Using nanoparticles to encapsulate an Aurora B kinase inhibitor improved the efficacy and tolerability of the drug and allowed less frequent dosing in preclinical models, according to researchers.

“The AZD2811 nanoparticles identified in this study have the potential to increase efficacy at tolerable doses using a more convenient dosing regimen, which may in turn extend the utility of Aurora B kinase inhibition to a broader range of hematological and solid tumor cancer indications,” wrote Susan Ashton of AstraZeneca, and her colleagues (Sci Transl Med. 2016 Feb 10. doi: 10.1126/scitranslmed.aad2355 ).

“The improved bone marrow profile observed with slow-releasing nanoparticles may enable efficacious combination treatments” with chemotherapy, radiotherapy, or poly(adenosine diphosphate–ribose) polymerase (PARP) inhibitors.

The study was undertaken because a free-drug version of the agent, known as AZD1152, had led to a significant improvement in the complete response rate of acute myeloid leukemia compared to standard of care in a phase II trial. Efficacy, however, was associated with major toxicities, including myelosuppression. Further, AZD1152 had to be administered as a 7-day continuous intravenous infusion.

By using the Accurin nanoparticle platform to vary drug release kinetics, the researchers devised a formulation to maximize the therapeutic effect of the kinase inhibitor while sparing healthy tissue. AZD1152 is a water-soluble prodrug of AZD2811, which the researchers used to develop their the nanoparticle formulation.

AZD2811 was encapsulated in polymeric nanoparticles termed Accurins, which are composed of block copolymers of poly-D,L-lactide (PLA) and poly(ethylene glycol) (PEG). Accurins accumulate in tumors, increasing the drug’s concentration and duration of exposure to the cancer cells. Organic acid counterions were used to increase encapsulation efficiency and decrease the release rate of AZD2811.

“We identified a formulation profile that could deliver active drug for more than 1 week, resulting in prolonged target inhibition in tumor tissue together with improved preclinical efficacy and therapeutic index over the AZD1152 prodrug in several animal models,” they wrote.

In nude rats bearing human colorectal adenocarcinoma SW620 xenografts, the nanoparticles inhibited kinase over a 96-hour time course, while the free drug resulted in complete enzyme recovery at 24 hours. Nanoparticles inhibited tumor growth by over 90%, compared with 58% for the free drug at twice the dose, and showed little toxicity as evidenced by stable body weight. Nanoparticles were retained in the tumor xenografts for up to 6 days, while the free drug was undetected in tumors 24 hours after administration.

“Although we selected a lead formulation using a tumor model (SW620) that supported the AZD1152 program – and, as such, we had extensive comparator data from which to benchmark the tolerability, PD, and efficacy of candidate nanoparticles – the model is subject to the known limitations of xenografted human tumor cell lines in assessing therapeutic candidates in oncology. Moreover, although rat bone marrow is commonly used to model myelotoxicity in humans, interrogation of the nanoparticle dose and schedule in patients may be required to achieve optimal clinical results,” they concluded.

AstraZeneca funded the study. Dr. Ashton and several coauthors are current or former employees and shareholders of AstraZeneca or BIND. The companies are developing the drug and technologies.

tor@frontlinemedcom.com

Ads