Disparate responses of tumour vessels to angiotensin II: tumour volume-dependent effects on perfusion and oxygenation

Genetic variants in the renin-angiotensin-aldosterone system: Impact on cancer risk, prognosis, and therapeutic directions

Although renin-angiotensin-aldosterone system (RAAS) is known to maintain blood pressure and electrolyte balance, it has recently been linked to a number of biological processes such as angiogenesis, tumorigenesis, metastasis, and cellular proliferation, increasing the risk of cancer development and progression. Multiple genetic variants have been found to affect the genes encoding RAAS components, altering gene transcription and protein expression. This review provides an up-to-date insight into the role of RAAS in carcinogenesis, as well as the impact of RAAS genetic variants on the risk of cancer development, progression, and patient survival and outcomes, as well as response to treatment. This paves the way for the application of precision medicine in cancer risk assessment and management by implementing preventative programs in individuals at risk and guiding the therapeutic direction in cancer patients.

The Ability of the Nitric Oxide Synthases Inhibitor T1023 to Selectively Protect the Non-Malignant Tissues

Previously, we showed that a nitric oxide synthase (NOS) inhibitor, compound T1023, induces transient hypoxia and prevents acute radiation syndrome (ARS) in mice. Significant efficacy (according to various tests, dose modifying factor (DMF)-1.6-1.9 against H-ARS/G-ARS) and safety in radioprotective doses (1/5-1/4 LD10) became the reason for testing its ability to prevent complications of tumor radiation therapy (RT). Research methods included studying T1023 effects on skin acute radiation reactions (RSR) in rats and mice without tumors and in tumor-bearing animals. The effects were evaluated using clinical, morphological and histological techniques as well as RTOG classification. T1023 administration prior to irradiation significantly limited the severity of acute RSR. This was due to a decrease in radiation alteration of the skin and underlying tissues, and the preservation of the functional activity of cell populations that are critical in the pathogenesis of radiation burn. The DMF values for T1023 for skin protection were 1.4-1.7. Moreover, its radioprotective effect was fully selective to normal tissues in RT models of solid tumors-T1023 reduced the severity of acute RSR and did not modify the antitumor effects of γ-radiation. The results indicate that T1023 can selectively protect the non-malignant tissues against γ-radiation due to hypoxic mechanism of action and potentiate opportunities of NOS inhibitors in RT complications prevention.

Clinical applicability of renin-angiotensin system inhibitors in cancer treatment

The renin-angiotensin system (RAS) regulates physiological functions of the cardiovascular system, kidneys, and other tissues. Various in vivo and in vitro studies have shown that RAS plays a pivotal role in the development of malignant tumors, while several retrospective studies have confirmed that patients undergoing long-term RAS inhibitors (RASi) treatment have a lowered risk of cancer. Moreover, blocking RAS has been shown to inhibit tumor growth, metastasis, and angiogenesis in various experimental models of malignant tumors. Herein, we review the available RASi-related literature and provide an analysis using the scientific atlas software VOSviewer. We observed that recent studies have primarily focused on gene expression, tumor biology, and survival analysis. Through an in-depth data analysis from the Cancer Genome Atlas (TCGA) and Genotype Tissue Expression (GTEx), we identified the impact of AGTR1, an essential component of RAS, on tumors, and we discuss the underlying biological mechanism of RASi. Furthermore, we outline the research progress and potential use of RASi in tumor treatment. Overall, RASi may be a promising adjunct in cancer therapy.

Renin-Angiotensin System in the Tumor Microenvironment

For enhancing the antitumor effects of current immunotherapies including immune-checkpoint blockade, it is important to reverse cancer-induced immunosuppression. The renin-angiotensin system (RAS) controls systemic body fluid circulation; however, the presence of a local RAS in tumors has been reported. Furthermore, the local RAS in tumors influences various immune and interstitial cells and affects tumor immune response. RAS stimulation through the angiotensin II type 1 receptor has been reported to inhibit tumor immune response. Therefore, RAS inhibitors and combined treatment with immunotherapy are expected in the future. In this chapter, we provide a background on the RAS and describe the tumor environment with regard to the RAS and tumor immune response.

Renin-angiotensin inhibitors reprogram tumor immune microenvironment: A comprehensive view of the influences on anti-tumor immunity

Renin-angiotensin system inhibitors (RASi) have shown potential anti-tumor effects that may have a significant impact in cancer therapy. The components of the renin-angiotensin system (RAS) including both, conventional and alternative axis, appear to have contradictory effects on tumor biology. The mechanisms by which RASi impair tumor growth extend beyond their function of modulating tumor vasculature. The major focus of this review is to analyze other mechanisms by which RASi reprogram the tumor immune microenvironment. These involve impairing hypoxia and acidosis within the tumor stroma, regulating inflammatory signaling pathways and oxidative stress, modulating the function of the non-cellular components and immune cells, and regulating the cross-talk between kalli krein kinin system and RAS.

Targeting the renin-angiotensin system to improve cancer treatment: Implications for immunotherapy

Renin-angiotensin system (RAS) inhibitors (RASi)-widely prescribed for the treatment of cardiovascular diseases-have considerable potential in oncology. The RAS plays a crucial role in cancer biology and affects tumor growth and dissemination directly and indirectly by remodeling the tumor microenvironment. We review clinical data on the benefit of RASi in primary and metastatic tumors and propose that, by activating immunostimulatory pathways, these inhibitors can enhance immunotherapy of cancer.

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

Functional regulation of HIF-1α under normoxia--is there more than post-translational regulation?

The hypoxia-inducible factor-1 (HIF-1) is an oxygen-regulated transcriptional activator playing a pivotal role in mammalian physiology and disease pathogenesis, e.g., HIF-1 is indispensable in a broad range of developmental stages in different tumors. Its post-translational regulation via PHDs under the influence of hypoxia is widely investigated and accepted. Different non-hypoxic stimuli such as lipopolysaccharides (LPS), thrombin, and angiotensin II (Ang II), have been proven to enhance HIF-1 levels through activation of regulative mechanisms distinct from protein stabilization. Some of these stimuli specifically regulate HIF-1α at the transcriptional, post-transcriptional, or translational level, whereas others additionally influence post-translational modifications. Thus, it is difficult for the investigators to discern the impact of the different mechanisms leading to functional HIF-1 protein. Nevertheless, profound knowledge of additional regulatory networks appears to depict new therapeutic opportunities and thus is an interesting and important field for further investigations.

Activation of P-glycoprotein (Pgp)-mediated drug efflux by extracellular acidosis: in vivo imaging with 68Ga-labelled PET tracer

PURPOSE

In vitro it has been shown that the functional activity of P-glycoprotein (Pgp), an important drug transporter responsible for multidrug resistance, can be strongly increased by extracellular acidosis. Here mitogen-activated protein kinases (MAPK) (p38, ERK1/2) seem to play an important role for signal transduction. However, it is unclear whether these effects are also relevant in vivo.

METHODS

With the newly developed PET tracer Schiff base-based (68)Ga-MFL6.MZ the functional Pgp activity was visualized under acidic conditions and during inhibition of MAPKs non-invasively by means of microPET in rat tumours. Tumours were acidified either by inspiratory hypoxia (8% O(2)) or by injection of lactic acid. Inhibitors of the MAPK were injected intratumourally.

RESULTS

With increasing tumour volume the tumour pH changed from 7.0 to 6.7 and simultaneously the Pgp activity increased almost linearly. When the tumour was acidified by direct lactic acid injection the PET tracer uptake was reduced by 20% indicating a higher transport rate out of the cells. Changing the inspiratory O(2) fraction to 8% dynamically led to a reduction of extracellular pH and in parallel to a decrease of tracer concentration. While inhibition of the p38 pathway reduced the Pgp transport rate, inhibition of ERK1/2 had practically no impact.

CONCLUSION

An acidic extracellular environment significantly stimulates the Pgp activity. The p38 MAPK pathway plays an important role for Pgp regulation in vivo, whereas ERK1/2 is of minor importance. From these results new strategies for overcoming multidrug resistance (e.g. reducing tumour acidosis, inhibition of p38) may be developed.

The renin-angiotensin system and malignancy

The renin-angiotensin system (RAS) is usually associated with its systemic action on cardiovascular homoeostasis. However, recent studies suggest that at a local tissue level, the RAS influences tumour growth. The potential of the RAS as a target for cancer treatment and the suggested underlying mechanisms of its paracrine effects are reviewed here. These include modulation of angiogenesis, cellular proliferation, immune responses and extracellular matrix formation. Knowledge of the RAS has increased dramatically in recent years with the discovery of new enzymes, peptides and feedback mechanisms. The local RAS appears to influence tumour growth and metastases and there is evidence of tissue- and tumour-specific differences. Recent experimental studies provide strong evidence that drugs that inhibit the RAS have the potential to reduce cancer risk or retard tumour growth and metastases. Manipulation of the RAS may, therefore, provide a safe and inexpensive anticancer strategy.

Targeting tumor stroma and exploiting mature tumor vasculature to improve anti-cancer drug delivery

The identification of a critical role of tumour stroma in the regulation of tumour interstitial fluid pressure and the simultaneous discovery of the impact of anti-angiogenic drugs on tumour hemodynamics have provided new potential for improving tumour delivery of anti-cancer drugs. Here, we review the most recent studies investigating how tumour-associated fibroblasts and macrophages as well as the extracellular matrix itself may be targeted to facilitate delivery of both low-molecular weight drugs and macromolecules. In addition, we summarize the current understanding of the use of vasoactive compounds, radiotherapy and vascular-disrupting agents as potential adjuvants to maximize tumour delivery of anti-cancer drugs. The impact of these strategies on the diffusive and convective modes of drug transport is discussed in the light of Fick's and Starling's laws. Finally, we discuss how transcytosis through caveolae may also be exploited to optimize the selective delivery of conventional chemotherapy to the subendothelial tumour cell compartment.

Endothelin-1 Is a Critical Mediator of Myogenic Tone in Tumor Arterioles

Although derived from the host tissue, the tumor vasculature is under the influence of the tumor microenvironment and needs to adapt to the resistance to blood flow inherent to the dynamics of tumor growth. Such vascular remodeling can offer selective targets to pharmacologically modulate tumor perfusion and thereby improve the efficacy of conventional anticancer treatments. Radiotherapy and chemotherapy can, indeed, take advantage of a better tumor oxygenation and drug delivery, respectively, both partly dependent on the tumor blood supply. Here, we showed that isolated tumor arterioles mounted in a pressure myograph have the ability, contrary to size-matched healthy arterioles, to contract in response to a transluminal pressure increase. This myogenic tone was exquisitely dependent on the endothelin-1 pathway because it was completely abolished by the selective endothelin receptor A (ETA) antagonist BQ123. This selectivity was additionally supported by the large increase in endothelin-1 abundance in tumors and the higher density of the ETA receptors in tumor vessels. We also documented by using laser Doppler microprobes and imaging that administration of the ETA antagonist led to a significant increase in tumor blood flow, whereas the perfusion in control healthy tissue was not altered. Finally, we provided evidence that acute administration of the ETA antagonist could significantly stimulate tumor oxygenation, as determined by electron paramagnetic resonance oximetry, and increase the efficacy of low-dose, clinically relevant fractionated radiotherapy. Thus, blocking the tumor-selective increase in the vascular endothelin-1/ETA pathway led us to unravel an important reserve of vasorelaxation that can be exploited to selectively increase tumor response to radiotherapy.

Modulation of the tumor vasculature functionality by ionizing radiation accounts for tumor radiosensitization and promotes gene delivery

The ultimate goal of radiotherapy is to induce irreversible damages in genetically unstable, fast-growing cancer cells while minimizing the cytotoxic effects on host tissues. The satus of the tumor vasculature is particular because it is located within the tumor but mostly arises from host cells. The aim of this study was to characterize the effects of low-dose irradiation on the function of endothelial cells lining tumor vessels. Using isolated arterioles mounted on a pressure myograph, we first documented that the nitric oxide (NO)-mediated vasorelaxation that was defective in tumor vessels was completely restored following local tumor irradiation. Immunoblot analyses revealed that this was attributable to an increase in the abundance of the endothelial NO synthase while the expression of its physiological inhibitor, caveolin-1, was reduced. We further showed that the potentiation of the NO-dependent pathway induced a marked increase in tumor blood flow and oxygenation that determined the higher sensitivity of the tumor to further irradiation. Finally, we documented that the NO-mediated effects of irradiation on the tumor vasculature increased the delivery and expression of a reporter gene into the tumor. Thus, low-dose irradiation of endothelial cells within a tumor is a key determinant of the effectiveness of radiotherapy and may offer a new strategy to increase gene and/or drug delivery to the tumor.

Differential oxygen dynamics in two diverse Dunning prostate R3327 rat tumor sublines (MAT-Lu and HI) with respect to growth and respiratory challenge

PURPOSE

Since hypoxia may influence tumor response to therapy and prognosis, we have compared oxygenation of tumors known to exhibit differential growth rate and tissue differentiation.

METHODS AND MATERIALS

Regional tumor oxygen tension was measured using 19F nuclear magnetic resonance echo planar imaging relaxometry of hexafluorobenzene, which provided dynamic maps with respect to respiratory intervention. Investigations used two Dunning prostate R3327 rat tumor sublines: the fast growing, highly metastatic MAT-Lu and the moderately well-differentiated, slower growing HI.

RESULTS

Both sublines showed significantly higher oxygen tension in smaller tumors (<2 cm(3)) than in larger tumors (>3.5 cm(3)). Pooled data showed that MAT-Lu tumors exhibited greater hypoxia compared with the size-matched HI tumors (p < 0.0001). Respiratory challenge (oxygen or carbogen) produced significant increases in mean pO(2) for tumors of both sublines (p < 0.0001). However, initially hypoxic regions displayed very different behavior in each subline: those in the HI tumors responded rapidly with significant elevation in pO(2), while those in the MAT-Lu tumors showed little response to respiratory intervention.

CONCLUSIONS

These results concur with hypotheses that hypoxia is related to tumor growth rate and degree of differentiation. Under baseline conditions, the differences were subtle. However, response to respiratory intervention revealed highly significant differences, which, if held valid in the clinic, could have prognostic value.

The influence of combretastatin A-4 and vinblastine on interstitial fluid pressure in BT4An rat gliomas

The influence of combretastatin A-4 disodium phosphate (CA-4, 50mg/kg intraperitoneally (i.p.)) and vinblastine (2mg/kg i.p.) on interstitial fluid pressure (IFP) was assessed in BT4An rat gliomas implanted subcutaneously in the neck. Furthermore the growth inhibitory effect of vinblastine and the distribution of fluorescence-conjugated vinblastine (BODIPY-vinblastine) were investigated. Tumors at different volumes were compared. Whereas CA-4 had no major influence on IFP, independent of tumor size, vinblastine increased the IFP in neoplasms above 8 cm(3) (P=0.03). Vinblastine yielded a significant tumor response only in tumors below 2.1 cm(3) (P=0.03). The distribution of BODIPY-vinblastine was heterogeneous and comparable despite tumor volume differences. We conclude that the influence of vinblastine on IFP is more pronounced than that of CA-4 in BT4An neck tumors, and that vinblastine may reduce subsequent drug delivery to solid tumors by increasing the IFP.

Tumor vasculature is targeted by the combination of combretastatin A-4 and hyperthermia

BACKGROUND AND PURPOSE

Combretastatin A-4 disodium phosphate (CA-4) enhances thermal damage in s.c. BT(4)An rat gliomas. We currently investigated how CA-4 and hyperthermia affect the tumor microenvironment and neovasculature to disclose how the two treatment modalities interact to produce tumor response.

METHODS

By confocal microscopy and immunostaining for von Willebrand factor, we examined the extent of vascular damage subsequent to CA-4 (50 mg/kg) and hyperthermia (waterbath 44 degrees C, 60 min). The influence on tumor oxygenation was assessed using interstitial pO(2)-probes (Licox system) and by immunostaining for pimonidazole. We examined the direct effect of CA-4 on the tumor cell population by flow cytometry (cell cycle distribution) and immunostaining for beta-tubulin (cytoskeletal damage).

RESULTS

Whereas slight vascular damage was produced by CA-4 in the BT(4)An tumors, local hyperthermia exhibited moderate anti-vascular activity. In tumors exposed to CA-4 3 h before hyperthermia, massive vascular damage ensued. CA-4 reduced the pO(2) from 36.1 to 17.6 mmHg (P=0.01) in the tumor base, and tumor hypoxia increased slightly in the tumor center (pimonidazole staining). Extensive tumor hypoxia developed subsequent to hyperthermia or combination therapy. Despite a profound influence on beta-tubulin organization in vitro, CA-4 had no significant effect on the cell cycle distribution in vivo.

CONCLUSION

Our results indicate that the anti-vascular activity exhibited by local hyperthermia can be augmented by previous exposure to CA-4.

Tumor oxygen dynamics with respect to growth and respiratory challenge: investigation of the Dunning prostate R3327-HI tumor

We recently described a novel approach to measuring regional tumor oxygen tension using (19)F nuclear magnetic resonance echo planar imaging relaxometry (FREDOM) of hexafluorobenzene. We have now applied this technique to evaluate in detail the oxygen tension dynamics in the relatively slowly growing, moderately well-differentiated Dunning prostate R3327 HI rat tumor with respect to tumor growth and respiratory challenge. Seven individual tumors were assessed repeatedly over a period of 5 weeks ( approximately 4 volume doubling times). For small tumors (<1 cm(3)), the mean pO(2) ranged from 28 to 44 Torr under baseline conditions, decreasing to less than 10 Torr when the tumors reached 5 to 6 cm(3), with a strong inverse correlation between the baseline tumor oxygen tension and the tumor size. The hypoxic fraction (defined as the percentage of the voxels with pO(2) <10 Torr) increased significantly with tumor growth. Administration of oxygen or carbogen produced a significant increase (P < 0.0001) in tumor oxygenation at all stages of tumor growth. Most interestingly, even regions of these tumors that were initially poorly oxygenated responded rapidly, and significantly, to respiratory intervention, in contrast to the behavior of the faster-growing rat prostate tumors investigated previously.

Vinblastine and hyperthermia target the neovasculature in BT(4)AN rat gliomas: therapeutic implications of the vascular phenotype

PURPOSE

The antivascular and antitumor activity of vinblastine and hyperthermia at different tumor volumes were examined in the subcutaneous (s.c.) BT(4)An rat glioma model.

METHODS AND MATERIALS

The influence of vinblastine (3 mg/kg) and hyperthermia (44 degrees C/60 min) on tumor growth was assessed in small (100 mm(3)) and large (200 mm(3)) BT(4)An tumors. To disclose how vinblastine and hyperthermia interacted in the neoplasms, tumor blood flow and the extent of vascular damage, hypoxia, cell proliferation, and apoptosis were assessed after treatment. The content of smooth muscle cells/pericytes in the tumor vasculature was examined in small and large tumors to assess how the vascular phenotype changed during tumor growth.

RESULTS

In the large tumors, vinblastine reduced the blood flow, but the tumor growth was not affected. The combination of drug and local heating yielded massive vascular damage and a significant tumor response. The small neoplasms had a higher content of smooth muscle cells/pericytes in the vessel walls (host vasculature), and the tumor vasculature displayed a higher resistance to vascular damage than the large neoplasms. Yet, vinblastine alone exhibited a potent antiproliferative activity and induced massive apoptosis in the small tumors, and the drug significantly inhibited tumor growth. The addition of hyperthermia yielded no additional growth delay in the small tumors.

CONCLUSION

The antivascular properties of vinblastine and hyperthermia can be exploited to facilitate vascular damage in BT(4)An solid tumors with a low content of host vasculature.