Talon Therapeutics' liposomal formulation of vincristine has become the first drug therapy specifically approved for a rare form of acute lymphoblastic leukaemia in the US.
The drug, called Marqibo, has been cleared by the FDA to treat Philadelphia chromosome-negative (PH-) ALL, a rapidly progressing form of the haematological malignancy that occurs in around 1,400 patients per year in the US.
It is also the first drug to reach the market for Talon, which is due to report its second-quarter results next week but posted a $30m loss in the first quarter of 2012.
Marqibo is indicated for use after two or more prior rounds of anti-leukaemia therapy, and meets a major unmet medical need because there are currently no approved or standard-of-care treatment options in Ph- ALL, according to the FDA.
People with adult ALL also have a poor prognosis, with high annual relapse rates and a five-year survival rate of just 7 per cent.
It was registered under the FDA's accelerated approval programme on the back of a single 65-patient phase II clinical trial - called RALLY - which showed 15 per cent of patients treated with drug achieved a complete response (CR), or a complete response with incomplete blood count recovery (CRi).
"With current multi-agent chemotherapy regimens, up to 90 per cent of newly diagnosed adult ALL patients will achieve an initial CR and CRi, however only 28 to 39 per cent achieve long-term disease control," said the FDA at an advisory committee meeting to review the Marqibo dossier earlier this year.
"For patients in third or fourth relapse or in a second relapse that is refractory to therapy, survival is expected to be weeks," it added.
Encapsulating vincristine in liposomes overcomes many of the dosing and toxicity limitations of conventional vincristine, and also prevents the drug from accumulating in the body, which can lead to serious side effects and dose interruptions.
Talon licensed the Marqibo formulation in 2006 from Tekmira of Canada, which nets a $1m milestone payment following US approval. It says it intends to file for approval of the product in Europe next year, and is understood to be looking for a development partner for the drug outside the US.
Analysts have suggested Marqibo could bring in annual sales in excess of $100m in Ph- ALL alone, with significant upside if Talon can get additional indications approved.
Further down the line, Talon is hoping to develop Marqibo as a first-line therapy for ALL and also for non-Hodgkin's lymphoma (NHL), a much larger patient population that could open up a market for the drug worth billions of dollars. Non-liposomal vincristine is already an approved, standard therapy for NHL.
Meanwhile, Talon is also developing liposomal formulations of other widely-used cancer drugs, including vinorelbine (Alocrest) and topotecan (Brakiva), as well as menadione to treat skin rash associated with epidermal growth factor receptor (EGFR) inhibitors such as Roche's Tarceva (erlotinib), Bristol-Myers Squibb/Merck KGaA/Eli Lilly's Erbitux (cetuximab) and Amgen/Takeda's Vectibix (panitumumab).
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