Potential value of color-coded dynamic breast-specific gamma-imaging; comparing (99m)Tc-(V)-DMSA, (99m)Tc-MIBI, and (99m)Tc-HDP in a mouse mammary tumor model

Head-To-Head Comparison of Biological Behavior of Biocompatible Polymers Poly(Ethylene Oxide), Poly(2-Ethyl-2-Oxazoline) and Poly[N-(2-Hydroxypropyl)Methacrylamide] as Coating Materials for Hydroxyapatite Nanoparticles in Animal Solid Tumor Model

Nanoparticles (NPs) represent an emerging platform for diagnosis and treatment of various diseases such as cancer, where they can take advantage of enhanced permeability and retention (EPR) effect for solid tumor accumulation. To improve their colloidal stability, prolong their blood circulation time and avoid premature entrapment into reticuloendothelial system, coating with hydrophilic biocompatible polymers is often essential. Most studies, however, employ just one type of coating polymer. The main purpose of this study is to head-to-head compare biological behavior of three leading polymers commonly used as “stealth” coating materials for biocompatibilization of NPs poly(ethylene oxide), poly(2-ethyl-2-oxazoline) and poly[N-(2-hydroxypropyl)methacrylamide] in an in vivo animal solid tumor model. We used radiolabeled biodegradable hydroxyapatite NPs as a model nanoparticle core within this study and we anchored the polymers to the NPs core by hydroxybisphosphonate end groups. The general suitability of polymers for coating of NPs intended for solid tumor accumulation is that poly(2-ethyl-2-oxazoline) and poly(ethylene oxide) gave comparably similar very good results, while poly[N-(2-hydroxypropyl)methacrylamide] was significantly worse. We did not observe a strong effect of molecular weight of the coating polymers on tumor and organ accumulation, blood circulation time, biodistribution and biodegradation of the NPs.

In Situ In Vivo radiolabeling of polymer-coated hydroxyapatite nanoparticles to track their biodistribution in mice

The imaging of healthy tissues and solid tumors benefits from the application of nanoparticle probes with altered pharmacokinetics, not available to low molecular weight compounds. However, the distribution and accumulation of nanoprobes in vivo typically take at least tens of hours to be efficient. For nanoprobes bearing a radioactive label, this is contradictory to the requirement of minimizing the radiation dose for patients by using as-short-as-feasible half-life radionuclides in diagnostics. Thus, we developed a two-stage diagnostic concept for monitoring long-lasting targeting effects with short-lived radioactive labels using bone-mimicking biocompatible polymer-coated and colloidally fully stabilized hydroxyapatite nanoparticles (HAP NPs) and bone-seeking radiopharmaceuticals. Within the pretargeting stage, the nonlabeled nanoparticles are allowed to circulate in the blood. Afterward, ^99mTc-1-hydroxyethylidene-1.1-diphosphonate (^99mTc-HEDP) is administered intravenously for in situ labeling of the nanoparticles and subsequent single-photon emission computed tomography/computed tomography (SPECT/CT) visualization. The HAP NPs, stabilized with tailored hydrophilic polymers, are not cytotoxic in vitro, as shown by several cell lines. The polymer coating prolongs the circulation of HAP NPs in the blood. The nanoparticles were successfully labeled in vivo with ^99mTc-HEDP, 1 and 24 h after injection, and they were visualized by SPECT/CT over time in healthy mice.

The use of molecular breast imaging to assess response in women undergoing neoadjuvant therapy for breast cancer: a pilot study

PURPOSE OF THE REPORT

To report our findings from a prospective pilot study evaluating the accuracy of molecular breast imaging (MBI) in assessing tumor response to neoadjuvant therapy (NT) for breast cancer.

MATERIALS AND METHODS

Twenty patients with newly diagnosed invasive breast cancer who were scheduled to receive NT underwent MBI before beginning and after completing NT before surgery. MBI was performed using a dual-detector cadmium-zinc-telluride gamma camera system mounted on a modified mammography gantry after patients had received an intravenous injection of 20 mCi of 99mTc sestamibi. Tumor extent was measured on MBI, and tumor-to-background (T/B) ratios of radiotracer uptake were determined through region-of-interest analysis. Pathologic measurement of tumor size was used as a standard and compared with post-NT tumor size derived from MBI.

RESULTS

Three patients in whom post-NT MBI could not be performed because of scheduling problems were excluded from analysis. Eighteen cancers were diagnosed in 17 patients. A correlation coefficient of r = 0.681 (P = 0.002) was found between MBI and residual tumor size. The average T/B ratio on MBI decreased from a pretreatment value of 3.0 to a posttreatment value of 1.4. The relative decrease in T/B ratio did not appear to be predictive of response.

CONCLUSIONS

Measurements of tumor size by MBI and T/B ratios are limited in their predictive value regarding the pathologic extent of residual disease in women treated with NT for breast cancer. Alternate tumor-specific radiopharmaceuticals should be evaluated to provide information to improve planning and monitoring of breast cancer treatment.