A phase I and pharmacokinetic study of oral lapatinib administered once or twice daily in patients with solid malignancies.

PURPOSE: This study determined the range of tolerable doses, clinical safety, pharmacokinetics, and preliminary evidence of clinical activity following once or twice daily administration of lapatinib in patients with solid malignancies. EXPERIMENTAL DESIGN: Cancer patients (n = 81) received oral doses of lapatinib ranging from 175 to 1,800 mg once daily or 500 to 900 mg twice daily. Clinical assessments of safety and antitumor activity were recorded and blood was sampled for pharmacokinetic assessments. The effect of a low-fat meal on lapatinib pharmacokinetics was assessed in a subset of patients. RESULTS: Lapatinib was well tolerated, such that dose escalation was limited at 1,800 mg once daily only by pill burden. Twice-daily dosing was implemented to further explore tolerability, and was limited by diarrhea to 500 mg twice daily. The most commonly reported adverse events with once-daily dosing were diarrhea (48%), nausea (40%), rash (40%), and fatigue (38%) and with twice-daily dosing were diarrhea (85%), rash (54%), and nausea (34%). Lapatinib serum concentrations accumulated upon repeated dosing, increasing nearly in proportion with dose, and were significantly increased when dosed with food or administered twice daily. One patient with head and neck cancer achieved a confirmed complete response and 22 patients had stable disease of >or=8 weeks including three patients with stable disease of >10 months (renal, lung, and salivary gland cancers). CONCLUSION: Lapatinib was well tolerated following once and twice daily administration. Systemic exposure to lapatinib was dependent on the dose, duration and frequency of dosing, and prandial state. Clinical activity was observed.

Hormone-refractory breast cancer remains sensitive to the antitumor activity of heat shock protein 90 inhibitors.

PURPOSE: The antiestrogen tamoxifen (Tam) has been used as therapy against estrogen receptor (ER)-positive breast cancer for decades. Most tumors respond initially, but resistance frequently develops. The ER exists in a multiprotein complex containing the molecular chaperone heat shock protein (Hsp) 90, which is known to regulate the stability and activity of this receptor. Therefore, we investigated a ligand-independent approach to hormonal therapy that depletes cellular levels of the receptor by inhibiting the function of Hsp90. EXPERIMENTAL DESIGN: The activity of the Hsp90 inhibitor geldanamycin (GA) and its clinically relevant derivative, 17-allylamino-17-demethoxygeldanamycin (17AAG), was examined at the molecular and cellular levels using Tam-resistant MCF-7 breast cancer cells both in vitro and in tumor xenografts. RESULTS: The ER was depleted by GA in several Tam-resistant cell lines, as were other Hsp90 client proteins such as Akt and Raf-1. Unexpectedly, Tam inhibited ER depletion by GA but had no effect on destabilization of Akt or Raf-1. When SCID mice supplemented with Tam were treated with 17AAG, their tumors also showed no decrease in ER levels as measured by immunofluorescent staining and laser scanning cytometry. In these same tumors, however, decreased Akt and Raf-1 levels were observed. Drug administration also led to inhibition of tumor xenograft growth. The mechanism by which Tam inhibits GA-mediated ER depletion is unclear, but immunoprecipitation experiments showed that Tam does not inhibit the ability of GA to alter the ER-chaperone complex. CONCLUSIONS: Based on its ability to deplete the ER as well as other critical signaling molecules in Tam-resistant breast cancer, 17AAG may provide a useful alternative treatment for patients with recurrent, hormone-refractory breast cancer that should be explored further in Phase II trials. In this context, combined treatment with 17AAG and Tam should be avoided because Tam may inhibit the ability of 17AAG to deplete the ER, potentially reducing its anticancer activity.