A Rationally Designed Novel Polymer for Safe and Synergistic Delivery of High Dose Bortezomib, Pomalidomide/Lenalidomide, and Dexamethasone for Multiple Myeloma

Introduction. Synergistic delivery of free drugs is highly challenging due to each drug's unique pharmacokinetics and biodistribution profiles. The standard of care Bortezomib, Pomalidomide/Lenalidomide, and Dexamethasone only demonstrates synergy in a specific concentration window. This specific concentration window has been proven difficult to reach using free drugs. Whereas the Bortezomib, Pomalidomide/Lenalidomide, and Dexamethasone drug combination is the standard of care for patients, an improved method to deliver drugs more specifically to the tumor in higher concentration and at their synergistic ratios would greatly improve the clinical outcome of Multiple Myeloma patients treatments.

Methods and Results. We developed a novel 10 nm biodegradable bottlebrush polymer made of various PEG macromonomers conjugated to clinically used Myeloma drugs, including Bortezomib, Pomalidomide, Lenalidomide, and Dexamethasone. By combining the different macromonomer-drug conjugates together, we defined the most synergistic drug ratio by using the Chou-Talalay method in MM.1S, and KMS11 cell lines. Before evaluating the efficacy of the combination therapy in-vivo, we determined the maximum tolerated dose (MTD) for the Bortezomib bottlebrush alone by monitoring body weight loss, performing H&E staining in all major organs, and performing blood test panels. We successfully injected up to 25x the tolerated dose of free Bortezomib (0.75 mg/kg once a week) with our novel bottlebrush polymer conjugated to Bortezomib (18.75 mg/kg) without signs of toxicity in healthy Balb/c mice. We next evaluated the efficacy of Bortezomib bottlebrush in an orthotopic model of MM.1S_GFP⁺_/Luc⁺ Multiple Myeloma. We determined by fluorescence imaging of harvested organs and by flow cytometry that approx. 5% of the injected dose of bottlebrush Bortezomib (0.95 mg/kg) accumulated in the bone marrow. As a result, this improved and safer delivery technique allowed us to increase by 12 and 10 days the long-term survival of the MM.1S_GFP⁺_/Luc⁺ SCID mice, as compared to free Bortezomib (0.75 mg/kg) and low dose Bortezomib bottlebrush (0.75 mg/kg), respectively (p-value = 0.038, Mann-Whitney). In order to improve the long-term survival and to reach a complete response, we are currently investigating the use of the combination of the 3 drugs: Bortezomib, Pomalidomide, Dexamethasone simultaneously loaded in our bottlebrush at synergistic ratios and comparing the efficacy and toxicity of this combination to the 3 different single loaded bottlebrushes and to the efficacity and toxicity of the free drug combination.

Conclusion. In conclusion, we developed a novel polymer enabling the controlled loading of multiple drugs at their optimal synergistic ratios. In addition, we demonstrated that the conjugation of the drug on our polymer enables the safe delivery of a higher tolerated dose in the body compared to treatments using free drugs and provided improved in-vivo therapeutic outcomes.