM - more than a hypoxic tracer, exhibits tracer accumulation in tumor which is linked to the redox potential and reactive oxygen species (ROS). The authors concluded that 64Cu-ATSNM is a marker of over-reduced cell state and thus an indirect marker for hypoxia imaging. The affinity of 64Cu-ATSM for over reduced cells was observed to be a complex phenomenon. And to provide a definitive and convincing mechanism, more in vivo studies are needed to prove the diagnostic utility of 64Cu-ATSM

Assessment of lymph nodes and prostate status using early dynamic curves with 18F-choline PET/CT in prostate cancer

Introduction: Dynamic image acquisition with 18F-Choline (FCH) PET/CT in prostate cancer is mostly used to overcome the bladder repletion which could obstruct the loco-regional analysis. The aim was to analyze early dynamic FCH acquisitions to define pelvic lymph node or prostate pathological status. Material and methods: Retrospective analysis was performed on 39 patients for initial staging (n=18), or after initial treatment (n=21). Patients underwent ten-minute dynamic acquisitions centered on the pelvis, after injection of 3-4 MBq/kg of FCH. Whole body images were acquired about one hour after injection using a PET/CT GE Discovery LS (GE-LS) or Siemens Biograph mCT (mCT). Maximum and mean SUV according to time were measured on nodal and prostatic lesions. SUVmean was corrected for partial volume effect (PVEC) with suitable recovery coefficients. The status of each lesion was based on histological results or patient follow-up (>6 months). A Mann-Whitney test and ANOVA were used to compare mean and receiver operating characteristic curve analysis.Results: The median PSA was 8.46 ng/mL and the median Gleason score was 3+4. Ninety-two lesions (43 lymph nodes and 49 prostate lesions) were analyzed, including 63 malignant lesions. In early dynamic acquisitions, the maximum and mean SUV were significantly higher, respectively on mCT and GE-LS, in malignant versus benign lesions (p<0.001, p<0.001). Area under the ROC curve showed a trend to better sensitivity and specificity for early acquisitions, compared with late acquisitions (SUVmax 0.92 versus 0.85 respectively) Mean SUV without PVEC, allowed better discrimination of benign from malignant lesions, in comparison with maximum and mean SUV (with PVEC), for both early and late acquisitions. For patients acquired on mCT, area under the ROC curve showed a trend to better sensitivity and specificity for early acquisitions, compared with late acquisitions (SUVmax AUC 0.92 versus 0.85 respectively).Conclusion: Assessment of lymph nodes and prostate pathological status with early dynamic imaging using PET/CT FCH allowed prostate cancer detection in situations where proof of malignancy is difficult to obtain

Pharmacokinetics and Dosimetry Studies for Optimization of Pretargeted Radioimmunotherapy in CEA-Expressing Advanced Lung Cancer Patients

Objectives. A phase I pretargeted radioimmunotherapy trial (EudractCT 200800603096) was designed in patients with metastatic lung cancer expressing carcinoembryonic antigen (CEA) to optimize bispecific antibody and labelled peptide doses, as well as the delay between their injections.Methods. Three cohorts of 3 patients received the anti-CEA x anti-histamine-succinyl-glycine (HSG) humanized trivalent bispecific antibody (TF2) and the IMP288 bivalent HSG-peptide. Patients underwent a pre-therapeutic imaging session S1 (44 or 88 nmol/m2 of TF2 followed by 4.4 nmol/m2, 185 MBq, of 111In-labelled IMP288), and, 1-2 weeks later, a therapy session S2 (240 or 480 nmol/m2 of TF2 followed by 24 nmol/m2, 1.1 GBq/m2, 177Lu-labeled IMP288). The pretargeting delay was 24 or 48 hours. The dose schedule was defined based on pre-clinical TF2 pharmacokinetic studies, on our previous clinical data using the previous anti-CEA pretargeting system and on clinical results observed in the first patients injected using the same system in the Netherlands.Results. TF2 pharmacokinetics (PK) was represented by a two-compartment model in which the central compartment volume was linearly dependent on the patient's surface area. PK were remarkably similar, with a clearance of 0.33 +/- 0.03 L/h per m2. 111In- and 177Lu-IMP288 PK were also well represented by a two-compartment model. IMP288 PK were faster (clearance 1.4 to 3.3 l/h). The central compartment volume was proportional to body surface area and IMP288clearance depended on the molar ratio of injected IMP288 to circulating TF2 at the time of IMP288 injection. Modelling of image quantification confirmed the dependence of IMP288 kinetics on circulating TF2, but tumour activity PK were variable. Organ absorbed doses were not significantly different in the 3 cohorts, but the tumour dose was significantly higher with the higher molar doses of TF2 (p < 0.002). S1 imaging predicted absorbed doses calculated in S2. Conclusion. The best dosing parameters corresponded to the shorter pretargeting delay and to the highest TF2 molar doses. S1 imaging session accurately predicted PK as well as absorbed doses of S2, thus potentially allowing for patient selection and dose optimization

A pretargeting system for tumor PET imaging and radioimmunotherapy

International audienceLabeled antibodies, as well as their fragments and antibody-derived recombinant constructs, have long been proposed as general vectors to target radionuclides to tumor lesions for imaging and therapy. They have indeed shown promise in both imaging and therapeutic applications, but they have not fulfilled the original expectations of achieving sufficient image contrast for tumor detection or sufficient radiation dose delivered to tumors for therapy. Pretargeting was originally developed for tumor immunoscintigraphy. It was assumed that directly-radiolabled antibodies could be replaced by an unlabeled immunoconjugate capable of binding both a tumor-specific antigen and a small molecular weight molecule. The small molecular weight molecule would carry the radioactive payload and would be injected after the bispecific immunoconjugate. It has been demonstrated that this approach does allow for both antibody-specific recognition and fast clearance of the radioactive molecule, thus resulting in improved tumor-to-normal tissue contrast ratios. It was subsequently shown that pretargeting also held promise for tumor therapy, translating improved tumor-to-normal tissue contrast ratios into more specific delivery of absorbed radiation doses. Many technical approaches have been proposed to implement pretargeting, and two have been extensively documented. One is based on the avidin-biotin system, and the other on bispecific antibodies binding a tumor-specific antigen and a hapten. Both have been studied in preclinical models, as well as in several clinical studies, and have shown improved targeting efficiency. This article reviews the historical and recent preclinical and clinical advances in the use of bispecific-antibody-based pretargeting for radioimmunodetection and radioimmunotherapy of cancer. The results of recent evaluation of pretargeting in PET imaging also are discussed