Targeting breast tumors with pH (low) insertion peptides.

Area of Science:

• Oncology
• Biochemistry
• Molecular Imaging

Background:

• Extracellular acidity and elevated glycolysis are hallmarks of aggressive tumors, promoting malignant cell progression and multidrug resistance.
• Targeting tumor acidity offers a promising strategy for diagnosing and treating aggressive and metastatic cancers.
• pH (low) insertion peptides (pHLIPs) are pH-sensitive agents designed to deliver imaging or therapeutic payloads to cancer cells within tumors.

Purpose of the Study:

• To investigate the targeting capabilities of three fluorescently labeled pHLIP variants (WT-pHLIP, Var3-pHLIP, and Var7-pHLIP) in highly metastatic 4T1 mammary tumors and spontaneous breast tumors.
• To evaluate the biodistribution, tumor accumulation, and specificity of pHLIPs in preclinical breast cancer models.
• To assess the colocalization of pHLIPs with key metabolic markers of tumor acidity and glycolysis.

Main Methods:

• Utilized three fluorescently labeled pHLIP variants (WT-pHLIP, Var3-pHLIP, Var7-pHLIP) for in vivo targeting studies.
• Administered pHLIPs to mice bearing 4T1 mammary tumors and FVB/N-Tg (MMTV-PyMT)634Mul spontaneous breast tumors.
• Analyzed pHLIP distribution within tumors and nonmalignant tissues, and assessed colocalization with 2-deoxyglucose, Pimonidazole, and lactate dehydrogenase A.

Main Results:

• All tested pHLIP variants demonstrated excellent targeting of both breast tumor models, with increasing tumor accumulation over 4 hours post-injection.
• Var3- and Var7-pHLIPs exhibited faster blood clearance compared to the parent WT-pHLIP.
• Minimal staining of nonmalignant stromal tissues was observed, indicating good tumor specificity.
• pHLIP distribution within tumors colocalized with markers of glucose metabolism (2-deoxyglucose) and hypoxia (Pimonidazole).
• The highest degree of colocalization was observed between fluorescent pHLIPs and lactate dehydrogenase A, a key enzyme in tumor acidification.

Conclusions:

• pHLIPs effectively target and accumulate in various breast tumor models, including highly metastatic and spontaneous types.
• The faster blood clearance of Var3- and Var7-pHLIPs enhances their potential for in vivo applications.
• pHLIPs show high tumor specificity with minimal uptake in surrounding healthy tissues.
• pHLIPs serve as valuable tools for monitoring tumor metabolic changes, such as acidity and glycolysis.
• pHLIP-based strategies offer a promising platform for the selective delivery of imaging and therapeutic agents to breast tumors.