Acute lymphoblastic leukemia (ALL) can be a devastating disease, with approximately 30% of patients dying five years after their diagnosis. The blood cancer is most common in children and young people and originates from lymphocyte over-proliferation within the bone marrow. ALL usually requires an intensive and cytotoxic chemotherapy regimen to overcome.
Discoveries in emerging drug modalities could not only improve the risk of adverse events but could also deliver improved survival rates for cancer and other serious diseases. For example, siRNA therapy can silence disease-related genes by targeting a particular mRNA sequence for degradation – opening doors for treating diseases like ALL.
However, of the five siRNA therapies approved by the US Food and Drug Administration, none are indicated for hematological cancers despite clinical need. BioXconomy spoke to Mohammad Nasrullah, pharmaceutical sciences PhD candidate at the University of Alberta, about the potentials of siRNA therapy for ALL and other blood cancers. His recent paper in Advanced Healthcare Materials – coming on the heels of his presentation at TIDES USA this year – explores the efficacy of lipopolymer nanoparticles (LPNPs) to deliver siRNA therapies to ALL cells in mouse models.
Balancing payloads
“We saw a void in the market,” explained Nasrullah. “There is no siRNA therapy for malignancies and there is no siRNA therapy for blood cancers. Blood cells are hard to transfect. So to overcome this issue, we began to design our lipopolymer.”
He and his team at the University of Alberta set out to design LPNPs that could get siRNAs to the right tissue. The first step was to find a way to avoid preferential hepatic accumulation of the drug, a recurring problem in lipid nanoparticle (LNP) drug delivery systems. Nasrullah and his colleagues attempted to solve this issue by conjugating the lipid to polyethyleneimine.
“Polyethyleneimine is a polymer that is very well-known for delivering nucleic acid payloads,” Nasrullah said. “At high molecular weights, they are very efficient but are not well tolerated and show some cellular toxicity. At lower weights, however, the efficiency goes down.”
“This is when we began to theorize ways of taking low molecular weight polyethyleneimine, which is safe, and improving its efficacy. We conjugated the low molecular weight [version] with different lipids, screening over 100 candidates until we identified PEI-C, which we reported in our paper.”
Fusion frenzy
Nasrullah’s team targeted a potent oncogene fusion responsible for an aggressive ALL subtype with poor prognosis in infant, pediatric, and adult cases, known as KMT2A:AFF1. The KMT2A gene, when functioning correctly, is a transcriptional coactivator essential for hematopoiesis, but when fused with transcription elongation factor AFF1, it gives rise to several malignancies.
The aim of the study was to selectively silence this fusion site ex vivo in human peripheral blood mononuclear cells and mouse bone marrow stromal cells using siRNA. They set out to compare engineered PEI-C to leading commercial reagent, RNAiMAX – and were astonished at the results.
“We showed that compared to RNAiMAX, our PEI-C lipid polymer nanoparticle outperformed,” commented Nasrullah. “In bone marrow stromal cell, the RNAiMAX showed around 20% siRNA uptake, whereas our PEI-C performed at 60%.”
He also highlighted siRNA uptakes of up to 93% utilizing the PEI-C lipopolymer versus 12.2% with RNAiMAX in SEM cells. Further molecular analysis confirmed effective silencing of the KMT2A:AFF1 fusion as well as downregulation of BCL2, a proto-oncogene.
The team then moved on to in vivo models to test their systems. They found that their LPNP approach achieved successful targeting of leukemia-associated organ systems in mouse models. When delivered intravenously, siRNA distribution was significantly higher in extrahepatic tissues such as the spleen, bone marrow, and lungs, all of which were higher than those in the liver.
They also observed that their LPNP-siRNAs led to increased cancer cell apoptosis and reduced ALL burden. Most excitingly, the siRNA against the KMT2A::AFF1 fusion improved overall survival – ALL mice treated with LPNP-delivered siRNA lived around ten days longer than the control group.
Patients in mind
With this preclinical success in hand, the researchers hope human trials won’t be far behind.
“Our ultimate goal is to get to clinical trials in two years, but the next step is performing this in primary patient cells,” explained Nasrullah. “Based on the preliminary data, we’re positive. We hope to translate our academic successes into commercial investment.”
But there are still barriers to cross with siRNA therapy. One significant hurdle in the safety of these treatments, including off-target induced toxicity that can limit effective delivery of the siRNA payload.
Nasrullah believes LPNPs may also be able to offer a solution.
“The biggest adverse event for this kind of therapy is immunogenicity,” he noted. “That’s why when we use siRNA therapy for patients, we also have to use an immunosuppressing agent. This is a big challenge for lipid nanoparticles, but when testing our lipopolymer in human blood cells, there was not much stimulation of pro-inflammatory cytokines.”
So what could the future look like for LPNPs, and the siRNA therapies they can deliver?
“We are now collecting primary cells from all different forms of leukemia and have recently also had successes in targeting lung cancer and breast cancer,” commented Nasrullah.
“In the next ten years, siRNA therapy and chemotherapy will co-exist, but in 20–25 years conventional chemotherapy will most likely be completely replaced.”
Beyond leukemia, BioXconomy has reported on siRNA treatment of colorectal cancer, vision loss, kidney disease, heart disease, neurodegenerative disorders, and neurological conditions. Now, Nasrullah and his team’s breakthrough lipopolymer adds to other innovations in the field of therapeutic RNAi. Their contribution could be the key to further unlocking the potential of siRNAs. In the next two decades, the harsh side effects and adverse events of chemotherapy may indeed be a thing of the past.
Quotes have been lightly edited for clarity.