B-B4-DM1

Active targeting is more effective than conventional passive targeted drug delivery systems in increasing therapeutic efficacy and minimizing systemic toxicities. Importantly, the nanoparticle-based targeted drug delivery systems combine active and passive targeting properties and significantly enhance therapeutic efficacy. In this study, we utilized ultrasmall superparamagnetic iron oxide (uSPIO) nanoparticles conjugated with anti-prostate-specific membrane antigen (PSMA) 5D3 monoclonal antibody, mertansine (DM1) antitubulin agent, and fluorophore to develop a targeted uSPIO-5D3-DM1-AF488/CF750 nanotheranostic for PSMA(+) prostate cancer (PC) therapy. This agent enables multimodality in vivo imaging using near-infrared (NIR) fluorescence and magnetic resonance imaging (MRI). uSPIO-5D3-DM1-AF488 is selectively internalized into PSMA-positive cells by receptor-mediated endocytosis, and uSPIO-5D3-DM1-CF750 exhibited 1.62 and 166.2 ng/mL IC₅₀ values in PSMA(+) and PSMA(-) cells, respectively. The image-guided therapeutic study was conducted in vivo in human PC xenograft mouse models bearing bilateral PSMA(±) tumors (n = 10, two 10 mg/kg doses on days 1 and 14). The therapeutic results exhibited a significant control of the growth of PSMA(+) tumors starting at day 5 (p = 0.05) and significantly improved efficacy after day 9 (p = 0.0005) during the treatment period (t = 21 days). We observed the PSMA-specific uptake of uSPIO-5D3-DM1-CF750 in tumors in NIR IVIS Xenogen images and T₁- and T₂-weighted MRI with 20.6% and 42% reduction of overall T₁ and T₂, respectively. Approximately 70% of mice with PSMA(+) tumors treated with uSPIO-5D3-DM1-CF750 survived or did not exceed the threshold level of the tumor size during the treatment. Ex vivo biodistribution study proved 50% and 45% higher uptake of uSPIO-5D3-DM1-CF750 by PSMA(+) tumors compared to untargeted uSPIO-DM1-CF750 by PSMA(+) tumors and uSPIO-5D3-DM1-CF750 by PSMA(-) tumors, respectively. ICP-MS analysis demonstrated a 73% increase in uSPIO-5D3-DM1-CF750 uptake by PSMA(+) tumors compared to PSMA(+) tumors treated with pure uSPIO. The toxicological results reveal the safe profile in systemic toxicities without life-threatening changes in the complete blood count and clinical chemistry profile of toxicology.

Mertansine (DM1), a potent tumor-killing maytansinoid, requires conjugation to antibodies or incorporation into nanocarriers due to its high toxicity. However, these carriers often result in undesirable biodistribution, leading to rapid and long-term accumulation in the kidneys or liver and potentially increased toxicity. To overcome this limitation, we used the hydrophilic, biocompatible, and stealth properties of polyacrylamide (PAAm) as a scaffold to develop water-soluble PAAm-DM1 polymer prodrugs, leveraging PAAm's previous success in delivering paclitaxel via subcutaneous administration. To monitor distribution and predict efficacy, we have imparted Positron Emission Tomography (PET) imaging capabilities to well-defined PAAm-DM1 polymer prodrugs. Our studies demonstrated the same tumor accumulation and the same distribution of PAAm-DM1 in the main organs such as liver, kidneys muscle, regardless of delivery route (subcutaneous or intravenous). Interestingly, tumor accumulation of PAAm-DM1 was primarily driven by passive accumulation, as indicated by PET imaging, without significantly altering treatment efficacy. This suggests complex mechanisms, possibly involving immune system interactions by influencing notably the metabolism and clearance. To enhance therapeutic outcomes, we combined the polymer prodrug with immunotherapy, specifically anti-CTLA4. Our findings highlight the promising potential of PAAm-DM1, offering a novel formulation strategy for DM1 in cancer therapy.