MSI Reveals Heterogeneous PARP Inhibitor Distribution in Ovarian Tumors

Overview

A multimodal imaging study demonstrated significant heterogeneity in the intratumoral distribution of PARP inhibitors in ovarian cancer, with lysosomes identified as reservoirs that create hotspots of drug accumulation. This spatial variability correlates with distinct gene expression patterns and may influence therapeutic efficacy and resistance.

Background

PARP inhibitors have revolutionized treatment for high-grade serous ovarian carcinoma but resistance remains a clinical challenge. Tumor heterogeneity and its impact on drug distribution within tumors are not well understood. To investigate this, researchers employed a multimodal pipeline combining mass spectrometry imaging, spatial transcriptomics, and immunohistochemistry on ex vivo cultured tumor slices. This approach allowed direct visualization and analysis of drug uptake independent of vascular factors.

Data Highlights

Mass spectrometry imaging showed marked heterogeneity in drug accumulation across patients, tumor sites, and within individual tumor slices. High-drug regions were enriched for apoptotic and DNA damage response gene signatures. Niraparib and rucaparib-rich areas exhibited strong lysosomal transcriptomic signals. Cell experiments confirmed rucaparib colocalization with lysosomes within 30 minutes, and modulation of lysosomal pH or content altered intracellular levels of rucaparib and niraparib but not olaparib.

Key Findings

• PARP inhibitor distribution is highly heterogeneous within ovarian tumors at single-cell resolution.
• Lysosomes act as reservoirs for weak-base PARP inhibitors (niraparib, rucaparib), leading to localized drug accumulation hotspots.
• Olaparib does not accumulate in lysosomes, indicating differential intracellular handling among PARP inhibitors.
• Regions with high drug accumulation show enrichment of apoptotic and DNA damage response gene signatures.
• Lysosomal drug storage may sustain nuclear drug levels and enhance DNA damage, potentially affecting therapeutic response.
• Variability in drug accumulation driven by lysosomal sequestration could contribute to clinical resistance.

Clinical Implications

Understanding intratumoral heterogeneity in PARP inhibitor distribution can inform personalized treatment strategies for ovarian cancer. Targeting lysosomal drug sequestration mechanisms may enhance drug efficacy and overcome resistance. Future clinical approaches might integrate molecular tumor profiling to optimize PARP inhibitor selection and dosing.

Conclusion

This study highlights the critical role of lysosomes in modulating PARP inhibitor distribution within ovarian tumors, revealing a novel mechanism of drug heterogeneity that may impact therapeutic outcomes. Further research is needed to translate these findings into personalized treatment strategies.

Related Resources & Content

1. Hall et al. 2024 -- MSI Maps Uneven Drug Exposure in Ovarian Tumors