Toxicology, safety and herb-drug interactions in cancer therapy

Cancer patients always seek alternative approaches without advising the oncologists about their use of herbal/dietary supplements. There are increased reports on the interaction of herbal medicines and anticancer drugs that is becoming a safety concern. For example, a clinical study in cancer patients reported that treatment of Hypericum perforatum (St John's wort) at 900 mg/day orally for 18 days decreased the plasma levels of the active metabolite of irinotecan, SN-38, by 42%. In healthy subjects, 2 weeks of treatment with St John's wort at 900 mg/day significantly decreased the systemic exposure of imatinib by 32%. In women with advanced breast cancer, coadministration of garlic supplement reduced the clearance of docetaxol by 23.1-35.1 %, although the difference did not achieve statistical significance. A recent clinical trial in patients with resected breast or colon cancer has revealed that Chinese herbal medicines did not alleviate chemotherapy_ induced haematological toxicity, but significantly reduced drug-induced nausea. Most anticancer drugs undergo Phase I and/or II metabolism and are substrates of P-glycoprotein, breast cancer resistance protein, multidrug resistance associated proteins, and/or other transporters. Induction and inhibition of these enzymes and transporters is considered an important mechanism for herb-anticancer drug interactions. Timely identification of the herbal medicines involved and victim anticancer drugs is important to remind both oncologists and cancer patients of the Possible safety concerns arising from combined use of herbs with any anticancer drugs. Monitoring plasma concentrations of concurrently administered anticancer drugs and observing for possible signs of clinical toxicity are necessary when herbal remedies is used concurrently