Stem Cell Transplants Restore Fertility in Monkeys

Injections of banked sperm-making stem cells can restore fertility to male non-human primates. This work comes from stem cell researchers at the University of Pittsburgh School of Medicine and the Magee-Womens Research Institute and was published in the journal Cell Stem Cell.

This is a remarkable finding because some men or boys must undergo cancer treatment before they have their families. Since cancer drugs destroy dividing cells and do not discriminate between normal cells and cancer cells, the stem cells that make sperm tend to take a serious beating during chemotherapy. The cancer might be destroyed, but the patient will be rendered sterile.

The senior investigator for this work, Kyle Orwig, associate professor in the Department of Obstetrics, Gynecology and Reproductive Medicine at the University of Pittsburgh School of Medicine said: “Men can bank sperm before they have cancer treatment if they hope to have biological children later in their lives,” he says. “But that is not an option for young boys who haven’t gone through puberty, can’t provide a sperm sample, and are many years away from thinking about having babies.”

Young boys that have yet to experience puberty do not yet make any sperm, but they have a modicum of spermatogonial stem cells in their testes that are waiting in the wings to produce sperm during puberty. During puberty, neurons in a part of the brain called the hypothalamus release a 10-amino acid peptide called “gonadotropin releasing hormone” (GnRH). Because these neurons release their GnRH into blood vessels that feed the pituitary gland, just below the hypothalamus, it flows directly to the pituitary.

GnRH stimulates the anterior lobe of the pituitary to release two trophic hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are collectively known as gonadotropins. FSH initiates sperm cell production in the tubules within the testes and LH stimulates the synthesis of the steroid hormone testosterone, which is necessary for sperm maturation.

Orwig and his colleagues wanted to determine if it is possible to restore fertility by freezing and banking these spermatogonial stem cells and then reintroducing them back into the testes after the completion of chemotherapy. Orwig and others took biopsies from the testes of young, adult male macaque monkeys that had yet to experience puberty. This tissue was cryopreserved in small samples. Then the monkeys were treated with chemotherapy agents that are known to reduce fertility.

A few months after chemotherapy treatment, Orwig and his colleagues transplanted each monkey’s own spermatogonial stem cells into their own testes by means of ultrasound-guided surgery. Nine of twelve adult animals showed restoration of sperm production and three of five very young animals that had not yet experienced puberty demonstrated an ability to make functional sperm after they reached maturity.

In a second experiment, spermatogonial stem cells from unrelated monkeys were transplanted into infertile animals. These transplanted cells generated sperm that had the DNA fingerprint of the donor. Because the testes contain a barrier to the immune system that prevents access of the sperm to the immune system, the implanted tissue could survive without being attacked by the immune system. This is a problem is males who have immune responses to sperm. For example, men who have had a vasectomy or make homosexuals have immune responses to human sperm. Laboratory tests showed that sperm from transplant recipients successfully fertilized 81 eggs that lead to embryos that developed normally. Donor parentage was confirmed in these embryos.

“This study demonstrates that spermatogonial stem cells from higher primates can be frozen and thawed without losing their activity, and that they can be transplanted to produce functional sperm that are able to fertilize eggs and give rise to early embryos,” Orwig says.

Several centers in the U.S. and elsewhere are already banking testicular tissue for young male cancer patients. This is in future anticipation that new stem cell-based therapies will be developed that will help them achieve pregnancy and have their own biological children. Thus this proof-of-principle experiment has generated no small degree of excitement for clinicians and patients who have compromised fertility.

According to Orwig, “These patients and their families are the pioneers that inspire our research and help drive the development of new medical breakthroughs.” He continued: “Many questions remain to be answered,” Orwig notes. “Should we re-introduce the spermatogonial cells as soon as treatment is over, or wait until the patient is considered cured of his disease, or when he is ready to start a family? How do we eliminate the risk of cancer recurrence if we give back untreated cells that might include cancer cells? These are issues we still must work through, but this study does show us the concept is feasible.”

Geron Corporation Announces Phase II Trial for Brain-Specific Anticancer Drug GNR1005

After a successful completion of a Phase I study, Geron Corporation announces the initiation of a phase II trial for its GRN1005 anticancer drug. This drug was designed to specifically treat tumors that have metastasized (spread) to the brain from the lung. This clinical trial is called GRABM-L, which stands for GRN1005 Against Brain Metastases – Lung cancer). This phase II trial is designed to determine the efficacy of GRN1005 in patients with brain metastases arising from non-small cell lung cancer (NSCLC).

GRN1005 is a novel cancer drug that consists of three molecules of the anticancer drug paclitaxel linked to a 19 amino acid peptide (Angiopep-2). This 19-amino acid peptide binds to a receptor called the “lipoprotein receptor-related protein 1” (LRP1), which is one of the most highly expressed receptors on the surface of the blood-brain barrier (BBB). Brain tumor treatment is exceedingly difficult because the central nervous system is surrounded by the BBB. The BBB prevents molecules from entering the brain unless they can bind specific receptors. When GRN1005 binds to the LRP1 receptor, the binding facilitates “receptor-mediated transport,” or transcytosis, across the BBB into the brain tissue. Conveniently, LRP1 is also very heavily expressed in many tumors. Therefore, once GRN1005 enters the brain, it can gain entry into tumor cells. GRN1005 is a “prodrug,” which means that the form that the patient takes is inactive, but the drug becomes active once it enters cells and is cleaved by enzymes called “esterases” to release active paclitaxel from the peptide.

Geron’s Executive Vice President, Head of R&D and Chief Medical Officer, Stephen M. Kelsey, M.D., said: “With the treatment of the first patient in the GRABM-L study, we have initiated both of the planned Phase 2 clinical trials of GRN1005 in patients with cancer metastases in the brain, a significant unmet medical need for which there are currently no approved drug therapies. We have been encouraged by the preliminary evidence of anti-tumor activity against brain metastases observed in the Phase 1 study of GRN1005, and we hope to confirm these results in our Phase 2 trials.”

The purpose of GRABM-L Phase 2 study is to determine the efficacy, safety and tolerability of GRN1005 in patients with brain metastases from Non-Small Cell Lung Cancer. The trial plans to enroll 50 patients, who will receive one intravenous dose of GRN1005 every three weeks (650 mg/m2). The primary efficacy endpoint for the trial is the response of the tumors to the drug during the course of treatment.

Patients with brain cancer, particularly secondary tumors that are the result of metastases, currently have few options. The reason for this treatment dead-end is the difficulty in getting antitumor drugs to effectively cross the blood-brain barrier and enter the tumor. Preclinical and Phase 1 data indicate that GRN1005 not only transports paclitaxel into tumors inside the brain through LRP1-mediated transport, but also has activity against tumors outside the brain.

Data on safety and tolerability, and preliminary evidence of anti-tumor activity of GRN1005 were documented in two separate Phase 1 multi-center, open-label, dose escalation clinical trials, conducted by Angiochem, Inc. In these trials, patients with heavily pre-treated progressing, advance-stage solid tumors and brain metastases (n=56; including NSCLC) and patients with recurrent or progressive malignant glioma (n=63) were treated with GRN1005. Final data were presented at the 2011 AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics in November. The data were encouraging. In patients with brain metastases from solid tumors, overall response rate was 20% (4/20) by one-dimensional assessment when treated with a dose of 650 mg/m2 of GRN1005 administered as single-agent therapy once every three weeks. Anti-tumor activity was observed against metastases inside the brain and in organs outside the brain, such as the liver, lung and lymph nodes.

Geron’s clinical development plan for GRN1005 includes two Phase 2 clinical trials in patients with brain metastases arising from either breast cancer (GRABM-B) or non-small cell lung cancer (GRABM-L). Top-line data from both studies are expected to be available by the end of the second quarter of 2013.