Targeted Therapy Delivers Chemo Directly to Ovarian Cancer Cells

With a novel therapeutic delivery system, a research team led by scientists at The University of Texas M. D. Anderson Cancer Center has successfully targeted a protein that is over-expressed in ovarian cancer cells. Using the EphA2 protein as a molecular homing mechanism, chemotherapy was delivered in a highly selective manner in preclinical models of ovarian cancer, the researchers report in the July 29 issue of the Journal of the National Cancer Institute.

EphA2 is attractive for such molecularly targeted therapy because it has increased expression in ovarian and other cancers, including breast, colon, prostate and non-small cell lung cancers and in aggressive melanomas, and its expression has been associated with a poor prognosis.

“One of our goals has been to develop more specific ways to deliver chemotherapeutic drugs,” said senior author Anil K. Sood, M.D., professor and in the Departments of Gynecologic Oncology and Cancer Biology at M. D. Anderson. “Over the last several years we have shown that EphA2 is a target that is present quite frequently in ovarian and other cancers, but is either present in low levels or is virtually absent from most normal adult tissues. EphA2’s preferential presence on tumor cells makes it an attractive therapeutic target.”

The researchers used a carrier system to deliver chemotherapy directly to ovarian cancer cells. The immunoconjugate contains an anti-EphA2 monoclonal antibody linked to the chemotherapy drug monomethyl auristatin phenylalanine (MMAF) through the non-cleavable linker maleimidocaproyl. Research has shown that auristatins induce cell cycle arrest at the G – M border, disrupt microtubules and induce apoptosis (programmed cell death) in cancer cells.

The investigators evaluated the delivery system’s specificity in EphA2-positive HeyA8 and EphA2-negative SKMel28 ovarian cancer cells through antibody-binding and internalization assays. They also assessed viability and apoptosis in ovarian cancer cell lines and tumor models and examined anti-tumor activity in orthotopic mouse models with mice bearing HeyA8-luc and SKOV3ip1 ovarian tumors.

According to Sood, who is also co-director of both the Center for RNA Interference and Non-Coding RNA and the Blanton-Davis Ovarian Cancer Research Program at M. D. Anderson, the immunoconjugate was highly specific in delivering MMAF to the tumor cells that expressed EphA2 while showing minimal uptake in cells that did not express the protein. In the models, the therapy inhibited tumor growth in treated mice by 85 percent – 98 percent compared to control mice.

“Once we optimized the dosing regimen, the drug was highly effective in reducing tumor growth and in prolonging survival in preclinical animal models,” Sood said. “We actually studied bulkier masses because that is what one would see in a clinical setting where there are pre-existent tumors, and even in this setting the drug was able to reduce or shrink the tumors.”

As for future research with the EphA2-silencing therapy, Sood said, “We are gearing up to bring it to phase I clinical trials. A lot of the safety studies are well under way or nearing completion and we anticipate that this drug will enter clinical trials within the next few months.”

He added that his group is simultaneously conducting preclinical testing on other chemotherapy drugs to determine which agents might combine well with the immunoconjugate used in the current study.

“There is growing interest in molecularly targeted therapy so that we are not indiscriminately killing normal cells,” Sood noted. “The goal is to make the delivery of chemotherapy more specific. The immunoconjugate we used is in a class of drugs that is certainly quite attractive from that perspective.”

Source: University of Texas M. D. Anderson Cancer Center

Chemotherapy Drug Resistance Linked to Genetic Variant in Women with Breast Cancer

Researchers have found links between an individual’s genetics and their response to treatment with chemotherapy. The findings, by researchers at the National Cancer Institute (NCI), part of the National Institutes of Health, and colleagues, show how a genetic variant, located in the SOD2 gene, may affect how a person responds to the chemotherapy drug cyclophosphamide. Cyclophosphamide is used in the treatment of breast and other cancers.

The SOD2 gene produces a key protein that protects cells from damage by molecules known as reactive oxygen species, or free radicals. Reactive oxygen species are produced by normal cellular processes and the action of some chemotherapy drugs. The findings represent the first preliminary evidence pointing toward a mechanism and a potential biomarker for cyclophosphamide resistance in breast cancer patients. The study appeared online June 9, 2009, in Clinical Cancer Research.

“This study shows how, with the progress of individualized medicine, a diagnostic test may be developed that determines whether a patient has certain genetic variations that may modify the effect of certain chemotherapies,” said study author Sharon Glynn, Ph.D., of NCI’s Center for Cancer Research.

“In the future, such tests may be used to guide the treatment of patients with the SOD2 variation, ensuring that they receive a therapy that is more effective than cyclophosphamide-based therapies,” added senior author Stefan Ambs, Ph.D., also of the Center for Cancer Research.

Most genes in human cells are present in two copies — one inherited from the mother and the other inherited from the father. These gene copies can vary from one another. Some variations in genes play an important role in how a gene is expressed or how its protein product functions.

The variant identified by the researchers in the SOD2 gene affects both the structure and the function of the encoded protein, an enzyme known as manganese superoxide dismutase (MnSOD) and affects the ability of MnSOD to reach its proper location in the cell and its activity level. MnSOD normally functions inside cellular compartments known as mitochondria and helps protect cells from damage caused by reactive oxygen species formed during cellular metabolism. Excessive levels of reactive oxygen species can be toxic to cells. Indeed, some anticancer drugs depend on increased production of reactive oxygen species to kill cancer cells. Furthermore, some studies have indicated that, because MnSOD neutralizes reactive oxygen species, it can modify the effects of chemotherapy drugs. For example, in laboratory and animal models, increased activity of MnSOD protects cells against the toxic effects of doxorubicin, which is a widely used anticancer drug.

In the new study, the research team investigated whether the variation affected survival in two separate groups of women with breast cancer: 248 women in the United States and 340 women in Norway. Some of the women received chemotherapy, and some did not receive chemotherapy. The team first analyzed DNA from the women to determine their genotype, meaning which types of the SOD2 gene they had. The researchers found that, among patients who received chemotherapy, those who had one form had decreased survival and those with another form had the poorest survival. In contrast, the genotype of SOD2 did not affect survival among those who did not receive chemotherapy.

Next, the team looked at the relationship between SOD2 genotype and the type of chemotherapy the women received. The data were analyzed according to which of three types of commonly used chemotherapy drugs were administered: doxorubicin, 5-fluorouracil, or cyclophosphamide. Both doxorubicin and cyclophosphamide generate reactive oxygen species in cancer cells during treatment. The researchers determined that the presence of a particular variant was associated with decreased survival of patients treated with chemotherapy regimens that contained any of the three drugs. However, the most significant effects were found with the drug cyclophosphamide. Women with a distinct variant form of SOD2 and who received cyclophosphamide-containing chemotherapy had the poorest survival.

The research team says more work is necessary to confirm these findings and to examine the precise mechanism by which a genotype influences the response of cancer cells to cyclophosphamide. The team plans to examine the influence of several variations on the resistance to other chemotherapies.

Source: National Institutes of Health (NIH), 6/9/2009

Second Round High Dose Chemo May Cure Testicular Cancer

Physicians from Indiana University report that increasing the dosage of anticancer drugs after the failure of first-line chemotherapy may lead to more succesful outcomes for men with testicular cancer.

The report published in the New England Journal of Medicine states that a considerable number of male patients with germ cell tumor are cured when they are treated with a second round of high dosage chemotherapy after the first round of chemotherapy has failed.

Unusual sensitivity of testicular cells to anticancer medicines is assumed to be behind these successful treatments. This treatment, however, cannot be extended to other types of cancers.

“Induced Menopause” Can Protect Women’s Fertility After Chemotherapy

A therapy that temporarily shuts down the ovaries could protect the fertility of women with cancer who are undergoing chemotherapy, say researchers.

Australian scientists used a drug to turn off a hormonal "switch" in the brain that triggers ovulation.
Once the woman’s chemotherapy has ended, the drug is stopped and the ovaries switch back on with their store of eggs in tact.

Source: BBC News (7/4/07)