Scientists have developed a pill that appears in pre-clinical research to “annihilate” all solid cancer tumours and leave healthy cells unaffected.

Researchers at City of Hope, one of the US’ largest cancer research and treatment organisations, published a study on Tuesday detailing early test results of “cancer-killing pill” AOH1996.

The drug targets a cancerous variant of proliferating cell nuclear antigen (PCNA) – a protein that in its mutated form is “critical” in DNA replication and repair of all “expanding tumours”, City of Hope said.

Our cancer-killing pill is like a snowstorm that closes a key airline hub, shutting down all flights in and out only in planes carrying cancer cells

Linda Malkas, a professor in the Californian treatment centre’s department of molecular diagnostics and experimental therapeutics, has been developing the pill over the past 20 years.

She said: “PCNA is like a major airline terminal hub containing multiple plane gates.

“Data suggests PCNA is uniquely altered in cancer cells, and this fact allowed us to design a drug that targeted only the form of PCNA in cancer cells.

“Our cancer-killing pill is like a snowstorm that closes a key airline hub, shutting down all flights in and out only in planes carrying cancer cells.”

The professor called the results “promising” but made clear that research has found AOH1996 can suppress tumour growth in cell and animal models, and the first phase of a clinical trial in humans is underway.

No one has ever targeted PCNA as a therapeutic because it was viewed as ‘undruggable,’ but clearly City of Hope was able to develop an investigational medicine for a challenging protein target

The pill has been shown to be effective in treating cells derived from breast, prostate, brain, ovarian, cervical, skin and lung cancers.

It was tested in more than 70 cancer cell lines and found to selectively kill cancer cells by disrupting the normal cell reproductive cycle, according to the research centre.

PCNA has previously been deemed “undruggable”.

Lead author of the study, Long Gu, said: “No one has ever targeted PCNA as a therapeutic because it was viewed as ‘undruggable,’ but clearly City of Hope was able to develop an investigational medicine for a challenging protein target.”

The study – titled “Small Molecule Targeting of Transcription-Replication Conflict for Selective Chemotherapy” – was published in the Cell Chemical Biology journal.