1400 Enhancing intratumoral drug delivery by altering tumor vasculature using histotripsy tumor ablation

Background

Despite the significant advancement of cancer immunotherapy, many solid tumors remain refractory to treatment in part due to their immunosuppressive microenvironment. The highly pro-angiogenic nature of the tumor microenvironment gives rise to the abnormal vascular network, which then supports and sustains tumor growth and metastasis.¹ For this reason, restoration of normal vascular anatomy has been a desirable target for cancer therapeutics. It has been found that the C-X-C motif chemokine receptor 4 (CXCR4)/C-X-C ligand 12 (CXCL12) axis mediates the extensive angiogenesis observed in solid tumors.² Unfortunately, conventional treatment approaches like radiotherapy have been shown to paradoxically upregulate the expression of hypoxia-inducible factor 1 (HIF-1), the transcription factor that regulates hypoxia responses.³ Therefore, there is a need for alternative approaches to overcome the microenvironmental limitations posed by resistant tumors. Histotripsy is a non-invasive tumor ablation modality that uses high-intensity focused ultrasound to induce mechanical disruption of cellular and subcellular structures. Preliminary data from our laboratory demonstrate that histotripsy treatment downregulates hypoxia and has the potential to remodel the tumor vasculature, effectively interrupting angiogenesis and enhancing tumor perfusion.

Methods

Immunocompetent C57BL/6 mice bearing bilateral flank tumors (B16F10 melanoma and mT4 pancreatic adenocarcinoma tumors) were treated with sham or 70% tumor histotripsy ablation. One-week post-treatment, tail-vein injection of doxorubicin, a chemotherapeutic drug with intrinsic fluorescent properties, was performed. Additionally, mice were treated with AMD-070, a CXCR4 antagonist. Serial microscopic analyses were performed to examine vascular architectural changes, and drug delivery was quantitated with spectral imaging.

Results

Histotripsy-treated tumors revealed increased doxorubicin uptake compared to the sham treatment group, suggesting enhanced perfusion after histotripsy. Additionally, we observed an increase in intratumoral blood vessel diameter, a decrease in the degree of angiogenesis and endothelial expression of CXCR4. Angiogenic features such as total vessel length and vasculature branches were significantly reduced following histotripsy treatment, indicative of vascular normalization.

Conclusions

Histotripsy enhances drug delivery to solid tumors, which could be facilitated by vascular normalization and increased blood vessel diameter. CXCR4 may also play a role in the vascular normalization, providing a molecular mechanism involved in the vascular anatomical alterations observed post-histotripsy. Furthermore, enhanced drug perfusion gives additional insights by which immune cells could infiltrate solid tumors as previously studied. The ability of histotripsy to alter tumor vasculature and enhance perfusion opens a new avenue for the use of combinatorial approaches to improve the efficacy of therapeutic drugs to solid tumors that are otherwise resistant to current standard of care treatment.

Acknowledgements

This work was funded by NIH R01CA269394, NIH R01CA211217, and VA I01BX005267.

References

Liu ZL, Chen HH, Zheng LL, Sun LP, Shi L. Angiogenic signaling pathways and anti-angiogenic therapy for cancer. Sig Transduct Target Ther. 2023;8:198. Mortezaee K. CXCL12/CXC4 axis in the microenvironment of solid tumors: a critical mediator of metastasis. Life Sciences 2020;249:117534. Telarovic I, Wenger RH, Pruschy M. Interfering with tumor hypoxia for radiotherapy optimization. J Exp Clin Cancer Res. 2021;40:197.

Ethics Approval

All animal experiments conducted were reviewed and approved by the VA Ann Arbor Healthcare System and the University of Michigan IACUC protocol (1597602), in compliance with the U.S. Animal Welfare Act, The Guide for the Care and Use of Laboratory Animals, the Office of Laboratory Animal Welfare, and Public Health Service Policy.

Consent

All authors have approved of the abstract submission.