Etoposide (trade name Etopophos) is a semisynthetic derivative of podophyllotoxin that exhibits antitumor activity. It has been in clinical use for more than two decades and remains one of the most highly prescribed anticancer drugs in the world. The primary cytotoxic target for etoposide is topoisomerase II. This ubiquitous enzyme regulates DNA under- and over winding, and removes knots and tangles from the genome by generating transient double-stranded breaks in the double helix. Etoposide kills cells by stabilizing a covalent enzyme-cleaved DNA complex (known as the cleavage complex) that is a transient intermediate in the catalytic cycle of topoisomerase II. The accumulation of cleavage complexes in treated cells leads to the generation of permanent DNA strand breaks, which trigger recombination/repair pathways, mutagenesis, and chromosomal translocations. If these breaks overwhelm the cell, they can initiate death pathways. Thus, etoposide converts topoisomerase II from an essential enzyme to a potent cellular toxin that fragments the genome. Although the topoisomerase II-DNA cleavage complex is an important target for cancer chemotherapy, there also is evidence that topoisomerase II-mediated DNA strand breaks induced by etoposide and other agents can trigger chromosomal translocations that lead to specific types of leukemia. Etopophos (etoposide phosphate) is indicated in the management of the following neoplasms: Refractory Testicular Tumors-and for Small Cell Lung Cancer. The in vitro cytotoxicity observed for etoposide phosphate is significantly less than that seen with etoposide, which is believed due to the necessity for conversion in vivo to the active moiety, etoposide, by dephosphorylation. The mechanism of action is believed to be the same as that of etoposide.

Acridine carboxamide (XR5000) is a tricyclic acridine-based (or carboxamide-based) drug with dual topoisomerase inhibitor and potential antineoplastic activities. Acridine carboxamide inhibits both topoisomerases I and II and intercalates into DNA, resulting in DNA damage, the disruption of DNA repair and replication, the inhibition of RNA and protein synthesis, and cell death. Acridine carboxamide has been used in trials studying the treatment of lung cancer and brain and central nervous system tumors. In clinical trials acridine carboxamide did not show efficacy when tested against various types of cancers.

Fostriecin, an antitumor antibiotic produced by Streptomyces pulveraceus, is a strong inhibitor of serine/threonine protein phosphatases type 2A and type 4, and inhibits the catalytic activity of partially purified Topo II (type II topoisomerase) in a non-competitive manner.

Daniquidone, also known as Batracylin, is a water-insoluble heterocyclic amide with potential antineoplastic activity. Daniquidone inhibits topoisomerases I and II, thereby inhibiting DNA replication and repair, and RNA and protein synthesis. Batracylin advanced as an anticancer agent to Phase I clinical trials where dose limiting hemorrhagic cystitis (bladder inflammation and bleeding) was observed.

Tafluposide (also known as F 11782) is an epipodophyllotoxin derivative patented by Pierre Fabre Medicament as an antitumor agent. Tafluposide acts as a catalytic inhibitor of topoisomerases I and II, that capable of completely inhibiting the DNA-binding activity of topoisomerase. In preclinical models single or multiple i.p. doses of Tafluposide proves highly active against the s.c. grafted B16 melanoma, significantly increasing survival and inhibiting tumor growth. Tafluposide inhibits the number of pulmonary metastatic foci of the melanoma by 99%. In human tumor xenograft studies, multiple i.p. doses of Tafluposide results in major inhibitory activity against breast) tumors, as well as causing definite tumor regression. Significant activity was also recorded Tafluposide against the refractory lung xenografts.

Retelleptine (SR-95325 B) is an antitumoral agent. This ellipticine derivative exhibits high toxicity against several rodent tumor models. Retelliptine is thought to intercalate with DNA and inhibit topoisomerase II during DNA replication. A phase I study reported possible drug-related toxicity sporadically such as somnolence, bronchospasm, dry mouth, and vomiting.

Asulacrine, also known as CI-921, an inhibitor of topoisomerase II, participated in clinical trials phase II for the treatment of cancer. In spite of the positive and promising results, this drug showed the toxicity, phlebitis that blocks its implementation in the future.

Chlorsulfaquinoxaline is a halogenated derivative of sulfaquixonaline, an immunosuppressive and antifungal agent used in the control of coccidiosis in poultry, rabbit, sheep, and cattle. In vitro, Chlorsulfaquinoxaline acts as a topoisomerases IIα and IIβ poison, thus inhibiting DNA replication. Chlorsulfaquinoxaline shows good activity against human tumor cells in the human tumor colony-forming assay and subsequently has shown activity against murine and human solid tumors. No major objective antitumor responses was observed during Chlorsulfaquinoxaline Phase II clinical evaluation in non-small-cell lung cancer and metastatic colorectal cancer. Chlorsulfaquinoxaline was well tolerated with hypoglycemia being the most clinically significant toxicity.

Mitindomide was studied as an antineoplastic agent that inhibited the activity of the topoisomerase II. The drug underwent preclinical development; however, this study was discontinued.

Elsamitrucin is a heterocyclic antineoplastic antibiotic isolated from the bacterium Actinomycete strain J907-21. Elsamitrucin intercalates into DNA at guanine-cytosine (G-C)-rich sequences and inhibits topoisomerase I and II, resulting in single-strand breaks and inhibition of DNA replication. It demonstrated a broad spectrum of in vitro cytotoxicity against tumor cell lines. According to the results of Phase II trials elsamitrucin is not an active drug in patients with metastatic breast cancer, colorectal cancer, non-small cell lung cancer or ovarian cancer, however, it showed modest activity in patients with relapsed or refractory non-Hodgkin's lymphoma.