Adenoviral Transduction of Human Acid Sphingomyelinase into Neo-Angiogenic Endothelium Radiosensitizes Tumor Cure

Abstract

These studies define a new mechanism-based approach to radiosensitize tumor cure by single dose radiotherapy (SDRT). Published evidence indicates that SDRT induces acute microvascular endothelial apoptosis initiated via acid sphingomyelinase (ASMase) translocation to the external plasma membrane. Ensuing microvascular damage regulates radiation lethality of tumor stem cell clonogens to effect tumor cure. Based on this biology, we engineered an ASMase-producing vector consisting of a modified pre-proendothelin-1 promoter, PPE1(3x), and a hypoxia-inducible dual-binding HIF-2α-Ets-1 enhancer element upstream of the asmase gene, inserted into a replication-deficient adenovirus yielding the vector Ad5H2E-PPE1(3x)-ASMase. This vector confers ASMase over-expression in cycling angiogenic endothelium in vitro and within tumors in vivo, with no detectable enhancement in endothelium of normal tissues that exhibit a minute fraction of cycling cells or in non-endothelial tumor or normal tissue cells. Intravenous pretreatment with Ad5H2E-PPE1(3x)-ASMase markedly increases SDRT cure of inherently radiosensitive MCA/129 fibrosarcomas, and converts radiation-incurable B16 melanomas into biopsy-proven tumor cures. In contrast, Ad5H2E-PPE1(3x)-ASMase treatment did not impact radiation damage to small intestinal crypts as non-dividing small intestinal microvessels did not overexpress ASMase and were not radiosensitized. We posit that combination of genetic up-regulation of tumor microvascular ASMase and SDRT provides therapeutic options for currently radiation-incurable human tumors.

Axitinib sensitization of high Single Dose Radiotherapy

“…While previous studies in animal tumor models have suggested that tumor microvascular damage yields no critical contribution to tumor cure by radiation [1–3], genetic and pre-clinical studies in our laboratory found disruption of tumor vasculature obligate for cure with SDRT at exposures exceeding 10 Gy [4–6]. This endothelial cell dysfunction results from activation of acid sphingomyelinase (ASMase), converting sphingomyelin to the second messenger ceramide in the endothelial plasma membrane.…”

Evolving concepts in cancer therapy through targeting sphingolipid metabolism

“…Immunohistochemistry showed that blood vessels infiltrating the tumor were undamaged in the irradiated ASMase KO mouse. Mice with either B16-F1 melanomas or MCA/129 fibrosarcomas had their tumors radiosensitized after intravenous injection of an adenoviral vector containing ASMase under control of an endothelial cell-specific promoter [162]. Interestingly, while the total numbers of transduced tumor endothelial cells was relatively low, in vitro transduction of endothelial cells showed most ASMase activity to be in the conditioned medium, suggesting a role for secretory ASMase in initiating radiation-induced cell death [162].…”

“…Mice with either B16-F1 melanomas or MCA/129 fibrosarcomas had their tumors radiosensitized after intravenous injection of an adenoviral vector containing ASMase under control of an endothelial cell-specific promoter [162]. Interestingly, while the total numbers of transduced tumor endothelial cells was relatively low, in vitro transduction of endothelial cells showed most ASMase activity to be in the conditioned medium, suggesting a role for secretory ASMase in initiating radiation-induced cell death [162]. Therefore, through modification of radiation-induced ASMase activation, it may be possible to both increase damage to tumor vasculature and through inhibition to lessen damage to normal blood vessels.…”

“…A third problem is that until recently many of the compounds used to inhibit sphingolipid metabolism exhibit non-specific effects or were not effective at clinically tolerable doses [125, 267, 268]. While there is accumulating evidence that targeting sphingolipid metabolism may be of use in cancer therapy, a better understanding of the role of sphingolipid metabolism in cancer cell survival and other key cancer cell functions is required [162]. This, coupled with better, more specific inhibitors will be required before they can be reliably used in a clinical setting.…”

Spinal metastases: From conventional fractionated radiotherapy to single-dose SBRT

“…46 Biological modifiers now used in experimental tumor models enable up to a 6 Gy de-escalation of the dose required for single dose tumor cure without affecting normal tissue sensitivity. 47 If such tumor-selective dose reduction could convert 24 Gy tumor cure to a 15-18 Gy isoeffect in clinical settings, it would significantly simplify the treatment of spine tumors, as it will reduce or eliminate the risk of collateral cord toxicity. It should, however, be emphasized that these approaches are still at an experimental phase and must await further development before being introduced into clinical practice.…”