AACR 2019 – TG Therapeutics still has some explaining to do on umbralisib

It was all good news for TG Therapeutics' umbralisib as long as you ignored the side-effects of PI3K inhibitors. The New York group yesterday disclosed data showing that umbralisib, which targets the delta isoform of the PI3K receptor, had achieved an overall response rate that met its target guidance of 40-50% in marginal zone lymphoma. The data came from a 69-patient, second-line cohort of the Unity-NHL trial, which will be presented at the upcoming AACR meeting. On efficacy umbralisib appears to match Imbruvica, the only agent approved in this setting, which achieved an overall response rate of 46% in a trial that won accelerated approval. However, PI3K-blocking agents are known for having greater toxicity than Imbruvica, a Bruton’s tyrosine kinase inhibitor. Approved PI3K inhibitors like Zydelig and Copiktra have black box warnings of fatal diarrhoea, colitis and infections, while Imbruvica has no such warnings. TG did not disclose safety information from Unity-NHL, stating only that it was “currently being analysed”. This did not seem to faze investors, who sent shares up 31% yesterday, providing a trigger for a fund-raising: TG sold $25.2m worth of shares and secured a $60m venture debt facility with Hercules Capital. The group hopes to use the data as the basis for a US accelerated approval application by the end of the year.