Cancer Biology & Therapy

1. Cancer Biology & Therapy

2. Cancer Neoplastic cells and tissue are characterized by abnormal genetic content, altered chromosome structures, and uncontrolled growth, usually accompanied by loss of cellular differentiation (anaplasia). Abnormal genetic content include • Mutation (inserion, deletion, substitution); translocation which can results in structural changes in the karyological appearance of the cell chromosomes leading to modified cellular regulation. The diseased cells and cell aggregates are described as tumor, neoplasms or cancer and occur in benign (nonvirulent) or malignant (virulent) states. Karyology: Branch of cytology deals with the number and appearance of chromosome.

3. Anaplasia The term anaplasia literally means "to form backward". It implies dedifferentiation, or loss of structural and functional differentiation of normal cells. A change in the structure and orientation of cells, characterized by a loss of differentiation and reversion to a more primitive form. Anaplastic cells display marked pleomorphism. The nuclei are characteristically extremely hyperchromatic(darkly stained) and large. The nuclear-cytoplasmic ratio may approach 1:1 instead of the normal 1:4 or 1:6. Giant cells that are considerably larger than their neighbors may be formed and possess either one enormous nucleus or several nuclei (syncytia). Anaplastic nuclei are variable and bizarre in size and shape. More important, mitoses are often numerous and distinctly atypical. Also, anaplastic cells usually fail to develop recognizable patterns of orientation to one another.

4. Cancer is a pathological condition or disease in which an abnormal and uncontrolled mutiplication and spread of cells occur within the body. Cancer are of different types: • Carcinoma-solid tumor arising from epithelial cells • Sarcoma-tumors originated from connective tissue and often of a fibrous in nature • Leukemias and lymphoma-malignancy that arise from the hematopoietic system. Leukemia is an abnormal increase of immature white blood cells. Lymphoma is a cancer of the lymphocytes, a type of cell that forms part of the immune system. Neoplasm can be divided into benign and malignant types. Benign type does not cause pronounced damage to tissue and more or less harmless. Malignant type is dangerous and likely to cause illness and death.

5. Mechanism of cancer development The mechanism by which malignant neoplasms originate in humans are still not clear. Carcinogenesis (the creation of malignant neoplastic cells) appears to be caused by- • Activation of specific dominant growth genes, called oncogenes or • Loss of tumor suppressor genes (Rb, p53) Protooncogenes when activated, form oncogenes that cause uncontrolled proliferation which are the characteristics of the neoplastic state. Activation of protooncogene occur by exposure of cells to chemicals, radiation and viruses.

6. Reasons of developing cancer 1. Abnormal Karyotype: Karyotype describes the total morphological characteristics of chromosomes of an individual species in terms of no, form, size and arrangemant within the nucleus. If there is any change in the no, size and arrangement of chromosomes, it will be abnormal karyotype, ultimately lead to cancer. E.g. in down syndrome 21st pair chromosomes contain 3 chromosome instead of 2 i.e. total of 47 chromosome lead to physically or mentally disable children.

7. 2. Translocation: Translocation means rearrangement of genetic materials within sister chromosomes (homologous) or transfer of a segment of one chromosome to another (non-homologous). E.g. in some patients with colorectal cancer (cancer of large intestine) rearrangement of chromosome between 8 and 16 occursas well as loss of chromosome 4 and 18 occurs.

8. 3. Mutation: Mutation means change in genetic content. It occurs in three ways- • Insertion/addition (most dangerous) • Substitution (less dangerous) a) Transition- substitution of purine base base by purine (A by G or G by A) or pyrimidine base by pyrimidine (C by T or T by C) b) Transversion-means substitution of pyrimidine by purine (C by G or T by A) or purine by pyrimidine (A by C or G by T) • Deletion- means loss of a portion (base or nucleic acid) of chromosome which may result abnormal cellular growth that leads to tumor. ACC AGU ------ ACC AUG (Substitution) AC AGU (Deletion of C) ACC GAGU (Addition of G)

9. 4. Abnormal genetic control: Continuous production of protein (due to abnormal amount or higher amount of RNA synthesis) will cause cancer. 5. Altered chromosomal structure: Due to chemical, radiation if there is any modification of chromosomal structure it will lead to cancer. 6. Mutation of mismatch repairing enzyme- Mismatch repairing enzyme repairs the mismatch portion of gene (such as thiamine kinase and thymidylate synthetase). Mismatch repairing enzyme identifies wrong sequence and then DNA polymerase repair it. E. coli- Mut S, Mut L and Mut H Human body- hm SH2 and hm LH1 Due to mutation these two enzymes cannot work (repair) which develop cancer.

10. 7. Activation of oncogene: Protooncogene is the inactive form which is activated by the exposure of cells to chemicals, radiation and viruses and responsible for cancer production. The most common oncogene found in human tumor belong to the “ras’’ gene family. When, ras (glycine) is converted to ras (valine) due to mutation it cannot be recognized by GAP (GTPase activating protein), so ras-GTP remains active for long time. ras-GTP acts as oncogene which cause cancer in humans. PO4 ras –GDP (inactive) GTP GAP GDP ras –GTP (active)

11. 8. Loss of activity of tumor suppressor gene-tumorsuppressor gene are present in human body which suppress excessive cellular growth. E.g. • Rb- it is a tumor suppressor gene which suppress retinoblastoma (tumor of the eye). Due to loss of activity of Rb gene retinoblastoma occurs. • p53- it is a tumor suppressor gene which protects genomic stability and helps in apoptosis. Due to loss of activity of this p53 gene cancer develops. 9. Some oncogene act by blocking apoptosis- Some oncogene such as bcl12 act by blocking apoptosis (auto and programmed cell death) 10. Anaplasia: there are some cells (nervous cells, kidney cells) which remain in dormant state (no division occurs) but anaplasia causes sudden uncontrolled growth of cells which ultimately lead to cancer.

12. Growth cycle of mammalian cell DNA Synthesis Pre DNA Synthesis Premitosis Mitosis & Cell division Prophase Metaphase Telophase Anaphase

13. Cell cycle can be classified in 5 phases • G0 phase (resting phase)- the cells are dormant i.e. cells are not in cell division. • G1 phase (pre DNA synthesis)-precursor for DNA are formed. • S phase (synthetic phase)- DNA synthesis occurs. • G2 phase (premitotic synthesis)- premitotic structural development occurs. • M phase – mitosis occurs to produce two daughter cells, each of which can continue the cycle by entering into G1 phase or can enter into resting phase, G0.

14. Growth fraction • Growth fraction is defined as the fraction of cells which are progressing through the cell cycle.

15. Anticancer drugs work on cells that are in cell division. The effectiveness of most anticancer drugs is greater on cells that are progressing through the cell cycle compared to cells that are resting in the G0 phase. • The cells of the hair follicles, bone marrow and intestinal epithelium are the most rapidly dividing cells and are especially sensitive to inhibition by anticancer drugs.

16. Of the four major types of tumors the faster growing leukemia and lymphoma are more responsive to treatment with drugs than the slower growing solid tumor such as carcinoma and sarcoma. • The outer or more recently synthesized portions of many solid tumors are well vascularized due to angiogenesis and are readily accessible to drugs. • The inner and older portion of many solid tumors are hypoxic and often necrotic because angiogenesis is inadequate. So the inner cells of these tumors are poorly accessible to the drugs. The delivery of drugs to the inner portions of solid tumor is a major unsolved problems.

17. Classification of anticancer drugs • Five major classes 1. Alkylating agent i) Nitrogen mustard- Mechlorethamine, melphan, chlorambucil, cyclophosphamide ii) Nitrourea- Carmustine (BCNU- bis-chloroethylnitrosourea), Lomustine (CCNU-chloroethycyclohexaylnitrosourea) iii) Others- Cisplatin, Carboplatin, Busulfan, Dacarbazine, Procarbazine

18. 2. Antimetabolite- Methotrexate, mercaptopurine, thioguanine, fluorourracil, cytarabine, azathioprine 3. Antibiotics- Daunorubicin, Doxorubicin, Bleomycin, Dactinomycin, Mitomycin 4. Plant alkaloids- Vincristine, vinblastine, etoposide, taxol 5. Hormonal agents- Prednisone, tamoxifen

19. Alkylating agent Alkylation refers to the covalent attachment of alkyl groups to the other molecules. The process of alkylation takes place through chemical formation of a positively charged carbonium ion (also called carbocation). The positively charged group subsequently reacts with an electron rich site, particularly on DNA or RNA to form modified nucleic acids. Most of the clinically used alkylating drugs have two alkylating groups, thus promoting the formation of covalent crosslinkink between adjacent strands of nucleic acids. The cross prevent subsequent separation of the dual strands of DNA during cell cycling.

20. Mechlorethamine • Reacts with the N-7 position of the deoxyguanylate. • With free DNA and RNA, alkylation occurs predominantly at the N-7 position of the guanine base, with only minor alkylation at O-6 or N-3 of guanine, at N-1, N-3 or N-7 of adenine or at N-3 of cytocine.

21. Cyclophosphamide • It undergoes a combination of enzymatic and chemical activation to form the active phosphoramide mustard alkylating agent.