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Elucidation of the mechanism enabling tumor selective prodrug monotherapy
K Bosslet1, R Straub, M Blumrich
1Hoechst Research Laboratories, Marburg, Germany.
Abstract:
Elucidation of the mechanism enabling tumor selective PMT in vivo with appropriate glucuronyl-spacer-doxorubicin prodrugs, such as HMR 1826, is important for the design of clinical studies, as well as for the development of more selective drugs. Enzyme histochemistry, immunohistochemistry, and the terminal deoxytransferase technique were applied using human cryopreserved cancer tissues, normal human, monkey, and mouse tissues, and human tumor xenografts to examine mechanisms underlying the selectivity of successful PMT with HMR 1826. It could unambiguously be shown by enzyme histochemistry that necrotic areas in human cancers are the sites in which lysosomal beta-glucuronidase is liberated extracellularly in high local concentrations. The cells responsible for the liberation of the enzyme are mainly acute and chronic inflammatory cells, as shown by IHC. Furthermore, it could be demonstrated that beta-glucuronidase liberated in necrotic areas of tumors can activate HMR 1826, resulting in increased doxorubicin deposition in human tumor xenografts or in human lung cancers subjected to extracorporal perfusion, compared to chemotherapy with doxorubicin. Additionally, the doxorubicin load to normal tissues was significantly reduced compared to chemotherapy with doxorubicin. Surprisingly, the increased doxorubicin deposition in tumors also resulted in strong antitumor effects also in cancers resistant to maximum tolerated doses of systemic doxorubicin. Finally, toxicity studies in mice and monkeys revealed an excellent tolerability of HMR 1826, up to a dose of 3 g/m2 (monkeys). These data suggest that HMR 1826 is a promising candidate for clinical development.
Insights
Tumor-selective prodrug activation of glucuronyl-doxorubicin (HMR 1826) occurs in necrotic cancer areas. This targeted drug delivery increases doxorubicin in tumors while reducing normal tissue exposure, showing promise for resistant cancers.
Area of Science:
- Oncology
- Pharmacology
- Biochemistry
Background:
- Tumor-selective prodrug activation (PMT) is crucial for developing targeted cancer therapies.
- Glucuronyl-spacer-doxorubicin prodrugs, like HMR 1826, offer potential for enhanced drug delivery.
- Understanding the precise mechanisms of PMT is vital for clinical application and drug development.
Purpose of the Study:
- To elucidate the mechanism of tumor-selective prodrug activation (PMT) in vivo.
- To investigate the role of beta-glucuronidase in activating HMR 1826 within tumor microenvironments.
- To evaluate the efficacy and safety of HMR 1826 compared to doxorubicin chemotherapy.
Main Methods:
- Enzyme histochemistry and immunohistochemistry were used on human and animal tissues, including tumor xenografts.
- Terminal deoxytransferase technique was applied to analyze tissue samples.
- In vitro and in vivo studies assessed drug deposition, antitumor effects, and toxicity.
Main Results:
- Necrotic areas in human cancers were identified as sites of extracellular lysosomal beta-glucuronidase release, primarily by inflammatory cells.
- Beta-glucuronidase successfully activated HMR 1826, leading to increased doxorubicin deposition in tumors.
- HMR 1826 demonstrated reduced doxorubicin load in normal tissues and significant antitumor effects, even in doxorubicin-resistant cancers.
- Toxicity studies showed excellent tolerability of HMR 1826 in mice and monkeys.
Conclusions:
- HMR 1826 is activated by beta-glucuronidase in tumor necrotic areas, enabling targeted doxorubicin delivery.
- This prodrug strategy enhances tumor drug accumulation and efficacy while minimizing systemic toxicity.
- HMR 1826 shows significant promise as a clinical candidate for cancer treatment, including resistant malignancies.