Bangalore: In a development that could lead to the treatment of the most aggressive form of breast cancer, scientists say they have tested a DNA vaccine that provides complete protection in mice.
Reporting in Monday’s issue of Cancer Research, researchers from Wayne State University, Michigan, say their Her-2 positive vaccine eliminated tumours in mice, even in cancers that have turned resistant to anti-Her-2 drugs, without any toxicity. The group has also done a pilot test in humans.
“In collaboration with Karolinska Institute (in Sweden), a pilot clinical trial with one of our Her-2 vaccine constructs has been conducted in stage IV breast cancer patients and safety was demonstrated,” said lead author Wei-Zen Wei, Karmanos Cancer Institute, Wayne, in an email. “Our findings add support to further the testing.”
About 25-30% of breast cancers are caused by cells excessively manufacturing a protein called Her-2, which is otherwise produced in low concentrations by normal breast cells. Her-2 positive tumours are found to be more aggressive than other types. Surveys done in India, says Vinod Raina, head of medical oncology at the All India Institute of Medical Sciences in New Delhi, show that Her-2 is over-expressed in about 25% of breast cancers.
Anti-Her-2 drugs such as trastuzumab (brand name: Herceptin) and lapatinib (brand name: Tykerb) are most effective against this cancer but many patients either develop resistance to them or their cancer turns metastatic (spreads to other organs), which is difficult to treat.
This new vaccine relies on a person’s own activated immunity and acts even in drug-resistant cancer, says Wei. “The vaccine could potentially eliminate the need to even use these therapies,” she says, anticipating that it might also be used in cancer-free women to prevent initial development of these tumours.
The vaccine uses the DNA sequence that produces the Her-2 receptor along with an immune stimulant. The two are placed inside an inert bacterial plasmid (extra chromosomal DNA found in bacteria) and injected inside the body using electrical pulses.
It is exciting that we can put our immunity to better use against cancer, says an oncologist from the Tata Memorial Hospital, Mumbai; but, he cautions, we must wait for further results. “I say this because Herceptin is associated with approximately 5% cardio-toxicity and we are unable to clearly explain the mechanism,” says this breast cancer specialist, who doesn’t want to be named as he is not authorized to speak to the media.
His hypothesis: What if Her-2 vaccination targets a person’s own immunity against his/her heart? “We should temper our enthusiasm till we have more real (human) data,” he adds.
The enthusiasm is also toned down by cost considerations. For instance, the cervical cancer vaccine has hit the market but at a cost of more than $350 (Rs16,065) (generics haven’t arrived yet), it’s unaffordable to a large population of women in India.
While Wei says that “since vaccines are not given continuously as drugs, it should be less costly”, Dr Raina thinks it might hit the price wall but the situation is not so hopeless given how the Glivec International Patient Assistance Program has benefited thousands of leukemia patients in India.
“I am sure there’ll be solutions and alternatives (when this new vaccine comes).”