Xanadu Targets Cancer Drug Discovery With Quantum Computing

Some cancer treatments target tumors with light.

Photodynamic therapy utilizes photosensitizers, which are compounds that remain dormant in tissue until activated by a specific wavelength of light. Once activated, these molecules react with oxygen to destroy nearby tumor cells. This approach offers precision, and allows light to be aimed directly at the tumor and sparing healthy tissues often damaged by chemotherapy.

The challenge lies in discovering improved versions of these molecules. In an August 13 press release, Xanadu Quantum Technologies and the University of Alberta have announced a collaboration to address this, and they believe that quantum computing can provide a solution.

This research partnership didn’t include peer-reviewed results or benchmarks. It signifies an agreement between Xanadu’s algorithms group and Professor Alex Brown’s chemistry lab to investigate a complex chemistry problem. This context is important when considering discussions about accelerating drug discovery.

The intricacies of photosensitizer molecules

A photosensitizer’s effectiveness hinges on its behavior after light absorption. The molecule transitions to an excited state, persists briefly, and then transfers its energy to oxygen, generating reactive species that damage the tumor. All critical properties, such as the responsive wavelength, efficiency in inducing cell death, and duration of activity, are determined by this excited state.

Excited states are particularly challenging for standard computational chemistry. Though classical methods capably model molecules in their ground state, simulating excited configurations (where multiple electron arrangements are intricately intertwined) causes approximations to fail. Researchers typically resort to expensive and time-consuming experiments or use classical computer simulations that omit crucial interactions affecting drug efficacy.

Professor Brown has dedicated years to benchmarking these simulations, identifying the limitations of classical tools. Xanadu’s hypothesis is that a quantum computer can navigate the complexities that classical methods can’t.

The potential of quantum machines in this field

The rationale is that electrons in a molecule adhere to quantum mechanics. Simulating these on a classical computer requires translating quantum behavior into ordinary bits, which quickly becomes computationally intensive as the molecule’s size increases. A quantum computer, conversely, inherently stores quantum information. In principle, it can represent the entangled electron states of an excited molecule without the exponential complexity that overwhelms classical hardware.

Quantum chemistry is one of the few fields where quantum machines are genuinely expected to offer a future advantage. Xanadu has previously published work on simulating light-matter interactions in photosensitizers, indicating that this partnership is a continuation of their existing research. As Christian Weedbrook, Xanadu’s founder and CEO, explained:

“By leveraging early fault-tolerant quantum computers to model critical light-matter interactions within photosensitizers, we are positioning quantum computing as a highly competitive method for accelerating photodynamic drug discovery.”

The phrase “early fault-tolerant” carries significant implications.

Bridging the gap between press release and practical application

Fault-tolerant quantum computers aim to detect and correct their own errors, enabling prolonged calculations without succumbing to noise. Currently, no such machine exists at the scale required for complex chemistry. Xanadu is developing photonic fault-tolerant hardware, and “early fault-tolerant” honestly indicates that a fully functional version is not yet available.

Thus, this partnership focuses on designing algorithms for a machine still under development. The chemical objective is valid, the classical limitations are real, and the theoretical basis for quantum’s potential is sound. What’s missing is a practical demonstration: a quantum computer modeling a specific photosensitizer’s excited states more effectively than the best classical method, on currently available hardware, at a scale useful to a chemist. This outcome isn’t present here, as the work is just starting.

This development doesn’t immediately bring new cancer treatments closer for patients. Though photodynamic therapy is an established clinical tool, the quantum aspect is far upstream, within the computational stage and identifying candidate molecules. Even a successful outcome would only yield better candidate molecules for laboratory testing, followed by years of trials, with no guarantee of clinical success.

What is concrete is a well-aligned collaboration addressing a genuinely difficult chemistry problem. Everything beyond that remains aspirational.