"Minicells" May Be the Best Way to Deliver Cancer Medication

Cancer patients may soon receive their chemotherapy treatments by "mini-cells", which would minimize the side effects common to anti-cancer medication. In this week's issue of the journal Cancer Cell, Himanshu Brahmbhatt and Jennifer MacDiarmid, of EnGeneIC Pty. Ltd., in Sydney, Australia, report on the creation of agents termed EnGeneIC Delivery Vehicles (EDVs). EDVs are drug delivery vehicles which are made from bacteria, loaded with the anti-cancer drug of choice, and then injected into the patient. Because the vehicles contain antibodies specific to the cancer itself, they release their payload only upon encountering actual tumors, not healthy tissue.

During normal bacterial cell division, the single bacterium splits down the middle to become two "daughter" bacteria, both of equal size. In the case of EDVs, the EnGeneIC researchers have found a way to promote unequal bacterial division, whereupon the bacterium splits at its end, forming small cytoplasmic "buds". These "buds", measuring an average of 400 nanometers (nm) in size, contain no genetic material, and so do not infect and multiply in the host organism.

Antibodies are then attached to the EDVs, enabling them to target a specific tissue. In the case of breast cancer, the Her2 antibody is attached to the EDVs, allowing them to bind Her2-expressing breast tumor tissue. "Within 2 hours of intravenous administration greater than 30% of the dose ends up in the tumour microenvironment" states Brahmbhatt.

Once bound, the EDVs are internalized by the cells and broken down, whereupon they release their toxic compounds. This is helpful not only in terms of poisoning the tumor, but also for minimizing the amount of drug required to help the patient.

There are additional uses for EDVs beyond simple drug delivery. The vehicles may also be used to transport RNAi, a molecule involved in gene silencing via destruction of an organism's messenger RNA (mRNA). One example of the benefits of RNAi is that cancers previously resistant to various drug treatments, due to production of mRNA which codes for a resistance protein, may be rendered sensitive again.