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Targeting brain tumours: apoferritin nanocage for delivery of novel analogues of temozolomide


 Treatment for glioblastoma multiforme (GBM) consists of surgery, radiotherapy and temozolomide (TMZ) chemotherapy. Nevertheless, patient prognosis remains poor; in England 5-year survival is < 10%. Resistance to TMZ is a major obstacle thwarting successful treatment, due to overexpression of the O6-methylguanine DNA-methyltransferase (MGMT) and deficiency in mismatch repair (MMR). To overcome resistance, novel N3-substituted analogues of TMZ have been developed. An N3-propargyl analogue, T3, has promising activity irrespective of MGMT or MMR status. However, poor brain drug bioavailability and systemic toxicity remain to be resolved. We use apoferritin (AFt) as a biocompatible nano-delivery system for encapsulation of therapeutic agents via molecular diffusion, through channels in the AFt cage. Around 520 molecules of TMZ and T3 per AFt cage were encapsulated. AFt`s small size (diameter: 12 nm) and numerous transferrin receptor recognition sites on its surface; alongside enhanced expression of transferrin receptors (TfR1; which sequester AFt) on the membranes of cancer cells, offer a dual targeting approach towards greater cancer-selectivity. The encapsulated agents have demonstrated significantly increased anti-tumour activity in brain cancer GBM cell lines, U373V (vector control) and U373M (MGMT over-expressing), with growth inhibition GI50 values < 1 μM, compared to > 30 μM for naked drugs. Clonogenic and cell cycle analyses further corroborate these findings. Hence, the AFt nano-delivery system offers a promising route for enhanced specificity, selectivity and potency of TMZ analogues.