Peptide-based molecular beacons for cancer imaging and therapy

Peptide-based molecular beacons are Förster resonance energy transfer-based target-activatable probes. They offer control of fluorescence emission in response to specific cancer targets and thus are useful tools for in vivo cancer imaging. With our increasing knowledge about human genome in health and disease, peptide-based “smart” probes are continually developed for in vivo optical imaging of specific molecular targets, biological pathways and cancer progression and diagnosis. A class of fluorescent photosensitizers further extends the application of peptide beacons to cancer therapeutics. This review highlights the applications of peptide beacons in cancer imaging, the simultaneous treatment and response monitoring and smart therapeutics with a focus on recent improvements in the design of these probes.     

Protein scaffold-based molecular probes for cancer molecular imaging

Protein scaffold molecules are powerful reagents for targeting various cell signal receptors, enzymes, cytokines and other cancer-related molecules. They belong to the peptide and small protein platform with distinct properties. For the purpose of development of new generation molecular probes, various protein scaffold molecules have been labeled with imaging moieties and evaluated both in vitro and in vivo. Among the evaluated probes Affibody molecules and analogs, cystine knot peptides, and nanobodies have shown especially good characteristics as protein scaffold platforms for development of in vivo molecular probes. Quantitative data obtained from positron emission tomography, single photon emission computed tomography/CT, and optical imaging together with biodistribution studies have shown high tumor uptakes and high tumor-to-blood ratios for these probes. High tumor contrast imaging has been obtained within 1 h after injection. The success of those molecular probes demonstrates the adequacy of protein scaffold strategy as a general approach in molecular probe development.     

Autophagy orchestrates adaptive responses to targeted therapy in endometrial cancer

Targeted therapies in endometrial cancer (EC) using kinase inhibitors rarely result in complete tumor remission and are frequently challenged by the appearance of refractory cell clones, eventually resulting in disease relapse. Dissecting adaptive mechanisms is of vital importance to circumvent clinical drug resistance and improve the efficacy of targeted agents in EC. Sorafenib is an FDA-approved multitarget tyrosine and serine/threonine kinase inhibitor currently used to treat hepatocellular carcinoma, advanced renal carcinoma and radioactive iodine-resistant thyroid carcinoma. Unfortunately, sorafenib showed very modest effects in a multi-institutional phase II trial in advanced uterine carcinoma patients. Here, by leveraging RNA-sequencing data from the Cancer Cell Line Encyclopedia and cell survival studies from compound-based high-throughput screenings we have identified the lysosomal pathway as a potential compartment involved in the resistance to sorafenib. By performing additional functional biology studies we have demonstrated that this resistance could be related to macroautophagy/autophagy. Specifically, our results indicate that sorafenib triggers a mechanistic MAPK/JNK-dependent early protective autophagic response in EC cells, providing an adaptive response to therapeutic stress. By generating in vivo subcutaneous EC cell line tumors, lung metastatic assays and primary EC orthoxenografts experiments, we demonstrate that targeting autophagy enhances sorafenib cytotoxicity and suppresses tumor growth and pulmonary metastasis progression. In conclusion, sorafenib induces the activation of a protective autophagic response in EC cells. These results provide insights into the unopposed resistance of advanced EC to sorafenib and highlight a new strategy for therapeutic intervention in recurrent EC.     

Prospects for prostate cancer imaging and therapy using high-affinity TRPM8 activators

One of the best-studied temperature-gated channels is transient receptor potential melastatin 8 (TRPM8), which is activated by cold and cooling agents, such as menthol. Besides inducing a cooling sensation in sensory neurons, TRPM8 channel activation also plays a major role in physiopathology. Indeed, TRPMP8 expression increases in early stages of prostate cancer and its involvement in prostate cell apoptosis has recently been demonstrated. Thus, as TRPM8 is a tumor marker with significant potential use in diagnosis, as well as a target for cancer therapy, there is a need for new TRPM8-specific ligands. In this study, we investigated the action of "WS" compounds on TRPM8 channels. We compared the affinity of these molecules to that of menthol and icilin. This enabled us to identify new TRPM8 agonists. The menthol analog with the highest affinity, WS-12, had an EC(50) value about 2000 times lower than that of menthol and is, therefore, the highest-affinity TRPM8 ligand known to date. Finally, incorporating a fluorine atom in the WS-12 retained 75% of the activity of the parent compound. The high affinity of this new TRPM8 ligand and the possibility of incorporating a radiohalogen could thus be useful for diagnosis, monitoring and, perhaps, even therapy of prostate cancer.     

Assessing protein patterns in disease using imaging mass spectrometry

Direct tissue profiling and imaging mass spectrometry (MS) provides a detailed assessment of the complex protein pattern within a tissue sample. MALDI MS analysis of thin tissue sections results in over of 500 individual protein signals in the mass range of 2 to 70 kDa that directly correlate with protein composition within a specific region of the tissue sample. To date, profiling and imaging MS has been applied to multiple diseased tissues, including human gliomas and nonsmall cell lung cancer. Interrogation of the resulting complex MS data sets has resulted in identification of both disease-state and patient-prognosis specific protein patterns. These results suggest the future usefulness of proteomic information in assessing disease progression, prognosis, and drug efficacy.     

In vivo optical molecular imaging of matrix metalloproteinase activity following celecoxib therapy for colorectal cancer

We present an optical molecular imaging approach to measure the efficacy of the cyclooxygenase-2 (COX-2) inhibitor celecoxib on tumor growth rate through its effect on matrix metalloproteinase (MMP) activity. A xenograft model of colorectal cancer was generated in nude mice, which were then randomized to receive celecoxib versus vehicle. MMP activity was measured by an enzyme-activatable optical molecular probe. A novel genetically engineered mouse (GEM) model of colorectal cancer was also used to assess celecoxib's effect on MMP activity, which was measured by quantitative fluorescence colonoscopy. Subcutaneously implanted xenograft tumors were 84% (SD 20.2%) smaller in volume in the treatment group versus the control group. Moreover, treated animals exhibited only a 7.6% (SEM 9%) increase in MMP activity versus 106% (SEM 8%) for untreated animals. There was an apparent linear relationship (r = .91) between measured MMP activity and tumor growth rate. Finally, in the GEM model experiment, treated murine tumors remained relatively unchanged in volume and MMP activity; however, untreated tumors grew significantly and showed an increase in MMP activity. This method may provide for the improved identification of patients for whom COX-2 inhibition therapy is indicated by allowing one to balance the patient's cardiovascular risk with the cancer's responsiveness to celecoxib.     

Novel approaches to cancer therapy using oncolytic viruses

The goal of oncolytic therapy is to exploit the innate ability of viruses to infect tumor cells, replicate in tumor cells, and produce selective oncolysis while sparing normal cells. Although the concept that viruses can be oncolytic is not new, it is only in the last three decades that efforts have been directed at genetically mutating viruses to specifically target characteristics of cancer cells. Several viruses have the potential to infect, replicate and lyse tumor cells, each taking advantage of different host cancer cell biology. This review will focus on the major viruses under current investigation for oncolytic therapy, the mechanism by which they specifically eradicate tumors, and the clinical strategies currently under investigation.     

Survivin mRNA antagonists using locked nucleic acid, potential for molecular cancer therapy

We have investigated the effects of different locked nucleic acid modified antisense mRNA antagonists against Survivin in a prostate cancer model. These mRNA antagonists were found to be potent inhibitors of Survivin expression at low nanomolar concentrations. Additionally there was a pronounced synergistic effect when combining the mRNA antagonists against Survivin with the chemotherapeutic Taxol. This effect was demonstrated at concentrations of antagonists far lower than any previously demonstrated, indicating the high potential of locked nucleic acid for therapeutic use. Further characterisations in vivo are ongoing.     

Nanomaterials for cancer therapy and imaging

A variety of organic and inorganic nanomaterials with dimensions below several hundred nanometers are recently emerging as promising tools for cancer therapeutic and diagnostic applications due to their unique characteristics of passive tumor targeting. A wide range of nanomedicine platforms such as polymeric micelles, liposomes, dendrimers, and polymeric nanoparticles have been extensively explored for targeted delivery of anti-cancer agents, because they can accumulate in the solid tumor site via leaky tumor vascular structures, thereby selectively delivering therapeutic payloads into the desired tumor tissue. In recent years, nanoscale delivery vehicles for small interfering RNA (siRNA) have been also developed as effective therapeutic approaches to treat cancer. Furthermore, rationally designed multi-functional surface modification of these nanomaterials with cancer targeting moieties, protective polymers, and imaging agents can lead to fabrication versatile theragnostic nanosystems that allow simultaneous cancer therapy and diagnosis. This review highlights the current state and future prospects of diverse biomedical nanomaterials for cancer therapy and imaging.     

Molecular imaging of akt enables early prediction of response to molecular targeted therapy

Development of noninvasive, real-time molecular imaging tools to assess responsiveness of a given therapy may be a critical component of the success of individualized therapy approach for patients. Toward this, we have previously developed and validated molecular sensors for Akt and caspase-3 activity, and in this report, we have explored the utility of these reporters in assessing the responsiveness of tumors to a combination of gemcitabine (Gem) and cetuximab (Cet) delivered in two opposite schedules. We found that human head and neck cancer (UMSCC1) xenografts responded significantly better in a schedule where cetuximab was administered after gemcitabine when compared with the schedule of cetuximab followed by gemcitabine. Wilcoxon two-sample tests suggested that the difference in tumor volumes in two schedules became significant on day 7 (P > .05 on day 4, and P < .05 on days 7 and 10), and the difference in activity of Akt in two schedules became significant on day 4 (P < .05 on days 4, 6, and 10). Using Akt reporter activity and cubic spline interpolation, the distinction between the two schedules could be detected 2 days before using the tumor volume, suggesting that molecular imaging of Akt may allow early prediction of therapy responsiveness. We did not observe a significant difference between the two schedules in the caspase-3 activity. In summary, this proof-of-concept study provides a basis for using molecular imaging of Akt as an early indicator of therapeutic efficacy.     

Chemotherapy and molecular therapy in cervical cancer

In recent years, the treatment of locally-advanced and metastatic cervical cancer has improved greatly due to the introduction of targeted therapies, new chemotherapy combinations, and emerging treatments. Candidates for potentially curative treatment are those patients with good functional status without associated comorbidities. Numerous trials have demonstrated that chemotherapy prolongs survival versus supportive care alone. In addition, polychemotherapy schemes are superior to single agent regimens. Targeted molecular agents have proven beneficial in the treatment of cervical cancer. Second-line treatment should be considered standard practice in patients with good functional status. Finally, given the poor survival outcomes in patients with metastatic disease, participation in clinical studies should always be considered the best option.     

Phospholipid-coated targeted microbubbles for ultrasound molecular imaging and therapy

Phospholipid-coated microbubbles are ultrasound contrast agents that, when functionalized, adhere to specific biomarkers on cells. In this concise review, we highlight recent developments in strategies for targeting the microbubbles and their use for ultrasound molecular imaging (UMI) and therapy. Recently developed novel targeting strategies include magnetic functionalization, triple targeting, and the use of several new ligands. UMI is a powerful technique for studying disease progression, diagnostic imaging, and monitoring of therapeutic responses. Targeted microbubbles (tMBs) have been used for the treatment of cardiovascular diseases and cancer, with therapeutics either coadministered or loaded onto the tMBs. Regardless of which disease was treated, the use of tMBs always resulted in a better therapeutic outcome than non-tMBs when compared in vitro or in vivo.     

Novel siRNA-based molecular beacons for dual imaging and therapy

Short interfering RNAs (siRNAs) have become a mainstream tool reliably used to study and silence protein expression. We offer a proof-of-principle demonstration that siRNAs may be modified into a siRNA-based molecular beacon that activates upon binding to sequence-specific mRNA in cells while mediating RNA interference. We successfully demonstrate detection and knockdown of telomerase expression in human breast cancer cells. This probe provides a novel look at siRNA target validation that is not currently possible in live cells and holds promising potential in biological applications for disease detection and therapy based on mRNA expression, such as a telomerase-targeted siRNA probe in cancer.     

Cellular responses to replication stress: Implications in cancer biology and therapy

DNA replication is essential for cell proliferation. Any obstacles during replication cause replication stress, which may lead to genomic instability and cancer formation. In this review, we summarize the physiological DNA replication process and the normal cellular response to replication stress. We also outline specialized therapies in clinical trials based on current knowledge and future perspectives in the field.     

Autophagy and cancer therapy cardiotoxicity: From molecular mechanisms to therapeutic opportunities

Cardiotoxicity is a major drawback of anticancer therapies, often hindering optimal management of cancer. Among the most cardiotoxic agents are anthracyclines (AC) that, despite being cardiotoxic, are highly effective in the treatment of a wide variety of cancers, spanning from hematological malignancies to solid tumors. Modern imaging techniques can identify patients at risk of developing cardiotoxicity, but treatment options are still limited and ineffective, partly because the molecular mechanisms underlying AC cardiac side effects are still incompletely understood. Although AC cardiotoxicity was initially ascribed to the trigger of cell-damaging oxidative stress, antioxidants fail to prevent anthracycline-induced cardiotoxicity (AIC), suggesting the involvement of additional mechanisms. Among these, the cellular recycling process, named autophagy, recently emerged to play a key role in AIC, but whether autophagy activation is beneficial or detrimental in this context is still controversial. This review will summarize recent evidence on the role of autophagy in AIC in the attempt to reconcile the controversial findings in the field. Finally, we will describe major regulator of cardiac autophagy that may represent good candidates for therapeutic intervention in AIC.     

Plaque imaging and characterization using magnetic resonance imaging: towards molecular assessment

Identification of high-risk atherosclerotic lesions prone to rupture and thrombosis may greatly decrease the morbidity and mortality associated with atherosclerosis. High-resolution magnetic resonance imaging (MRI) has recently emerged as one of the most promising techniques for the non-invasive study of atherothrombotic disease, as it can characterize plaque composition and monitor its progression. The development of MRI contrast agents that specifically target components of the atherosclerotic plaque may enable non-invasive detection of high-risk lesions. This review discusses the use of high-resolution MRI for plaque detection and characterization and the potentials of "Molecular Imaging" using a variety of molecules present in atherosclerotic plaques that may serve as targets for specific contrast agents to allow the identification of high-risk atherosclerotic lesions in-vivo. Ultimately, such agents may enable treatment of "high-risk" patients prior to lesion progression and occurrence of complications.