68Ga-TRAP-(RGD)3 Hybrid Imaging for the In Vivo Monitoring of αvß3-Integrin Expression as Biomarker of Anti-Angiogenic Therapy Effects in Experimental Breast Cancer

The Role of PET/CT in Breast Cancer

Female breast cancer has surpassed lung cancer as the most commonly diagnosed cancer worldwide, with an estimated 2.3 million new cases (11.7%), followed by lung cancer (11.4%) The current literature and the National Comprehensive Cancer Network (NCCN) guidelines state that ¹⁸F-FDG PET/CT is not routine for early diagnosis of breast cancer, and rather PET/CT scanning should be performed for patients with stage III disease or when conventional staging studies yield non-diagnostic or suspicious results because this modality has been shown to upstage patients compared to conventional imaging and thus has an impact on disease management and prognosis. Furthermore, with the growing interest in precision therapy in breast cancer, numerous novel radiopharmaceuticals have been developed that target tumor biology and have the potential to non-invasively guide the most appropriate targeted therapy. This review discusses the role of ¹⁸F-FDG PET and other PET tracers beyond FDG in breast cancer imaging.

Synthesis and Anti-Angiogenic Activity of Novel c(RGDyK) Peptide-Based JH-VII-139-1 Conjugates

Peptide-drug conjugates are delivery systems for selective delivery of cytotoxic agents to target cancer cells. In this work, the optimized synthesis of JH-VII-139-1 and its c(RGDyK) peptide conjugates is presented. The low nanomolar SRPK1 inhibitor, JH-VII-139-1, which is an analogue of Alectinib, was linked to the α_νβ₃ targeting oligopeptide c(RGDyK) through amide, carbamate and urea linkers. The chemostability, cytotoxic and antiangiogenic properties of the synthesized hybrids were thoroughly studied. All conjugates retained mid nanomolar-level inhibitory activity against SRPK1 kinase and two out of four conjugates, geo75 and geo77 exhibited antiproliferative effects with low micromolar IC₅₀ values against HeLa, K562, MDA-MB231 and MCF7 cancer cells. The activities were strongly related to the stability of the linkers and the release of JH-VII-139-1. In vivo zebrafish screening assays demonstrated the ability of the synthesized conjugates to inhibit the length or width of intersegmental vessels (ISVs). Flow cytometry experiments were used to test the cellular uptake of a fluorescein tagged hybrid in MCF7 and MDA-MB231 cells that revealed a receptor-mediated endocytosis process. In conclusion, most conjugates retained the inhibitory potency against SRPK1 as JH-VII-139-1 and demonstrated antiproliferative and antiangiogenic activities. Further animal model experiments are needed to uncover the full potential of such peptide conjugates in cancer therapy and angiogenesis-related diseases.

Non-conventional and Investigational PET Radiotracers for Breast Cancer: A Systematic Review

Breast cancer is one of the most common malignancies in women, with high morbidity and mortality rates. In breast cancer, the use of novel radiopharmaceuticals in nuclear medicine can improve the accuracy of diagnosis and staging, refine surveillance strategies and accuracy in choosing personalized treatment approaches, including radioligand therapy. Nuclear medicine thus shows great promise for improving the quality of life of breast cancer patients by allowing non-invasive assessment of the diverse and complex biological processes underlying the development of breast cancer and its evolution under therapy. This review aims to describe molecular probes currently in clinical use as well as those under investigation holding great promise for personalized medicine and precision oncology in breast cancer.

Association between [68Ga]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model

Radiolabeled RGD peptides targeting expression of α_vβ₃ integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [⁶⁸Ga]NODAGA-RGDyK to α_vβ₃ integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [⁶⁸Ga]NODAGA-RGDyK for 90 min at 37 °C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [⁶⁸Ga]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [⁶⁸Ga]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis.

Synthesis and biological studies of c(RGDyK) conjugates of cucurbitacins

Cucurbitacins (CUCUs) are triterpenoids known to display potent cytotoxic effects; however, their clinical application is limited due to poor pharmacokinetics and systemic toxicity. This work focuses on the development of c(RGDyK)-CUCU conjugates for the selective delivery of CUCUs to integrin-overexpressing cancer cells. The activity of the conjugates against various cancer cells was studied. They exhibited a mild cytostatic effect to six cancer cell lines and a cytotoxic effect against integrin-overexpressing MCF-7 and A549 cells. Their chemical and metabolic stability was extensively studied using LC-MS analysis. The conjugates maintained high affinity for α_vβ₃ integrin receptors. c(RGDyK) conjugation via a PEG linker was beneficial for CUCU-D and the resulting conjugate was approximately three-times more active than the free CUCU-D in MCF7 cells.

Radiolabeled Peptides for SPECT and PET Imaging in the Detection of Breast Cancer: Preclinical and Clinical Perspectives

Breast cancer is the most common cancer in women worldwide. Due to the heterogeneous nature of breast cancer, the optimal treatment and expected response for each patient may not necessarily be universal. Molecular imaging techniques could play an important role in the early detection and targeted therapy evaluation of breast cancer. This review focuses on the development of peptides labeled with SPECT and PET radionuclides for breast cancer imaging. We summarized the current status of radiolabeled peptides for different receptors in breast cancer. The characteristics of radionuclides and major techniques for peptide labeling are also briefly discussed.

Peptide-functionalized liposomes as therapeutic and diagnostic tools for cancer treatment

Clinically efficacious medication in anticancer therapy has been successfully designed with liposome-based nanomedicine. The liposomal formulation in cancer drug delivery can be facilitated with a functionalized peptide that mediates the specific drug delivery opportunities with increased drug penetrability, specific accumulation in the targeted site, and enhanced therapeutic efficacy. This review aims to focus on recent advances in peptide-functionalized liposomal formulation techniques in cancer diagnosis and treatment regarding recently published literature. It also will highlight different aspects of novel liposomal formulation techniques that incorporate surface functionalization with peptides for better anticancer effect and current challenges in peptide-functionalized liposomal drug formulation.

Radiolabeled Peptides and Antibodies in Medicine

Radiolabeled peptides are a relatively new, very specific radiotracer group, which is still expanding. This group is very diverse in terms of peptide size. It contains very small structures containing several amino acids and whole antibodies. Moreover, radiolabeled peptides are diverse in terms of the binding aim and therapeutic or diagnostic applications. The majority of this class of radiotracers is utilized in oncology, where the same structure can be used in therapy and diagnostic imaging by varying the radionuclide. In this study, we collected new reports of radiolabeled peptide applications in diagnosis and therapy in oncology and other fields of medicine. Radiolabeled peptides are also increasingly being used in rheumatology, cardiac imaging, or neurology. The studies collected in this review concern new therapeutic and diagnostic procedures in humans and new structures tested on animals. We also performed an analysis of clinical trials, which concerns application of radiolabeled peptides and antibodies that were reported in the clinicaltrials.gov database between 2008 and 2018.

The association of 18F-fluorodeoxyglucose PET/computed tomography parameters with tissue gastrin-releasing peptide receptor and integrin αvβ3 receptor levels in patients with breast cancer

OBJECTIVE

Gastrin-releasing peptide receptor (GRPR) and integrin αvβ3 receptors are significantly associated with primary breast cancer, neovascular endothelial, and metastatic tumor cells. We aimed to evaluate GRPR and integrin αvβ3 receptor staining, F-FDG uptake patterns and possible prognostic factors in breast cancer.

METHODS

Ninety lesions of 87 subjects diagnosed with breast cancer were included in this prospective study. The sections were stained with GRPR and integrin αvβ3. Subjects were divided into four molecular subgroups: luminal A, luminal B, triple negative and HER2. PET/CT imaging was performed on all subjects. The groups were compared in terms of GRPR and integrin αvβ3 staining properties, possible prognostic factors and mean SUVmax values.

RESULTS

Increased F-FDG uptake was significantly associated with estrogen receptor and progesterone receptor negativity. Molecular subtypes were significantly associated with mean integrin scores (P = 0.030), while histopathological subtypes were significantly associated with mean GRPR scores (P = 0.029). Increased integrin αvβ3 expression is significantly associated with ER and PR negativity. Additionally, GRPR score was significantly correlated with estrogen receptor and progesterone receptor expression scores and a negative statistically significant correlation was detected between integrin and progesterone receptor scores. Mean primary lesion SUVmax had a statistically significant positive correlation with integrin αvβ3 score.

CONCLUSION

GRPR and integrin αvβ3 expression results are complementary to F-FDG PET/CT findings, and are also significantly correlated with hormone receptors associated with aggressive subtypes. These results may pave the way for GRPR and integrin αvβ3 targeted imaging with Ga-labeled molecules and systemic radionuclide treatment with Lu-labeled compounds.

Rapid Thermodynamically Stable Complex Formation of [nat/111In]In3+, [nat/90Y]Y3+, and [nat/177Lu]Lu3+ with H6dappa

A phosphinate-bearing picolinic acid-based chelating ligand (H₆dappa) was synthesized and characterized to assess its potential as a bifunctional chelator (BFC) for inorganic radiopharmaceuticals. Nuclear magnetic resonance (NMR) spectroscopy was employed to investigate the chelator coordination chemistry with a variety of nonradioactive trivalent metal ions (In³⁺, Lu³⁺, Y³⁺, Sc³⁺, La³⁺, Bi³⁺). Density functional theory (DFT) calculations explored the coordination environments of aforementioned metal complexes. The thermodynamic stability of H₆dappa with four metal ions (In³⁺, Lu³⁺, Y³⁺, Sc³⁺) was deeply investigated via potentiometric and spectrophotometric (UV-vis) titrations, employing a combination of acidic in-batch, joint potentiometric/spectrophotometric, and ligand-ligand competition titrations; high stability constants and pM values were calculated for all four metal complexes. Radiolabeling conditions for three clinically relevant radiometal ions were optimized ([¹¹¹In]In³⁺, [¹⁷⁷Lu]Lu³⁺, [⁹⁰Y]Y³⁺), and the serum stability of [¹¹¹In][In(dappa)]^3- was studied. Through concentration-, time-, temperature-, and pH-dependent labeling experiments, it was determined that H₆dappa radiolabels most effectively at near-physiological pH for all radiometal ions. Furthermore, very rapid radiolabeling at ambient temperature was observed, as maximal radiolabeling was achieved in less than 1 min. Molar activities of 29.8 GBq/μmol and 28.2 GBq/μmol were achieved for [¹¹¹In]In³⁺ and [¹⁷⁷Lu]Lu³⁺, respectively. For H₆dappa, high thermodynamic stability did not correlate with kinetic inertness-lability was observed in serum stability studies, suggesting that its metal complexes might not be suitable as a BFC in radiopharmaceuticals.

Molecular Imaging in Breast Cancer

Breast cancer (BC) is the most common cancer among females with more than 2 million new cases diagnosed worldwide in 2018. Although the prognosis in the majority of cases in the early stages combined with appropriate treatment is positive, there are still about 30% of patients who will develop locoregional diseases and distant metastases. Molecular imaging is very important in the diagnosis, staging, follow-up, and radiotherapy planning. Additionally, it is useful in characterizing lesions, prognosis, and therapy response in BC patients. Nuclear medicine imaging modalities (SPECT and PET) are of indispensable importance in diagnosis (positron emission mammography), staging (sentinel lymph node detection), and follow-up with¹⁸F-FDG and tumor characterization. Among many available PET tracers, the most commonly used are ¹⁸F-FLT, ¹⁸F-FES, ¹⁸F-FDHT, ⁶⁴Cu DOTA trastuzumab (bevacizumab), ⁶⁸Ga-PSMA, ⁶⁸Ga-RM2 (gastrin-releasing peptide receptor), ¹⁸F-fluorooctreotide (SSTR), and ⁶⁸Ga-TRAP (RGD)-3αvβ3-integrin. Molecular imaging helps in evaluation of tumor heterogeneity, allowing a shift from one-size-fits-all-approach to era of personalized medicine and precision oncology.

18F-labeled magnetic nanoparticles for monitoring anti-angiogenic therapeutic effects in breast cancer xenografts

PURPOSE

To develop a novel fluorine-18 (¹⁸F)-labeled arginine-glycine-aspartic acid (RGD)-coupled ultra-small iron oxide nanoparticle (USPIO) (hereafter, referred to as ¹⁸F-RGD@USPIO) and conduct an in-depth investigation to monitor the anti-angiogenic therapeutic effects by using a novel dual-modality PET/MRI probe.

METHODS

The RGD peptide and ¹⁸F were coupled onto USPIO by click chemistry. In vitro experiments including determination of stability, cytotoxicity, cell binding of the obtained ¹⁸F-RGD@USPIO were carried out, and the targeting kinetics and bio-distribution were tested on an MDA-MB-231 tumor model. A total of 20 (n = 10 per group) MDA-MB-231 xenograft-bearing mice were treated with bevacizumab or placebo (intraperitoneal injections of bevacizumab or a volume-equivalent placebo solution at the dose of 5 mg/kg for consecutive 7 days, respectively), and underwent PET/CT and MRI examinations with ¹⁸F-RGD@USPIO before and after treatment. Imaging findings were validated by histological analysis with regard to β₃-integrin expression (CD61 expression), microvascular density (CD31 expression), and proliferation (Ki-67 expression).

RESULTS

Excellent stability, low toxicity, and good specificity to endothelial of ¹⁸F-RGD@USPIO were confirmed. The best time point for MRI scan was 6 h post-injection. No intergroup differences were observed in tumor volume development between baseline and day 7. However, ¹⁸F-RGD@USPIO binding was significantly reduced after bevacizumab treatment compared with placebo, both on MRI (P < 0.001) and PET/CT (P = 0.002). Significantly lower microvascular density, tumor cell proliferation, and integrin β₃ expression were noted in the bevacizumab therapy group than the placebo group, which were consistent with the imaging results.

CONCLUSION

PET/MRI with the dual-modality nanoprobe, ¹⁸F-RGD@USPIO, can be implemented as a noninvasive approach to monitor the therapeutic effects of anti-angiogenesis in breast cancer model in vivo.

[68Ga]RGD Versus [18F]FDG PET Imaging in Monitoring Treatment Response of a Mouse Model of Human Glioblastoma Tumor with Bevacizumab and/or Temozolomide

PURPOSE

The aim of this study was to evaluate positron emission tomography (PET) imaging with [⁶⁸Ga]NODAGA-c(RGDfK) ([⁶⁸Ga]RGD), in comparison with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG), for early monitoring of the efficacy of an antiangiogenic agent associated or not with chemotherapy, in a mouse model of glioblastoma (GB).

PROCEDURES

Mice bearing U87MG human GB cells line were parted into five groups of five mice each. One group was imaged at baseline before the treatment phase; another group was treated with bevacizumab (BVZ), another group with temozolomide (TMZ), another group with both agents, and the last one was the control group. Tumors growth and biological properties were evaluated by caliper measurements and PET imaging at three time points (baseline, during treatment t1 = 4-6 days and t2 = 10-12 days). At the end of the study, tumors were counted and analyzed by immunohistochemistry (CD31 to evaluate microvessel density).

RESULTS

The tumor volume assessed by caliper measurements was significantly greater at t1 in the control group than in the TMZ + BVZ-treated group or in the BVZ-treated group. At t2, tumor volume of all treated groups was significantly smaller than that of the control group. [¹⁸F]FDG PET failed to reflect this efficacy of treatment. In contrast, at t1, the [⁶⁸Ga]RGD tumor uptake was concordant with tumor growth in controls and in treated groups. At t2, a significant increase in tumor uptake of [⁶⁸Ga]RGD vs. t1 was only observed in the TMZ-treated group, reflecting a lack of angiogenesis inhibition, whereas TMZ + BVZ resulted in a dramatic tumor arrest, reduction in microvessel density and stable tumor [⁶⁸Ga]RGD uptake.

CONCLUSIONS

[⁶⁸Ga]RGD is a useful PET agent for in vivo angiogenesis imaging and can be useful for monitoring antiangiogenic treatment associated or not with chemotherapy.

Targeting tumor cells and neovascularization using RGD-functionalized magnetoliposomes

Purpose

Magnetoliposomes (MLs) have shown great potential as magnetic resonance imaging contrast agents and as delivery vehicles for cancer therapy. Targeting the MLs towards the tumor cells or neovascularization could ensure delivery of drugs at the tumor site. In this study, we evaluated the potential of MLs targeting the αvβ3 integrin overexpressed on tumor neovascularization and different tumor cell types, including glioma and ovarian cancer.

Methods

MLs functionalized with a Texas Red fluorophore (anionic MLs), and with the fluorophore and the cyclic Arginine-Glycine-Aspartate (cRGD; cRGD-MLs) targeting the αvβ3 integrin, were produced in-house. Swiss nude mice were subcutaneously injected with 10⁷ human ovarian cancer SKOV-3 cells. Tumors were allowed to grow for 3 weeks before injection of anionic or cRGD-MLs. Biodistribution of MLs was followed up with a 7T preclinical magnetic resonance imaging (MRI) scanner and fluorescence imaging (FLI) right after injection, 2h, 4h, 24h and 48h post injection. Ex vivo intratumoral ML uptake was confirmed using FLI, electron paramagnetic resonance spectroscopy (EPR) and histology at different time points post injection.

Results

In vivo, we visualized a higher uptake of cRGD-MLs in SKOV-3 xenografts compared to control, anionic MLs with both MRI and FLI. Highest ML uptake was seen after 4h using MRI, but only after 24h using FLI indicating the lower sensitivity of this technique. Furthermore, ex vivo EPR and FLI confirmed the highest tumoral ML uptake at 4 h. Last, a Perl’s stain supported the presence of our iron-based particles in SKOV-3 xenografts.

Conclusion

Uptake of cRGD-MLs can be visualized using both MRI and FLI, even though the latter was less sensitive due to lower depth penetration. Furthermore, our results indicate that cRGD-MLs can be used to target SKOV-3 xenograft in Swiss nude mice. Therefore, the further development of this particles into theranostics would be of interest.

Measurement of Tumor Hypoxia in Patients With Locally Advanced Cervical Cancer Using Positron Emission Tomography with 18F-Fluoroazomyin Arabinoside

PURPOSE

To assess cervical tumor hypoxia using the hypoxia tracer ¹⁸F-fluoroazomycin arabinoside (¹⁸F-FAZA) and compare different reference tissues and thresholds for quantifying tumor hypoxia.

METHODS AND MATERIALS

Twenty-seven patients with cervical cancer were studied prospectively by positron emission tomography (PET) imaging with ¹⁸F-FAZA before starting standard chemoradiation. The hypoxic volume was defined as all voxels within a tumor (T) with standardized uptake values (SUVs) greater than 3 standard deviations from the mean gluteus maximus muscle SUV value (M) or SUVs greater than 1 to 1.4 times the mean SUV value of the left ventricle, a blood (B) surrogate. The hypoxic fraction was defined as the ratio of the number of hypoxic voxels to the total number of tumor voxels.

RESULTS

A ¹⁸F-FAZA-PET hypoxic volume could be identified in the majority of cervical tumors (89% when using T/M or T/B > 1.2 as threshold) on the 2-hour static scan. The hypoxic fraction ranged from 0% to 99% (median 31%) when defined using the T/M threshold and from 0% to 78% (median 32%) with the T/B > 1.2 threshold. Hypoxic volumes derived from the different thresholds were highly correlated (Spearman's correlation coefficient ρ between T/M and T/B > 1-1.4 were 0.82-0.91), as were hypoxic fractions (0.75-0.85). Compartmental analysis of the dynamic scans showed k₃, the FAZA accumulation constant, to be strongly correlated with hypoxic fraction defined using the T/M (Spearman's ρ=0.72) and T/B > 1.2 thresholds (0.76).

CONCLUSIONS

Hypoxia was detected in the majority of cervical tumors on ¹⁸F-FAZA-PET imaging. The extent of hypoxia varied markedly between tumors but not significantly with different reference tissues/thresholds.

Radioactive Main Group and Rare Earth Metals for Imaging and Therapy

Radiometals possess an exceptional breadth of decay properties and have been applied to medicine with great success for several decades. The majority of current clinical use involves diagnostic procedures, which use either positron-emission tomography (PET) or single-photon imaging to detect anatomic abnormalities that are difficult to visualize using conventional imaging techniques (e.g., MRI and X-ray). The potential of therapeutic radiometals has more recently been realized and relies on ionizing radiation to induce irreversible DNA damage, resulting in cell death. In both cases, radiopharmaceutical development has been largely geared toward the field of oncology; thus, selective tumor targeting is often essential for efficacious drug use. To this end, the rational design of four-component radiopharmaceuticals has become popularized. This Review introduces fundamental concepts of drug design and applications, with particular emphasis on bifunctional chelators (BFCs), which ensure secure consolidation of the radiometal and targeting vector and are integral for optimal drug performance. Also presented are detailed accounts of production, chelation chemistry, and biological use of selected main group and rare earth radiometals.

Integrin-targeted quantitative optoacoustic imaging with MRI correlation for monitoring a BRAF/MEK inhibitor combination therapy in a murine model of human melanoma

PURPOSE

To investigate αvβ3-integrin-targeted optoacoustic imaging and MRI for monitoring a BRAF/MEK inhibitor combination therapy in a murine model of human melanoma.

MATERIALS AND METHODS

Human BRAF V600E-positive melanoma xenograft (A375)-bearing Balb/c nude mice (n = 10) were imaged before (day 0) and after (day 7) a BRAF/MEK inhibitor combination therapy (encorafenib, 1.3 mg/kg/d; binimetinib, 0.6 mg/kg/d, n = 5) or placebo (n = 5), respectively. Optoacoustic imaging was performed on a preclinical system unenhanced and 5 h after i. v. injection of an αvβ3-integrin-targeted fluorescent probe. The αvβ3-integrin-specific tumor signal was derived by spectral unmixing. For morphology-based tumor response assessments, T2w MRI data sets were acquired on a clinical 3 Tesla scanner. The imaging results were validated by multiparametric immunohistochemistry (ß3 -integrin expression, CD31 -microvascular density, Ki-67 -proliferation).

RESULTS

The αvβ3-integrin-specific tumor signal was significantly reduced under therapy, showing a unidirectional decline in all animals (from 7.98±2.22 to 1.67±1.30; p = 0.043). No significant signal change was observed in the control group (from 6.60±6.51 to 3.67±1.93; p = 0.500). Immunohistochemistry revealed a significantly lower integrin expression (ß3: 0.20±0.02 vs. 0.39±0.05; p = 0.008) and microvascular density (CD31: 119±15 vs. 292±49; p = 0.008) in the therapy group. Tumor volumes increased with no significant intergroup difference (therapy: +107±42 mm3; control +112±44mm3, p = 0.841). In vivo blocking studies with αvβ3-integrin antagonist cilengitide confirmed the target specificity of the fluorescent probe.

CONCLUSIONS

αvβ3-integrin-targeted optoacoustic imaging allowed for the early non-invasive monitoring of a BRAF/MEK inhibitor combination therapy in a murine model of human melanoma, adding molecular information on tumor receptor status to morphology-based tumor response criteria.

18F-FDG-PET/CT and diffusion-weighted MRI for monitoring a BRAF and CDK 4/6 inhibitor combination therapy in a murine model of human melanoma

Background

The purpose of the study was to investigate a novel BRAF and CDK 4/6 inhibitor combination therapy in a murine model of BRAF-V600-mutant human melanoma monitored by ¹⁸F–FDG-PET/CT and diffusion-weighted MRI (DW-MRI).

Methods

Human BRAF-V600-mutant melanoma (A375) xenograft-bearing balb/c nude mice (n = 21) were imaged by ¹⁸F–FDG-PET/CT and DW-MRI before (day 0) and after (day 7) a 1-week BRAF and CDK 4/6 inhibitor combination therapy (n = 12; dabrafenib, 20 mg/kg/d; ribociclib, 100 mg/kg/d) or placebo (n = 9). Animals were scanned on a small animal PET after intravenous administration of 20 MBq ¹⁸F–FDG. Tumor glucose uptake was calculated as the tumor-to-liver-ratio (TTL). Unenhanced CT data sets were subsequently acquired for anatomic coregistration. Tumor diffusivity was assessed by DW-MRI using the apparent diffusion coefficient (ADC). Anti-tumor therapy effects were assessed by ex vivo immunohistochemistry for validation purposes (microvascular density – CD31; tumor cell proliferation – Ki-67).

Results

Tumor glucose uptake was significantly suppressed under therapy (∆TTL_Therapy − 1.00 ± 0.53 vs. ∆TTL_Control 0.85 ± 1.21; p < 0.001). In addition, tumor diffusivity was significantly elevated following the BRAF and CDK 4/6 inhibitor combination therapy (∆ADC_Therapy 0.12 ± 0.14 × 10⁻³ mm²/s; ∆ADC_Control − 0.12 ± 0.06 × 10⁻³ mm²/s; p < 0.001). Immunohistochemistry revealed a significant suppression of microvascular density (CD31, 147 ± 48 vs. 287 ± 92; p = 0.001) and proliferation (Ki-67, 3718 ± 998 vs. 5389 ± 1332; p = 0.007) in the therapy compared to the control group.

Conclusion

A novel BRAF and CDK 4/6 inhibitor combination therapy exhibited significant anti-angiogenic and anti-proliferative effects in experimental human melanomas, monitored by ¹⁸F–FDG-PET/CT and DW-MRI.

Novel c(RGDyK)-based conjugates of POPAM and 5-fluorouracil for integrin-targeted cancer therapy

Aim: Alkylating agents and antimetabolites are cytotoxic drugs commonly used in cancer treatment. These medications are often associated with serious side effects on normal tissues and organs. Methodology: To improve the pharmacological profile of the alkylating agent POPAM and the antimetabolite 5-fluorouracil, novel integrin-targeted delivery systems based on c(RGDyK) were successfully synthesized. The new conjugates were tested in vitro against different cancer cells such as PC3, SKOV3, A549, MCF7 and MBA-MB-321. Results & conclusion: The c(RGDyK) conjugates of POPAM demonstrated better inhibitory effects and selectivity compared with c(RGDyK) and POPAM. The c(RGDyK) conjugates of 5-FUA demonstrated diverse inhibitory effects compared with c(RGDyK) and 5-FUA related to the levels of integrin expression, the conjugate stability and sensitivity of cancer cells to 5-FUA.

Response Assessment of 68Ga-DOTA-E-[c(RGDfK)]2 PET/CT in Lung Adenocarcinoma Patients Treated with Nintedanib Plus Docetaxel

Nintedanib is an oral angiokinase inhibitor used as second-line treatment for non-small cell lung cancer. New radiotracers, such as ⁶⁸Ga-DOTA-E-[c(RGDfK)]², that target α_vβ₃ integrin might have an impact as a noninvasive method for assessing angiogenesis inhibitors. Methods: From July 2011 through October 2015, 38 patients received second-line nintedanib plus docetaxel. All patients underwent PET/CT with ⁶⁸Ga-DOTA-E-[c(RGDfK)]² radiotracer and blood-sample tests to quantify angiogenesis factors (fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor AB) before and after completing 2 therapy cycles. Results: Of the 38 patients, 31 had available baseline and follow-up PET/CT. Baseline lung tumor volume addressed with ⁶⁸Ga-DOTA-E-[c(RGDfK)]² PET/CT correlated with serum vascular endothelial growth factor levels, whereas baseline lung/liver SUV_max index correlated with platelet-derived growth factor AB. After treatment, the overall response rate and disease control rate were 7.9% and 47.3%, respectively. A greater decrease in lung tumor volume (-37.2% vs. -27.6%) was associated with a better disease control rate in patients (P = 0.005). Median progression-free survival was 3.7 mo. Nonsmokers and patients with a higher baseline lung tumor volume were more likely to have a higher progression-free survival (6.4 vs. 3.74 [P = 0.023] and 6.4 vs. 2.1 [P = 0.003], respectively). Overall survival was not reached. Patients with a greater decrease in lung SUV_max (not reached vs. 7.1 mo; P = 0.016) and a greater decrease in the lung/spleen SUV_max index (not reached vs. 7.1; P = 0.043) were more likely to have a longer overall survival. Conclusion:⁶⁸Ga-DOTA-E-[c(RGDfK)]² PET/CT is a potentially useful tool for assessing responses to angiogenesis inhibitors. Further analysis and novel studies are warranted to identify patients who might benefit from this therapy.