Non-invasive monitoring of the therapeutic response in sorafenib-treated hepatocellular carcinoma based on photoacoustic imaging

Modulation of the tumour microenvironment in hepatocellular carcinoma by tyrosine kinase inhibitors: from modulation to combination therapy targeting the microenvironment

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide. Tyrosine kinase inhibitors (TKIs) remain the backbone of systematic therapy for advanced hepatocellular carcinoma. Sorafenib and lenvatinib are currently approved as first-line therapeutic drugs, and regorafenib and cabozantinib are applied as second-line treatments. With inhibition of angiogenesis as the main target, TKIs exert a profound effect on the tumour microenvironment (TME). The TME is a complex mixture of cellular and noncellular components surrounding the tumour mass, and is associated with tumour progression partially through the epithelial-mesenchymal transition. Specifically, the TME of HCC is characterized by profound extracellular matrix remodelling and an immunosuppressive microenvironment. The purpose of this review is to provide a summary of TME remodelling mediated by four Food and Drug Administration approved TKIs in HCC and thus summarize the rationale and potential targets for combination therapy. The modulatory effect of TKIs on the TME of HCC was reported to enhance the antitumour effect of TKIs through pyroptosis of macrophages and subsequent natural killer cell activation, T cell activation, regulatory T cell reduction in HCC. Meanwhile, TKIs also induce drug resistance via M2 polarization and accumulation, recruitment of tumour-associated neutrophils, and induction of the epithelial-mesenchymal transition. In conclusion, the effect of TKIs on TME can enhance its antitumour effect, but might also partially contribute to the drug resistance that hinders the progression of TKIs as treatment for HCC. Additionally, the effect of TKIs also provides the rationale for combination therapy, including combining TKIs with immune checkpoint inhibitors, to facilitate increased drug efficacy of TKIs.

Molecular Imaging of Tumor Microenvironment to Assess the Effects of Locoregional Treatment for Hepatocellular Carcinoma

Liver cancer is one of the leading causes of cancer deaths worldwide. Among all primary liver cancers, hepatocellular carcinoma (HCC) is the most common type, representing 75%‐85% of all primary liver cancer cases. Median survival following diagnosis of HCC is approximately 6 to 20 months due to late diagnosis in its course and few effective treatment options. Interventional therapy with minimal invasiveness is recognized as a promising treatment for HCC. However, due to the heterogeneity of HCC and the complexity of the tumor microenvironment, the long‐term efficacy of treatment for HCC remains a challenge in the clinic. Tumor microenvironment, including factors such as hypoxia, angiogenesis, low extracellular pH, interstitial fluid pressure, aerobic glycolysis, and various immune responses, has emerged as a key contributor to tumor residual and progression after locoregional treatment for HCC. New approaches to noninvasively assess the treatment response and assist in the clinical decision‐making process are therefore urgently needed. Molecular imaging tools enabling such an assessment may significantly advance clinical practice by allowing real‐time optimization of treatment protocols for the individual patient. This review discusses recent advances in the application of molecular imaging technologies for noninvasively assessing changes occurring in the microenvironment of HCC after locoregional treatment.

Spatiotemporal Coherence Weighting for In Vivo Cardiac Photoacoustic Image Beamformation

Photoacoustic (PA) image reconstruction generally utilizes delay-and-sum (DAS) beamforming of received acoustic waves from tissue irradiated with optical illumination. However, nonadaptive DAS reconstructed cardiac PA images exhibit temporally varying noise which causes reduced myocardial PA signal specificity, making image interpretation difficult. Adaptive beamforming algorithms such as minimum variance (MV) with coherence factor (CF) weighting have been previously reported to improve the DAS image quality. In this article, we report on an adaptive beamforming algorithm by extending CF weighting to the temporal domain for preclinical cardiac PA imaging (PAI). The proposed spatiotemporal coherence factor (STCF) considers multiple temporally adjacent image acquisition events during beamforming and cancels out signals with low spatial coherence and temporal coherence, resulting in higher background noise cancellation while preserving the main features of interest (myocardial wall) in the resultant PA images. STCF has been validated using the numerical simulations and in vivo ECG and respiratory-signal-gated cardiac PAI in healthy murine hearts. The numerical simulation results demonstrate that STCF weighting outperforms DAS and MV beamforming with and without CF weighting under different levels of inherent contrast, acoustic attenuation, optical scattering, and signal-to-noise (SNR) of channel data. Performance improvement is attributed to higher sidelobe reduction (at least 5 dB) and SNR improvement (at least 10 dB). Improved myocardial signal specificity and higher signal rejection in the left ventricular chamber and acoustic gel region are observed with STCF in cardiac PAI.

Therapeutic response monitoring after targeted therapy in an orthotopic rat model of hepatocellular carcinoma using contrast-enhanced ultrasound: Focusing on inter-scanner, and inter-operator reproducibility

Purpose

To assess therapeutic response monitoring after targeted therapy in an orthotopic rat model of hepatocellular carcinoma (HCC) using CEUS with focusing on inter-scanner and inter-operator reproducibility.

Materials and methods

For reproducibility, CEUS was performed using two different US scanners by two operators in sixteen rat models of HCC. Using perfusion analysis software (VueBox ®), eleven parameters were collected, and intra-class correlation coefficient (ICC) was used to analyze reproducibility. Then seventeen rat models of HCC were divided into treatment group (n = 8, 30 mg/kg/day sorafenib for five days) and control group (n = 9). CEUS was performed at baseline and 14 days after first treatment, and changes of perfusion parameters were analyzed.

Results

In treatment group, CEUS perfusion parameters showed a significant change. The peak enhancement (PE, 2.50 x10³±1.68 x10³ vs 5.55x10²±4.65x10², p = 0.010) and wash-in and wash out AUC (_WiWoAUC, 1.07x10⁵±6.48 x10⁴ vs 2.65x10⁴±2.25x10⁴, p = 0.009) had significantly decreased two weeks after treatment. On the contrary, control group did not show a significant change, including PE (1.15 x10³±7.53x10² vs 9.43x10²± 7.81 x10², p = 0.632) and _WiWoAUC (5.09 x10⁴±3.25x10⁴ vs 5.92 x10⁴±3.20x10⁴, p = 0.646). For reproducibility, the various degrees of inter-scanner reproducibility were from poor to good (ICC: <0.01–0.63). However, inter-operator reproducibility of important perfusion parameters, including _WiAUC, _WoAUC, and _WiWoAUC, ranged from fair to excellent (ICC: 0.59–0.93) in a different scanner.

Conclusion

Our results suggest that CEUS is useful for assessment of the treatment response after targeted therapy and with fair to excellent inter-operator reproducibility.

Combined treatment of sorafenib and doxorubicin-loaded microbubble-albumin nanoparticle complex for hepatocellular carcinoma: A feasibility study

Purpose

To assess the feasibility of the combined sorafenib (SOR) and doxorubicin-loaded microbubble-albumin nanoparticle complex (DOX-MAC) treatment effect in an orthotopic rat model of hepatocellular carcinoma (HCC).

Materials and methods

Sixty-two rats with N1-S1 hepatoma were divided into four groups according to the treatment methods, i.e. G1 (SOR and DOX-MAC; n = 12), G2 (SOR; n = 15), G3 (DOX-MAC; n = 12), G4 (DOX; n = 11), and G5 (normal saline; n = 12). We performed the theragnostic, contrast-enhanced ultrasound examination and treatment at the baseline, one-week, and two-weeks. Tumor volume and perfusion parameters were compared at each time point and the differences between all of the groups over time were analyzed using repeated measures ANOVA. We also analyzed the apoptotic index and microvessel density (MVD) per each tumor specimen in all of the groups.

Results

The tumors increased from the beginning in all of the groups to the final follow-up, whereas the tumor growth in the G1 group and the G2 group was inhibited during the treatment period compared to the baseline tumor volume (P = 0.016 and P = 0.031). The G1 group resulted in tumor growth inhibition compared to the control group (P = 0.008). The G1 group showed that the peak enhancement and wash-in area under the curve were lower than that of the G4 group (P = 0.010 and 0.022). However, there was no difference in perfusion parameters in the other treated group compared to control group. The MVD of the G1 group tumor was lower than that of the G4 group (P = .016).

Conclusion

Our results suggest that the combination therapy of SOR and DOX-MAC can cause inhibition of tumor growth after treatment and that this therapy can be adequately monitored using the theragnostic DOX-MAC agent.

Minimally invasive photothermal ablation assisted by laparoscopy as an effective preoperative neoadjuvant treatment for orthotopic hepatocellular carcinoma

Nanoparticle-based photothermal ablation (PTA) has been intensively investigated recently. However, the poor biocompatibility of most PTA agents and potential long-term toxicity obstruct their clinical translation. Meanwhile, previous PTA studies are limited to surface tumors because of insufficient light penetration depth of near-infrared (NIR) light for deep abdominal tumors. Therefore, minimally invasive PTA combined with biocompatible agents may pave a promising way to treat deep orthotopic hepatocellular carcinoma (HCC). Herein, a multifunctional agent based on superparamagnetic iron oxide (SPIO) and new indocyanine green (IR820) was constructed with good biocompatibility. Outstanding fluorescence, photoacoustic and magnetic resonance imaging capabilities were observed in vitro. Additionally, in vivo results indicated that early-stage HCC (diameter less than 2 mm) could be effectively detected by this agent. Furthermore, for the first time, we developed minimally invasive laparoscopic-assisted photothermal ablation (L-A PTA) method coupled with this agent to completely ablate orthotopic HCC in nude mice model, neither recurrences nor obvious side effects were observed during the experiments. Remarkable shrinkage of primary tumor and disappearance of intrahepatic metastasis were also observed. In summary, minimally invasive L-A PTA is an effective preoperative neoadjuvant treatment for HCC.

Estimating blood oxygenation from photoacoustic images: can a simple linear spectroscopic inversion ever work?

Linear spectroscopic inversions, in which photoacoustic amplitudes are assumed to be directly proportional to absorption coefficients, are widely used in photoacoustic imaging to estimate blood oxygen saturation because of their simplicity. Unfortunately, they do not account for the spatially varying wavelength-dependence of the light fluence within the tissue, which introduces "spectral coloring," a potentially significant source of error. However, accurately correcting for spectral coloring is challenging, so we investigated whether there are conditions, e.g., sets of wavelengths, where it is possible to ignore the spectral coloring and still obtain accurate oxygenation measurements using linear inversions. Accurate estimates of oxygenation can be obtained when the wavelengths are chosen to (i) minimize spectral coloring, (ii) avoid ill-conditioning, and (iii) maintain a sufficiently high signal-to-noise ratio (SNR) for the estimates to be meaningful. It is not obvious which wavelengths will satisfy these conditions, and they are very likely to vary for different imaging scenarios, making it difficult to find general rules. Through the use of numerical simulations, we isolated the effect of spectral coloring from sources of experimental error. It was shown that using wavelengths between 500 nm and 1000 nm yields inaccurate estimates of oxygenation and that careful selection of wavelengths in the 620- to 920-nm range can yield more accurate oxygenation values. However, this is only achievable with a good prior estimate of the true oxygenation. Even in this idealized case, it was shown that considerable care must be exercised over the choice of wavelengths when using linear spectroscopic inversions to obtain accurate estimates of blood oxygenation. This suggests that for a particular imaging scenario, obtaining accurate and reliable oxygenation estimates using linear spectroscopic inversions requires careful modeling or experimental studies of that scenario, taking account of the instrumentation, tissue anatomy, likely sO₂ range, and image formation process.

Non-measurable infiltrative HCC: is post-contrast attenuation on CT a sign of tumor response?

OBJECTIVES

To evaluate the value of CT attenuation to assess the response to sorafenib in infiltrative/endovascular non-measurable advanced hepatocellular carcinoma (HCC).

METHODS

From 2007 to 2014, patients with infiltrative HCC ± tumor-in-vein (TIV) were retrospectively included. Attenuation of tumors and TIV were measured at baseline and follow-up on arterial and portal venous phase CT by two independent radiologists. Attenuation changes (overall and as per Choi criteria) and Child-Pugh score were correlated to overall survival.

RESULTS

Forty patients were included (38 men, 95%). Attenuation of both the tumors and TIV was significantly lower in follow-up CT than on baseline CT (p = 0.002 (arterial), and p = 0.001 (portal) for tumor, and p = 0.004 (arterial) and p < 0.001 (porta) for TIV). Median attenuation of TIV was significantly lower than that of the tumor in follow-up images (p = 0.010). Median OS for the entire cohort was 4 ± 1 months (95% CI: 2.1-5.9), with estimated OS rates at 6, 12, and 24 months of 43%, 29 and 12%, respectively. Baseline and follow-up CT attenuation in tumors and TVI were not correlated with survival. Survival was not significantly increased in patients with Choi criteria >15% CT HU decrease in the tumor and/or TIV during follow-up. Only Child-Pugh A (HR 4.9 (95%CI 2.3-10.7), p < 0.001) was identified as an independent factor of improved survival on multivariate analysis.

CONCLUSION

Despite significant changes under sorafenib, tumor attenuation of infiltrative/endovascular non-measurable HCC may be of limited value to assess survival in this subgroup of patients with very poor prognosis.

KEY POINTS

• Attenuation of both tumors and tumor-in-vein decreases after sorafenib. • Attenuation decrease is more marked in the tumor-in-vein than in the tumor. • Attenuation decrease is not associated with longer overall survival.

Inter-operator variability and source of errors in tumour response assessment for hepatocellular carcinoma treated with sorafenib

OBJECTIVES

To assess the inter-operator concordance and the potential sources of discordance in defining response to sorafenib in hepatocellular carcinoma (HCC).

METHODS

All patients who received sorafenib between September 2008 and February 2015 were scrutinised for this retrospective study. Images were evaluated separately by three radiologists with different expertise in liver imaging (operator 1, >10 years; operator 2, 5 years; operator 3, no specific training in liver imaging), according to: response evaluation radiological criteria in solid tumours (RECIST) 1.1, modified RECIST (mRECIST) and response evaluation criteria in cancer of the liver (RECICL).

RESULTS

The overall response concordance between the more expert operators was good, irrespective of the criteria (RECIST 1.1, ĸ = 0.840; mRECIST, ĸ = 0.871; RECICL, ĸ = 0.819). Concordance between the less expert operator and the other colleagues was lower. The most evident discordance was in target lesion response assessment, with expert operators disagreeing mostly on lesion selection and less expert operators on lesion measurement. As a clinical correlate, overall survival was more tightly related with "progressive disease" as assessed by the expert compared to the same assessment performed by operator 3.

CONCLUSIONS

Decision on whether a patient is a responder or progressor under sorafenib may vary among different operators, especially in case of a non-specifically trained radiologist. Regardless of the adopted criteria, patients should be evaluated by experienced radiologists to minimise variability in this critical instance.

KEY POINTS

• Inter-operator variability in the assessment of response to sorafenib is poorly known. • The concordance between operators with expertise in liver imaging was good. • Target lesions selection was the main source of discordance between expert operators. • Concordance with non-specifically trained operator was lower, independently from the response criteria. • The non-specifically trained operator was mainly discordant in measurements of target lesions.

Photoacoustic Imaging as an Early Biomarker of Radio Therapeutic Efficacy in Head and Neck Cancer

The negative impact of tumor hypoxia on radiotherapeutic efficacy is well recognized. However, an easy to use, reliable imaging method for assessment of tumor oxygenation in routine clinical practice remains elusive. Photoacoustic imaging (PAI) is a relatively new imaging technique that utilizes a combination of light and ultrasound (US) to enable functional imaging of tumor hemodynamic characteristics in vivo. Several clinical trials are currently evaluating the utility of PAI in cancer detection for breast, thyroid, and prostate cancer. Here, we evaluated the potential of PAI for rapid, label-free, non-invasive quantification of tumor oxygenation as a biomarker of radiation response in head and neck cancer.

Methods: Studies were performed human papilloma virus- positive (HPV+) and -negative (HPV-) patient-derived xenograft (PDX) models of head and neck squamous cell carcinoma (HNSCC). PAI was utilized for longitudinal assessment of tumor hemodynamics (oxygenation saturation and hemoglobin concentration) before, during and after fractionated radiation therapy (fRT). Imaging datasets were correlated with histologic measures of vascularity (CD31), DNA damage (phosphorylated γH2AX) and statistical modeling of tumor growth.

Results: A differential response to fRT was observed between HPV+ and HPV- xenografts. Temporal changes in tumor hemodynamics (oxygen saturation and hemoglobin concentration) measured by PAI showed significant association with treatment outcomes. PAI-based changes in oxygen saturation were detected within days after initiation of fRT prior to detectable change in tumor volume, highlighting the potential of PAI to serve as an early biomarker of therapeutic efficacy. Consistent with PAI results, immunohistochemical staining of vascularity (CD31) and DNA damage (phosphorylated γH2AX) revealed distinct patterns of response in HPV+ and HPV- xenografts.

Conclusion: Collectively, our observations demonstrate the utility of PAI for temporal mapping of tumor hemodynamics and the value of PAI read-outs as surrogate measures of radiation response in HNSCC.

Hemispherical photoacoustic imaging of myocardial infarction: in vivo detection and monitoring

OBJECTIVES

This study aimed to demonstrate the capacity for noninvasive localisation and characterisation of myocardial infarction (MI) in vivo using a hemispherical photoacoustic imaging (PAI) system. MI remains a leading cause of morbidity and mortality worldwide. To enable optimal treatment of patients, timely and accurate diagnosis and longitudinal monitoring is critical.

METHODS

Ischaemia was induced in Balb/c mice by ligation of the left anterior descending artery. The hemispherical PAI system, equipped with 128 ultrasonic transducers spirally distributed on the surface, along with parallel data acquisition, was applied for imaging of the mouse heart.

RESULTS

Our study showed that hemispherical PAI can delineate thoracic vessels and the morphology of the entire heart. Longitudinal PAI images revealed gradual expansion of the infarcted area along with necrosis and fibrosis, which were quantitatively validated by triphenyltetrazolium chloride staining. After MI modelling, the photoacoustic (PA) signal intensity decreased by 399.1 ± 56.3 (p < 0.001), a ~2.5-fold reduction compared to that of healthy cardiac tissue. The calculated size of the enlarged heart, 10.4 ± 6.0 mm² (p < 0.001), represents an increase of ~18% versus that of a healthy heart.

CONCLUSIONS

PAI enables MI diagnosis and injury localisation with its capabilities for both deep organ imaging and lesion region differentiation.

KEY POINTS

• Photoacoustic imaging (PAI), combining optical absorption and ultrasonic resolution, can delineate cardiac anatomy. • PAI can diagnose myocardial infarction lesions with 10 mm imaging depth in vivo. • Quantified results are in excellent agreement with enzyme and histological examinations. • PAI can serve as a complementary modality to SPECT and ultrasound imaging. • This study will encourage further PAI development for clinical use.