The couple, with family and friends and through the help of public appeals, had raised $69,000 for just such a mercy dash, however the day they were due to fly out new cost estimates for the four-month trial skyrocketed from $120,000 to upwards of $400,000.
An appeal in the Herald two weeks ago netted the family another $20,000 and attracted the attention of Mr Watson, who now lives in London, and Mr Glenn, who lives in Sydney.
"Both Eric and I are parents and while we can't comprehend what Ryan and Keri are going through, as parents we do know the lengths we would go to if we were in this situation with one of our own children," Mr Glenn said.
The business partners donated the money to help towards the cost of the treatment and to encourage others to follow suit.
Just 10 days of treatment can cost up to £25,000 pounds ($49,000).
It's hoped the trial will buy Chace precious months so that he can have another transplant, this time with a bone marrow match. A second transplant within a year of the first one could kill Chace.
Speaking from the Royal Marsden Hospital in Surrey, just south of London, Mr Topperwien said only yesterday unscheduled procedures to resolve a blood clotting issue which had interrupted Chace's first drug fusion, had set the couple back £4000.
Chace's hospital room alone was £795 per day.
Mrs Topperwien said they were "blown away" by the generosity of the expatriate businessmen.
"They seem very committed to trying to attract other donations which for us, faced with the huge financial costs, it is very relieving to say the least," Mrs Topperwien said.
"This has taken a huge amount of pressure off us and our whanau, who are working tirelessly to fundraise for Chace. This is an incredibly stressful situation, but to know that we have the support of all these people is amazing."
Mr Watson even had some of his children's toys delivered to the hospital and offered the use of his family's nanny. "My son is the same age as Chace, so together Owen and I have jointly committed $50,000 to assist the family with the astronomical costs, but also as a way of providing momentum to the $70,000 already raised.
"We're keen to encourage other New Zealand business people to get involved and donate."
He plans to meet the family this weekend and take his three year old to play with Chace.
Behind the scenes a New Zealand doctor living in London has also been supporting the family.
Dr Kate Hersov, director and co-founder of Medikidz - an organisation which helps to explain to seriously ill children what is happening to them and which Mr Glenn invests in - has found the Topperwiens a new place to live when their free accommodation runs out.
And with her connections within the UK health system, she is working hard to help bring down the costs of Chace's treatment.
The group will also target other expatriate Kiwis for help through KEA UK, a networking group with 8000 members. "I've been to see Ryan, Keri and Chace and given the circumstances they are doing remarkably well," Dr Hersov said.
"I recognise when you're on the other side of the world, dealing with your worst nightmare, having a fellow Kiwi, who is a doctor and who knows the UK health system is reassuring."
In the meantime the Topperwiens' family back home are organising a bone-marrow drive among Maori and Pacific Islanders to try to find a match for Chace.
How to help
Donations to the Chace Topperwien fundraising account 123217016311100 at ASB.
For more information on bone marrow donation visit bonemarrow.org.nz
