How Lapatinib Ditosylate (Tykerb) Works

Lapatinib ditosylate is an anti-cancer medication included in the category of kinase inhibitors and used as targeted therapy to treat patients with cancer. This means that its mechanism of action is focused on blocking the action of the abnormal protein that signals cancer cells to multiply, which is expected to result in cancer growth stopping or slowing down. “The ditosylate salt of lapatinib, a synthetic, orally-active quinazoline with potential antineoplastic activity,” note the National Cancer Institute (NCI) Drug Dictionary about the drug, which “reversibly blocks phosphorylation of the epidermal growth factor receptor (EGFR), ErbB2, and the Erk-1 and-2 and AKT kinases; it also inhibits cyclin D protein levels in human tumor cell lines and xenografts.”

Lapatinib Ditosylate (Tykerb) for Breast Cancer

Lapatinib ditosylate was first approved by the U.S. Food and Drug Administration (FDA) on March 13, 2007, to be used in combination with capecitabine (Xeloda®) for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress HER2 (ErbB2) and who have received prior therapy including an anthracycline, a taxane, and trastuzumab (Herceptin®). On January 29, 2010, the FDA expanded the indications of lapatinib ditosylate to be used as well in combination with letrozole (Femara®) in postmenopausal women with hormone receptor positive metastatic breast cancer that overexpresses the HER2 receptor and for whom hormonal therapy is indicated. The drug is commercialized in the country under the brand name Tykerb by the company GlaxoSmithKline.

The approvals were based on two randomized trials, which demonstrated the efficacy and safety of lapatinib ditosylate in combination with each of the drugs. “Patients were randomly assigned to receive either lapatinib ditosylate 1,250 mg once daily on days 1-21 plus capecitabine 2,000 mg/m2/day on days 1-14 every 21 days, or to receive capecitabine alone at 2,500 mg/m2/day on days 1-14 every 21 days. The median TTP [time-to-progression] based on the investigator assessment was 23.9 vs. 18.3 weeks for the lapatinib ditosylate combination and capecitabine alone arms, respectively,” explain the NCI about the first trial. “EGF30008 was a multinational randomized placebo-controlled trial of lapatinib plus letrozole versus placebo plus letrozole in patients with hormone receptor-positive metastatic breast cancer who had not received prior therapy for metastatic disease. The lapatinib plus letrozole combination had a median PFS [progression-free survival] of 35.4 weeks, compared to 13.0 weeks for the placebo plus letrozole arm.”

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