Improvement of Tumor Hypoperfusion and Hypoxia via Low-intensity Ultrasound-stimulated Microbubbles Combined with...

Hypoperfusion and related hypoxia are critical factors that contribute to therapeutic resistance in solid tumors. Ultrasound-stimulated microbubble (USMB) has been approved to enhance tumor perfusion, albeit with limited efficacy. This study was aimed to investigate whether combining USMB with alprostadil, a vasodilatory agent, could further improve tumor perfusion and alleviate hypoxia, thereby enhancing drug delivery.

Sixty-nine rabbits bearing VX2 tumors were included in this study. USMB treatment was conducted using a modified diagnostic ultrasound at low intensity (mechanical index 0.24). Tumor perfusion was assessed using contrast-enhanced ultrasound. Hypoxia was evaluated by measuring hypoxia-inducible factor-1α (HIF-1α) and D-lactic acid (D-LA) levels. A pathway inhibition experiment was conducted to explore underlying mechanisms. Doxorubicin was administered to evaluate drug delivery efficacy.

Tumor perfusion was increased following combination therapy, USMB or alprostadil monotherapy, with the combination treatment producing the most pronounced improvement. Furthermore, the combined therapy resulted in the most significant reduction in HIF-1α and D-LA. The pathway inhibition study revealed that USMB led to elevated adenosine triphosphate (ATP) levels in tumors, while cyclic adenosine monophosphate levels were reduced upon pathway inhibition. Nitric Oxide production was highest after combination treatment and markedly decreased following pathway inhibition. Notably, the concentration of doxorubicin within the tumor was highest following combined therapy.

The combination of USMB and alprostadil alleviates hypoperfusion and hypoxia in solid tumors synergistically, which is most likely related to the ATP signaling pathway. This protocol is an effective approach of enhancing drug delivery.