Pharmacokinetic evaluation of vadimezan (ASA404, 5,6-dimethylxanthenone-4-acetic acid, DMXAA)

TREX1 as a Novel Immunotherapeutic Target

Mutations in the TREX1 3' → 5' exonuclease are associated with a spectrum of autoimmune disease phenotypes in humans and mice. Failure to degrade DNA activates the cGAS-STING DNA-sensing pathway signaling a type-I interferon (IFN) response that ultimately drives immune system activation. TREX1 and the cGAS-STING DNA-sensing pathway have also been implicated in the tumor microenvironment, where TREX1 is proposed to degrade tumor-derived DNA that would otherwise activate cGAS-STING. If tumor-derived DNA were not degraded, the cGAS-STING pathway would be activated to promote IFN-dependent antitumor immunity. Thus, we hypothesize TREX1 exonuclease inhibition as a novel immunotherapeutic strategy. We present data demonstrating antitumor immunity in the TREX1 D18N mouse model and discuss theory surrounding the best strategy for TREX1 inhibition. Potential complications of TREX1 inhibition as a therapeutic strategy are also discussed.

Synthetic Chiral Derivatives of Xanthones: Biological Activities and Enantioselectivity Studies

Many naturally occurring xanthones are chiral and present a wide range of biological and pharmacological activities. Some of them have been exhaustively studied and subsequently, obtained by synthesis. In order to obtain libraries of compounds for structure activity relationship (SAR) studies as well as to improve the biological activity, new bioactive analogues and derivatives inspired in natural prototypes were synthetized. Bioactive natural xanthones compromise a large structural multiplicity of compounds, including a diversity of chiral derivatives. Thus, recently an exponential interest in synthetic chiral derivatives of xanthones (CDXs) has been witnessed. The synthetic methodologies can afford structures that otherwise could not be reached within the natural products for biological activity and SAR studies. Another reason that justifies this trend is that both enantiomers can be obtained by using appropriate synthetic pathways, allowing the possibility to perform enantioselectivity studies. In this work, a literature review of synthetic CDXs is presented. The structures, the approaches used for their synthesis and the biological activities are described, emphasizing the enantioselectivity studies.

Vascular priming enhances chemotherapeutic efficacy against head and neck cancer

PURPOSE

The need to improve chemotherapeutic efficacy against head and neck squamous cell carcinomas (HNSCC) is well recognized. In this study, we investigated the potential of targeting the established tumor vasculature in combination with chemotherapy in head and neck cancer.

METHODS

Experimental studies were carried out in multiple human HNSCC xenograft models to examine the activity of the vascular disrupting agent (VDA) 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in combination with chemotherapy. Multimodality imaging (magnetic resonance imaging, bioluminescence) in conjunction with drug delivery assessment (fluorescence microscopy), histopathology and microarray analysis was performed to characterize tumor response to therapy. Long-term treatment outcome was assessed using clinically-relevant end points of efficacy.

RESULTS

Pretreatment of tumors with VDA prior to administration of chemotherapy increased intratumoral drug delivery and treatment efficacy. Enhancement of therapeutic efficacy was dependent on the dose and duration of VDA treatment but was independent of the chemotherapeutic agent evaluated. Combination treatment resulted in increased tumor cell kill and improvement in progression-free survival and overall survival in both ectopic and orthotopic HNSCC models.

CONCLUSION

Our results show that preconditioning of the tumor microenvironment with an antivascular agent primes the tumor vasculature and results in enhancement of chemotherapeutic delivery and efficacy in vivo. Further investigation into the activity of antivascular agents in combination with chemotherapy against HNSCC is warranted.

DMXAA (Vadimezan, ASA404) is a multi-kinase inhibitor targeting VEGFR2 in particular

The flavone acetic acid derivative DMXAA [5,6-dimethylXAA (xanthenone-4-acetic acid), Vadimezan, ASA404] is a drug that displayed vascular-disrupting activity and induced haemorrhagic necrosis and tumour regression in pre-clinical animal models. Both immune-mediated and non-immune-mediated effects contributed to the tumour regression. The vascular disruption was less in human tumours, with immune-mediated effects being less prominent, but nonetheless DMXAA showed promising effects in Phase II clinical trials in non-small-cell lung cancer. However, these effects were not replicated in Phase III clinical trials. It has been difficult to understand the differences between the pre-clinical findings and the later clinical trials as the molecular targets for the agent have never been clearly established. To investigate the mechanism of action, we sought to determine whether DMXAA might target protein kinases. We found that, at concentrations achieved in blood during clinical trials, DMXAA has inhibitory effects against several kinases, with most potent effects being on members of the VEGFR (vascular endothelial growth factor receptor) tyrosine kinase family. Some analogues of DMXAA were even more effective inhibitors of these kinases, in particular 2-MeXAA (2-methylXAA) and 6-MeXAA (6-methylXAA). The inhibitory effects were greatest against VEGFR2 and, consistent with this, we found that DMXAA, 2-MeXAA and 6-MeXAA were able to block angiogenesis in zebrafish embryos and also inhibit VEGFR2 signalling in HUVECs (human umbilical vein endothelial cells). Taken together, these results indicate that at least part of the effects of DMXAA are due to it acting as a multi-kinase inhibitor and that the anti-VEGFR activity in particular may contribute to the non-immune-mediated effects of DMXAA on the vasculature.