Buy Generic Erlotinib | Information

US Brand Name: Buy generic Tarceva Online

Active substance: Erlotinib

Indian Brand: Erlonat

Manufacturer: Natco

Dosage: 150 mg

Type of packaging:  30 tabs per bottle

Delivery time: 7 – 14 days.

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Mechanism

Erlotinib is an EGFR inhibitor. The drug follows Iressa (gefitinib), which was the first drug of this type. Erlotinib specifically targets the epidermal growth factor receptor (EGFR) tyrosine kinase, which is highly expressed and occasionally mutated in various forms of cancer. It binds in a reversible fashion to the adenosine triphosphate (ATP) binding site of the receptor. For the signal to be transmitted, two EGFR molecules need to come together to form a homodimer. These then use the molecule of ATP to trans-phosphorylate each other on tyrosine residues, which generates phosphotyrosine residues, recruiting the phosphotyrosine-binding proteins to EGFR to assemble protein complexes that transduce signal cascades to the nucleus or activate other cellular biochemical processes. By inhibiting the ATP, formation of phosphotyrosine residues in EGFR is not possible and the signal cascades are not initiated.

Resistance to treatment

Erlotinib bound to ErbB1 at 2.6A resolution; surface colour indicates hydrophobicity.

As with other ATP competitive small molecule tyrosine kinase inhibitors, such as imatinib (Gleevec) in CML, patients rapidly develop resistance. In the case of erlotinib this typically occurs 8–12 months from the start of treatment. Over 50% of resistance is caused by a mutation in the ATP binding pocket of the EGFR kinase domain involving substitution of a small polar threonine residue with a large nonpolar methionine residue (T790M). While proponents of the ‘gatekeeper’ mutation hypothesis suggest this mutation prevents the binding of erlotinib through steric hindrance, research suggests that T790M confers an increase in ATP binding affinity reducing the inhibitory effect of erlotinib.

Approximately 20% of drug resistance is caused by amplification of the hepatocyte growth factor receptor, which drives ERBB3 dependent activation of PI3K.

Other cases of resistance can involve numerous mutations, including recruitment of a mutated IGF-1 receptor to dimerise with EGFR so forming a heterodimer. This allows activation of the downstream effectors of EGFR even in the presence of an EGFR inhibitor. Some IGR-1R inhibitors are in various stages of development (based either around TKIs such as AG1024 or AG538 or pyrrolo[2,3-d]-pyrimidine derivatives such as NVP-AEW541). The monoclonal antibody figitumumab which targets the IGF-1R is currently undergoing clinical trials.

Another cause of resistance can be inactivating mutations of the PTEN tumour suppressor which allow increased activation of Akt independent of stimulation by EGFR.

The most promising approach to combating resistance is likely to be combination therapy. Commencing treatment with a number of different therapeutic agents with differing modes of action is thought to provide the best defence against development of T790M and other resistance conferring mutations.

Why is this medication prescribed?

Erlotinib is used to treat non-small cell lung cancer that has spread to nearby tissues or to other parts of the body in patients who have already been treated with at least one other chemotherapy medication and have not gotten better. Erlotinib is also used in combination with another medication (gemcitabine [Gemzar]) to treat pancreatic cancer that has spread to nearby tissues or to other parts of the body. Erlotinib is in a class of medications called kinase inhibitors. It works by blocking the action of an abnormal protein that signals cancer cells to multiply. This helps slow or stop the spread of cancer cells.