HTL0039732 in Participants With Advanced Solid Tumours

The trial will investigate HTL0039732, a novel specific E-type prostanoid receptor 4 (EP4) antagonist, as a monotherapy and in combination with atezolizumab, a monoclonal antibody that binds to the programmed death ligand 1 (PD-L1). The trial may be expanded in future to also evaluate HTL0039732 in combination with other approved anti-cancer therapies. HTL0039732 is a small molecule drug that blocks activation of EP4 receptors by prostaglandin E2 (PGE2), a naturally occurring substance in the body. Prostaglandin E2 may be elevated in cancer and signalling via the EP4 receptor can lead to suppression of immune activity, allowing the cancer to escape from the immune system. Blocking the EP4 receptor may relieve that immunosuppression, allowing the immune system to be active against the cancer again. Atezolizumab is an established immune checkpoint inhibitor that overcomes a key immunosuppressive signal and improves the magnitude and quality of tumour-specific T-cell responses, resulting in improved anti-cancer activity. It, and other similar agents, are approved for the treatment of several different types of cancer. As a common mechanism of immune suppression, immune checkpoint inhibitors also have a role in combination immunotherapies and combining EP4 inhibition by HTL0039732 with PD-L1 blockade by atezolizumab, is expected to have increased activity. The trial will investigate HTL0039732 as a monotherapy and in combination with atezolizumab, and potentially with other approved anti-cancer therapies, in participants with advanced solid tumours (Phase 1 Part A) and in participants with advanced solid tumours where PGE2/EP4 signalling is believed to be more prevalent or significant (Phase 1 Part B and Phase 2a). This is a first-in-human clinical trial and is split as follows: * Phase 1 is the 'dose escalation' phase, where two groups (known as Part A and Part B) of participants with solid tumours will receive increasing doses of HTL0039732 to find the safest dose. * Part A participants will receive HTL0039732 as a single agent. * Part B participants will receive HTL0039732 in combination with atezolizumab. * More Parts may be added in future for participants to receive HTL0039732 in combination with other approved anti-cancer therapies. * Phase 2a is the 'dose expansion' phase, where participants grouped according to the type of cancer they have will receive the recommended Phase 2 dose (RP2D) of HTL0039732 in combination with atezolizumab, and potentially in combination with other approved anti-cancer therapies. Phase 2a will follow a response enrichment approach; activity of the investigational medicinal products will be assessed in each group and ongoing recruitment will focus on tumour types with promising signals. The main aims of the clinical trial are to find out: * The most appropriate dose of HTL0039732 administered on its own, and the most appropriate dose/s of HTL0039732 to take forward for further investigation in combination with atezolizumab and with other approved anti-cancer therapies. * More about any potential side effects of HTL0039732 when given alone and in combination with atezolizumab and other approved anti-cancer therapies.