Anticancer Drug; The latest classification of anti cancer drug

Anticancer or antineoplastic drugs are used to treat malignancies, or cancerous growths&control the growth of cancerous cells. Cancer is commonly defined as the uncontrolled growth of cells, with loss of differentiation and commonly, with metastasis, the spread of cancer to other tissues and organs. Cancers are malignant growths. In contrast, benign growths remain encapsulated and grow within a well-defined area. Drug therapy may be used alone or in combination with other treatments such as surgery or radiation therapy.

The top 10 best-selling (in terms of revenue) cancer drugs list

Polyfunctional alkylating agents

• Nitrosourea
•  Mustards (Nitrogen Mustards)
• Methanesulphonates (Busulphan)
• Ethylenimines

Other Alkylating Drugs

• Procarbazine (Matulane)
• Dacarbazine (DTIC)
• Altretamine (Hexalen)
• Cisplatin (Platinol)

Antimetabolites

•  Antifolic acid compounds (Methotrexate)
• Amino acid Antagonists (Azaserine)

Purine antagonists

• Mercaptopurine (6-MP)
• Thioguanine (6-TG)
• Fludarabine Phosphate
• Cladribine (Leustatin)
• Pentostatin (Nipent)

Pyrimidine antagonists

• Mucositis
• Fluorouracil (5-FU)
• Cytarabine (ARA-C)
• Azacitidine

Plant alkaloids

• Vinblastine (Velban)
• Vincristine (Oncovin)
• Etoposide (VP-16,VePe-sid)
• Teniposide (Vumon)
• Topotecan (Hycamtin)
• Irinotecan (Camptosar)
• Paclitaxel (Taxol)
• Docetaxel (Taxotere)

Antibiotics

• Anthracyclines
• Doxorubicin (Adriamycin, Rubex, Doxil)
• Daunorubicin (DaunoXome)
• Dactinomycin (Cosmegen)
• Idarubincin (Idamycin)
• Plicamycin (Mithramycin)
• Mitomycin (Mutamycin)
• Bleomycin (Blenoxane)

Monoclonal Antibodies Hormonal agents

• Tamoxifen (Nolvadex)
• Flutamide (Eulexin)
• Gonadotropin-Releasing Hormone Agonists
• (Leuprolide and Goserelin (Zoladex))
• Aromatase Inhibitors
• Aminoglutethimide
• Anastrozole (Arimidex)

Miscellaneous anticancer drugs

• Amsacrine
• Hydroxyurea (Hydrea)
• Asparaginase (El-spar)
• Mitoxantrone (Novantrone)
• Mitotane
• Retinoic Acid Derivatives
• Bone Marrow Growth Factors
• Amifostine

Newer and experimental approaches

Hematopoietic stem cell transplant approaches – Stem cell harvesting and autologous or allogeneic stem cell transplant have been used to allow for higher doses of chemotherapeutic agents where dosages are primarily limited by hematopoietic damage. Years of research in treating solid tumors, particularly breast cancer, with hematopoeitic stem cell transplants, has yielded little proof of efficacy. Hematological malignancies such as myeloma, lymphoma, and leukemia remain the main indications for stem cell transplants.

Isolated infusion approaches – Isolated limb perfusion (often used in melanoma), or isolated infusion of chemotherapy into the liver or the lung have been used to treat some tumors. The main purpose of these approaches is to deliver a very high dose of chemotherapy to tumor sites without causing overwhelming systemic damage. These approaches can help control solitary or limited metastases, but they are by definition not systemic, and, therefore, do not treat distributed metastases or micrometastases.

Targeted delivery mechanisms – Specially-targeted delivery vehicles aim to increase effective levels of chemotherapy for tumor cells while reducing effective levels for other cells. This should result in an increased tumor kill and/or reduced toxicity. Specially-targeted delivery vehicles have a differentially higher affinity for tumor cells by interacting with tumor-specific or tumor-associated antigens.
In addition to their targeting component – they also carry a payload – whether this is a traditional chemotherapeutic agent, or a radioisotope or an immune-stimulating factor. Specially-targeted delivery vehicles vary in their stability, selectivity, and choice of target, but, in essence, they all aim to increase the maximum effective dose that can be delivered to the tumor cells. Reduced systemic toxicity means that they can also be used in sicker patients, and that they can carry new chemotherapeutic agents that would have been far too toxic to deliver via traditional systemic approaches.

Nanoparticles – Nanoparticles have emerged as a useful vehicle for poorly-soluble agents such as paclitaxel. Protein-bound paclitaxel (e.g., Abraxane) or nab-paclitaxel was approved by the U.S. Food and Drug Administration (FDA) in January 2005 for the treatment of refractory breast cancer and allows reduced use of the Cremophor vehicle usually found in paclitaxel. Nanoparticles made of magnetic material can also be used to concentrate agents at tumor sites using an externally applied magnetic field.

Polyfunctional alkylating agents of Anticancer Drug

Common Structural Features

•  bis(chloroethyl)amine
• ethylenimine
• nitrosoureas

Not cell-cycle specific –  Cells most susceptible in late G1 and S phase– Blocks in G2
Most useful agents

• Cyclophosphamide (Cytoxan)
• ifosfamide
• Mechlorethamine
• Melphalan (Alkeran)
• Chlorambucil (Leukeran)     Secondary agents
• Thiopental (Thioplex)
• Ovarian cancer
• Busulfan (Mylan)
• Chronic myeloid leukemia

Major nitrosoureas

• Carmustine (BCNU)
• Lomustine (CCNU)
• Semustine (methyl CCNU)

Polyfunctional Alkylating Drugs

• Mechanism of Action: Alkyl group transfer  and Major interaction: Alkylation of DNA
• Primary DNA alkylation site: N7 position of guanine (other sites as well)
  the interaction may involve single strands or both strands (cross-linking, due to bifunctional  characteristics)
• Other interactions: these drugs react with carboxyl, sulfhydryl, amino, hydroxyl, and phosphate groups of other cellular constituents
• These drugs usually form a reactive intermediate ethyleneimonium ion

Polyfunctional Alkylating Drug Resistance

• Increased ability to repair DNA defects
• Decreased cellular permeability to the drug
• Increased glutathione synthesi
• inactivates alkylating agents through conjugation reactions (catalyzed by glutathione S-transferase)
• Polyfunctional Alkylating Drugs:

  Genotoxic carcinogens, able to damage DNA by alkylation reactions, represent a very diverse class of agents which are capable of producing a wide range of DNA modifications. The mechanisms leading to genetic changes as a result of exposure to alkylating agents (AAs) have been studied in male germ cells of Drosophila using a structure-activity relationship approach (SAR).

• The analytical tools available concern both genetic and molecular assays. The genetic tests enable to quantify excision repair and clastogenic potency of the AA after treatment of post-meiotic male germ cells and to determine the degree of germ-cell specificity, i.e., the mutagenic effectiveness in the post- versus premeiotic cell stages. For a selected group of alkylating agents, the molecular spectra have been studied in post-meiotic cell stages.
• On the basis of these descriptors, clear SAR’s between genotoxic activity in germ cells and physicochemical parameters (s-values and O6/N7-alkylguanine adducts) and carcinogenic potency in rodents became apparent, resulting in five distinct classes of alkylating agents so far.
• These classes are: 1) SN2-type monofunctional AAs, 2) SN1-type monofunctional AAs, 3) polyfunctional AAs, 4) agents able to form etheno-DNA adducts, and 5) aflatoxin B1 (AFB1) a bulky-adduct forming agent. The recent finding that the molecular data obtained with Drosophila and data of the specific locus tests in male mice show remarkable similarities for most genotoxic agents supports the view that Drosophila is a useful model system for the study of transgenerational damage.

Pharmacological Effects: Polyfunctional Alkylating Drugs

• Injection site damage (vesicant effects) and systemic toxicity.
• Toxicity:dose-related primarily affecting rapidly dividing cells bone marrow
  GI tract nausea and vomiting within less than an hour– with mechlorethamine, carmustine (BCNU) or cyclophosphamide Emetic effects: CNS reduced by pre-treatment with phenothiazines or cannabinoids.
  gonads
• Cyclophosphamide cytotoxicity depends on activation by microsomal enzyme system. Hepatic microsomal P450 mixed-function oxidase catalyzes the conversion of cyclophosphamide to the active forms:
• hydroxycyclophosphamide  aldophosphamide
• Major Toxicity: bone marrow suppression dose-related suppression of myelopoiesis: primary effects on megakaryocytes platelets granulocytes. Bone marrow suppression is worse when alkylating agents are combined with other myelosuppressive drugs and/or radiation (dose reduction required)
• If bone marrow suppression is severe, treatment may have to be suspended and then re-initiated upon hematopoietic recovery. Long-term consequences of alkylating agent treatment include: ovarian failure (common) testicular failure (common) acute leukemia (rare)

Oral Route of Administration

Cyclophosphamide (Cytoxan), melphalan (Alkeran), chlorambucil (Leukeran), busulfan (Myleran), lomustine (CCNU, CeeNU)

• Cyclophosphamide (Cytoxan):   most useful alkylating agent at present.
• Busulfan (Myleran): specificity for granulocytes — chronic myelogenous leukemia

Nitrosoureas

• Not cross-reactive (with respect to tumor resistance) with other alkylating drugs.
• Nonenzymatic by transformation required to activate compounds. Highly lipid-soluble– crosses the blood-brain barrier (BBB useful in treating brain tumors
• Act by cross-linking: DNA alkylation
• More effective against cells in plateau phase than cells in the exponential growth phase
• The major route of elimination: urinary excretion of antidiabetic agents.

Other Alkylating Drugs

• Procarbazine (Matulane)
• Methylhydrazine derivative
• Active in Hodgkin’s disease (combination therapy)
• Teratogenic, mutagenic, leukemogenic.
• Dacarbazine (DTIC)

References

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